Determination of total iodine in serum and urine samples by ion chromatography with pulsed amperometric detection – Studies on analyte loss, optimization of sample preparation procedures, and validation of analytical method

• Serum/urine of obese/healthy children was accessed for iodine content using IC-PAD.
• Optimization of various sample preparation procedures was carried out.
• Recovery was higher with alkaline than acidic digestion followed by ammonification.
• Loss of analyte was higher for urine samples than serum samples.
• Obese children have a lower iodine content in serum/urine than healthy children.

A fast, accurate and precise ion chromatography method with pulsed amperometric detection was applied to evaluate a variety of parameters affecting the determination of total iodine in serum and urine of 81 subjects, including 56 obese and 25 healthy Polish children. The sample pretreatment methods were carried out in a closed system and with the assistance of microwaves. Both alkaline and acidic digestion procedures were developed and optimized to find the simplest combination of reagents and the appropriate parameters for digestion that would allow for the fastest, least time consuming and most cost-effective way of analysis. A good correlation between the certified and the measured concentrations was achieved. The best recoveries (96.8% for urine and 98.8% for serum samples) were achieved using 1 ml of 25% tetramethylammonium hydroxide solution within 6 min for 0.1 ml of serum/urine samples. Using 0.5 ml of 65% nitric acid solution the best recovery (95.3%) was obtained when 7 min of effective digestion time was used. Freeze–thaw stability and long-term stability were checked. After 24 weeks 14.7% loss of iodine in urine, and 10.9% in serum samples occurred. For urine samples, better correlation (R2 = 0.9891) of various sample preparation procedures (alkaline digestion and application of OnGuard RP cartidges) was obtained. Significantly lower iodide content was found in samples taken from obese children. Serum iodine content in obese children was markedly variable in comparison with the healthy group, whereas the difference was less evident when urine samples were analyzed. The mean content in serum was 59.12 ± 8.86 μg/L, and in urine 98.26 ± 25.93 for obese children when samples were prepared by the use of optimized alkaline digestion reinforced by microwaves. In healthy children the mean content in serum was 82.58 ± 6.01 μg/L, and in urine 145.76 ± 31.44 μg/L.