A simple dilute-and-shoot approach using UV photochemical vapor generation for the determination of iodine in alcoholic beverages by ICP-MS

Abstract

A novel method using photochemical vapour generation (PVG) for the determination of iodine in alcoholic beverages by inductively coupled plasma mass spectrometry (ICP-MS) is presented. The procedure consisted in simply diluting 1.0 mL of an alcoholic beverage (cachaça, vodka, whisky, brandy and gin were analyzed) to a final volume of 15 mL with deionized water prior to introduction in the PVG reactor for the generation of volatile iodine species. The native ethanol content in the samples (approximately 40 % v/v, before dilution) was proven sufficient to produce radicals upon UV irradiation, which ultimately resulted in the release of volatile iodine compounds to the gas phase. The process was systematically evaluated to reach the optimum operating conditions of 1.0 L min-1 Ar as the carrier gas, 1400 W ICP RF power, sample flow rate of 8.08 mL min-1 and 49 s of sample solution exposition to UV photons in the PVG reactor. Two distinct gas-liquid separators (GLS) with internal volumes of 3.1 and 6.5 mL were evaluated. The GLS with an internal volume of 6.5 mL was selected, as it resulted in higher sensitivity for the analyte. Matrix effects required standard addition calibration to be employed to determine the iodine concentrations, which ranged from ca. 21 to 386 μg L-1. Detection and quantification limits were determined as 0.1 and 0.3 μg L-1, respectively. The trueness was verified by comparing the results with those obtained by ICP-MS with pneumatic nebulization, following sample digestion in closed vessels. No significant statistical difference was observed when a paired t-test was applied and the sensitivity achieved from analyte introduction using PVG was 64 % higher when compared to the use of a pneumatic nebulizer. The samples were also spiked with known amounts of the analyte and recoveries ranged from 95 to 105 %, with relative standard deviations better than 9 %.