Ion chromatographic analysis of disinfectant by-products
Barron, Leon (2005) Ion chromatographic analysis of disinfectant by-products. PhD thesis, Dublin City University.
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The complete development of chromatographic methods to determine daily concentrations of the haloacetates (HAs) monochloro- (MCA), dichloro- (DCA), trichloro- (TCA), monobromo- (MBA), dibromo- (DBA), chlorodifluoro- (CDFA) trifluoro- (TFA), dichlorobromo- (DCBA) and chlorodibromoacetates (CDBA) as well as the oxyhalides bromate, chlorate, perchlorate and iodate are presented. This work is divided into seven sections. Firstly, Chapter 1.0 deals with a full understanding of the background to disinfectant by-product formation and analysis, including explanation of all instrumentation required to complete the area of research. Following this, a review of current technologies for the determination of HAs and oxyhalides in modern treated drinking water is discussed. Chapter 2.0 investigates a micro-bore Dionex lonPac AS11-HC as a possible column of choice for ion exchange chromatography of the first seven HAs listed only. The method utilises suppressed conductivity detection with a gradient of sodium hydroxide. Analytical performance characteristics for linearity, reproducibility and limits of detection are presented also. In a brief study, the effect of column temperature was investigated for the developed method with this column and van’t Hoff plots are included here. For determinations of HAs in real drinking water samples, Chapter 3.0 offers solid phase extraction as a possible solution and was investigated using a solid phase extraction cartridge with a stationary phase of hyper-crosslinked polystyrene-divinylbenzene copolymer. Selectivity, percent recovery, capacity and reproducibility studies were carried out on LiChrolut EN cartridges. Under optimised conditions average recoveries for MCA, DCA, TCA, MBA and CDFA spiked in dinking water samples ranged from 62 to 88 %, with an optimum preconcentration factor of 25. The reproducibility of recovery data for the above HAs was found to range from 12 to 29 % based upon six repeat recovery experiments. This method coupled with the IC method in Chapter 2.0 was then applied to the analysis of some real dinking water samples. Improvements in sensitivity are tackled in Chapter 4.0 with addition of Dionex eluent generation and carbonate removal modules. Noise levels decreased by a factor of one third with this new instrumentation. The reproducibility and accuracy of eluent preparation is assessed and compared with manually prepared eluents. The developed method was then applied to the analysis of 5 drinking water samples. Separations with a micro-bore Dionex lonPac AS16 are also shown here. Once more, analytical performance characteristics of linearity, reproducibility and limits of detection are presented along with a brief investigation of the effect column temperature on separation. This new method was then combined with the SPE method in Chapter 2.0 for the determination of HAs in a drinking water sample. Chapter 5.0 deals further with improvements in sensitivity with the use of a monolithic cation exchange type suppressor. Noise levels were dramatically reduced and direct detection of HAs was possible without preconcentration. However, some SPE was carried out along with this IC method and was sensitive to the range of HAs typically expected in drinking water. The effect of doubling the ethylvinylbenzenedivinylbenzene copolymer sorbent was investigated showing a requirement for double the reagent volumes for effective preconcentration and was virtually independent of eluting agent concentration. Chapter 6.0 presents results gathered from UV and MS detectors as alternatives to suppressed conductivity. UV wavelength optimisation, linearity, limits of detection and reproducibility are presented. For IC-MS a suitable interface for coupling the 1C eluate to the electrospray chamber is presented along with optimisation of all parameters for maximum sensitivity to HAs. The developed suppressed conductivity-UV-MS method was then applied to a spiked drinking water sample. Chapter 7.0 discusses the possibility of separating both oxyhalides and HAs on one column with the use of combined temperature and eluent concentration gradients. This chapter discusses in detail the effect of temperature on the separation of HAs and oxyhalides on the AS 16 column and measured versus actual column temperatures are presented. Full optimisation of the dual temperature and eluent concentration gradient for conductivity detection only are presented and applied to a drinking water sample. Following on from this, analytical performance data for reproducibility for n = 30 replicates, LOD and linearity for both suppressed conductivity and mass spectrometric detection is presented. The method was then applied to the analysis of HAs and oxyhalides in a soil sample and a drinking water sample using both detectors.
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