Measurement of trace components in aqueous solutions with near and mid infrared Fourier transform spectroscopy

University dissertation from Department of Physics, P.O. Box 118, SE-221 00 Lund, Sweden

Abstract: This thesis treats various aspects of the measurement of trace components in aqueous solutions with Fourier transform infrared spectroscopy. This technique has several applications from such diverse fields as dairy industry and biomedical optics. The use of infrared spectroscopy for trace component quantification is made difficult by the large absorption of water which dominates the spectrum. The signals from the trace components are small in comparison and must be detected under circumstances where the water spectrum determines both instrument configuration and usable wavenumber regions. In addition the absorption of water may be changed by the presence of other components in the solution or by variations in temperature. The papers, upon which this thesis is based, are concerned with several aspects relating to this problem. The influence of the water absorption spectrum and the configuration of spectrometers are discussed. One publication treats the problem of selection of optimal transmission cell pathlength for measurement of trace components in aqueous solutions. Another publication presents a dual-beam, optical null, Fourier transform spectrometer for measurements of trace components in the near infrared spectral range that offers an improvement compared to traditional Fourier transform spectrometers. A third publication presents measurements of the temperature induced variations of the absorption spectrum of water and of aqueous solutions of glucose. In addition, two specific applications, both concerning the measurement of trace components in spent dialysate, are demonstrated. One manuscript describes the application of the the dual-beam spectrometer to measure real-time, on-line, concentrations of urea in spent dialysate during treatment of patients. Finally, a manuscript demonstrates the feasability of simultaneous measurement of urea, phosphate, and glucose concentrations in spent dialysate with mid infrared transmission spectroscopy.

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