Abstract
In order to secure the safety of drinking water in Japan, perchlorate has recently been added to the list of examination regulated items under the Water Supply Law set by the Ministry of Health, Labour and Welfare on April 1, 2009. Accordingly the target value for perchlorate residue in tap water was newly set at 25 μg/L on April 1, 2011. A sensitive analytical method for the residual level of perchlorate in tap water was examined using large-loop injection ion chromatography. The retention time of perchlorate using ion chromatograph was 37.0 min by gradient analysis with potassium hydroxide in the concentration range from 2.5 mM to 40 mM. However, an isocratic run of potassium hydroxide of 65 mM shortened the retention time to 11.0 min. In addition, by increasing the volume of the injection sample from 200 μL to 1000 μL, the limit of determination was lowered from 3.5 μg/L to 0.40 μg/L. Furthermore, 100 mL of a water sample was put into a Teflon beaker and heated using a hot plate to concentrate to 10 mL (10 times). By using the concentrated sample, it was possible to measure a limit of determination of 0.08 μg/L, which is almost equal to 1/300 of the target value of 25 μg/L. An analysis of perchlorate in tap water in Hyogo prefecture was conducted using this method. As a result, the frequency of detection was 42%, and the range of detection was from 0.08 to 0.30 μg/L.
