Plasma Protein Contents Determined by Fourier-Transform Infrared Spectrometry

Fourier-transform infrared (FT-IR) spectrometry has been used to measure small molecules in plasma. We wished to extend this use to measurement of plasma proteins.We analyzed plasma proteins, glucose, lactate, and urea in 49 blood samples from 35 healthy subjects and 14 patients. For determining the concentration of each biomolecule, the method used the following steps: (a) The biomolecule was sought for which the correlation between spectral range areas of plasma FT-IR spectra and concentrations determined by comparison method was greatest. (b) The IR absorption of the biomolecule at the most characteristic spectral range was calculated by analyzing pure samples of known concentrations. (c) The plasma concentration of the biomolecule was determined using the FT-IR absorption of the pure compound and the integration value obtained for the plasma FT-IR spectra. (d) The spectral contribution of the biomolecule was subtracted from the plasma FT-IR spectra, and the resulting spectra were saved for further analyses. (e) The same method was then applied to determining the concentrations of other biomolecules by sequentially comparing the resulting FT-IR spectra.Results agreed with those obtained by clinical methods for the following biomolecules when analyzed in the following order: albumin, glucose, fibrinogen, IgG(2), lactate, IgG(1), alpha(1)-antitrypsin, alpha(2)-macroglobulin, transferrin, apolipoprotein (Apo)-A(1), urea, Apo-B, IgM, Apo-C(3), IgA, IgG(4), IgG(3), IgD, haptoglobin, and alpha(1)-acid glycoprotein.FT-IR spectrometry is a useful tool for determining concentrations of several plasma biomolecules.