Simultaneous determination of sodium hydroxide, sodium carbonate and sodium chloride concentrations in aqueous solutions by near-infrared spectrometry

Abstract

The quantitative analysis of solutions containing various concentrations of sodium hydroxide, sodium chloride and sodium carbonate, over the range 0–15%m/m, has been carried out by near-infrared (NIR) spectrometry. Errors, caused by a high concentration of one salt when determining small amounts of another, have been investigated. The standard errors of the computed results from NIR measurements of each ion were: hydroxide, 0.12; carbonate, 0.34; and chloride, 0.52%. The measurements were made using a liquid sample cup in a fixed-filter NIR instrument and it was concluded that this was a practical system for continuous monitoring of the sodium hydroxide concentration in a process line even when contamination from hydrochloric acid and carbon dioxide occurred.