Flow injection systems have great potential for sample handling and analysis in process analytical chemistry. The flexibility and versatility of flow injection manifolds can he utilized in specific applications of sample conditioning and analysis. An overview of various flow injection methods, including flow reversals, double injection, and sequential injection is given, as well as different clean-up methods, such as gas diffusion, solid phase extraction, dialysis, and solvent extraction. Calibration techniques, such as single standard and multivariate calibration are also discussed. In addition, different aspects of process analytical chemistry, in particular sampling and sample handling, are discussed. The papers in this thesis describe a number of flow systems, where gradient-, gas diffusion-, and solid phase extraction- methodologies are applied, all of which have potential use in process analytical chemistry. Paper I is focused on multicomponent analysis of mixtures of organic acids by mathematically extracting information from complex spectra. The selectivity is improved by generating pH-gradients in the flow system. In paper II, the methodology of sensor injection is described and electrochemical and spectroscopic sensors are implemented in a sequential injection system. The method is illustrated by using pH sensors and a glucose electrode. Ammonia and ammonium ions are determined on-line to a bioprocess by gas diffusion in paper III. The benefit of frequent re-calibrations and in-line cleaning sequences are demonstrated. Finally a method for on-line determination of o-diphenols in the kraft process has been developed (paper IV). The o-diphenols are isolated from black liquor samples by solid phase extraction and thereafter transferred to a high performance liquid chromatography system for separation and quantification. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1996, Härtill 4 uppsatser</p> / digitalisering@umu

Bioanalytical chemistry is a challenging field, often involving complex samples, such as blood, plasma, serum or urine. In many applications, sample cleanup is the most demanding and time-consuming step. In the work underlying this thesis a novel dynamic miniature extractor, known as a hollow-fibre liquid-phase microextractor (HF-LPME), was designed, evaluated and studied closely when used to clean plasma samples. Aqueous-organic-aqueous liquid extraction, in which the organic liquid is immobilised in a porous polypropylene membrane, was the principle upon which the extractor was based, and this is discussed in all the papers associated with this thesis. This type of extraction is known as supported-liquid membrane extraction (SLM). The aim of this work was the development of a dynamic system for SLM. It was essential that the system could handle small sample volumes and had the potential for hyphenations and on-line connections to, for instance, LC/electrospray-MS. The design of a miniaturised HF-LPME device is presented in Paper I. The extraction method was developed for some weakly acidic pesticides and these were also used for evaluation. In the work described in Paper II, the method was optimised on the basis of an experimental design using spiked human plasma samples. Paper III presents a detailed study of the mass-transfer over the liquid membrane. The diffusion through the membrane pores was illustrated by a computer-simulation. Not surprisingly, the more lipophilic, the greater the retention of the compounds, as a result of dispersive forces. The main focus of the work described in Paper IV was to make the HF/LPME system more versatile and user-friendly; therefore, the extractor was automated by hyphenation to a SIA system. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript.