Chemometric determination of lipidic parameters in serum using ATR measurements of dry films of solvent extracts†
Attenuated total reflectance (ATR) infrared spectroscopy of dried organic extracts of serum samples has been evaluated as a fast method for the determination of triglycerides, cholesterol, high density lipoprotein (HDL) and low density lipoprotein (LDL). After careful selection of solvents based on green parameters, serum samples were extracted using hexane–isopropanol and ethyl acetate–ethanol mixtures. Microscopy studies and comparison with standard spectra were performed in order to investigate whether the proposed methodology is suitable for the quantification of lipids in serum samples. The results of these preliminary studies confirmed that the variations in the IR spectra of sample extracts could be related quantitatively to variations in the concentrations of the target analytes. Then, ATR spectra of the dried sample extracts were obtained and direct measurement of the spectra were carried out and modelled using partial least squares (PLS) and reference concentrations. PLS models obtained from the extracts of the two mixtures were compared with those obtained from direct measurement of sera samples. The prediction errors obtained using the proposed approach were considerably (between 27 and 72%) better than those obtained by the direct measurements of sera. For triglycerides and cholesterol relative errors below 9% and 12% respectively were obtained with this method, which are comparable to the tolerance for the errors of the control analysis established at the hospital. For HDL and LDL, the errors found were between 18 and 20%. The incorporation of a preprocessing extraction step, involves time and solvent consumption. However, the results obtained provide evidence that the proposed method provides, in a few minutes and using simple instrumentation and with minimum cost, important information about the lipidic profile of patients sera at a good screening confidence level.