QUANTITATIVE-ANALYSIS OF IMPURITIES IN EPSILON-CAPROLACTAM BY RAMAN-SPECTROSCOPY

Laser Raman spectroscopy was used for the quantitative analysis of the most common impurities contained in epsilon-caprolactam: adipic acid, sodium sulfate and ammonium sulfate. Calibration graphs were construc ted from spectra obtained from pellets with known quantities of epsilo n-caprolactam and each of the impurities. Linear relationships between the caprolactam content and the ratio of the relative intensities at characteristic wavelengths were found for the impurities examined. The calibration lines were defined as: adipic acid-epsilon-caprolactam I- 915/I-746 = chi(cap)(-1) 0.62 - 0.58; ammonium sulfate-epsilon-caprola ctam I-975/I-746 = chi(cap)(-1) 2.78 - 2.23; and sodium sulfate-epsilo n-caprolactam I-994/I-746 = chi(cap)(-1) 4.26 - 4.45. I is the relativ e Raman intensity at the wavenumber noted by the subscript and chi(cap ) is the molar fraction of caprolactam. The detection limits are bette r than 1 mol% for the impurities examined.