Determination of Glycolic Acid in Cosmetics by Online Liquid Chromatography-Fourier Transform Infrared Spectrometry
An isocratic online liquid chromatography Fourier transform infrared procedure has been developed for the determination of glycolic acid in cosmetics. The method involves the ultrasound-assisted extraction of glycolic acid from the samples with an acetonitrile:phosphate buffer (25 mM, pH 2.7) (3:97 v/v). The extracts were centrifuged and filtered before their injection into the chromatography system, which was equipped with a C18 column and used a flow rate of 150 microL min(-1). FTIR spectra were acquired using a time-resolved rapid scan mode. To calculate the chromatograms, the spectral area was integrated between 1288 and 1215 cm(-1), with baseline correction established between 1319 and 1150 cm(-1), after correcting for the eluent spectral background. Peak area values of the extracted sample chromatograms were interpolated from an external calibration curve. The method provided a limit of detection of 0.034 mg mL(-1) and a relative standard deviation of 6% for five measurements at the 0.174 mg mL(-1) concentration level. Recovery values obtained by spiking 400 mg of three commercially available samples with amounts of glycolic acid from 3.7 to 9.8 mg ranged between 99.6 and 101%. The results obtained for the commercial samples agree well with their declared concentrations. An attempt to directly determine glycolic acid by attenuated total reflectance measurements using partial least squares calibration showed that results were strongly influenced by compounds coextracted from the matrix.
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