[Simultaneous determination of iodide and thiocyanate powdered milk using ion chromatography with mixed-mode column]

The contents of iodide and thiocyanate are important detection items in powdered milk quality testing. Due to the complexity of the powdered milk matrix, chromatographic analysis is easily subjected to interference. Acclaim Mixed-Mode WAX-1 column incorporated both hydrophobic and weak anion-exchange properties was used to separate iodide and thiocyanate from interfering substances in powdered milk matrix, and detected by Ultraviolet (UV) detection. After powdered milk was dissolved in water, the protein was precipitated by acetonitrile. Then OnGuard RP pre-treatment column was used to remove the organic matters which might pollute the column. The eluent was acetonitrile-100 mmol/L phosphate buffer (pH 6)-water (45:5:50,v/v/v). The UV detection wavelength was 226 nm. The limits of detection of iodide and thiocyanate were 4.6 microg/L and 13.8 microg/L respectively, and the relative standard deviations of peak areas were 1.2% (n = 6) and 1.7% (n = 6) for 0.2 mg/L iodide and thiocyanate standard solutions. The method is accurate and reliable, and has wide linear range, low limit of detection. This method provides a viable approach for powdered milk quality dairy products.