Programmed Temperature Vaporizer Research Articles

In-situ acetylation followed by liquid-liquid extraction and gas chromatography – mass spectrometry for the determination of bromophenols in urine

A novel and simple method combining in-situ acetylation, liquid-liquid extraction and gas chromatography-mass spectrometry (GC-MS) has been developed for the quantification of 10 bromophenols in urine, used as biomarkers of exposure to polybrominated diphenyl ethers. The analytical process involves an enzymatic hydrolysis of the bromophenol glucuronide fraction followed by an aqueous derivatization of the phenol group with acetic anhydride. A subsequent liquid-liquid extraction of the sample with hexane allows the injection of the organic layer, using a programmed temperature vaporizer, into a gas chromatograph coupled to a single quadrupole mass spectrometer. Quantification is performed by the standard addition method. Limits of detection are in the pg mL−1 range. Trueness, assessed in terms of percentages of recovery, varies between 100 % and 118 % in synthetic urine and between 79 % and 117 % in human urine. Precision, assessed at two different levels, 0.25 ng mL−1 and 2.5 ng mL−1, shows values of relative standard deviation below 14 % both in intra- and inter-day studies for both matrices. The method has been applied to the analysis of seven urine samples, measuring concentrations higher than the LOQ in three of them. These levels are in agreement with others found in literature, but they have been obtained by applying a much simpler and faster protocol. In addition, the replacement of silylating reagents by acetic anhydride, to derivatize the phenol moiety, provides a greener alternative to other GC-MS procedures published up to date.

Sensitive analysis of selenium speciation in natural seawater by isotope-dilution and large volume injection using PTV-GC-ICP-MS

Although oceans play a key role in the global selenium (Se) cycle, there is currently very little quantitative information available on the distribution of Se concentrations and Se speciation in marine environments. In general, determining Se concentration and speciation in seawater is highly challenging due to very low Se levels ((sub)ng⋅L−1), whereas matrix elements interfering Se pre-concentration and detection are up to the g⋅L−1 levels. In this study, we established a sensitive method for the determination of the various Se chemical fractions present in natural seawater, i.e. selenite (SeIV), selenate (SeVI), organic Se-II + Se0 and total Se, using species-specific isotope dilution gas chromatography coupled to inductively coupled plasma mass spectrometry (ID-GC-ICP-MS). We compared different derivatization reagents and optimized specific pre-treatment protocols, including a microwave assisted oxidation protocol for the determination of total Se and organic Se-II + Se0 using H2O2. To increase sensitivity, we developed an online pre-concentration method based on large volume injection (LVI) using a programmed temperature vaporization (PTV) inlet. Eventually, the developed method achieved low absolute and methodological detection limits, i.e., respectively, 0.1–0.3 pg and 0.9–3.1 ng.L-1 for the different fractions. The accuracy of our method was of 2% for a certified reference material (CRM) diluted in artificial seawater while the precision was better than 4% for a freshwater CRM in artificial seawater matrix as well as two common seawater CRMs certified for trace elements excluding Se. As a proof-of-concept, we quantified the various Se fractions in a large number of natural water samples from the Baltic and North Seas, encompassing a wide range of salinity (7–35 psu), which shows that its detection limits are sufficient to determine total Se, SeIV, SeVI and organic Se-II + Se0 concentrations in brackish and marine systems.

Development of a Gas Chromatography with High-Resolution Time-of-Flight Mass Spectrometry Methodology for BDNPA/F.

Analysis of thermally labile compounds such as bis(2,2-dinitropropyl) acetal/formal (BDNPA/F), an energetic plasticizer, is usually performed via liquid chromatography (LC) as opposed to gas chromatography (GC) due to thermal decomposition in the inlet or the analytical column. While LC is a powerful technique, the analysis of volatile and semivolatile compounds is best suited to GC. Herein, a method was developed for a gas chromatograph coupled to high-resolution mass spectrometer (GC-HRMS), utilizing a programmable temperature vaporizer (PTV) inlet. A subset of the native compounds and several produced by the thermal decomposition of BDNPA/F in the inlet were evaluated by using multiple PTV inlet parameters to determine the optimal ramp rate and final temperature of the inlet (60 °C/min from 60 to 325 °C). The optimized GC-HRMS method nearly reduced all thermal decomposition, allowing for an excellent separation to be obtained. Furthermore, multiple ionization methods, including electron impact (EI), negative chemical ionization (NCI), and positive chemical ionization (PCI), were used to explore the many chemical differences between the BDNPA/F samples. A preliminary investigation of the benefits of using GC-HRMS to evaluate the chemical differences between unaged and aged BDNPA/F samples for unique insight was evaluated.

Optimization and Validation of a Method to Determine Enolones and Vanillin Derivatives in Wines-Occurrence in Spanish Red Wines and Mistelles.

Understanding the chemical nature of wine aroma demands accurate quantitative determinations of different odor-active compounds. Quantitative determinations of enolones (maltol, furaneol, homofuraneol, and sotolon) and vanillin derivatives (vanillin, methyl vanillate, ethyl vanillate, and acetovanillone) at low concentrations are complicated due to their high polarity. For this reason, this paper presents an improved and automated version for the accurate measure of these common trace wine polar compounds (enolones and vanillin derivatives). As a result, a faster and more user-friendly method with a reduction of organic solvents and resins was developed and validated. The optimization of some stages of the solid phase extraction (SPE) process, such as washing with an aqueous solution containing 1% NaHCO3 at pH 8, led to cleaner extracts and solved interference problems. Due to the polarity of these type of compounds, an optimization of the large volume injection was also carried out. Finally, a programmable temperature vaporization (PTV) quartz glass inlet liner without wool was used. The injector temperature was raised to 300 °C in addition to applying a pressure pulse of 180 kPa for 4 min. Matrix effects were solved by the use of adequate internal standards, such as ethyl maltol and 3',4'-(methylenedioxy)acetophenone. Method figures of merit were highly satisfactory: good linearity (r2 > 0.98), precision (relative standard deviation, RSD < 10%), high recovery (RSD > 89%), and low detection limits (<0.7 μg/L). Enolones and vanillin derivatives are associated with wine aging. For this reason, the methodology was successfully applied to the quantification of these compounds in 16 Spanish red wines and 12 mistelles. Odor activity values (OAV) indicate that furaneol should be considered an aroma impact odorant in red wines and mistelles (OAV > 1) while homofuraneol and sotolon could also produce changes in their aroma perceptions (0.1 < OAV < 1).

A new JECFA method for GC-MS determination of propylene chlorohydrine residues in hydroxypropylated starches.

Propylene chlorohydrins (PCH) are formed as byproducts in the reaction between starch and propylene oxide (PO). For hydroxypropylated starch (HP-starch) applications in food, JECFA set the maximum allowed total propylene chlorohydrin (PHC-t) residues level at 1 mg/kg. To develop an improved analytical method for the determination of the PCH-t content in starches in the low mg/kg range to replace the outdated JECFA method. A new GC-MS method that utilizes aqueous methanol as extraction medium for PCH. The GC-MS system is equipped with a programmable temperature vaporization injector and Stabilwax-DA column using helium as carrier gas. The quantitative detection is achieved in the selected ion monitoring mode. This single laboratory validation (SLV) study showed good linear calibrations for both 1-chloro-2-propanol (PCH-1) and 2-chloro-1-propanol (PCH-2) in the concentration range of 0.5-4 mg/kg in dry starch. The lower limit of quantitation of PCH-1 and PCH-2 was 0.2-0.3 mg/kg in dry starch, the relative standard deviation reproducibility (RSDR) at the concentration level of 1-2 mg/kg in dry starch was 3-5%, and the recovery values for both PCH-1 and PCH-2 were in the range of 78-112% at a concentration level of about 0.6 mg/kg in dry starch.Compared with the current, outdated JECFA method, the new GC-MS method is more sustainable, less laborious and therefore more economical. The analytical capacity of the new method is 4-5 times higher than the analytical capacity of the old JECFA method. The GC-MS method is fit for a Multi Laboratory Trial (MLT). Based on the results of this SLV and the MLT (will be published in a second paper), the Joint FAO/WHO Expert Committee on Food Additives has recently decided to replace the outdated GC-FID JECFA method for the new GC-MS method for the determination of PCH-t content in starches.

Hyphenation of liquid chromatography and pyrolysis-flame ionization detection/mass spectrometry for polymer quantification and characterization

Size-exclusion chromatography (SEC) hyphenated to pyrolysis-gas chromatography (Py-GC) has been demonstrated as a powerful tool in polymer analysis. A main limitation to the wider application of the method are the long second-dimension Py-GC analysis times, resulting in limited first-dimension sampling and/or long overall run times. Therefore, we set out to develop an online hyphenated SEC×Py-MS/FID method, removing the GC separation and allowing for a drastically reduced second-dimension analysis time compared to SEC-Py-GC. The pyrolysis method had a cycle time of 1.31 min, which was facilitated by liquid nitrogen cooling of the programmable temperature vaporizer (PTV) used for pyrolysis. The developed method featured no molar mass discrimination for masses above ±1.3 kDa, rendering it applicable to most commercial polymer systems. The method was demonstrated on multiple samples, including a complex industrial sample, yielding chemical composition heterogeneity and in some cases sequence heterogeneity information over the molar mass distribution.

Development and Validation of a Residue Analysis Method for Ethylene Oxide and 2-Chloroethanol in Foods by Gas Chromatography Tandem Mass Spectrometry

A selective and sensitive method is reported for the residue analysis of ethylene oxide (EO) in diverse matrices, namely sesame, cumin, wheat, tea, spices, herbs, dehydrated fruits, food additives, grapes, and tomatoes. The study modified the European Union reference method (EN 15662) by performing the sample extraction (with acetonitrile) at <10 °C, cleanup through dispersive-solid phase extraction with C18 and primary secondary amine sorbents, and analysis using gas chromatography tandem mass spectrometry with selected reaction monitoring. Injections were performed through a programmable temperature vaporizer port. The sample preparation process provided a limit of quantification of 10 ng/g for both EO and 2-CE and effectively minimized matrix effects. Recoveries of both EO and 2-CE ranged from 74 to 120% at 10, 20, and 50 ng/g with precision RSDs of <12%, satisfying the SANTE/11312/2021 guidelines of analytical method validation. The HorRat (Horwitz ratio) values of 0.31–0.40 indicated high interlaboratory (n = 6 laboratories) method reproducibility. The results of incurred residues in sesame (0.055–0.1 mg/kg), cumin (0.008–0.013 mg/kg), and coriander (0.01–0.025 mg/kg) demonstrated satisfactory extraction efficiency and precision (RSDs < 10%) in test results. The method is highly suitable for regulatory analysis of EO in diverse food matrices.

Nitrogen carrier gas for the separation of trace explosives on CI-GC/MS.

Fluctuations in ultra high purity (UHP) helium supply has the potential to negatively impact critical research efforts. Disruptions have increased significantly with suppliers prioritizing delivery to medical facilities. Due to the greater demand for helium, supply issues are likely to continue through the coming years. Many gas chromatography (GC)-based analytical methods rely on the supply of UHP helium, including those developed for the quantification of trace explosives. Vapor validation is critical in establishing sensor performance, limits of detection, and instrument performance. An alternate carrier gas must be established to maintain these critical functionalities. To circumvent the UHP helium disruptions, UHP nitrogen was explored as a replacement carrier gas in negative mode chemical ionization-gas chromatography/mass spectrometry (CI-GC/MS). Although, hydrogen is considered an acceptable alternative to helium in most GC-based separations, its' use as a replacement was omitted due to reactivity resulting in degradation of the CI-MS detector and incompatibility with the programmable temperature vaporization inlet on the GC used in this work. Herein discusses the method development of nitrogen carrier gas in the separation of an explosives mixture. Adjustments in flow rate, initial oven temperature, and ramp rate were made to achieve comparable analysis to that of helium. By lowering the flow rate and initial oven temperature peak resolution and sensitivity increased when using nitrogen carrier gas. Development of this method allows for continual laboratory output in times of helium scarcity.

Determination of UV Filters in Surface Water by VA‐DLLME‐SFOD Technique Coupled with GC‐MS/MS

AbstractA simple, rapid, and sensitive method is developed for the determination of UV filters in river waters by applying the vortex‐assisted dispersive liquid–liquid microextraction based on solidified floating organic droplet technique followed by the injector port silylation (IPS) in a gas chromatography‐tandem mass spectrometry system. Statistical experimental design methods including general factorial design, one factor at a time, and central composite face‐centered design are used for optimization purposes. Under optimized conditions, 460 µL of acetone and 30 µL of 2‐dodecanone are rapidly injected into a 10 mL water sample with 10% (w/v) NaCl at pH 2.5 and vortexed for 3 min. After centrifugation, 2 µL of the separated organic solvent is subjected to auto‐IPS with 1 µL of bis (trimethylsilyl) trifluoroacetamide containing 1% trimethylchlorosilane, at 260 °C for 4.5 min in programmable temperature vaporization mode. As a result of the validation studies, the intra‐day and inter‐day precision indicated as relative standard deviation are less than 12.4% and 18.8%, respectively. For all UV filters, detection limits are between 1.1 and 5.5 ng L−1 and limit of quantitation values are between 3.1 and 16.6 ng L−1. Successful recovery of extraction values (77.1%–107.4%) and good enrichment factors (231–350) are obtained.

Online Solid-Phase Extraction of Prometon and Prometryne Using MIL-101(Cr) as Sorbent before Gas Chromatographic Analysis: A Computational and Experimental Study and Comparison between Splitless and PTV Inlets.

In this study, prometryne and prometon were extracted and preconcentrated from aqueous media using an online solid-phase extraction-thermal desorption method coupled with gas chromatography-flame ionization detector (GC-FID), equipped with two different inlets: split and programmable temperature vaporizer (PTV). For this purpose, the applicability of Tenax and a metal-organic framework were investigated as solid-phase sorbents. Several effective parameters on the extraction efficiency, such as the amount of sorbent, sample volume, sample pH and thermal desorption procedure were optimized. The analytical performance of the proposed methods showed an excellent linear dynamic range for prometon and prometryne (0.25-100μg/L) and relative standard deviation less than 4.01%. Moreover, the detection limits below 0.20 and 0.35μg/L were determined for prometon and prometryne, respectively. Additionally, molecular docking was applied to clarify the adsorption nature and binding energy of MIL-101(Cr) toward the studied analytes, which indicated an appropriate correlation between computational and experimental results. Finally, the proposed method was developed and validated for prometon and prometryne and successfully applied for their extraction from agricultural water, spiked with prometon and prometryne through its direct introduction into the GC inlet.

Determination of Volatiles in Flue-Cured Tobacco by Gas Chromatography–Mass Spectrometry (GC–MS) with Chemometrics

This study reports the utilization of two-step headspace (HS) to profile the volatile compounds of flue-cured tobacco. The relationship between the volatile components and geographic origin was investigated using multivariate data analysis. To avoid the impact of adsorption caused by tobacco on the HS extraction, the tobacco was soaked by saturated NaCl solutions prior to the HS sampling. However, the introduction of water vapor may affect the subsequent gas chromatography–mass spectrometry (GC–MS) analysis. Thus, two-step HS, which is based on the coupling of the programmed temperature vaporizer inlet and HS autosampler, was employed to remove the water vapor while simultaneously preconcentrating the volatile compounds. The repeatability and stability were evaluated, and 80 compounds were identified from 25 flue-cured tobacco samples. Both principal component analysis (PCA) and hierarchical clustering analysis (HCA) revealed that the volatile components of flue-cured tobacco were closely related to the geographic origin. Furthermore, the characteristic volatiles of the flue-cured tobacco from different regions were illustrated using partial least squares discriminant analysis (PLS-DA). The presented work provided a simple and reliable way to profile the volatile components and characterize geographic origin of tobacco and tobacco products.

TOTAD interface: A review of its application for LVI and LC-GC

Abstract Large volume injection (LVI) in gas chromatography (GC) and online liquid chromatography-gas chromatography (LC-GC) are useful techniques for analyzing the compounds present at very low concentrations in complex samples since they substantially increase the sensitivity of the analysis and simplify sample preparation. LVI avoids the need to concentrate the extract and even the extraction step itself by directly injecting the sample. In online LC-GC, the liquid chromatography (LC) step acts as the sample preparation and/or fractionation step. The main problem in both techniques is the selective elimination of the large volume of solvent without losing the analytes. The TOTAD (through oven transfer adsorption–desorption) interface, based on a widely modified PTV (programmed temperature vaporizer) injector, allows large volumes to be injected into the gas chromatograph using both nonpolar and polar solvents, including water. Consequently, online LC-GC can be carried out whether the LC step is in the normal phase or the reversed phase. Various methods for analyzing trace compounds in food and environmental samples have been developed for LVI and online LC-GC using the TOTAD interface. Such analysis methods require the optimization of several variables common to LVI and online LC-GC and specific variables involved in online LC-GC, which must be optimized by taking into account the nature of the analytes and the characteristics of the sample matrix. This article reviews how each of these variables affects the performance of the analysis.

Development of a method for the determination of polyamines including N-acetylated forms in human saliva via benzoylation and gas chromatography-mass spectrometry

A simple method for the determination of polyamines and their N-acetylated forms was developed using benzoyl chloride as derivatization reagent, and 1,6-diaminohexane as internal standard, followed by liquid-liquid extraction with ethyl acetate. The organic extract was injected in a gas chromatograph using a programmed temperature vaporizer and the determination and quantification was performed with a quadrupole mass spectrometer. There was no matrix effect with the proposed method, so internal calibration was used to quantify the corresponding derivatives. Good linear responses were obtained in the range from the limits of detection to 500 µg L−1 (50 µg L−1 for spermidine), with correlation coefficients varying from 0.9591 to 0.9968. The limits of quantification (S/N = 10) ranged 1.0 – 8.3 µg L−1. Recoveries were found between 82 – 117%, showing the good accuracy of the proposed method. Intra- and inter-day precision assays, expressed as relative standard deviation (RSD) were evaluated at two different concentration levels (low and high), showing values in the range of 2.4 – 6.1% and 5.2 – 9.0% for repeatability and reproducibility, respectively (6.9 – 9.7% and 14.1 – 14.6% for spermidine). Successful determination of the studied polyamines and their N-acetylated forms was performed on the saliva of 17 volunteers.

Screening and confirmation of 244 pesticide residues in chilli by gas chromatography-quadrupole time-of-flight mass spectrometry

建立了辣椒中244种农药残留的QuEChERS前处理结合气相色谱-四极杆/飞行时间质谱(GC-Q-TOF/MS)快速筛查确证方法。鲜辣椒和干辣椒样品分别采用经-20 ℃冷冻的乙腈和1%(v/v)乙酸化乙腈提取,经盐析分层、分散固相萃取净化和浓缩后加入内标并复溶,HP-5MS UI色谱柱(30 m×0.25 mm×0.25 μm)分离,程序升温不分流进样,GC-Q-TOF/MS全扫描模式采集,内标法定量。比较了分析保护剂(AP)和基质匹配校准法对基质效应的补偿效果,最终选择采用基质匹配校准法来补偿基质效应并进行样品中农药残留的校准定量。设置定性筛查中的保留时间最大偏差为±0.25 min,精确质量偏差阈值为±20×10 -6。对鲜辣椒中244种农药残留和干辣椒中222种农药残留进行了定量方法验证,实验结果表明,采用建立的数据库和分析方法可以对辣椒进行农药残留的高通量筛查和定量分析。在空白辣椒样品中添加不同水平的目标化合物,以信噪比S/N≥10对应的添加水平作为定量限(LOQ)。鲜辣椒中最大残留限量(MRL)≤0.05 mg/kg的44种农药在鲜辣椒中LOQ≤0.010 mg/kg,线性范围在0.01~1.00 mg/L,在1倍和2.5倍LOQ添加水平下,回收率在60%~120%的农药种类占比分别为88.64%和100%;鲜辣椒中暂无MRL规定或MRL>0.05 mg/kg的200种农药在鲜辣椒中LOQ≤0.025 mg/kg,线性范围在0.05~1.00 mg/L,在1倍、2倍和10倍LOQ添加水平下,回收率在60%~120%的农药种类占比分别为49.50%、87.00%和89.50%; 244种农药的线性相关系数(r 2)均大于0.99。222种农药在干辣椒中LOQ≤0.15 mg/kg,线性范围在0.04~1.00 mg/L, r 2≥0.99的比例为95.46%,在1倍、2倍和10倍LOQ添加水平下,回收率在60%~120%占比分别为72.52%、73.42%和81.53%。应用建立的筛查确证方法对市售的12份鲜辣椒样品和14份干辣椒样品进行农药残留筛查分析,从9份鲜辣椒样品和3份干辣椒样品中筛查出8种农药化合物,经人工鉴定均为阳性,定量结果显示,8种农药化合物均未超过其在GB 2763-2019《食品安全国家标准食品中农药最大残留限量》所规定的MRL。方法快速、简单、高效、可靠,适用于鲜辣椒及干辣椒中多种农药残留的筛查分析。

A Toolbox for the Determination of Nitroaromatic Explosives in Marine Water, Sediment, and Biota Samples on Femtogram Levels by GC-MS/MS.

To determine the amount of the explosives 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, and its metabolites in marine samples, a toolbox of methods was developed to enhance sample preparation and analysis of various types of marine samples, such as water, sediment, and different kinds of biota. To achieve this, established methods were adapted, improved, and combined. As a result, if explosive concentrations in sediment or mussel samples are greater than 10 ng per g, direct extraction allows for time-saving sample preparation; if concentrations are below 10 ng per g, techniques such as freeze-drying, ultrasonic, and solid-phase extraction can help to detect even picogram amounts. Two different GC-MS/MS methods were developed to enable the detection of these explosives in femtogram per microliter. With a splitless injector, limits of detection (LODs) between 77 and 333 fg/µL could be achieved in only 6.25 min. With the 5 µL programmable temperature vaporization—large volume method (PTV-LVI), LODs between 8 and 47 fg/µL could be achieved in less than 7 min. The detection limits achieved by these methods are among the lowest published to date. Their reliability has been tested and confirmed by measuring large and diverse sample sets.

Determination of Polycyclic Aromatic Hydrocarbons in Agricultural Products

The procedure for the determination of polycyclic aromatic hydrocarbons (PAH) in agricultural products on the example of five crops (rapeseed, sunflower, flax, corn, soybeans) by gas chromatography mass spectrometry (GC-MS) was developed. It was showed the advantage of using binary mixtures of organic solvents "hexanedichloromethane" for PAH extraction. The time of Soxhlet extraction is from 6 to 8 hours at optimized conditions. The fractionation and purification of extracts by column chromatography on deactivated alumina was optimized. The article presents the optimization of sample injection in the programmed temperature vaporization (PTV) mode, parameters of gas chromatographic separation and mass spectrometric detection in determining 16 priority PAH in agricultural products. The recoveries, correctness and accuracy of the proposed method were checked by “spikes” with concentrations 0.5, 1.0, 2.5, 5.0 μg kg-1. The linearity of the method was determined by calibration curves obtained for three measurements of calibration solutions with concentrations of 0.5-100 ng mL-1. The effectiveness of the proposed combination of sample preparation and analysis by PTV-GC-MS was studied for linearity, accuracy, matrix effects and reproducibility. The method was validated by linearity, accuracy, matrix effect and reproducibility.

Empirical determination of explosive vapor transport efficiencies.

The transport efficiency of 2,4-dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazinane (RDX) trace vapors through tubing materials that commonly constitute vapor handling infrastructures have been determined for a variety of tubing dimensions and sampling conditions. Using a programmable temperature vaporization inlet coupled with a gas chromatography mass spectrometer (PTV-GC-MS), the explosive vapors were quantified both with and without a length of tubing of a specific material in the sampling flow path. At vapor temperatures of 30 °C and 66 °C, minimal attenuations were observed for 2,4-DNT and TNT vapor concentrations when the tubing material was in-line with the sampling flow path, indicating that the transport is largely unaffected by interactions with the surface of the tubing materials. In contrast, RDX vapors showed large attenuations as a function of both sampling conditions and tubing materials/dimensions. For those experiments where attenuated RDX vapor transport was observed, the mass sequestered by interactions between the flowing vapor and the internal tubing surface was determined to be in the range of tens to hundreds of picograms. Of all the materials examined for RDX transport, fluorinated ethylene propylene (FEP) tubing resulted in the least amount of mass loss to surface interactions, with vapor transport efficiencies (VTEs) between 95-100%. However, for some materials, the combination of tubing dimensions and sampling conditions resulted in no RDX transport, even after sampling more than 250.0 L of vapor through the tubing.

Multiple headspace sampling coupled to a programmed temperature vaporizer – Gas chromatograph-mass spectrometer for the determination of polycyclic aromatic hydrocarbons in water and saliva

Here we describe the development of a multiple headspace sampling methodology coupled to a programmed temperature vaporizer and a gas chromatograph-mass spectrometer (MHS-PTV-GC-MS) for the determination of 13 polycyclic aromatic hydrocarbons (PAHs) which are considered widespread environmental pollutants. Coupling with the PTV in solvent vent mode made it possible to enrich the analytes present in the headspace through multiple extractions and transfers to the injector previous to the chromatographic run. All parameters affecting the headspace generation, extraction, and stepwise transfer to the PTV were optimised. The method was successfully validated using UHQ-water, for thirteen PAHs, with limits of detection (LODs) in the range of 1.0–11 ng L−1. The method was also validated in saliva, with LODs in the range of 1.4–43 ng L−1. Intra- and inter-day repeatability values expressed as relative standard deviation percentage (RSD) were found to be lower or equal to 8.3% and 12.6%, respectively, in water, and 15.2% and 10.0% in saliva. Furthermore, all calibrations presented good linear behaviour (R2 values >0.98) and fitted to the model according to ANOVA model validation. This method was applied to the quantification of PAHs in 14 saliva samples from 11 subjects, both non-smokers and smokers. PAHs were not detected in saliva from non-smokers and light-smokers above the LODs. However, these compounds could be found in saliva samples from heavy smokers taken right after smoking. A study of the same subjects in saliva samples provided one hour later was also conducted to evaluate the concentration change in time.

Valorization of humin type byproducts from pyrolytic sugar conversions to biobased chemicals

The pyrolytic sugar fraction, obtained by an aqueous extraction of pyrolysis oil, is an attractive source for sugar-derived platform chemicals. However, solids (humin) formation occurs to a significant extent during hydrolysis and subsequent acid-catalyzed conversion processes. In this study, we report investigations on possible conversion routes (pyrolysis, liquefaction) of such humin byproducts to biobased chemicals. Experiments were carried out with a model humin made from a representative technical pyrolytic sugar and the product was characterized by elemental analysis, GPC, TGA, HPLC, GC-MS, FT-IR and NMR. The obtained humin sample is soluble in organic solvents (dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), and isopropanol (IPA)), in contrast to typical more condensed humins from glucose and fructose, allowing characterization using NMR and GPC. All analyses reveal that the humins are oligomeric in nature (Mw of about 900 g/mol) and consist of sugar and furanic fragments linked with among others (substituted) aliphatic, ester units and, in addition, phenolic fragments with methoxy groups. The humins were used as a feed for catalytic pyrolysis and catalytic liquefaction experiments. Catalytic pyrolysis experiments (mg scale, programmable temperature vaporizer (PTV)-GC–MS, 550 °C) with HZSM-5−50 as the catalyst gave benzene-toluene-xylene-naphthalene-ethylbenzene mixtures (BTXNE) in 5.1 wt% yield based on humin intake. Liquefaction experiments (batch reactor, 350 °C, 4 h, isopropanol as both the solvent and hydrogen donor and Pt/CeO2 (4.43 wt% Pt) catalyst) resulted in 80 wt% conversion of the humin feed to a product oil with considerable amounts of phenolics and aromatics (ca. 24.7 % based on GC detectables in the humin oil). These findings imply that the techno-economic viability of pyrolysis oil biorefineries can be improved by converting humin type byproducts to high value, low molecular weight biobased chemicals.

Differentiation and identification of fentanyl analogues using GC-IRD

Fentanyl analogues and their positional isomers have similar chemical structural configurations making them difficult to identify and differentiate. Gas chromatography coupled to a gas-phase infrared detector (GC-IRD) is a useful and powerful tool for the unambiguous identification of fentanyl compounds where traditional analytical techniques such as gas chromatography–mass spectrometry (GC–MS) offer limited information for this class of compounds. In this study, we demonstrate the utility of GC-IRD and show how this complementary information enables the identification of fentanyl analogues (2- and 3- furanylfentanyl, 2-furanylbenzylfentanyl, crotonylfentanyl, cyclopropylfentanyl, methoxyacetylfentanyl, carfentanil, meta-fluoroisobutyryl fentanyl, para-fluoroisobutyryl fentanyl and ortho-fluoroisobutyryl fentanyl) when combined with GC–MS data. A description of the operating conditions including how the optimization of GC-IRD parameters can enhance the spectral resolution and unambiguous identification of these fentanyl analogues is presented, for the first time. In particular, the effects of light pipe temperatures, acquisition resolution, the use of a programmed temperature vaporizing (PTV) inlet, and the analytical concentration of the sample were evaluated. A real-world case example illustrates the current challenges frequently encountered in casework and how the implementation of GC-IRD may overcome some of these challenges in fentanyl differentiation and identification.