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

Jun Bai Shu, Meena Rani, Raj Suryanarayanan, John F. Carpenter, Rajiv Nayar, Mark C. Manning

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


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 β-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.

Original languageEnglish (US)
Pages (from-to)2439-2447
Number of pages9
JournalJournal of Pharmaceutical Sciences
Issue number10
StatePublished - Oct 2004


  • Crystallinity
  • Glycine
  • Lyophilization
  • NIR
  • Sucrose


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