Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2004
Publication Date: 6/1/2004
Citation: Lehotay, S.J., Mastovska, K. Evaluation of common organic solvents for gas chromatographic analysis and stability of multiclass pesticide residues. Journal of Chromatography A. 2004 p. 259-272. Interpretive Summary: Selection of the ideal solvent is a key factor in the testing of pesticide residues in foods using gas chromatography (GC), yet it has not been comprehensively discussed before. The ideal solvent should: (i) provide sufficient solubility and stability of the pesticides of interest; (ii) be used in the extraction and/or clean-up step to avoid an additional solvent exchange step; (iii) permit optimal GC analysis in terms of sensitivity, reproducibility, and speed; and (iv) be non-hazardous and inexpensive. This study addresses each of these aspects and evaluates six organic solvents commonly featured in either sample preparation (acetonitrile, acetone, and ethyl acetate) or solvent exchange (toluene, isooctane, and hexane) with the emphasis placed on stability studies of selected pesticides in the given solvents. Acetonitrile was found to be the most suitable solvent for extraction of a wide polarity range of pesticide residues from produce, and adding a small amount of acetic acid to it slows degradation of problematic pesticides for better analysis. This study provides practical recommendations on selection of the most suitable solvent for pesticide residue analysis and proposes solutions to several real-world problems associated with the use of particular solvents.
Technical Abstract: In this study, we evaluated the suitability of 6 common organic solvents for gas chromatographic (GC) analysis of pesticides with respect to comprehensive needs. Three of these, acetone, acetonitrile (MeCN) and ethyl acetate (EtAc), represent extraction solvents commonly used in multiresidue methods for determination of pesticides in produce. The other three, isooctane, hexane and toluene, often serve as exchange solvents before GC analysis. An ideal solvent for GC analysis of multiclass pesticide residues should be compatible with: the analytes, sample preparation, and GC analysis. This study addressed each aspect with emphasis placed on stability studies of selected pesticides in the given solvents to assess their overall suitability in multiclass analysis. In terms of stability, the exchange solvents proved to be superior to the more polar extraction solvents. Degradation of N-trihalomethylthio fungicides in MeCN was observed only in certain lots of the tested MeCN, but even if it occurred, the stability of these analytes as well as that of dicofol and chlorothalonil was dramatically improved by the addition of 0.1% acetic acid (v/v). Dicofol and chlorothalonil were also unstable in acetone, and pesticides with a thioether group degraded in the tested EtAc. Formation of isomers of certain pyrethroids was recorded in the chromatograms from MeCN and acetone solutions, but this effect more likely occurred during the GC injection than in solution. For several reasons, MeCN was chosen to be the most suitable solvent for extraction of a wide polarity range of pesticide residues from produce.