Matrix Influence on Determination of Organochlorine Pesticide Residues in Water by Solid Phase Extraction Coupled to Gas Chromatography-Mass Spectrometry

The presence of a sample matrix is one of the most important practical considerations in gas chromatography analysis as there are potentially numerous problems associated with matrix based injections. This paper aims to highlight the distinction between blank sample analysis and real sample analysis using automated solid phase extraction (SPE) and gas chromatography-mass spectrometry. Four reversed sorbent phases, including a Supelco LC-18, Strata C-18-E and Strata-X (styrene divinyl benzene) were used for SPE method development using an automated Gilson GX-271 AspecTM liquid handling instrument to determine the best solid phase and treatment for optimum organochlorine determination. The method developed proved to be valid when tested against parameters such as calibration range, coefficient of regression, linearity, repeatability and sensitivity. The StrataX and LC-18 cartridges produced the best recoveries, varying between 90% and 130% for most analytes. The LC-18 was selected for further analysis of the matrix effects as it showed greater reproducibility and method parameter robustness. Various real matrix sample volumes were tested on the selected LC-18 cartridge to determine its optimum maximum matrix load for efficient recoveries (breakthrough volume equivalent). A 100 ml sample volume was determined as the optimum matrix load volume as it produced more precise recoveries than other spiked sample matrix volumes. Visual comparison and analysis of selective ion monitoring chromatograms of both matrix based and matrix-free extracts indicate that there are significant matrix effects potentially capable of adversely affecting the chromatographic system from producing accurate identification and quantification of target analytes.