Automatic determination of fat in milk by use of a flow injection system with a piezoelectric detector

A new method for the direct determination of total fat in milk by use of a quartz crystal microbalance was developed. The method is based on a (micro) extraction procedure that is carried out in a flow injection system. Samples are diluted with an ethanol-water mixture and injected into the flow system, where they are mixed with n-hexane in an extraction coil. The analyte is determined in the organic phase. The calibration thus achieved is linear in the range 0.20-0.45% w/v, and the relative standard deviation is ±3.2% (n=11; P=0.05). The throughput is 12 samples per hour. The proposed method was used to determine fat matter in milk samples; the results were found to be competitive with those of official methods for the same purpose. Copyright (C) 2000 Elsevier Science B.V