Headspace Method Research Articles

Changes in N2O emissions from agricultural water samples with storage time at low temperature measured with headspace methods

Changes in N2O emissions from agricultural water samples with storage time at low temperature measured with headspace methods

Efficient Estimation of ascorbic acid in vitamin C tablets enabled by phase-transfer strategy

In this paper, we introduced a novel phase-transfer strategy tailored for the efficient batch detection of ascorbic acid in vitamin C tablets. This method entailed the reaction between ascorbic acid and an excess of potassium permanganate. Subsequent reaction of the residual potassium permanganate with sodium oxalate in an acidic medium led to the generation of carbon dioxide. The quantification of the produced carbon dioxide was achieved using headspace GC, enabling the indirect measurement of ascorbic acid. The obtained findings revealed that the headspace method exhibited satisfied precision with a relative standard deviation of less than 2.11 % and high sensitivity with a limit of quantitation of 0.27 μmol. These results firmly establish the reliability of this innovative approach for determining ascorbic acid. In addition, the highly automated feature of headspace method significantly enhances the efficiency of batch sample detection and reduces the errors caused by human operation. Thus, the adoption of the transformed phase strategy has demonstrated its effectiveness in assessing ascorbic acid, especially for large-scale sample analysis in industrial applications, owing to its efficiency, precision, and sensitivity.

The remarkable effects of the non-volatile matrix of wine on the release of volatile compounds evaluated by analysing their release to the headspaces

Six Spanish wines with different wine-making styles were completely dearomatised and later reconstituted to their original volume with a standard volatile solution containing 15 wine aroma compounds with broad differences in physicochemical characteristics. The headspace composition of the reconstituted wines was evaluated using an automated dynamic headspace (DHS) method combined with thermal desorption (TD) and gas chromatography–mass spectrometry (GC–MS). This method provides a snapshot of the volatile profiles transferred to the headspace in non-equilibrium conditions. The results showed that the non-volatile matrix of the wine significantly affected the transference to the headspace of the 15 aroma compounds. Differences between wines for butanoic and hexanoic acids, DMS and vanillin are above factors 5, 4 or 3, respectively, while for ethyl acetate, ethyl decanoate, 3-methylbutan-1-ol, 2-phenylethan-1-ol or 4-ethylphenol are close to a factor 2. Only ethyl butanoate was uniformly transferred. The release of DMS was related to copper levels, while pH explained part of the release of fatty acids. However, most effects of volatility are difficult to explain. Results strongly indicate that a sample-specific correction for volatility is required to interpret the sensory effects of aroma volatiles.

Floral scents of the protogynous aroid Spathiphyllum cannifolium: Investigating the chemistry and timing of emission at female and male phases

AbstractSpathiphyllum is a Neotropical aroid genus whose inflorescences are composed of protogynous bisexual flowers that emit strong perfumes. These scents serve as both attractants and rewards for male euglossine pollinators. We investigated the inflorescence scent of S. cannifolium, asking whether inflorescence at female and male phases differ in scent traits. For this, we collected scent samples from inflorescence at the two phases using dynamic headspace methods and analyzed them by a gas chromatograph coupled to a mass spectrometer (GC‐MS). The inflorescence scent of S. cannifolium consisted of 26 compounds, with benzyl acetate as major component (ca. 80% of the scent bouquet). We found no quantitative or qualitative differences between scents of inflorescences at female and male phases, nor in the emission time. However, when considering the timing of scent emission among individuals, we observed two general plant groups. Some individuals emitted more scent at 06:00, while others emitted more scent at 09:00, independent of the sexual phase. The similarity of floral scents between the sexes might promote floral constancy by male euglossine pollinators and consequently alternate pollinator flow between inflorescences at female and male phases. The occurrence of the two general patterns of scent emission can be interpreted as a way to ensure the pollination service. Since plants emit scents in the morning, even outside the peak emission period, this would enable these plants to attract pollinators that are active at different times than the peak emission of floral scents. This way, it would ensure the flow of pollen, even if it occurs at a low frequency.

Microplastic Volatile Organic Compounds Found within Chrysaora chesapeakei in the Patuxent River, Maryland

Microplastics are tangible particles of less than 0.2 inches in diameter that are ubiquitously distributed in the biosphere and accumulate in water bodies. During the east-coast hot summers (23–29 °C) of 2021 and 2022, June through September, we captured copious amounts of the jellyfish Chrysaora chesapeakei, a predominant species found in the Patuxent River of the Chesapeake Bay in Maryland on the United States East Coast. We determined that their gelatinous bodies trapped many microplastics through fluorescent microscopy studies using Rhodamine B staining and Raman Spectroscopy. The chemical nature of the microplastics was detected using gas chromatography–mass spectroscopy headspace (SPME-GC-MS) and solvent extraction (GC-MS) methods through a professional commercial materials evaluation laboratory. Numerous plastic-affiliated volatile organic compounds (VOCs) from diverse chemical origins and their functional groups (alkanes, alkenes, acids, aldehydes, ketones, ethers, esters, and alcohols) along with other non-microplastic volatile organic compounds were observed. Our findings corroborate data in the available scientific literature, distinguishing our finding’s suitability.

Greenhouse gases capture applying impregnated silica with ionic liquids, deep eutectic solvents, and natural deep eutectic solvents.

The development of technologies to capture greenhouse gases (GHGs) like carbon dioxide (CO2) and nitrous oxide (N2O) is vital for climate change mitigation. Ionic liquids (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NADES) are promising absorbents to abate GHGs emissions. However, their high viscosity limits the gas-liquid contact, as consequence of the mass transfer. To overcome this, their impregnation onto porous silica gel has been carried out, increasing the gas-liquid contact area. The present study analyzes the effect of size particle of silica gel impregnated with ILs, DES, and NADES over the CO2 and N2O capture at atmospheric conditions. The degree of impregnation of silica particles was determined by thermogravimetric analysis (TGA). The identification of functional groups present on the surface of silica, ILs, DES, and NADES was performed using Fourier-transform infrared spectroscopy (FTIR), and their crystalline structure was determined by X-ray diffraction (XRD). The partition coefficient of CO2 and N2O between gas and ILs, DES, and NADES was determined by a static headspace method. Results show that the degree of solvent impregnation on silica gel ranged from 36.8 to 43.0% w/w, the partition coefficient of CO2 in the impregnated silica varied from 0.005 to 0.067, and for N2O, from 0.005 to 0.032. This suggests that impregnated particles have a greater affinity for N2O compared to CO2. Using impregnated particles requires only 40% of the bulk solvent to achieve a similar GHG capture capacity compared to using bulk solvents.

Nanofiber films based on anthocyanins for quantitative detection of pathogenic bacteria

Pathogenic microbial infections have been regarded as one of the serious factors triggering serious food poisoning and infectious disease outbreaks. Therefore, early detection of pathogenic bacteria is of great importance for food safety, environmental monitoring, and clinical diagnosis. Here, nanofiber sensing films for the visual detection of S. aureus concentrations using polyvinyl alcohol (PVA) as a substrate and anthocyanin as an indicator material were prepared by electrostatic spinning technology. To avoid the loss of dye migration and side effects on the bacteria during the contact detection method, the headspace method was used to detect the concentration of bacteria. The results show that the fiber films can monitor S. aureus at 2 × 102 cfu/mL (ΔE = 7.6) by headspace. Scatter density matrix and correlation analysis yielded that the b* value of the film was the main factor in the variation of bacterial concentrations. Combined with a support vector machine (SVM) supervised learning algorithm for non-linear data, the model was trained to accurately classify S. aureus concentrations with an accuracy of 91%, which is important for accurately controlling pathogenic bacteria and safeguarding human health.

First forensic quantification, source-identification and health risk estimation of volatile organic carbons in the anthropogenically impacted Omi-Asoro Stream in Ilesa, Nigeria

This study quantified the volatile organic compounds (VOCs) in the Omi-Asoro Stream located in Ilesa town, Nigeria, to understand their sources and health risks to humans. The VOCs were measured in 2023 according to the US EPA equilibrium headspace method using a gas chromatograph (GC) and detected by a flame ionization detector (FID). Their human health risk assessments via ingestion and dermal contact were also estimated. The results showed that dissolved oxygen (DO) ranged 0.5–4.8 mg/L. Chemical oxygen demand (COD) was exceptionally high (March: 181.3 ± 45.5 mg/L; July: 180.7 ± 25.7 mg/L) in the industrial waste discharge area. Twenty-two and eighteen sets of VOCs were detected in March and July, respectively. 1,2-dibromo-3-chloropropane (DBCP) was the predominant VOC in the stream accounting for 18% (March) and 19% (July). DBCP, 1,2-dichlorobenzene+nbutylbenzene (oDCB+bBZ) and hexachlorobutadiene+1,2,4-trichlorobenzene (HCBD+TCB) were ubiquitous in the stream with 100% detection frequency. Disinfectants/fumigants, cleaning agents, industrial solvents, agrochemicals and plastic materials were the main sources of the VOCs. No individual VOC posed a non-carcinogenic risk (HI) in both months of the study. However, the total HI via ingestion route in March posed a non-carcinogenic health risk to children (HIsum = 1.03). BDCM, TeCA, TCP and pDCB posed a high carcinogenic risk to humans via ingestion with values in the range of (0.00219–5.07) × 10−2 for both months. TCP also posed a high carcinogenic risk (range of 10−4) via dermal contact to humans. The highly impaired water quality of the stream was due to industrial, agricultural and other anthropogenic activities.

Urbanization and weather dynamics co-dominated the spatial-temporal variation in pCO2 and CO2 fluxes in small montanic rivers draining diverse landscapes

Rivers have been widely reported as important CO2 emitters to the atmosphere. Rapid urbanization has a profound impact on the carbon biogeochemical cycle of rivers, leading to enhanced riverine CO2 evasions. However, it is still unclear whether the spatial–temporal patterns of CO2 emissions in the rivers draining diverse landscapes dominated by urbanization were stable, especially in mountainous areas. This study carried out a two-year investigation of water environmental hydrochemistry in three small mountainous rivers draining urban, suburban and rural landscapes in southwestern China, and CO2 partial pressure (pCO2) and fluxes (fCO2) in surface water were measured using headspace equilibrium method and classical thin boundary layer model. The average pCO2 and fCO2 in the highly urbanized river were of 4783.6 μatm and 700.0 mmol m−2 d−1, conspicuously higher than those in the rural river (1525.9 μatm and 123.2 mmol m−2 d−1), and the suburban river presented a moderate level (3114.2 μatm and 261.2 mmol m−2 d−1). It provided even clearer evidence that watershed urbanization could remarkably enhance riverine CO2 emissions. More importantly, the three rivers presented different longitudinal variations in pCO2, implying diversified spatial patterns of riverine CO2 emissions as a result of urbanization. The urban land can explain 49.6–69.1% of the total spatial variation in pCO2 at the reach scale, indicating that urban land distribution indirectly dominated the longitudinal pattern of riverine pCO2 and fCO2. pCO2 and fCO2 in the three rivers showed similar temporal variability with higher warm-rainy seasons and lower dry seasons, which are significantly controlled by weather dynamics, including monthly temperature and precipitation, but seem to be impervious to watershed urbanization. High temperature-stimulated microorganisms metabolism and riched-CO2 runoff input lead much higher pCO2 in warm-rainy seasons. However, it showed more sensitivity of pCO2 to monthly weather dynamics in urbanized rivers than that in rural rivers, and warm-rainy seasons showed hot moments of CO2 evasion for urban rivers. TOC, DOC, TN, pH and DO were the main controls on pCO2 in the urban and suburban rivers, while only pH and DO were connected with pCO2 in the rural rivers. This indicated differential controls and regulatory processes of pCO2 in the rivers draining diverse landscapes. Furthermore, it suggested that pCO2 calculated by the pH-total alkalinity method would obviously overestimate pCO2 in urban polluted rivers due to the inevitable influence of non-carbonate alkalinity, and thus, a relatively conservative headspace method should be recommended. We highlighted that urbanization and weather dynamics co-dominated the multiformity and uncertainty in spatial–temporal patterns of riverine CO2 evasions, which should be considered when modeling CO2 dynamics in urbanized rivers.

The effect of pioneer carrion beetles on the emission of volatile organic compounds and carrion insect community assembly.

Mechanisms of carrion insect succession have been interpreted separately from interspecific interactions between early and later colonists or from changes in volatile organic compounds perceived by insects resulting from the progression of decomposition. To link these perspectives, we examined through laboratory and field experiments whether the modification of volatile organic compounds by early colonists could be a mechanism of succession. In the laboratory experiment, we used Necrophila japonica (Coleoptera, Staphylinidae) as an early colonist and examined its effects on the emissions of important volatile attractants for carrion insects, dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) from carcasses. We collected DMDS and DMTS, using the static headspace method, under the following conditions: (i) rat carcass, (ii) rat carcass with artificial damage to the abdomen, (iii) rat carcass fed on by 10 Ne. japonica individuals, and (iv) 10 Ne. japonica individuals, and analyzed the collected gases using a gas chromatograph-mass spectrometer. After 12 and 30 h, carcasses fed on by Ne. japonica emitted higher concentrations of DMDS and DMTS than in other conditions. In the field experiment, we examined the effects of DMDS and DMTS on the attraction of carrion insects using traps baited with a mixture of DMDS and DMTS, hexane (odors unrelated to carcasses), or an empty microtube. Traps baited with DMDS and DMTS attracted more necrophagous species and individuals than traps not baited with this combination. These results showed that accelerated emissions of DMDS and DMTS from carcasses caused by early colonists may contribute to community assembly during carrion insect succession.

A new direct extraction by gas-chromatography with flame ionization detector coupled to head space method for the determination of alcohol content of high matrix wine products

Detection, identification, and quantitation of alcohol in any matrix rich medium is a common practice although sample preparation is inevitable and time consuming. A sensitive, precise and ultimately wide range method for detection, identification and quantification of main content/residual/impurity alcohols without any matrix interference that can be used for production phase quality control, pharmaceutical and/or bio-technological refinement or toxicological evaluation and for forensics is always needed. Even for quality control also for toxicological considerations, ethanol (EtOH) and very similar compound methanol has to be detected and identified definitely becomes vital. However, with the fermented products, the matrix becomes a challenging process, makes the methods inefficient or more extraction methods have to be implanted. Here we propose a new simple and reliable direct extraction method has been developed for the determination of alcohol content of high matrix wine products using the gas-chromatography with flame ionization detector coupled to head space. The method was developed with a rich and complex component mixture of fermented alcoholic beverages (wine) with very high matrix effects. Isopropanol (IPA) was preferred as an internal standard, and Triton X-100 (TX-100) was used as diluting solution in this method. The amount of TX-100, extraction temperature, and the total volume of solution in head space vial (20 mL) were optimized. 2.5% TX-100, 80 °C extraction temperature, and 2.0 ml of total volume were used as optimum condition. Stationary phase was the fused silica, Agilent J&W DB-624 column (30 m x 320 m x 1.8 m) and Helium was used as a mobile phase. GC oven temperature programme was 40C (5 min), 5C/min ramp to 60C (0 min) and 30C/min to 150C (1 min). Performance of the method was assessed by evaluating the recovery, accuracy, precision, linearity, limits of detection (LOD) and limit of quantification (LOQ). Calibration curve was drawn between the concentration of 2.5% to 15.0% EtOH (y = 1.572x – 0.702, R² = 0.9960, y; the ratio of peak area of EtOH to IPA, x: EtOH%). The slopes of standard addition and external calibration curve were statistically same. Recovery of the method was 97.5 ± 3.5 for tree different concentrations and the precision was %5.8 (n= 11). LOD and LOQ were calculated as 0.80% and 2.5%, respectively. The proposed method has a potential for application into the industry and academia with determination of the alcohol content/residual/impurity and also check the quality and content of the fermented medium without the effect of matrix.

Method Comparison for the Identification and Characterization of Odorants from Scots Pine (Pinus sylvestris L.) and Oriented Strand Boards (OSB) Made Thereof by GC-MS and GC-FID/O Using Different Headspace Techniques

Volatile organic compounds (VOCs) from wood and wood composites are important contributors to odor profiles of indoor environments and can significantly influence human health and well-being. GC-MS/FID and gas chromatography (GC) with olfactometric detection (GC-O) are employed for the identification and characterization of odorants. Four different sample preparation methods are evaluated on wood strands and isocyanate adhesive–based oriented strand boards (OSBs) made from Pinus sylvestris L.: among these, dynamic headspace extraction thermal desorption ((dynamic) HS-TD), head space solid phase microextraction (HS-SPME), head space solid phase microextraction Arrow (HS-SPME Arrow), and liquid injection of a CH2Cl2 solvent extract. The olfactometric investigation revealed over 30 odor-active substances of cyclic and acyclic monoterpene, monoterpenoid ketone, monoterpenoid aldehyde, monoterpenoid alcohol, monoterpenoid ester, aliphatic aldehyde, alcohol, and acid and phenolic chemistry. Compared to liquid injection, (dynamic) HS-TD was found to result in a similar number of odorants (20 vs. 24), whereas HS SPME Arrow shows good performance with minimal instrumental effort, notably for monoterpene and aldehyde compounds. Native wood vs. OSB showed high concentrations of saturated and unsaturated aldehydes for the wood board sample. These findings demonstrate the capability of headspace methods for odorant detection and their suitability for standardization towards a database for wood and wood composites.

Identification of volatile organic compounds in purple and white soybean flowers by HS-SPME/GC-MS

This study aimed to establish a method for the extraction, enrichment, and identification of volatile organic compounds (VOCs) released by the flowers of purple (BRS 399) and white (DONMARIO 6563) soybean varieties. We tested the Static Headspace (HS) and Solid Phase Microextraction (SPME) methods using various fibre types: PDMS (Polydimethylsiloxane), PDMS/DVB (Divinylbenzene), and PDMS/DVB/CAR (Carboxen). We employed gas chromatography–mass spectrometry (GC–MS) to identify the VOCs. The SPME method with PDMS/DVB and PDMS/DVB/CAR fibres yielded the highest number of extracted compounds for both soybean cultivars. Notably, 67 compounds were detected in Glycine max. L for the first time. Using the developed method, we were able to detect 52 and 57 VOCs in the purple and white soybean varieties, respectively, including ketones, alcohols, aldehydes and benzenoids. In conclusion, the method we developed effectively identified VOCs in soybean flowers, thus enriching our understanding of the interactions between soybean flowers and their pollinators.

Application of the Static Headspace Method as a Tool for Rapid Control of Fennel Seed Tea Vapors

Background:: In recent years, there have been tensions surrounding the accessibility of drugs at pharmacies. This situation has led people to turn to alternative medicine with increased use of plants as medicines. Nevertheless, a good knowledge of the plant's chemical composition is necessary for its proper use due to the presence of toxic products. Objective:: The research objectives are to expand a novel use of the static headspace technique to control the chemical composition of the vapor of fennel seed tea (Foeniculum vulgare Mill.) and also constitute an attempt to develop a targeted qualitative analytical method for quality control and safety assurance of a consumer product. Methods:: This study qualitatively investigated the amount of estragole in fennel herbal tea vapour by successful rehabilitation of the static headspace gas chromatography/mass spectrometry method. In addition, an analysis is conducted on the total phenolic and flavonoid content in both tea and methanol extract. Antioxidant activities of all extracts were measured and compared to Gallic acid. Results:: The fennel seed tea showed total phenolic and flavonoid contents at 187.7 ± 17.1 GAE/100 g and 133.8 ± 9.07 mg CE/100 g, respectively. Fennel seeds tea exhibited good DPPH anti-radical action with an IC50 of 92.38 ± 10.64 mg/g. Even though studies on the total phenols, flavonoid contents, and antioxidant activity of this herbal tea have all yielded positive outcomes, the application of the static headspace method combined with gas chromatography and mass spectrometry indicated the presence of estragole at 37.63 ± 3.77%. This compound was found at 80.67 ± 0.29% in the essential oil. Conclusion:: The application of this method has made it possible to reduce the handling time by eliminating the extraction step and solvent use. The presence of estragole at an alarming level makes it clear that employing plants as medicines must be regulated.

A rapid dynamic headspace method for authentication of whiskies using artificial neural networks

A rapid headspace analysis method for the authenticity testing of whiskies of different brands and years was developed for a low cost, deployable atmospheric pressure ionisation mass spectrometer, which required minimal sample preparation. Principal component analysis was applied to the time-averaged mass spectra, the classification results for which were compared against artificial neural network methods. The artificial neural network was found to outperform PCA, achieving ≥95% accuracy for all sampling conditions, with only two misclassifications under the ideal conditions, while requiring less development time.

Large methane emission during ice-melt in spring from thermokarst lakes and ponds in the interior Tibetan Plateau

The magnitudes of annual CO2 and CH4 emissions from thermokarst lakes and ponds are uncertain due to scarce measurements on the Tibetan Plateau (TP) and limited data on emissions during ice-melt. To evaluate the importance of CO2 and CH4 emissions during late winter and spring among the whole year, surface water CO2 and CH4 concentrations were measured with the headspace method in ten thermokarst lakes and ponds in 2020–2021 on the TP. The concentrations of CH4 and CO2 under ice in winter (CH4, 1.05–127.16 μmol/L, CO2, 13.24–95.57 μmol/L) were 3–4 orders of magnitude and several times higher than those in summer (CH4, 0.02–2.34 μmol/L, CO2, 7.26–49.18 μmol/L), respectively. The CH4 concentrations and fluxes during ice-melt increased with as the depth of the thermokarst lakes and ponds increased. However, the variation in CO2 concentration was not significant in depth. Snowfall events played an important role in influencing gas exchange during ice-melt. In the ten lakes researched, 42.2% and 19.2% of the annual CH4 and CO2 fluxes occurred during ice-melt, respectively. Our results indicated that CH4 and CO2 accumulation in winter should be considered when evaluating annual carbon budgets in thermokarst lakes and ponds on the TP and similarly high fluxes during ice-melt might occur in other thermokarst lakes and ponds.

The Dynamic Nature of a Static Headspace Above Frozen Leaf Biomass From a Toxic Brazilian Plant

A static headspace method of sampling coupled to a conventional instrumental analytical probe, gas chromatography mass spectrometry (GCMS), has been applied to examine the volatile fraction above leaf tissue from Palicourea marcgravii, a toxic Brazilian plant that causes sudden death in livestock, and two other surrogate species (Lippia alba and Plectranthus spp.). 
 
 The unusual total ion chromatogram obtained for the plant of interest is discussed and explained by considering the “dynamic” nature of the static headspace when intact cellular biomass is present and frozen leaves are analyzed concerning the presence and production of methyl salicylate (MeSA), which is this plants main toxin.

GC-MS analysis of honeybee products derived from medicinal plants

BackgroundHoneybees provide a wealth of valuable natural products containing health-promoting bioactive compounds, including honey, bee bread, bee venom, bee pollen, propolis, and royal jelly. In the present study, we investigated the chemical composition of four honeybee products (bees, honey, royal jelly, and bee bread) derived from three medicinal plants (marjoram, trifolium, and citrus) using headspace GC-MS.ResultsGC-MS analysis coupled with the headspace method resulted in identification of 24 volatile compounds in marjoram honey, 14 volatile compounds in trifolium honey, and 25 volatile compounds in citrus honey, e.g., some of these compounds appeared in all three types of honey aroma, which are 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, 2-furancarboxaldehyde, 5-(hydroxymethyl) and other unique compounds specific for each type where 23 compounds were from marjoram bees, 38 compounds from trifolium bees, and about 37 compounds were identified in citrus bees where 2,4-decadienal, (E, E) and methyl N-methyl anthranilate were common in all. Furthermore, the volatile compounds of all three types of royal jelly aroma were acetic acid, 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, 8-nonen-2-one and furfural where one compound appeared in both marjoram and trifolium royal jelly that is 2-furancarboxaldehyde,5-(Hydroxymethyl) and the volatile compounds in marjoram and citrus are 2,3-butanediol and 5-methylfurfural also only one volatile compound appear in both trifolium and citrus royal jelly that is furfur alcohol, Finally, 3 compounds from marjoram bee bread, 30 volatile compounds from trifolium bee bread, and 3 volatile compounds in citrus bee bread were identified.ConclusionsA detailed metabolomic analysis of the four honey product groups revealed an intriguing chemical diversity, with each sample exhibiting its own chemical fingerprint.

Experimental Determination of Air/Water Partition Coefficients for 21 Per- and Polyfluoroalkyl Substances Reveals Variable Performance of Property Prediction Models.

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals of high environmental concern. However, reliable data for the air/water partition coefficients (Kaw), which are required for fate, exposure, and risk analysis, are available for only a few PFAS. In this study, Kaw values at 25 °C were determined for 21 neutral PFAS by using the hexadecane/air/water thermodynamic cycle. Hexadecane/water partition coefficients (KHxd/w) were measured with batch partition, shared-headspace, and/or modified variable phase ratio headspace methods and were divided by hexadecane/air partition coefficients (KHxd/air) to obtain Kaw values over 7 orders of magnitude (10-4.9 to 102.3). Comparison to predicted Kaw values by four models showed that the quantum chemically based COSMOtherm model stood out for accuracy with a root-mean-squared error (RMSE) of 0.42 log units, as compared to HenryWin, OPERA, and the linear solvation energy relationship with predicted descriptors (RMSE, 1.28-2.23). The results indicate the advantage of a theoretical model over empirical models for a data-poor class like PFAS and the importance of experimentally filling data gaps in the chemical domain of environmental interest. Kaw values for 222 neutral (or neutral species of) PFAS were predicted using COSMOtherm as current best estimates for practical and regulatory use.

Monoterpene alcohols induced by sweet potato weevil larvae deter conspecific adults from feeding and oviposition.

Intraspecific competition is shared in the insect world, especially under the condition of limited food and space resources. To avoid intraspecific competition and increase offspring survival, insects have evolved various effective strategies. A widely-accepted tactic is employing chemical cues, which are frequently utilized as indicators of conspecific colonization. The sweet potato weevil (SPW), Cylas formicarius, is a destructive pest of sweet potatoes. Its larvae bore into sweet potatoes and alter the emission of odors. The present study aimed to investigate whether volatiles associated with SPW larvae feeding influence the behavioral preference of conspecific adults. Volatiles from SPW larvae-infested sweet potatoes were collected by a head-space method and analyzed using gas chromatography-electroantennogram detector (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Five compounds eliciting EAD responses from the antennae of both male and female adult SPW were identified from sweet potatoes with the third-instar larvae, including linalool, citronellol, nerol, geraniol, and ipomeamarone. Four monoterpene alcohols significantly repelled SPW adults from feeding and oviposition at higher doses in the behavioral preference bioassays. Among them, geraniol displayed the strongest repellent activities for SPW feeding and oviposition. These results suggested that SPW larvae could reduce colonization of adult SPWs by inducing monoterpene alcohols, thereby avoiding intraspecific competition. The present study demonstrated that volatile monoterpene alcohols induced by SPW larvae are chemical cues of larvae occupation for SPW adults to change their behavioral preference. Unveiling factors that mediate avoidance of intraspecific competition could help develop repellents or oviposition deterrents for SPW control. © 2023 Society of Chemical Industry.