Rapid quantitative analysis of magnesium stearate in tablets using laser-induced breakdown spectroscopy.

Purpose: Laser-induced breakdown spectroscopy (LIBS) was evaluated for its potential as a process analytical tool for the rapid determination of magnesium stearate (MgSt) distribution within and between tablets as well as between batches in a typical manufacturing run, and for the comparison of direct-compression and roller-compaction processes.

Methods: These studies were conducted using a prototype instrument and a commercial PharmaLIBS unit, both based on pulsed Nd:YAG laser radiation at 1064 nm. The intensity of a magnesium spectral line either at 517.27 or 518.36 nm was used, depending on the product, to quantitate the MgSt concentration in the tablets.

Results: Using internal standardization, it was possible with the prototype instrument to accurately quantitate MgSt at the 0.5% level in two different products. For eight batches of one product, using 10 tablets from each batch, the intra-tablet, intra-batch, and inter-batch MgSt %RSDs were found to be 13.8%, 5.4% and 7.4%, respectively. Further studies were conducted with the commercial LIBS unit, which showed similar performance as the prototype unit. In particular, it was found that different depth-profile distributions of MgSt were associated with roller-compacted tablets and direct-compressed tablets.

Conclusion: These findings illustrate the potential of LIBS to be developed as a process analytics tool for the direct and rapid determination of MgSt content and distribution in tablets.