title: Considerations on the quantitative analysis of apparent amorphicity of milled lactose by Raman spectroscopy.
abstract: The main purpose of the study was to evaluate various pre-processing and quantification approaches of Raman spectrum to quantify low level of amorphous content in milled lactose powder. To improve the quantification analysis, several spectral pre-processing methods were used to adjust background effects. The effects of spectral noise on the variation of determined amorphous content were also investigated theoretically by propagation of error analysis and were compared to the experimentally obtained values. Additionally, the applicability of calibration method with crystalline or amorphous domains in the estimation of amorphous content in milled lactose powder was discussed. Two straight baseline pre-processing methods gave the best and almost equal performance. By the succeeding quantification methods, PCA performed best, although the classical least square analysis (CLS) gave comparable results, while peak parameter analysis displayed to be inferior. The standard deviations of experimental determined percentage amorphous content were 0.94% and 0.25% for pure crystalline and pure amorphous samples respectively, which was very close to the standard deviation values from propagated spectral noise. The reasonable conformity between the milled samples spectra and synthesized spectra indicated representativeness of physical mixtures with crystalline or amorphous domains in the estimation of apparent amorphous content in milled lactose.
authors.affiliation: Department of Pharmacy, Uppsala University, Uppsala, Sweden. Electronic address: samaneh.pazesh@farmaci.uu.se.
authors.forename: Samaneh
authors.initials: S
authors.lastname: Pazesh
authors.affiliation: Department of Pharmacy, Uppsala University, Uppsala, Sweden.
authors.forename: Lucia
authors.initials: L
authors.lastname: Lazorova
authors.affiliation: Recipharm Pharmaceutical Development AB, Solna, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Berggren
authors.affiliation: Department of Pharmacy, Uppsala University, Uppsala, Sweden.
authors.forename: Göran
authors.initials: G
authors.lastname: Alderborn
authors.affiliation: Department of Pharmacy, Uppsala University, Uppsala, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Gråsjö
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods*; D007785:Lactose / Q000032:analysis* / Q000737:chemistry; D025341:Principal Component Analysis; D013059:Spectrum Analysis, Raman / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D007785:Lactose
keywords: Amorphous content; Lactose; Milling induced disorder; Principal component analysis (PCA); Raman spectroscopy; Spectral data analysis