A valve-switching based ion chromatography strategy for simultaneous determination of trace cations in table salt

An ion chromatography method was established for monitoring trace K⁺, Mg²⁺, and Ca²⁺ in table salt. A valve-switching technique was used as on-line method to eliminate the interference of Na⁺. The salt sample was dissolved in deionised water, and appropriate amounts were passed through 0.22 μm filter membrane before sampling. The Na⁺ was transferred to waste while other cations were retained on a Dionex CG12A column and then separated by a Dionex CS12A column. The eluent was 16 mmol/L methane sulphonic acid; the suppressor was a Dionex SC-CERS with a current of 47 mA. The sample loop was 25 μL and the flow rate was 1.0 mL/min. The linearities curves for all three cations were satisfactory in the range 0.0200-1.00 mg/L, and the correlation coefficients (r) were ≥0.999. The limits of detection (LODs) of the three cations were 0.00170-0.00645 mg/L based on a signal-to-noise ratio(S/N) of 3, and the limits of quantitation (LOQs) were 0.00567-0.0215 mg/L based on a S/N of 10. Average recoveries ranged from 103.9% to 112.4% (n = 6) and repeatability results were acceptable with relative standard deviation of less than 6.24% (n = 6). The concentrations of K⁺, Mg²⁺, and Ca²⁺ in salt samples were additionally determined by atomic absorption spectrometry. The results were consistent with the valve-switching method, and the relative differences for the three cations were each less than 10% (n = 3). The ranges for K⁺, Mg²⁺, and Ca²⁺ in six salt samples were 0.0640-0.411 g/kg, N.D-1.16 g/kg, 0.0494-1.43 g/kg, respectively. The contents of K⁺, Mg²⁺, and Ca²⁺ in coarse salt were significantly higher than refined salt. This method can improve efficiency, reduce operations, and achieve degree of automated analysis. It is accurate, sensitive and selective and can be applied for the simultaneously detection of the three cations in salts.