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Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270Jessie Butler, Alexander N. Semyonov, and Pat O’Brien Thermo Fisher Scientific, Austin, TX, USA
2 Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Jessie Butler, Alexander N. Semyonov, Pat O’Brien Thermo Fisher Scientific, Austin, Texas, USA
Conclusion GC-MS analysis of SVOCs was performed in accordance with US EPA Method 8270 on a TRACE 1310 GC coupled with an ISQ single quadrupole mass spectrometer utilizing hydrogen as a carrier gas. Key modifications to both GC and MS hardware and methods necessary for successful migration to hydrogen carrier were performed. The final, optimized EPA Method 8270 fully was migrated to hydrogen carrier gas with improved peak shape, resolution, and run time. The ISQ GC-MS was stable and maintained good ion ratio stability after injecting 5% diesel samples.
Resolution was good and peak shape was improved
Linearity met the criteria of the method
Sensitivity was within a factor of 2 of that obtained with helium carrier gas
Ion ratio stability and robustness were good
Run time was shortened
References 1. EPA Method 8270D, Semi-volatile Organic Compounds by Gas Chromatography/
Mass Spectrometry (GC/MS) Rev. 4, 2007, Environmental Protection Agency.
Overview Purpose: Optimize US EPA Method 8270 with hydrogen carrier gas
Methods: Configure hydrogen carrier with smaller id column and installation of hydrogen kit on mass spectrometer
Results: Improved peak shape, resolution, and run time
Introduction The global helium shortage and price increase of this non-renewable noble gas cause more and more laboratories to migrate to hydrogen as a carrier gas. This transition is easy for the gas chromatography (GC) methods utilizing FID, TCD, ECD, and other non-mass-selective detectors. However, for the gas chromatography- mass spectrometry (GC-MS) methods, especially complex and regulated ones, migration to hydrogen carrier gas presents significant challenges. In addition to the changes in chromatographic conditions of the run due to the physical property differences of hydrogen, its chemical reactivity brings about chemical reactions in the mass spectrometer’s ion source that do not occur with helium.
The analysis of semi-volatile organic compounds (SVOCs) in wastewater by United States Environmental Protection Agency (EPA) Method 82701 involves identification and quantitation of more than 120 analytes of varying chemical structure, polarity and volatility. The diversity of the analytes in this method presents particular challenges when migrating from helium to hydrogen carrier.
GC-MS analysis of SVOCs was performed in accordance with EPA Method 8270 on the Thermo Scientific™ TRACE™ 1310 GC coupled to a Thermo Scientific™ ISQ™ single quadrupole mass spectrometer using helium or hydrogen as carrier gases. Key modifications to both GC and MS hardware and methods are necessary for successfully switching to hydrogen. The final, optimized EPA Method 8270 was fully migrated to hydrogen carrier gas with improved peak shape, resolution, and run time.
Methods Sample Preparation
All standards were prepared in methylene chloride. A performance mix containing pentachlorophenol, DFTPP, benzidine, and p,p’-DDT was made at a concentration of 50 ppm. A calibration curve was prepared from 1 to 200 ppm with internal standards and surrogates at 40 ppm.
Gas Chromatography
An instant connect split/splitless injector module was used in the split mode. The standard Thermo Scientific™ TraceGOLD™ TG-5MS capillary column (30 m x 0.25 mm x 0.5 µm) was replaced with a TraceGOLD TG-5MS column of smaller i.d. (20 m x 0.18 mm x 0.36 µm). A one microliter injection was made.
Mass Spectrometry
The ISQ mass spectrometer was equipped with the new hydrogen kit and preconditioned by baking out with an elevated hydrogen carrier flow rate.
Data Analysis
Data was collected using Thermo Scientific™ Xcalibur™ 2.0 acquisition software, and processing was performed using Thermo Scientific™ Target 4.14 software. Xcalibur software was configured for direct target processing. A typical chromatogram of a 40 ppm standard is shown in Figure 1.
FIGURE 1. TIC of 40 ppm standard with hydrogen carrier gas
ResultsStabilization Bake Out for Hydrogen Carrier Gas
When switching from helium to hydrogen as a carrier gas, a brief stabilization period is required. If using a hydrogen generator, no gas filters are necessary. Gas lines should be plumbed with pre-cleaned 1/8” stainless steel tubing. If a cylinder of hydrogen is used, grade UHP 5.0 or better is required with inline gas purifiers. The hydrogen kit is installed in the mass spectrometer. The source temperature is set to 350 °C for bake out. The hydrogen carrier is set to 4 mL/min. The filament is turned on for one hour during the bake out period. After bake out, the hydrogen flow is reduced to 1 mL/min, and the source temperature was set to 325 °C. Figures 2–5 show the effect of bake out. The hydrogen gas strips the contamination off the entire flow path. If water is present in the gas lines, a m/z of 19 is seen. This is due to protonation of water (M+1). Other ions typical of chemical ionization and protonation are also seen, m/z 29 and m/z 41 (Figure 2). Elevated levels of low mass hydrocarbons are observed in the calibration gas spectrum (Figure 4). These all are reduced after the one hour bake out.
Compounds: R2 = >0.99 nitrophenols nitroanilines dinitrophenols 4,6-dinityrophenol-2-methylphenol trichlorophenols dinitrotoluenes hexachlorocyclopentadiene tribromophenol pentachlorophenol butylbenzylphthalate di-n-octylphthalatebis(2 ethylhexyl)phthalate
FIGURE 6. Comparison of inlet pressure for helium and hydrogen for a 0.25 mm and 0.18 mm i.d. column
FIGURE 8. Improvement of Peak Shape for Indeno[1,2,3-cd]pyrene (peak1) & benzo[g,h,i]perylene (peak 2)
FIGURE 9. Critical Separation of benzo[g&h]flouranthene
FIGURE 13. Ion Ratios for DFTPPSelecting the Appropriate Column Dimensions and Inlet Pressure
Due to the lower viscosity of hydrogen carrier gas as compared to helium, a lower head pressure is required to obtain 1 mL/min of column flow rate. By reducing the i.d. of the column, the pressure may be set to usable level (Figure 6). Also note the reduction in the vapor volume of methylene chloride at higher pressures (Figure 7).
Sensitivity
The sensitivity of the method using hydrogen carrier was within a factor of two to that achieved with helium. The average Instrument Detection Limit (IDL) with helium was 0.082 ppm and 0.15 ppm with hydrogen. The chart in Figure 12 shows most of the IDLs at around 0.1 ppm. Replicate injections of the standard were made at 1 ppm.
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6.83
3.85
10.24
9.198.987.904.56
12.3510.276.26 7.645.18
6.97 11.198.066.455.65 6.08
5.34 8.41
11.163.88 4.6111.449.763.34
7.01 9.45 11.724.267.37 10.79 12.558.844.67
5.955.02
9.973.31
2.25 2.981.80
2.51
8.4810.54 12.17 12.70
NL:5.35E8TIC MS level8
FIGURE 2. Air/water spectrum before bake out
FIGURE 3. Air/water spectrum after bake out
m/z 19
m/z 19
m/z 18 m/z 18
m/z 29
m/z 28
m/z 28
m/z 29
FIGURE 4. Cal gas (FC-43) spectrum before bake out
FIGURE 5. Cal gas (FC-43) spectrum after bake out
RT: 0.000 - 13.008
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7.0318.596
5.7954.039
9.808
3.016
1.368
2.002 6.358 7.8747.075 9.423 11.1144.6983.281 5.057 10.099 11.5208.953 12.8018.309
6.802
9.338
5.4303.730
2.719
6.035 7.633 9.0366.849 10.4119.5774.3673.000 4.721 10.7422.6811.079 1.526 11.648 12.000
NL:2.12E8TIC MSlevel1
NL:1.55E8TIC MS1ng
FIGURE 7. Methylene chloride solvent tailing at low vs. high inlet pressures
8 psi
13 psi
Robustness and Ion Ratio Stability
The stability of ion ratios for DFTPP was studied. The values were very stable. The performance is shown in Figure 13. Next, a robustness study was run by injecting 30 of 5 % diesel samples in methylene chloride. The samples also contained 40 ppm of the internal standards. The diesel sample TIC is shown in Figure 14. A chart was plotted of the internal standards in Figure 15. A check standard was run after each set of 10 diesel samples. All check standards met the QC criteria for the method.
RT: 11.87 - 13.34
11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13.0 13.1 13.2 13.3Time (min)
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12.29
12.50
12.5312.34 12.5612.37 12.63 12.72 12.76 12.87 12.9312.81 13.1213.01 13.17 13.2613.0612.2612.11 12.1412.0211.9711.8812.65
13.23
12.72 12.75 12.9412.84 12.87 12.98 13.0312.25 13.1312.27 12.3712.2112.16 12.5212.05 12.4211.90 12.0912.03 12.46 12.5411.94
NL:5.23E6m/z= 275.50-276.50 MS level5
NL:7.26E6m/z= 275.50-276.50 MS level5
RT: 10.26 - 10.43
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10.4210.26
NL:1.19E7m/z= 251.50-252.50 MS level5
RT: 11.06 - 11.20
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11.11
11.16 11.17 11.19 11.2011.0811.07
NL:6.19E6m/z= 251.50-252.50 MS level5
Peak Shape and Resolution
The advantage of hydrogen carrier is that higher than helium linear velocities can be used without sacrificing resolution. With less residence time in the stationary phase, the late eluting polynuclear aromatic hydrocarbons (PNAs) come out with a narrower peak width (Figure 8). The critical separation of benzo[g&h]flouranthene was easily achieved (Figure 9).
Hydrogen
Helium
Hydrogen Helium
RT: 0.00 - 13.26
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7.76
6.21 6.77 8.18
7.30
4.55
5.65 7.313.43 5.09
8.57
4.01
8.92
7.79 9.25
7.015.97
5.505.29 6.55
9.564.92
7.47
3.75 9.854.352.80 3.21
10.133.192.63 10.24
11.472.572.151.96 10.681.70 10.95 11.62 12.01 13.2312.80
NL:6.22E8TIC MSdiesel5
Run Time
The run time was reduced by using a smaller i.d. column (TG-5MS 20 m x 0.18 mm x 0.36 µm) and hydrogen carrier gas. The more commonly used column with helium is the TG-5MS 30 m x 0.25 mm x 0.5 µm (Figure 16).
FIGURE 14. TIC 5 % diesel sample
FIGURE 10. Comparison of linearity with helium and hydrogen carrier (the compounds on the insert required R2 fit with hydrogen)
FIGURE 16. Comparison of run time with hydrogen and helium at 1 mL/min
FIGURE 12. Instrument Detection Limits (ppm) Average = 0.15 ppm
Butylbenzyl phthalate Dichlorobenzidine Di-n-octylphthlate
Bis-2-chloroisopropylether
FIGURE 15. Stability of internal standard areas during injection of 5% diesel
C:\chem\...\level8.d\level8 12/5/2012 2:04:03 PM
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6.83
3.8510.24
9.198.987.904.56
12.3510.276.26 7.645.186.97 11.198.065.65
8.4111.163.88 4.61 11.449.763.34 7.014.2610.79 12.558.84
3.31
2.25 2.981.80 2.51
12.708.80 13.21 13.849.447.58 12.43 14.6212.1310.717.46 10.656.63
8.59 13.969.56 13.158.066.14 10.899.0111.27 15.37
9.61 18.0815.857.22 12.575.36 15.335.34 10.02
6.04 6.76
18.71
3.8415.92
2.82
11.32 18.913.24 16.42 17.112.65 4.17
NL:5.35E8TIC MSlevel8
NL:1.12E8TIC MS03091102_110309112925
Hydrogen 1 mL/min (TG-5MS 20 m x 0.18 mm x 0.36µm)
Helium 1 mL/min (TG-5MS 30 m x 0.25 mm x 0.5µm)
FIGURE 11. Typical linearity plots with hydrogen carrier
Linearity
A linearity study was performed in the range of concentration from 1 to 200 ppm in CH2Cl2. The results are shown in Figures 10 and 11 below. Helium carrier gave lower relative percent standard deviations (%RSD) than hydrogen but still met the criteria for the method. A few compounds required the fit of least squares (R2 = > 0.99).
© 2013 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries. This information is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others.
3Thermo Scientific Poster Note • PN10326_e 05/13S
Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270 Jessie Butler, Alexander N. Semyonov, Pat O’Brien Thermo Fisher Scientific, Austin, Texas, USA
Conclusion GC-MS analysis of SVOCs was performed in accordance with US EPA Method 8270 on a TRACE 1310 GC coupled with an ISQ single quadrupole mass spectrometer utilizing hydrogen as a carrier gas. Key modifications to both GC and MS hardware and methods necessary for successful migration to hydrogen carrier were performed. The final, optimized EPA Method 8270 fully was migrated to hydrogen carrier gas with improved peak shape, resolution, and run time. The ISQ GC-MS was stable and maintained good ion ratio stability after injecting 5% diesel samples.
Resolution was good and peak shape was improved
Linearity met the criteria of the method
Sensitivity was within a factor of 2 of that obtained with helium carrier gas
Ion ratio stability and robustness were good
Run time was shortened
References 1. EPA Method 8270D, Semi-volatile Organic Compounds by Gas Chromatography/
Mass Spectrometry (GC/MS) Rev. 4, 2007, Environmental Protection Agency.
Overview Purpose: Optimize US EPA Method 8270 with hydrogen carrier gas
Methods: Configure hydrogen carrier with smaller id column and installation of hydrogen kit on mass spectrometer
Results: Improved peak shape, resolution, and run time
Introduction The global helium shortage and price increase of this non-renewable noble gas cause more and more laboratories to migrate to hydrogen as a carrier gas. This transition is easy for the gas chromatography (GC) methods utilizing FID, TCD, ECD, and other non-mass-selective detectors. However, for the gas chromatography- mass spectrometry (GC-MS) methods, especially complex and regulated ones, migration to hydrogen carrier gas presents significant challenges. In addition to the changes in chromatographic conditions of the run due to the physical property differences of hydrogen, its chemical reactivity brings about chemical reactions in the mass spectrometer’s ion source that do not occur with helium. The analysis of semi-volatile organic compounds (SVOCs) in wastewater by United States Environmental Protection Agency (EPA) Method 82701 involves identification and quantitation of more than 120 analytes of varying chemical structure, polarity and volatility. The diversity of the analytes in this method presents particular challenges when migrating from helium to hydrogen carrier. GC-MS analysis of SVOCs was performed in accordance with EPA Method 8270 on the Thermo Scientific™ TRACE™ 1310 GC coupled to a Thermo Scientific™ ISQ™ single quadrupole mass spectrometer using helium or hydrogen as carrier gases. Key modifications to both GC and MS hardware and methods are necessary for successfully switching to hydrogen. The final, optimized EPA Method 8270 was fully migrated to hydrogen carrier gas with improved peak shape, resolution, and run time.
Methods Sample Preparation
All standards were prepared in methylene chloride. A performance mix containing pentachlorophenol, DFTPP, benzidine, and p,p’-DDT was made at a concentration of 50 ppm. A calibration curve was prepared from 1 to 200 ppm with internal standards and surrogates at 40 ppm.
Gas Chromatography
An instant connect split/splitless injector module was used in the split mode. The standard Thermo Scientific™ TraceGOLD™ TG-5MS capillary column (30 m x 0.25 mm x 0.5 µm) was replaced with a TraceGOLD TG-5MS column of smaller i.d. (20 m x 0.18 mm x 0.36 µm). A one microliter injection was made.
Mass Spectrometry
The ISQ mass spectrometer was equipped with the new hydrogen kit and preconditioned by baking out with an elevated hydrogen carrier flow rate.
Data Analysis
Data was collected using Thermo Scientific™ Xcalibur™ 2.0 acquisition software, and processing was performed using Thermo Scientific™ Target 4.14 software. Xcalibur software was configured for direct target processing. A typical chromatogram of a 40 ppm standard is shown in Figure 1.
FIGURE 1. TIC of 40 ppm standard with hydrogen carrier gas
Results
Stabilization Bake Out for Hydrogen Carrier Gas
When switching from helium to hydrogen as a carrier gas, a brief stabilization period is required. If using a hydrogen generator, no gas filters are necessary. Gas lines should be plumbed with pre-cleaned 1/8” stainless steel tubing. If a cylinder of hydrogen is used, grade UHP 5.0 or better is required with inline gas purifiers. The hydrogen kit is installed in the mass spectrometer. The source temperature is set to 350 °C for bake out. The hydrogen carrier is set to 4 mL/min. The filament is turned on for one hour during the bake out period. After bake out, the hydrogen flow is reduced to 1 mL/min, and the source temperature was set to 325 °C. Figures 2–5 show the effect of bake out. The hydrogen gas strips the contamination off the entire flow path. If water is present in the gas lines, a m/z of 19 is seen. This is due to protonation of water (M+1). Other ions typical of chemical ionization and protonation are also seen, m/z 29 and m/z 41 (Figure 2). Elevated levels of low mass hydrocarbons are observed in the calibration gas spectrum (Figure 4). These all are reduced after the one hour bake out.
Compounds: R2 = >0.99 nitrophenols nitroanilines dinitrophenols 4,6-dinityrophenol-2-methylphenol trichlorophenols dinitrotoluenes hexachlorocyclopentadiene tribromophenol pentachlorophenol butylbenzylphthalate di-n-octylphthalate bis(2 ethylhexyl)phthalate
FIGURE 6. Comparison of inlet pressure for helium and hydrogen for a 0.25 mm and 0.18 mm i.d. column
FIGURE 8. Improvement of Peak Shape for Indeno[1,2,3-cd]pyrene (peak1) & benzo[g,h,i]perylene (peak 2)
FIGURE 9. Critical Separation of benzo[g&h]flouranthene
FIGURE 13. Ion Ratios for DFTPP Selecting the Appropriate Column Dimensions and Inlet Pressure
Due to the lower viscosity of hydrogen carrier gas as compared to helium, a lower head pressure is required to obtain 1 mL/min of column flow rate. By reducing the i.d. of the column, the pressure may be set to usable level (Figure 6). Also note the reduction in the vapor volume of methylene chloride at higher pressures (Figure 7).
Sensitivity
The sensitivity of the method using hydrogen carrier was within a factor of two to that achieved with helium. The average Instrument Detection Limit (IDL) with helium was 0.082 ppm and 0.15 ppm with hydrogen. The chart in Figure 12 shows most of the IDLs at around 0.1 ppm. Replicate injections of the standard were made at 1 ppm.
RT: 0.00 - 13.27
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6.83
3.85
10.24
9.198.987.904.56
12.3510.276.26 7.645.18
6.97 11.198.066.455.65 6.08
5.34 8.41
11.163.88 4.6111.449.763.34
7.01 9.45 11.724.267.37 10.79 12.558.844.67
5.955.02
9.973.31
2.25 2.981.80
2.51
8.4810.54 12.17 12.70
NL:5.35E8TIC MS level8
FIGURE 2. Air/water spectrum before bake out
FIGURE 3. Air/water spectrum after bake out
m/z 19
m/z 19
m/z 18 m/z 18
m/z 29
m/z 28
m/z 28
m/z 29
FIGURE 4. Cal gas (FC-43) spectrum before bake out
FIGURE 5. Cal gas (FC-43) spectrum after bake out
RT: 0.000 - 13.008
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7.0318.596
5.7954.039
9.808
3.016
1.368
2.002 6.358 7.8747.075 9.423 11.1144.6983.281 5.057 10.099 11.5208.953 12.8018.309
6.802
9.338
5.4303.730
2.719
6.035 7.633 9.0366.849 10.4119.5774.3673.000 4.721 10.7422.6811.079 1.526 11.648 12.000
NL:2.12E8TIC MS level1
NL:1.55E8TIC MS 1ng
FIGURE 7. Methylene chloride solvent tailing at low vs. high inlet pressures
8 psi
13 psi
Robustness and Ion Ratio Stability
The stability of ion ratios for DFTPP was studied. The values were very stable. The performance is shown in Figure 13. Next, a robustness study was run by injecting 30 of 5 % diesel samples in methylene chloride. The samples also contained 40 ppm of the internal standards. The diesel sample TIC is shown in Figure 14. A chart was plotted of the internal standards in Figure 15. A check standard was run after each set of 10 diesel samples. All check standards met the QC criteria for the method.
RT: 11.87 - 13.34
11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13.0 13.1 13.2 13.3Time (min)
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12.5312.34 12.5612.37 12.63 12.72 12.76 12.87 12.9312.81 13.1213.01 13.17 13.2613.0612.2612.11 12.1412.0211.9711.8812.65
13.23
12.72 12.75 12.9412.84 12.87 12.98 13.0312.25 13.1312.27 12.3712.2112.16 12.5212.05 12.4211.90 12.0912.03 12.46 12.5411.94
NL:5.23E6m/z= 275.50-276.50 MS level5
NL:7.26E6m/z= 275.50-276.50 MS level5
RT: 10.26 - 10.43
10.26 10.27 10.28 10.29 10.30 10.31 10.32 10.33 10.34 10.35 10.36 10.37 10.38 10.39 10.40 10.41 10.42Time (min)
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10.3610.33
10.4210.26
NL:1.19E7m/z= 251.50-252.50 MS level5
RT: 11.06 - 11.20
11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19Time (min)
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11.14
11.11
11.16 11.17 11.19 11.2011.0811.07
NL:6.19E6m/z= 251.50-252.50 MS level5
Peak Shape and Resolution
The advantage of hydrogen carrier is that higher than helium linear velocities can be used without sacrificing resolution. With less residence time in the stationary phase, the late eluting polynuclear aromatic hydrocarbons (PNAs) come out with a narrower peak width (Figure 8). The critical separation of benzo[g&h]flouranthene was easily achieved (Figure 9).
Hydrogen
Helium
Hydrogen Helium
RT: 0.00 - 13.26
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7.76
6.21 6.77 8.18
7.30
4.55
5.65 7.313.43 5.09
8.57
4.01
8.92
7.79 9.25
7.015.97
5.505.29 6.55
9.564.92
7.47
3.75 9.854.352.80 3.21
10.133.192.63 10.24
11.472.572.151.96 10.681.70 10.95 11.62 12.01 13.2312.80
NL:6.22E8TIC MS diesel5
Run Time
The run time was reduced by using a smaller i.d. column (TG-5MS 20 m x 0.18 mm x 0.36 µm) and hydrogen carrier gas. The more commonly used column with helium is the TG-5MS 30 m x 0.25 mm x 0.5 µm (Figure 16).
FIGURE 14. TIC 5 % diesel sample
FIGURE 10. Comparison of linearity with helium and hydrogen carrier (the compounds on the insert required R2 fit with hydrogen)
FIGURE 16. Comparison of run time with hydrogen and helium at 1 mL/min
FIGURE 12. Instrument Detection Limits (ppm) Average = 0.15 ppm
Butylbenzyl phthalate Dichlorobenzidine Di-n-octylphthlate
Bis-2-chloroisopropylether
FIGURE 15. Stability of internal standard areas during injection of 5% diesel
C:\chem\...\level8.d\level8 12/5/2012 2:04:03 PM
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Rel
ativ
e A
bund
ance
6.83
3.8510.24
9.198.987.904.56
12.3510.276.26 7.645.186.97 11.198.065.65
8.4111.163.88 4.61 11.449.763.34 7.014.2610.79 12.558.84
3.31
2.25 2.981.80 2.51
12.708.80 13.21 13.849.447.58 12.43 14.6212.1310.717.46 10.656.63
8.59 13.969.56 13.158.066.14 10.899.0111.27 15.37
9.61 18.0815.857.22 12.575.36 15.335.34 10.02
6.04 6.76
18.71
3.8415.92
2.82
11.32 18.913.24 16.42 17.112.65 4.17
NL:5.35E8TIC MS level8
NL:1.12E8TIC MS 03091102_110309112925
Hydrogen 1 mL/min (TG-5MS 20 m x 0.18 mm x 0.36µm)
Helium 1 mL/min (TG-5MS 30 m x 0.25 mm x 0.5µm)
FIGURE 11. Typical linearity plots with hydrogen carrier
Linearity
A linearity study was performed in the range of concentration from 1 to 200 ppm in CH2Cl2. The results are shown in Figures 10 and 11 below. Helium carrier gave lower relative percent standard deviations (%RSD) than hydrogen but still met the criteria for the method. A few compounds required the fit of least squares (R2 = > 0.99).
© 2013 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries. This information is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others.
4 Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Jessie Butler, Alexander N. Semyonov, Pat O’Brien Thermo Fisher Scientific, Austin, Texas, USA
Conclusion GC-MS analysis of SVOCs was performed in accordance with US EPA Method 8270 on a TRACE 1310 GC coupled with an ISQ single quadrupole mass spectrometer utilizing hydrogen as a carrier gas. Key modifications to both GC and MS hardware and methods necessary for successful migration to hydrogen carrier were performed. The final, optimized EPA Method 8270 fully was migrated to hydrogen carrier gas with improved peak shape, resolution, and run time. The ISQ GC-MS was stable and maintained good ion ratio stability after injecting 5% diesel samples.
Resolution was good and peak shape was improved
Linearity met the criteria of the method
Sensitivity was within a factor of 2 of that obtained with helium carrier gas
Ion ratio stability and robustness were good
Run time was shortened
References 1. EPA Method 8270D, Semi-volatile Organic Compounds by Gas Chromatography/
Mass Spectrometry (GC/MS) Rev. 4, 2007, Environmental Protection Agency.
Overview Purpose: Optimize US EPA Method 8270 with hydrogen carrier gas
Methods: Configure hydrogen carrier with smaller id column and installation of hydrogen kit on mass spectrometer
Results: Improved peak shape, resolution, and run time
Introduction The global helium shortage and price increase of this non-renewable noble gas cause more and more laboratories to migrate to hydrogen as a carrier gas. This transition is easy for the gas chromatography (GC) methods utilizing FID, TCD, ECD, and other non-mass-selective detectors. However, for the gas chromatography- mass spectrometry (GC-MS) methods, especially complex and regulated ones, migration to hydrogen carrier gas presents significant challenges. In addition to the changes in chromatographic conditions of the run due to the physical property differences of hydrogen, its chemical reactivity brings about chemical reactions in the mass spectrometer’s ion source that do not occur with helium.
The analysis of semi-volatile organic compounds (SVOCs) in wastewater by United States Environmental Protection Agency (EPA) Method 82701 involves identification and quantitation of more than 120 analytes of varying chemical structure, polarity and volatility. The diversity of the analytes in this method presents particular challenges when migrating from helium to hydrogen carrier.
GC-MS analysis of SVOCs was performed in accordance with EPA Method 8270 on the Thermo Scientific™ TRACE™ 1310 GC coupled to a Thermo Scientific™ ISQ™ single quadrupole mass spectrometer using helium or hydrogen as carrier gases. Key modifications to both GC and MS hardware and methods are necessary for successfully switching to hydrogen. The final, optimized EPA Method 8270 was fully migrated to hydrogen carrier gas with improved peak shape, resolution, and run time.
MethodsSample Preparation
All standards were prepared in methylene chloride. A performance mix containing pentachlorophenol, DFTPP, benzidine, and p,p’-DDT was made at a concentration of 50 ppm. A calibration curve was prepared from 1 to 200 ppm with internal standards and surrogates at 40 ppm.
Gas Chromatography
An instant connect split/splitless injector module was used in the split mode. The standard Thermo Scientific™ TraceGOLD™ TG-5MS capillary column (30 m x 0.25 mm x 0.5 µm) was replaced with a TraceGOLD TG-5MS column of smaller i.d. (20 m x 0.18 mm x 0.36 µm). A one microliter injection was made.
Mass Spectrometry
The ISQ mass spectrometer was equipped with the new hydrogen kit and preconditioned by baking out with an elevated hydrogen carrier flow rate.
Data Analysis
Data was collected using Thermo Scientific™ Xcalibur™ 2.0 acquisition software, and processing was performed using Thermo Scientific™ Target 4.14 software. Xcalibursoftware was configured for direct target processing. A typical chromatogram of a 40 ppm standard is shown in Figure 1.
FIGURE 1. TIC of 40 ppm standard with hydrogen carrier gas
ResultsStabilization Bake Out for Hydrogen Carrier Gas
When switching from helium to hydrogen as a carrier gas, a brief stabilization period is required. If using a hydrogen generator, no gas filters are necessary. Gas lines should be plumbed with pre-cleaned 1/8” stainless steel tubing. If a cylinder of hydrogen is used, grade UHP 5.0 or better is required with inline gas purifiers. The hydrogen kit is installed in the mass spectrometer. The source temperature is set to 350 °C for bake out. The hydrogen carrier is set to 4 mL/min. The filament is turned on for one hour during the bake out period. After bake out, the hydrogen flow is reduced to 1 mL/min, and the source temperature was set to 325 °C. Figures 2–5 show the effect of bake out. The hydrogen gas strips the contamination off the entire flow path. If water is present in the gas lines, a m/z of 19 is seen. This is due to protonation of water (M+1). Other ions typical of chemical ionization and protonation are also seen, m/z 29 and m/z 41 (Figure 2). Elevated levels of low mass hydrocarbons are observed in the calibration gas spectrum (Figure 4). These all are reduced after the one hour bake out.
Compounds: R2 = >0.99 nitrophenols nitroanilines dinitrophenols 4,6-dinityrophenol-2-methylphenol trichlorophenols dinitrotoluenes hexachlorocyclopentadiene tribromophenol pentachlorophenol butylbenzylphthalate di-n-octylphthalate bis(2 ethylhexyl)phthalate
FIGURE 6. Comparison of inlet pressure for helium and hydrogen for a 0.25 mm and 0.18 mm i.d. column
FIGURE 8. Improvement of Peak Shape for Indeno[1,2,3-cd]pyrene (peak1) & benzo[g,h,i]perylene (peak 2)
FIGURE 9. Critical Separation of benzo[g&h]flouranthene
FIGURE 13. Ion Ratios for DFTPPSelecting the Appropriate Column Dimensions and Inlet Pressure
Due to the lower viscosity of hydrogen carrier gas as compared to helium, a lower head pressure is required to obtain 1 mL/min of column flow rate. By reducing the i.d. of the column, the pressure may be set to usable level (Figure 6). Also note the reduction in the vapor volume of methylene chloride at higher pressures (Figure 7).
Sensitivity
The sensitivity of the method using hydrogen carrier was within a factor of two to that achieved with helium. The average Instrument Detection Limit (IDL) with helium was 0.082 ppm and 0.15 ppm with hydrogen. The chart in Figure 12 shows most of the IDLs at around 0.1 ppm. Replicate injections of the standard were made at 1 ppm.
RT: 0.00 - 13.27
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
5
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15
20
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30
35
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45
50
55
60
65
70
75
80
85
90
95
100
Rel
ativ
e A
bund
ance
6.83
3.85
10.24
9.198.987.904.56
12.3510.276.26 7.645.18
6.97 11.198.066.455.65 6.08
5.34 8.41
11.163.88 4.6111.449.763.34
7.01 9.45 11.724.267.37 10.79 12.558.844.67
5.955.02
9.973.31
2.25 2.981.80
2.51
8.4810.54 12.17 12.70
NL:5.35E8TIC MSlevel8
FIGURE 2. Air/water spectrum before bake out
FIGURE 3. Air/water spectrum after bake out
m/z 19
m/z 19
m/z 18 m/z 18
m/z 29
m/z 28
m/z 28
m/z 29
FIGURE 4. Cal gas (FC-43) spectrum before bake out
FIGURE 5. Cal gas (FC-43) spectrum after bake out
RT: 0.000 - 13.008
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
10
20
30
40
50
60
70
80
90
1000
10
20
30
40
50
60
70
80
90
100
Rel
ativ
e A
bund
ance
7.0318.596
5.7954.039
9.808
3.016
1.368
2.002 6.358 7.8747.075 9.423 11.1144.6983.281 5.057 10.099 11.5208.953 12.8018.309
6.802
9.338
5.4303.730
2.719
6.035 7.633 9.0366.849 10.4119.5774.3673.000 4.721 10.7422.6811.079 1.526 11.648 12.000
NL:2.12E8TIC MSlevel1
NL:1.55E8TIC MS1ng
FIGURE 7. Methylene chloride solvent tailing at low vs. high inlet pressures
8 psi
13 psi
Robustness and Ion Ratio Stability
The stability of ion ratios for DFTPP was studied. The values were very stable. The performance is shown in Figure 13. Next, a robustness study was run by injecting 30 of 5 % diesel samples in methylene chloride. The samples also contained 40 ppm of the internal standards. The diesel sample TIC is shown in Figure 14. A chart was plotted of the internal standards in Figure 15. A check standard was run after each set of 10 diesel samples. All check standards met the QC criteria for the method.
RT: 11.87 - 13.34
11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13.0 13.1 13.2 13.3Time (min)
0
10
20
30
40
50
60
70
80
90
1000
10
20
30
40
50
60
70
80
90
100
Rel
ativ
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bund
ance
12.29
12.50
12.5312.34 12.5612.37 12.63 12.72 12.76 12.87 12.9312.81 13.1213.01 13.17 13.2613.0612.2612.11 12.1412.0211.9711.8812.65
13.23
12.72 12.75 12.9412.84 12.87 12.98 13.0312.25 13.1312.27 12.3712.2112.16 12.5212.05 12.4211.90 12.0912.03 12.46 12.5411.94
NL:5.23E6m/z= 275.50-276.50 MS level5
NL:7.26E6m/z= 275.50-276.50 MS level5
RT: 10.26 - 10.43
10.26 10.27 10.28 10.29 10.30 10.31 10.32 10.33 10.34 10.35 10.36 10.37 10.38 10.39 10.40 10.41 10.42Time (min)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Rel
ativ
e A
bund
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10.3610.33
10.4210.26
NL:1.19E7m/z= 251.50-252.50 MS level5
RT: 11.06 - 11.20
11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19Time (min)
0
5
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15
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50
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60
65
70
75
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95
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Rel
ativ
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bund
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11.14
11.11
11.16 11.17 11.19 11.2011.0811.07
NL:6.19E6m/z= 251.50-252.50 MS level5
Peak Shape and Resolution
The advantage of hydrogen carrier is that higher than helium linear velocities can be used without sacrificing resolution. With less residence time in the stationary phase, the late eluting polynuclear aromatic hydrocarbons (PNAs) come out with a narrower peak width (Figure 8). The critical separation of benzo[g&h]flouranthene was easily achieved (Figure 9).
Hydrogen
Helium
Hydrogen Helium
RT: 0.00 - 13.26
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Rel
ativ
e A
bund
ance
7.76
6.21 6.77 8.18
7.30
4.55
5.65 7.313.43 5.09
8.57
4.01
8.92
7.79 9.25
7.015.97
5.505.29 6.55
9.564.92
7.47
3.75 9.854.352.80 3.21
10.133.192.63 10.24
11.472.572.151.96 10.681.70 10.95 11.62 12.01 13.2312.80
NL:6.22E8TIC MSdiesel5
Run Time
The run time was reduced by using a smaller i.d. column (TG-5MS 20 m x 0.18 mm x 0.36 µm) and hydrogen carrier gas. The more commonly used column with helium is the TG-5MS 30 m x 0.25 mm x 0.5 µm (Figure 16).
FIGURE 14. TIC 5 % diesel sample
FIGURE 10. Comparison of linearity with helium and hydrogen carrier (the compounds on the insert required R2 fit with hydrogen)
FIGURE 16. Comparison of run time with hydrogen and helium at 1 mL/min
FIGURE 12. Instrument Detection Limits (ppm) Average = 0.15 ppm
Butylbenzyl phthalate Dichlorobenzidine Di-n-octylphthlate
Bis-2-chloroisopropylether
FIGURE 15. Stability of internal standard areas during injection of 5% diesel
C:\chem\...\level8.d\level8 12/5/2012 2:04:03 PM
RT: 0.00 - 20.01
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (min)
0
10
20
30
40
50
60
70
80
90
1000
10
20
30
40
50
60
70
80
90
100
Rel
ativ
e A
bund
ance
6.83
3.8510.24
9.198.987.904.56
12.3510.276.26 7.645.186.97 11.198.065.65
8.4111.163.88 4.61 11.449.763.34 7.014.2610.79 12.558.84
3.31
2.25 2.981.80 2.51
12.708.80 13.21 13.849.447.58 12.43 14.6212.1310.717.46 10.656.63
8.59 13.969.56 13.158.066.14 10.899.0111.27 15.37
9.61 18.0815.857.22 12.575.36 15.335.34 10.02
6.04 6.76
18.71
3.8415.92
2.82
11.32 18.913.24 16.42 17.112.65 4.17
NL:5.35E8TIC MSlevel8
NL:1.12E8TIC MS03091102_110309112925
Hydrogen 1 mL/min (TG-5MS 20 m x 0.18 mm x 0.36µm)
Helium 1 mL/min (TG-5MS 30 m x 0.25 mm x 0.5µm)
FIGURE 11. Typical linearity plots with hydrogen carrier
Linearity
A linearity study was performed in the range of concentration from 1 to 200 ppm in CH2Cl2. The results are shown in Figures 10 and 11 below. Helium carrier gave lower relative percent standard deviations (%RSD) than hydrogen but still met the criteria for the method. A few compounds required the fit of least squares (R2 = > 0.99).
© 2013 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries. This information is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others.
5Thermo Scientific Poster Note • PN10326_e 05/13S
Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Jessie Butler, Alexander N. Semyonov, Pat O’Brien Thermo Fisher Scientific, Austin, Texas, USA
Conclusion GC-MS analysis of SVOCs was performed in accordance with US EPA Method 8270 on a TRACE 1310 GC coupled with an ISQ single quadrupole mass spectrometer utilizing hydrogen as a carrier gas. Key modifications to both GC and MS hardware and methods necessary for successful migration to hydrogen carrier were performed. The final, optimized EPA Method 8270 fully was migrated to hydrogen carrier gas with improved peak shape, resolution, and run time. The ISQ GC-MS was stable and maintained good ion ratio stability after injecting 5% diesel samples.
Resolution was good and peak shape was improved
Linearity met the criteria of the method
Sensitivity was within a factor of 2 of that obtained with helium carrier gas
Ion ratio stability and robustness were good
Run time was shortened
References 1. EPA Method 8270D, Semi-volatile Organic Compounds by Gas Chromatography/
Mass Spectrometry (GC/MS) Rev. 4, 2007, Environmental Protection Agency.
Overview Purpose: Optimize US EPA Method 8270 with hydrogen carrier gas
Methods: Configure hydrogen carrier with smaller id column and installation of hydrogen kit on mass spectrometer
Results: Improved peak shape, resolution, and run time
Introduction The global helium shortage and price increase of this non-renewable noble gas cause more and more laboratories to migrate to hydrogen as a carrier gas. This transition is easy for the gas chromatography (GC) methods utilizing FID, TCD, ECD, and other non-mass-selective detectors. However, for the gas chromatography- mass spectrometry (GC-MS) methods, especially complex and regulated ones, migration to hydrogen carrier gas presents significant challenges. In addition to the changes in chromatographic conditions of the run due to the physical property differences of hydrogen, its chemical reactivity brings about chemical reactions in the mass spectrometer’s ion source that do not occur with helium.
The analysis of semi-volatile organic compounds (SVOCs) in wastewater by United States Environmental Protection Agency (EPA) Method 82701 involves identification and quantitation of more than 120 analytes of varying chemical structure, polarity and volatility. The diversity of the analytes in this method presents particular challenges when migrating from helium to hydrogen carrier.
GC-MS analysis of SVOCs was performed in accordance with EPA Method 8270 on the Thermo Scientific™ TRACE™ 1310 GC coupled to a Thermo Scientific™ ISQ™ single quadrupole mass spectrometer using helium or hydrogen as carrier gases. Key modifications to both GC and MS hardware and methods are necessary for successfully switching to hydrogen. The final, optimized EPA Method 8270 was fully migrated to hydrogen carrier gas with improved peak shape, resolution, and run time.
MethodsSample Preparation
All standards were prepared in methylene chloride. A performance mix containing pentachlorophenol, DFTPP, benzidine, and p,p’-DDT was made at a concentration of 50 ppm. A calibration curve was prepared from 1 to 200 ppm with internal standards and surrogates at 40 ppm.
Gas Chromatography
An instant connect split/splitless injector module was used in the split mode. The standard Thermo Scientific™ TraceGOLD™ TG-5MS capillary column (30 m x 0.25 mm x 0.5 µm) was replaced with a TraceGOLD TG-5MS column of smaller i.d. (20 m x 0.18 mm x 0.36 µm). A one microliter injection was made.
Mass Spectrometry
The ISQ mass spectrometer was equipped with the new hydrogen kit and preconditioned by baking out with an elevated hydrogen carrier flow rate.
Data Analysis
Data was collected using Thermo Scientific™ Xcalibur™ 2.0 acquisition software, and processing was performed using Thermo Scientific™ Target 4.14 software. Xcalibursoftware was configured for direct target processing. A typical chromatogram of a 40 ppm standard is shown in Figure 1.
FIGURE 1. TIC of 40 ppm standard with hydrogen carrier gas
ResultsStabilization Bake Out for Hydrogen Carrier Gas
When switching from helium to hydrogen as a carrier gas, a brief stabilization period is required. If using a hydrogen generator, no gas filters are necessary. Gas lines should be plumbed with pre-cleaned 1/8” stainless steel tubing. If a cylinder of hydrogen is used, grade UHP 5.0 or better is required with inline gas purifiers. The hydrogen kit is installed in the mass spectrometer. The source temperature is set to 350 °C for bake out. The hydrogen carrier is set to 4 mL/min. The filament is turned on for one hour during the bake out period. After bake out, the hydrogen flow is reduced to 1 mL/min, and the source temperature was set to 325 °C. Figures 2–5 show the effect of bake out. The hydrogen gas strips the contamination off the entire flow path. If water is present in the gas lines, a m/z of 19 is seen. This is due to protonation of water (M+1). Other ions typical of chemical ionization and protonation are also seen, m/z 29 and m/z 41 (Figure 2). Elevated levels of low mass hydrocarbons are observed in the calibration gas spectrum (Figure 4). These all are reduced after the one hour bake out.
Compounds: R2 = >0.99 nitrophenols nitroanilines dinitrophenols 4,6-dinityrophenol-2-methylphenol trichlorophenols dinitrotoluenes hexachlorocyclopentadiene tribromophenol pentachlorophenol butylbenzylphthalate di-n-octylphthalatebis(2 ethylhexyl)phthalate
FIGURE 6. Comparison of inlet pressure for helium and hydrogen for a 0.25 mm and 0.18 mm i.d. column
FIGURE 8. Improvement of Peak Shape for Indeno[1,2,3-cd]pyrene (peak1) & benzo[g,h,i]perylene (peak 2)
FIGURE 9. Critical Separation of benzo[g&h]flouranthene
FIGURE 13. Ion Ratios for DFTPP Selecting the Appropriate Column Dimensions and Inlet Pressure
Due to the lower viscosity of hydrogen carrier gas as compared to helium, a lower head pressure is required to obtain 1 mL/min of column flow rate. By reducing the i.d. of the column, the pressure may be set to usable level (Figure 6). Also note the reduction in the vapor volume of methylene chloride at higher pressures (Figure 7).
Sensitivity
The sensitivity of the method using hydrogen carrier was within a factor of two to that achieved with helium. The average Instrument Detection Limit (IDL) with helium was 0.082 ppm and 0.15 ppm with hydrogen. The chart in Figure 12 shows most of the IDLs at around 0.1 ppm. Replicate injections of the standard were made at 1 ppm.
RT: 0.00 - 13.27
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Rel
ativ
e A
bund
ance
6.83
3.85
10.24
9.198.987.904.56
12.3510.276.26 7.645.18
6.97 11.198.066.455.65 6.08
5.34 8.41
11.163.88 4.6111.449.763.34
7.01 9.45 11.724.267.37 10.79 12.558.844.67
5.955.02
9.973.31
2.25 2.981.80
2.51
8.4810.54 12.17 12.70
NL:5.35E8TIC MSlevel8
FIGURE 2. Air/water spectrum before bake out
FIGURE 3. Air/water spectrum after bake out
m/z 19
m/z 19
m/z 18 m/z 18
m/z 29
m/z 28
m/z 28
m/z 29
FIGURE 4. Cal gas (FC-43) spectrum before bake out
FIGURE 5. Cal gas (FC-43) spectrum after bake out
RT: 0.000 - 13.008
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
10
20
30
40
50
60
70
80
90
1000
10
20
30
40
50
60
70
80
90
100
Rel
ativ
e A
bund
ance
7.0318.596
5.7954.039
9.808
3.016
1.368
2.002 6.358 7.8747.075 9.423 11.1144.6983.281 5.057 10.099 11.5208.953 12.8018.309
6.802
9.338
5.4303.730
2.719
6.035 7.633 9.0366.849 10.4119.5774.3673.000 4.721 10.7422.6811.079 1.526 11.648 12.000
NL:2.12E8TIC MSlevel1
NL:1.55E8TIC MS1ng
FIGURE 7. Methylene chloride solvent tailing at low vs. high inlet pressures
8 psi
13 psi
Robustness and Ion Ratio Stability
The stability of ion ratios for DFTPP was studied. The values were very stable. The performance is shown in Figure 13. Next, a robustness study was run by injecting 30 of 5 % diesel samples in methylene chloride. The samples also contained 40 ppm of the internal standards. The diesel sample TIC is shown in Figure 14. A chart was plotted of the internal standards in Figure 15. A check standard was run after each set of 10 diesel samples. All check standards met the QC criteria for the method.
RT: 11.87 - 13.34
11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13.0 13.1 13.2 13.3Time (min)
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10
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Rel
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12.29
12.50
12.5312.34 12.5612.37 12.63 12.72 12.76 12.87 12.9312.81 13.1213.01 13.17 13.2613.0612.2612.11 12.1412.0211.9711.8812.65
13.23
12.72 12.75 12.9412.84 12.87 12.98 13.0312.25 13.1312.27 12.3712.2112.16 12.5212.05 12.4211.90 12.0912.03 12.46 12.5411.94
NL:5.23E6m/z= 275.50-276.50 MS level5
NL:7.26E6m/z= 275.50-276.50 MS level5
RT: 10.26 - 10.43
10.26 10.27 10.28 10.29 10.30 10.31 10.32 10.33 10.34 10.35 10.36 10.37 10.38 10.39 10.40 10.41 10.42Time (min)
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5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
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90
95
100
Rel
ativ
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10.3610.33
10.4210.26
NL:1.19E7m/z= 251.50-252.50 MS level5
RT: 11.06 - 11.20
11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19Time (min)
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100
Rel
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bund
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11.14
11.11
11.16 11.17 11.19 11.2011.0811.07
NL:6.19E6m/z= 251.50-252.50 MS level5
Peak Shape and Resolution
The advantage of hydrogen carrier is that higher than helium linear velocities can be used without sacrificing resolution. With less residence time in the stationary phase, the late eluting polynuclear aromatic hydrocarbons (PNAs) come out with a narrower peak width (Figure 8). The critical separation of benzo[g&h]flouranthene was easily achieved (Figure 9).
Hydrogen
Helium
Hydrogen Helium
RT: 0.00 - 13.26
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
0
5
10
15
20
25
30
35
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45
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55
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Rel
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7.76
6.21 6.77 8.18
7.30
4.55
5.65 7.313.43 5.09
8.57
4.01
8.92
7.79 9.25
7.015.97
5.505.29 6.55
9.564.92
7.47
3.75 9.854.352.80 3.21
10.133.192.63 10.24
11.472.572.151.96 10.681.70 10.95 11.62 12.01 13.2312.80
NL:6.22E8TIC MS diesel5
Run Time
The run time was reduced by using a smaller i.d. column (TG-5MS 20 m x 0.18 mm x 0.36 µm) and hydrogen carrier gas. The more commonly used column with helium is the TG-5MS 30 m x 0.25 mm x 0.5 µm (Figure 16).
FIGURE 14. TIC 5 % diesel sample
FIGURE 10. Comparison of linearity with helium and hydrogen carrier (the compounds on the insert required R2 fit with hydrogen)
FIGURE 16. Comparison of run time with hydrogen and helium at 1 mL/min
FIGURE 12. Instrument Detection Limits (ppm) Average = 0.15 ppm
Butylbenzyl phthalate Dichlorobenzidine Di-n-octylphthlate
Bis-2-chloroisopropylether
FIGURE 15. Stability of internal standard areas during injection of 5% diesel
C:\chem\...\level8.d\level8 12/5/2012 2:04:03 PM
RT: 0.00 - 20.01
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (min)
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6.83
3.8510.24
9.198.987.904.56
12.3510.276.26 7.645.186.97 11.198.065.65
8.4111.163.88 4.61 11.449.763.34 7.014.2610.79 12.558.84
3.31
2.25 2.981.80 2.51
12.708.80 13.21 13.849.447.58 12.43 14.6212.1310.717.46 10.656.63
8.59 13.969.56 13.158.066.14 10.899.0111.27 15.37
9.61 18.0815.857.22 12.575.36 15.335.34 10.02
6.04 6.76
18.71
3.8415.92
2.82
11.32 18.913.24 16.42 17.112.65 4.17
NL:5.35E8TIC MSlevel8
NL:1.12E8TIC MS03091102_110309112925
Hydrogen 1 mL/min (TG-5MS 20 m x 0.18 mm x 0.36µm)
Helium 1 mL/min (TG-5MS 30 m x 0.25 mm x 0.5µm)
FIGURE 11. Typical linearity plots with hydrogen carrier
Linearity
A linearity study was performed in the range of concentration from 1 to 200 ppm in CH2Cl2. The results are shown in Figures 10 and 11 below. Helium carrier gave lower relative percent standard deviations (%RSD) than hydrogen but still met the criteria for the method. A few compounds required the fit of least squares (R2 = > 0.99).
© 2013 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries. This information is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others.
6 Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Fast GC-MS Analysis of Semi-Volatile Organic Compounds: Migrating from Helium to Hydrogen as a Carrier Gas in US EPA Method 8270
Jessie Butler, Alexander N. Semyonov, Pat O’Brien Thermo Fisher Scientific, Austin, Texas, USA
Conclusion GC-MS analysis of SVOCs was performed in accordance with US EPA Method 8270 on a TRACE 1310 GC coupled with an ISQ single quadrupole mass spectrometer utilizing hydrogen as a carrier gas. Key modifications to both GC and MS hardware and methods necessary for successful migration to hydrogen carrier were performed. The final, optimized EPA Method 8270 fully was migrated to hydrogen carrier gas with improved peak shape, resolution, and run time. The ISQ GC-MS was stable and maintained good ion ratio stability after injecting 5% diesel samples.
Resolution was good and peak shape was improved
Linearity met the criteria of the method
Sensitivity was within a factor of 2 of that obtained with helium carrier gas
Ion ratio stability and robustness were good
Run time was shortened
References 1. EPA Method 8270D, Semi-volatile Organic Compounds by Gas Chromatography/
Mass Spectrometry (GC/MS) Rev. 4, 2007, Environmental Protection Agency.
Overview Purpose: Optimize US EPA Method 8270 with hydrogen carrier gas
Methods: Configure hydrogen carrier with smaller id column and installation of hydrogen kit on mass spectrometer
Results: Improved peak shape, resolution, and run time
Introduction The global helium shortage and price increase of this non-renewable noble gas cause more and more laboratories to migrate to hydrogen as a carrier gas. This transition is easy for the gas chromatography (GC) methods utilizing FID, TCD, ECD, and other non-mass-selective detectors. However, for the gas chromatography- mass spectrometry (GC-MS) methods, especially complex and regulated ones, migration to hydrogen carrier gas presents significant challenges. In addition to the changes in chromatographic conditions of the run due to the physical property differences of hydrogen, its chemical reactivity brings about chemical reactions in the mass spectrometer’s ion source that do not occur with helium.
The analysis of semi-volatile organic compounds (SVOCs) in wastewater by United States Environmental Protection Agency (EPA) Method 82701 involves identification and quantitation of more than 120 analytes of varying chemical structure, polarity and volatility. The diversity of the analytes in this method presents particular challenges when migrating from helium to hydrogen carrier.
GC-MS analysis of SVOCs was performed in accordance with EPA Method 8270 on the Thermo Scientific™ TRACE™ 1310 GC coupled to a Thermo Scientific™ ISQ™ single quadrupole mass spectrometer using helium or hydrogen as carrier gases. Key modifications to both GC and MS hardware and methods are necessary for successfully switching to hydrogen. The final, optimized EPA Method 8270 was fully migrated to hydrogen carrier gas with improved peak shape, resolution, and run time.
MethodsSample Preparation
All standards were prepared in methylene chloride. A performance mix containing pentachlorophenol, DFTPP, benzidine, and p,p’-DDT was made at a concentration of 50 ppm. A calibration curve was prepared from 1 to 200 ppm with internal standards and surrogates at 40 ppm.
Gas Chromatography
An instant connect split/splitless injector module was used in the split mode. The standard Thermo Scientific™ TraceGOLD™ TG-5MS capillary column (30 m x 0.25 mm x 0.5 µm) was replaced with a TraceGOLD TG-5MS column of smaller i.d. (20 m x 0.18 mm x 0.36 µm). A one microliter injection was made.
Mass Spectrometry
The ISQ mass spectrometer was equipped with the new hydrogen kit and preconditioned by baking out with an elevated hydrogen carrier flow rate.
Data Analysis
Data was collected using Thermo Scientific™ Xcalibur™ 2.0 acquisition software, and processing was performed using Thermo Scientific™ Target 4.14 software. Xcalibursoftware was configured for direct target processing. A typical chromatogram of a 40 ppm standard is shown in Figure 1.
FIGURE 1. TIC of 40 ppm standard with hydrogen carrier gas
ResultsStabilization Bake Out for Hydrogen Carrier Gas
When switching from helium to hydrogen as a carrier gas, a brief stabilization period is required. If using a hydrogen generator, no gas filters are necessary. Gas lines should be plumbed with pre-cleaned 1/8” stainless steel tubing. If a cylinder of hydrogen is used, grade UHP 5.0 or better is required with inline gas purifiers. The hydrogen kit is installed in the mass spectrometer. The source temperature is set to 350 °C for bake out. The hydrogen carrier is set to 4 mL/min. The filament is turned on for one hour during the bake out period. After bake out, the hydrogen flow is reduced to 1 mL/min, and the source temperature was set to 325 °C. Figures 2–5 show the effect of bake out. The hydrogen gas strips the contamination off the entire flow path. If water is present in the gas lines, a m/z of 19 is seen. This is due to protonation of water (M+1). Other ions typical of chemical ionization and protonation are also seen, m/z 29 and m/z 41 (Figure 2). Elevated levels of low mass hydrocarbons are observed in the calibration gas spectrum (Figure 4). These all are reduced after the one hour bake out.
Compounds: R2 = >0.99 nitrophenols nitroanilines dinitrophenols 4,6-dinityrophenol-2-methylphenol trichlorophenols dinitrotoluenes hexachlorocyclopentadiene tribromophenol pentachlorophenol butylbenzylphthalate di-n-octylphthalatebis(2 ethylhexyl)phthalate
FIGURE 6. Comparison of inlet pressure for helium and hydrogen for a 0.25 mm and 0.18 mm i.d. column
FIGURE 8. Improvement of Peak Shape for Indeno[1,2,3-cd]pyrene (peak1) & benzo[g,h,i]perylene (peak 2)
FIGURE 9. Critical Separation of benzo[g&h]flouranthene
FIGURE 13. Ion Ratios for DFTPPSelecting the Appropriate Column Dimensions and Inlet Pressure
Due to the lower viscosity of hydrogen carrier gas as compared to helium, a lower head pressure is required to obtain 1 mL/min of column flow rate. By reducing the i.d. of the column, the pressure may be set to usable level (Figure 6). Also note the reduction in the vapor volume of methylene chloride at higher pressures (Figure 7).
Sensitivity
The sensitivity of the method using hydrogen carrier was within a factor of two to that achieved with helium. The average Instrument Detection Limit (IDL) with helium was 0.082 ppm and 0.15 ppm with hydrogen. The chart in Figure 12 shows most of the IDLs at around 0.1 ppm. Replicate injections of the standard were made at 1 ppm.
RT: 0.00 - 13.27
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6.83
3.85
10.24
9.198.987.904.56
12.3510.276.26 7.645.18
6.97 11.198.066.455.65 6.08
5.34 8.41
11.163.88 4.6111.449.763.34
7.01 9.45 11.724.267.37 10.79 12.558.844.67
5.955.02
9.973.31
2.25 2.981.80
2.51
8.4810.54 12.17 12.70
NL:5.35E8TIC MSlevel8
FIGURE 2. Air/water spectrum before bake out
FIGURE 3. Air/water spectrum after bake out
m/z 19
m/z 19
m/z 18 m/z 18
m/z 29
m/z 28
m/z 28
m/z 29
FIGURE 4. Cal gas (FC-43) spectrum before bake out
FIGURE 5. Cal gas (FC-43) spectrum after bake out
RT: 0.000 - 13.008
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
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7.0318.596
5.7954.039
9.808
3.016
1.368
2.002 6.358 7.8747.075 9.423 11.1144.6983.281 5.057 10.099 11.5208.953 12.8018.309
6.802
9.338
5.4303.730
2.719
6.035 7.633 9.0366.849 10.4119.5774.3673.000 4.721 10.7422.6811.079 1.526 11.648 12.000
NL:2.12E8TIC MSlevel1
NL:1.55E8TIC MS1ng
FIGURE 7. Methylene chloride solvent tailing at low vs. high inlet pressures
8 psi
13 psi
Robustness and Ion Ratio Stability
The stability of ion ratios for DFTPP was studied. The values were very stable. The performance is shown in Figure 13. Next, a robustness study was run by injecting 30 of 5 % diesel samples in methylene chloride. The samples also contained 40 ppm of the internal standards. The diesel sample TIC is shown in Figure 14. A chart was plotted of the internal standards in Figure 15. A check standard was run after each set of 10 diesel samples. All check standards met the QC criteria for the method.
RT: 11.87 - 13.34
11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 13.0 13.1 13.2 13.3Time (min)
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12.29
12.50
12.5312.34 12.5612.37 12.63 12.72 12.76 12.87 12.9312.81 13.1213.01 13.17 13.2613.0612.2612.11 12.1412.0211.9711.8812.65
13.23
12.72 12.75 12.9412.84 12.87 12.98 13.0312.25 13.1312.27 12.3712.2112.16 12.5212.05 12.4211.90 12.0912.03 12.46 12.5411.94
NL:5.23E6m/z= 275.50-276.50 MS level5
NL:7.26E6m/z= 275.50-276.50 MS level5
RT: 10.26 - 10.43
10.26 10.27 10.28 10.29 10.30 10.31 10.32 10.33 10.34 10.35 10.36 10.37 10.38 10.39 10.40 10.41 10.42Time (min)
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10.3610.33
10.4210.26
NL:1.19E7m/z= 251.50-252.50 MS level5
RT: 11.06 - 11.20
11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 11.16 11.17 11.18 11.19Time (min)
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11.14
11.11
11.16 11.17 11.19 11.2011.0811.07
NL:6.19E6m/z= 251.50-252.50 MS level5
Peak Shape and Resolution
The advantage of hydrogen carrier is that higher than helium linear velocities can be used without sacrificing resolution. With less residence time in the stationary phase, the late eluting polynuclear aromatic hydrocarbons (PNAs) come out with a narrower peak width (Figure 8). The critical separation of benzo[g&h]flouranthene was easily achieved (Figure 9).
Hydrogen
Helium
Hydrogen Helium
RT: 0.00 - 13.26
0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (min)
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7.76
6.21 6.77 8.18
7.30
4.55
5.65 7.313.43 5.09
8.57
4.01
8.92
7.79 9.25
7.015.97
5.505.29 6.55
9.564.92
7.47
3.75 9.854.352.80 3.21
10.133.192.63 10.24
11.472.572.151.96 10.681.70 10.95 11.62 12.01 13.2312.80
NL:6.22E8TIC MSdiesel5
Run Time
The run time was reduced by using a smaller i.d. column (TG-5MS 20 m x 0.18 mm x 0.36 µm) and hydrogen carrier gas. The more commonly used column with helium is the TG-5MS 30 m x 0.25 mm x 0.5 µm (Figure 16).
FIGURE 14. TIC 5 % diesel sample
FIGURE 10. Comparison of linearity with helium and hydrogen carrier (the compounds on the insert required R2 fit with hydrogen)
FIGURE 16. Comparison of run time with hydrogen and helium at 1 mL/min
FIGURE 12. Instrument Detection Limits (ppm) Average = 0.15 ppm
Butylbenzyl phthalate Dichlorobenzidine Di-n-octylphthlate
Bis-2-chloroisopropylether
FIGURE 15. Stability of internal standard areas during injection of 5% diesel
C:\chem\...\level8.d\level8 12/5/2012 2:04:03 PM
RT: 0.00 - 20.01
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6.83
3.8510.24
9.198.987.904.56
12.3510.276.26 7.645.186.97 11.198.065.65
8.4111.163.88 4.61 11.449.763.34 7.014.2610.79 12.558.84
3.31
2.25 2.981.80 2.51
12.708.80 13.21 13.849.447.58 12.43 14.6212.1310.717.46 10.656.63
8.59 13.969.56 13.158.066.14 10.899.0111.27 15.37
9.61 18.0815.857.22 12.575.36 15.335.34 10.02
6.04 6.76
18.71
3.8415.92
2.82
11.32 18.913.24 16.42 17.112.65 4.17
NL:5.35E8TIC MS level8
NL:1.12E8TIC MS 03091102_110309112925
Hydrogen 1 mL/min (TG-5MS 20 m x 0.18 mm x 0.36µm)
Helium 1 mL/min (TG-5MS 30 m x 0.25 mm x 0.5µm)
FIGURE 11. Typical linearity plots with hydrogen carrier
Linearity
A linearity study was performed in the range of concentration from 1 to 200 ppm in CH2Cl2. The results are shown in Figures 10 and 11 below. Helium carrier gave lower relative percent standard deviations (%RSD) than hydrogen but still met the criteria for the method. A few compounds required the fit of least squares (R2 = > 0.99).
© 2013 Thermo Fisher Scientific Inc. All rights reserved. All trademarks are the property of Thermo Fisher Scientific Inc and its subsidiaries. This information is not intended to encourage use of these products in any manner that might infringe the intellectual property rights of others.
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