Pyrohydrolysis Coupled to Ion Chromatography for Sensitive Determination of Iodine in Food-Related Materials

Abstract

For the determination of iodine in food-related materials, the biological sample was decomposed using a pyrohydrolytic procedure. A sample vessel made from mullite, in which an aliquot of sample was taken, was placed in a quartz tube, and heated at 100°C through 820°C step by step under wet oxygen flow. Iodine in the sample was separated by evaporation as hydrogen iodide and collected in a dilute sodium hydroxide solution. After the basic solution containing the analyte was neutralized by adding hydrochloric acid, iodine in the solution was determined by using ion chromatography with ultraviolet absorption detection. The operating conditions for the pyrohydrolytic decomposition procedure were examined. Under the optimized conditions, organic constituents in the sample were completely decomposed since the analyte species were converted to the iodide ion. The detection limit of 0.01 µg g⁻¹ iodine was established with a reproducibility of 1.2% when a sample of 500 mg was taken. This method was applied to the determination of iodine in various certified reference materials and food samples with satisfactory results.

Keywords:

• Food-related materials
• Iodine
• Ion chromatography
• Pyrohydrolytic decomposition

Notes

^a Sample, NIST SRM 1549 (Non-fat milk powder) 100 mg, n = 3.

^b Decreased to 100°C with ramp time of 2.5 min.

^c Because of various peaks on chromatography, no peak separation was achieved.

^a Values in parentheses are not certified.

^b Sample amount taken, 100 mg. Average ±standard deviation, n = 3.

^c Sample amount taken, 500 mg. Average ±standard deviation, n = 3.

^d Sample amount taken, 100∼ 500 mg. Average ±standard deviation, n = 11.

^e Sample amount taken, 10 mg. Average ±standard deviation, n = 3.

^a Average ± standard deviation, n = 3.

^b 1.25 µg g⁻¹iodine was added. Recovery, 94%.

^c 2.5 µg g⁻¹iodine was added. Recovery, 94%.