Simultaneous determination of iodide and creatinine in human urine by flow analysis with an on-line sample treatment column

This work presents the first flow system for direct analysis of iodide and creatinine suitable for screening of human urine samples. The system had a mini-column packed with strong anion exchange resin for on-line extraction of iodide. After injection of a sample on the column the unretained urine sample was analyzed for creatinine in one section of the flow system using the Jaffe's reaction with spectrometric detection at 520 nm. Iodide was eluted off with 1.42 mL 5 M NaNO3. A 150 μL fraction of the eluate was analyzed in another section of the same flow system for iodide using the kinetic-spectrometric Sandell-Kolthoff reaction. At the optimum condition, the sample throughput was 12 samples per h. The linear working range covered the normal levels of iodide and creatinine in human urine: 0-200 μg I L(-1) and 50-1200 mg creatinine L(-1), respectively. Recoveries tested in 10 samples were 87-104% for iodide and 89-104% for creatinine. Bland-Altman plots (n = 50) showed that the scatter of the differences between values obtained by this method and those of reference methods, for both iodide and creatinine, was within mean ± 2SD.