Development and validation of a solid phase Microextraction method for simultaneous determination of pesticide residues in fruits and vegetables by gas chromatography

Chai, Mee Kin (2008) Development and validation of a solid phase Microextraction method for simultaneous determination of pesticide residues in fruits and vegetables by gas chromatography. PhD thesis, University of Malaya.

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Modern trends in analytical chemistry are towards the simplification and miniaturization of sample preparation, as well as the minimization of organic solvent usage. In view of this, several novel micro-extraction techniques have been developed in order to reduce the analysis step, increase the sample throughput and to improve the quality and the sensitivity of analytical methods. One of the emerging techniques is solid-phase microextraction (SPME). A headspace solid phase microextraction (HS-SPME) method has been developed for the determination of eight pesticides in fruits and vegetables by using gas chromatography with an electron capture detector (ECD) followed by gas chromatography – mass spectrometry (GC-MS) confirmation. Factors such as fiber coating, extraction and desorption parameters, stirring rate, ionic strength, pH, the fiber depth in the injector, the effect of dilution, the effects of organic solvents and washing by different solutions were studied and optimized. The optimized HS-SPME conditions were obtained using 100 μm polydimethylsiloxane (PDMS) fiber, 10% NaCl, 2% (vol/weight) of methanol/acetone (1:1) with optimum dilution, HS extraction at 60 oC for 30 min; with 800 rpm without any pH adjustment. Desorption was done at 240 oC for 10 min. Good linearity, detection limits, precision and sensitivity were obtained with this method for all the investigated pesticides. The regression coefficients in the linearity were better than 0.9950 in all cases with the relative standard deviation (RSD) value less than 7%. The detection limits ranged from 0.01 μg/L to 1.0 μg/L, with repeatability ranging from 0.3% to 3.7% and intermediate precision from 0.8% to 2.5%. The optimized procedures resulted in more than 80% recovery for all the investigated fruit and vegetable samples with RSD values below 5%. The developed HS-SPME with the internal quality control method applied to the analysis of ten real local samples. All the pesticide residues detected were lower than the MRLs. As a comparison, a solid phase extraction (SPE) and headspace single drop microextraction (HS-SDME) were applied to quantify all the investigated pesticides. HS-SPME and SPE showed the better results than HS-SDME in terms of detection limits, precision and recovery. However, HS-SPME possessed the advantages of speed and reduced solvent usage than that of the SPE method. A gas chromatography (GC) method has been developed to analyze simultaneously separate nine different pesticide formulations using the internal standard method. A mixture of pure standard solution spiked with 1-chloro-4-fluoro benzene as the internal standard was injected into the GC-ECD and a six point calibration curve that demonstrated a linear range was established for each target compound. Samples of each formulation, mixed with internal standard were analyzed five times to obtain coefficients of variation which are less than 1%. Three concentration levels of each formulation were determined and the results were within the specification with the accuracies obtained were within 98.1% to 101.9%. This method involves a quick analysis and without any sample pre-treatment process. This measurement method can be very useful for determining pesticide formulations in routine analysis.

Item Type: Thesis (PhD)
Subjects: Q Science > Q Science (General)
Date Deposited: 31 Jul 2013 03:06
Last Modified: 31 Jul 2013 03:06

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