Photoassisted vapor generation in the presence of organic acids for ultrasensitive determination of Se by electrothermal-atomic absorption spectrometry following headspace single-drop microextraction

A method is described for the determination of selenium at the pg/mL level by electrothermal-atomic absorption spectrometry using in situ photogeneration of Se vapors, headspace sequestration onto an aqueous microdrop containing Pd(II) and subsequent injection in a graphite tube. Several organic acids (formic, oxalic, acetic, citric and ethylenediaminetetraacetic) have been tried for photoreduction of Se(IV) into volatile Se compounds under UV irradiation. Experimental variables such as UV irradiation time, organic acid concentration, Pd(II) concentration in the drop, sample and drop volumes, extraction time and pH were fully optimized. Low-molecular weight acids such as formic and acetic provided optimal photogeneration of volatile Se species at a 0.6 mol/L concentration. Citric and ethylenediaminetetraacetic acid allowed to use a concentration as low as 1 mmol/L, but extraction times were longer than for formic and acetic acids. Photogeneration of (CH₃)₂Se from Se(IV) in the presence of acetic acid provided a detection limit of 20 pg/mL, a preconcentration factor of nearly 285 and a precision, expressed as relative standard deviation, of 4%. Analytical performance seemed to depend not only on the photogeneration efficiency obtained with each acid but also on the stability of the vapors in the headspace. The method showed a high freedom from interferences caused by saline matrices, but interferences were observed for transition metals at a relatively low concentration.     

Needle‐trap device for the sampling and determination of chlorinated volatile compounds

A needle‐trap device, with immobilized sorbent inside the syringe, coupled with GC–MS was applied for air sampling and determination of chlorinated volatile organic compounds such as dichloromethane, trichloromethane, and tetrachloromethane. The application of a needle trap packed with combination of three sorbents including Tenax TA, Carbopack X, and Carboxen 1000 resulted in detection limits of few pg for chlorinated volatile compounds and recoveries of 99.2–102.8%. The extraction and desorption parameters were optimized within the study. As a result, the precision determined as RSD was equal to 5.05 and 3.03 and 6.52% for dichloromethane, trichloromethane, and tetrachloromethane, respectively. The storage time for chlorinated compounds up to 48 h and reusability of the needle‐trap device were verified. The obtained results have proved the ability of needle traps to compete with other solventless sampling and sample preparation extraction techniques.     

Sampling and determination of volatile organic compounds with needle trap devices

In this study, a sorbent was immobilized inside a needle resulting in the development of a needle trap (NT) device. This device was applied to extract organic components from gaseous samples and to introduce an enriched mixture into a conventional gas chromatography (GC) injector. Construction of this simple and integrated sampling/extraction/sample introduction device was optimized by considering different ways to immobilize a sorbent in the needle, packing single and multiple-layer sorbent beds, and applying different desorption strategies into the GC injector. A carrier gas system was modified to minimize the carryover for the needle trap with a sealed tip (NT-1), and a narrow-neckliner was used for the blunt-tip needle trap (NT-2). Breakthrough in the device was investigated by connecting two NT-2 devices in series. The needle trap performed very well as an exhaustive spot sampler, as well as in a time-weighted average (TWA) operation. The linear velocity of the mobile phase has no influence on the sampling rate of the needle trap. Validation results against the standard NIOSH 1501 method using charcoal tubes for indoor air surveys demonstrated good accuracy for the NT approach. The reproducibility of the NT-2 was about 1% for benzene. The detection limits for FID detection and for 25 ml gas sample were 0.23 ng/l, 2.10 ng/l and 1.12 ng/l for benzene, ethylbenzene and o-xylene, respectively.     

Solid-phase dynamic extraction for the enrichment of polar volatile organic compounds from water

Headspace solid-phase dynamic extraction coupled to gas chromatography-mass spectrometry (HS-SPDE-GC/MS) was evaluated for the trace determination of polar volatile organic compounds (PVOC) from aqueous matrices. The target compounds included 3 ethers and 12 alcohols. Four SPDE needle coatings with different phase polarities and sorption properties (WAX, 1701, PDMS, PDMS/AC) were tested. The effects of extraction temperature, number of extraction cycles, and ionic strength on partitioning of the target compounds have been investigated in detail, including the determination of salting-out constants for the investigated compounds. Lowest method detection limits (MDLs) were obtained with the WAX and the PDMS/AC phase. The WAX phase showed MDLs for ethers in the range of 0.06 microg/L (MTBE) to 0.8 microg/L (1,4-dioxane) and for alcohols between 0.02 microg/L (3-methyl-1-pentanol) and 3.5 microg/L (1-propanol). The evaluated MDLs for ethers with the PDMS/AC were in the range 0.06 microg/L (MTBE) to 1.2 microg/L (1,4-dioxane) and for alcohols between 0.004 microg/L (1-hexanol) and 4.9 microg/L (ethanol). Using either of these two phases, SPDE provides comparable or better sensitivities for the investigated compounds than other enrichment techniques, high sample throughput because of full automation, and short extraction times as well as a high robustness of the extraction phase because of its protection inside the steel needle. SPDE applicability has been demonstrated for the determination of fusel oils in different alcoholic beverages.     

The active and passive sampling of benzene, toluene, ethyl benzene and xylenes compounds using the inside needle capillary adsorption trap device

A new and simple method of solventless extraction of volatile organic compounds (VOCs) from air is presented. The sampling device has an adsorbing carbon coating on the interior surface of a hollow needle, and is called the inside needle capillary adsorption trap (INCAT). This paper describes a study of the reproducibility in the preparation and sampling of the INCAT device. In addition, this paper examines the effects of sample volume in active sampling and exposure time in passive sampling on the analyte adsorption. Analysis was achieved by sampling the air from an environmental chamber doped with benzene, toluene, ethyl benzene and xylenes (BTEX) compounds. Initial rates of adsorption were found to vary among the different compounds, but ranged from 0.0099 to 0.016 nmol h(-1) for passive sampling and from 2.2 to 10 nmol h(-1) for active sampling. Analysis was done by thermal desorption of the adsorbed compounds directly into a gas chromatograph injection port. Quantification of the analysis was done by comparison to actively sampled activated carbon solid phase extraction (SPE) measurements.     

Preparation and application of a coated‐fiber needle extraction device

In this study, a needle‐trap device with fibers coated with a molecularly imprinted polymer was developed for separation. A number of heat‐resistant Zylon filaments were longitudinally packed into a glass capillary, followed by coating with a molecularly imprinted polymer. Then, the molecularly imprinted polymer coating was copolymerized and anchored onto the surface of the fibers. The bundle of synthetic fibers coated with the molecularly imprinted polymer was packed into a 21G stainless‐steel needle and served as an extraction medium. The coated‐fiber needle extraction device was used to extract volatile organic compounds from paints and gasoline effectively. Subsequently, the extracted volatile organic compounds were analyzed by gas chromatography. Calibration curves of gaseous benzene, toluene, ethylbenzene, and o‐xylene in the concentration range of 1–250 μg/L were obtained to evaluate the method, acceptable linearity was attended with correlation coefficients above 0.998. The limit of detection of benzene, toluene, ethylbenzene, and o‐xylene was 11–20 ng/L using the coated‐fiber needle‐trap device. The relative standard deviation of needle‐to‐needle repeatability was less than 8% with an extraction time of 20 min. The loss rates after storage for 3 and 7 days at room temperature were less than 30%.     

Determination of Gaseous Formic and Acetic Acids by a Needle-Type Extraction Device coupled to a Gas Chromatography-Barrier Discharge Ionization Detector

Gaseous formic acid (FA) and acetic acid (AA) were concentrated by a needle-type extraction device, and the extracted analytes were determined using a gas chromatography-barrier discharge ionization detector. An activated carbon particle showed good extraction/desorption performance for FA and AA. The limit of quantification for FA and AA was 900 and 180 ng L^?1 at sample volumes of 100 mL, and 150 and 30 ng L^?1 at a sample volume of 600 mL, respectively. The storage performance of the analytes in the extraction needle was quantitatively evaluated at different temperatures, and the applicability of the proposed method to determine FA and AA in air samples was demonstrated.     

In-tube extraction for enrichment of volatile organic hydrocarbons from aqueous samples

In-tube extraction (ITEX) is a novel solventless extraction technique in which a headspace syringe with a needle body filled with a sorbent (here: Tenax TA) is used. The analytes are extracted from sample headspace by dynamic extraction. The needle body is surrounded by a separate heater, which is used for thermal desorption of analytes into the injection port of a GC system. We report here for the first time the optimization and evaluation of a fully automated analytical method based on ITEX. As target analytes, 19 common groundwater contaminants such as halogenated volatiles and monoaromatic compounds have been chosen. Method related parameters such as extraction temperature, number of extraction cycles, extraction and desorption volume as well as extraction and desorption flow rates were investigated in detail. The linear dynamic range of the ITEX method ranged over six orders of magnitude between 0.028 microg/L and 1218 microg/L with linear correlation coefficients between 0.990 and 0.998 for the investigated compounds. Method detection limits for monoaromatic compounds were between 28 ng/L (ethylbenzene) and 68 ng/L (1,2,4-trimethylbenzene). For halogenated volatile organic compounds, method detection limits between 48 ng/L (chloroform) and 799 ng/L (dichloromethane) were obtained. The precision of the method with external calibration was between 3.1% (chloroform ethylbenzene) and 7.4% (1,2,3-trimethylbenzene).     

Inside needle capillary adsorption trap device for headspace solid-phase dynamic extraction based on polyaniline/hexagonally ordered silica nanocomposite

Highly porous polyaniline/hexagonally ordered silica sorbent was used for fabrication of the inside needle capillary adsorption trap (INCAT) device. Polyaniline/SBA-15 nanocomposite was synthesized via chemical polymerization technique. The fabricated INCAT device was evaluated to the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography (GC)-mass spectrometry (MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, sampling flow rate, desorption time, and desorption temperature. In optimum conditions (extraction temperature 55 °C, extraction time 20 min, ionic strength 20% (w/v), flow rate 4.5 mL min(-1), desorption temperature 270 °C, desorption time 3 min) the repeatability for one INCAT device (n = 4), expressed as relative standard deviation, was between 4.2 and 10.2% for the tested compounds. The quantitation limits for the studied compounds were between 1 and 5 pg mL(-1). The developed method was successfully applied to spring water sample which was spiked with PAHs with the relative recovery percentages of 87.3-109.1%. The developed method offers the advantage of being simple to use, with shorter analysis times, lower cost of equipment, and thermal stability.     

Combination of corona discharge ion mobility spectrometry with a novel reagent gas and two immiscible organic solvent liquid-liquid-liquid microextraction for analysis of clomipramine in biological samples

A novel and sensitive method based on combination of two immiscible organic solvents hollow fiber-based liquid-liquid-liquid microextraction and corona discharge ion mobility spectrometry (HF-LLLME-CD-IMS) was employed for the analysis of clomipramine in human urine and plasma. The effect of formic, acetic and propionic acid as the reagent gas (dopant) on the corona discharge ion mobility signal was investigated. The influence of dopant amount was also studied. Optimum mass flow rates of the dopants were 3.7, 1.1 and 1.0 μmol min(-1) for formic, acetic and propionic acid, respectively. Experimental parameters influencing the extraction efficiency of HF-LLLME, such as NaOH concentration as donor solution, ionic strength of the sample, stirring rate, and extraction time were investigated and optimized. Under the optimum conditions, analytical parameters such as linearity, precision and limit of detection were also evaluated. The linear dynamic range was from 1 to 100 μg L(-1) (r(2)=0.9980) and the limit of detection was 0.35 μg L(-1). Intra- and inter-day precisions were satisfactory with a relative standard deviation (RSD) of 5.9 and 6.7%, respectively. The proposed method was satisfactorily applied for the determination of clomipramine in human plasma and urine.     

Dynamic headspace: a single-step extraction for isotopic analysis of microg/L concentrations of dissolved chlorinated ethenes

In this study a dynamic headspace method was developed to measure the carbon isotope values of dissolved chlorinated ethenes at microg/L concentrations. A gas chromatograph/combustion/isotope ratio mass spectrometer (GC/C/IRMS) was modified to include a headspace extraction system followed by a cryogenic trap. Extracting headspace from a 160 mL vial with 80 mL of aqueous solution and 40 g of NaCl for 8-12 min resulted in accurate and reproducible delta13C values for trichloroethene (TCE) and cis-1,2-dichloroethene (cDCE) at concentrations of 50-75 microg/L. Based on these results a conservative lower limit of quantitation of 38 microg/L can be calculated for these compounds. For more volatile compounds such as tetrachloroethene (PCE) and vinyl chloride (VC), field data analyzed using this method indicate a lower limit of quantitation in the tens of microg /L range.     

Comparison of Needle Concentrator with SPME for GC Determination of Benzene, Toluene, Ethylbenzene, and Xylenes in Aqueous Samples

A method of solventless extraction of volatile organic compounds from aqueous samples has been developed and validated. A new arrangement in which the internal volume of a needle capillary adsorption trap is completely filled with Porapak Q, as adsorbent material, and wet alumina, as a source of desorptive water vapor flow, is presented. The device has been used for head-space sampling of benzene, toluene, ethylbenzene, and xylenes (BTEX) from water samples and compared with solid-phase microextraction. Under the same sampling conditions the analytical characteristics of the device for the BTEX compounds are better than those of solid-phase microextraction. Limits of detection and quantification are below 0.5 μ g L⁻¹.     

Fiber-packed needle for dynamic extraction of aromatic compounds

A fiber-packed needle was developed as a novel extraction device for gas-chromatographic analysis of trace organic compounds in aqueous samples. In the extraction device, a bundle of the polymer-coated filaments as the sorbent material was longitudinally packed into a specially designed needle. The extraction was made by pumping the aqueous sample solution into the needle extraction device, and the subsequent desorption process was carried out with a flow of desorption solvent through the needle in a heated gas chromatograph injector. The needle device showed an excellent thermal stability for repeated use without any deterioration of extraction performance, and no carryover effect was observed after the optimization of the desorption conditions. Additionally, the extraction efficiency of the fiber-packed needle could be enhanced by optimizing the number of packed filaments. The selectivity for various compounds could be also tuned using an appropriate combination of the fibrous medium and the coating polymer. The relative standard deviation for run to run was from 3.88 to 4.55% (n = 5), and that for needle to needle was 7.21% (n = 3), clearly suggesting a good repeatability of the needle extraction technique developed. Upon successful optimization of the extraction conditions, a rapid extraction of trace organic compounds from an aqueous sample matrix was successfully demonstrated, where each extraction process was completed within 10 min.     

Evaluation of needle trap micro-extraction and automatic alveolar sampling for point-of-care breath analysis

Needle trap devices (NTDs) have shown many advantages such as improved detection limits, reduced sampling time and volume, improved stability, and reproducibility if compared with other techniques used in breath analysis such as solid-phase extraction and solid-phase micro-extraction. Effects of sampling flow (2–30 ml/min) and volume (10–100 ml) were investigated in dry gas standards containing hydrocarbons, aldehydes, and aromatic compounds and in humid breath samples. NTDs contained (single-bed) polymer packing and (triple-bed) combinations of divinylbenzene/Carbopack X/Carboxen 1000. Substances were desorbed from the NTDs by means of thermal expansion and analyzed by gas chromatography-mass spectrometry. An automated CO₂-controlled sampling device for direct alveolar sampling at the point-of-care was developed and tested in pilot experiments. Adsorption efficiency for small volatile organic compounds decreased and breakthrough increased when sampling was done with polymer needles from a water-saturated matrix (breath) instead from dry gas. Humidity did not affect analysis with triple-bed NTDs. These NTDs showed only small dependencies on sampling flow and low breakthrough from 1–5 %. The new sampling device was able to control crucial parameters such as sampling flow and volume. With triple-bed NTDs, substance amounts increased linearly with increasing sample volume when alveolar breath was pre-concentrated automatically. When compared with manual sampling, automatic sampling showed comparable or better results. Thorough control of sampling and adequate choice of adsorption material is mandatory for application of needle trap micro-extraction in vivo. The new CO₂-controlled sampling device allows direct alveolar sampling at the point-of-care without the need of any additional sampling, storage, or pre-concentration steps.     

高效液相色谱-质谱法测定性保健品中脱水吗啡、西地那非、前列地尔

建立了高效液相色谱-电喷雾电离质谱法同时测定性保健品中违禁药物脱水吗啡、西地那非和前列地尔的分析方法。样品用甲醇超声提取,用Zorbax Eclipse XDB-C18柱分离,以乙腈-0.5%甲酸水溶液作为流动相,以保留时间和质荷比对分离出的组分予以定性确证,用峰面积进行定量。结果表明,脱水吗啡、西地那非和前列地尔的线性范围分别为50.0~5000.0 μg/L,10.0~1000.0 μg/L和40.0~4000.0 μg/L,检出限(以信噪比为3计)分别为20.0,4.0和10.0 μg/L。样品的加标平均回收率为89%~95%,相对标准偏差为9.5%~11%。该方法简便、快速、灵敏,适用于含中药成分的性保健品中这3种药物的同时分析。     

New Grafted Nanosilica-Based Sorbent for Needle Trap Extraction of Polycyclic Aromatic Hydrocarbons from Water Samples Followed by GC/MS

In this work, the preparation of a new grafted nanosilica-based sorbent was extensively investigated. An inexpensive modifier, cis-9-octadecenoic acid (oleic acid) was selected to be grafted on the surface of the nanosilica particles as the support. The grafting process was accurately confirmed by Fourier transform infra-red spectrometry (FT-IR). Applicability of the prepared sorbent was thoroughly examined by needle trap extraction (NTE) method. The grafted sorbent was dispersed in the appropriate solvent and carefully packed inside a steel needle. Feasibility of the method was completely examined using polycyclic aromatic hydrocarbons (PAHs), as model compounds. For extraction of analytes from aqueous samples, the prepared needle trap device (NTD) was placed in the headspace of the sample and another needle was also inserted into the sample solution to purge the circulating headspace into the sample. For increasing the extraction efficiency, influencing parameters including extraction time and temperature, flow rate of analyte through the needle trap, the ionic strength, desorption temperature, and time were optimized. The limit of detection (LOD) and relative standard deviation (RSD) values of the method under optimized conditions were 2?C5 ng L^?1 and 1.1?C4.8%, respectively. The RSD% for fluorene was somewhat higher and a value of 16.8% at 40 ng L^?1 was achieved. Finally the developed method was applied to the analysis of tap water and Zayandeh-roud river samples and the relative recovery (RR %) values were found to be in the range of 77?C109%, under the optimized conditions.     

Microwave-assisted headspace controlled temperature liquid-phase microextraction of chlorophenols from aqueous samples for gas chromatography-electron capture detection

A modified headspace liquid-phase microextraction (HS-LPME) method was studied for the extraction of chlorophenols (CPs) from aqueous samples with complicated matrices, before gas chromatographic (GC) analysis with electron capture detection (ECD). Microwave heating was applied to accelerate the evaporation of CPs into the headspace, and an external-cooling system was used to control the sampling temperature. Conditions influencing extraction efficiency, such as the LPME-solvent, the sampling position of LPME, the sampling temperature, microwave power, and irradiation time (the same as sampling time), sample pH, and salt addition were thoroughly optimized. Experimental results indicated that the extraction of CPs from a 10mL aquatic sample (pH 1.0) was achieved with the best efficiency through the use of 1-octanol as solvent, microwave irradiation of 167W, and sampling at 45 degrees C for 10min. The detections were linear in the concentration of 5.0-100microg/L for 2,4-dichlorophenol (2,4-DCP), and 0.5-10microg/L for 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP). Detection limits were found to be 0.7, 0.04, 0.07, and 0.08microg/L for 2,4-DCP, 2,4,6-TCP, 2,3,4,6-TeCP, and PCP, respectively. A landfill leachate sample was analyzed with recovery between 83 and 102%. The present method was proven to serve as a simple, sensitive, and rapid procedure for CP analysis in an aqueous sample.     

Use of solid-phase microextraction for the detection of acetic acid by ion-trap gas chromatography-mass spectrometry and application to indoor levels in museums

A simple and efficient method using solid-phase microextraction (SPME) and gas chromatography-ion trap mass spectrometry (GC-ITMS) was developed for the analysis of acetic acid in air. The choice of the SPME fibre revealed to be critical as well as the sampling and desorption time. A dilution vessel was used for calibration. The precision of the method was found to be 4.7% relative standard deviation (RSD) and the detection limit 5.7 microg m(-3). The SPME-GC-MS technique was applied to the analysis of acetic acid in museum atmospheres.     

Dynamic hollow fiber protected liquid phase microextraction and quantification using gas chromatography combined with electron capture detection of organochlorine pesticides in green tea leaves and ready-to-drink tea

The dynamic hollow fiber protected liquid phase microextraction (DHFP-LPME) technique was evaluated for the extraction of organochlorine pesticides (OCPs) in green tea leaves and ready-to-drink tea prior to gas chromatography combined-electron capture detection (GC-ECD) analysis. A conventional microsyringe with a 1.5 cm length of hollow fiber attached to its needle was connected to a syringe pump to perform the extraction. The microsyringe was used as both the microextraction device and the sample introduction device for GC-ECD analysis. In this work, the organochlorine pesticides were extracted and condensed to a volume of 3 microl of organic extracting solvent (1-octanol) confined within a 1.5 cm length of hollow fiber. The effects of extraction solvent, extraction time, sample agitation, plunger speed, and extraction temperature and salt concentration content on the extraction performance were also investigated. Good enrichments were achieved (34-297-fold) with this method, and good repeatabilities of extraction were obtained, with full name (RSDs) below 12.57%. Detection limits were much below 1 microg l(-1) for ready-to-drink tea and much below 1 microg g(-1) for green tea leaves.     

A liquid-phase microextraction method, combining a dual gauge microsyringe with a hollow fiber membrane, for the determination of organochlorine pesticides in aqueous solution by gas chromatography/ion trap mass spectrometry

A liquid-phase microextraction (LPME) method has been demonstrated for the extraction and determination of organochlorine pesticides (OCPs) in aqueous solution. The method combines a dual gauge microsyringe with a hollow fiber membrane (LPME/DGM-HF) followed by detection by gas chromatography/ion trap mass spectrometry (GC/ITMS). The advantages include speed, low solvent and sample consumption, simplicity and ease of use. The extraction time, solvent selection, salt concentration and sample stirring rate have been investigated in order to optimize extraction efficiency. The viability is evaluated by measuring the linearity and detection limit of the five OCPs in aqueous solution. Detection linearity for the OCPs has been achieved over a range of concentrations between 1 and 500 microg/L (r2 > 0.930), with a detection limit of 0.1 microg/L for each OCP.