Determination of anions at the ng/1 level by means of switching valves to eliminate the water-dip interference

Abstract

It is well known that anions, such as chloride, nitrate and sulphate can be determined relatively easily at the μg/1 level using an on-line concentrator column. In recent years, however, ultra-pure water containing only ng/1 levels of anions or cations is demanded by the most advanced semiconductor factories or power generation plants. For the determination of anions and cations at the ng/1 level in such ultra-pure water, higher sensitivity is required. To achieve this, it is necessary to eliminate the water-dip which interferes with the determination of chloride at the ng/1 level. We developed and tested a water-dip cutting system consisting of switching valves and a water-dip cutting column. When we combined this with an on-line concentration system, we were able to determine chloride, nitrite, bromide, nitrate, phosphate and sulphate at the ng/1 level.