Optimization and validation of enzyme-linked immunosorbent assay for the determination of endosulfan residues in food samples

In this study, an enzyme-linked immunosorbent assay (ELISA) was optimized and applied to the determination of endosulfan residues in 20 different kinds of food commodities including vegetables, dry fruits, tea and meat. The limit of detection (IC(15)) was 0.8 microg kg(-1) and the sensitivity (IC(50)) was 5.3 microg kg(-1). Three simple extraction methods were developed, including shaking on the rotary shaker at 250 r min(-1) overnight, shaking on the rotary shaker for 1 h and thoroughly mixing for 2 min. Methanol was used as the extraction solvent in this study. The extracts were diluted in 0.5% fish skin gelatin (FG) in phosphate-buffered saline (PBS) at various dilutions in order to remove the matrix interference. For cabbage (purple and green), asparagus, Japanese green, Chinese cabbage, scallion, garland chrysanthemum, spinach and garlic, the extracts were diluted 10-fold; for carrots and tea, the extracts were diluted 15-fold and 900-fold, respectively. The extracts of celery, adzuki beans and chestnuts, were diluted 20-fold to avoid the matrix interference; ginger, vegetable soybean and peanut extracts were diluted 100-fold; mutton and chicken extracts were diluted 10-fold and for eel, the dilution was 40-fold. Average recoveries were 63.13-125.61%. Validation was conducted by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The results of this study will be useful to the wide application of an ELISA for the rapid determination of pesticides in food samples.