Determination of inorganic anions in seawater samples by ion chromatography with ultraviolet detection using monolithic octadecylsilyl columns coated with dodecylammonium cation

Abstract

A fast and sensitive ion chromatographic method for the simultaneous determinations of six inorganic anions [iodate (IO 3- ), bromate (BrO 3- ), bromide (Br - ), nitrite (NO 2- ), nitrate (NO 3- ), and iodide (I - )] in seawater is described using dodecylammonium (DA + )-coated monolithic octadecylsilyl (ODS) columns, a concentrated aqueous NaCl mobile phase containing dodecylammonium chloride (DAC), and a UV detector. The DA + -coated monolithic ODS columns show greater retention for iodate and weaker retention for iodide, compared to dilauryldimethylammonium (DDA + )-coated monolithic ODS columns. Six anions were determined within 12 min with baseline separation without interferences by matrix ions, such as Cl - and SO 42- , in seawater, compared to a DA + -coated particulate ODS column (it took 25 min per sample) obtained previously. The detection limits (DLs) were comparable to the DA + -coated particulate ODS column: IO 3- (7.7 μg L -1 ), BrO 3- (20), Br - (88), NO 2- (0.9), NO 3- (1.9), and I - (0.9) with a 100-μL sample injection. A larger sample volume injection lowered the DLs of IO 3- , BrO 3- , and I - . The good performance was maintained for ca. 2 years examined. The robust IC system developed in the present work was successfully applied to real seawater samples without sample dilution in the recovery rates of 93 - 104% for all ions. 2016