For the determination of free iodine the samples are extracted on solid phase extraction cartridges. The probe is centrifuged and 50 μl of the supernatant are injected into the HPLC system. The isocratic separation via HPLC at 30°C uses a ``reversed phase``column. One run lasts 10 minutes. The chromatograms are recorded by an electrochemical detector with a silver working electrode. The quantification is performed with the delivered standard; the concentration is calculated via integration of the peak areas or heights. Sample Types: urine. Time: 5 minutes ? The measurement of free iodine in urine is a valuable tool for the determination of the supply with iodine. The measurement of the direct intake of iodine is rather difficult. Therefore the determination of iodine in urine is well accepted as an index of iodine uptake. The fecal excretion is negligible.