Ion-chromatographic determination of seven common anions in electronic-grade, water-miscible solvents

An ion-chromatographic method has been developed to determine seven common anions in electronic-grade acetone, isopropyl alcohol, methanol, and N-methyl-2-pyrrolidone (NMP), solvents whose cleanliness is vital to the manufacturing of semiconductor devices. The system requires only a pump, conductivity detector, and switching valve as hardware. A calibration study was conducted first, by preparing and analyzing 11 concentrations (between 0.3 and 6.0 ng/g) in deionized (DI) water. Subsequently, a spiking study was performed by spiking each solvent at each of nine concentrations (between 50 and 500 ng/g). Dilutions of 1-100 (w/w) were prepared and analyzed. For each anion, recovered concentrations were estimated using the appropriate calibration curve. For each recovery curve, uncertainties in predicted concentrations were between +/-20 and +/-150 ng/g (except for phosphate in acetone), at 95% confidence. Recoveries were between 82% and 112% for all anions in all solvents, except for nitrite and nitrate in acetone, nitrite in methanol, and fluoride in N-methyl-2-pyrrolidone.