Flow injection, vibrational spectroscopy and multivariate calibration techniques for on-line process monitoring
The fundamental concepts of process analytical chemistry are presented in Chapter One, which also discusses the different approaches and advantages of performing process analysis in-situ. The principles and instrumentation of flow injection analysis are presented with particular emphasis on multi-detemiinations and process applications. Flow injection analysis with Fourier transform infrared detection is proposed as a potential on-line monitoring technique highlighting its ability for simultaneous multi-analyte determinations. The principles of chemometric data analysis are summarised in Chapter Two along with the systematic approach to data analysts used in this thesis. Algorithms for experimental design, data pre-processing, exploratory data analysis (RCA) and multivariate calibration (PGR and PLS1) are described. Chapter Three describes the development and optimisation of an automated flow injection manifold coupled with a Fourier transform infrared detector for the determination of toluene, ethyl benzene and o-xylene in an n-hexane matrix by univariate calibration. In addition, Fourier transform infrared spectra are acquired of experimentally designed synthetic mixtures of the above analytes using the automated Fl manifold, and the multivariate calibration algorithms PGR, PLS1 and PLS2 are employed to quantify individual species. A critical evaluation of spectral preprocessing algorithms is reported. The following chapter describes the development of an automated internally coupled valve flow injection manifold, with Fourier transform infrared detection, for the determination of sucrose in aqueous matrices. Chapter Four describes the optimisation of the data acquisition system and reports on the critical comparison of univariate and multivariate calibration approaches, and results are presented for the determination of sucrose in commercially available fruit juices. The on-line monitoring of the synthesis of sodium glycinate in water using Fourier transform detection is described in Chapter Five. Fourier transform infrared spectral analysis of the reaction using continuous flow analysis with real time Gram Schmidt data analysis is compared to the results acquired via an automated flow injection manifold. The use of a simplex designed calibration set to mimic spectral changes in the reaction mixture to facilitate multivariate calibration is also presented. Chapter Six compares the analytical performance of a thermostabilised attenuated total reflectance flow cell with a water cooled mid-infrared fibre optic probe. Univariate and multivariate calibration algorithms are used to process reaction data sets along with gas chromatographic reference data. A detailed discussion of proposed approaches to reduce analysis time and increase information in reaction development programs is presented. The thesis concludes with an investigation of the quantitative nature of Raman spectroscopy. Experimentally designed calibration sets containing aqueous herbicide formulation samples are analysed in glass vials, with a critical evaluation of long term instrumental stability measured in terms of reproducibility and repeatability. The effects of pre-processing Raman spectral data sets, in the absence of sample matrix signals, using nonmalisation and multiple scatter correction are discussed.