Infrared spectral analysis: A new attempt for amniotic fluid analysis

Infrared spectral analysis gives the information about molecules and substituted groups. However, conventional infrared spectrophotometers have been used only for qualitative purposes because of their poor sensitivity and low S/N-ratio. We developed here a new spectrophotometric system and studied its availability for quantitative analyses of minute amount water-containing samples such as amniotic fluid. A conventional infrared spectrophotomer was converted to a Fourier transform type based on the theory of the Michelson's interferometer. To improve the sensitivity, an HgCdTe detector was employed. A special sample chamber was constructed by combining the attenuated total reflection method with a vacuum-drying technique. In this chamber, a water-containing sample was firmly attached onto the prism surface, and infrared spectra were obtained from the solid component of the sample. As a result, both the sensitivity and the S/N-ratio were markedly (44 times) improved as compared with a conventional system, indicating that quantitative analyses are now possible with this infrared spectrophotometer. Using this novel system, we could directly obtain the infrared spectra of samples of the human amniotic fluid, one of the water-containing clinical materials which could not be studied with conventional infrared spectrophotometers without pretreatment. Since a very small amount of a sample, such as 60 μl, can be analyzed only in 8 minutes by this system, this new method is expected to be widely utilized in a variety of medical fields.