On-line gel permeation chromatography–attenuated total reflectance–Fourier transform infrared determination of lecithin and soybean oil in dietary supplements

Gel permeation chromatography (GPC) with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometry detection has been proposed for the simultaneous determination of lecithin and soybean oil in dietary supplements. The method involves the extraction of analytes with dichloromethane in an ultrasound water bath and the injection of 2 ml of centrifuged and filtered extracts into the system integrated by two Envirogel GPC columns (19 mm × 150 mm, 19 mm × 300 mm) coupled on-line. Dichloromethane was used as mobile phase. A method has been developed to select the most appropriated wavenumber to be used for the determination of each considered compound from the calculation of a factor which maximizes the analyte signal minimizing the interferent contributions, being selected the detection wavenumbers of 1034 and 1138 cm−1 for lecithin and soybean oil, respectively in the first order derivative ATR-FTIR spectra. The method provides limits of detection of 2 and 4 mg ml−1 for lecithin and soybean oil and repeatability values, measured as relative standard deviation, of 2.5% and 3.4% being extended the linear range till 100 mg ml−1 for lecithin and up to 50 mg ml−1 for soybean oil. Accurate results were found for 10 synthetic samples and 7 commercial dietary supplement preparations.