New method for faecal fat determination by mid-infrared spectroscopy, using a transmission cell: an improvement in standardization

Abstract

Current techniques used in clinical laboratories for faecal fat determination, such as the Van de Kamer method, are not very accurate or precise. This became apparent when results obtained by different laboratories were compared, and could explain the disappointing performance of near-infrared and mid-infrared spectroscopy since the accuracy of these techniques depends upon the accuracy of the calibration used (i.e. inaccurate wet chemical analysis). In order to improve standardization, we developed and tested a new quantitative method in three laboratories, based on Fourier transform infrared (FT-IR) spectroscopy. Fatty acids were extracted from faecal samples with acidified petroleum ether-ethanol and the extracts were dried and dissolved in chloroform. An infrared spectrum of the extracts was recorded in the range 4000-650 cm^x1, using an infrared transmission cell. Standard mixtures of stearic and palmitic acids (65:35) were used for calibration. Quantification was based on the absorbance band of the CH ₂ group (2855 cm^x1) of free fatty acids and fatty acid glycerol esters. The calibration curve showed excellent linearity. The correlation coefficient between the titrimetric Van de Kamer and FT-IR methods was 0·96 ( y=1⋅12 x 0⋅02, standard error of prediction=0⋅89 g% fat). No significant difference was found when the FT-IR results of 28 faecal samples from patients were compared between two different university hospital laboratories. The new FT-IR method, using primary standards, is simple and rapid, and provides satisfactory intra- and inter-laboratory precision for the diagnosis and monitoring of steatorrhoea.