Organophosphorus pesticides HPLC analysis

High-performance LC in the reversed-phase mode (RP-8 or RP-18 column) with UV detection (254 nm) and isocratic conditions was evaluated for the analysis of 15 organophosphorus pesticides. Typically the method could be used to analyze azinphosmethyl in water at 0.5 /rg/L. This compares favorably with GC, since this compound is very difficult to analyze by that method. For other pesticides, such as fenitrothion, which is readily analyzed by GC, the HPLC method can be used for confirmation purposes (31). 

The HPLC/MS technique used in EPA Method 8321 is best suited for analysis of thermally unstable compounds that are hard to analyze with conventional GC methods, such as organophosphorus pesticides, chlorinated herbicides, and carbamates. In this technique, the detection with mass spectrometry provides the ultimate selectivity. The sensitivity for each individual compound depends on the interferences in a given environmental matrix and on the chemical nature of the analyte. 

Second detector confirmation is another compound confirmation technique. Two detectors with selectivity to different functional groups are connected in series to one column or in parallel to two columns. For example, two detectors, a UV/VIS detector and a fluorometer, connected in series to the HPLC column are used in the EPA Method 8310 for analysis of PAH compounds. If the second detector is connected to a second column of a dissimilar polarity, then the confirmation becomes even more reliable. An example of such a configuration is organophosphorus pesticides analysis the samples may be initially analyzed with an NPD, and then confirmed on a different column with an ECD or a FPD. 

Kwakman and co-workers (1992) used disk extraction to isolate organophosphorus pesticides on-line with gas chromatography for rapid analysis. The method is on-line for sorption and elution using ethyl acetate as a desorbing solvent and a retention time gap approach for the GC analysis. The detection limit was 10 to 30 ng/L in tapwater and 50 to 100 ng/L in river water. Barcelo and co-workers (1993) and Molina and co-workers (1994) also found that organophosphorus pesticides and triazines could be effectively isolated on disks for further analysis by HPLC/MS using thermospray and electrospray. 

A Cis disk has been used to remove chlorotriazine, atrazine, metabolites, organophosphorus compounds, phenylurea, and carbamate pesticides from seawater prior to analysis by HPLC [392],... 

Pesticides. There are numerous references to the use of HPLC/MS for the analysis of pesticides and herbicides [14, 16-20]. Some major classes of pesticides and herbicides including carbamate, triazines, organophosphorus, and phenolic acid have been analyzed by HPLC/MS using Cl or ion evaporation ionization. While these ionization techniques often resulted in excellent sensitivity (thermospray/MS full scan detection limits of 1-10 ng), usually only [M+H] and/or [M+NH4] ions were formed. This limitation can be overcome using tandem4MS [20], moving belt [17], and most recently through the use of particle beam HPLC/MS. 

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