Sample preparation using liquid membrane extraction techniques

A brief review is given of membrane extraction techniques that are seen as suitable for the extraction of various chemicals in water samples. Membrane-based extraction methods have now gained popularity as methods of choice in the extraction of both ionisable and non-ionisable molecules from different samples. The main attractive features for these techniques include the use of minimal organic solvents, high selectivity and clean-up efficiency, with high enrichment factors. In most cases the overall cost involved is low due to the simplicity of the techniques which normally involve relatively fewer steps and handling procedures as compared to many other sample-preparation techniques. The various forms and the configurations of membrane-based techniques are another attractive feature which allows the possibility of hyphenation with separation instruments such as gas/liquid chromatographs and even capillary electrophoresis.Keywords: liquid membrane extraction techniques, sample preparation, water monitoring, organic and inorganic compound

Fatty acids composition in South African freshwater fish as indicators of food quality

Lipid classes and fatty acid composition of three commercially important freshwater fish species Oreochromis mossambicus (Mozambique tilapia), Clarias gariepinus (African catfish) and Cyprinus carpio (carp) obtained from an aquaculture, different river systems and fish markets from different provinces in South Africa were investigated. Fatty acids were extracted from the fish fillets through the Folch extraction method (using chloroform: methanol at the ratio of 2:1). Generally, tilapia fish species was found to be the richest in fatty acid composition. In all fish species analysed, palmitic acid (16:0) was found to be the most abundant fatty acid ranging from 18.24 to 21.84%. Appreciable quantities of essential polyunsaturated fatty acid such as docosahexaenoic (DHA) (22:6 n-3, 3.92 to 6.16%), eicosapentaenoic acid (EPA) (20:5 n-3, 1.91 to 2.92%) and arachidonic acid (20:4 n-6, 7.19 to 8.50%) were also found. Observations show that fish species obtained from Gauteng Province are richer in fatty acids compared to those in Limpopo Province. The study points out that all fish species investigated contain appreciable levels of Omega-3 (n-3) polyunsaturated fatty acids (PUFA) and are therefore suitable for an unsaturated low-fat diet. This is important especially for poor communities who cannot afford to get a balanced diet, rich in some essential fatty acids.Therefore, it is important to determine the nutritional value of local fish, since it significantly contribute to a healthy diet in rural communities.Keywords: fatty acid composition, lipids, freshwater fish, Omega -3 and Omega-6, polyunsaturated fatty acids, EPA, DH

An ion-imprinted polymer for the selective extraction of mercury(II) ions in aqueous media

A double-imprinted polymer exhibiting high sensitivity for mercury(II) in aqueous solution is presented. Polymer particles imprinted with mercury(II) were synthesised by copolymerising the functional and cross-linking monomers, N’–[3– (Trimethoxysilyl)–propyl]diethylenetriamine (TPET) and tetraethylorthosilicate (TEOS). A double-imprinting procedure employing hexadecyltrimethylammonium bromide (CTAB), as a second template to improve the efficiency of the polymer, was adopted. The imprinted polymer was characterised by FTIR, scanning electron microscopy (SEM) and the average size determined by screen analysis using standard test sieves. Relative selective coefficients (k`) of the imprinted polymer evaluated from selective binding studies between Hg2+ and Cu2+ or Hg2+ and Cd2+ were 10 588 and 3 147, respectively. These values indicated highly-favoured Hg2+ extractions over the 2 competing ions. The results of spiked and real water samples showed high extraction efficiencies of Hg2+ ions, (over 84%) as evaluated from the detected unextracted Hg2+ ions by ICP-OES. The method exhibited a dynamic response concentration range for Hg2+ between 0.01 and 20 μg/mℓ, with a detection limit (LOD, 3σ) of 0.000036 μg/mℓ (36 ng/ℓ) that meets the monitoring requirements for the USA EPA of 2 000 ng/ℓ for Hg2+ in drinking water. Generally, the data (n=10) had percentage relative standard deviations (%RSD) of less than 4%. Satisfactory results were also obtained when the prepared sorbent was applied for the pre-concentration of Hg2+ from an aqueous certified reference material. These findings indicate that the double-imprinted polymer has potential to be used as an efficient extraction material for the selective pre–concentration of mercury(II) ions in aqueous environments

Seasonal variation of chloro-s-triazines in the Hartbeespoort Dam catchment, South Africa

Seasonal variation of eight chloro-s-triazine herbicides and seven major atrazine and terbuthylazine degradation products was monitored in the Hartbeespoort Dam catchment using gas chromatography–mass spectrometry (GC–MS) and liquid chromatography-mass spectrometry (LC-MS/MS). Lake, river and groundwater were sampled from the Hartbeespoort Dam catchment over four seasons and the downstream Jukskei River was monitored during the winter season. Triazine herbicide concentrations in the Hartbeespoort Dam were in the order atrazine > simazine > propazine > ametryn > prometryn throughout the four seasons sampled. Triazine herbicide concentrations in the Hartbeespoort Dam surface water were highest in summer and gradually decreased in successive seasons of autumn, winter and spring. Terbuthylazine was the only triazine herbicide detected at all sampling sites in the Jukskei River, though atrazine recorded much higher concentrations for the N14 and Kyalami sites, with concentrations of 923 and 210 ng L− 1 respectively, compared to 134 and 74 ng L− 1 for terbuthylazine. Analytical results in conjunction with river flow data indicate that the Jukskei and Crocodile Rivers contribute the greatest triazine herbicide loads into the Hartbeespoort Dam. No triazine herbicides were detected in the fish muscle tested, showing that bioaccumulation of triazine herbicides is negligible. Atrazine and terbuthylazine metabolites were detected in the fish muscle with deethylatrazine (DEA) being detected in both catfish and carp muscle at low concentrations of 0.2 and 0.3 ng g− 1, respectively. Desethylterbuthylazine (DET) was detected only in catfish at a concentration of 0.3 ng g− 1. With atrazine herbicide groundwater concentrations being > 130 ng L− 1 for all seasons and groundwater ∑ triazine herbicide concentrations ranging between 527 and 367 ng L− 1, triazine compounds in the Hartbeespoort Dam catchment may pose a risk to humans and wildlife in light findings of endocrine and immune disrupting atrazine effects by various researchers

Morphological and chemical characteristics of microplastics in surface water of the Vaal River, South Africa

DATA AVAILABILITY : Data are available on request.Microplastics research in South Africa has focused on marine and coastal areas, with limited studies reporting microplastics in freshwaters. To address this gap, we conducted this study to investigate the presence, abundance, physical characteristics, and chemical composition of microplastics in the surface water of the Vaal River, one of the most important freshwater systems in South Africa. Twenty-two surface water samples were collected along 60 km of the middle part of the river using a 55 μm plankton net. Samples were treated by acid digestion, and MPs were separated by density separation. Physical identification was performed using a Nikon stereomicroscope, and chemical composition was identified using Raman spectroscopy. MPs were observed in all samples with 0.13 to 2.52 particles/m3 concentrations. Microplastics ranged in size from 0.06 – 4.95 mm, with more than 89% less than 2 mm, and 81% were fragments (39%) and fibers (42%). Microplastics were observed in numerous colours, of which green, black, and blue were the most dominant, representing 22%, 19%, and 18%, respectively. Chemical analysis revealed the polymer types as high-density polyethylene (HDPE), polypropylene (PP), and low-density polyethylene (LDPE). In addition, two colourants, pigment yellow 83 and carbon black, were detected. This study provides new data on microplastic occurrence and characteristics in the Vaal River system and offers a baseline for future monitoring. Our findings confirm that the Vaal River is under a real threat of microplastic contamination, which could impact its role as a significant freshwater system in South Africa.Open access funding provided by University of the Witwatersrand. This project was supported by the Royal Society, UK.http://link.springer.com/journal/40710hj2024ChemistrySDG-06:Clean water and sanitatio

Microplastic abundance and sources in surface water samples of the Vaal River, South Africa

DATA AVAILABILITY : Data are available upon request.Microplastics (MPs) have emerged as a global environmental concern due to their persistent nature. In South Africa, microplastic research has primarily focused on marine systems. However, recent years have seen a shift in focus to studying MPs in South African freshwaters. In this study, MPs with a minimum size of 0.055 mm in surface water of the Vaal River, South Africa, were reported. MPs were 100% prevalent, with a mean numerical abundance of 0.68 ± 0.64 particles/m3. Small-sized MPs of < 1 mm accounted for the largest proportion. MPs were chemically identified as high-density polyethylene, low-density polyethylene, and polypropylene according to their Raman spectra. The prevalence of fragments (41.6%) and fibers (38.5%) over pellets (8.1%) indicates that microplastics are from secondary sources. The prevalence of polyethylene and polypropylene is consistent with microplastics being from secondary sources. These polymers are commonly used in single-use plastics, packing bags, textiles, and containers. These characteristics are of great concern due to their implications on the bioavailability and toxicological impacts of MPs. Consequently, these properties may pose more hazards to aquatic biota inhabiting the Vaal River.The Royal Society, UK, and funded by Government’s Grand Challenges Research Fund (GCRF). Open access funding provided by University of the Witwatersrand.http://link.springer.com/journal/128hj2024ChemistrySDG-06:Clean water and sanitatio

Sample Preparation of Organic Compounds in Environmental Analysis using Liquid Membrane Extraction

This thesis demonstrates the potential of the liquid membrane extraction technique as an alternative method for the analysis of trace ionisable organic compounds in the environment. Liquid membrane based extraction methods for the analysis of s-triazine herbicides and phenolic compounds were developed. Selectivity of the technique was demonstrated by extraction the above compounds in river water, river water spiked with high amounts of humic substances, wastewater and hydroponic nutrient solution for growing vegetables. Extracts from the various matrices analysed by reverse phase liquid chromatography with UV detection showed that they were free of interfering peaks. This therefore highlighted the liquid membrane technique as capable of selectively discriminating both polar and non-polar matrix components. Basic studies on the important parameters that influence the extraction and selectivity of the liquid membrane extraction technique were also performed. Studies showed that the first condition to achieving any extraction is analyte dissolution into the membrane. This is influenced by the polarity of both the analyte and membrane. With hydrophobic interactions as as the main mechanism of analyte dissolution into the membrane, analytes with octanol-water partition coefficients higher than 100 can be successively extracted in n-undecane or dihexyether as membrane liquids. In order to obtain high enrichment factors, complete trapping of the analytes in the acceptor is necessary. High enrichment factors can further be obtained within a relatively short extraction time by using high donor flow rate for compounds with octanol-water partition coefficients higher than 100 as the amount extracted per unit time increases for compounds with such polarity

Simultaneous determination of naproxen, ibuprofen and diclofenac in wastewater using solid-phase extraction with high performance liquid chromatography

The occurrence and removal efficiency for naproxen, ibuprofen and diclofenac in two of eThekwini Municipality’s wastewater treatment plants (WWTPs), Kingsburgh and Umbilo, were investigated. This paper describes a simple method that can be used routinely for the simultaneous determination of such compounds in the influent and effluent of the WWTPs. Target compounds were extracted from wastewater and pre-concentrated using the optimized Oasis MAX solid-phase extraction (SPE) method. During SPE, the pH of wastewater samples was adjusted to 2.5; then 100 mL of each sample was loaded onto a pre-conditioned cartridge. The SPE cartridge was rinsed with methanol:water (10:90%, v:v) prior to sequential elution of retained analytes with 2 mL methanol, followed by 2 mL methanol and acetic acid (90:10, v:v) and 2 mL of 2% (v:v) formic acid diluted using a mixture of methanol and acetic acid (40:60, v:v). The eluted analytes from the SPE cartridge were quantified using high performance liquid chromatography (HPLC) equipped with photo diode array detection. The analytical method was validated by spiking deionized water with 5 and 50 μg·L-1 of target compounds, for which the recovery range of 76 to 98% was achieved with good precision. The instrument quantification limits obtained were 0.1 μg·L-1, for naproxen and 0.4 μg·L-1 for both ibuprofen and diclofenac. The detected concentrations for naproxen, ibuprofen and diclofenac in the influent of both WWTPs were in the ranges of 15–20 μg·L-1, 55–69 μg·L-1 and 6.4–16 μg·L-1, respectively. In effluent, the detected concentrations for naproxen, ibuprofen and diclofenac were in the ranges of 0.6–1.1, 2.1–4.2 and 1.4–2.0 μg·L-1, respectively. Overall, the employed SPE-HPLC method led to rapid pre-concentration of target compounds prior to their trace quantification in wastewater samples

Comparison of antioxidant activity of Moringa oleifera and selected vegetables in South Africa

The antioxidant activity of the leaves and flowers of the&nbsp;Moringa oleifera&nbsp;plant were investigated and the results were compared to those of selected vegetables (cabbage, spinach, broccoli, cauliflower and peas). Antioxidant activity was determined by analysing the total phenolics content, total flavonoids content, reducing power and radical scavenging activity using the 2,2-diphenyl-1-picrylhydrazyl free radical method. The total phenolics content of moringa was almost twice that of the vegetables and the total flavonoids content was three times that of the selected vegetables. The reducing power of moringa was higher than that of the vegetables and the percentage of free radicals remaining was lower compared with the vegetables. These results combined show that moringa is a good source of antioxidants. This finding also explains why moringa forms part of the diet of people in many developing countries, especially in the southern hemisphere