Near-infrared spectroscopy for liquids of microliter volume using capillaries with wall transmission

In the present study we propose a capillary tube method for measuring near-infrared (NIR) spectra of microliter liquid and solution samples. This method enables one to measure NIR spectra of liquids and solutions of only 2.5 µl. As an example of the capillary tube method, Fourier-transform NIR spectra of benzene were measured using a capillary tube with a diameter of 1 mm. Positions and intensities of the NIR bands in the spectra obtained by the capillary tube were almost identical to those measured using a quartz cuvette cell. Moreover, capillary NIR spectra of human blood serum obtained from a patient with backbone neoplasm were also measured. Subtraction of the NIR spectrum of water from those of human blood serum develops unambiguously some NIR bands due to blood components such as proteins and glucose. Our results suggest that capillary NIR spectroscopy will open new areas of NIR applications for small amounts of liquid and solution samples.