Equivalence of packed and capillary GC columns for detection of foreign fat in butter by use of the triglyceride formula method
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In conjunction with triglyceride formulae the analysis of triglycerides (TG) by low-resolution gas chromatography can be used for the detection of foreign fat in butterfat. The equivalence of a 5-m capillary column (HT-SimDist) and the commonly used packed column (OV-1) was checked by testing the purity of 50 widely varying samples of milk fat in accordance with regulation 2771/99 of the European Community (EC). As well as the resolution the analysed TG contents and relative standard deviations were virtually equivalent for both types of column, and were in accordance with the EC regulation. For instance, the mean absolute differences between the TG C54 content of 50 samples (± standard deviation) determined by use of the capillary column and two different packed columns were only 0.05 (±0.04) and 0.11 (±0.07)%, respectively; the correlation coefficients were r=0.9996 and 0.9993, respectively. The same applied to the repeatability of S values, calculated from TG formulae for qualitative and quantitative detection of foreign fat. Irrespective of the column used, none of the samples exceeded stipulated limits for S values of pure milk fats. For all the samples the differences between S values obtained from packed and capillary column data did not exceed the reproducibility limits stipulated by EC regulation 2771/99. This resulted in a correlation coefficient of r=0.94 for S values (n=50) calculated by use of the total TG formula. The corresponding correlation coefficient between results obtained with the two packed columns was r=0.95. Although these results establish the equivalence of packed and capillary columns for low-resolution TG analysis, this equivalence should not be taken for granted but, because of occasional diffuculties, be re-checked by each laboratory wishing to use a capillary rather than packed column to monitor the purity of milk fat.
Key WordsGas chromatography Packed vs capillary columns Triglycerides Foreign fat detection Milk fat
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