Quantification of glycine crystallinity by near-infrared (NIR) spectroscopy

Quantification of glycine crystallinity by near-infrared (NIR) spectroscopy
July 2004
Shu Jun Bai 1, Meena Rani 2, Raj Suryanarayanan 2, John F. Carpenter 1, Rajiv Nayar 3, Mark C. Manning 1 4 *
1Center for Pharmaceutical Biotechnology, University of Colorado Health Sciences Center, Denver, Colorado 80262
2College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55455
3HTD BioSystems. Hercules, California 94547
4HTD BioSystems-Colorado, Loveland, Colorado 80538
Journal of Pharmaceutical Sciences, Volume 93, Issue 10 , Pages 2439 - 2447
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Abstract
The object of this investigation was to use near-infrared (NIR) spectroscopy for quantification of glycine crystallinity. Glycine samples, with different degrees of crystallinity, were obtained by physically mixing different proportions of crystalline -glycine with amorphous glycine. NIR spectra were obtained, directly from samples in glass vials, over the wavelength range of 1100-2500 nm. A partial least squares (PLS) model was developed to correlate the NIR spectral changes with the degree of crystallinity. Using this model, a standard error of calibration (SEC) of 2.1% was obtained with an r2 value of 0.996. Cross validation was used to test the precision of the quantitative model, resulting in a standard error of prediction (SEP) of 3.2%. These results indicate that NIR spectroscopy is well suited to the measurement of glycine crystallinity in lyophilized products. Employing the PLS model, the crystallinity of glycine in freeze-dried sucrose-glycine mixtures was evaluated. At a sucrose to glycine ratio >4, glycine crystallization during lyophilization was inhibited. Conversely, at ratios 0.67, glycine remained substantially crystalline. At intermediate compositions, the glycine was partially crystalline. ? 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:2439-2447, 2004