Determination of trace ammonium and alkali metal ions in a clean room by ion chromatography

Abstract

A method for determining trace amounts of ammonium and alkali metal ions by ion chromatography was examined. Tetramethyl ammonium hydroxide solution (40 mM) was used as the regenerant at a flow rate of 10 ml/min, which gave a lower background intensity. For optimum peak separation and sensitivity, a solution containing 25 mM hydrochloric acid and 0.25 mM 2, 3-diaminopropionic acid monohydrochloride was employed as the eluent at a flow rate of 1.0 ml/min. The detection limit (with the RSD) by this method was NH₄: 10 ppb (0.67%), Li : 2 ppb (0.96%), Na : 5 ppb (0.99%), and K: 10 ppb (0.54%). It was found out that this analytic method was high in sensitivity and accuracy and could be applied to the determination of trace ammonium and alkali metal ions in a VLSI clean room.