Theses and dissertations (Applied Sciences)

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Analysis of selected organic pollutants in water using various concentration techniques
(2014-08-08) Ramphal, Sayjil Rohith; Moodley, Kandasamy Govindsamy; Chetty, Deenadayalan Kisten
Among persistent organic pollutants, chlorobenzenes are some of the most frequently encountered compounds in aqueous systems. These compounds can enter the environment via natural and anthropogenic sources, and are ubiquitous due to their extensive use over the past several decades. Several chlorobenzene compounds, once in the environment, can biologically accumulate, and are reputed to be carcinogens and extremely hazardous to health. Several chlorobenzenes are listed as priority pollutants by the United States Environmental Protection Agency. Excessive exposure to these compounds affects the central nervous system, irritates skin and upper respiratory tract, hardens skin and leads to haematological disorders including anaemia. In spite of these harmful effects, chlorobenzenes are still used widely as process solvents and raw materials in the manufacture of pesticides, chlorinated phenols, lubricants, disinfectants, pigments and dyes. In the light of the above, it is imperative to monitor the levels of chlorinated benzenes in all types of surface waters, using low-cost but sensitive methods of preconcentration and detection. In this study, a simple and relatively cheap preconcentration method using direct immersion solid phase microextraction (DI-SPME) followed by gas chromatography equipped with a flame ionisation detector (GC-FID) was developed for the analysis of 7 chlorinated benzenes in dam water. Experimental parameters affecting the extraction efficiency of the selected chlorobenzenes, such as fibre type, sample size, rate of agitation, salting-out effect and extraction time, were optimised and applied to the Grootdraai Dam water samples. The optimised method comprises the use of a 100 µm polydimethylsiloxane (PDMS) fibre coating; 5 ml sample size; 700 revolutions per minute rate of agitation and an extraction time of 30 minutes. The calibration curves were linear with correlation coefficients ranging from 0.9957–0.9995 for a concentration range of 1–100 ng/ml. The respective limits of detection and quantification for each analyte was as follows: 1,3-dichlorobenzene, 0.02 and 0.2 ng/ml; 1,4-dichlorobenzene, 0.04 and 0.4 ng/ml; 1,2-dichlorobenzene, 0.02 and 0.2 ng/ml; 1,2,4-trichlorobenzene, 0.3 and 2.7 ng/ml; 1,2,4,5-tetrachlorobenzene, 0.09 and 0.9 ng/ml; 1,2,3,4-tetrachlorobenzene, 0.07 and 0.7 ng/ml; pentachlorobenzene, 0.07 and 0.7 ng/ml. Recoveries ranged from 83.6–107.2% with relative standard deviation of less than 9%, indicating that the method has good precision, is reliable and free of matrix interferences. Water samples collected from the Grootdraai Dam were analysed using the optimised conditions to assess the potential of the method for trace level screening and quantification of chlorobenzenes. The method proved to be efficient, as 1,3 dichlorobenzene, 1,4-dichlorobenzene and pentachlorobenzene were detected at concentrations of 0.4 ng/ml, 1.7 ng/ml and 1.4 ng/ml, respectively.
Detection methods of organic acid in steam/water circuits and optimisation using HPLC-UV
(2009) Ramrung, Arthi; Moodley, Kandasamy Govindsamy; Chetty, Deenadayalan Kisten
This study was mainly a response to a challenge faced by ESKOM in its coal-fired power stations. In spite of using high purity water to drive the turbines, the latter were damaged by ‘pitting’, possibly related to acids generated at high temperatures. In the light of this a relatively simple method for determination of short chain organic acids was identified by comparing the efficacies of several methods. It was found that high performance liquid chromatography (HPLC) method preceded by derivatization (with o-nitrophenyl hydrazine) is suitable for analyzing mixtures of simple acids at ppb levels. Calibration was effected by using methanoic acid (formic acid), ethanoic acid (acetic acid), propanoic acid (propionic acid) and butanoic acid (butyric acid). The HPLC instrument used was from Thermo Separations with P2000 pump, SN 4000 interface and UV1000 with a column heater. A comparative study between the HPLC methods using ion exclusion and partition chromatography was carried out in order to find a suitable method that can be used with aqueous environmental samples. The two essential columns that were used were ion exclusion Phenomenex Rezex OA column and a Nucleodur C8 column. The method of partition chromatography using a C8 column showed the most success using a mobile phase consisted of acidified water using HCl (pH4.5) along with a 60:40 Acetonitrile/Methanol mixture. Both isocratic and gradient programs were utilized. Limits of detection were improved from 800ppb (formic acid), 480ppb (acetic), 350ppb (propionic) and 680ppb (butyric acid) to 25ppb (acetic), 60ppb (propionic) and 90ppb (butyric). Samples used in analysis were collected from the main stream, economiser, condensers, polishing plant and turbines of the Tutuka Power Station in Mpumalanga province and analysed using with final developed method
Development of methods for the separation and characterization of natural organic matter in dam water
(2015-01-15) Sobantu, Pinkie; Chetty, Deenadayalan Kisten; Moodley, Kandasamy Govindsamy
This project arose out the need for a simple method to analyse NOM on a routine basis. Water samples were obtained from the Vaal dam, which is one of the dams used by a hydroelectric power station. Analysis was preceded by separation of NOM into the humic and non-humic portions. The humic portion was separated into two fractions by employing a non-ionic resin (DAX-8) to separate humic acid from fulvic acid. High performance size exclusion chromatography (HPSEC), equipped with an Ultraviolet( UV) detector and an Evaporative Light Scattering (ELS) detector connected in series, was used to obtain molecular weight distribution information and the concentration levels of the two acids. Mixed standards of polyethylene oxide/glycol were employed to calibrate the selected column. Suwanee River humic acid standard was used as a certified reference material. The molecular weight distributions (MWDs) of the isolated fractions of humic and fulvic acids were determined with ELSD detection as weight-average (Mw), number-average (Mn) and polydispersity (ρ) of individual NOM fractions. The Mw/Mn ratio was found to be less than 1.5 in all the fractions, indicating that they have a low and narrow size fraction. An increase in Mn and Mw values, with increasing wavelength for all three humic substances (HS) examined was observed. The HS, isolated from the dam water, was found to be about the same molecular weight as the International Humic Acid Standard (IIHSS). For the fulvic acid standard, the molecular weight was estimated to be around 7500 Da. Characterization of NOM was done to assist in the identification of the species present in the water. FTIR-ATR was used to as a characterization tool to identify the functional groups in the structure of the humic and fulvic acid respectively present in the Vaal Dam. Analysis of the infrared (IR) spectra indicated that the humic acids of the Vaal dam have phenolic hydroxyl groups, hydroxyl groups, conjugated double bond of aromatic family (C=C), and free carboxyl groups. The isolation method has proved to be applicable and reliable for dam water samples and showed to successfully separate the humic substances from water and further separate the humic substances into its hydrophobic acids, namely, humic and fulvic acids. It can be concluded that the Eskom Vaal dam composes of humic substance which shows that the technique alone gives a very good indication of the characteristics of water. The HPSEC method used, equipped with UV and ELSD was able to identify the molecular weight range of NOM present in source water as it confirmed that the Eskom Vaal dam contains humic substances as humic acid and fulvic acid and these pose a health concern as they can form disinfectant byproducts in the course of water treatment with chemicals. FTIR characterization was successful as important functional groups were clearly assigned. Lastly, the use of the TOC and DOC values to calculate SUVA was also a good tool to indicate the organic content in water. It is recommended to use larger amounts of water must be processed to obtain useful quantities of the humic and fulvic acid fractions.
Optimisation of HPLC-based methods for the separation and detection of herbicide glyphosate and its major metabolite in water
(2010) Madikizela, Lawrence Mzukisi; Moodley, Kandasamy Govindsamy; Chetty, Deenadayalan Kisten
Water storage dams play an important part in the collection and purification of water destined for human consumption. However, the nutrient rich silt in these dams promotes rapid growth of aquatic plants which tend to block out light and air. Glyphosate is universally used as the effective non-selective herbicide for the control of aquatic plants in rivers and dams. Invariably there is residual glyphosate present in water after spraying of dams and rivers with glyphosate herbicide. The amount of residual glyphosate is difficult to determine on account of high solubility of glyphosate in water. Thus a method of sample preparation and a sensitive HPLC method for the detection of trace amounts of glyphosate and its major metabolite aminomethylphosphonic acid (AMPA) in water is required. A crucial step in sample preparation is pre-column derivitization of glyphosate with 9-fluorenylmethyl chloroformate (FMOC-Cl). For sample pretreatment, water samples were derivatized with FMOC-Cl at pH 9, extracted with ethyl acetate and sample clean-up was carried out by passing a sample through the SPE cartridge. For SPE, recovery studies were done to choose a suitable cartridge for glyphosate and AMPA analysis. The following cartridges were compared, namely, C18, Oasis HLB and Oasis MAX SPE cartridges. Best recoveries (101% for glyphosate and 90% for AMPA) were obtained using 500 mg of C18 solid-phase extraction cartridge. The eluent from SPE cartridge was injected into HPLC column. Three types of separation columns (namely; C18 column, silica based amino column and polymeric amino column) were compared for the separation of glyphosate and AMPA. The best separation of glyphosate and AMPA in water samples was achieved using a polymeric amino column and a mobile phase at pH 10 which contained a mixture of acetonitrile and 0.05 M phosphate buffer (pH 10) 55:45, (v/v) respectively. The method was validated by spiking tap water , deionized water and river water at a level of 100 μg/l. Recoveries were in the range of 77% -111% for both analytes. The method was also used in determining the levels of glyphosate and AMPA in environmental samples. This method gave detection limits of 3.2 μg/l and 0.23 μg/l for glyphosate and AMPA respectively. The limits of quantification obtained for this method were 10.5 μg/l and 3.2 μg/l for glyphosate and AMPA respectively.