Development of the detection threshold concept from a close look at sorption occurrence inside a glass vial based on the in-vial vaporization of semivolatile fatty acids

Full Evaporative Vacuum Extraction─A Quantitative and Green Approach for Analysis of Semivolatile Organic Compounds in Drinking Water and Surface Water Using GC-MS

Full evaporative vacuum extraction (FEVE) was developed in this work for analysis of a broad range of semivolatile organic compounds (SVOCs) in drinking water and surface water. Sorbent pens are used in a two-stage process that first evaporates the sample matrix through sorbent beds under vacuum to recover the lighter SVOCs, followed by the application of a higher temperature and stronger vacuum to the sample vial to recover the remaining heavier SVOCs once the matrix has evaporated. After extraction, the sorbent pens are desorbed into a GC-MS using a uniquely designed "splitless" delivery system to maximize sensitivity. Critical extraction and desorption parameters that affect the method performance were optimized. After FEVE, the sorbent pens can be stored for 7-10 days at room temperature while maintaining a less than 15% loss in analyte recovery. As a proof of concept, 10 drinking water and surface water samples were analyzed using this method. 69 analytes were detected in these water samples, with the highest concentration of 1986 ng/L for bromacil. Heptachlor epoxide, chlorpyrifos, metolachlor, butachlor, and 2,3',4',5-tetrachlorobiphenyl were detected in four samples. None of the analytes were above the health and safety thresholds set by California Proposition 65.

The feasibility and temporal storability of gas phase standards of volatile organic compounds prepared through liquid phase vaporization in polyester aluminum bags at room temperature

Currently, the presence of many classes of volatile organic compounds (VOCs) in indoor air is well recognized. There is an impetus to accurately quantify airborne VOCs for the proper assessment of their human health risks. VOC standards prepared in a solvent are often vaporized in N₂ gas-filled sampling bags for external calibration as the use of grab sampling bags is a common practice for the collection of real ambient air samples. Such practices can nontheless be subject to many sources of biases in their calibration (e.g., VOC chemical reaction with the solvent, adsorption on the bag interior surface, or leakage). The main goal of this work is to measure the temporal stability of 11 VOC targets (benzene, toluene, o-xylene, styrene, propionaldehyde, n-butyraldehyde, isovaleraldehyde, valeraldehyde, acrylonitrile, isoprene, and methyl ethyl ketone) selected in this research over 24 h which started 10 min after the injection and vaporization of liquid-phase standards (all prepared in methanol solvent) into polyester aluminum (PEA) bags containing 1 atm N₂. Although all tested VOCs showed gradual decreases of their concentrations (e.g., >17% in 24 h), the aromatic hydrocarbon VOCs (namely BTXS) yielded the best relative recoveries (e.g., decreases of 11%-30% in 24 h) and relative errors (e.g., relative standard error (RSE) = 2.14-3.59%) in 5 replicate tests. A good linear relationship was established between the 24 h VOC relative recovery and molecular weight (R² > 0.81). The results of this study offers valuable clues to properly reduce the bias in the calibration of gas-phase VOC standards when calibrating the system through the vaporization of liquid-phase VOC standards prepared in a solvent.

Recent advances in breath analysis to track human health by new enrichment technologies

Detection of biomarkers in exhaled breath has been gaining increasing attention as a tool for diagnosis of specific diseases. However, rapid and accurate quantification of biomarkers associated with specific diseases requires the use of analytical methods capable of fast sampling and preconcentration from breath matrix. In this regard, solid phase microextraction and needle trap technology are becoming increasingly popular in the field of breath analysis due to the unique benefits imparted by such methods, such as the integration of sampling, extraction, and preconcentration in a single step. This review discusses recent advances in breath analysis using these sample preparation techniques, providing a summary of recent developments of analytical methods based on breath volatile organic compounds analysis, including the successful identification of various biomarkers related to human diseases.

Insights into the storage stability of ammonia in polyester aluminum bags

A list of gaseous odorants such as ammonia (and hydrogen sulfide) are generally collected using rigid containers or flexible bags for quantitative analysis. The aim of this investigation was to assess the stability of polyester aluminum bags used for gaseous ammonia sampling and storage. To this end, ammonia standards were prepared at two concentration levels of low (7.8 ppm) and high concentrations (39 ppm) and stored in the polyester ammonia bags for durations of 0, 1, 2, 4, and 6 days. These samples were then analyzed at each interval by an impinger-based indophenol method utilizing a spectrophotometer. At each pre-set period, three different mass loadings of ammonia samples were collected from the storage bag to obtain response factors (RF) for comparison between different elapsed times set for the storage. Subsequently, the relative recovery values for each interval were computed by dividing the RF for each sampling day by that of the 0^th day. The relative recovery values for low and high concentration standards decreased with increasing storage time as 82.9% (day 1) to 36% (day 6) and 89.9% (day 1) to 59.7% (day 6), respectively. As such, the potentially superior recovery of ammonia from polyester aluminum bags was demonstrated (e.g., relative to other storage options introduced previously) to support its practical merit as storage media.

Confounding effect of benign pulmonary diseases in selecting volatile organic compounds as markers of lung cancer

Lung cancer (LC) is a leading cause of cancer-related morbidity and mortality globally, and exhaled breath testing has been considered as a fast, convenient and non-invasive way to diagnose LC in its early stages. Volatile organic compounds (VOCs), as markers of LC in exhaled breath, have been widely investigated for cancer diagnosis. However, few studies have reported on the interference of benign pulmonary diseases (BPD) in the selection of VOC markers for LC. During this study, 207 samples were analyzed using thermal desorption instrumentation/gas chromatography/mass spectrometry (TD-GCMS) to detect C₆-C₃₀ VOCs, and all samples were divided into four groups: LC group, BPD group, lung disease (LD) group (including LC group and BPD group) and healthy group. To make up for the deficiency of detecting low carbon hydrocarbons (<C₆), 277 samples were analyzed using solid-phase micro-extraction/gas chromatography/mass spectrometry (SPME-GCMS), divided among the four groups. VOC markers were selected by reference to the receiver operating characteristics curve. With the comparisons among the LC group, BPD group and healthy group from TD-GCMS and SPME-GCMS results, we found that exhaled VOCs are capable of discriminating LC group versus healthy group and BPD group versus healthy group with a consistency of 70%-80%. However, no VOCs can be selected with good discrimination capability between the LC group and BPD group, indicating that BPD interferes significantly in VOC marker selection for LC. To discriminate breath samples from the LD group and healthy group, 11 VOCs, including ten selected from TD-GCMS and one from SPME-GCMS, were chosen as markers for LD diagnosis. The sensitivity, specificity and overall accuracy of the diagnostic model established using ten VOCs were 80.8%, 84% and 82.7%, and those of the model established by using one VOC were 75.6%, 78.9% and 76.7%. These results validate that LD patients can be effectively discriminated and diagnosed using exhaled VOC analysis. (Clinical trial registration number: ChiCTR-DCD-15007106.).

Sorptive process and breakthrough behavior of odorous volatile compounds on inert surfaces

The use of glass impinger is an important device for sampling and handling when measuring volatile organic compounds (SVOCs). Thus, it is important to check for possible analyte losses to the inner glass surface when carrying out sample analysis with the aid of impinger system. In this research, we evaluated the sorptive loss patterns of vapor-phase semi-volatile organic compounds [SVOCs (n = 10): acetic acid (ACA), propionic acid (PPA), i-butyric acid (IBA), n-butyric acid (BTA), i-valeric acid (IVA), n-valeric acid (VLA), phenol (PhAl), p-cresol (p-C), indole (ID), and skatole (SK)] on inert surfaces of an impinger in reference to sampling bags. The gaseous standard of these SVOCs (48–406 ppb) in polyester aluminum (PEA) bags was passed through an empty impinger in 1 L steps. The exiting SVOCs were collected on three-bed sorbent tubes for subsequent analysis by thermal desorption-gas chromatography-mass spectroscopy (TD-GC-MS). Impinger wall sorption capacities ranged from 2.0 to 21.0 ng cm⁻². The 10% breakthrough adsorption capacities on the impinger wall for acids, phenols, and indoles ranged from 1.21 ± 0.15 to 5.39 ± 0.79, 0.92 ± 0.12 to 13.4 ± 2.25, and 4.47 ± 0.42 to 5.23 ± 0.35 ng cm⁻², respectively. The observed sorptive patterns suggest that the sorptive losses of the volatile fatty acids, phenols, and indoles can occur very effectively at low ppb levels onto a glass surface.

Analysis of volatile organic compounds in compost samples: A potential tool to determine appropriate composting time

Changes in volatile organic compound contents in compost samples during pig manure composting were studied using a headspace, solid-phase micro-extraction method (HS-SPME) followed by gas chromatography with mass spectrometric detection (GC/MS). Parameters affecting the SPME procedure were optimized as follows: the coating was carbon molecular sieve/polydimethylsiloxane (CAR/PDMS) fiber, the temperature was 60°C and the time was 30min. Under these conditions, 87 compounds were identified from 17 composting samples. Most of the volatile components could only be detected before day 22. However, benzenes, alkanes and alkenes increased and eventually stabilized after day 22. Phenol and acid substances, which are important factors for compost quality, were almost undetectable on day 39 in natural compost (NC) samples and on day 13 in maggot-treated compost (MC) samples. Our results indicate that the approach can be effectively used to determine the composting times by analysis of volatile substances in compost samples. An appropriate composting time not only ensures the quality of compost and reduces the loss of composting material but also reduces the generation of hazardous substances. The appropriate composting times for MC and NC were approximately 22days and 40days, respectively, during the summer in Zhejiang.

Comparison of Adsorption/Desorption of Volatile Organic Compounds (VOCs) on Electrospun Nanofibers with Tenax TA for Potential Application in Sampling

The objective of this study was to compare the adsorption/desorption of target compounds on homemade electrospun nanofibers, polystyrene (PS) nanofibers, acrylic resin (AR) nanofibers and PS-AR composite nanofibers with Tenax TA. Ten volatile organic compounds (VOCs) were analyzed by preconcentration onto different sorbents followed by desorption (thermal and solvent orderly) and analysis by capillary gas chromatography. In comparison to Tenax TA, the electrospun nanofibers displayed a significant advantage in desorption efficiency and adsorption selectivity. Stability studies were conducted as a comparative experiment between PS-AR nanofibers and Tenax TA using toluene as the model compound. No stability problems were observed upon storage of toluene on both PS-AR nanofibers and Tenax TA over 60 hours period when maintained in an ultra-freezer (-80°C). The nanofibers provided slightly better stability for the adsorbed analytes than Tenax TA under other storage conditions. In addition, the nanofibers also provided slightly better precision than Tenax TA. The quantitative adsorption of PS-AR nanofibers exhibited a good linearity, as evidenced by the 0.988-0.999 range of regression coefficients (R). These results suggest that for VOCs sampling the electrospun nanofibers can be a potential ideal adsorbent.

Metal organic frameworks as sorption media for volatile and semi-volatile organic compounds at ambient conditions

In this research, we investigated the sorptive behavior of a mixture of 14 volatile and semi-volatile organic compounds (four aromatic hydrocarbons (benzene, toluene, p-xylene, and styrene), six C₂-C₅ volatile fatty acids (VFAs), two phenols, and two indoles) against three metal-organic frameworks (MOFs), i.e., MOF-5, Eu-MOF, and MOF-199 at 5 to 10 mPa VOC partial pressures (25 °C). The selected MOFs exhibited the strongest affinity for semi-volatile (polar) VOC molecules (skatole), whereas the weakest affinity toward was volatile (non-polar) VOC molecules (i.e., benzene). Our experimental results were also supported through simulation analysis in which polar molecules were bound most strongly to MOF-199, reflecting the presence of strong interactions of Cu²⁺ with polar VOCs. In addition, the performance of selected MOFs was compared to three well-known commercial sorbents (Tenax TA, Carbopack X, and Carboxen 1000) under the same conditions. The estimated equilibrium adsorption capacity (mg.g⁻¹) for the all target VOCs was in the order of; MOF-199 (71.7) >Carboxen-1000 (68.4) >Eu-MOF (27.9) >Carbopack X (24.3) >MOF-5 (12.7) >Tenax TA (10.6). Hopefully, outcome of this study are expected to open a new corridor to expand the practical application of MOFs for the treatment diverse VOC mixtures.

A simple method for the accurate determination of the Henry's law constant for highly sorptive, semivolatile organic compounds

A novel technique is developed to determine the Henry's law constants (HLCs) of seven volatile fatty acids (VFAs) with significantly high solubility using a combined application of thermal desorber/gas chromatography/mass spectrometry (TD/GC/MS). In light of the strong sorptive properties of these semi-volatile organic compounds (SVOCs), their HLCs were determined by properly evaluating the fraction lost on the surface of the materials used to induce equilibrium (vial, gas-tight syringe, and sorption tube). To this end, a total of nine repeated experiments were conducted in a closed (static) system at three different gas/liquid volume ratios. The best estimates for HLCs (M/atm) were thus 7,200 (propionic acid), 4,700 (i-butyric acid), 4,400 (n-butyric acid), 2,700 (i-valeric acid), 2,400 (n-valeric acid), 1,000 (hexanoic acid), and 1,500 (heptanoic acid). The differences in the HLC values between this study and previous studies, if assessed in terms of the percent difference, ranged from 9.2% (n-valeric acid) to 55.7% (i-valeric acid). We overcame the main cause of errors encountered in previous studies by performing the proper correction of the sorptive losses of the SVOCs that inevitably took place, particularly on the walls of the equilibration systems (mainly the headspace vial and/or the glass tight syringe).