Authors

C. Kai MengAgilent Technologies, Inc.2850 Centerville RoadWilmington, DE 19808-1610USA

Michael J. SzelewskiAgilent Technologies, Inc.2850 Centerville RoadWilmington, DE 19808-1610USA

Abstract

Agilent Technologies' fast GC/MSDmethod can significantly speed up thescreening of PCB congeners. Agilent'sGC method translation software (avail-able free from the Agilent TechnologiesWeb site,http://www.chem.agilent.com/cag/servsup/usersoft/main.html#mxlator)was used in developing the new methodbased on a standard 42-min method. A15-m × 0.25-mm × 0.25-mmmmm AgilentHP-5MS column was used to increaseanalysis speed up to four-fold. The timesavings were implemented in incre-ments (down to 10.5 minutes) to verifythe predictability of scaling and theaffect of scaling on the signal-to-noiseratio.

Fast Screening of PCB Congeners Using theAgilent 6890/5973N GC/MSD System

Key Words

RTL, PCB, polychlorinated biphenyls,congeners, environmental, screening,fast GC, method translation, 5973,6890, MTL

Introduction

Polychlorinated biphenyls (PCBs) area group of 209 individual compounds(known as congeners) with varyingharmful effects. Chronic (long term)exposure to some PCB formulationsby inhalation in humans results in respiratory tract symptoms, gastroin-testinal effects, mild liver effects, andeffects on the skin and eyes such aschloracne, skin rashes, and eye irritation.

PCBs are no longer produced in theUnited States and are no longer usedin the manufacture of new products.Smaller amounts of PCBs may bereleased to the air from disposal sitescontaining transformers, capacitors,and other PCB wastes, incineration ofPCB-containing wastes, and improperdisposal of the compounds to openareas. Today, PCBs are still detectedin water and soil due to the environ-mental recycling of the compound.PCBs have been detected in foodsand they bio-accumulate through the

food chain, with some of the highestconcentrations found in fish.

The analysis of PCBs normally isaccomplished using GC with an electron-capture detector (ECD).Because of the drastically differenttoxicity of the different congeners, itis of great interest to identify the indi-vidual congeners using a mass spectrometer (MS).

Agilent Technologies has developedtechniques to solve the peak identifi-cation problem based on Agilent'sretention time locking (RTL) and amass spectral library that containsthe locked retention times and char-acteristic ions for all 209 PCB con-geners. A GC/MSD method wasdeveloped based on a standard42-min method1 to screen for all con-geners. A specific combination ofcolumn stationary phase, carrier-gasflow rate, and oven temperature pro-gramming is required to lock all thecompounds to an expected retentiontimetable2. Compound identificationbased only on spectral searchingalone is difficult when the isomershave the same mass spectra.

The screening tool, integrated withinAgilent's ChemStation for MSD soft-ware, searches for all 209 congenersby first checking and integrating the

Application

Gas Chromatography

May 2000

2

expected target ion within theexpected time window. If the targetion is found, the software will thensearch and integrate the three quali-fier ions within the expected timewindow. Last, the software will printout a report showing "hits" and "possi-ble hits" (ratios of characteristic ionsthat do not match the expectedvalues in the library within specifiedlimits).

In order to improve laboratory pro-ductivity, we scaled the method forfour-fold speed-up. While a 30-m ×0.25-mm × 0.25-µm Agilent HP-5MScolumn is used for standard speed, a 15-m × 0.25-mm × 0.25-µm AgilentHP-5MS column is used for thefour-fold speed. These faster methodswere able to be scaled exactly as pre-dicted by using a combination of Agilent's method translation (MTL)and RTL software.

Often, when speeding up GC meth-ods, an analyst trades resolution forincreased analysis speed. This loss ofresolution can complicate peak iden-tification, even with a mass selectivedetector (MSD). However, becausescaling was exact, the faster methodscan be used with precisely scaledcongener libraries, making thescreening process even more power-ful and adaptable to individual needs.

Experimental

The GC method translation softwaretool was used to find operating condi-tions for the faster methods. Figure 1is a screen capture of the MTL soft-ware data entry showing the originalconditions and the new chromato-graphic conditions for a four-foldspeed gain. The column flow rate,which is helpful to avoid exceedingMSD pumping capacity3, also is foundin the table. In this study, a turbopump that could handle the 3.8 mL/min carrier flow was used.The program also determined therequired column head pressure andcorresponding oven ramp. The Agilent 6890 GC fast oven option(220/240V in the U.S.) was required

Figure 1. Screen capture showing the method translation (MTL) software data entry used ina 4X speed-gain translation.

for the faster oven ramp used in thisstudy.

General chromatographic conditionsare listed in Table 1. The RTL stan-dard used was a mixture of pesticidesand PCB congeners at 10 ppm. A 15-m× 0.25-mm × 0.25-µm Agilent HP-5MScolumn (part number 19091S-431)was used. The head pressure deter-mined by the method translation soft-ware (18 psi) was used as the startingpoint for retention time locking. Thecolumn head pressure required tolock retention times of the com-pounds to the library (the originalretention time divided by four) wasdetermined using the automated RTLprocess integrated within the AgilentChemStation for MSD.

A very important modification to the

MS method is changing the defaultvalues of "Use mass range from" to–0.50 to +0.50 amu (the defaultvalues are –0.3 to +0.7). The changescan be made from the "Extracted IonChromatograms…" dialog boxselected from the "Chromatogram" onthe menu bar.

Figure 2 shows the results of theshortened analysis times. The twochromatograms look extremely similar, except that the time axis isscaled proportionally. It is interestingto note that the last peak in the 4X analysis came out before the first

peak of the 1X analysis. BecauseMTL followed by RTL scales methodsvery precisely, scaled screeninglibraries for corresponding time

Table 1. Chromatographic Conditions

Speed Standard Four-fold

GC 110 V 220/240 VColumn 30-m × 0.25-mm × 0.25-mm 15-m × 0.25-mm × 0.25-mm

Agilent HP-5MS (part Agilent HP-5MS (part number 19091S-433) number 19091S-431)

Injection mode Splitless SplitlessColumn head pressure 18.0 psi 18.0 psiColumn flow (mL/min) 1.9 3.8Inlet control mode Constant pressure Constant pressureCarrier gas Helium HeliumInjector Temperature 250 °C 250 °COven Temperature 70 (2 min) 70 (0.5 min)

Ramp 1 25 °C/min 100150 (0 min) 150 (0 min)

Ramp 2 3 °C/min 12200 (0 min) 200 (0 min)

Ramp 3 8 °C/min 32280 (10 min) 280 (2.5 min)

Oven equilibration 2 min 2 minInjection volume 1 mL 1 mLLiner 5183-4647 5183-4647

MS Conditions (Turbo pump)Solvent delay 3 min 0.9 minTune file Atune.u Atune.uLow mass 50 amu 50 amuHigh mass 550 amu 550 amuThreshold 200 200Sampling 3 1Scans/sec 1.52 5.56Quad Temperature 150 °C 150 °CSource Temperature 230 °C 230 °CTransfer line Temperature 280 °C 280 °CAcquisition mode Scan (EI) Scan (EI)

3

reductions can be obtained by divid-ing the retention times in the libraryby the speed gain (which does nothave to be an integer).

Conclusion

The highly accurate and reproduciblepressure and temperature control ofthe Agilent 6890 GC allows precisescaling of a standard 42-min GC/MSDmethod. The run time was shortenedto 10.5 minutes using a fast ovenramp rate and a 15-meter 250-microncolumn. The combination of MTL andRTL facilitated scaling and yieldedexact scaling. RTL libraries can bescaled accurately to correspond tothe faster analyses. The GC/MSD con-ditions used are the same as the fastpesticide method4, which allows forscreening pesticides and PCB congeners in a single analysis.

References1. B. D. Quimby, L.M. Blumberg,

M. S. Klee, and P. L. Wylie, "Precise Time-Scaling of GasChromatographic Methods UsingMethod Translation and RetentionTime Locking," Application Note 228-401, Agilent publicationnumber 5967-5820E, May 1998.

2. H. Prest, P. L. Wylie, K. Weiner,and D. Agnew, "Efficient Screen-ing for Pesticides and EndocrineDisrupters Using the HP 6890/5973 GC/MSD System," Agilentpublication number 5968-4884E,April 1999.

3. H. Prest, "GC Column Selectionand Pumping Considerations forElectron and Chemical IonizationMSD operation," Agilent publica-tion number 5968-7958E, November 1999.

4. C. Kai Meng and MichaelSzelewski, "Fast Screening of Pesticides and Endocrine Disrupters Using the Agilent 6890/5973N GC/MSDSystem, Part II", Agilent publica-tion number 5980-1057E, May 2000.

Abundance

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010.00 15.00 20.00Time 25.00 30.00

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1X

4X

39 PCB Congeners

HP-5MS, 30-m × 0.25-mm × 0.25-µm

HP-5MS, 15-m × 0.25-mm × 0.25-µm

Figure 2. The TICs of the standard speed and fast (4X) analyses. The standard analysis (1X)was 42 minutes long.

Agilent shall not be liable for errors contained herein or forincidental or consequential damages in connection with thefurnishing, performance, or use of this material.

Information, descriptions, and specifications in this publicationare subject to change without notice.

Copyright© 2000Agilent Technologies, Inc.

Printed in the USA 5/20005980-1472E