Environmental analysis derivatization techniques

Although an excellent detector for PAEis, the fluorometer is not widely used in environmental analysis, as the number of environmental pollutants with fluorescent spectra is limited. The sensitivity and selectivity of the fluorometer are also used in the A-methyl carbamate pesticide analysis (EPA Method 8318). These compounds do not have the capacity to fluoresce however, when appropriately derivatized (chemically altered), they can be detected fluorome-trically. The process of derivatization takes place after analytes have been separated in the column and before they enter the detector. This technique, called post column derivatization, expands the range of applications for the otherwise limited use of the fluorometer. 

Several derivatization techniques have been developed for trace analysis of bromate in drinking water (see Section 10.1), because concentrations below 2 pg/L cannot be determined by suppressed conductivity detection without preconcentration [55]. Even at lowest microgram/Liter levels, bromate has been classified as carcinogenic by the World Health Organization (WHO) and the American Environmental Protection Agency (EPA) [56]. Lower detection limits cannot be achieved by enlarging the injection volume, because sample matrix... 

Reversed-phase HPLC followed by post-column derivatization and subsequent fluorescence detection is the most common technique for quantitative determination of oxime carbamate insecticides in biological and environmental samples. However, for fast, sensitive, and specific analysis of biological and environmental samples, detection by MS and MS/MS is preferred over fluorescence detection. Thus, descriptions and recommendations for establishing and optimizing HPLC fluorescence, HPLC/ MS, and HPLC/MS/MS analyses are discussed first. This is followed by specific rationales for methods and descriptions of the recommended residue methods that are applicable to most oxime carbamates in plant, animal tissue, soil, and water matrices. 

One of the known disadvantages of the use of GC is the need for previous derivatization of some of the most polar pesticides before analysis can be carried out [40]. These derivatization steps might produce low-efficiency results in complex wastewater matrices, which make the analysis rather difficult and cumbersome. However, the reproducibility in retention times when using GC techniques is so precise, that specific identifications of pesticides can be made even in complex environmental samples. 

For the determination of organotin compounds (tributyltin, triphenyltin, triethyltin, and tetra-ethyltin) a MAE is proposed before the normal phase (NP) HPLC/UV analysis [35], In organotin and arsenic speciation studies, hydride generation is the most popular derivatization method, combined with atomic absorption and fluorescence spectroscopy or ICP techniques [25,36], Both atmospheric pressure chemical ionization (APCI)-MS and electrospray ionization ESI-MS are employed in the determination of butyltin, phenyltin, triphenyltin, and tributyltin in waters and sediments [37], A micro LC/ESI-ion trap MS method has been recently chosen as the official EPA (Environmental Protection Agency) method (8323) [38] it permits the determination of mono-, di-, and tri- butyltin, and mono-, di-, and tri-phenyltin at concentration levels of a subnanogram per liter and has been successfully applied in the analysis of freshwaters and fish [39], Tributyltin in waters has been also quantified through an automated sensitive SPME LC/ESI-MS method [40],... 

Increased use of liquid chromatography/mass spectrometry (lc/ms) for structural identification and trace analysis has become apparent. Thermo-spray lc/ms has been used to identify by-products in phenyl isocyanate precolumn derivatization reactions Liquid chromatography/thermospray mass spectrometric characterization of chemical adducts of DNA formed during in vitro reaction lias been proposed as an analytical technique to detect and identify those contaminants in aqueous environmental samples which have a propensity to be genotoxic, t.e.. to covalently bond to DNA. 

One challenge in the analysis of the CWA is the analysis of their precursors and degradation products, which are often nonvolatile. The CWA degrade, for example, hydrolyze or oxidize easily. Traditional IR sampling techniques, like KBr pellets and liquid cells are well suited for analysis of neat or concentrated nonvolatile chemicals. Environmental samples containing these kind of chemicals, however, normally require derivatization before GC/FTIR analysis. 

Derivatization is the most studied sample preparation method for the chromatographic analysis of environmental samples (Figure 2.6). It is a sample preparation process in which analytes are chemically modihed in order to optimize their possibility of separation and detection by chromatographic techniques. The aim of derivatization depends on the nature of analytes and it has different purposes as a function of chromatographic techniques used (GC or HPLC). Derivatization in GC is used in order ... 

HPLC with ESI produces mostly molecular ions and few to no molecular fragments. This limits the use of LC-MS in the differentiation of isomers. Two atmospheric pressure ionization (API) interfaces allow for the formation of molecular ion, [PAH]" , yet in general, derivatization and additives are required to induce fragmentation. ESI is an interface that transfers ions from the mobile phase into the gaseous phase for introduction into the mass spectrometer so that atmospheric pressure chemical ionization (APCI) can cause ionization of chemical species in the gaseous phase. Both techniques can be operated in the positive- or negative-ion mode. Reports exist for the ionization of PAHs by both techniques, although there are few actual applications to the analysis of real environmental samples. 

Trichothecene mycotoxins are secondary metabolites of various fungal species. Structures of some trichothecene mycotoxins of interest to the US ARMY are given in Figure 1. Several methods have been reported for the analysis of these toxins (1-11, 15). Of these, mass spectrometry techniques are both sensitive and definitive when applied to toxicologic and environmental samples. With current technology, the most sensitive and qualitatively definitive analytical technique for the determination of these toxins is derivatization with an electron deficient moiety followed by analysis with negative ion chemical ionization gas chromatography-mass spectrometry (NICI-GC/HS). 

See also Fluorescence Instrumentation Derivatization Quantitative Analysis. Laser-Based Techniques. Phosphorescence Principles and Instrumentation. Polycyclic Aromatic Hydrocarbons Determination Environmental Applications. Quality Assurance Internal Standards. 

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