Packed-column gas chromatograms

Figure 5. Packed column gas chromatograms of PCBs In representative samples from the study site.

Figure 14.8 shows a detailed schematic representation of a natural gas analysis System, which fully complies with GPA standardization (8). This set-up utilizes four packed columns in connection with a TCD and one capillary column in connection with an FID. The contents of both sample loops, which are connected in series, are used to perform two separate analyses, one on the capillary column and one on the packed columns. The resulting chromatograms are depicted in Figure 14.9. 

A comparison of packed-column 10 SE-30 gas chromatograms before and after base extraction is shown in Figure 6 for pH 12. The rise and fall of the base line hump in the later portion of the chromatogram was dramatically reduced. This result was verified by observing the same phenomenon with chromatograms at pH 11 and 11.5. 

Figure 24-8 Chromatogram of alcohol mixture at 40°C using packed column (2 mm inner diameter x 76 cm long) containing 20% Carbowax 20M on Gas-Chrom R support and flame ionization detector. [Courtesy Norman Pearson.]...

Gas chromatograms were obtained on a twin Hewlett-Packard model 5750 Research Chromatograph. The dual columns were 6-m lengths of copper tubing 3 mm in diameter, packed with 3% OV-1 on Chromosorb G-HP (methylsilicone on calcined diatomaceous earth). Samples were introduced as about 10% solutions in carbon bisulfide. Detection was by hydrogen-flame ionization, the non-sample contribution from the idle column being subtracted from the total contribution of the active column to provide a sample chromatograph corrected for extraneous ionization. 

Beezhold and Stout [68] studied the effect of using mixed standards on the determination of PCBs. Mixtures of Arochlors 1254 and 1260 were used as comparison standards and gas chromatograms of these mixtures were compared with those obtained from a hexane extract of the sample after clean-up on a Florasil column. Polychlorinated biphenyls were separated from DDT and its analogues on a silica gel column activated for 17h and with 2% (w/w) of water added. The extracts were analysed on a silanised glass column packed with 5% DC-200 and 7.5% QF-1 on Gas Chrom Q (80-100 mesh) operated at 195°C with nitrogen as carrier gas (50-60mL min-1) and a tritium detector. 

Packed GC columns afforded moderately well-resolved, reproducible profiles of the hydrocarbon fraction. Each gas chromatogram contained 40 peaks corresponding to a set of standardized retention time windows. Further details about the collection of this data can be found in the literature [90],... 

Fig. 5.15. Gas chromatogram of N-acetyl-n-propyl esters of 17 amino acids. Conditions glass column, 106 cm X 3 mm I.D., packed with a mixture (1 1) of 0.7% Carbowax 6000 on Chromosorb G (80— 100 mesh, HP) and 0.7% Carbowax 6000 plus 0.05% tetracyanoethyl pentaerythritol on the same support nitrogen flow-rate, 30 ml/min temperature programme, 6°C/min, 100-240°C. (Reproduced from J. Chromatogr., 36 (1968) 42, by courtesy of J.R. Coulter.)...

The earliest of GC analyses were performed on columns packed with a solid support coated with a nonvolatile liquid phase. Packed columns are not frequently used today as they have been replaced by capillary columns where the hquid phase is immobilized on the internal surface of the capillary. As there are numerous liquid phases available, it is now possible to obtain commercial columns that will separate not only the methyl esters but also the underivatized fatty acids. This advancement obviates the need for derivatization and the associated problems. A typical chromatogram of free fatty acids is displayed in Figure 3. Individual isomers of CLA are now available to aid in the identification of isomers in the chromatogram. Gas chromatography can provide quantitative information on the degree of conjugation, positional, and geometric isomer distribution when suitable standards are available. 

FIGURE 19. Gas chromatogram of (1) C4H9As(CF3)2, (2) (C4H9)2AsCF3. Operating conditions ft column packed with 15% w/w SE-30 on Fluoropak 80 column temperature 100 °C, helium carrier gas pressure lOp.s.i., helium flow rate 35cc/m. Reproduced from Reference 168 by permission of Preston Publications, Inc. 

Beckett and Triggs were interested in the determination of nicotine and its main metabolite cotinine in urine. An acidified urine was extracted with diethyl ether to remove impurities, the urine was made alkaline with sodium hydroxide and the nicotine extracted with diethyl ether. Cotinine was extracted from urine with methylene chloride after basification of the sample with ammonia. On concentration of the solution, the gas chromatography was carried out on a packed column treated with KOH using Carbowax 20 M as stationary phase. A relative recovery of 95-100 % for the two alkaloids was obtained with respect to their internal standard, chlorophentermine for nicotine and lignocaine for cotinine, which were added to the urine at the start of the assay procedure. Typical chromatograms are given in Figure 4. 

For the assay of cocaine in Eiythroxyion coca Lam. from three locations in Peru, Turner et al.3 worked out a gas chromatographic method. The alkaloids were extracted by refluxing the powdered leaf samples (1.00 g) with ethanol (40 ml) for 15 minutes. The filtrate was evaporated to dryness under reduced pressure in a rotary evaporator, the residue dissolved in 20 ml chloroform and the alkaloids extracted into 1.5 aqueous citric acid. The pH of the solution was adjusted to 8.2 with sodium bicarbonate and the alkaloid bases extracted with chloroform. After evaporation the residue was dissolved in ethanol containing the internal standard (androst-4-ene-3,17-dione) and gas chromatographed on a packed column of 6 % OV-1 on Chromo-sorb W. A typical chromatogram is shown in Figure 9.2 and the results of the analysis in Table 9.6. 

Ephedrine and ist isomer pseudoephedrine are alkaloids in Ephedra species. Brochmann-Hans-sen and Baerheim Svendsen reported the first gas chromatographic separation of these two alkaloids in a study on the separation and identification of 11 sympathomimetic amines on a 1.15 % SE-30 packed column at 104°C. However, ephedrine and pseudoephedrine could not be separated as such, but were separated as their oxazolidine derivatives after treatment with acetone. A typical chromatogram is given in Tale 13.1. 

Sobol and Sperling developed a method for quantitative determination of heroin and the compounds mentioned. Two chromatograms were run of each sample one after derivatization with N,0-bis(trimethylsilylJtrifluoroacetamide and one by direct gas chromatography of the sample - in both cases on a packed column with 3 % OV-25 on Gas Chrom Q. Typical chromatograms are given in Figure 14.2. 

The first systematic investigation on the gas chromatographic separation of xanthine de-rivatives was published by Reisch and Walker. The naturally occurring xanthines, caffeine, theobromine and theophylline, as well as a number of derivatives, were gas chromatographed on an 1.5 % packed SE-30 column on Chromosorb W. In Table 20.1 the compounds are given and and in Figure 20.1 typical gas chromatograms. 

Plasma samples of 1.0 ml were alkalinized (NaOH), the internal standard (mepivacaine) added and the mixture extracted with chloroform. The chloroform solution was evaporated and the residue redissolved in methanol (25 yl). 1.5 yl of the methanol solution was injected for the gas chromatographic analysis on a packed column of 3 % OV-17 on Chromosorb P. A typical chromatogram is given in Figure 20.5. Peak height ratio measurements produced linear standard curves in the 0.25-10.0 yg/ml range. Absolute sensitivity from a 1.0 ml plasma sample was 0.1 yg/ml. The relative deviation of a 2.0 yg/ml pooled plasma standard curve (done repeatedly over several months) was 5.2 5 . 

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