A high-throughput analysis of volatile compounds with various polarities using headspace stir bar sorptive extraction.

Long sample extraction time is usually necessary in the analysis of volatile flavour compounds to achieve high extraction efficiency. However, the long extraction time reduces sample throughput, which results in waste of labour and energy. Therefore, in this study, an improved headspace-stir bar sorptive extraction was developed to extract volatile compounds with varying polarities in a short time. With the aim of achieving high throughput, extraction conditions were selected and optimised based on the combinations of different extraction temperatures (80-160 °C), extraction times (1-61 min), and sample volumes (50-850 µL) through the response surface methodology with Box-Behnken design. After obtaining the preliminary optimal conditions (160 °C, 25 min, and 850 µL), the effect of cold stir bars with shorter extraction time on the extraction efficiency was evaluated. The cold stir bar improved the overall extraction efficiency with better repeatability, and the extraction time was further shortened to 1 min. Then, the effects of different ethanol concentrations and salt additions (sodium chloride or sodium sulfate) were studied, and 10% ethanol concentration with no salt addition provided the highest extraction efficiency for most compounds. Finally, it was verified that the high-throughput extraction condition was feasible for the volatile compounds spiked in a honeybush infusion.

Online water sampling-quickMix-assisted miniscale liquid-liquid extraction coupled with full evaporation dynamic headspace concentration of polybrominated diphenyl ethers.

Polybrominated diphenyl ethers (PBDEs) are commonly used as flame retardants in daily household products and have been found to be detrimental to human and animal health. Being highly stable, accumulation can take place easily in the environment. In our previous studies, an innovative sample preparation method named miniscale liquid-liquid extraction (msLLE) coupled to full evaporation dynamic headspace (FEDHS) concentration was developed, and then successfully coupled to an online water sampling system, allowing full automation from water sampling to sample preparation, sample detection and analysis. In the present work, the fully automated online sampling-quickMix-assisted-msLLE-FEDHS platform was optimized and applied to PBDEs in environmental aqueous samples. The online sampling system was set up with a modified sample vial (to have an inlet and outlet), two tubings and a peristaltic pump which was programmed to control the water flow into and out of the vial. After adding 2 mL of the extractant (n-hexane), and 7 mL of sampled water to a 10-mL vial, msLLE was enabled, assisted with a quickMix module to ensure a quick and efficient mode of mixing between the organic and aqueous phases. The organic extract was then transferred to the FEDHS setup for selective trapping and concentration of the PBDEs, while the solvent was removed. The trap consisted of Tenax TA adsorbent, which has favorable π-interaction with the PBDEs but not with n-hexane. Subsequently, the adsorbent tube was automatically transported to the injector of the gas-chromatography mass-spectrometric (GC-MS) system to thermally desorb the trapped PBDEs for detection and analysis. The optimized methodology was found to achieve low limits of detection (0.0031 to 0.018 µg/L) with good linearity (r2 ≥ 0.9932) and satisfactory absolute extraction recoveries (between 61.4% and 80.9%). The analysis of PBDEs in spiked genuine water sample attained satisfactory and repeatable relative recoveries (between 106.1% and 132.6% with%RSDs ≤ 8.6%).

Public sentiments towards the use of Wolbachia-Aedes technology in Singapore.

BACKGROUND: Wolbachia technology is a novel vector control approach that can reduce mosquito populations and the risk of mosquito-borne diseases, which has recently gained popularity amongst countries. In 2016, Singapore embarked on a multi-phased field study named Project Wolbachia - Singapore, to evaluate the use of Wolbachia technology as an Aedes aegypti mosquito population suppression tool to fight dengue. Due to the novelty of this technology in Singapore, this study aims to understand the public's acceptance and sentiments towards the use of Wolbachia technology. METHODS: Several public sentiment survey approaches - including online, face-to-face in the streets, as well as door-to-door household surveys - were conducted. RESULTS: The surveys conducted prior to the first field releases and implementation of the project revealed high support for the use of Wolbachia technology in Singapore. A household perception survey conducted in the interim of the first project phase was encouraging, with the majority of the respondents being aware of the project and having no concerns with the release of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes in their neighbourhood. CONCLUSIONS: The study reveal high support for the use of Wolbachia technology in Singapore and also provided invaluable insights that were used in the development of a public communications and engagement framework model, which thus helped to guide these elements in the subsequent phases and expansion of the project.

Comparison of automated mixer-assisted mini-scale liquid-liquid extraction coupled with full evaporation dynamic headspace extraction with United States Environmental Protection Agency methods for the gas chromatography-mass spectrometric analysis of chlorinated benzenes.

Three modes of facilitating mini-scale-liquid-liquid-extraction (msLLE) prior to automated integration with full evaporation dynamic headspace (FEDHS) extraction were evaluated in this work. For msLLE, 1.2 mL of dichloromethane (DCM) was added to a conical-bottomed vial containing 7 mL of aqueous sample. The solution was then subjected to three different mixing modes, namely vortex-assistance (where a "whirlpool" was created in the solution), agitation-assistance (where the vial was rotated in circular motion) and quickMix-assistance (where the vial was shaken at a high speed). Vortex-assistance was performed manually while the other two modes were automated using a commercial autosampler. Following this, the DCM extract was transferred automatically to another vial and was then vaporized and sent through a Tenax TA sorbent tube in the FEDHS step. Due to the stronger π interaction between the sorbent and the analytes of interest, the analytes were selectively concentrated while the DCM vapor passed through unhampered. After FEDHS, the analytes were thoroughly desorbed into a gas chromatography-mass spectrometric system for analysis. The applicability of this procedure was validated in the extraction of six chlorinated benzenes (CBs) (1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,4,5-tetrachlorobenzne and hexachlorobenzene) from aqueous samples. The quickMix-assisted msLLE-FEDHS approach achieved good absolute extraction recoveries (between 74.2% and 88.7%), low limits of detection (between 0.0006 and 0.0116 µg/L), good linearity (r2≥0.9920), good repeatability (between 1.9% and 8.4%, and good reproducibility (between 9.0% and 13.6%). It was found to be superior to the methods published by the United States Environmental Protection Agency. Five consecutive fully automated quickMix-assisted-msLLE-FEDHS-GC-MS runs spanned only ca. 4 hr.

Enhanced extraction using a combination of stir bar sorptive extraction and thin film-solid phase microextraction.

Sorptive extraction techniques have experienced increased popularity, but they face limitations in dynamic range and sensitivity. In this study, a new method combining stir bar sorptive extraction (SBSE) and thin-film solid-phase microextraction (TFSPME) was developed, and optimization for extraction temperature (70 °C) and time (120 min) was carried out. Polydimethylsiloxane (PDMS)-coated SBSE and PDMS/carboxen (PDMS/CAR)-coated TFSPME were used, and both headspace and direct immersion extraction modes were also studied. Using 40 selected volatile compounds, the combined method generally gave a wider linearity range with lower minimum limits (2 to 3 orders), satisfactory coefficient of determination (R2>0.980), and improved sensitivity when compared to SBSE-only or TFSPME-only techniques. Furthermore, despite the combined use of two extraction devices, the repeatability (<13.1 %) and reproducibility (<13.4 %) of the combined method were comparable to SBSE-only or TFSPME-only results. Higher recoveries of up to 20% were also achieved by the combined method. Compared to the conventional SBSE method, the new method provided superior performance in terms of dynamic range and sensitivity for compounds of various polarities. In conclusion, this study provided insights on the suitability of the various extraction methods for compounds of different chemical properties which could aid in future applications for volatiles analysis in food, biological, and environmental sectors.

Environmentally friendly etching of stainless steel wire for plunger-in-needle liquid-phase microextraction of polycyclic aromatic hydrocarbons.

An environmentally friendly method of etching a stainless steel plunger wire, to replace the conventional hydrofluoric acid approach, was developed for plunger-in-needle liquid phase-microextraction (PIN-LPME). The one-step etching procedure was performed by immersing the plunger wire in a ferric chloride-hydrochloric acid (FeCl3-HCl) solution. The etched wire was then used for LPME as the organic solvent holder. After solvent coating, the wire was directly exposed to a water sample for extraction of polycyclic aromatic hydrocarbons (PAHs), which were then subjected to thermal desorption in the injector of a gas chromatograph for gas chromatography-mass spectrometric (GC-MS) analysis. The parameters affecting PIN-LPME efficiencies (i.e., extraction solvent, solvent coating mode and time, stirring rate, extraction time and salting effect) were also investigated. Under the most favourable conditions, PIN-LPME-GC-MS exhibited high enrichment factors of between 70 and 349 for the 9 PAHs, low detection limits (between 0.006 and 0.058 ng mL-1), and good precision (with relative standard deviations ranging from 4.4% to 9.7%). The developed method was successfully applied for the extraction and determination of PAHs in tap, river and drain water samples. Good relative recoveries of the PAHs over the range of 84.3-101.9% were obtained with spiked genuine water samples.

Mosquitoes (Diptera: Culicidae) of Singapore: Updated Checklist and New Records.

Prior to 1965, Singapore was part of the Malaya (now Malaysia) and was usually not mentioned when mosquito records were reported for Malaya. Consequently, many species that occurred in Singapore were not listed in the world mosquito catalog, and the available checklist for Singapore since 1986 is incomplete, with some imprecise species information. In updating this checklist, we examined and verified mosquito specimens collected from Singapore in various depositories, including a thorough review of past taxonomic literature. Here, we report a checklist of 182 mosquito species, 33 new distribution records, and a consolidated status list of vectors for Singapore. As Singapore is a travel hub and hosts one of the busiest container ports in the world, there is a risk of introducing mosquito species and their associated pathogens of human disease to the country. Hence, the distribution records are important to increase our knowledge on mosquito ecology as well as to understand the risk of newly introduced vectors and their associated pathogens.

A fully automated analytical platform integrating water sampling-miniscale-liquid-liquid extraction-full evaporation dynamic headspace concentration-gas chromatography-mass spectrometry for the analysis of ultraviolet filters.

A fully automated analytical platform that seamlessly integrates online water sampling-sample preparation-gas chromatography-mass spectrometry (GC-MS) was developed for ultraviolet (UV) filters in this work. The online water sampling system consisted of a conventional sample vial (slightly modified to have both inlet and outlet ports), two tubings and a peristaltic pump, which controlled the water flow into and out of the vial. The sample preparation segment consists of miniscale liquid-liquid extraction (msLLE), coupled to full evaporation dynamic headspace concentration (FEDHS) on a commercial dual-arm autosampler. The extract from the msLLE step was subjected to a derivatization step, before being passed through a Tenax TA sorbent tube at the FEDHS stage. UV filters were used as model compounds in this work due to their potential endocrine and developmental toxicities, including benzhydrol, 2-ethylhexyl salicylate, homosalate, 2-hydroxy-4-methoxybenzophenone, 3-(4'-methylbenzylidene) camphor and benzophenone. The analytes (of which the first four underwent derivatization, by virtue of them possessing hydroxyl groups, but not the last two) were concentrated on the sorbent, and were thermally desorbed before being introduced to the GC-MS system for analysis. An orthogonal array design (OAD) strategy was employed to facilitate the optimization of the msLLE and derivatization factors while univariate optimization was performed for FEDHS. The optimized settings achieved low limits of detection (0.6-9.7 ng L-1) with good linearity (r2 ≥ 0.9926), and satisfactory absolute extraction recoveries (62.0%-80.7%) were obtained. The fully automated online water sampling-extraction/concentration-detection approach was demonstrated by applying it to the analysis of swimming pool water. Relative recoveries of the analytes in the pool water ranged from 85.4% to 118.2%. The described procedure has the potential to be a fully automated online water sampling-msLLE-FEDHS-GC-MS platform for the purpose of conducting routine onsite water analysis.

Miniscale Liquid-Liquid Extraction Coupled with Full Evaporation Dynamic Headspace Extraction for the Gas Chromatography/Mass Spectrometric Analysis of Polycyclic Aromatic Hydrocarbons with 4000-to-14 000-fold Enrichment.

A new sample preparation approach of combining a miniscale version of liquid-liquid extraction (LLE), termed miniscale-LLE (msLLE), with automated full evaporation dynamic headspace extraction (FEDHS) was developed. Its applicability was demonstrated in the extraction of several polycyclic aromatic hydrocarbons (PAHs) (acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, and pyrene) from aqueous samples. In the first step, msLLE was conducted with 1.75 mL of n-hexane, and all of the extract was vaporized through a Tenax TA sorbent tube via a nitrogen gas flow, in the FEDHS step. Due to the stronger π-π interaction between the Tenax TA polymer and PAHs, only the latter, and not n-hexane, was adsorbed by the sorbent. This selectivity by the Tenax TA polymer allowed an effective concentration of PAHs while eliminating n-hexane by the FEDHS process. After that, thermal desorption was applied to the PAHs to channel them into a gas chromatography/mass spectrometric (GC/MS) system for analysis. Experimental parameters affecting msLLE (solvent volume and mixing duration) and FEDHS (temperature and duration) were optimized. The obtained results achieved low limits of detection (1.85-3.63 ng/L) with good linearity (r(2) > 0.9989) and high enrichment factors ranging from 4200 to 14 100. The optimized settings were applied to the analysis of canal water sampled from an industrial area and tap water, and this methodology was compared to stir-bar sorptive extraction (SBSE). This innovative combined extraction-concentration approach proved to be fast, effective, and efficient in determining low concentrations of PAHs in aqueous samples.

External quality assessment of dengue and chikungunya diagnostics in the Asia Pacific region, 2015.

OBJECTIVE: To conduct an external quality assessment (EQA) of dengue and chikungunya diagnostics among national-level public health laboratories in the Asia Pacific region following the first round of EQA for dengue diagnostics in 2013. METHODS: Twenty-four national-level public health laboratories performed routine diagnostic assays on a proficiency testing panel consisting of two modules. Module A contained serum samples spiked with cultured dengue virus (DENV) or chikungunya virus (CHIKV) for the detection of nucleic acid and DENV non-structural protein 1 (NS1) antigen. Module B contained human serum samples for the detection of anti-DENV antibodies. RESULTS: Among 20 laboratories testing Module A, 17 (85%) correctly detected DENV RNA by reverse transcription polymerase chain reaction (RT-PCR), 18 (90%) correctly determined serotype and 19 (95%) correctly identified CHIKV by RT-PCR. Ten of 15 (66.7%) laboratories performing NS1 antigen assays obtained the correct results. In Module B, 18/23 (78.3%) and 20/20 (100%) of laboratories correctly detected anti-DENV IgM and IgG, respectively. Detection of acute/recent DENV infection by both molecular (RT-PCR) and serological methods (IgM) was available in 19/24 (79.2%) participating laboratories. DISCUSSION: Accurate laboratory testing is a critical component of dengue and chikungunya surveillance and control. This second round of EQA reveals good proficiency in molecular and serological diagnostics of these diseases in the Asia Pacific region. Further comprehensive diagnostic testing, including testing for Zika virus, should comprise future iterations of the EQA.

Gravitraps for management of dengue clusters in Singapore.

Although Singapore has an intensive dengue control program, dengue remains endemic with regular outbreaks. We report development and use of a novel adult oviposition trap, the Gravitrap, in managing dengue cluster areas. The Gravitrap is a simple, hay infusion-filled cylindrical trap with a sticky inner surface to serve as an oviposition site for gravid female Aedes mosquitoes. Wire gauze fitted above the water level minimizes the risk of it being an unwanted breeding habitat. The Gravitrap was deployed in 11 dengue cluster areas throughout Singapore. Aedes aegypti was the predominant mosquito caught in the trap and some (5.73%) were found to be positive for dengue virus.

First detection of chikungunya infection and transmission in Brunei Darussalam.

This report describes the chikungunya cases and local transmission detected in Brunei Darussalam for the first time, despite the country being situated in a region that has experienced a multitude of outbreaks over the years. A combined strategy of active case detection, patient isolation and vector control measures was deployed in an attempt to avert further transmission. The findings have important public health implications for international surveillance and control strategies for this re-emerging disease.