Simultaneous Analysis of Hexaconazole, Myclobutanil, and Tebuconazole Residues in Apples and Soil by SPE Clean-Up and GC with Nitrogen-Phosphorus Detection

A facile and sensitive method utilizing capillary gas chromatography with nitrogen phosphorus detection (GC-NPD) has been developed and validated for simultaneous analysis of hexaconazole, myclobutanil, and tebuconazole, three broad-spectrum systemic fungicides, in apples and soil. Two samples were fortified with the three pesticides and subjected to ultrasonic extraction, followed by solid-phase extraction (SPE) to remove coextractives, before analysis by GC-NPD. SPE procedures were performed on PSA cartridges (500 mg, 3 mL), the analytes being eluted with n-hexane-acetone (9:1 v/v, 2 mL). Recovery of three pesticides from the fortified apple and soil samples ranged from 94.5 to 107.3% with relative standard deviations less than 9.7% at the three spike levels (0.01, 0.1, and 0.5 mg kg(-1)). Limits of quantification of the method for apple and soil were 0.01 mg kg(-1), sufficiently below the maximum residue limits. Direct confirmation of the analytes in samples was achieved by gas chromatography-mass spectrometry (GC-MS).