Cloud point method applied to the extraction and preconcentration of thiabendazole pesticide from whole grape juice samples and amperometric detection by HPLC.

A cloud point method was developed and applied for the first time to extract and preconcentrate thiabendazole (TBZ) from commercial whole grape juice samples, with determination by high performance liquid chromatography coupled to electrochemical detection (HPLC/EC), using a cathodically pretreated boron-doped diamond electrode (BDD). The best conditions for extraction and preconcentration of TBZ by cloud point extraction (CPE) were performed at pH 6.0, by adding 1 mL of the surfactant Tergitol TMN-6 at 10% (mass-to-mass ratio), without heating (at 27 °C) and ultrasonic stirring time of (20 kHz) for 60 min. The HPLC/EC determination was duly validated in a C8 column, in mobile phase with a 69 : 31 ratio (V/V) of phosphate buffer (pH 7.0):ACN, at a flow rate of 1.2 mL min-1 and electrochemical detection with BDD electrode by applying 1.40 V × Ag/AgCl (3.0 mol L-1). Under these conditions, the procedure showed a preconcentration factor (FC) of 21.7, and limits of detection (LOD) and quantification (LOQ) of 6.64 × 10-9 mol L-1 (or 1.33 µg L-1) and 1.66 × 10-8 mol L-1 (or 3.34 µg L-1), respectively. The method provided a percent recovery of 81% to 98%, with a coefficient of variation between 3% and 15%.

Electrochemical determination of thiabendazole pesticide extracted and preconcentrated from tomato samples by cloud point extraction.

A procedure for electroanalytical determination of the fungicide TBZ extracted and preconcentrated from tomatoes by the cloud-point extraction (CPE) technique was developed and validated in this work. The analytical technique used for this determination was HPLC coupled to an electrochemical detector (HPLC/EC), with a BDD electrode. The main variables of the CPE process were evaluated using a 24 full factorial design. The optimal condition of CPE was achieved by using Tergitol (19% v/v), NaCl (0.83 g), ultrasonic stirring time of 15 min and a temperature of 36 °C. Under these conditions, the preconcentration factor obtained was 5.7. The limits of detection (LOD) and quantification (LOQ) were 2.7 × 10-8 mol L-1 (or 5.4 µg L-1) and 5.5 × 10-8 mol L-1 (or 11 µg L-1), respectively. The average recovery values varied from 80.7% to 115.1% and the precision (average of 3 days) was less than 15%, indicating the good accuracy and precision of the method developed here. Upon applying the method to examine commercial tomatoes, TBZ was detected in one of the three analyzed samples.