Enhancement of Fourier transform infrared spectrometry by the flow-injection technique: Transmittance and internal total reflectance cell in a single-line system

Abstract

The ability of flow-injection analysis (FIA) system to perform automated dilutions when coupled to a Fourier transform infrared (FT-IR) spectrometric detector and to perform multi-component determinations was studied. Two types of flow cell, a transmittance cell and a cylindrical internal total reflectance (Circle) cell, were applied to the FIA/FT-IR system. The physical characteristics of the cells and their signal outputs were compared and analyzed. First-order frequency domain, first-order time domain and second-order frequency-time domain spectra were obtained. Multi-component analyses of ternary organic mixtures containing acetone, ethanol and tetrahydrofuran in carbon tetrachloride were performed. Continuous-flow measurements of analytes from 1 to 2% by volume were used for the analysis of organic mixtures using the transmittance cell. With the Circle cell, a stopped-flow technique was used to enhance the signal-to-noise ratio by increasing the data collection time at will. Multi-component determinations of 7–60% acetone, 3–20% ethanol and 1–20% tetrahydrofuran in carbon tetrachloride (the essentially linear regions for each) was performed. A multivariate calibration method, partial least squares, was used for the determinations, with errors of predictions of 3.6, 5.7 and 3.0% for acetone, ethanol and tetrahydrofuran, respectively.