NONINVASIVE IDENTIFICATION OF MATERIALS INSIDE USP VIALS WITH RAMAN-SPECTROSCOPY AND A RAMAN SPECTRAL LIBRARY

A commercial dispersive Raman spectrometer operating at 785 nm with a CCD detector was used to acquire spectra of USP reference materials in side amber USP vials. The laser and collection beams were directed thr ough the bottom of the vials, resulting in a 60% loss of signal. The R aman shift was calibrated with a 4-acetamidophenol standard, and spect ral response was corrected with a luminescent standard. After these co rrections, the Raman spectra obtained inside the USP vial and on open powders differed by less than 5%. A spectral library of 309 reference materials was constructed, with spectral acquisition times ranging fro m 1 to 60 s. Of these, 8% had significant fluorescent background but o bservable Raman features, while 3% showed only fluorescence. A blind t est of 26 unknowns revealed the accuracy of the library search to be 8 8-96%, depending on search algorithm, and 100% if operator discretion was permitted. The tolerance of the library search to degraded signal- to-noise ratio, resolution, and Raman shift accuracy were tested, and the search was very robust. The results demonstrate that Raman spectro scopy provides a rapid, noninvasive technique for compound identificat ion.