Preconcentration and Determination of 2,6-Dichlorobenzamide in Water by Stir Bar Extraction and High-Performance Liquid Chromatography–Tandem Mass Spectrometry

Polyacrylate stir bar sorptive extraction (SBSE) of 2,6-dichlorobenzamide followed by liquid desorption and analysis by liquid chromatography–tandem mass spectrometry using electrospray ionization is presented. The parameters influencing the methods were optimized and included a stirring speed of 500 revolutions per minute, an extraction time of two hours, a sample volume of 15 milliliters, 30 percent NaCl, and liquid desorption using acetonitrile under ultrasonication for fifteen minutes. A reverse phase C<inf>18</inf> column was used with isocratic elution (50 percent acetonitrile and 50 percent 5 millimoles per liter aqueous ammonium acetate buffer at pH 2.4), a flow rate of 0.4 milliliter per minute, and an injection volume of 10 microliters. Quantitative analysis was carried out by multiple reaction monitoring using positive polarity. The developed method required low sample volume (15 milliliters) and provided satisfactory figures of merit with a limit of detection of 0.002 microgram per liter, a limit of quantification of 0.006 microgram per liter, and good precision (inter-day relative standard deviation below 10 percent). The polyacrylate Twister was employed for up to twenty-five extraction and liquid desorption cycles. The applicability of the method was assessed by analyzing ground water collected at five sites in North Italy. The concentrations of 2,6-dichlorobenzamide were between 0.070 and 0.282 microgram per liter. Preliminary results on the use of polar stir bars for the determination of other polar pesticides in water are also provided.