Method Development and Validation of Gas Chromatography Methods using Nitrogen Phosphorus Detector (GC-NPD) and Isotope Dilution Triple Quadrupole Mass Spectrometry (GC-IDMS/MS) for the Determination of Chlorpyrifos in Mango
Pesticides residue determination in fruits like chlorpyrifos is important due to its health effects on humans. Thus, there is a need for sensitive and accurate methods for better quantification. In this study, the performance of two gas chromatographic detection methods, nitrogen phosphorus detector (GC-NPD) and isotope dilution triple quadrupole mass spectrometer (GC-IDMS/MS), for the determination of chlorpyrifos in mango was evaluated to be used for the development of candidate reference material. Other than liquid-liquid extraction (LLE), Quick, Easy, Cheap, Efficient, Rugged and Safe (QuEChERS) sample extraction and dispersive solid phase extraction (dSPE) clean-up procedures were optimized to extract chlorpyrifos from the sample matrix. Comprehensive method validations were performed in GC-NPD and GC-IDMS/MS with HP-5 capillary column to establish linearity, the limit of detection (LOD), the limit of quantification (LOQ), accuracy, repeatability, and intermediate precision using freeze-dried mango samples. The LOD and LOQ were 2.35 and 3.47 µg kg-1 for GC-NPD, and 1.23 and 1.85 µg kg-1 for GC-IDMS/MS, respectively. Matrix-matched calibration curves showed excellent linearity of r2=0.999 for both GC-NPD and GC-IDMS/MS protocols. Acceptable repeatability was obtained for three spike concentrations of 10, 30, and 60 µg kg-1 (n=10) and intermediate precision for 0.5-, 1- and 3-months in the same three-spike concentrations (n=3) expressed as relative standard deviation (RSD) ranging from 0.34-5.61 % for GC-NPD and 0.46-4.22 % for GC-IDMS/MS. Satisfactory mean recoveries (n=10) were achieved: 88.48-109.81% in GC-NPD and 97.61-108.40% in GC-IDMS/MS. GC-IDMS/MS and GC-NPD methods were fit for the purpose of quantifying chlorpyrifos in Philippine mango accurately with the use of isotope dilution technique and traceability to international standards by the application of gravimetric sample preparation.
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