title: Determination of trace amounts of β tegafur in commercial α tegafur by powder X-ray diffractometric analysis.
abstract: OBJECTIVE
  The main objective of this work was to develop a suitable analytical technique for determining trace amounts of the thermodynamically stable solid form in bulk samples of metastable form, to a sensitivity of 0.005%-1.0%. Tegafur (5-fluoro-1-(tetrahydro-2-furyl)-uracil) α and β crystalline forms were used as a model for this problem.
  
  
  METHODS
  The trace content of the thermodynamically stable β polymorphic form in tegafur samples was increased by promoting phase transition from the bulk of thermodynamically metastable α form to β form, and achieving sufficient β form content for a quantitative powder X-ray diffractometry (PXRD) analysis. The phase transition was stimulated by adding water to the samples and then grinding in controlled conditions (temperature, time, grinding speed). A calibration line was constructed using the least squares method.
  
  
  RESULTS
  By using a solvent that does not form hydrates with the analysed polymorphs, it was possible to promote the phase transformation from metastable form to the thermodynamically stable form. After sample preparation, the thermodynamically stable solid form content in the analysed mixture had increased proportionally to the initial weight fraction (0.005%-1.0%) of the stable form seed crystals in the samples, and the coefficient of proportionality was 43.0±0.9, with a standard deviation S(n) =1.5%.
  
  
  CONCLUSIONS
  A simple, sensitive, semi-quantitative analytical method was developed for the low-level determination of the thermodynamically stable polymorphic form in mixtures of thermodynamically stable and metastable polymorphs.
authors.affiliation: The Faculty of Chemistry, University of Latvia, Riga, Latvia. sanitapetkune@yahoo.com
authors.forename: Sanita
authors.initials: S
authors.lastname: Petkune
authors.forename: Raitis
authors.initials: R
authors.lastname: Bobrovs
authors.forename: Andris
authors.initials: A
authors.lastname: Actiņš
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D016018:Least-Squares Analysis; D011208:Powders; D005641:Tegafur / Q000032:analysis* / Q000737:chemistry; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D011208:Powders; D005641:Tegafur