title: Near-infrared imaging for studying homogeneity of protein-sugar mixtures.
abstract: OBJECTIVE
  To investigate the applicability of near-infrared (NIR) imaging for assessing the homogeneity of dried protein-sugar formulations.
  
  
  METHODS
  Physical mixtures of lysozyme and trehalose in different ratios were prepared and analyzed by near-infrared (NIR) imaging with a spatial resolution of 10 or 40 microm. To define and select the best imaging strategy, besides visual inspection of the images, several approaches for data processing were tested: single wavelength intensity, peak/height ratio of two specific wavelengths, correlation coefficient with a reference spectrum and principal component analysis (PCA). In order to relate the contrast directly to concentration differences of lysozyme and trehalose, quantitative models were created based on correlation coefficient and partial least squares (PLS) regression. The selected imaging method was applied to compare the homogeneity of a supercritical fluid (SCF) dried and a freeze-dried lysozyme-trehalose mixture.
  
  
  RESULTS
  All tested methods confirmed each other and showed spatial heterogeneity in the lysozyme and trehalose contents of the physical mixtures. However, multivariate data processing methods (correlation coefficient and PCA/PLS) resulted in more distinct contrasts than univariate approaches (single wavelength analysis) and allowed a quantitative estimation of the homogeneity. As shown by NIR imaging in combination with the correlation coefficient or the PLS method, the SCF dried lysozyme-trehalose formulation was at least as homogeneous as its lyophilized counterpart, at 10 microm pixel size resolution.
  
  
  CONCLUSIONS
  NIR imaging is a useful tool for studying the homogeneity of dried protein-sugar formulations.
authors.affiliation: Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS), Utrecht, The Netherlands.
authors.forename: Natasa
authors.initials: N
authors.lastname: Jovanović
authors.forename: Ad
authors.initials: A
authors.lastname: Gerich
authors.forename: Andréanne
authors.initials: A
authors.lastname: Bouchard
authors.forename: Wim
authors.initials: W
authors.lastname: Jiskoot
mesh_terms: D000465:Algorithms; D002241:Carbohydrates / Q000032:analysis*; D025924:Chromatography, Supercritical Fluid; D003627:Data Interpretation, Statistical; D003952:Diagnostic Imaging; D005612:Freeze Drying; D009113:Muramidase / Q000032:analysis; D025341:Principal Component Analysis; D011506:Proteins / Q000032:analysis*; D019265:Spectroscopy, Near-Infrared; D014199:Trehalose / Q000032:analysis
chemical_list: D002241:Carbohydrates; D011506:Proteins; D014199:Trehalose; D009113:Muramidase