Determination of fluoride ions in urinary stones by ion chromatography

A method of the ion chromatographic determination of fluoride ions in urinary stones has been developed. Sample preparation of solid mineral-organic samples includes dissolution in concentrated hydrochloric acid, dilution with deionized water, and the elimination of excess calcium and magnesium cations by adding a KU-2 sulfo cation exchanger in the H-form to samples and filtration through a membrane filter. Anions were separated on a Shim-pack IC-AIS anion-exchange column (100 x 4.6 mm) with elution with a mixture of 2.0 mM phthalic acid and 1.2 mM sodium hydroxide (pH 3.5). The linearity range of the fluoride ions in the obtained solutions of urinary stones with conductometric detection was 0.01-300 mg/L, the limit of detection calculated by the 3s-test was 0.004 mg/L. The quantitative determination of fluoride ions in 20 samples of urinary stones was performed; in 80% of cases the presence of fluorides in the stones at a level from 0.01 to 4 mg/g of the stone was detected. The average concentration of the fluoride ions was 0.3 mg/g of stone. For 20% of the samples an elevated concentration of fluoride ions compared to the average one was found.