Pesticide chemical derivatization techniques

Figure 1. Variation in number of publications dealing with chemical derivatization techniques for pesticides from 1962-1978 ((-)-) total (including fungicides) (A) herbicides (O OC s (including Mirex, PCB s, etc.) (Q) DP s)...

The above brief review illustrates that chemical derivatization techniques have been used extensively for the confirmation of identity of organochlorine residues. In most instances, the lower limits of detectability of the derivatives are substantiaUy lower than the established tolerance values for the parent compounds. Taken in conjunction with the many other modes of derivatization—e.g., during or after gas chromatography (59)— the analyst has a vast array of modification procedures at hand to aid in residue identification. They can be employed for residues in soil, biological, fat, and nonfat extracts and can be successfuUy extended, especially the more specific tests, to the identification of crosscontaminants in pesticide formulations and also fertilizer mixtures. So far, these latter two cases have only been a fringe area of application (60,61). 

Fourier transform infrared spectroscopy negative ion spectroscopy and immunochemical technology are the subjects of several chapters. A chapter on cleanup presents a general challenge for all types of analytical techniques. Chemical derivatization of pesticides and metabolites enhances the detectability and ability to analyze small quantities of pesticide residues. 

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. 

Another product of esterase cleavage is p-nitrophenol (PNP), which is generated in the human body by the degradation of parathion, parathion-methyl and parathion-ethyl. Some methods for the determination of PNP in urine are summarized in Table 9.5. PNP can, for example, be determined in the urine of occupationally exposed subjects by means of GC-ECD. Sample preparation involves acid hydrolysis, extraction with diethyl ether, derivatization with diazoethane and purification on silica gel columns. The LOD was 20 pg L with a recovery of 85-98%. This method has also been used in a study on selected pesticide residues and metabolites in urine from a survey of the US general population.In the context of another survey study, a more complicated technique to detect PNP in urine has recently been used by Hill et involving GC-MS-MS with positive chemical ionization after derivatization with l-chloro-3-iodopropane. The authors also used this method for the determination of the metabolite TCP and 10 other analytes in urine.Sample preparation involved hydrolysis with p-glucuronidase, several extraction steps using different solvents and purification by SPE (silica gel column). The LOD was 1 pg L with an inter-assay RSD... 

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