[Validation Study on the Developed Method for Cyanide in Various Mineral Waters]

A method for the determination of two kinds of cyanide, namely cyanide ion and cyanogen chloride, in various mineral waters (MWs) has been developed and validated. MWs are varying in the degree of hardness and carbonation. The results of two carbonated MWs obtained through the validated official method for cyanide analysis in tap water did not meet the criteria of the validation guideline for MW in Japan. Furthermore, in the pH adjustment during pretreatment, some MWs did not reach approximately pH 2.4, the level assumed in tap water quality tests. After five-fold dilution of the samples with phosphate buffer, the specified pH value of 2.4 was achieved, leading to the improvements in trueness. The validation tests of the method with the additional dilution step showed the trueness from 93.0 to 103.8%, RSDs of repeatability and within-laboratory reproducibility below 3.83% and 4.68%, respectively. These values fulfill the criteria on both analytes. The developed method indicated the potential applicability for accurate determination of cyanide ion and cyanogen chloride in a range of commercially available MW products.