Headspace Single-drop Microextraction Research Articles

Headspace-single drop microextraction based visual colorimetry for non-chromatographic speciation analysis of nitrite and nitrate in environmental water sample

In this work, a visual colorimetric method based on headspace-single drop microextraction (HS-SDME) was developed for the non-chromatographic speciation analysis of nitrite and nitrate. The method adequately exploited the individual chemical vapor conditions of nitrite and nitrate that were converted to NO by specific reductants. Gaseous NO underwent a diazotization reaction with chromogenic reagent through the HS-SDME process to change from colorless to purplish-red. Instead of using large, time-consuming and relatively complicated chromatographic equipment for separation, the species of nitrite and nitrate could be analyzed by simply changing the reagents. Meanwhile, the extraction method effectively mitigated the matrix interference of solution and improved the sensitivity of method, with intuitive discrimination of color by the naked eye. The limits of detection were 0.07 μg/mL for nitrite and 0.2 μg/mL for nitrate, respectively. This method has been applied to analysis of real environmental water samples, which also effectively extended the application scope of HS-SDME device.

Water as a green solvent for sustainable sample preparation: single drop microextraction of N-nitrosamines from losartan tablets.

Water, renowned for its sustainability and minimal toxicity, is an ideal candidate for environmentally friendly solvent-based microextraction. However, its potential as an extractant solvent in miniaturized sample preparation remains largely unexplored. This paper pioneers using water as the extraction solvent in headspace single-drop microextraction (HS-SDME) for N-nitrosamines from losartan tablets. Autonomous HS-SDME is executed by an Arduino-controlled, lab-made Cartesian robot, using water for the online preconcentration of enriched extracts through direct injection into a column-switching system. Critical experimental parameters influencing HS-SDME performance are systematically explored through univariate and multivariate experiments. While most previously reported methods for determining N-nitrosamines in pharmaceutical formulations rely on highly selective mass spectrometry detection techniques to handle the strong matrix effects typical of pharmaceutical samples, the water-based HS-SDME method efficiently eliminates the interfering effects of a large amount of the pharmaceutical active ingredient and tablet excipients, allowing straightforward analysis using high-performance liquid chromatography with ultraviolet detection (HPLC-UV-Vis). Under optimized conditions, the developed method exhibits linear responses from 100 to 2400ngg-1, demonstrating appropriate detectability, precision, and accuracy for the proposed application. Additionally, the environmental sustainability of the method is assessed using the AGREEprep methodology, positioning it as an outstanding green alternative for determining hazardous contaminants in pharmaceutical products.

A dual-mode fluorometric and colorimetric sensor based on N-doped carbon dots for selective and sensitive detection of nitrite in food samples

A highly sensitive and selective nitrite sensing platform based on nitrogen-doped carbon quantum dots (N-CDs), by means of a headspace single drop microextraction process, was constructed for dual-mode fluorometric and visual colorimetric determination of nitrite. In this system, the two-channel selective sensing of nitrite was achieved at the same time, with color ranging from colorless to red and N-CDs fluorescence quenching gradually. Meanwhile, gaseous NO was generated from the redox chemical vapor generation process and further extracted into a single drop, which effectively improving the analytical sensitivity and alleviating the matrix interference. By fluorescence and colorimetry, the limits of detection were calculated to be 0.03 and 0.08 μg mL−1, respectively, while 0.8 μg mL−1 nitrite was discernable by the naked eye. This method was utilized to analysis of diversified real food samples (vegetables, milk and ham), and the results were proved to be nearly consistent with a standard method. Furthermore, the storage conditions of vegetable juice have also been explored.

Head Space Single Drop Micro Extraction Gas Chromatography Flame Ionization Detection (HS-SDME-GC-FID) Method for the Analysis of Common Fatty Acids.

Post-marketing/surveillance studies show that most of the many vegetable oils that are sold with health-promoting claims or statements with high nutritional values and are beneficial against diseases are off-limits of related monographs/criteria. Defining the oil with a fast, cheap, and efficient analytical method is needed to express fatty acids in any herbal product to authenticate, trace, specify, and classify the content.The majority of the after marketing/surveillance studies shows that most of the many vegetable oils that are sold with health-promoting claims or statements with high nutritional values and are beneficial against diseases are off-limits of related monographs/criteria. Defining the oil with fast, cheap and efficient analytical method to express fatty acids in any herbal product, to authenticate, trace, specify and classify the content is needed. Here, we define a new simple tool with a headspace single drop microextraction (HS-SDME) method coupled with a gas chromatography-flame ionization detector (GC-FID) for the analysis of common fatty acids (FAs) in oils. Linolenic acid, γ-linolenic acid, and linoleic acid in olive oil, thyme oil, and fish oil were determined. Derivatization was performed with 0.2 mL of 2 mol/L KOH in methanol to transfer the FAs of oils into their methyl esters (FAMEs). Then, FAMEs were extracted using a head space single drop, which is 2.0 μL of sodium dodecyl sulfate:1-butanol (1:3, v/v) mixture. The most suitable extraction condition was that 360 μL of the FAMEs, 2.0 mL vial, 0.07 g NaCl as a salting-out effect, 45 °C extraction temperature, and 35 min extraction time. The precision of the method was below 12%, with accuracy validated by the GC-FID reference method.The most suitable extraction condition was that 360 μL of the fatty acid methyl esters (FAMEs), 2.0 mL vial, 0.07 g NaCl as a salting-out effect, 45 °C extraction temperature, and 35 min extraction time. The precision of the method was below 12% with an accuracy validated by the GC-FID reference method. The HS-SDME can be used effectively for extracting FAs from oils for improved analysis of other FAs. The method is of direct importance and relevance for the herbal, pharmaceutical, and cosmetics industries.The HS-SDME can be used for effectively for extracting fatty acids from oils for improved analysis of other fatty acids while the method is direct importance and relevance for herbal, pharmaceutical, cosmetics industry.

Combination of headspace single-drop microextraction with smartphone-based on-drop colorimetric detection for determination of ammonia and total nitrogen in environmental and food samples

In the present study, a simple, environmentally friendly and inexpensive analytical method was proposed based on the combination of headspace single-drop microextraction with smartphone-based on-drop colorimetric detection for determination of ammonia (free ammonia and ammonium ion) in environmental and food samples. This method was also coupled with micro Kjeldahl digestion for determining total nitrogen content (or protein) in foods. Ammonia was extracted into an aqueous microdrop containing o-phthalaldehyde (OPA)-Na2SO3 reagent, and simultaneously converted to a colored derivative (1-sulfonatoisoindole). The colored microdrop was directly imaged by smartphone camera as a detector, and the captured image was processed with a color recognition app for ammonia quantification. The influence of experimental variables on the sensitivity of this method was studied. The linear range of the method was achieved from 0.25 to 10 mg L−1 for ammonium with the detection limit of 0.07 mg L−1. The intraday and interday relative standard deviations were between 2.5 and 5.5 % at the concentration levels of 0.5 and 5 mg L−1. This method was satisfactorily applied to determining ammonia and total nitrogen in environmental and food samples with ammonia and total nitrogen recoveries in the range of 90–109 %. In comparison with the Berthelot and classical Kjeldahl methods, there was no considerable difference in accuracy between these methods and the present method.

Enhancing peroxidase-like activity of AuNPs through headspace reaction: A signal amplification strategy for colorimetric and fluorescent sensing of trace Hg2+

BackgroundRecently, headspace single-drop microextraction (HS-SDME) has attracted some attention for developing sensitive and selective colorimetric assays due to its excellent capability to reduce matrix interference and enrich analytes. However, the single droplet limits direct visual observation of color change and its quantitative measurement suffers from reduced optical path length. Therefore, amplifying the detection signals in both volume and intensity is an important and challenging task for improving the sensitivity, stability, and accuracy of such colorimetric analysis. ResultsIn this study, a "headspace-nanoenzyme" (HS-NE) strategy was proposed that successfully addressed these challenges and enabled the colorimetric and fluorescent dual-mode detection of trace Hg2+. Atomic Hg0, generated via chemical vapor generation (CVG), underwent headspace reaction with AuNPs droplet to form Au@HgNPs, thus catalyzing the oxidation of o-phenylenediamine (OPD) in the presence of H2O2. The absorbance and fluorescence intensity of oxidized OPD were proportion to the concentration of Hg2+ in the sample solution. Due to the greatly enhanced peroxidase-like activity by Au@HgNPs, the limit of detection was as low as 0.98 nM and 0.21 nM for the colorimetric and fluorescent modes, respectively. The applicability of this assay was further demonstrated with determination of Hg2+ in real environmental and biological samples. Moreover, a convenient and cost-effective paper-based sensing platform was fabricated for rapid on-site detection of Hg2+. Significance and noveltyThis novel HS-NE strategy combines HS-SDME and nanoenzyme-based sensing to achieve dual effects of eliminating matrix interference and amplifying the measurement signal, resulting in improved accuracy, enhanced stability, high sensitivity, and exceptional selectivity, with great potential for on-site determination of trace Hg2+.

Headspace single drop microextraction based visual colorimetry for highly sensitive, selective and matrix interference-resistant determination of sulfur dioxide in food samples.

Excessive intake of SO2, a widely-used food additive, is able to cause respiratory, cardiovascular and neurological disease. For effectively monitoring SO2 level, we have developed a headspace single drop microextraction based visual colorimetry for highly sensitive and selective sensing of SO2 with TMB (3,3',5,5'-tetramethylbenzidine) as a classic chromogenic reagent. A combination of single drop and headspace microextraction integrated merits of high extraction efficiency, low consumption of reagents and excellent matrix interference-resistant ability. The colorimetric principle was based on oxidation of TMB, and SO2 could compete with TMB to preferentially react with ·OH, resulting in the fading of color blue that could be easily read out by naked eye. LOD was calculated to be 0.53μM and 5μM by UV-vis and naked eye, respectively. The method was successfully utilized to analysis of food samples, and the experimental device was miniaturized and easy to construct, thus showing a promising potential in field analysis.

Combination of headspace single-drop microextraction (HS-SDME) with a nickel-embedded paper-based analytical device for cyanide quantification

BackgroundCyanide anion can be found in foodstuffs, tobacco smoke and a variety of types of waters, mainly originating from anthropogenic activities. Due to its highly toxic nature, several agencies have established limits for cyanide levels in water. Additionally, monitoring cyanide levels in biological samples, such as blood and urine, is crucial for obtaining clinical information about the health condition of patients. Therefore, there is a pressing need for the development of simple, cost-effective, and reliable analytical methods capable of quantifying cyanide at low concentrations. ResultsThis study presents a novel analytical method for the selective and sensitive determination of cyanide based on analyte volatilization, pre-concentration via single-drop microextraction (SDME) using a selective reagent, and colorimetric quantification using a paper-based analytical device. For this, 10 mL of a liquid sample was acidified with phosphoric acid and the generated HCN was collected using a single drop of 3 μL of a palladium dimethylglyoximate solution (Pd (DMG)22−) positioned in the flask headspace using a syringe. The reaction of Pd (DMG)22− leads to the formation of Pd(CN)42− and the demasking of the organic ligand. After 15 min of extraction time, the reagent drop was added to a paper-based analytical device that has been previously impregnated with 3 μL of nickel chloride, resulting in the formation of a red precipitate of nickel (II) dimethylglyoximate. Digital images of the paper-based device were captured and the red channel (R) was used for quantification purposes. Under optimized conditions, the method demonstrates a suitable linear relation (r2 > 0.99) ranging from 26 to 286 μg L−1 and a limit of detection of 5 μg L−1. SignificanceAs a proof of concept, cyanide levels were quantified in water and urine samples using this method. The proposed approach offers high sensitivity and selectivity while requiring only a small volume of reagents. Furthermore, it exhibits a high degree of portability for in-situ applications.

Comparing π-complexation capabilities of ionic liquids containing silver(I) and copper(I) ions by headspace single drop microextraction in combination with high-performance liquid chromatography.

Selective π-complexation capabilities of silver(I) and copper(I) ions can be effectively facilitated in ionic liquids. To understand the effects of environmental factors that influence the π-complexation of these metal ions with analytes, techniques that employ small volumes of ionic liquid that can be readily analyzed are desired. In this study, headspace single drop microextraction coupled with HPLCis used to investigate a diverse set of environmental factors on the metal ion-mediated complexation with aromatic compounds in ionic liquid media. Silver(I) and copper(I) bis[(trifluoromethyl)sulfonyl]imide salts were both studied by dissolving them in the 1-decyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ionic liquid and employing the mixture as extraction media for aromatic compounds. Water and acetonitrile within the sample solution were observed to interfere with the complexation of silver(I) ions and aromatic compounds, while ethylene glycol and triethylene glycol did not. The temperature and extraction times were optimized to fully facilitate the π-complexation capabilities of metal ions in ionic liquid media. Partition coefficients between the sample headspace and metal ion were determined using a three-phase equilibria model. Although no discernable difference in analyte partitioning between the headspace and ionic liquid solvent was observed, analyte partition coefficients to silver(I) ion tended to be greater compared to copper(I) ion.

Headspace single-drop microextraction combined with nanodrop spectrophotometry for ultra-trace detection of ethanethiol using a suspended drop of AuNPs as a plasmonic sensor

It is challenging to achieve ethanethiol extraction, enrichment in a single-drop microextraction system, and an assay with good sensitivity and selectivity for analyzing food analytes in complex matrices. In this study, we combined headspace single-drop microextraction (HS-SDME) with nanodrop array spectrophotometry applied for ultra-trace determination of ethanethiol. A suspended drop of gold nanoparticles (AuNPs) solution was utilized for sensing ethanethiol as an acceptor phase. The thiol portion of ethanethiol molecules binds to the negatively charged AuNPs. Thus, the aim of target enrichment was attained, while matrix effects interference was also minimized. The approach can be used for the direct detection of ethanethiol in food without any sample pretreatment. The obtained range of linearity was 1–1000 µM and 100–1000 nM. The detection limits were 66.62 nM, comparable with those of previously reported methods. The method successfully determined ethanethiol in food (beverage, non-alcoholic beer, and cheese).

Ionic Liquid-Based Magnetic Needle Headspace Single-Drop Microextraction Combined with HPLC/UV for the Determination of Chlorophenols in Wastewater.

A magnetic needle headspace single-drop microextraction (MN-HS-SDME) method coupled to HPLC/UV has been developed. Trihexyl(tetradecyl)phosphonium chloride was employed as an ionic liquid (IL) solvent for the headspace extraction of some chlorophenol (CP) compounds from wastewater samples. Despite of the nonmagnetic character of the IL, a significant improvement in the extraction efficiency was obtained by the magnetization of the single-drop microextraction needle using a pair of permanent disk magnets. A simplex method for the fast optimization of the experimental conditions (e.g., stirring speed, ionic strength, pH, extraction time and temperature) was used. The coefficients of determination (R2) varied between 0.9932 and 0.9989, the limits of detection were from 0.004 to 0.007μgmL-1 and the relative recoveries were in the range of 88-120% for the studied analytes. The developed MN-HS-SDME HPLC/UV method was successfully applied to the determination of CPs in industrial wastewater.

A rapid and green GC-MS method for the sampling of volatile organic compounds in spices and flowers by concurrent headspace single-drop microextraction and solid-phase microextraction.

The equilibrium rather than the exhaustive nature of headspace single-drop microextraction (HS-SDME) and headspace solid-phase microextraction (HS-SPME) allowed the concurrent sampling of volatile organic compounds (VOCs) on the same sample in the same vial in a dual extraction configuration. This has avoided the necessity of conducting a separate set of experiments and was found to produce results in the time duration of a single sample preparation experiment. The results obtained by HS-SDME were validated against those found by the standard method of HS-SPME. Rectilinear calibration was made for certain VOCs tested as analytes over the range of 0.01-8 μg g-1, and the average values of R2, LOD and LOQ were found to be, respectively, 0.9992, 1.9 ng g-1 and 5.7 ng g-1 in HS-SDME, and 0.9991, 3.1 ng g-1 and 9.1 ng g-1 in HS-SPME. The spiked recoveries and RSD were, respectively, 100.5% and 3.3% in HS-SDME and 98.1% and 3.6% in HS-SPME. HS-SDME is convenient to perform and produce results in a much cheaper way than HS-SPME and free from the inconveniences of memory effects. With GC-MS, this method has also been implemented as a rapid, reliable and green procedure (by GAPI and AGREE tools) for the sampling of VOCs in real samples of spices, flowers, and a beetle nut chewing sample illicitly containing tobacco.

Silver-modified nitrogen-doped graphene quantum dots as a sensor for formaldehyde in milk using headspace micro-extraction on a single-drop of aqueous nanoparticles dispersion

BackgroundFraudulent practices used to distort the quality of milk and derivatives include the addition of formaldehyde. ResultsA formaldehyde sensor was developed based on the luminescence of newly proposed N-doped graphene quantum dots modified with silver (N-GQDs-Ag) that were prepared using a simple method. A microdroplet of the nanoparticle dispersion was used to collect formaldehyde vapor by headspace single-drop micro-extraction (HS-SDME). After, the microdroplet was diluted in water, the nanoparticle photoluminescence quenching, caused by the analyte, was measured. The strong luminescent quenching allowed a detection limit at 1.7 × 10−4% w/v. Response was selective towards formaldehyde. SignificanceThe method was effective and a cost-effective method for screening analysis of milk samples with matrix interferences minimized due to the nature of nanoparticle (prepared using Tollen's reagent) and due to the probing at the headspace of the sample cell. Results were statistically similar to those obtained using liquid chromatography.

Gas flow-assisted headspace-single drop microextraction to determine benzene, toluene, ethylbenzene and xylene in aqueous samples

In this study, a gas flow-assisted headspace-single drop microextraction method was used to extract, pre-concentrate and measure benzene, toluene, ethylbenzene and xylenes compounds in aqueous samples through gas chromatography. This extraction method is very simple, cheap and environmentally friendly as well as consumes very small amounts of organic solvents. In this extraction method, occurring at the liquid–gas interface, the target analytes interact with the gas molecules in the bubbles. The independent variables such as solvent type, solvent volume, extraction time and ionic strength of the solution were investigated. Under optimal conditions, the dynamic linear range of the method was 0.74–100.0 μg L−1, limit of detection was 0.52–0.63 μg L−1 and, enhancement factor were 241–357. Intraday and interday precision for all the goal analytes were<5.1 % and 8.7 %, respectively. Finally, this extraction method was successfully used to extract, pre-concentrate and measure goal compounds in aqueous samples with asatisfactory recoveryin the range of 84.2–102.4 %.

Deep eutectic solvents-based headspace single-drop microextraction for the chromatographic determination of phenols and aliphatic alcohols in atmospheric air

In this work, the possibility for gas chromatography determination of volatile organic compounds in atmospheric air with preliminary microextraction into single drop of a deep eutectic solvent is presented for the first time. Highly toxic compounds (phenol, o-cresol) and aliphatic alcohols (methanol, n-butanol, n-pentanol) were selected as analytes for which low MPCs in the atmospheric air were established. A eutectic mixture of natural, environmentally friendly substances menthol and thymol was used as an extractant. The resulting eutectic solvent forms a stable drop that allows the rapid extraction of analytes from the gas phase. 30 min of sampling is enough to achieve sensitivity at the level of maximum permissible concentrations of these analytes in atmospheric air. At the same time, the volatility of the components of the eutectic compound themselves made it possible to introduce this solvent directly into the gas chromatograph without dilution. The developed procedure was used to analyze real air samples and standard gas mixtures. The limits of detection for analytes were in the range 0.001–0.01 mg L−1. The RSD for all analytes was <5 %. This sample preparation method can be easily and efficiently combined with subsequent chromatographic detection.

Three-Dimensional Printed Microdevice to Enhance Headspace Microextraction for Enrichment of Histamine in Milk.

In this work, a three-dimensional (3D) printed microdevice was designed to fix a drop of extractant that was applied to the enrichment of the most toxic biogenic amine, histamine, by headspace single-drop microextraction (HS-SDME). Concomitantly, based on the hybridization chain reaction of the histamine aptamer isothermal nucleic acid amplification strategy, a new fluorescence sensing method was developed to realize the highly sensitive detection of histamine. This is the first application of a 3D-printed microdevice to realize the HS-SDME process, which, among other advantages, effectively solves the problem of unstable and variable drop volumes that can plague traditional SDME and ensures the accuracy and repeatability of the extraction process. The calibration linear range of this SDME-fluorescence method was from 10 pM to 5 μM (R2 > 0.98), and the limit of detection was as low as 3 pM. In addition, the method was successfully demonstrated to determine histamine spiked in milk, with recoveries of between 93% and 104%, and relative standard deviations of less than 5%. The method established in this study has important practical significance for food safety monitoring and human health and provides new ideas and solutions for the design and application of biosensors.

Comparative study of headspace and headspace single drop microextraction combined with GC for the determination of methanol in wine

In this work, headspace single-drop microextraction (HS-SDME) method and headspace (HS) method were developed and compared to determine methanol by gas chromatography with flame ionization detector (GC-FID). Several factors influencing extraction efficiency, such as extraction time, temperature, sample volume, stirring rate and extraction solvent were investigated and the optimal conditions could be obtained using 2.0 µL DMF as extractant, 45 °C as heating temperature, 5 min as extraction time, 6 mL sample volume and 1.5 g KCl as addition of salt. The obtained dynamic range of HS-SDME-GC-FID was from 0.05 to 2 mg·L−1 with the limit of detection (LOD) of 0.001 mg·L−1 and that of HS-GC-FID was from 10.0 to 400.0 mg L−1 with LOD of 0.5 mg·L−1. The relative standard deviations (RSD) of HS-SDME-GC-FID was 1.9% (n = 5, C = 0.005 mg·L−1), 4.8%(n = 5, C = 0.02 mg·L−1) and 3.3%(n = 5, C = 0.1 mg·L−1), then the RSD of HS-GC-FID was 4.4%(n = 5, C = 5 mg·L−1), 5.8%(n = 5, C = 20 mg·L−1) and 4.0%(n = 5, C = 40 mg·L−1). Clearly, compared with HS-GC-FID, HS-SDME-GC-FID possessed lower LOD and better reproducibility and both of them were applied to determine methanol in imported wine and the recoveries for the spiked samples were between 83.99 and 117.24%. Overall, HS-SDME approach was confirmed to be a more sensitive and efficient sample pretreatment method and could separate matrix effectively.

Back Cover: Single bubble in‐tube microextraction coupled with capillary electrophoresis

DOI: 10.1002/elps.202100216 The cover picture shows three modes of headspace liquid phase microextraction (HS-LPME) in-line coupled with CE. Headspace single drop microextraction (HS-SDME)-CE: When a single drop of the acceptor phase (blue) is formed at the inlet of a separation capillary filled with a run buffer (pale pink), the analytes evaporated from the sample donor solution (green) into the HS are extracted into the drop leaving less- or non-volatile matrix components in the sample. After extraction, a portion of the drop containing enriched analytes is injected into the capillary for CE analysis. Due to the large volume ratio between the sample donor solution and the acceptor drop, and the large surface-to-volume ratio of the drop, the sample enrichment factors obtained with SDME are quite high for a given extraction time, compared with other conventional LPME techniques. However, it is critical to maintain the drop stably attached to the capillary during extraction and thus it is rather difficult to carry out SDME for a long time especially under harsh conditions such as elevated temperature. Headspace in-tube microextraction (HS-ITME)-CE: Using a liquid plug in the capillary inlet as an acceptor phase instead of a hanging drop, the shortcomings of the hanging drop can be resolved. In HS-ITME-CE, the capillary inlet containing the acceptor plug is simply placed in the HS above a sample solution. Since the acceptor phase is well protected by the capillary, a long extraction at a temperature as high as 90°C can be performed with ease. Furthermore, since the enriched acceptor plug is already inside the capillary, the whole extract can be utilized for the subsequent CE analysis without additional injection step. Single bubble in-tube microextraction (SB-ITME)-CE: For a short extraction time, the extraction efficiency of HS-SDME or HS-ITME was not maximized because it takes some time for the analytes to fill the HS and reach saturated concentrations, especially for compounds of low volatility. By using a single bubble as a micro-HS formed at the inlet of a separation capillary immersed in the sample donor solution, the HS extraction can be expedited without waiting for the HS equilibration. Since the surface-to-volume ratio of the submicroliter bubble is much higher than that of a conventional HS of a few milliliters or more, the analyte concentrations in the bubble can be replenished much more rapidly for short extraction times. SB-ITME demonstrated higher sample enrichments than HS-ITME for a short HS extraction of chlorophenols in water.

Deep Eutectic Solvents-Based Headspace Single Drop Microextraction for the Chromatographic Determination of Volatile Organic Compounds in Atmospheric Air

Deep Eutectic Solvents-Based Headspace Single Drop Microextraction for the Chromatographic Determination of Volatile Organic Compounds in Atmospheric Air

Gas Flow-Assisted Headspace-Single Drop Microextraction to Determine Benzene, Toluene, Ethylbenzene and Xylene in Aqueous Samples

Gas Flow-Assisted Headspace-Single Drop Microextraction to Determine Benzene, Toluene, Ethylbenzene and Xylene in Aqueous Samples