Optimisation of HPLC-based methods for the separation and detection of herbicide glyphosate and its major metabolite in water

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.</jats:p

Hollow fibre liquid phase microextraction of pharmaceuticals in water and Eichhornia crassipes

This work describes a simple and rapid method for the simultaneous isolation, enrichment, and quantitation of selected pharmaceuticals in aqueous environmental samples and Eichhornia crassipes. This was achieved by developing a hollow fiber liquid phase microextraction (HF-LPME) technique coupled with ultra-high-pressure liquid chromatography-high resolution mass spectrometry for the simultaneous extraction, pre- concentration and quantitation of four non-steroidal anti-inflammatory drugs (NSAIDs) and three antiretroviral drugs (ARVDs) from aqueous matrices and different segments of water hyacinth plant species. The target compounds for NSAIDs were naproxen (NAP), fenoprofen (FENO), diclofenac (DICLO) and ibuprofen (IBU) whereas the selected ARVDs included emtricitabine (FTC), tenofovir disoproxil (TD) and efavirenz (EFV). A multivariate approach by means of a half-fractional factorial design was used to optimize the HF-LPME technique focusing on six factors; donor phase (DP) pH, acceptor phase (AP) pH, extraction time, stirring rate, supported liquid membrane carrier composition (SLM carrier comp.) and salt content. Four of these factors (DP pH, AP pH, stirring rate and extraction time) were identified as vital for an enhanced enrichment of each of the selected NSAIDs and four of the previously mentioned vital factors including the SLM carrier composition were classified as significant for the selected ARVDs from aqueous samples into the hollow fiber. These essential factors were further paired according to their level of significance. The paired significant factors were then optimized using central composite designs (CCD) where empirical quadratic response models were used to visualize the response surface through contour plots, surface plots and optimization plots of the response outputs. The optimized factors for individual analytes belonging to each class were then altered to universal conditions for their simultaneous extraction from same sample solution. The acceptability of the universal conditions was defined using desirability studies. A composite desirability value of 0.7144 was obtained when the optimum factors of the three ARVDs were applied for their simultaneous extraction while a simultaneous extraction of NSAIDs had a desirability value of 0.7735. This implied that the set conditions were ideal for a combined extraction of the target compounds from the donor phase into the acceptor phase across a supported liquid membrane impregnated with a carrier molecule. For the simultaneous extraction of ARVDs, the universal optimum HF- LPME conditions were found to be DP pH of 4, AP HCl conc. of 200 mM (pH = 0.4) with SLM carrier comp. set at 4.5 (%w/w) and stirring at 1000 rpm. Under optimum conditions, the enrichment factors (EF) for ARVDs from aqueous phase were 78 (FTC), 111 (TD) and 24 (EFV). These conditions yielded recoveries in the range of 96 to 111%. The sensitivity of the analytical method through limits of quantification (LOQ) for the selected ARVDs in wastewater samples were 0.033 μg L-1 (FTC), 0.10 μg L-1 (TD) and 0.53 μg L-1 (EFV). The LOQ values were computed for surface water samples using the same target ARVDs were 0.169 μg L-1 (FTC), 0.018 μg L-1 (TD) and 0.113 μg L-1 (EFV). For NSAIDs, the overall conditions were DP pH of 10, AP pH of 3 at an extraction time of 60 min with stirring rate at 1000 rpm. The recoveries yielded under these optimum conditions for the target compounds ranged from 86 to 116%. The EF for the target NSAIDs from aqueous media were 49 (NAP), 126 (FENO), 93 (DICLO) and 156 (IBU). The LOQ values for each target NSAID in wastewater samples were 0.47 μg L-1 (NAP), 0.09 μg L-1 (FENO), 0.59 μg L-1 (DICLO) and 0.49 μg L-1 (IBU). The specific universal conditions were then used in the analysis of ARVDs in wastewater and surface water whereas for NSAIDs analysis, only wastewater samples were analysed. The surface water samples were obtained from North of Johannesburg in Hartbeespoort dam and the wastewater samples were collected from various wastewater treatment plants located in Durban, KwaZulu-Natal. The technique was also applied in the analysis of the target compounds in plant samples obtained from Hartbeespoort dam in North of Johannesburg, Umgeni river located in Springfield (Durban in KwaZulu-Natal) and Mbokodweni river located in south of Durban city, KwaZulu-Natal. The plant samples were first cut and separated into different segments (roots, stems and leaves) and the target analytes then extracted into 20 mL water using an optimized microwave assisted extraction technique (MAE). The HF-LPME technique initially optimized for water samples was then applied for pre-concentration of the target pharmaceuticals from the MAE water extract. Factors that were optimized for MAE technique were irradiation time and temperature for ARVDs whereas irradiation time and solvent volume were optimized for the extraction of NSAIDs. For extraction of both ARVDs and NSAIDs, the optimum irradiation time was 20 min while the irradiation temperature was set at 90 ̊C during the extraction of ARVDs and 100 ̊C for NSAIDs. Generally, the studied ARVDs were all detected in most samples with concentrations for FTC (0.11 – 3.10), TD (0.10 – 0.25) and EFV (1.09 up to 37.3) μg L-1 recorded in wastewater samples. EFV had the highest concentration of 37.3 μg L-1 in the wastewater effluent. The concentration of ARVDs in the roots of the water hyacinth ranged from 7.4 to 29.6 μg kg-1, 0.97 to 11.42 μg kg-1 in the stem and 0.98 to 9.98 μg kg-1 in the leaves of the aquatic plant. Roots of the water hyacinth plant had higher concentrations of the investigated ARVDs. Lastly, the NSAIDs were also detected in various wastewater samples with concentration for NAP (1.15 to 3.30) μg L-1, FENO (&lt;LOQ to 2.03) μg L-1, DICLO (0.36 to 3.13) μg L-1 and IBU (&lt;LOQ to 0.92) μg L-1. In this case, NAP had the highest concentration in the wastewater effluent. In terms of the water hyacinth plant, the concentration range in the roots of the plant was 2.76 to 4.74 μg kg-1, whereas in the stem of the plant, the concentration range was 0.21 to 3.22 μg kg-1 and the leaves accumulated 0.11 to 3.35 μg kg-1 of the selected NSAIDs in study. This indicated that the roots of the water hyacinth in this case has the highest uptake of the target compounds. Overall, hollow fiber liquid phase microextraction proved to be an ideal tool for isolating and pre-concentrating the selected antiretroviral drugs from aqueous and plant samples. A manuscript on the results of analysis of ARVDs has been accepted in the Journal of Hazardous Materials and is presented in this dissertation as manuscript 2 in Section 4.2. In the analysis of NSAIDs, a manuscript has been submitted to a peer reviewed journal that is recognized by the Department of Higher Education in South Africa and is presented in this study as Paper 3 in Section 4.2. Manuscript 1 given as Section 4.3 is an article already published in Journal of Environmental and Chemical Engineering. The article is a review of adsorbents and removal approaches of NSAIDs from contaminated water bodies.</jats:p

Development of a paper-based microfluidic device for the quantification of ammonia in industrial wastewater

Ammonia is a toxic pollutant increasingly found in urban and industrial wastewater and unprotected surface water. Industry discharges and fertilizer run-off release ammonia into sewers and streams, overloading wastewater treatment plants and causing fish deaths in surface water such as rivers, sea and lakes. The purpose of this study was to develop and evaluate the effectiveness of the microfluidic paper-based device (µPAD) for the quantification of ammonia in wastewater. The µPAD fabricated had an oval-shaped pattern which was designed using CorelDraw software. The hydrophilic zones were created by printing a chromatographic paper with a Xerox wax printer (Xerox colorqube 8570). The modified version of the colorimetric method using Nessler reagent was combined with microfluidic technologies to create a low-cost monitoring system for detection of ammonia in wastewater. The method allows for ammonia determination in the range of 0–5 ppm (mg/L) with a limit of detection of 3.34 ppm. This study indicated that a µPAD was successfully used to quantify the concentration of ammonia in wastewater.</jats:p