Multiresidue Determination of Acidic Pesticides in Water by HPLC-DAD with Confirmation by GC-MS Using Conversion to the Methyl Ester with Trimethylsilyldiazomethane

Abstract

A multiresidue pesticide methodology is studied and results for acidics are reported here, with base/neutral to follow. This work studies a literature procedure as a possible general approach to many pesticides and potentially other analytes that are considered to be liquid chromatographic (LC) candidates, rather than gas chromatographic (GC) ones. The analysis of the sewage effluent of a major southwestern U.S. city serves as an example of the application of the methodology to a real sample. Recovery studies were also conducted to validate the proposed extraction step. A gradient elution program was followed for the high-performance LC (HPLC) leading to a general approach for acidics. Confirmation of identity was by electron ionization-GC-mass spectrometry (MS) after conversion of the acids to the methyl ester (or other appropriate methylation) by means of trimethylsilyldiazomethane. The 3,4-dichlorophenoxyacetic acid is used as an internal standard to monitor the reaction, and polychlorobiphenyl #19 is used for the quantitation internal standard. Although others have reported similar analyses of acids, conversion to the methyl ester is by means of diazomethane itself, rather than by the more convenient and safe trimethylsilyldiazomethane. Thus, the present paper supports the use of trimethylsilyldiazomethane with all of these acids (trimethylsilyldiazomethane has been used in environmental work with some phenoxyacetic acid herbicides) and further supports the usefulness of this reagent as a potential replacement for diazomethane. The HPLC approach here could also serve as the separation basis for an LC-MS solution for confirmation of identity, as well as quantitation.

Evaluation of non-invasive biomonitoring of 2,4-Dichlorophenoxyacetic acid (2,4-D) in saliva

“…These samples were analyzed by negative ion chemical ionization by GC-MS, as performed in Smith et al (2012). For samples of low concentrations (physiological in vitro and in vivo experiments), an alternative derivatization method was needed for increased sensitivity (Moy and Brumley, 2003; Ranz et al, 2008). In this method, samples were reconstituted with 120 µL of toluene and 80 µL of methanol and derivatized with 20 µL of dimethylsilydiazomethane (TMSD) to yield methyl esters of 2,4-D and Triclopyr.…”

Preparation of the methyl ester of hyaluronan and its enzymatic degradation

“…In contrast, trimethylsilyl diazomethane (TMSD) is a mild, high-yielding esterification procedure that has been successfully used for the methylation of the carboxyl groups in a variety of compounds. 37 The methyl-esterification of hyaluronan was optimized using trimethylsilyl diazomethane. The optimal conditions for esterification of carboxyl groups of glucuronate residues were established using 1D NMR characterization of the derivatives.…”

Development and validation of thin layer chromatography method for simultaneous determination of seven chlorophenoxy and benzoic acid herbicides in water

“…Liquid chromatography is a method preferred over gas chromatography as it does not require sample derivatization [10,14] prior to the analysis. Detectors such as ultraviolet [15,16], diode array [17,18], elec tron capture [19] and mass spectrometry [20,21], were used. However, a few published data could be found for thin layer stationary phases used in the determina tion of herbicides in water samples [22,23].…”