Rapid screening for ethyl carbamate in stone-fruit spirits using FTIR spectroscopy and chemometrics

Ethyl carbamate (EC, urethane, C2H5OCONH2) is a known genotoxic carcinogen of widespread occurrence in fermented food and beverages with the highest concentrations being found in stone-fruit spirits. Time-consuming procedures requiring extraction and gas chromatographic-mass spectrometric determination are regarded as reference procedures for the analysis of EC in alcoholic beverages. In this study, the rapid method of Fourier transform infrared (FTIR) spectroscopy in combination with partial least-squares (PLS) regression using selected wavelength bands is applied for the first time to the screening analysis of EC in stone fruit spirits (analysis time only 2 min). Apart from the actual content of EC in the sample, additional information was available from the FTIR spectra. This included data concerning the EC precursor hydrocyanic acid (HCN) and the maximum EC concentration which could be formed during storage. The PLS procedure was validated using an independent set of samples (Q(2) = 0.71-0.76, SEP = 0.42-0.67). The method was found to lack the accuracy required for a quantitative determination; it could only be used semi-quantitatively in the context of a screening analysis. If a rejection level of 0.8 mg L(-1) is applied as cut-off, overall correct classification rates of 85-91% for the calibration set and 77-85% for the validation set were achieved. False negative results can be avoided by lowering the cut-off to 0.6 mg L(-1). Through use of FTIR screening, 60-70% of all samples can be classified as negative and removed, leaving only conspicuous analysis results exceeding cut-off to be confirmed by complex and labour-intensive reference analyses.