Sample preparation for gas chromatographic determination of halogenated volatile organic compounds in environmental and biological samples

In this review, the wide spectrum of the techniques of isolation and/or preconcentration and final determination of halogenated volatile organic compounds (HVOCs) in water, air, soil, sediment and biological fluids are presented and discussed. The techniques discussed are solvent microextraction, solid phase extraction, gas extraction (static and dynamic techniques), membrane processes and passive sampling. Also, direct techniques, such as direct aqueous injection into gas chromatography (GC) column and membrane inlet mass spectrometry, are presented. Main attention is paid to the practical application of these techniques during all HVOCs determination.     

Determination of volatile organics in drinking water with USEPA method 524.2 and the ion trap detector

New drinking water regulations require the monitoring of eight volatile organic compounds that have established maximum contaminant levels (MCLs) and 51 other volatile organics for which MCLs are not established. A laboratory analytical method (Method 524.2) for the determination of 58 of these compounds is investigated, and precision and accuracy data are obtained. The method uses a standard inert gas purge extraction, isolation of the volatile organics on a three-stage solid-phase trap, thermal desorption into a gas chromatograph, separation with a fused-silica capillary column, and identification and measurement with a relatively low cost, benchtop ion trap detector that functions as a mass spectrometer. At a concentration of 2 micrograms/L (2 parts per billion), the grand mean measurement accuracy for 54 compounds was 95% of the true value with a mean relative standard deviation (RSD) of 4%. At 0.2 micrograms/L (200 parts per trillion), the grand mean measurement accuracy for 52 compounds was 95% of the true value with a mean RSD of 3%.     

Analysis of organic compounds in environmental samples by headspace solid phase microextraction

The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds. This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.     

Microanalysis of Volatile Organic Compounds (VOCs) in Water Samples – Methods and Instruments

Volatile organic compounds (VOCs), due to their toxicity and persistence in the environment, are particularly important pollutants. Some of these compounds are mutagens, teratogens or carcinogens, while others are responsible for the degradation of organoleptic parameters such as taste and odour of water. This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in water samples. A wide spectrum of techniques for the isolation and preconcentration of the aforementioned pollutants for trace organic analysis by gas chromatography are presented and discussed. The advantages and disadvantages of these techniques are discussed and novel developments are also taken into consideration.     

Rapid Extraction of Volatile Compounds Using a New Simultaneous Microwave Distillation: Solvent Extraction Device

Simultaneous distillation–extraction (SDE) is routinely used by analysts for sample preparation prior to gas chromatography analysis. In this work, a new process design and operation for microwave assisted simultaneous distillation–solvent extraction (MW-SDE) of volatile compounds was developed. Using the proposed method, isolation, extraction and concentration of volatile compounds can be carried out in a single step. To demonstrate its feasibility, MW-SDE was compared with the conventional technique, SDE, for gas chromatography-mass spectrometry (GC-MS) analysis of volatile compounds in a fresh aromatic herb, Zygophyllum album L., a wild salty desert herb belonging to the family Zygophyllaceae. SDE method required a long time (3 h) to isolate the volatile compounds, and large amounts of organic solvent (200 mL of hexane) for further extraction, while MW-SDE needed shorter time (only 30 min) to prepare the sample, and less amount of organic solvent (10 mL of hexane). These results show that MW-SDE–GC-MS is a simple, rapid and solvent-less method for the determination of volatile compounds from aromatic plants.     

Selective removal of water in purge and cold-trap capmary gas chromatographic analysis of volatile organic traces in aqueous samples

The design and features of an on-line purge and cold-trap pre-concentration device for rapid analysis of volatile organic compounds in aqueous samples are discussed. Excessive water is removed from the purge gas by a condenser or a water permeable membrane in order to avoid blocking of the capillary cold-trap. Synthetic mixtures covering concentrations ranging from tenths to tens of ppb's and different chemical classes are used to study the effect of various process factors on the efficiency and selectivity of water removal as well as on the purging recovery. The importance of the concentration of the solutes, the flow rate in conjunction with the volume of the purge gas, and the temperature of the condenser, the cold-trap and the sample is emphasized. Theoretical models describing the purge process and the blocking of the cold-trap agree fairly well with the highly reproducible experimental results (σ = 2–4%). Both the condenser and the Nafion membrane successfully remove water, although some compounds, dependent on volatility and polarity, are partly or completely lost. It is shown that non-polar volatile organic compounds are efficiently enriched so that recoveries between 80–100% and a detection limit of 1 ppt can be obtained. The applicability of the system is illustrated on some examples.     

Application of dispersive liquid–liquid microextraction and gas chromatography with mass spectrometry for the determination of oxygenated volatile organic compounds in effluents from the production of petroleum bitumen

We present a new procedure for the determination of oxygenated volatile organic compounds in samples of postoxidative effluents from the production of petroleum bitumens using dispersive liquid–liquid microextraction and gas chromatography with mass spectrometry. The eight extraction parameters were optimized for 43 oxygenated volatile organic compounds. The detection limits obtained ranged from 0.07 to 0.82 μg/mL for most of the analytes, the precision was good (relative standard deviation below 2.91% at the 5 μg/mL level and 4.75% at the limit of quantification), the recoveries for the majority of compounds varied from 70.6 to 118.9%, and the linear range was wide, which demonstrates the usefulness of the procedure. The developed procedure was used for the determination of oxygenated volatile organic compounds in samples of raw postoxidative effluents and in effluents after chemical treatment. In total, 23 compounds at concentration levels from 0.37 to 32.95 μg/mL were identified in real samples. The same samples were also analyzed in the SCAN mode, which resulted in four more phenol derivatives being identified and tentatively determined. The studies demonstrated the need for monitoring volatile organic compounds content in effluents following various treatments due to the formation of secondary oxygenated volatile organic compounds.     

Fast analysis of volatile organic compounds and disinfection by-products in drinking water using solid-phase microextraction-gas chromatography/time-of-flight mass spectrometry

A fast method was developed for the extraction and analysis of volatile organic compounds, including disinfection by-products (DBPs), with headspace solid-phase microextraction (HS-SPME) and gas chromatography/mass spectrometry (GC/MS) techniques. A GC/time-of-flight (TOF)-MS instrument, which had fast acquisition rates and powerful deconvolution software, was used. Under optimum conditions total runtime was 45s. Volatile organic compounds (VOCs), including purgeable A and B compounds (listed in US Environmental Protection Agency method 624), were identified in standard water samples. Extraction times were 1min for more volatile compounds and 2min for less volatile compounds. The method was applied to the analysis of water samples treated under different disinfection processes and the results were compared with those from a liquid-liquid extraction method.     

Method for evaluating the kinetics of dynamic gas extraction

Summary New methods have been developed for the study of the kinetics of the dynamic gas extraction process based on instrumental recording of the extraction curve and division into half-lives whose temporal values can be employed for the calculation of the distribution coefficient. The dependence of this process on the thermodynamical system as well as on instrumental factors for the testing of field equipment was determined using toluene dissolved in water, by means of which in connection with sorption process isolation, enrichment and preservation of volatile organic compounds in samples were achieved.

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Auswertung der Kinetik der dynamischen Gasextraktion

     

Comprehensive Study of the Organic‐Solvent‐Free CDI‐Mediated Acylation of Various Nucleophiles by Mechanochemistry

Acylation reactions are ubiquitous in the synthesis of natural products and biologically active compounds. Unfortunately, these reactions often require the use of large quantities of volatile and/or toxic solvents, either for the reaction, purification or isolation of the products. Herein we describe and discuss the possibility of completely eliminating the use of organic solvents for the synthesis, purification and isolation of products resulting from the acylation of amines and other nucleophiles. Thus, utilisation of N,N′‐carbonyldiimidazole (CDI) allows efficient coupling between carboxylic acids and various nucleophiles under solvent‐free mechanical agitation, and water‐assisted grinding enables both the purification and isolation of pure products. Critical parameters such as the physical state and water solubility of the products, milling material, type of agitation (vibratory or planetary) as well as contamination from wear are analysed and discussed. In addition, original organic‐solvent‐free conditions are proposed to overcome the limitations of this approach. The calculations of various green metrics are included, highlighting the particularly low environmental impact of this strategy.     

Evaluation of simulant migration of volatile nitrosamines from latex gloves and balloons by HS-SPME-GC-MS

Nitrosamines are a group of carcinogens that have been found in various latex products. Methods have been developed for extraction, concentration and detection of simulant migration of volatile nitrosamines from latex gloves and balloons. After glove samples or balloon samples were treated with artificial sweat and artificial saliva, headspace solid-phase microextraction and gas chromatography with mass spectrometer detection were performed. Eight volatile nitrosamines were extracted by a fused silica fiber coated with carboxen-polydimethylsioxane, and solid-phase microextraction conditions were optimized. The developed method was successfully used to analyze simulant migration of volatile nitrosamines from latex gloves and balloons. The described methods are rapid and simple, with adequate sensitivity and without organic solvent.     

气提吸附／热脱附／气相色谱－质谱法分析污水中的痕量有机物

采用气提吸附／热脱附／气相色谱－质谱法对齐鲁公司所处地区工业污水进行分析。方法采用Ｔｅｎａｘ－ＧＣ吸附剂对样品进行气提吸附，脱附时样品直接进入色谱仪汽化室，一次进样即可完成全组分分析，共检测出含四氯丙醚在内的４０种有机组分，测定了各组分的程序升温保留指数。气相色谱－质谱法测定出四氯丙醚三个异构体的结构。     

Layered double hydroxide/poly(vinylpyrrolidone) coated solid phase microextraction Arrow for the determination of volatile organic compounds in water

Today, wide variety of adsorbents have been developed for sample pretreatment to concentrate and separate harmful substances. However, only a few solid phase microextraction Arrow adsorbents are commercially available. In this study, we developed a new solid phase microextraction Arrow coating, in which nanosheets layered double hydroxides and poly(vinylpyrrolidone) were utilized as the extraction phase and poly(vinyl chloride) as the adhesive. This new coating entailed higher extraction capacity for several volatile organic compounds (allyl methyl sulfide, methyl propyl sulfide, 3‐pentanone, 2‐butanone, and methyl isobutyl ketone) compared to the commercial Carboxen 1000/polydimethylsiloxane coating. Fabrication parameters for the coating were optimized and extraction and desorption conditions were investigated. The validation of the new solid phase microextraction Arrow coating was accomplished using water sample spiked with volatile organic compounds. Under the optimal conditions, the limits of quantification for the five volatile organic compounds by the new solid phase microextraction Arrow coating and developed gas chromatography with mass spectrometry method were in the range of 0.2‐4.6 ng/mL. The proposed method was briefly applied for enrichment of volatile organic compounds in sludge.     

Headspace Single-Drop Microextraction with Gas Chromatography for Determination of Volatile Halocarbons in Water Samples

A simple, rapid and inexpensive procedure for extraction and analysis of volatile halocarbons in water samples was presented using the headspace single-drop microextraction (HS-SDME) technique and gas chromatography with microcell electron capture detector (GC-μECD). Operation parameters. such as extraction solvent. headspace volume. organic drop volume. salt concentration. temperature and sampling time, were studied and optimized. Extraction of 10 volatile halocarbon compounds was achieved using the optimized method. Calibration curves of 10 target compounds yielded good linearity in the respective range of concentration (R ² ≥ 0.9968, chlorodibromomethane in the concentration range of 0.05–50 μg/L). The limits of detection were found between 0.002 (tetrachloroethene) and 0.374μg/L (1,1,2-trichloroethane). and relative standard deviations (RSD%) ranged between 4.3 (chloroform) and 9.7% (1,1,2,2-tetrachloroethane). Spiked recoveries of tap water and ground water agreed well with the known values between 118.97 (20.0μg/L of 1,1,2-trichloroethane) and 82.61% (10.0μg/L of tetrachloroethene), demonstrating that the HS-SDME combined GC-μECD was a useful and reliable technique for the rapid determination of volatile halocarbon compounds in water samples.     

Selectivity of solid-phase extraction phases in the determination of biodegradation products

The extraction techniques connected with gas chromatography were used to describe quantitatively and qualitatively the biodegradation process. We investigated the biodegradation of hydrocarbons and non-ionic surfactants. Solid-phase extraction (SPE) and liquid-liquid extraction were used for the isolation of the non-degraded compounds and their degradation products. The selectivity of SPE has a significant influence on the isolation and preconcentration of organic compounds from water.     

A microfluidic device for open loop stripping of volatile organic compounds

The detection of volatile organic compounds is of great importance for assessing the quality of water. In this contribution, we describe a miniaturized stripping device that allows fast online detection of organic solvents in water. The core component is a glass microfluidic chip that facilitates the creation of an annular-flowing stream of water and nitrogen gas. Volatile compounds are transferred efficiently from the water into the gas phase along the microfluidic pathway at room temperature within less than 5 s. Before exiting the microchip, the liquid phase is separated from the enriched gas phase by incorporating side capillaries through which the hydrophilic water phase is withdrawn. The gas phase is conveniently collected at the outlet reservoir by tubing. Finally, a semiconductor gas sensor analyzes the concentration of (volatile) organic compounds in the nitrogen gas. The operation and use of the stripping device is demonstrated for the organic solvents THF, 1-propanol, toluene, ethylbenzene, benzaldehyde, and methanol. The mobile, inexpensive, and continuously operating system with liquid flow rates in the low range of microliters per minute can be connected to other detectors or implemented in chemical production line for process control.

Ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction for the separation and determination of estrogens in water samples by high‐performance liquid chromatography with fluorescence detection

An ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction method was proposed for the extraction and concentration of 17‐α‐estradiol, 17‐β‐estradiol‐benzoate, and quinestrol in environmental water samples by high‐performance liquid chromatography with fluorescence detection. 1‐Hexyl‐3‐methylimidazolium tetrafluoroborate was applied as foaming agent in the foam flotation process and dispersive solvent in microextraction. The introduction of the ion‐pairing and salting‐out agent NH₄PF₆ was beneficial to the improvement of recoveries for the hydrophobic ionic liquid phase and analytes. Parameters of the proposed method including concentration of 1‐hexyl‐3‐methylimidazolium tetrafluoroborate, flow rate of carrier gas, floatation time, types and concentration of ionic liquids, salt concentration in samples, extraction time, and centrifugation time were evaluated. The recoveries were between 98 and 105% with relative standard deviations lower than 7% for lake water and well water samples. The isolation of the target compounds from the water was found to be efficient, and the enrichment factors ranged from 4445 to 4632. This developing method is free of volatile organic solvents compared with regular extraction. Based on the unique properties of ionic liquids, the application of foam floatation, and dispersive liquid–liquid microextraction was widened.     

Stability of compressed gas mixtures containing low level volatile organic compounds in aluminum cylinders

Compressed gas mixtures containing up to twenty-six volatile organic compounds (VOCs) in a balance of nitrogen have been prepared and analyzed at the National Institute of Standards and Technology (NIST). The mixtures are contained in aluminum cylinders and the hydrocarbons included are aromatic or aliphatic, both saturated and unsaturated and some containing a halogen, oxygen or nitrogen atom. The individual compounds are present at concentrations ranging from 0.1–3000 nmol/mol and the relative standard uncertainty in the concentration of each is between ±2–5%. The stability of the mixtures over various time intervals is discussed.     

A Simple Liquid Chromatographic Method for Quantitative Extraction of Hydrophobic Compounds from Aqueous Solutions

Abstract

We are reporting a rapid, high-capacity liquid chromatographic method for quantitative extraction and concentration of hydrophobic compounds from biological fluids and aqueous solutions. Samples are injected into commerically-available cartridges (Sep-Pak C^18R) containing a microparticulate, reversed phase packing which retains hydrophobic compounds. Inorganic salts and organic hydrophilic contaminants are removed with a water wash. Hydrophobic compounds are eluted quantitatively with minimal volumes (～5 ml) of organic solvents. As demonstrated with radiolabeled taurocholate, thin-láyer chromatography, enzymatic fluorimetry and capillary gas chromatography, complete recovery of bile salts from large volumes of urine, serum, amniotic fluid and hydrolysis reaction mixtures was achieved at flow rates up to 20 ml/min. A single cartridge concentrated approximately 50 mg of either taurocholate or the more polar bile salt, taurolithocholate sulfate. The technique is simple and applicable to the isolation of a wide range of hydrophobic compounds from aqueous solutions.     

Sample preparation for the analysis of volatile organic compounds in air and water matrices

This review summarizes literature data from the past 5 years on new developments and/or applications of sample preparation methods for analysis of volatile organic compounds (VOC), mainly in air and water matrices. Novel trends in the optimization and application of well-established airborne VOC enrichment techniques are discussed, like the implementation of advanced cooling systems in cryogenic trapping and miniaturization in adsorptive enrichment techniques. Next, focus is put on current tendencies in integrated sampling-extraction-sample introduction methods such as solid phase microextraction (SPME) and novel in-needle trapping devices. Particular attention is paid to emerging membrane extraction techniques such as membrane inlet mass spectrometry (MIMS) and membrane extraction with a sorbent interface (MESI). For VOC enrichment out of water, recent evolutions in direct aqueous injection (DAI) and liquid-liquid extraction (LLE) are highlighted, with main focus on miniaturized solvent extraction methods such as single drop microextraction (SDME) and liquid phase microextraction (LPME). Next, solvent-free sorptive enrichment receives major attention, with particular interest for innovative techniques such as stir bar sorptive extraction (SBSE) and solid phase dynamic extraction (SPDE). Finally, recent trends in membrane extraction are reviewed. Applications in both immersion and headspace mode are discussed.