Comparison of a disposable sorptive sampler with thermal desorption in a gas chromatographic inlet, or in a dedicated thermal desorber, to conventional stir bar sorptive extraction-thermal desorption for the determination of micropollutants in water

The presence of micropollutants in the aquatic environment is a worldwide environmental concern. The diversity of micropollutants and the low concentration levels at which they may occur in the aquatic environment have greatly complicated the analysis and detection of these chemicals. Two sorptive extraction samplers and two thermal desorption methods for the detection of micropollutants in water were compared. A low-cost, disposable, in-house made sorptive extraction sampler was compared to SBSE using a commercial Twister sorptive sampler. Both samplers consisted of polydimethylsiloxane (PDMS) as a sorptive medium to concentrate micropollutants. Direct thermal desorption of the disposable samplers in the inlet of a GC was compared to conventional thermal desorption using a commercial thermal desorber system (TDS). Comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS) was used for compound separation and identification. Ten micropollutants, representing a range of heterogeneous compounds, were selected to evaluate the performance of the methods. The in-house constructed sampler, with its associated benefits of low-cost and disposability, gave results comparable to commercial SBSE. Direct thermal desorption of the disposable sampler in the inlet of a GC eliminated the need for expensive consumable cryogenics and total analysis time was greatly reduced as a lengthy desorption temperature programme was not required. Limits of detection for the methods ranged from 0.0010 ng L−1 to 0.19 ng L−1. For most compounds, the mean (n = 3) recoveries ranged from 85% to 129% and the % relative standard deviation (% RSD) ranged from 1% to 58% with the majority of the analytes having a % RSD of less than 30%.The National Research Foundation (NRF)http://www.elsevier.com/locate/aca2018-09-01hj2017Chemistr

Non-invasive sorptive extraction for the separation of human skin surface chemicals using comprehensive gas chromatography coupled to time-of-flight mass spectrometry : a mosquito-host biting site investigation

Variation in inter-human attractiveness to mosquitoes, and the preference of mosquitoes to bite certain regions on the human host, are possible avenues for identifying lead compounds as potential mosquito attractants or repellents. We report a practical, non-invasive method for the separation and detection of skin surface chemical compounds and comparison of skin chemical profiles between the ankle and wrist skin surface area sampled over a 5-day period of a human volunteer using comprehensive gas chromatography coupled to time-of-flight mass spectrometry. An in-house made polydimethylsiloxane passive mini-sampler, worn as an anklet or a bracelet, was used to concentrate skin volatiles and semi-volatiles prior to thermal desorption directly in the gas chromatography. A novel method for the addition of an internal standard to sorptive samplers was introduced through solvent modification. This approach enabled a more reliable comparison of human skin surface chemical profiles. Compounds that were closely associated with the wrist included 6-methyl-1-heptanol, 3-(4-isopropylphenyl)-2-methylpropionaldehyde, 2-phenoxyethyl isobutyrate, and 2,4,6-trimethyl-pyridine. Conversely, compounds only detected on the ankle region included 2-butoxyethanol phosphate, 2-heptanone, and p-menthan-8-ol. In addition to known human skin compounds we report two compounds, carvone and (E)-2-decenal, not previously reported. Limits of detection ranged from 1 pg (carvone) to 362 pg (indole).Dr Hubert Manderyhttp://www.jss-journal.comhj2021Chemistr

Determination of endocrine disrupting chemicals and antiretroviral compounds in surface water : a disposable sorptive sampler with comprehensive gas chromatography - time-of-flight mass spectrometry and large volume injection with ultra-high performance liquid chromatography-tandem mass spectrometry

Many rural dwellers and inhabitants of informal settlements in South Africa are without access to treated water and collect untreated water from rivers and dams for personal use. Endocrine disrupting chemicals (EDCs) have been detected in surface water and wildlife of South Africa. EDCs are often present in complex environmental matrices at ultra-trace levels complicating detection thereof. We report a simplified multi-residue approach for the detection and quantification of EDCs, emerging EDCs, and antiretroviral drugs in surface water. A low cost (less than one US dollar), disposable, sorptive extraction sampler was prepared in-house. The disposable samplers consisted of polydimethylsiloxane (PDMS) tubing fashioned into a loop which was then placed in water samples to concentrate EDCs and emerging pollutants. The PDMS samplers were thermally desorbed directly in the inlet of a GC, thereby eliminating the need for expensive consumable cryogenics. Comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) was used for compound separation and identification. Linear retention indices of EDCs and emerging pollutants were determined on a proprietary Crossbond® phase Rtx®-CLPesticides II GC capillary column. In addition, large volume injection of surface water into an ultra-performance liquid chromatograph tandem mass spectrometer (UPLC–MS/MS) was used as complementary methodology for the detection of less volatile compounds. Large volume injection reduced tedious and costly sample preparation steps. Limits of detection for the GC method ranged from 1 to 98 pg/l and for the LC method from 2 to 135 ng/l. Known and emerging EDCs such as pharmaceuticals, personal care products and pesticides, as well as the antiretroviral compounds, efavirenz and nevirapine, were detected in surface water from South Africa at concentration levels ranging from 0.16 ng/l to 227 ng/l.The National Research Foundation (NRF)http://www.elsevier.com/locate/chroma2018-05-05Chemistr

Controlling mosquitoes with semiochemicals : a review

The use of semiochemicals in odour-based traps for surveillance and control of vector mosquitoes is deemed a new and viable component for integrated vector management programmes. Over 114 semiochemicals have been identifed, yet implementation of these for management of infectious diseases such as malaria, dengue, chikungunya and Rift Valley fever is still a major challenge. The difculties arise due to variation in how diferent mosquito species respond to not only single chemical compounds but also complex chemical blends. Additionally, mosquitoes respond to diferent volatile blends when they are looking for a mating partner, oviposition sites or a meal. Analytically the challenge lies not only in correctly identifying these semiochemical signals and cues but also in developing formulations that efectively mimic blend ratios that diferent mosquito species respond to. Only then can the formulations be used to enhance the selectivity and efcacy of odour-based traps. Understanding how mosquitoes use semiochemical cues and signals to survive may be key to unravelling these complex interactions. An overview of the current studies of these chemical messages and the chemical ecology involved in complex behavioural patterns is given. This includes an updated list of the semiochemicals which can be used for integrated vector control management programmes. A thorough understanding of these semiochemical cues is of importance for the development of new vector control methods that can be integrated into established control strategies.University of Pretoria Institute for Sustainable Malaria Control (UP ISMC), National Research Foundation (NRF) and L’OréalUNESCO For Women in Science sub-Saharan African Programme.http://www.parasitesandvectors.compm2020ChemistryForestry and Agricultural Biotechnology Institute (FABI

Secondary Metabolite Profile and Pharmacological Opportunities of Lettuce Plants following Selenium and Sulfur Enhancement

Selenium (Se) is an essential trace nutrient for humans and animals owing to its role in redox regulation, thyroid hormone control factors, immunity, inflammatory reactions, brain activities, and carbohydrate regulation. It is also important to support muscle development, as well as for reproductive and cardiovascular well-being. Furthermore, sulfur is known to be a healing element, due to the remarkable function of specialized and secondary S-containing compounds. The scope of the current study was to determine the impact of Se and S enrichment on the secondary metabolite accumulation and antibacterial and NO inhibition activities in green and red leaf lettuce (V1 and V2, respectively) As with antibacterial activity, the acetone extract of green (V1) lettuce treated with adequate (S1) and higher S (S2) under Se-limiting conditions showed the ability to inhibit nitric oxide (NO) release from macrophages. NO production by macrophages was inhibited by 50% at respective concentrations of 106.1 ± 2.4 and 101.0 ± 0.6 μg/mL with no toxic effect on the cells, in response to S1 and S2, respectively, under Se-deficient conditions (Se0). Furthermore, the red cultivar (V2) exhibited the same effect as the green cultivar (V1) regarding NO inhibition, with IC50 = 113.0 ± 4.2 μg/mL, in response to S1/Se2 treatments. Collectively, the promising NO inhibitory effect and antibacterial activity of red lettuce under the above-mentioned conditions might be attributed to the production of flavonoid glycosides and phenylpropanoic acid esters under the same condition. To the best of our knowledge, this is the first report to show the novel approach of the NO inhibitory effect of Se and S enrichment in food crops, as an indicator for the potential of Se and S as natural anti-inflammatory agents

Potential for identifying plant-based toxins on San hunter-gatherer arrowheads

The antiquity of the use of hunting poisons has received much attention in recent years. In this paper we present the results of a pilot study designed to detect the presence of organic compounds, typically of less than 1200 Da, from poisonous plants that may have been used as hunting poisons in the past. We used ultra-performance liquid chromatography connected to a Synapt G2 high-resolution MS-QTOF mass spectrometer (UPLC-QTOF-MS) to provisionally identify plant-based toxins present in (1) extracts of fresh plant material, (2) a blind control recipe consisting of three plant ingredients and (3) a Hei||om arrow poison of unknown ingredients. Although not all expected toxic compounds were identified, those that were identified compared favourably with those reported in the literature and confirmed through databases, specifically the Dictionary of Natural Products and ChemSpider. MS/MS fragmentation patterns and accurate mass were used for tentative identification of compounds because archaeological residues usually contain insufficient material for unambiguous identification using nuclear magnetic resonance. We highlight the potential of this method for accurately identifying plant-based toxins present on archaeological artefacts and unique (albeit non-toxic) chemical markers that may allow one to infer the presence of toxic plant ingredients in arrow poisons. Any chemical study of archaeological material should consider the unique environmental degradative factors and be sensitive to the oxidative by-products of toxic compounds

Chemical profiling of the human skin surface for malaria vector control using combined chromatography and mass spectrometry techniques

The World Health Organisation (WHO) estimated that 216 million cases of malaria occurred worldwide in 2016 with most of the cases diagnosed in the African Region (90%) (WHO, World Malaria Report, 2017). Odour mosquito lures are currently being used as part of integrated vector control strategies in the fight against malaria. Variation in inter-human attractiveness to mosquitoes, as well as the preference of mosquitoes to bite certain regions on the human host are possible avenues for identifying lead compounds as potential attractants. In this study, methods were developed to chemically profile the human skin surface with the aim of determining the compounds responsible for attracting the mosquito vector to its human host. Two different areas of the human skin, namely wrist and ankles, were compared as well as inter-human attractiveness to mosquitoes following a 1 hour sampling period. Skin surface compounds were concentrated using a polydimethylsiloxane (PDMS) sampler. Sampling was followed by analyses with comprehensive gas chromatography – time of flight mass spectrometry (GC×GC-TOFMS) and ultra-performance liquid chromatography – ion-mobility spectrometry – high resolution mass spectrometry (UPLC-IMS-HRMS). The chemical skin profile data sets were compared using multivariate statistical methods, such as principal component and discriminant analyses. Compounds responsible for the differences in the chemical profiles were tentatively identified based on a comparison of sample mass spectra to that of the NIST14 library for the GC analyses. Accurate mass, isotope fit values and fragmentation patterns were compared to online ChemSpider databases for the LC analyses. Binary compare using an OPLS-DA Model highlighted the differences between the ankle and wrists groups for the LC-MS data sets. Viburtinal and Menaquinol, as well as Allodeoxycholic acid and N,N-Diethylbenzeneacetamide, were tentatively identified, using the Human Metabolome Database. These form plausible lead markers for the wrist and ankle groups, respectively. A comprehensive list of collision cross section data of human skin chemicals was compiled for LC amenable markers. This multi-approach gave a comprehensive human skin chemical profile consisting of volatile, semi-volatile, and non-volatile compounds.Thesis (PhD (Chemistry))--University of Pretoria, 2021.L’Oréal-UNESCO For Women in Science sub-Saharan African ProgrammeChemistryPhD (Chemistry)Restricte

Identification of micropollutants by combined chromatography and mass spectrometry techniques

The presence of micropollutants in South African aquatic systems has emerged as an issue of public health concern. Micropollutants, such as endocrine disrupting chemicals (EDCs) and antiretroviral compounds, have previously been detected in surface water of South Africa. Micropollutants are often present in complex environmental matrices at ultra-trace levels, complicating their detection. In order to address shortcomings with traditional sample preparation methods, an inhouse developed cheap, disposable polydimethylsiloxane (PDMS) sorptive sampler was developed. The validity of the PDMS sampler was established by comparison with a commercial stir bar sorptive sampler (SBSE). The sample introduction process into a gas chromatograph (GC) was also simplified by using thermal desorption of a PDMS sampler directly in the inlet liner of a GC. Direct thermal desorption was validated by comparison to time-consuming thermal desorption using an expensive commercial thermal desorption system (TDS). With the aim of identifying a vast range of micropollutants in aquatic systems comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS) was employed. The increased selectivity, sensitivity and larger peak capacity of GC×GC-TOFMS allows the identification of more compounds in complex matrices when compared to conventional GC-MS. An initial screening using sorptive extraction techniques and GC×GC-TOFMS tentatively identified various micropollutants, including EDCs, in surface water samples from the Rietvlei Nature Reserve, Gauteng, South Africa. Ultra-high pressure liquid chromatography coupled to mass spectrometry (UHPLCQTOFMS) was used as a complementary analytical technique in conjunction with GC×GC-TOFMS. Solid phase extraction (SPE) and large volume injection (LVI) sample preparation steps preceded analysis by UHPLC-QTOFMS. SPE is more time consuming and uses expensive solvents, however, adds selectivity to the sample preparation step, by reducing possible matrix interferences which can be problematic with LVI. Matrix matched calibration curves were constructed to identify and quantify target analytes in surface water samples. After validation of the analytical methods using chemometric approaches, these methods were employed to detect micropollutants in surface water from a metropolitan area (Rietvlei Nature Reserve, Gauteng) and a rural area (Albasini and Nandoni Dams, Limpopo Province) in South Africa. Limits of detection (LOD) for the GC methods ranged from 1 to 98 pg/L for the PDMS loop and 1 to 190 pg/L for SBSE. The LODs for the LC methods ranged from 1.97 to 135 ng/L for LVI and 73 pg/L to 57.3 ng/L for SPE. The two simplified methods, the in-house developed PDMS loop with GC×GCTOFMS, and LVI with UHPLC-QTOFMS, were used as complementary methods to detect micropollutants, such as EDCs, in surface water. EDCs such as pharmaceuticals, personal care products and pesticides, as well as the antiretroviral compounds, efavirenz and nevirapine, were detected in surface water from South Africa at concentration levels ranging from 0.16 ng/L to 227 ng/L. As they have not been reported in literature before, experimental linear retention indices are provided for the target analytes on the proprietary phase Rtx®- CLPesticides II column. Lastly, the variance between different sampling sites was investigated using principal component analysis (PCA). PCA revealed a difference in micropollutant profile between sampling sites in the metropolitan and the rural area.Dissertation (MSc)--University of Pretoria, 2017.National Research Foundation (NRF)ChemistryMScUnrestricte

Chemical profiling of the human skin surface for malaria vector control via a non-invasive sorptive sampler with GCxGC-TOFMS

Volatile organic compounds (VOCs) and semi-VOCs detected on the human skin surface are of great interest to researchers in the fields of metabolomics, diagnostics, and skin microbiota and in the study of anthropophilic vector mosquitoes. Mosquitoes use chemical cues to find their host, and humans can be ranked for attractiveness to mosquitoes based on their skin chemical profile. Additionally, mosquitoes show a preference to bite certain regions on the human host. In this study, the chemical differences in the skin surface profiles of 20 human volunteers were compared based on inter-human attractiveness to mosquitoes, as well as inter- and intra-human mosquito biting site preference. A passive, non-invasive approach was followed to sample the wrist and ankle skin surface region. An in-house developed polydimethylsiloxane (PDMS) passive sampler was used to concentrate skin VOCs and semi-VOCs prior to thermal desorption directly in the GC inlet with comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS). Compounds from a broad range of chemical classes were detected and identified as contributing to the differences in the surface skin chemical profiles. 5-Ethyl-1,2,3,4-tetrahydronaphthalene, 1,1′-oxybisoctane, 2-(dodecyloxy)ethanol, α,α-dimethylbenzene methanol, methyl salicylate, 2,6,10,14-tetramethylhexadecane, 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester, 4-methylbenzaldehyde, 2,6-diisopropylnaphthalene, n-hexadecanoic acid, and γ-oxobenzenebutanoic acid ethyl ester were closely associated with individuals who perceived themselves as attractive for mosquitoes. Additionally, biological lead compounds as potential attractants or repellants in vector control strategies were tentatively identified. Results augment current knowledge on human skin chemical profiles and show the potential of using a non-invasive sampling approach to investigate anthropophilic mosquito-host interactions.Dr. Hubert Manderyhttp://link.springer.com/journal/2162021-07-01hj2020Chemistr

Mass spectral studies on the human skin surface for mosquito vector control applications

Human skin surface chemical cues comprise a complex mixture of compounds that mosquitoes use to locate and select their human host, based on inter- and intra-human variation in chemical profiles. The complexity of the skin surface matrix calls for advanced analytical techniques to enable separation and identification of biomarkers, which may be used as topical attractants and repellants in future mosquito vector control programmes. The perceived mosquito attractiveness between 20 volunteers and the preference of mosquitoes to bite certain regions, namely, ankle versus wrist, of the human host were investigated in this study, by comparing skin surface chemical profiles. Ion mobility was combined with high resolution mass spectrometry to provide additional confidence in biological marker discovery and identification of human skin surface compounds. This study employed a non-intrusive sampling scheme using a polydimethylsiloxane (PDMS) sampler and solvent desorption analysed with ultra-performance liquid chromatography with ion mobility high-resolution mass spectrometry (UPLC-IMS-HRMS). Statistical approaches guided the identification of 14 biological markers discerning difference in perceived mosquito attractiveness and 20 biomarkers associated with the different skin regions sampled. A broad range (m/z 96.0437 to 788.6095) of chemical compounds was detected from a variety of classes (including sugars, steroids, fatty acids, peptides and peptide derivatives, and compounds of food origin). Ten compounds were unequivocally identified on the human skin surface, and caffeine was reported on the human skin surface for the first time. Furthermore, 77 compounds, of which 64 to the authors' knowledge have not previously been reported, were detected on the human skin surface using accurate mass, collision cross section (CCS) values and fragmentation patterns. This approach enabled comprehensive human skin surface chemical profiling and provides an extensive list of tentatively identified skin surface compounds together with accurate mass values and adducts with their corresponding CCS values.Supporting Information S1: Experimental SectionSupporting Information S2: Tables and FiguresDr. Hubert Manderyhttp://wileyonlinelibrary.com/journal/jms2021-11-17hj2021Chemistr