Biological reference materials for the verification of sample preparation and measurement by low resolution NMR

Summary

The measurement of the solid fat index is of great importance to determine the technological quality of fats used in the agro-food industry. Pulse or continuous wave low resolution nuclear magnetic resonance may be used to perform the measurements fairly rapidly, and very simply. IUPAC has published several methods for sample preparation, with precise indications as to the procedure to follow. The reproducibility is however often inadequate, whereas the repeatability is very good. This may simply be due to an incorrect calibration of the apparatus, introducing a constant bias in the results of a particular laboratory. It may also be due to slight differences in the tempering the samples undergo. Because of their polymorphism, the crystallization of triglycerides is in fact greatly influenced by this thermal pretreatment. A need for reference samples was therefore felt, in part to verify the instrument adjustment but, more important, in order to control the whole sequence of actions performed before the measurement itself. The French Institut National Agronomique and the Institut des Corps Gras carried out a ring test involving 9 experienced French laboratories to determine standard SFI curves, using several thermal pretreatment procedures. Reference samples and the corresponding SFI values for 4 of the most commonly used fats are now available to quality control laboratories. This study is now to be extended, through the BCR, to the rest of Europe.