Interlaboratory study of the method for direct determination of volatile compounds in alcoholic products using ethanol as internal standard

A collaborative interlaboratory study of the method of direct determination of volatile compounds in spirit drinks and alcoholic products was performed. The proposed method employs ethanol, the major volatile component of an alcoholic product, as an internal standard. For the experiment realization, 9 laboratories from 4 countries – Belarus, Czech Republic, Turkey, Russia – were supplied with standard solutions for gas chromatographic measurements. Five aqueous ethanol 40 % (v/v) standard solutions containing target compounds in concentrations ranging from 10 to 400 mg/L of absolute alcohol were gravimetrically prepared and delivered to the participants. The interlaboratory study was evaluated according to the ISO 5725 standards and the «EuroChem» guide. The repeatability limits (within-laboratory precision) varied between 0.4 and 7.5 % for all samples and compounds, showing a sufficiently high repeatability of the method. The reproducibility limits (between-laboratory precision) were found to vary within a satisfactory range of 0.5–10.0 %. Precision of the method was well within the range predicted by the Horwitz equation for all analytes. In the study experimental estimation of trueness was performed for the first time. Analysis of the obtained results showed that the bias of the method is insignificant at the significance level 5 %. The experimentally determined concentrations of the analytes compared well to the gravimetrical values, thus showing very satisfactory accuracy of the method. The results of the interlaboratory study confirmed that the method «ethanol as internal standard» is robust and reliable and can be used as a standard method for the determination of volatile compounds in water-ethanol samples. Moreover, this method can be validated in any one laboratory without performing additional experimental studies based on the results obtained by validation of the traditional method.