GC, procedure

Owing to poor volatihty, derivatization of nicotinic acid and nicotinamide are important techniques in the gc analysis of these substances. For example, a gc procedure has been reported for nicotinamide using a flame ionisation detector at detection limits of - 0.2 fig (58). The nonvolatile amide was converted to the nitrile by reaction with heptafluorobutryic anhydride (56). For a related molecule, quinolinic acid, fmol detection limits were claimed for a gc procedure using either packed or capillary columns after derivatization to its hexafluoroisopropyl ester (58). 

Cortes et al. [18] have quantitatively determined polymer additives in a polycarbonate homopolymer and an ABS terpolymer. In that case, a multidimensional system consisting of a microcolumn SEC was coupled on-line to either capillary GC or a conventional LC system. The results show losses of certain additives when using the conventional precipitation approach. An at-column GC procedure has been developed for rapid determination (27 min) of high-MW additives (ca. 1200Da) at low concentrations (lOOppm) in 500- xL SEC fractions in DCM for on-line quality control (RSD of 2-7%) [36], Also, SEC-NPLC has been used for the analysis of additives in dissolution of polymeric... 

As an example of AEDA, Fig. 16.2 shows a plot of the FD factors of the odorants of parsley versus their retention indices this plot is termed an FD chromatogram. As usual in dilution analyses, the result in Fig. 16.2 is not corrected for losses of odorants during the isolation and GC procedures therefore, not only the odorants showing the highest FD factors (nos. 1, 2, 7 and 13 in Fig. 16.2) were identified but also all of the 14 odorants appearing in the FD-factor range of 4-512. The result is presented in the legend to Fig. 16.2. 

Therefore, to check the possibility of using this IR procedure in our Laboratory, it was decided to evaluate the procedure against the recommended NIOSH GC procedures. We have limited our study to the hydrocarbons JP-4 aviation fuel and PD-680 cleaning solvent. In addition to evaluating the IR method for charcoal tubes and vapor monitors, we also compared the two methods on actual field samples. 

SEPARATION AND QUANTIFICATION. Separation and quantification of components in mixtures extracted from real samples is accomplished by using standard quantitative GC procedures. 

Separation of TGs has been a general problem for many years. For several years such separations were carried out more or less by GC procedures. However, the GC method gives insufficient information to provide a complete TG composition of a complex mixture, even when combined with the total fatty acid composition or distribution. 

The soot concentration, hydrocarbon species and soot temperature in the immediate vicinity of the droplet displayed closely coupled behavior. Hydrocarbon species, listed in approximate order of concentration were C2H2, CH4, C2H4, C2H6 and C3fs. Resolution of the propane and propylene peaks was not possible under current GC procedure, and these concentrations are reported merely as C3 compounds. The hydrocarbons were found to decay in the same time frame as the growth of the soot concentration. The zone of chemical activity, defined as where the vaporized hydrocarbon products react to form soot, is approximately 2 cm, which corresponds to 13 msec, after which the soot concentration decays due apparently to oxidation. 

GC procedures are less useful for the analysis of drugs in hair. The enormous number of possible exogenous and endogenous compounds which can partly be found in hair make the interpretation of chromatograms with flame ionization detector (FID), nitrogen-phosphor flame ionization detector (NP-FID), or even with electron capture detector (ECD) very difficult. Therefore, the number of papers is very limited. 

The analysis of simple lipids can be done with good results using common analytical methods without any need for decreasing the molecular weight of the sample by techniques such as pyrolysis. HPLC, SFC or GC procedures were applied for simple lipid analysis, and even the mass spectra of some simple triglycerides are known. As an example, Figure 8.1.1 shows the El mass spectrum of tripalmitin (standard ionization condition). 

Yan, X., Wang, Z. and Barlow, P. (1993) Quantitative determination and profiling of total sulphur compounds in garlic health products using a simple GC procedure, Food Chem., 47(3), 289-294. 

Methods are avahable for detecting barbiturate overdose and abuse. To detect overdose, semiquantitative immunoassays suitable for detection of barbiturates in serum are avaUable and useful for this purpose. Capillary GC is also useful for this purpose, and a capillary GC procedure is described in the Chapter 34 Appendix that is formd on this book s accom-... 

Several HS-GC procedures, listing the retention data of as many as hundreds of compounds, for the screening of multiple VOCs have been published. ,9,10,23-25 Emits of detection (LODs) and hnear analytical ranges vary with particular methods, most procedures have typical LODs of O.lmgL and upper Emits of linearity (ULOL) to concentrations as high as 5000 mg L. ... 

The interlaboratory study showed overall that the GC procedure gave the best results, followed closely by IR and then FL. When the IR spectra were interpreted by those expert in oil spill matching, the IR results were significantly better than GC or FL, indicating that IR is the method most influenced by expert interpretation. 

Now that we are familiar with the basic Py—GC procedures, let us review their main applications. 

The Py-GC procedures and equipment are applicable to the ultimate analysis of polymers, and also to the analysis of copolymers if the ultimate composition of the monomers is different. Meade et al. [246] determined the oxygen content of organic compounds with the use of a carbon catalyst at 1050°C. Under these conditions, methane, hydrogen and carbon monoxide are formed and were separated on a column with molecular sieves. The application of Py—GC to determine the oxygen content of polymers has been described [247,248], and also the nitrogen content of positive photoresists [249]. 

Gas chromatographic separation of derivatized organotin compounds is the most popular and common method. Differences between the various GC procedures are located on the derivatization level rather than the type of capillary column. A selection of typical techniques which have been tested for sediment analysis at the occasion of three interlaboratory studies (TBT-spiked sediment, harbor sediment and coastal sediment) is given below. 

Even with the new sophisticated MS/MS techniques, sample volumes still have to be included at least between 5 and 10 ml. Therefore, a trace-enrichment step is usually performed and online procedures can be recommended. GC procedure still offers better separation efficiency and could be the method of choice if a derivatization step is not required. 

Various analytical methods of extremely high sensitivity are now available to measure minute concentrations of steroid hormones in blood. GC is frequently preferred over other measurement principles because of its high sensitivity and reliability. Since some of these GC procedures are technically involved, they are used more often in biomedical research laboratories than in a routine clinical environment. 

As mentioned in the Section 1, physico-chemical methodology for quantitative analysis of plant hormone focuses primarily on GC-SIM, although HPLC with selective fluorescence detection continues to be used for lAA analysis in some laboratories. Procedures, such as the 2-methylindolo-a-pyrone assay for lAA analysis [82], are now rarely utilised. With the exception of ethylene quantification [2] there is little use of non-MS-based GC detection techniques, despite the fact that selective analysis at the picogram level is achieved for ABA with an electron capture detector [83], and lAA and cytokinins with a nitrogen phosphorus detector [84,85]. The reason for the demise of these GC procedures is that the detectors are destructive and this precludes the reliable recovery of labelled internal standards for radioassay and isotopic dilution analysis. The usual compromise was to take two aliquots of the purified samples, one for GC analysis and the other for the determination of radioactivity. The accuracy of this approach is dependent upon the questionable assumption that the radioactivity in the purified sample is associated exclusively with the compound under study. In an attempt to circumvent this problem, a double standard isotope dilution procedure was devised for the quantitative analysis of lAA in which one internal standard was used to correct for losses during sample preparation and a second for GC quantification [86]. This procedure was used in several... 

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