Determination of trace sodium, lithium, magnesium, and potassium impurities in colloidal silica by slurry introduction into an atmospheric-pressure solution-cathode glow discharge and atomic emission spectrometry

Trace impurities of sodium, lithium, magnesium, and potassium in colloidal silica were determined by slurry introduction into an atmospheric-pressure solution-cathode glow discharge (SCGD). The applied voltage, solution flow rate, and distance between the metal anode and surface of the solution were optimized. Emission from K (766.5 nm), Na (589.0 nm), Mg (285.2 nm) and Li (670.8 nm) demonstrated a linear range of nearly 4 orders of magnitude (R-2 >= 0.998) and steady-state sample introduction yielded limits of detection of 0.7, 0.4, 0.5 and 0.2 ng mL(-1), respectively. For an integration time of 0.3 s, relative standard deviations (RSDs) from 1000 ng mL(-1) standard solutions introduced continuously were found to be better than 3% for all four elements. Transient sample introduction into the SCGD was also optimized and provided limits of detection for K, Na, Mg and Li of 3, 2, 2 and 0.8 ng mL(-1), respectively, and RSDs for 1000 ng mL(-1) standard solutions of better than 3%. Determined concentrations of trace impurities in colloidal silica agreed satisfactorily (accuracy from 1.3 to 7.7% and precision from 4 to 14%) with those obtained from inductively coupled plasma atomic emission spectrometry.