det report detector engineering & technology, inc.det-gc.com/dr69.pdf · agilent 6890/7890 and...

DETector Engineering & Technology, inc.486 North Wiget Lane Walnut Creek, CA 94598-2408 USAPhone: 925-937-4203; FAX: 925-937-7581www.det-gc.com e-mail: [email protected]

DET REPORTNO. 69 JUNE 2015

1.) “THINKING BEYOND THE NPD BOX” - INEXPENSIVE CONVERSION OF NPDEQUIPMENT TO MULTIPLE MODES OF SELECTIVE GC DETECTION.

2.) GC-CCID DIFFERENTIATION BETWEEN SATURATE VS. UNSATURATE AND MONO-UNSATURATE VS. POLYUNSATURATE FAMEs.

3.) TID-10 (TID-1) THERMIONIC SURFACE IONIZATION DETECTION OF DEGRADATIONPRODUCTS IN PETROLEUM AND BIOFUEL SAMPLES.

4.) TID-10 (TID-1) SELECTIVE DETECTION OF COMPOUNDS CONTAINING A FIVEMEMBER CARBON OR NITROGEN RING STRUCTURE.

By P.L. Patterson

1.) “THINKING BEYOND THE NPD BOX” - INEXPENSIVE CONVERSION OF NPDEQUIPMENT TO MULTIPLE MODES OF SELECTIVE GC DETECTION.

Figure 1 depicts the NPD equipment configuration used onAgilent 6890/7890 and Thermo Trace 1300 GC models, aswell as in DET retrofit hardware for other GC models. Thebasic components are an electrically heated ion source(bead) and a ion collector cylinder, contained in a detectorstructure that has provisions for adding H2, Air, and Makeupdetector gases in addition to effluent from the GC column.DET’s development of ceramic ion sources with differentcatalytic ionizing activities, combined with the availability forsupplying 3 different types of detector gases, allows NPDequipment to be transformed to modes of selectivedetection other than just NP. This conversion is both easyand inexpensive, and it provides a much wider range ofpossible applications for the same basic equipment.

There are 4 key operating parameters that determinecompound selectivity and sensitivity for the equipmentdepicted in Figure 1:1. Catalytic ionizing activity of the ion source as determinedby additives in the ceramic coating;2. Temperature of the ion source as determined by theelectrical heating current supplied;3. Composition of the detector gases supplied (e.g., N2, Air,O2, N2O, H2, and combinations thereof);4. The magnitude of the polarizing voltage between the ionsource and collector.Multiple modes of selective detection are achieved throughvarious permutations of these 4 key parameters. Selectivitypossibilities include compounds containing, O, N, P, Cl, Br,or I atoms, or NO2, CH2, Pyrrole, and certain other functionalgroups.

Figure 1. Basic components of NPD equipment. Different modesof selective detection are achieved through inexpensive changesin the type of ion source and the composition of detector gasessupplied. DET’s ceramic ion sources are $410 each. No otherdetector technology provides so much versatility for so little cost.

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2.) GC-CCID DIFFERENTIATION BETWEEN SATURATE VS. UNSATURATE AND MONO-UNSATURATE VS. POLY-UNSATURATE FAMEs

Catalytic Combustion Ionization Detection (CCID) is a GCdetector method in which the sample compound itselfprovides the fuel for a momentary burst of flame ionizationas it impacts the surface of a catalytically active ceramic.Since the process involves combustion ignition, the detectorgas environment must contain Oxygen to support thatcombustion. Also, there is a sample threshold amountbelow which there is not enough sample to fuel thecombustion. For a compound such as n-C16 , that thresholdlevel is in the range of 20 - 200 ng, depending on thetemperature of the ceramic ionizing surface, and theOxygen concentration in the detector gases.

The unique characteristic of CCID is that it selectivelydetects compounds containing chains of the Methylene(CH2) functional group. This includes Alkanes, Alkenes,FAMEs, and Triglycerides, amongst others. The otherunique characteristic of CCID is that it does not igniteresponses from Aromatic or Cyclo-Hydrocarbons.Therefore, this CCID technology provides an unprecedentedmeans of generating simplified GC fingerprints of selectedconstituents in otherwise complex Petroleum and Biofuelsamples.

CCID is a detection mode that is achieved through simpleand inexpensive conversion of NPD equipment. The keyelement in CCID is a TID-10 ion source (i.e., more robustversion of an earlier TID-1 ion source) which has anespecially high catalytic activity. TID-10 causes combustionignition to occur at relatively low temperatures in the rangeof 300 - 400oC, and that combustion is due to oxidation of CH2 functional groups. As a general rule, the more CH2

groups in a sample compound, the greater the signalresponse. Consequently, when CCID detection is applied toreal world Petroleum and Biofuel samples, it produceschromatograms in which responses of high boilingconstituents (i.e., bigger molecules with longer elutiontimes) are magnified relative to lower boiling constituents.

Previous DET Reports have described CCID detection ofcompounds containing Linear Chains of CH2 groups(examples, n-Alkanes, saturated FAMEs). Also discussedpreviously was that the presence of a Branched Methyl(CH3) group, or a Carbon Double Bond in a samplecompound’s molecular structure suppresses CCIDresponse even when the sample compound contains manyCH2 groups (e.g., Alkenes or iso-Alkanes vs. n-Alkanes).Further investigation of CCID characteristics revealed thatincreasing the Oxygen concentration in the detector gases

resulted in increasing the relative responses of bothBranched and Double Bonded compounds to magnitudesmore comparable to Linear Chain responses. Recent re-examination of previous data reveals that CCID alsoprovides additional differentiation between compoundscontaining one Carbon Double Bond (Mono-Unsaturates)and compounds containing Two or more Carbon DoubleBonds (Poly-Unsaturates). This is illustrated in Figure 2 forthe analysis of a mixture of Saturated and UnsaturatedFAME compounds. With a low concentration of Oxygen inthe detector gas, CCID detection (TID-1-Air) detected onlythe Saturates. With a higher concentration of Oxygen (TID-1-Oxygen), the Saturate peaks in the chromatogram wereaccompanied by additional peaks due to the Mono-Unsaturates in the sample, but not the Unsaturates. havingmore than one Carbon Double Bond.

The sample analyzed in Figure 2 was Supelco 77588-Uwhich was a 10 mg/mL solution of FAMEs mixed in theweight proportions shown. Several other features of theFigure 2 data are as follows:

1.) The solvent for the FAME sample was MethyleneChloride which can produce a large solvent peak from theTID-10 ion source. To avoid this baseline upset, the heatingcurrent to the ion source was turned off during solventelution through the detector. This was accomplished byactivating a “Heating Current OFF” run time event onThermo NPD electronics. Alternatively, sample dilutions insolvents that do not contain Cl atoms provide much lesssolvent tailing problems.

2.) For this diluted mixture of FAMEs, the CCIDchromatogram was missing some peaks for early elutingcompounds containing the lowest numbers of CH2 groupsbecause those compounds fell below the thresholdrequirement for combustion ignition.

3.) Compared to the FID chromatogram, the CCIDchromatogram exhibited increasing peak responses withincreasing length of CH2 chains in the FAME constituents.

4.) In the FID chromatogram, later eluting FAMEcompounds were not well resolved with the GC conditionsthat were used. CCID response differentiation betweenSaturates and Unsaturates provided clearer resolutionamongst these later eluting sample constituents.

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FAMEs SAMPLE: 1.) Butyric (C4:0), 4wt%; 2.) Caproic (C6:0), 4wt%; 3.) Caprylic (C8:0), 4wt%; 4.) Capric (C10:0), 4wt%; 5.) Undecanoic (C11:0), 2wt%; 6.) Lauric (C12:0), 4wt%;7.) Tridecanoic (C13:0), 2wt%; 8.) Myristic (C14:0), 4wt%; 9.) Myristoleic (C14:1), 2wt%;10.) Pentadecanoic (C15:0), 2wt%; 11.) cis-10-Pentadecenoic (C15:1), 2wt%;12.) Palmitic (C16:0), 6wt%; 13.) Palmitoleic (C16:1), 2wt%; 14.) Heptadecanoic (C17:0), 2wt%;15.) cis-10-Heptadecenoic (C17:1), 2wt%; 16.) Stearic (C18:0), 4wt%; 17.) Oleic (C18:1n9c), 4wt%; 18.) Elaidic (C18:1n9t), 2wt%; 19.) Linoleic (C18:2n6c), 2wt%;20.) Linolelaidic (C18:2n6t), 2wt%; 21.) ã-Linolenic (C18:3n6), 2wt%; 22.) á-Linolenic (C18:3n3), 2wt%; 23.) Arachidic (C20:0), 4wt%; 24.) cis-11-Eicosenoic (C20:1n9), 2wt%; 25.) cis-11,14-Eicosadienoic (C20:2), 2wt%:26.) cis-8,11,14-Eicosatrienoic (C20:3n6),2wt%; 27.) cis-11,14,17-Eicosatrienoic (C20:3n3),2wt%; 28.) Arachidonic (C20:4n6), 2wt%;29.) cis-5,8,11,14,17 Eicosapentaenoic(C20:5n3), 2wt%;30.) Heneicosanoic (C21:0), 2wt%; 31.) Behenic (C22:0), 4wt%; 32.) Erucic (C22:1n9), 2wt%;33.) cis-13,16-Docosadienoic (C22:2),2wt%;34.) cis-4,7,10,13,16,19-Docosahexaenoic(C22:6n3), 2wt%;35.) Tricosanoic (C23:0), 2wt%; 36.)Lignoceric (C24:0), 4wt%;37.) Nervonic (C24:1n9), 2wt%.

Figure 2. Comparison of FID and CCID responses for a mixture of Saturate andUnSaturate FAMEs. CCID data are chromatograms labeled “TID-1". TID-1 is anearlier, less robust version of a TID-10 ion source. TID-10 has the sameresponse as TID-1. CCID with Air detector gas responds only to the SaturateFAMEs. CCID with Oxygen detector gas includes added peaks due to Mono-Unsaturates, but not the Poly-Unsaturates.

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Figure 3 compares FID, CCID, and TID-1-Nitrogenchromatograms for a sample of B20 Biodiesel prepared asa dilution in Methylene Chloride. As indicated previously,TID-1 was an earlier, less robust ceramic formulation thatprovided the same response now obtained from a TID-10ion source. Also as mentioned earlier, the upsetting effectof a chlorinated solvent can be eliminated by turning off theheating current during solvent elution. That procedure wasused for the CCID and TID data of Fig. 3.

In Fig. 3, peaks labeled “C” refer to Linear Alkanes, whilepeaks labeled “F” are FAMEs. Whereas the FAME peaks inthe FID chromatogram were not well resolved, there wassufficient resolution in the CCID chromatogram to identifythe main FAME components, Palmitic (F12), Oleic (F17),and Stearic (F16). This peak resolution was a consequenceof the CCID differentiation between Saturates vs.Unsaturates, and Mono-Unsaturates vs. Poly-Unsaturates.

When the detector gas environment was changed toNitrogen, the prominent peaks due to Linear Alkanes andthe major FAMEs disappeared, but still leaving a number ofpeaks that have not yet been identified.

Fig. 3

3.) TID-10 (TID-1) THERMIONIC SURFACE IONIZATION DETECTION OFDEGRADATION PRODUCTS IN PETROLEUM AND BIOFUEL

Petroleum and Biofuel mixtures can degrade in time uponexposure to Air, and/or interaction with a storage vessel.Figures 4 - 6 illustrate how the selectivity and high sensitivityof TID-10 surface ionization can reveal degradation productsas they accumulate.

Figure 4 compares chromatograms of an aged B100Biodiesel sample that had acquired a slight rancid aroma.CCID detection provided resolution of the main FAMEconstituents plus enhanced peaks “d1 - d3" associated withoxidative degradation of the sample. Changing to Nitrogenas the detector gas provided even greater enhancement ofthe degradation peaks while eliminating the CCID typeresponse to the FAMEs. TID-10 is known to be especiallysensitive to Phenol, Carboxylic Acid, and Glycol typeOxygenated compounds.

Figure 5 illustrates the selective detection of degradationproducts that build up in time with usage of Motor Oils.Figure 6 illustrates extraneous contamination that can buildup with storage of Gasoline samples in commonly usedPolyethylene containers.

Fig. 4

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Fig.5

Fig. 6

4.) TID-10 (TID-1) SELECTIVE DETECTION OF COMPOUNDS CONTAINING A

FIVE MEMBER CARBON OR NITROGEN RING STRUCTURE

The Thermionic Surface Ionization process using a TID-10,

or its predecessor TID-1 ion source, is very sensitive to

compounds containing electronegative atoms or functional

groups, and the response often depends on where those

electronegative entities are located within a compound’s

molecular structure. One of the particular types of

compounds that respond selectively to TID-10 ionization are

those containing a five member ring structure. Figure 7

illustrates this in comparing FID, NPD, and TID-1 analyses

of a mixture of polynuclear Nitrogen and Hydrocarbon

compounds. In this figure, the FID responded to all the

components, NPD responded to all the N constituents , and

TID-1 responded to the N compounds, Indole and

Carbazole, which contain a five member Pyrrole type ring

structure. For analyses of Petroleum samples, its

noteworthy that TID-10 and TID-1 surface ionization

provides selectivity for the Pyrrole functional group, but not

the Pyridine group.

The TID-1 chromatogram in Figure 7 also exhibited some

indication of a lower level of selective response for Indene

and Fluorene. These are Hydrocarbon analogs of Indole

and Carbazole which also contain a five member ring

structure. Figure 8 provides a further illustration of TID-1

selectivity for Fluorene versus other Polynuclear

compounds. The analysis of a Cyclo-Hydrocarbon mixture

shown in Figure 9 provides further indication of TID-1

selectivity for five member ring structures with the selectivity

for Dicyclopentadienne.

TID-10 and TID-1 surface ion processes can contribute

selective responses in either an inert Nitrogen gas

environment or in an oxidizing Air or Oxygen gas

environment. Consequently, a CCID chromatogram of a

complex sample may also include peaks contributed by

direct thermionic surface ionization processes.

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Fig. 7

Fig. 8

Fig. 9

Equal Volumes, 1=cyclopentene, 2=cyclopentane,3=cyclohexane, 4=iso-octane, 5=toluene, 6=cycloheptane,7=cyclooctene, 8=cyclooctane, 9=dicyclopentadiene,10=n-dodecane.

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