Highly sensitive biochemical analysis using low-temperature infrared spectroscopy measurements

A sensitive infrared spectroscopic analysis of biochemical components in an aqueous solution is described. The infrared spectrum of an aqueous solution containing glucose, urea, and creatinine was measured at -4.7 degrees C by Fourier transform infrared spectroscopy (FT-IR) with an attenuated total reflection (ATR) crystal. The infrared absorption bands of these components increased by about 100 times at -4.7 degrees C as compared with those measured at 22 degrees C, This increase in the infrared absorption bands was found to occur because of segregation of the components ton-ard the surface of the ATR crystal caused by solidification of the sample solution. The creatinine concentration in an aqueous solution, prepared in the physiological range of human blood, was also estimated at -4.7 and 22 degrees C by using the partial least-squares (PLS) method. The correlation coefficient between the predicted concentrations by PLS and the prepared concentrations was 0.95 at -4.7 degrees C, but was 0.07 at 22 degrees C. Thus, the precision of the determination of creatinine was remarkably improved by using the low-temperature measurement.