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Characterizing Individual Protein Aggregates by Infrared Nanospectroscopy and Atomic Force Microscopy
Published on: September 12, 2019
Quantification of glycine crystallinity by near-infrared (NIR) spectroscopy
Shu Jun Bai1, Meena Rani, Raj Suryanarayanan
1Center for Pharmaceutical Biotechnology, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
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 beta-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 r(2) 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 < or =0.67, glycine remained substantially crystalline. At intermediate compositions, the glycine was partially crystalline.
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