2018 Volume 67 Issue 1 Pages 51-59
The effects of residual silanol groups of a reversed-phase C18 silica column which was precoated with dodecylammonium chloride (DAC) were examined for the determination of six inorganic anions [iodate ion (IO3−), bromate ion (BrO3−), bromide ion (Br−), nitrite ion (NO2−), nitrate ion (NO3−), and iodide ion (I−)] in seawater by ion chromatography. We used 0.3 M sodium chloride + 0.5 mM DAC + 5 mM phosphate buffer solution (pH 4.5) as an eluent (flow rate, 1 mL min−1) and a UV detector (225 nm) for determination. It was possible to measure the analyte ions within 19 minutes. On the reversed-phase C18 silica column with residual silanol groups, separation between Br− and NO2− was better than those of end-capped columns, thus, retention mechanisms of anions were considered. The repeatability was within 1.55 % (n = 5) of the relative standard deviation (RSD (%)) of retention time, peak area, and peak height, and also was within 2.97 % (n = 48) in a continuous measurement for 24 hours. The calibration curves showed good linearity with a correlation coefficient of r2 > 0.999. The detection limit (S/N = 3) was IO3− (8.3 μg L−1), BrO3− (24 μg L−1), Br− (92 μg L−1), NO2− (0.8 μg L−1), NO3− (3.2 μg L−1), and I− (1.0 μg L−1). Similar results were obtained at a flow rate of 1.5 mL min−1 (measurement time, 13 min per sample). The present method was applied to water samples from Seto Inland Sea waters. The recovery rate by the standard addition was in the range of 93 to 108 %. Further, the method was applied to the depth profiles of anions during the summer season at five points in the Seto Inland Sea (Hiroshima Bay).