Quantifying crystal form content in physical mixtures of (+/-)-tartaric acid and (+)-tartaric acid using near infrared reflectance spectroscopy.

The objective of this study was to use diffuse reflectance near infrared spectroscopy (NIRS) to determine racemic compound content in physical mixtures composed primarily of the enantiomorph and to assess the error, instrument reproducibility and limits of detection (LOD) and quantification (LOQ) of the method. Physical mixtures ranging from 0 to 25% (+/-)-tartaric acid in (+)-tartaric acid were prepared and spectra of the powder samples contained in glass vials were obtained using a Foss NIRSystems Model 5000 monochrometer equipped with a Rapid Content Analyzer scanning from 1100 to 2500 nm. A calibration curve was constructed by plotting (+/-)-tartaric acid weight percent against the 2(nd) derivative values of log (1/R) vs lambda at a single wavelength, normalized with a denominator wavelength (1480 nm/1280 nm).

(+-)-Tartaric acid.

(+-)-Tartaric acid, C(4)H(6)O(6), crystallized from ethanol in space group P 1 macro. The structure is characterized by five hydrogen bonds, including the formation of a centrosymmetric carboxylic acid dimer which forms infinite chains along the body diagonal. These chains form sheets via hydrogen bonding between alpha-hydroxyl groups.