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%).

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.

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.