In situ vapor generation inductively coupled plasma spectrometry for determination of iodine using a triple-mode microflow ultrasonic nebulizer after alkaline solubilization

Abstract

The analytical potential of a coupled continuous-microflow ultrasonic nebulizer triple-mode micro-capillary system (µ-USN/TCS) for the determination of iodine in biological samples by direct iodine vapor generation inductively coupled plasma optical emission spectrometry (VG-ICP-OES) has been investigated. The iodine atomic emission line at 183.038 nm was selected as the analytical line of interest. An extremely short oxidation reaction time between sample, acid and oxidant and a rapid separation of the reaction products is obtained by mixing the sample, sulfuric acid, hydrogen peroxide, and the sodium nitrite solution at the quartz oscillator, converting liquids into aerosol at the entrance to the spray chamber. A univariate approach and simplex optimization procedures were used to achieve optimized conditions and derive analytical figures of merit. Results showed that the analytical performance of the new system was superior to that of pneumatic nebulizer. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the µ-USN/TCS-VG-ICP-OES observed at a 15 µL min⁻¹ flow rate. The experimental concentration detection limits for iodine determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σ_blank criterion, peak height), were 1.6 ng mL⁻¹ for iodine. The method offers relatively good precision (RSD ranged from 2 to 4%) for liquid analysis and microsampling capability. Samples were prepared by solubilization with tetramethylammonium hydroxide (TMAH), permits complete sample solubilization and significantly reduces the risk of iodine evaporation, before iodine was quantified by USN-VG-ICP-OES. The accuracy of the method was verified using certified reference materials (NIST 1549 and NIST 1566b) and using a simple external calibration technique. The measured contents of elements in reference materials were in satisfactory agreement with the certified value (I). The method was applied to the determination of total iodine in different samples with satisfactory results.