Tablet Coating Thickness Measurements by Combined Raman Spectrometry and Laser Induced Breakdown Spectrometry Techniques

Abstract

For the first time, pharmaceutical tablet coating thickness is measured by combined Raman spectrometry (RS) and laser induced breakdown spectrometry (LIBS) techniques. Measurements by two methods (RS and LIBS) are performed during a single pump lamp flash of a pulsed Nd:YAG laser in the double pulse lasing mode. This approach combining a probe laser pulse (RS) followed by an ablating laser pulse (LIBS) allows depth profiling analysis. An additional advantage is a possible comparison of the results of measurements of molecular and elemental compositions within the same spot. It is shown that the published method for measuring the coating thickness by LIBS depth profiling leads to systematic errors. An approach for improving the accuracy of coating thickness data measurements by comparing the RS and LIBS is proposed.