Pesticide detection current methods

The importance of setting acceptable limits for pesticides in groundwater cannot be underestimated. With the sensitivity of current methods and the expansion of monitoring efforts, instances of pesticide detection in water are inevitable. Each of these instances will precipitate a crisis if the analytical values cannot be placed in perspective with regard to relative hazard. 

MS detection does not necessarily require as highly resolved GC separations as in the case of selective detectors because the likelihood of an overlapping mass spectral peak among pesticides with the same retention time is less than the likelihood of an overlapping peak from the same element. Unfortunately, this advantage cannot always be optimized because SIM and current gas chromatography/tandem mass spectrometry (GC/MS/MS) methods, it is difficult to devise sequential SIM or MS/MS retention time windows to achieve fast GC separations for approximately > 50 analytes in a single method. 

The increased use of IV-methyl carbamate insecticides in agriculture demands the development of selective and sensitive analytical procedures to determine trace level residues of these compounds in crops and other food products. HPLC is the technique most widely used to circumvent heat sensitivity of these pesticides. However, HPLC with UV detection lacks the selectivity and sensitivity needed for their analysis. In the late 1970s and early 1980s, HPLC using post-column hydrolysis and derivatization was developed and refined with fluorescence detection to overcome these problems. The technique relies on the post-column hydrolysis of the carbamate moiety to methylamine with subsequent derivatization to a fluorescent isoindole product. This technique is currently the most widely used HPLC method for the determination of carbamates in water" and in fruits and vegetables." " ... 

Several other environmental matrices have been analyzed for mercury content. These include coal fly ash (Horvat and Lupsina 1991 Lexa and Stulik 1989), coal dust (Wankhade and Garg 1989), minerals (Bichler 1991), pesticides (Sharma and Singh 1989), gasoline (Costanzo and Barry 1988), and oily waste (Campbell and Kanert 1992). The methods used include CVAAS, DCASV, NAA, spectrophotometry, and GC/altemating current plasma detection (ACPD). The data on each method for each matrix were insufficient for making comparisons. 

The result for chlorpyrifos in RM08 was gained by an enzyme sensor with amper-ometric detection. However, since the sensitivity of the sensor is not sufficient to differentiate between chlorpyrifos and chlorfenvinfos, and both were present in the sample, the outlying position of the result (indicated on Figure 5.2.3 - laboratory code 69) in the chlorpyrifos population is understandable. This method is currently under improvement with recombinant enzymes to gain specificity for various organophos-phorus pesticides. 

Several factors contribute to the attention currently given to pesticides in groundwater. One of the most important factors is the progress which has been made in analytical methodology. In the 60 s, methods were available to measure materials in the parts per million (ppm) range. In the 80 s, it is not uncommon to have methods which can detect some materials in the parts per trillion (ppt) range. This constitutes a one million-fold increase in sensitivity. 

This paper briefly examines the basis of spectrophotometry as a diagnostic method. It summarizes current and future applications of the method for detecting pesticides subject to enhanced degradation in soil. 

Endocrine and immunologic related adverse effects of pesticides are another example of an area where we need toxicologic testing methods that will detect both acute and chronic toxicity and provide a reliable basis for predicting human effects. Before we add new protocols to the current methodology, however, we need to evaluate the answers provided by our current methodology. 

Of the more-or-less pure organic constituents detectable in water as analytical methods improve, the insecticides, fungicides, and weedkillers probably have received the most attention. Although inland surface waters have been monitored for about a decade, essentially nothing is known about pesticide levels in the ocean, and existing information comes from indicator organisms. Even current quantitative data from water analyses stretch the limits of accuracy and confirmation of identity (23). 

This section contains an overview of the materials and techniques most widely used in TLC pesticide analysis at the current time. Additional information on specific layers and mobile phases and methods for sample preparation, development, detection, and quantification for a number of particular pesticides and samples are given in the Example Applications at the end of this entry. 

This chapter gives an overview of the composition of VOO and the analytical techniques that can be used to characterize it, covering three different areas of current interest authentication of VOO, characterization of the bioactive compounds and detection of pesticide residue metabolites. Particular attention has been paid to UHPLC coupled to MS, trying to show the evolution of the traditional LC methods to the newest trends in UHPLC-MS. 

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