Rapid analysis of liquid formulations containing sodium chloride using laser-induced breakdown spectroscopy

The purpose of this work was to demonstrate the possibilities offered by laser-induced breakdown spectroscopy (LIBS) for the direct and rapid analysis of pharmaceutical liquid formulations. Sodium chloride in solution was chosen as a model compound. A pulsed Nd:YAG laser (1064 nm) was used to produce a gaseous plasma from the liquid sample. The ensuing plasma emission was spectrally analysed, and the intensity of an atomic line from sodium was used to quantitate the sodium chloride. Using surface analysis of a flowing solution, the precision (%R.S.D.) of a measurement lasting 50 s (average of 50 laser shots at 1 shot/s) was approximately 0.5% for isotonic solutions. On a non-flowing solution, a 50 s measurement had an R.S.D. of 1.8%. Direct analysis in closed (transparent) bottles was possible but more complex, requiring the superimposition of two sequential laser sparks. Using a surface procedure, common commercial isotonic products (including injectable, bacteriostatic injectable, and nasal solutions) were analysed. Their sodium content (corresponding to 0.9% sodium chloride) was accurately determined in all cases, demonstrating the capabilities of LIBS for the rapid analysis of liquid pharmaceutical products.