ETHYL CARBAMATE FORMATION IN GRAIN BASED SPIRITS: PART II THE IDENTIFICATION AND DETERMINATION OF CYANIDE RELATED SPECIES INVOLVED IN ETHYL CARBAMATE FORMATION IN SCOTCH GRAIN WHISKY

Abstract

Ion chromatographic procedures are described for the identification and determination of a series of cyanide related precursors involved in ethyl carbamate formation in maturing grain whisky produced by the continuous distillation Coffey still process. These precursors include cyanide and copper cyanide complex anions, lactonitrile and isobutyraldehyde cyanohydrin (collectively determined as “measurable cyanide” or MC) and cyanate and thiocyanate anions. The components comprising MC may be determined individually using a pre-chromatographic separation procedure based on anion exchange resins. These techniques have been shown to be applicable for monitoring precursors involved in post-distillation ethyl carbamate formation in maturing grain whisky. Similar ion chromatographic procedures are described for the detection of a range of copper salts, incorporating cyanide, cyanate and thiocyanate, which are naturally occurring deposits within the copper Coffey still. These results are correlated with those based upon X-ray diffraction and secondary ion mass spectrometric techniques. Species identified included cuprous cyanide, cuprous thiocyanate, cuprous oxide, cuprous and cupric sulphide and copper cyanide cluster ions such as CuCN−, Cu(CN)2−, Cu2(CN)3− and Cu3(CN)4− and mixed species Cu(CN)2S−, CuSCN− and CuCNO+. In addition, an ion chromatographic procedure developed to investigate the role of carbamyl phosphate in ethyl carbamate formation, showed that conversion took place by means of its thermal decomposition into cyanate ion.