Splitless Injection Research Articles

Exploring thermal isomerisation in gas chromatography analyses using natural pyrethrins: Comparison of comprehensive two-dimensional and one-dimensional gas chromatography

This study aims to assess and qualitatively compare the visual presentation of chromatographic data from the isomerisation of natural pyrethrins – a group of pesticides derived from Chrysanthemum flowers – using one-dimensional gas chromatography (1DGC) and comprehensive two-dimensional gas chromatography (GC×GC). Molecular structural changes, such as thermal isomerisation in this case, occur during gas chromatography injection and separation, to provide characteristic patterns which may not be routinely recognised on the 1D chromatogram. To demonstrate the influence of analytical method parameters on isomerisation processes, variations in oven temperature (isothermal vs. temperature programmed analysis), inlet mode (split vs. splitless), inlet temperature, and carrier gas flow rate were investigated. Increasing oven temperature was the most significant factor affecting isomerisation. Splitless injection mode and increasing inlet temperature promoted isopyrethrin formation, while the effect of inlet temperature appeared minimal with a split injection technique, most likely due to the short residence time in the inlet. Increased carrier gas flow rates in a temperature programmed analysis reduced retention time and minimised isomerisation. The unique presentation of isopyrethrin peaks on a GC×GC contour plot allows for facile recognition of isomerisation especially at low concentrations, simplifies chromatogram interpretation, and aids in analyte identification. It also confirms that the isomerisation process is irreversible since the pyrethrin I and II compounds are absent throughout the bridge formation. These benefits support the use of GC×GC over 1DGC to study isomerisation. Additionally, due to limited data in the literature, Kováts retention indices and linear retention indices of the natural pyrethrins, including isopyrethrins, were experimentally determined on four columns: DB-5 ms UI, Rxi-17Sil MS, SLB-IL60i, and SLB-IL111i.

Phytochemical Screening and Quantitative Analysis of Annona muricata Leaf Ethanolic Extract by Gas Chromatography-Flame Ionization Detection (GC-FID)

Annona muricata (soursop) leaves have been traditionally used for medicinal purposes due to its potential antioxidant, anti-inflammatory, anticancer, antimicrobial, and analgesic properties. This study quantitatively determined the phytochemical composition of soursop leaf. Using a BUCK M910 Gas Chromatography with a flame ionization detector, the analysis of phytochemicals was carried out. A 15 m x 250 0.15 RESTEK MXT-1 column was used. Helium 5.0pa.s was used as the carrier gas, flowing at a rate of 40 ml/min, with a splitless injection of 2ul of sample at a linear velocity of 30cm/s. The injector temperature was 280⁰C. At first, operating at 200⁰C, the oven was then increased to 330⁰C at a rate of 3⁰C per minute, and this temperature was maintained for 5min. An operating temperature of 320⁰C was used by the detector. The result shows that soursop ethanolic extract contains phytochemicals that belong to the broad class flavonoids (a class of polyphenolic compounds). They include naringenin (5.92 ug/ml), flavan-3 ol (5.70 mg/l), rutin (2.79 ug/ml), flavanones (3.28 ug/ml), kaempferol (6.15 ug/ml), flavone (1.99 ug/ml), proanthocyanin (2.36 ug/ml). Other polyphenols (not flavonoids) present include resveratrol (7.03 ug/ml), tannin (2.90 ug/ml), catechin (2.49 ug/ml), and epicatechin (7.67 ug/g). The alkaloids found include lunamarin (4.72 ug/ml) and spartein (2.07 ug/ml) while saponins found include sapogernin (16.07 ug/ml) and sapogenin (3.08 ug/ml). Other classes of phytochemicals found include steroids, cyanogenic glycoside, anti-nutrient, and cardiac glycosides. Soursop leaf contains bioactive compounds such as flavonoids, polyphenols, alkaloids, steroids, cyanogenic glycoside and other phytochemicals with medicinal potentials.

Highly sensitive detection of polystyrene by on-line splitless pyrolysis-gas chromatography/mass spectrometry with cryo-trapping of pyrolyzates and forced venting of carrier gas

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been extensively used as a powerful tool for polymer analysis. In Py-GC/MS measurements, GC methods have usually employed split injection conditions for qualitative and quantitative analysis, but splitless injection of pyrolyzates to GC/MS has been reported to obtain higher sensitivity for small amount of analytes, since split ratio is inversely related to the amount of analyte entering the detection systems. However, the slower total carrier gas flow rate of splitless injection, which is necessary to keep the column flow rate at around a few mL/min, can increase residence time in the pyrolysis chamber, which can cause unfavorable secondary reactions of pyrolyzates such as decomposition and recombination in the pyrolyzer. In this study, we developed a new on-line splitless Py-GC/MS method called the Forced-Venting-and-Trap-Splitless (F-Splitless) method, based on cryo-trapping of pyrolyzates and forced venting of carrier gas under high carrier gas flow rate. Calibration curves measured by the F-Splitless method for polystyrene (PS) using the styrene monomer and trimer as key compounds show a good linearity over the concentration range from 0.01 ng to 100 ng. Limit of detection (LOD) and limit of quantification (LOQ) were 17 pg and 56 pg for the styrene monomer (S) based on the criterion of LOD: 3σ/a and LOQ: 10σ/a, where a is the slope of the calibration curve and σ is the standard deviation of the peak area of the minimum concentration, using the selected ion monitoring (SIM) mode. At a trace concentration level of PS, contamination from the environment was recognized. However, 100 pg of PS showed a signal to noise ratio (S/N) of 570 for S in SIM mode and 1.8 pg of PS could be quantified according to the criterion of LOQ based on signal to noise ratio (S/N), i.e., S/N = 10.

Thermal decomposition of CBD to Δ9-THC during GC-MS analysis: A potential cause of Δ9-THC misidentification

On the analysis of cannabidiol (CBD) e-liquid by gas chromatography-mass spectrometry, we experienced suspected thermal decomposition of CBD to Δ9-tetrahydrocannabinol (Δ9-THC). To clarify the factors involved in the decomposition, we evaluated the effects of the injection methods (splitless or split), injector temperatures (250, 225, 200, and 180 °C), and liner conditions (new liner or used liner) on the CBD decomposition. We also examined whether addition of methylamine to the dissolving solvent (methanol) inhibited the decomposition.Decomposition was not observed under split mode. However, under splitless mode, we observed that decomposition was promoted with the use of used liner and by high injector temperatures, and addition of methylamine to the dissolving solvent also suppressed the decomposition.Split injection was effective for preventing the decomposition; however, splitless injection enables detection of lower-concentrated Δ9-THC in CBD products than split injection. To balance sensitivity of Δ9-THC and inhibition of the thermal decomposition under splitless mode, we recommend using new liner for the analysis, addition of methylamine to the dissolving solvent, and maintenance of the injector temperature at 200 °C.

Achieving Higher Signal Response Than Splitless GC Injection by High-Pressure Headspace Sampling and Full Evaporation Technique

Achieving Higher Signal Response Than Splitless GC Injection by High-Pressure Headspace Sampling and Full Evaporation Technique

A fast, fully validated GC-MS method using a simplified pretreatment for the quantification of short and branched chain fatty acids in human stool.

The study of short (SCFAs) and branched chain fatty acids (BCFAs) in human stool related to gastrointestinal diseases, gut microbiota, metabolism, and diet has dramatically increased. As a result, a fast, reliable method with minimal pretreatment is needed for quantification of these metabolites (acetic, propionic, isobutyric, butyric, isovaleric, valeric, and caproic acid) in stool. Therefore, a GC-MS method meeting this criterion was developed. A bias sampling study showed no statistical difference (p>0.05) in analyte means when comparing 100 mg subsamples of homogenized to non-homogenized samples (n=6, p values 0.153-0.910). Stool samples were homogenized, diluted with 80:20 water:methanol (v/v), and adjusted to a pH of 1.5-2.5. Samples were vortexed, centrifuged, and directly injected into the GC-MS using pulsed splitless injection offering twofold-to-threefold signal enhancement over a 10:1 split injection. DB-FATWAX Ultra Inert Polyethylene Glycol (PEG) Column showed no peak tailing, reduced responses, or retention time shifts after 1,476 stool injections, while other columns failed before 361 injections. Intra- and inter-day accuracy for stool supernatant samples ranged from -10.21% to 8.88% and -13.25% to 9.91%, while intra- and inter-day precision ranged from 0.21% to 1.21% and 0.89% to 2.84% coefficient of variation (CV), respectively. This method demonstrates excellent linearity (0.9999-1.0000) and low limits of quantification (1.50-8.01 μM). Stool samples proved stable stored at -20°C up to 28 days, and recoveries ranged from 85.04% to 106.59%. Matrix effects in stool are non-significant determined by comparing standard and stool supernatant calibration curve slopes (p>0.05).

Split/Splitless Inlets in Gas Chromatography: What’s Up with All Those Different Glass Inlet Liners?

Over the winter break at the university where I work, I was ordering consumables for the upcoming semester. As I was browsing the web pages at a major vendor for glass inlet liners, I was again impressed by the many glass inlet liner options and geometries available for split and splitless inlets, still by far the most used today. In this installment, we review the processes that happen in the inlet when a sample is injected, and use this to make some sense of the many available inlet liner configurations. We generate some best practices and guidelines in selecting an inlet liner, but we see that there is no one single liner that fits all situations. Selecting the best inlet liner should be a step in all method development involving split or splitless injections.

Development, validation of a GC–MS method for the simultaneous measurement of amino acids, their PTM metabolites and AGEs in human urine, and application to the bi-ethnic ASOS study with special emphasis to lysine

A gas chromatography-mass spectrometry (GC–MS) method was developed and validated in relevant concentration ranges for the simultaneous measurement of l-lysine (Lys, L) and its Nε- and Nα-methylated (M), Nε- and Nα-acetylated (Ac), Nε-carboxymethylated (CM) and Nε-carboxyethylated (CE) metabolites in human urine. Analyzed Lys metabolites were the post-translational modification (PTM) products Nε-mono-, di- and trimethyllsine, Nε-MML, Nε-DML, Nε-TML, respectively, Nα-ML, Nε-AcL, Nα-AcL, and its advanced glycation end-products (AGEs) Nε-CML, Nε-CM-[2,4,4-2H3]Lys (d3-CML), Nε-CEL and furosine. AGEs of arginine (Arg) and cysteine (Cys) were also analyzed. De novo synthesized trideutero-methyl esters (R-COOCD3) from unlabelled amino acids and derivatives were used as internal standards. Native urine samples (10 µL aliquots) were evaporated to dryness under a stream of nitrogen. Analytes were esterified using 2 M HCl in methanol (60 min, 80 °C) and subsequently amidated by pentafluoropropionic anhydride in ethyl acetate (30 min, 65 °C). The generated methyl ester-pentafluoropropionyl (Me-PFP) derivatives were reconstituted in borate buffer and extracted immediately with toluene. GC–MS analyses were performed by split-less injection of 1-µL aliquots, oven-programmed separation and negative-ion chemical ionization (NICI). Mass spectra were generated in the scan mode (range, m/z 50–1000). Quantification was performed in the selected-ion monitoring (SIM) mode using a dwell time of 50 or 100 ms for each ion. The GC–MS method was suitable for the measurement of Lys and all of its metabolites, except for the quaternary ammonium cation Nε-TML. The Me-PFP derivatives of Lys, Arg and Cys and its metabolites eluted in the retention time window of 9 to 14 min. The derivatization of Nε-CML, d3-CML and Nε-CEL was accompanied by partial Nε-decarboxylation and formation of the Me-PFP Lys derivative. The lowest derivatization yield was observed for Nε-DML, indicating a major role of the Nε-DML group in Lys derivatization. The GC–MS method enables precise (relative standard deviation, RSD < 20%) and accurate (bias, < ± 20%) simultaneous measurement of 33 analytes in human urine in relevant concentration ranges. We used the method to measure the urinary excretion rates of Lys and its PTM metabolites and AGEs in healthy black (n = 39) and white (n = 41) boys of the Arterial Stiffness in Offspring Study (ASOS). No remarkable differences were found indicating no ethnic-related differences in PTM metabolites and AGEs except for Nε-monomethyllysine and S-(2-carboxymethylcysteine).

GC-MS Analysis of n-hexane Extract of Roots of Aerva lanata (Linn) Juss. ex. Schult.

Context: The roots of the plant Aerva lanata are extensively used in Indian System of Medicine to cure urinary stones, antidiabetic, diuretic and used as demulcent. Aim: To investigate the phytoconstituents from the n-hexane extract of the roots of Aerva lanata using GC-MS analysis. Materials and Methods Roots of Aerva lanata was extracted by Soxhlet extraction method using n-hexane. The chromatogram was recorded by injecting the extract by splitless injection mode into the GC MS 5975 C Agilent equipped with a QP- 5000 (quadrupole) Gas Chromatography–Mass Spectrometer. Results: 23 phytoconstituents were identified by close matches with standard MS spectra and compared with NIST- 11 and WILEY library data from n-hexane extract. The major compounds reported are oleic acid (21.68%), γ-sitosterol (10.67%), Stigmasterol (5.13%), 3-β,5-α-stigmast-7-en-3-ol (4.23 %) and other constituents were found to be in traceable quantities. Conclusion: GC-MS analysis of roots of Aerva lanata revealed certain interesting facts of presentation of various phytoconstituents. The presence of various phytoconstituents contributes to the medicinal activity of the plant.

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。

Assessing the content of a package of SGT-151 sold online

Introduction Synthetic cannabinoids (SCs) are novel psychoactive substances that mimic the effects of cannabis [1–3]. These products were sold via online shops and consisted of herbal mixtures sprayed with SCs [3]. Since then, a deluge of chemical variations of SCs has been occurring worldwide due to their synthesis in clandestine laboratories, often based on pharmaceutical research and patents, posing a growing challenge for authorities regarding regulation of these substances [1,3]. More recently, several highly potent compounds have emerged on the drug market, synthesised as stated in the patent application of Bowden and Williamson (“SGT-compounds”). These drugs are characterised by a cumyl substituent, which is attached to an indole, indazole or azaindole structure. One of the first cumyl-derivatives, CUMYL-PEGACLONE, was found in 2016 on the German drug market, being sold under the street name SGT-151 [1,2]. The present study aims to understand what is inside of a SGT-151 package sold in the internet as a ‘research chemical’. Materials and methods The cannabinoid identification was based on its mass spectra using the Cayman database (Chemical C. Cayman Spectral Library, vol. v08302018). GC/MS was the technique used to analyse the compound using a MEGA–5 MS capillary column (0.25 µm, 0.32 mm, 30m). Chromatographic analysis was carried out under the following conditions: injection volume 1 µL and splitless injection at 280 °c. The initial oven temperature was 100 °C for 3 min, ramped to 310 °C at a rate of 30 °C/min and held at 310 °C for 10 min. The MS conditions were as follows: ionisation energy was set at 70 eV; acquisition was carried out in a scan mode range of m/z 30–450. Helium was used as the carrier gas. For purification, a HPLC/DAD, operated by Clarity software, was used with a reversed-phase column. The mobile phase was a solvent gradient system consisting of (A) 5% 10 mM ammonia format and (B) 95% acetonitrile, optimised to achieve the best resolution. The results were recorded at λ = 252 nm. Results Figure 1(A) shows the GC/MS chromatogram of SGT-151. It is clear the presence of a peak corresponding to SGT-151 and several other peaks from other compounds. It was not possible to identify the remaining peaks. Figure 1(B) shows a GC/MS chromatogram after purification of the package content. Discussion and conclusions: The data gathered in this study shows that SGT-151 contains a significant amount of impurities. This working progress data is the initial step of a bigger project aiming to understand whether there are differences in the toxicity of pure and non-pure SGT-151 on human cell lines, once it is important to understand if the impurities may have any influence on the cytotoxicity, compared to substances in their pure form, since most of the times the substances that are sold on the streets are not 100% pure. Figure 1. GC/MS analysis: chromatogram before (A) and after (B) purification by HPLC/DAD and mass spectrum (C).

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.

Assessing the influence of neglected GC-FID variables on the multiple responses using multivariate optimization for the determination of ethanol and acetonitrile in radiopharmaceuticals

Analytical gas chromatography in line with a flame ionization detector (GC-FID) method was developed and validated for direct determination of organic solvents in [18F]fluoro-ethyl-tyrosine ([18F]FET), [18F]fluoromisonidazole ([18F]FMISO) and [18F]fluorothymidine ([18F]FLT). Variables of the splitless time (min) and injection temperature (°C) on the response of analysis time and resolution were optimized with the assistance of a two-level full factorial design and desirability function of Derringer. The proposed procedure was validated following the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2 (R1) guideline. Excellent linearity, R2 > 0.990, indicated that approximately 99% of the response variance could be predicted from ethanol and acetonitrile concentrations ranging from 0.5 to 6.0 mg mL−1 and 0.1 to 0.8 mg mL−1, respectively. The proposed procedure has proved to be selective, sensitive, and accurate (90–110%), with excellent repeatability and precision (RSD < 2%). In the robustness analysis, the findings from the calculated Standardized Effects Values (SE) were insignificant (p > 0.05) and demonstrated that the proposed method was robust for a splitless time of 1.0 ± 0.5 min and an injection temperature of 210 ± 10 °C. The proposed method was also successfully used for the quantitative determination of ethanol and acetonitrile in [18F]FET, [18F]FMISO, and [18F]FLT. Both solvents were well separated (R, 4.1–4.3) within 4.5 min. Therefore, the proposed method is relevant for routine quality control analysis of all 18F-radiopharmaceutical derivatives for the direct determination of ethanol and acetonitrile.

A Rapid Method for Direct Determination of Levulinic Acid in Soy Sauce

A simple and rapid method was developed to determine the levulinic acid level in soy sauce using megapore polar column (CP-Wax, 30 m × 0.53 mm) with splitless direct injection gas chromatography. Direct quantitative analysis of levulinic acid in soy sauce was carried out without any sample pretreatment procedure. A water-soluble compound, 1,6-hexanediol, was used as the internal standard. The detection limit for levulinic acid was 10 μg/mL. Recoveries from soy sauce and pickled condiment liquid were performed by spiking 2.5, 5.0, or 10.0 mg to 1 mL of test samples and were found to be at the range of 98∼103% with coefficients of variation less than 6.3%. Fourty-six food samples including animal and vegetable protein hydrolysate, pickle condiment liquid, and soy sauce were analyzed using the proposed method. Levulinic acid contents in pickled condiment liquid were found to be 2.1∼4.7 mg/mL and in soy sauce were 7.8∼24.5 mg/mL, which were higher than CNS regulated level (1.0 mg/mL), indicating commercial pickles and soy sauce might be adulterated with vegetable protein hydrolysate. These results were inconsistent with the labeling of "100% fermented soy sauce" on the packages.

Determination of methyl- and inorganic mercury in fish using focused microwave digestion followed by Cu++ addition, sodium tetraethylborate derivatization, n-heptane extraction, and gas chromatography-mass spectrometry

The analytical procedure for analysis of methyl- and inorganic mercury in fish was developed in this study. It involved microwave-assisted digestion with alkaline solution (tetra methyl ammonium hydroxide), addition of Cu++, aqueous-phase derivatization of mercury species with sodium tetraethylborate, and subsequent extraction with n-heptane. The various mercury derivatives were desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by electron impact mass spectrometry. Optimum conditions allowed the sample throughout to be controlled by the instrumental analysis time (about 8 min per sample) but not by the sample preparation step. At the irradiation power of 15-30, 45, and 60-75 W, sample heating times were only 3.5, 2.5, and 1.5 min, respectively. The recoveries of mercury species were 92.3-96.1% and 93.6-95.5% for methyl- and inorganic mercury, respectively. The proposed method was finally validated by the analysis of three biological certified reference materials (BCR CRM 464 tuna fish, NRC DORM-2 dogfish muscle, and NRC DOLT-2 dogfish liver).

Coupling of large volume injection with flow modulated two-dimensional gas chromatography

The coupling of large volume injection (LVI) with comprehensive two-dimensional gas chromatography (GC × GC) can be a powerful technique in the analysis of trace-level complex samples. The coupling of LVI and GC × GC using a cost efficiently operable pneumatic modulator based on capillary flow technology has been examined. The aim was to optimize the LVI parameters in the case of samples with compounds covering a wide boiling range. For the optimization of LVI 25 microliters of a solution containing 27 target compounds modelling the composition and the boiling range of diesel oils was used. The injection parameters were evaluated for peak shapes, reproducibility and peak volumes relative to peak volumes obtained using cold splitless injection. For all GC × GC experiments a non-polar first column (Rxi-5ms) and a polar second column (HP-INNOWax) were applied. Through extensive method optimization solvent vent proved to be an unsuitable technique for the injection of compounds covering a wide boiling range: at lower vent times peaks split, while higher vent times caused severe losses of highly volatile compounds. Therefore, a split-splitless LVI method was optimized. Injection speed, split vent time, splitless vent time and vent flow during split vent have been optimized. The developed method is suitable for the coupling of LVI with flow modulated GC × GC. Using the optimized split-splitless LVI parameters no peak distortion of the target compounds was observed. The relative peak volumes were between 60–120% for all compounds (80–120% for 13 compounds).

Investigation into the Analysis of Fentanyl in Postmortem Blood using Biocompatible Solid-Phase Microextraction

Over recent years, the abuse of fentanyl and other opioids has become a slow motion mass disaster in the United States resulting in an increased number of drug-related deaths. Various postmortem biological samples are collected by forensic pathologists during autopsy and then sent to a toxicology laboratory to be analyzed for the presence of various compounds such as fentanyl. This process can be time consuming and results in a backlog, potentially hindering an investigation. A possible solution is Biocompatible Solid-Phase MicroExtraction (BioSPME) fibers. These fibers can be directly inserted into a biological matrix and absorb drug compounds without the interference of macromolecules that may be present allowing for a faster analysis time. An initial method has been developed to analyze fentanyl in postmortem blood using BioSPME followed by GC-MS and LC-MS-MS analysis. BioSPME fibers were conditioned, washed, directly inserted into postmortem blood, washed, filtered, desorbed into solution, dried down and reconstituted. The extracted samples were screened by GC-MS and subsequently analyzed by LC-MS-MS. GC-MS was performed using splitless injection on a Rxi-5Sil MS column (30.0 m × 0.25 mm, 0.25 μm) in the SIM mode. Samples were confirmed using an AB SCIEX™ 3200 QTRAP® triple quadrupole mass spectrometer with ElectroSpray Ionization (ESI) source in the positive ion mode. Liquid Chromatography was performed on a Shimadzu® LC system using an Ascentis® Express Biphenyl column (50 mm × 2.1 mm, 2.7 μm) with the weak mobile phase of 0.1%(v/v) formic acid in water and the strong mobile phase of 0.1%(v/v) formic acid in acetonitrile for an analysis time of seven min per sample. This method was developed using bovine blood and then applied to 43 postmortem blood samples provided by the Lehigh County Coroner’s Office (Allentown, PA, USA).

Simultaneous detection of five flavoring agents in chewing gum by ultrasound-microwave synergistic extraction coupled with gas chromatography

So far, the identification and determination of flavor additives in food has gained extensive attention in the area of food safety. However, it remains a big challenge for simultaneous detection of diverse flavor agents. In this work, a novel gas chromatography method coupled with ultrasound-microwave synergistic extraction was developed for simultaneous detection of five flavor compounds, including butyl butyrate, menthol, methyl salicylate, eugenol and vanilline. In this strategy, ultrasound-microwave synergistic extraction was used to extract the five flavoring agents from chewing gum. The effects of extractants, solid-liquid ratio, extraction time and microwave power on extraction yield were researched by using orthogonal test. After the optimization of programme temperature and splitless injection, the five flavoring agents were well separated and simultaneously detected with wide linear ranges, low limits of detection, high accuracy and good repeatability. Therefore, this proposed method would hold great promise for assay application on the food safety.

The compound-independent calibration of polybrominated diphenyl ethers isomers using gas chromatography-inductively coupled plasma mass spectrometry

Compound-independent calibration (CIC) is a quantitative method that can quantify other compounds using a structure-independent compound as the calibrant. In this study, the potential and application of CIC method for the determination of polybrominated diphenyl ethers (PBDEs) using GC-ICP-MS was investigated. The effects of sample introduction conditions, the flow rate of the carrier gas, splitless delay time and the matrix of the complex sample on the response of 11 PBDEs compounds were explored. When pulsed splitless injection was used, the transmission efficiency of analytes from the inlet to the column can speed up with increasing injection temperature and pulse pressure, the elemental response of bromine of each analyte becomes closer. Under optimized chromatographic conditions, the response is independent of the compound can be found from the slope of the pure solution standard from tri- to hepta- brominated compounds (BDE 28 as reference) ranged from 0.968 to 1.001 (R2>0.998).The degradation ratio of BDE 209 in the GC-ICP/MS system was estimated by the CIC method to be 18.7%. During the determination of fish tissue sample, big difference of the elemental response ratio (BDE 28 as reference) was obtained range from 0.678 to 0.976. However, a similar elemental response was observed among isomers range from 0.990 to 1.056. This may mean that the isomers can be calibrated to each other in a complex matrix sample. The CIC method was validated by determination 3 PBDEs in NIST SRM 1947 frozen fish tissue certified reference materials using isomers as reference compounds. The recoveries of BDE 49 and BDE 66 were 105.7% and 88.1% by using BDE 47 as calibrants, and that of BDE 155 was 108.8% by using BDE 154 as calibrant.

Analysis of thermally labile pesticides by on-column injection gas chromatography in fruit and vegetables

Thermally labile pesticides (captafol, captan, dicofol, and folpet) are highly prone to suffer thermal degradation during sample introduction into a gas chromatograph (GC) to tetrahydrophthalimide (THPI), 4,4'-dichlorobenzophenone (DCBP), and phthalimide (PI), respectively, mainly produced in the glass liner of the injector. This undesired behavior leads to inaccurate qualitative and quantitative results. Direct on-column injection (OCI) technique is evaluated as an alternative to avoid or minimize compound alteration during the analysis. This configuration was studied and evaluated for the determination of this group of thermally troublesome pesticides. The OCI inlet was operated in "track oven" temperature and connected to a wide-bore deactivated guard column that is itself connected to a capillary GC analytical column. This technique has demonstrated to be useful for avoiding degradation generated in the hot inlet. Limitations observed for OCI in routine analysis were injection volume, guard column length, and maintenance issues. Analytical standards spiked in vegetable solutions were injected in OCI, not observing any thermal degradation rate. On the contrary, classical splitless injection (SLI) produced high degradation rates in all cases. This OCI approach was validated in citrate QuEChERS extracts of tomato, apple, and orange matrices for these four compounds and their corresponding transformation products (THPI, DCBP, and PI), evaluating recoveries, repeatability, linearity, and matrix effect. This set-up enabled the correct identification and quantitation for most compounds at LOQs of 0.010mg/kg in fruit and vegetable samples. The OCI grants evident differentiation between metabolites naturally occurring in food and thermal degradation products created during the analysis. Graphical abstract ᅟ.