Development of an Analytical Procedure for the Determination of Trihalomethanes in Leafy Vegetable by Headspace-SPME Followed by GC-ECD Determination

Abstract

An analytical procedure for the determination of trihalomethanes (i.e., CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃) in leafy vegetable matrices was developed consisting of headspace solid-phase microextraction (HS-SPME) followed by GC-electron capture detector (ECD) determination. Factors affecting the extraction yield were optimized by multivariate methods in two steps. First, a 2^5-1 fractional factorial design was applied to screen for and assess the effects and interactions of sample mass (g), extraction temperature (°C), extraction time (min), the salting-out effect, and total volume (mL). Second, a response surface methodology design, i.e., central composite design, was applied to optimize the variables found to have a significant impact on the extraction process (extraction time, extraction temperature, and total sample volume), thereby making it possible to simulate the behavior of all the analytes except CHBr₃. Finally, the multiple responses were simultaneously optimized using the desirability function. The optimum overall extraction conditions were achieved with an extraction time of 30 min, a temperature of 40 °C, and a total volume of 5 mL. These analytical conditions were validated by spiking plant samples at two concentration levels (2 and 5 mg kg⁻¹), which yielded accurate and precise results for the target analytes. Detection and quantitation limits ranged from 0.09 to 0.64 μg kg⁻¹ and 0.14 to 0.97 μg kg⁻¹, respectively. Finally, chloroform and bromoform were detected in lettuce irrigated with a chlorinated secondary effluent at concentrations of 1.01 and 0.33 μg kg⁻¹, respectively.