title: Quantitative analysis of entacapone isomers using surface-enhanced Raman spectroscopy and partial least squares regression.
abstract: Surface-enhanced Raman spectroscopy (SERS) and partial least squares (PLS) regression have been applied for the quantification of entacapone isomers E and Z in solution. Nine mixtures of isomers Z and E in ethanol ranging from 0% to 100% w/w were analyzed,  for a total entacapone concentration of 1 × 10(-3) mol L(-1). Upon deposition onto commercially available Klarite® gold plates, highly intense and reproducible SERS spectra were obtained from the entacapone isomers. Based on the spectral measurements,  a two-component PLS model for correlation of predicted and real content of the isomers mixtures was developed. Root-mean-square error of the predicted composition was found to be 8% of isomer Z in the isomers mixture, corresponding to the absolute concentration of 8 × 10(-5)  mol L(-1) of isomer Z in solution.
authors.affiliation: PLIVA Croatia, Teva Pharmaceutical Industries Ltd., Research and Development, Prilaz baruna Filipovića 29, HR-10000 Zagreb, Croatia. marina.ratkaj@pliva.com
authors.forename: Marina
authors.initials: M
authors.lastname: Ratkaj
authors.forename: Tomislav
authors.initials: T
authors.lastname: Biljan
authors.forename: Snežana
authors.initials: S
authors.lastname: Miljanić
mesh_terms: D002396:Catechols / Q000032:analysis* / Q000737:chemistry*; D007536:Isomerism; D016018:Least-Squares Analysis; D009570:Nitriles / Q000032:analysis* / Q000737:chemistry*; D015203:Reproducibility of Results; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D002396:Catechols; D009570:Nitriles; C071192:entacapone