In the manufacture of semiconductor materials, a great deal of attention is focused on minimizing sources of contamination. Yield and reliability can be significantly compromised by ionic contamination. Of particular interest are those chemicals that come into contact with micro- electronic circuitry, such as isopropyl alcohol, acetone, and N-methyl-2-pyrrolidone.
Analysis of trace anions in solvents by wet chemical methods is laborious and time consuming. Procedures involve evaporation of a large volume of sample for several hours on a hot plate. Anions are determined by either colorimetric or turbidimetric methods, and each anion must be determined separately.
This application note describes a method for determining trace anions in water-miscible organic solvents by ion chromatography. Anions are removed from the solvent matrix and concentrated on a 4-mm IonPac® AG9-HC column. These concentrated anions are then eluted to a 2-mm IonPac AS9-HC analytical column set, where separation occurs. Method detection limits (MDLs) for chloride, sulfate, phosphate, and nitrate are less than 1 μg/L. The procedure is automated and yields an analysis for the four anions in less than 45 min. This method is an improvement over a method previously reported using a 4-mm AS10 column because it yields lower method detection limits and can be applied to a variety of organic solvents.