Contamination, derivatization methods

In the last decade modifications to the pyrolysis process have been developed to improve analytical efficiency and increase detectability. In the same way as in conventional GC, derivatization reagents may be used to improve the chromatographic separation and response of polar compounds. In order to reduce the time required for the analysis, the risk of contamination and of losing part of the sample, on-line derivatization methods should be preferred and those based on quaternary ammonium hydroxides are certainly the most widely used. 

Three general methods exist for the resolution of enantiomers by Hquid chromatography (qv) (47,48). Conversion of the enantiomers to diastereomers and subsequent column chromatography on an achiral stationary phase with an achiral eluant represents a classical method of resolution (49). Diastereomeric derivatization is problematic in that conversion back to the desired enantiomers can result in partial racemization. For example, (lR,23, 5R)-menthol (R)-mandelate (31) is readily separated from its diastereomer but ester hydrolysis under numerous reaction conditions produces (R)-(-)-mandehc acid (32) which is contaminated with (3)-(+)-mandehc acid (33). 

The book is divided into four parts. Part I, The Fundamentals of GC/MS, includes practical discussions on GC/MS, interpretation of mass spectra, and quantitative GC/MS. Part II, GC Conditions, Derivatization, and Mass Spectral Interpretation of Specific Compound Types, contains chapters for a variety of compounds, such as acids, amines, and common contaminants. Also included are GC conditions, methods for derivatization, and discussions of mass spectral interpretation with examples. Part III, Ions for Determining Unknown Structures, is a correlation of observed masses and neutral losses with suggested structures as an aid to mass spectral interpretation. Part IV, Appendices, contains procedures for derivatization, tips on GC operation, troubleshooting for GC and MS, and other information which are useful to the GC/MS user. Parts I to III also contain references that either provide additional information on a subject or provide information about subjects not covered in this book. 

Most of the continuously monitored water contaminants are determined via gas chromatography-mass spectrometry (GC-MS). However, an adequate separation of polar compounds via GC typically requires derivatization of the polar moieties (e.g., BSTFA derivatives). In addition to this, as the analyte groups show different properties concerning the number and kind of functional groups, it is quite difficult to develop a universal derivatization procedure suitable for all the target analytes. Furthermore, the presence in wastewater of many other organic compounds requires the use of labeled standards, which can make application of this method unfeasible [35]. 

The compatibility of the chromatographic system with aqueous biological fluids (urine, serum), and the direct analysis of highly polar compounds with no need for hydrolysis and derivatization allow to reduce sample manipulation and the probability of artifact formation/analyte degrada-tion/contamination. In addition, the possibility of carrying out separate LC and MS experiments accounts for rapid and cost-effective method development. These features are highly considered in the forensic field where often the analyst is requested to deal with the setup of a method for an unusual analyte or substrate. 

Reported procedures for the determination of vinyl acetate in air used bubblers containing a solvent for trapping the vinyl acetate and a spectrometric method, usually following derivatization, for analysis (6-12). Nenasheva presented a procedure for determining vinyl acetate in air also contaminated... 

HPLC can conveniently be used to quantify psilocin and psilocybin in drug samples. As a quantitative method, it has a number of advantages over GC-MS. For example, HPLC does not require any thermal stability of the drug and hence derivatization is not needed. This eliminates the problems associated with ensuring complete derivatization and the risk of sample contamination. Although a number of reported HPLC analytical methods can be found in the literature, we will illustrate the procedure involved by describing a relatively simple method which has been recently reported by Musshoff et al. [4]. 

Conditions for the optimization of SPME of phenol and chlorophenol soil contaminants were investigated end analysis was by GC-FID. The method was applied to soil analysis after acute contamination in industrial sites. The method was validated by comparison with an EPA certified extraction method . Soil samples were suspended in water and the extracted phenols were acetylated in situ with acetic anhydride in the presence of potassium bicarbonate. Acid was added after the end of the derivatization and SPME was performed by placing a poly(dimethylsiloxane) fiber in the headspace. End analysis was performed by introducing the fiber into the injector of a GC-MS apparatus. LOD was in the sub-ppm range, with good precision, sensitivity and linearity . ... 

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