Fast screening of pesticide residues in fruit juice by solid-phase microextraction and gas chromatography–mass spectrometry

A new vanguard–rearguard analytical method for determining 54 pesticide residues in different fruit juices (natural and commercial orange, peach and pineapple juices were tested) is proposed. For that, in a first step, a fast screening (vanguard) method is applied for detecting those samples containing pesticides at concentrations above a pre-established cut-off value. In a second step, those samples are re-analyzed by a conventional pesticide residue (rearguard) method that confirms the presence of the pesticides and quantifies them. The sample process is very simple, fast and semiautomatic and therefore, it reduces significantly the average time required per sample, increases precision and minimizing human mistakes. Only 1 mL of juice sample is required for analysis. Pesticides are quickly extracted with ethyl acetate in a test tube, transferred to a mixture water:acetone 9:1 (v/v), and isolated by solid-phase microextraction (SPME). The SPME screening method only requires 10 min of SPME extraction. The SPME confirming/quantifying method requires 55 min of SPME extraction. The instrumental determination is carried out by gas chromatography–mass spectrometry (GC–MS) using a full scan acquisition mode for the screening method (less than 17 min of chromatographic run) and a tandem mass spectrometry (MS/MS) acquisition mode for the quantifying/confirming method (less than 70 min of chromatographic run). The use of full scan MS and tandem MS for the detection increase significantly the certainty of the results. Also, the combination of a solvent and SPME extractions and GC–MS/MS offers a significant selectivity and sensitivity with a proven reduction of false positive and negative cases. The use of a vanguard–rearguard strategy can reduce the 50% of the total time required for determining routinely juices in a laboratory by a traditional strategy (identification, confirmation and quantitation of the pesticides in the samples by a conventional analytical method).