Profiling of trace elemental impurities in caustic soda matrix by inductively coupled plasma mass spectrometric technique.

An inductively coupled plasma mass spectrometric (ICP-MS) technique method is developed for simultaneous determination of Li, Cr, Mn, Fe, Ni, Co, Cu, Sr, Ag, Cd, Ba, and Pb at trace level in caustic soda. Operational parameters of the instrument were optimized and suitable accessory (argon gas dilution) was used in the method. Direct aspiration of high total dissolved solids (TDS) samples (beyond 0.2% TDS) and highly alkaline NaOH is not suitable for the instrument; therefore, strategy of neutralization of NaOH by HNO3 was adopted to handle its high alkalinity. Suitable internal standards of low, mid, and high atomic masses were used with external calibration. Features such as matrix matching, calibration verification, interference correction, etc. were undertaken in this work. Neutralized caustic soda samples were spiked with the analytes with lower, middle, and higher concentration. The results of spiking with 30, 70, 140, and 200 ppb were examined. The method exhibited excellent accuracy and precision.