Methods to Detect Volatile Organic Compounds for Breath Biopsy Using Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry.

Volatile organic compounds (VOCs) are byproducts from metabolic pathways that can be detected in exhaled breath and have been reported as biomarkers for different diseases. The gold standard for analysis is gas chromatography-mass spectrometry (GC-MS), which can be coupled with various sampling methods. The current study aims to develop and compare different methods for sampling and preconcentrating VOCs using solid-phase microextraction (SPME). An in-house sampling method, direct-breath SPME (DB-SPME), was developed to directly extract VOCs from breath using a SPME fiber. The method was optimized by exploring different SPME types, the overall exhalation volume, and breath fractionation. DB-SPME was quantitatively compared to two alternative methods involving the collection of breath in a Tedlar bag. In one method, VOCs were directly extracted from the Tedlar bag (Tedlar-SPME) and in the other, the VOCs were cryothermally transferred from the Tedlar bag to a headspace vial (cryotransfer). The methods were verified and quantitatively compared using breath samples (n = 15 for each method respectively) analyzed by GC-MS quadrupole time-of-flight (QTOF) for compounds including but not limited to acetone, isoprene, toluene, limonene, and pinene. The cryotransfer method was the most sensitive, demonstrating the strongest signal for the majority of the VOCs detected in the exhaled breath samples. However, VOCs with low molecular weights, including acetone and isoprene, were detected with the highest sensitivity using the Tedlar-SPME. On the other hand, the DB-SPME was less sensitive, although it was rapid and had the lowest background GC-MS signal. Overall, the three breath-sampling methods can detect a wide variety of VOCs in breath. The cryotransfer method may be optimal when collecting a large number of samples using Tedlar bags, as it allows the long-term storage of VOCs at low temperatures (-80 °C), while Tedlar-SPME may be more effective when targeting relatively small VOCs. The DB-SPME method may be the most efficient when more immediate analyses and results are required.

Water-Resistant Polymeric Acid Membrane Catalyst for Acetone Detection in the Exhaled Breath of Diabetics.

Endogenous volatile organic compounds (VOCs) such as acetone in exhaled human breath are associated with metabolic conditions in the bloodstream. Development of compact, rapid detectors of exhaled breath chemical composition in clinical settings is challenging due to the small sample size that can be collected during a single exhalation as well as spectroscopic interference by the abundance of water. In this paper, we show that the activity of a catalytic polymer membrane (Nafion 117) toward the heterogeneous condensation reaction of immobilized resorcinol reagent with gas-phase acetone can be preserved even at 100% ambient relative humidity through the incorporation of organic acids such as vanillic or tiglic. The reaction produces a colored flavan product that permits highly selective and sensitive correlation to acetone concentration in exhaled breath. Such behavior suggests solvent displacement, analogous to homogeneous liquid-phase systems. However, unlike classic acid-base equilibria, the extent of optode water resistance is shown to increase with the pKa of the imbibed organic acid while peak signal intensity of the imbibed acid undergoes a bathochromic shift to longer wavelengths. These observations are consistent with competition between organic acid deprotonation by water in a mixed solvent system on the one hand and immobilization on the other. Finally, we demonstrate how when applied to the direct chemical analysis of acetone in exhaled human breath, the approach yields excellent correlation to blood glucose in diabetics.

Hand-Held Volatilome Analyzer Based on Elastically Deformable Nanofibers.

This study reports on a hand-held volatilome analyzer for selective determination of clinically relevant biomarkers in exhaled breath. The sensing platform is based on electrospun polymer nanofiber-multiwalled carbon nanotube (MWCNT) sensing microchannels. Polymer nanofibers of poly(vinylidene fluoride) (PVDF), polystyrene (PS), and poly(methyl methacrylate) (PMMA) incorporated with MWCNT exhibits a stable response to interferences of humidity and CO2 and provides selective deformations upon exposure of exhaled breath target volatilomes acetone and toluene, exhibiting correlation to diabetes and lung cancer, respectively. The sensing microchannels "P1" (PVDF-MWCNT), "P2" (PS-MWCNT), and "P3" (PMMA-MWCNT) are integrated with a microfluidic cartridge (µ-card) that facilitates collection and concentration of exhaled breath. The volatilome analyzer consists of a conductivity monitoring unit, signal conditioning circuitries and a low energy display module. A combinatorial operation algorithm was developed for analyzing normalized resistivity changes of the sensing microchannels upon exposure to breath in the concentration ranges between 35 ppb and 3.0 ppm for acetone and 1 ppb and 10 ppm for toluene. Subsequently, responses of volatilomes from individuals in the different risk groups of diabetes were evaluated for validation of the proposed methodology. We foresee that proposed methodology provides an avenue for rapid detection of volatilomes thereby enabling point of care diagnosis in high-risk group individuals.

Novel Zinc(II) Bis(Dipyrromethenate)-Doped Ethyl Cellulose Sensors for Acetone Vapor Fluorescence Detection.

In this paper, we report on the results of spectrofluorimetric study of new fluorescent sensor based on [Zn2L2] doped in ethyl cellulose. The sensor optical signal is based on the rapid fluorescence quenching in the presence of acetone vapor. The acetone vapor detection limit in a gas mixture by means of sensor based on [Zn2L2] doped in ethyl cellulose is 1.68 ppb. Being highly sensitive to the acetone acetone presence, instant in response and easy to use, the sensor can find an application for the noninvasive diagnostics of diabetes as well as for the monitoring of the content of acetone acetone in the air at industrial and laboratory facilities. Graphical Abstract.

Robust and Reversible Vapoluminescent Organometallic Copper Polymers.

Emissive organometallic polymers are an important class of functional materials characterized by the combined photoluminescent features of organometallic molecules and the properties of traditional polymers. In this work, the emissive organometallic complex, [CuBr(PPh3 )2 (4-methylpyridine)], is successfully, mechanically ground into a random copolymer built on 4-(diphenylphosphino)styrene (DPVP) and n-butyl acrylate (BA) monomers. The resultant hybrid materials successfully inherit the emissive centers, and are significantly reinforced by the copper complexes as chemical crosslinkers in the polymeric continuum. These organometallic polymers are also proved to have excellent vapoluminescent properties, exhibiting unique responses to many organic solvent vapors, reflecting their rapid loss and recovery of photoluminescence. Mechanically robust and flexible films prepared with these organometallic Cu(I)-polymers are tested as recoverable sensors for hazardous volatile chemical compounds (VOCs) such as toluene, acetone, chloroform, and dichloromethane, and the low limits of detection (LOD) can reach as low as 1 × 10-3 -8 × 10-3 mg L-1 (0.2-3.3 ppmV, parts per million-volume) for various VOCs. This work sheds lights on the design and fabrication of organometallic polymers for advanced applications.

[The influence of the packaging on the storage qualities of the volatile substances]. / Vliianie upakovki na sokhraniaemost' letuchikh veshchestv.

The objective of the present study was to evaluate the storage qualities of the acetone and ethanol aqueous solutions kept in the polyethylene flasks, polypropylene and glass tubes that were stored under different environmental temperature. It was shown that the acetone aqueous solution better retained its properties when stored in glass vials at room temperature as well as at 0° C and 4° C. The most pronounced decrease of acetone concentrations (from 70 up to 95%) was documented after its storage in the polyethylene flasks. The ethanol concentration fell down by 40% when stored in polyethylene flasks at room temperature.

Direct conversion of xylan to butanol by a wild-type Clostridium species strain G117.

Lignocellulosic biomass has great potential for use as a carbon source for the production of second-generation biofuels by solventogenic bacteria. Here we describe the production of butanol by a newly discovered wild-type Clostridium species strain G117 with xylan as the sole carbon source for fermentation. Strain G117 produced 0.86 ± 0.07 g/L butanol and 53.4 ± 0.05 mL hydrogen directly from 60 g/L xylan provided that had undergone no prior enzymatic hydrolysis. After process optimization, the amount of butanol produced from xylan was increased to 1.24 ± 0.37 g/L. In contrast to traditional acetone-butanol-ethanol (ABE) solventogenic fermentation, xylan supported fermentation in strain G117 and negligible amount of acetone was produced. The expression of genes normally associated with acetone production (adc and ctfB2) were down-regulated compared to xylose fed cultures. This lack of acetone production may greatly simplify downstream separation process. Moreover, higher amount of butanol (2.94 g/L) was produced from 16.99 g/L xylo-oligosaccharides, suggesting a major role for strain G117 in butanol production from xylan and its oligosaccharides. The unique ability of strain G117 to produce a considerable amount of butanol directly from xylan without producing undesirable fermentation byproducts opens the door to the possibility of cost-effective biofuels production in a single step. Biotechnol. Bioeng. 2016;113: 1702-1710. © 2016 Wiley Periodicals, Inc.

Comparison between Thermal Desorption Tubes and Stainless Steel Canisters Used for Measuring Volatile Organic Compounds in Petrochemical Factories.

OBJECTIVE: The purpose of this study was to compare thermal desorption tubes and stainless steel canisters for measuring volatile organic compounds (VOCs) emitted from petrochemical factories. METHODS: Twelve petrochemical factories in the Mailiao Industrial Complex were recruited for conducting the measurements of VOCs. Thermal desorption tubes and 6-l specially prepared stainless steel canisters were used to simultaneously perform active sampling of environmental air samples. The sampling time of the environmental air samples was set up on 6 h close to a full work shift of the workers. A total of 94 pairwise air samples were collected by using the thermal adsorption tubes and stainless steel canisters in these 12 factories in the petrochemical industrial complex. To maximize the number of comparative data points, all the measurements from all the factories in different sampling times were lumped together to perform a linear regression analysis for each selected VOC. Pearson product-moment correlation coefficient was used to examine the correlation between the pairwise measurements of these two sampling methods. A paired t-test was also performed to examine whether the difference in the concentrations of each selected VOC measured by the two methods was statistically significant. RESULTS: The correlation coefficients of seven compounds, including acetone, n-hexane, benzene, toluene, 1,2-dichloroethane, 1,3-butadiene, and styrene were >0.80 indicating the two sampling methods for these VOCs' measurements had high consistency. The paired t-tests for the measurements of n-hexane, benzene, m/p-xylene, o-xylene, 1,2-dichloroethane, and 1,3-butadiene showed statistically significant difference (P-value < 0.05). This indicated that the two sampling methods had various degrees of systematic errors. Looking at the results of six chemicals and these systematic errors probably resulted from the differences of the detection limits in the two sampling methods for these VOCs. CONCLUSIONS: The comparison between the concentrations of each of the 10 selected VOCs measured by the two sampling methods indicted that the thermal desorption tubes provided high accuracy and precision measurements for acetone, benzene, and 1,3-butadiene. The accuracy and precision of using the thermal desorption tubes for measuring the VOCs can be improved due to new developments in sorbent materials, multi-sorbent designs, and thermal desorption instrumentation. More applications of thermal desorption tubes for measuring occupational and environmental hazardous agents can be anticipated.

Biomonitoring for Exposure Assessment to Styrene in the Fibreglass Reinforced Plastic Industry: Determinants and Interferents.

Fifty-eight workers exposed to styrene were monitored in four fibreglass reinforced plastic industries of Central Italy. The aim of the study was to explore the factors that can influence the levels of styrene exposure biomarkers of the workers and the aspects that might interfere with the exposure assessment measures, such as the co-exposure to acetone. Personal monitoring of professional exposure to airborne styrene and acetone was carried out by Radiello samplers and GC/MS analysis. Biological monitoring was performed by the determination of urinary metabolites, mandelic (MA), and phenylglyoxylic (PGA) acids with HPLC/MS/MS and unmetabolized styrene in saliva and venous blood by HS/GC/MS. The median values of the four sites ranged between 24.1 to 94.0mg m(-3) and 7.3 to 331.1mg g(-1) creatinine for airborne styrene and MA + PGA, respectively. A good linear correlation was found between styrene in air and its urinary metabolites (r = 0.854). The median value for airborne styrene was found to exceed the (Threshold Limit Value - Time Weighted Average) of 85 mg m(-3) in one site for all the workers and in two if only moulders are considered. The multiple linear regression model showed that the determinants of urinary MA + PGA excretion were the type of process, workers' tasks, level of acetone co-exposure, and the use of respiratory protection devices. Data show that the simultaneous exposure to acetone modify the styrene metabolism with a reduction in the levels of (MA + PGA) excreted. A significant linear log-correlation was found between salivary levels of styrene and blood concentration (r = 0.746) sampled at the same t x time.

Monitoring of human chemical signatures using membrane inlet mass spectrometry.

This work is an attempt to assist border security crackdown on illegal human immigration, by providing essential results on human chemical signatures. Data was obtained using a portable quadrupole mass spectrometer coupled with a membrane probe for volunteers of both genders and under different conditions in a container simulator. During experiments, participants were asked to follow various protocols while volatile organic compounds emitted from their breath, sweat, skin, and other biological excretes were continuously being monitored. Experimental setups using different membrane materials (both hydrophilic and hydrophobic) including heating of the sampling probe and sampling flow rates were examined. From our measurements, significant information was obtained for NH3, CO2, water, and volatile organic compounds levels, illustrating a human chemical profile and indicating human presence in a confined space.

Study on particulates and volatile organic compounds removal with TiO2 nonwoven filter prepared by electrospinning.

UNLABELLED: In this study, polyvinyl alcohol (PVA) and titania (TiO2) Degussa P-25 were mixed to generate TiO2 nonwoven filters using electrospinning. The wires of titanium dioxide and the nonwoven binding titania nanofibers were formed using 14 kV voltage and a distance of 15 cm. A single-factor experimental method was used to investigate the effects of parameters such as initial concentration, retention time, and light source on acetone removal by nonwoven binding titania nanofibers. Furthermore, the effects of parameters such as gas pressure, particle size, initial concentration, and retention time on the removal of particulates were also assessed. The results showed that the degradation efficiency increased with decreasing initial concentrations and increasing retention time. The best operational conditions during this study for the removal of acetone using the TiO2 nonwoven filters were a retention time of 100 sec, initial acetone concentration of 250 ppm, and ultraviolet (UV) light source of 254 nm. Under those conditions, 99% acetone removal efficiency was obtained. In addition, 90% particulate matter removal efficiency was reached when the particulate size was greater than 200 nm and the reaction time was longer than 5 minutes. The prepared TiO2/nanofiber has good performance for volatile organic compounds (VOCs) and particulate removal at the same time. IMPLICATIONS: In this study, polyvinyl alcohol (PVA) and titania (TiO2) Degussa P-25 were mixed to generate TiO2 nonwoven filters using electrospinning. The results showed that the optimum operating conditions for the removal of acetone using the TiO2 nonwoven filters were a retention time of 100 sec, initial acetone concentration of 250 ppm, and UV light source of 254 nm. Under those conditions, 99% acetone removal efficiency was obtained.

A discriminant distance based composite vector selection method for odor classification.

We present a composite vector selection method for an effective electronic nose system that performs well even in noisy environments. Each composite vector generated from a electronic nose data sample is evaluated by computing the discriminant distance. By quantitatively measuring the amount of discriminative information in each composite vector, composite vectors containing informative variables can be distinguished and the final composite features for odor classification are extracted using the selected composite vectors. Using the only informative composite vectors can be also helpful to extract better composite features instead of using all the generated composite vectors. Experimental results with different volatile organic compound data show that the proposed system has good classification performance even in a noisy environment compared to other methods.

Evaluation of decontamination efficacy of cleaning solutions on stainless steel and glass surfaces contaminated by 10 antineoplastic agents.

OBJECTIVES: The handling of antineoplastic agents results in chronic surface contamination that must be minimized and eliminated. This study was designed to assess the potential of several chemical solutions to decontaminate two types of work surfaces that were intentionally contaminated with antineoplastic drugs. METHODS: A range of solutions with variable physicochemical properties such as their hydrophilic/hydrophobic balance, oxidizing power, desorption, and solubilization were tested: ultrapure water, isopropyl alcohol, acetone, sodium hypochlorite, and surfactants such as dishwashing liquid (DWL), sodium dodecyl sulfate (SDS), Tween 40, and Span 80. These solutions were tested on 10 antineoplastic drugs: cytarabine, gemcitabine, methotrexate, etoposide phosphate, irinotecan, cyclophosphamide, ifosfamide, doxorubicin, epirubicin, and vincristine. To simulate contaminated surfaces, these molecules (200ng) were deliberately spread onto two types of work surfaces: stainless steel and glass. Recovered by wiping with a specific aqueous solvent (acetonitrile/HCOOH; 20/0.1%) and an absorbent wipe (Whatman 903®), the residual contamination was quantified using high-performance liquid chromatography (HPLC) coupled to mass spectrometry. To compare all tested cleaning solutions, a performance value of effectiveness was determined from contamination residues of the 10 drugs. RESULTS: Sodium hypochlorite showed the highest overall effectiveness with 98% contamination removed. Ultrapure water, isopropyl alcohol/water, and acetone were less effective with effectiveness values of 76.8, 80.7, and 40.4%, respectively. Ultrapure water was effective on most hydrophilic molecules (97.1% for cytarabine), while on the other hand, isopropyl alcohol/water (70/30, vol/vol) was effective on the least hydrophilic ones (85.2% for doxorubicin and 87.8% for epirubicin). Acetone had little effect, whatever the type of molecule. Among products containing surfactants, DWL was found effective (91.5%), but its formulation was unknown. Formulations with single surfactant non-ionics (tween 40 and span 80) or anionic (SDS) were also tested. Finally, solutions containing 10(-2) M anionic surfactants and 20% isopropyl alcohol had the highest global effectiveness at around 90%. More precisely, their efficacy was the highest (94.8%) for the most hydrophilic compounds such as cytarabine and around 80.0% for anthracyclines. Finally, the addition of isopropyl alcohol to surfactant solutions enhanced their decontamination efficiency on the least hydrophilic molecules. Measured values from the stainless steel surface were similar to those from the glass one. CONCLUSION: This study demonstrates that all decontamination agents reduce antineoplastic contamination on work surfaces, but none removes it totally. Although very effective, sodium hypochlorite cannot be used routinely on stainless steel surfaces. Solutions containing anionic surfactant such as SDS, with a high efficiency/safety ratio, proved most promising in terms of surface decontamination.

Real-Time Monitoring of Breath Biomarkers with A Magnetoelastic Contactless Gas Sensor: A Proof of Concept.

In the quest for effective gas sensors for breath analysis, magnetoelastic resonance-based gas sensors (MEGSs) are remarkable candidates. Thanks to their intrinsic contactless operation, they can be used as non-invasive and portable devices. However, traditional monitoring techniques are bound to slow detection, which hinders their application to fast bio-related reactions. Here we present a method for real-time monitoring of the resonance frequency, with a proof of concept for real-time monitoring of gaseous biomarkers based on resonance frequency. This method was validated with a MEGS based on a Metglass 2826 MB microribbon with a polyvinylpyrrolidone (PVP) nanofiber electrospun functionalization. The device provided a low-noise (RMS = 1.7 Hz), fast (<2 min), and highly reproducible response to humidity (Δf = 46−182 Hz for 17−95% RH), ammonia (Δf = 112 Hz for 40 ppm), and acetone (Δf = 44 Hz for 40 ppm). These analytes are highly important in biomedical applications, particularly ammonia and acetone, which are biomarkers related to diseases such as diabetes. Furthermore, the capability of distinguishing between breath and regular air was demonstrated with real breath measurements. The sensor also exhibited strong resistance to benzene, a common gaseous interferent in breath analysis.

Simultaneous Biomechanical and Biochemical Monitoring for Self-Powered Breath Analysis.

The high moisture level of exhaled gases unavoidably limits the sensitivity of breath analysis via wearable bioelectronics. Inspired by pulmonary lobe expansion/contraction observed during respiration, a respiration-driven triboelectric sensor (RTS) was devised for simultaneous respiratory biomechanical monitoring and exhaled acetone concentration analysis. A tin oxide-doped polyethyleneimine membrane was devised to play a dual role as both a triboelectric layer and an acetone sensing material. The prepared RTS exhibited excellent ability in measuring respiratory flow rate (2-8 L/min) and breath frequency (0.33-0.8 Hz). Furthermore, the RTS presented good performance in biochemical acetone sensing (2-10 ppm range at high moisture levels), which was validated via finite element analysis. This work has led to the development of a novel real-time active respiratory monitoring system and strengthened triboelectric-chemisorption coupling sensing mechanism.

Comparative evaluation of bacterial and fungal removal of indoor and industrial polluted air using suspended and packed bed bioreactors.

The abatement of indoor volatile organic compounds (VOCs) represents a major challenge due to their environmental risk, wide nature and concentration variability. Biotechnologies represent a cost-effective, robust and sustainable platform for the treatment of hazardous VOCs at low and fluctuating concentrations. However, they have been scarcely implemented for indoor air purification. Thus, little is known about the influence of the reactor configuration or the VOC nature and concentration variability on the removal, resilience and the microbial population of bioreactor configurations susceptible to be implemented, both in indoors and industrial environments. The present study aims at comparing the removal performance of four VOCs with different hydrophobicity and molecular structure -acetone, n-hexane, α-pinene and toluene-at two inlet concentrations (5 and 400 mg m-3), which mimics the concentrations of contaminated indoor and industrial air. To this aim a stirred tank, flat biofilm and latex-based biocoated flat bioreactor were comparatively evaluated. The results demonstrated the superior performance of the stirred tank reactor for the removal of hydrophilic VOCs at high inlet concentrations, which achieved removals >99% for acetone and toluene. At low concentrations, the removal efficiencies of acetone, toluene and α-pinene were >97% regardless of the bioreactor configuration tested. The most hydrophobic gas, n-hexane, was more efficiently removed in the flat biofilm reactor without latex. The microbial community analyses showed that the presence of VOCs as the only carbon and energy source didn't promote the growth of dominant bacterial members and the populations independently evolved in each reactor configuration and operation mode. The fungal population was more diverse in the biofilm-based bioreactors, although, it was mainly dominated by uncultured fungi from the phylum Cryptomycota.

[Preparation and application of graphene oxide functionalized melamine-formaldehyde aerogel coated solid-phase microextraction tube].

Many solid-phase microextraction (SPME) sorbents have been developed from aerogels because of their low densities, large surface areas, and high porosities. Melamine-formaldehyde (MF) aerogel, made from melamine and formaldehyde by a sol-gel reaction, is one of the typical organic aerogels. MF aerogel has better mechanical strength, chemical stability and extraction performance than inorganic aerogels. The performance of the aerogel is limited in some fields, while composite aerogels can meet different requirements such as good mechanical strength and strong adsorption performance. Graphene oxide (GO) is a two-dimensional nanomaterial composed of a single layer of carbon atoms and provides π-π interaction by a large π-electron. In addition, the oxygen-containing groups at the edge of the lamellar structure improve the hydrophilicity of the material and can interact with various compounds. To improve the extraction performance of MF aerogel for polycyclic aromatic hydrocarbons (PAHs), GO/MF aerogels were prepared by functionalizing MF aerogel with GO. In this study, 1.2612 g of melamine and 80 mg of sodium carbonate were dissolved in 30 mL of water, and the mixture was heated to 80 ℃ under stirring. Then, 2.8 mL formaldehyde solution (37%) was slowly added, and a clear solution was obtained gradually. Next, 50 mg of GO powder was ultrasonically dispersed in 10.0 mL of water and evenly mixed with the above solution. After adjusting the pH to 1.5, the sol-gel process was performed for 48 h, then the gel was aged at room temperature for 24 h. The gel was then soaked in ethanol, acetone, and cyclohexane in turn to replace the solvent. Finally, the GO/MF aerogel was obtained by freeze-drying for 24 h. The GO/MF aerogel was characterized by scanning electron microscopy (SEM) and X-ray photoelectric spectroscopy (XPS), confirming that GO was successfully introduced into MF aerogel, while retaining its three-dimensional network and porous structure. GO/MF aerogel was coated onto the surface of a stainless steel wire to be used as sorbent. Four such wires were placed into a polyetheretherketone (PEEK) tube (0.75 mm i. d., 30 cm length) for in-tube (IT) SPME. The tube was combined with a high-performance liquid chromatography (HPLC) unit to construct an IT-SPME-HPLC online system. When the six-way valve was in the Load state, sample solution achieved online enrichment with analytes while it flowed through the extraction tube. After extraction, the valve was turned to the Inject state, and the analytes were eluted into the chromatographic column by the mobile phase at a flow rate of 1.0 mL/min for separation and detection with the detector. Under the same extraction conditions (sampling volume=30 mL, sampling rate=1.00 mL/min, and concentration of polycyclic aromatic hydrocarbons (PAHs, viz. naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorine (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla) and pyrene (Pyr))=5.00 µg/L), GO/MF aerogel-based tube was compared with that of MF aerogel-based tube. GO enhanced the enrichment efficiency of MF aerogel towards PAHs from 1.1 to 2.5 times, due to the increased number of adsorption sites and enhanced π-π interaction with PAHs. IT-SPME was affected by the sampling volume, sampling rate, concentration of organic solvent in sample, desorption solvent, desorption rate, and desorption time. To obtain accurate results, the main extraction and desorption conditions (sampling volume, sampling rate, organic solvent concentration, desorption time) were investigated carefully. As the sampling volume in the extraction tube was increased, the extraction efficiency was found to increase gradually until saturation. In this study, the extraction efficiency was investigated for sampling volumes ranging from 30 to 80 mL, and 70 mL was selected as a suitable sampling volume to achieve satisfactory extraction efficiency. The sampling rate affects not only the extraction efficiency, but also the extraction time. When the sample flows through the extraction tube at a low rate, it requires a long test time. Although the increase in sampling rate reduces the extraction time, it often decreases extraction efficiency. In addition, large sampling rate leads to high pressure in the tube, which in turn reduces the service life of the tube. Therefore, the effect of sampling rate (1.25-2.50 mL/min) on extraction efficiency was investigated, and good extraction efficiency and short test time were achieved when the sampling rate was 2 mL/min. High hydrophobic PAHs have poor solubility in water. An appropriate amount of organic solvent in the sample solution can improve the solubility of PAHs to obtain accurate analytical results. However, the extraction efficiency was affected by the added organic solvent. Thus, the effect of volume fraction of methanol (0, 0.5%, 1%, 2%, 3%, and 5%, v/v) on the extraction efficiency was investigated. The sample solution without methanol afforded better extraction efficiency and satisfactory repeatability. After online extraction, the desorption directly affects the desorption efficiency. The peak areas of the eight PAHs were investigated with different desorption times (0.2, 0.4, 0.6, 0.8, 1.0, and 2.0 min), and a desorption time of 2.0 min was required to fully desorb all analytes and reduce their residuals. The IT-SPME-HPLC-DAD method was established under the optimized conditions, and the limits of detection (LODs), linear equations, linear ranges, and correlation coefficients were obtained. The LODs of the eight PAHs were in the range of 0.001-0.005 µg/L, the quantitative ranges of the analytes were 0.003-15.0 µg/L for Fla and Pyr, 0.010-20.0 µg/L for Phe and Ant, and 0.017-20.0 µg/L for Nap, Acy, Ace and Flu, the enrichment factors were in the range of 2029-2875, and the analytical precision was satisfactory (intra-day RSD%≤4.8%, and inter-day RSD≤8.6%). Compared with some reported methods, the method reported herein provided higher sensitivity, wider linear range, and shorter test time. This method was applied to the detection of PAHs in common drinking water, including bottled mineral water and water from drinking fountain. The satisfactory recovery (76.3%-132.8%) obtained proves that the method is suitable for the determination of trace PAHs in real water samples, with high sensitivity, rapid testing, online detection, and good accuracy. The extraction tube also exhibited satisfactory durability and chemical stability.

Selective sensing of volatile organic compounds using novel conducting polymer-metal nanoparticle hybrids.

Conducting polymer-metal nanoparticle hybrids, fabricated by assembling metal nanoparticles on top of functionalized conducting polymer film surfaces using conjugated linker molecules, enable the selective sensing of volatile organic compounds (VOCs). In these conducting polymer-metal nanoparticle hybrids, selectivity is achieved by assembling different metals on the same conducting polymer film. This eliminates the need to develop either different polymers chemistries or device configurations for each specific analyte. In the hybrids, chemisorption of the analyte vapor induces charge redistribution in the metal nanoparticles and changes their work function. The conjugated linker molecule causes this change in the work function of the tethered nanoparticles to affect the electronic states in the underlying conducting polymer film. The result is an easily measurable change in the resistance of the hybrid structure. The fabrication of these sensing elements involved the covalent assembly of nickel (Ni) and palladium (Pd) metal nanoparticles on top of poly(3,4-ethylenedioxythiophene-co-thiophene-3-acetic acid), poly(EDOT-co-TAA), films using 4-aminothiophenol linker molecules. The change in resistance of hybrid Pd/poly(EDOT-co-TAA) and Ni/poly(EDOT-co-TAA) hybrid films to acetone and toluene, respectively, is observed to be in proportion to their concentrations. The projected detection limits are 2 and 10 ppm for toluene and acetone, respectively. A negligible response (resistance change) of the Pd/poly(EDOT-co-TAA) films to toluene exposure confirmed its selectivity for detecting acetone. Similarly, lack of response to acetone confirmed the selectivity of the Ni/poly(EDOT-co-TAA) stacks for detecting toluene. It is anticipated that the assembly of other metals such as Ag, Au and Cu on top of poly(EDOT-co-TAA) would provide selectivity for detecting and discriminating other VOCs.

Measurements of volatile compound contents in resins using a moisture analyzer.

The contents of volatile adhesive compounds, such as water, solvents, and residual unpolymerized monomers, affect the integrity and durability of adhesive bonding. However, there is no method available that can be used to rapidly assess the residual solvent or water contents of adhesive resins. This study examined the effectiveness of a digital moisture analyzer to measure the volatile compound contents of resins. Five self-etching adhesives and seven experimental light-cured resins prepared with different contents (0, 10, and 20% by weight) of water or solvents (acetone and ethanol) were examined in this study. The resins were prepared using different methods (with and without air blast or light-curing) to simulate the clinical conditions of adhesive application. Resin weight changes (% of weight loss) were determined as the residual volatile compound contents, using the moisture analyzer. After the measurements, the resin films were examined using a scanning electron microscope. The weight changes of the resins were found to depend on the amount of water or solvents evaporating from the resin. Water and solvents were evaporated by air blast or light-curing, but some of the water and solvents remained in the cured resin. The moisture analyzer is easy to operate and is a useful instrument for using to measure the residual volatile compound contents of adhesive resin.

In vivo chlorhexidine stabilization of hybrid layers of an acetone-based dentin adhesive.

The current in vivo study evaluated the degradation of dentin hybrid layers in deep occlusal-surface resin composite restorations using TEM. Caries-free premolars scheduled for extraction as part of orthodontic treatment were prepared and restored, then extracted after 12 months. The adhesive used was a single-bottle etch-and-rinse acetone-based product (Prime & Bond NT, Dentsply/Caulk). Control group restorations (n=8) were placed according to the manufacturer's instructions, while the experimental group received application of a 2% solution of chlorhexidine digluconate after etching and rinsing and prior to application of the adhesive. Extensive degradation was observed in all of the teeth in the control group after 12 months, while no degradation was observed in the experimental group. In vitro testing showed no significant difference in immediate microtensile bond strength between the control and experimental adhesive protocols.