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

Quantum Chemistry Study on Cl-Initiated Reactions of 2-Chloropropane and 2-Methylpropanoyl Halogen (Cl, Br, F): Mechanism, Kinetics, and Atmospheric Implications

Halogenated volatile organic compounds (HVOCs) pose significant bioaccumulative and toxicological risks, necessitating effective strategies for their removal. Here, we show, through a computational study employing density functional theory and coupled cluster methods, the detailed mechanism and kinetic properties of Cl-initiated degradation reactions of 2-chloropropane (2-CP, (CH3)2CHCl) and 2-methylpropanoyl halide ((CH3)2CHCOX, X = Cl, Br, F). The reaction rate constants of all the channels were calculated by the canonical variational transition state theory (CVT) with the correction of the small curvature tunneling effect (SCT) at 200-1000 K. The subsequent transformation pathways of the major radical products of (CH3)2CHCl and (CH3)2CHCOCl in the presence of O2, NO, and HO2 radical were investigated. The results elucidate the reaction pathways and rate constants, which are in excellent agreement with the experimental data at 296 K. We further explore the atmospheric implications of these reactions by assessing the atmospheric lifetime (τ) and ozone depletion potential (ODP). Additionally, we delve into the aquatic toxicity and bioaccumulation potential of the reactants and their transformation products. This study not only advances our knowledge of the atmospheric fate of halogenated hydrocarbons but also underscores the importance of considering the environmental and toxicological impacts in the development of HVOC mitigation strategies.

Determination of Volatile Halogenated Hydrocarbons in Drinking and Environmental Waters by Headspace Gas Chromatography

Volatile halogenated hydrocarbons (VHHs) are annually produced and released into the environment, posing a threat to public health. In this study, a simple, rapid, sensitive and automated method based on headspace and gas chromatography (GC) with electron-capture detection was described for the determination of VHHs in different concentration levels in water samples. The proposed headspace GC method was initially optimized, and the optimum experimental conditions found were 10-mL water sample containing 20% w/v sodium chloride placed in a 20-mL vial and stirred at 60°C for 35 min, and then 14 VHHs were well separated on DB-35 MS capillary column with a split ratio of 12.5: 1. The limits of detection were in the low μg/L level, ranging between 0.01 and 0.6 μg/L. Finally optimized method was applied for determination 14 VHHs in drinking and environmental waters. The total mean concentrations of VHHs were 34.962, 26.183, 3.228 and 647.344 μg/L in tap water, purified water with 1-year-old filter element, seawater and effluents, respectively. However, no VHHs was detected in purified water with a new filter element. The main composition is different among different water matrix, which may be attributed to their different sources.

Compound-specific carbon isotope analysis of volatile organic compounds in complex soil extracts using purge and trap concentration coupled to heart-cutting two-dimensional gas chromatography-isotope ratio mass spectrometry

Compound-specific carbon isotope analysis (CSIA) is a powerful tool to track the origin and fate of organic subsurface contaminants including petroleum and chlorinated hydrocarbons and is typically applied to water samples. However, soil can form a significant contaminant reservoir. In soil samples, it can be challenging to recover sufficient amounts of volatile organic compounds (VOC) to perform CSIA. Soil samples often contain complex contaminant mixtures and gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) is highly dependent on good chromatographic separation due to the conversion to a single analyte. To extend the applicability of CSIA to complex volatile organic compound mixtures in soil samples, and to recover sufficient amounts of target compounds for carbon CSIA, we compared two soil extraction solvents, tetraglyme (TGDE) and methanol, and developed a heart-cutting two-dimensional GC-GC-C-IRMS method. We used purge & trap concentration of solvent-water mixtures to increase the amount of analyte delivered to the column and thus lower method detection limits. We optimized purge & trap and chromatographic parameters for twelve target compounds, including one suffering from poor purge efficiency. By using a 30 m thick-film non-polar column in the first and a 15 m polar column in the second dimension, we achieved good chromatographic separation for the target compounds in difficult matrices and high accuracy (trueness and precision) for carbon isotopic analysis. Tetraglyme extraction was shown to offer advantages over methanol for purge & trap concentration, leading to lower target compound method detection limits for CSIA of soil samples. The applicability of the developed method was demonstrated for a case study on soil extracts from a former manufacturing facility. Our approach extends the applicability of CSIA to an important matrix that often controls the long-term fate of contaminants in the subsurface.

Preparation of Carbotrap/silica composite for needle trap field sampling of halogenated volatile organic compounds followed by gas chromatography/mass spectrometry determination

BACKGROUND

A needle trap device (NTD) was packed with Carbotrap/silica composite sorbent and applied for field sampling of halogenated volatile organic compounds (HVOCs) followed by gas chromatography/mass spectrometry (GC/MS) separation and determination.

METHODS

Carbotrap B, as a highly pure surface sorbent, was prepared using sol-gel method to improve its surface properties for adsorption/desorption of the target analytes. The effects of important experimental variables on the sampling and determination of trichloroethylene (thrCE) and tetrachloroethylene (tetCE) using the proposed NTD-GC/MS strategy were evaluated and optimized.

RESULTS

The results showed that sampling temperature and relative humidity interfered with sampling efficiency of the developed method and peak area responses of the analytes decreased with increasing temperature and relative humidity. The peak areas of the analytes increased with raising desorption temperature from 180 to 250 °C, and increasing desorption time from 1 to 3 min. The carryover experiments showed that the carryover effect disappeared after 3 min of desorption time. The Limits of Detection (LODs) and Limits of Quantitation (LOQs) of the analytes were in the range 0.01-0.03 and 0.05-0.09, respectively.

CONCLUSIONS

The results indicated that the developed NTD-GC/MS procedure can be used as a technology with high sensitivity for the field sampling and determination of HVOCs.

Extraction and quantification of chlorophenolate molecules in soils spiked with 2,4-dichlorophenol and 2,4,5-trichlorophenol

The compounds 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) are classified as priority pollutants, with potentially hazardous impacts on the environment. In soil, dissociation of the phenol group occurs, resulting in the simultaneous presence of neutral phenol and anionic phenolate. Although the toxicity of 2,4-DCP and 2,4,5-TCP to soil microbiota has been suggested to be mainly due to the phenolate anion, this hypothesis cannot be tested due to the lack of appropriate methods of extracting and quantifying the anionic form of these compounds (unlike the neutral form, which can be easily quantified). In this study, we developed a method that enables extraction and quantification of phenolate ions. The method could therefore be used to elucidate the processes that regulate the behaviour of chlorophenolic molecules in soil and to clarify the distribution and toxicity of these compounds in the edaphic environment. The proposed method uses saline solutions (CaCl₂, KCl and K₂SO₄) of low ionic strength to extract the chlorophenolate anion from soil, followed by sequential transformation of the anion from the aqueous solution to an organic solvent that enables subsequent identification and quantification of the molecule by gas chromatography. Two soils of contrasting pH were used to test whether the proposed method was practicable. The method enabled analysis of the distribution of the neutral and anionic forms of the chlorophenols in both types of soil considered and revealed the influence of soil pH in this distribution.

Selective Extraction of Organic Contaminants from Soil Using Pressurised Liquid Extraction

This study focuses on the application of sorbents in pressurised liquid extraction (PLE) cell to establish a selective extraction of a variety of organic contaminants (polycyclic aromatic hydrocarbons (PAHs), chlorpyrifos, phenol, pentachlorophenol, and sterols) from soil. The selectivity and efficiency of each sorbent depend on the properties of the material, extracting solvent, capacity factor, organic compounds of interest, and PLE operating parameters (temperature, pressure, and extraction time). Several sorbents (silica, alumina, and Florisil) were evaluated and with the proper choice of solvents, polar and nonpolar compounds were successfully separated in two fractions. Nonpolar compounds (PAHs, chlorpyrifos, and pentachlorophenol) were recovered in the first fraction using a polar sorbent such as Florisil or alumina, andn-hexane as eluting solvent, while more polar compounds (phenol and sterols) were recovered in the second fraction using methanol. Silica (5 g) was found to be effective for selective extraction with the satisfactory recoveries for all compounds (PAHs from 87.1–96.2%, chlorpyrifos 102.9%, sterols from 93.7–100.5%, phenol 91.9%, and pentachlorophenol 106.2%). The efficiency and precision of this extraction approach and the existing EPA Method 3545 were compared.

Determination of sevoflurane and its metabolite hexafluoroisopropanol by direct injection of human plasma into gas chromatography-tandem mass spectrometry

The developed method for trace analysis of volatile components in plasma allows direct injection of up to 150 samples to the GC-MS/MS system without injector cleaning. This method requires no modification of plasma and the working environment does not interfere with the determination of these analytes. The method allows simultaneous quantification of non-polar sevoflurane and its polar metabolite hexafluoroisopropanol (free, unconjugated form). It is characterized by high repeatability and sensitivity with the detection limit of 0.009 mg L(-1) for sevoflurane and 0.018 mg L(-1) for hexafluoroisopropanol and the linear range 0.050-150 mg L(-1). The method was used to determine the concentration of sevoflurane and hexafluoroisopropanol in plasma samples of 7 patients undergoing general anesthesia with sevoflurane. The average concentration of sevoflurane and free hexafluoroisopropanol was 57.2 mg L(-1) and 0.39 mg L(-1), respectively. The method can be applied for clinical monitoring, as well as for analytical toxicology.

Evaluation of low-cost disposable polymeric materials for sorptive extraction of organic pollutants in water samples

The capabilities of four commercially available and low cost polymeric materials for the extraction of polar and non-polar contaminants (logK(ow)=-0.07-6.88, from caffeine to octocrylene, respectively) from water samples was compared. Tested sorbents were polyethersulphone, polypropylene and Kevlar, compared to polydimethylsiloxane as reference material. Parameters that affect the extraction process such as pH and ionic strength of the sample, extraction time and desorption conditions were thoroughly investigated. A set of experimental partition coefficients (K(pw)), at two different experimental conditions, was estimated for the best suited materials and compared with the theoretical octanol-water (K(ow)) partition coefficients of the analytes. Polyethersulphone displayed the largest extraction yields for both polar and non-polar analytes, with higher K(pw) and lower matrix effects than polydimethylsiloxane and polypropylene. Thus, a sorptive microextraction method, followed by large volume injection (LVI) gas chromatography-tandem mass spectrometry (GC-MS/MS), was proposed using the former sorbent (2 mg) for the simultaneous determination of model compounds in water samples. Good linearity (>0.99) was obtained for most of the analytes, except in the case of 4-nonylphenol (0.9466). Precision (n=4) at 50 and 500 ng L(-1) levels was in the 2-24% and limits of detection (LODs) were in the 0.6-25 ng L(-1) range for all the analytes studied.