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A novel flameless operating mode is introduced, which improves the response of a multiple flame photometric detector (mFPD). The mFPD normally has analyte travel through 4 'worker' flames in series before entering a final 'analytical' flame where its emission is monitored. Here, it is found that when the analytical flame is not ignited, background luminescence is reduced over 30 times and the strong analyte chemiluminescence of the worker flames can be made to extend a large distance (~ 10 flame widths) into the analytical flame region where it is detected. This occurs for phosphorous (HPO*), quadratic sulfur (S2*), and linear sulfur (HSO*) emission. Conversely, carbon emission resides inside the worker flames and yields a small negative signal. As a result, very good selectivity over carbon is observed, and improved minimum detectable limits (MDL) of 4 pg S/s (S2*) and 0.3 pg P/s (HPO*) are obtained, which are up to 20 times lower than previous values reported for the mFPD. Further, linear sulfur (HSO*) yields an MDL of 6 pg S/s, which is over 3 times lower than values reported for other FPDs. Due to the worker flames present in this mode, other benefits of regular mFPD operation are maintained, like uniform analyte response and large quenching resistance. In application, a trace benzothiophene analyte is readily detected within a concentrated diesel fuel matrix in the flameless mFPD mode, while no response is observed in the conventional FPD mode. Results indicate that this flameless operating mode is advantageous for sulfur and phosphorous analysis. [ABSTRACT FROM AUTHOR]

Objective: In this study, we aimed to develop a headspace capillary gas chromatography method to quantify residual methanol, acetone, methylene chloride, diisopropyl ether, ethyl acetate, and n,n-dimethylformamide (DMF), in raw clobetasol propionate. Methods: The headspace gas chromatography method employs a chromatographic column packed with 6% cyanopropylphenyl-94% dimethylpolysiloxane as the stationary phase. The column temperature program initiated at 40 °C, was held for 10 min, then ramped up at 10 °C per minute to 220 °C, and maintained for 1 min. Nitrogen served as the carrier gas at a flow rate of 4.84 ml/min. The injection port temperature was set at 140 °C; the flame ionization detector (FID) operated at 250 °C, and the headspace equilibrium temperature was maintained at 105 °C with a 30 min equilibration time. Results: All six residual solvents exhibited complete separation, displaying strong linearity and achieving high recovery rates. Furthermore, the residual solvent levels in the six samples tested remained comfortably below the permissible limit. Conclusion: Our method is accurate, reliable, rapid, and sensitive, making it well-suited for the detection of organic residual solvents in raw clobetasol propionate. [ABSTRACT FROM AUTHOR]

A novel method for externally adjusting the column length during gas chromatography (GC) operation is introduced. The technique employs the controlled dehydration of a water stationary phase off a stainless-steel capillary column wall, which is then removed by the carrier gas. By halting the dehydration process (i.e. through adding water to the system) at specified times, partial column (i.e. coating) lengths are created as desired. For instance, since the phase is removed in a 'peeling' motion from inlet to outlet, then dehydrating 1/2 of the water coating away results in a 1/2 coated column remaining. This, in turn, acts analogous to a 1/2 column length in separations. In this way, direct and effective reduction in analyte retention time results from shortening column length. Adjustable lengths from 3/4 down to 1/10 of a full column are demonstrated. Good stability in maintaining new column lengths is realized, as analyte retention times vary by only about 1% RSD for most lengths and temperatures examined. Through calibration, column length can be predictably adjusted using system dehydration time, with changes being performed in a few minutes. Results indicate that this method could be useful for adjusting column length in-situ to accommodate various samples during GC operation. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the development of the method of high-temperature two-dimensional gas chromatography (HT-GC × GC) using a flow modulator for the analysis of a number of complex high-boiling samples. A method has been developed that allows to analyze complex samples with a temperature up to 360 °C using a combination of non-polar and mid-polar columns. We have achieved separations of such complex mixtures as products of thermal cracking of slack wax, vacuum gas oil (VGO) and the products of its processing, a product of catalytic processing of sludge sediments pyrolysate and products of polyethylene pyrolysis. The method makes it possible to achieve good resolution in the previously listed samples between the groups of aromatic and aliphatic hydrocarbons. In addition, the group of aliphatic hydrocarbons was resolved into separate constituent classes: alkanes, alkenes, alkadienes, and cycloalkanes. A good resolution was reached for sludge pyrolysis samples between the groups of polar compounds and aromatic and aliphatic hydrocarbons. Comparisons with other standardized methods illustrate the high potential of high-temperature two-dimensional gas chromatography for the analysis of high-boiling mixtures. [ABSTRACT FROM AUTHOR]

Chromatography is a separation method that utilizes differences in intermolecular interactions of the sample components with the mobile and stationary phases as the sample passes through the column. Acetic acid is a compound of focus in the study of pharmaceutical residues and short-chain fatty acids. Gas chromatography using polar capillary columns (DB-WAX) is an effective means of analyzing acetic acid. In one such solvent, dimethyl sulfoxide (DMSO), the retention time of the acetic acid shows a positive linear correlation with an equal volume increase of the DMSO solvent. We used the quantum chemistry calculation programs ORCA 5.0 and Multiwfn 3.7 with the DFT M062X/6-311 + + G(3d,2p) method to calculate the chromatographic separation parameters. We then analyzed formic acid for comparison and found the retention time of formic acid in the DB-WAX capillary column was longer than that of acetic acid. The retention time variation of formic acid in DMSO solvent compared with aqueous solvent was longer than that of acetic acid; the reason for this observation is that their retention time variation in DMSO solvent was related to the formation of strong hydrogen bonds. There are currently few studies focusing on quantum chemical calculations in chromatographic separations. Our studies using gas chromatography analysis and quantum chemical calculations explain the reasons for retention time variations. [ABSTRACT FROM AUTHOR]

A bromine-terminated triblock copolymer (Br-PCL-PDMS-PCL-Br) was synthesized and employed as the stationary phase for capillary gas chromatography (GC). The statically coated Br-PCL-PDMS-PCL-Br column showed the efficiency of 2260 plates/m determined by 1-octanol at 120 °C and moderate polarity. For evaluating the separation performance, a mixture of 23 analytes was employed and the commercial HP-35 and PEG-20 M columns were used as the reference columns. Also, the positional and cis-/trans-isomers were utilized to investigate the separation performance on the Br-PCL-PDMS-PCL-Br column. Moreover, it showed higher resolution of chloroaniline and bromoaniline isomers on the Br-PCL-PDMS-PCL-Br column than commercial HP-35 and PEG-20 M columns, and exhibited different retention behavior with HP-35 column. All the results indicated that there were multiple molecular recognition interactions between the Br-PCL-PDMS-PCL-Br stationary phase and the analytes, including H-bonding, dipole–dipole, CH···π, dispersion and halogen-bonding interactions. This work provided a research basis for exploring the application of block copolymer materials in the field of chromatographic analysis. [ABSTRACT FROM AUTHOR]

In this paper, SiO2@MOF-199 composite with core–shell structure was prepared by in-situ growth of MOF-199 on the surface of SiO2 microspheres, and SiO2@MOF-199 coated fiber was prepared for headspace solid phase microextraction (HS-SPME) of phthalate esters (PAEs) in plastic bottled milk. The prepared SiO2@MOF-199 has both mesoporous structure of SiO2 and microporous structure of MOF-199. The hierarchical porous structure not only gives the analyte higher adsorption performance, but also improves the diffusion rate of the analyte in SiO2@MOF-199. The coated fibers have good thermal stability and are relatively uniform in size and structure. The extraction conditions of the prepared fibers for PAEs were optimized by single factor optimization and response surface Box-Behnken design. Under optimized conditions, the fiber displays wide linear ranges of PAEs (dimethyl phthalate, diethyl phthalate and diallyl phthalate are 5–800 ng L−1, di-n-butyl phthalate, butyl benzyl phthalate and di-n-octyl phthalate are 50–1000 ng L−1), low limits of detection (0.3–19.8 ng L−1), and high enrichment factors (325–2089). The intra-day and inter-day relative standard deviations (RSD) for PAEs extractions using a single fiber were (4.7–8.5%) and (5.7–9.1%), respectively. The fiber-to-fiber reproducibility for three fibers prepared in parallel was 7.2–11.3% (RSD). The method was successfully applied to the extraction of PAEs from plastic bottled milk and to the quantitation by a gas chromatograph with a flame ionization detector. The average recoveries were 84.0% to 105%. [ABSTRACT FROM AUTHOR]

A water stationary phase is explored as a novel means of selectively separating unsaturated analytes in gas chromatography. Several unsaturated/saturated analyte pairs consisting mainly of carboxylic acids and alcohols were examined using both a 30-m conventional non-polar HP-5 column and an 11-m water phase column. For most investigated on the HP-5 column, analytes often eluted very close to each other (~ 6–12 s apart) with poor resolution. By comparison, the shorter water phase column well separated each of the analogue pairs by about 3–8 min or more. As well on the water phase, analytes with a triple bond were much more retained than those with two double bonds, which in turn were much more retained than those with one double bond. Conversely, on the HP-5 column these were poorly separated if at all. Additionally, cis/trans isomers were baseline resolved on the water phase but co-eluted on a 30-m conventional polar Carbowax column. Similarly, positional isomers varying the location of the double bond were found to separate with a selectivity value near 1.1 on the Carbowax column, whereas on the water phase column they yielded a value of 1.3 and eluted in the reverse order. Addition of various metal ion salts to the water phase was explored. While Ca2+ ion produced modest increases in selectivity, the addition of Ag+ ion was most influential and further increased the original water phase selectivity by a factor of 2.3. The mechanistic implications of OH–-pi bonding in the water phase was discussed as a potential origin for the selectivity observed. The method was applied to gasoline, essential oil, and food stuff analysis. Results indicate that this method could be a very useful means of selectively separating such unsaturated analytes. [ABSTRACT FROM AUTHOR]

The use of stimulants by professional and amateur athletes, as well as in the general population, to enhance their athletic performance represents a human health hazard. Methylhexaneamine (MHA) is a stimulant found in numerous dietary supplements and detected frequently in urine samples. The analytical process accepted by most Drug Testing Programs that employ urine use two methods, the first is an initial screening test, followed by a more specific method for the confirmation of presumptive positive urine specimens. For this reason, two specific analytical methods were developed and validated to determine MHA in urine based on its in situ derivatization with isobutyl chloroformate; the first was salting out assisted liquid–liquid extraction (SALLE) with gas chromatography coupled to mass spectrometry (GC–MS) and the second headspace solid-phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detector (GC–FID). Both methods were evaluated for precision (relative standard deviation < 10%), linearity (r2 > 0.98), accuracy at two concentration levels (recovery > 92%) and limit of detection (5–7 ng mL−1). The methods were successfully applied to analyze athletes' urine samples from Comisión Nacional de Cultura Física y Deporte (CONADE, Mexico). The proposed methodologies are sensitive, precise, accurate, fast, and miniaturized, and they are suitable specific methods to analyze MHA in urine for anti-doping or forensic purposes even with an affordable GC–FID system. [ABSTRACT FROM AUTHOR]

Antagonism of carbonic anhydrase, isozyme 3 (CAIII) has a strong potential in treating obesity, hyperlipidemia and cancer. The enzyme has a very low activity in hydrating carbon dioxide which makes it unresponsive to the majority of methods used against other CAs. In this study, a new evaluation method based on gas chromatography (GC) is considered for the screening of the inhibitory activity of various nicotinic acid derivatives against CAIII using immobilized pH-sensitive matrix pellets. The CA inhibitory activity of 14 nicotinic acid derivatives were studied using a GC method. The percentage of the inhibition of nicotinic acid derivatives against CA was calculated and found to be related to the molecular volume of the candidate inhibitor. This might be due to the limited size of CAIII's active site. A lower molecular volume correlates with the inhibitory effect of each candidate. This approach of analysis might be utilized in developing sensitive GC methods for other enzymes attributed with pH change in their media. Particularly, for those which require accurate and sensitive assay methods. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes were exposed to hydrothermal treatment for obtaining graphene oxide nanoribbons (GONRs). The fabricated graphene oxide nanoribbons have been morphologically and compositionally characterized via FE-SEM, XRD, and FT-IR techniques. The as-synthesized GONRs have been used as sorbent phase for headspace solid-phase microextraction of phthalate esters (PEs) from aqueous solutions. In this regard, the GC–FID analysis route has been used for quantification of PEs. The new SPME fiber shows remarkable analytical figures of merit including broad dynamic linear ranges, low limits of detection, as well as good stability and reasonable relative standard deviations for evaluation of PEs. The linearity of the method for analysis of PEs including DnBP, DnPP, DEHP, DEHA, BBP, and DMP was between the range of 0.05–100, 0.05–100, 0.1–100, 0.1–100, 0.2–100, and 0.5–100 μg L−1, respectively. The limits of detection (based on S/N = 3) and correlation coefficients were found to be in the range of 0.02–0.2 μg L−1 and 0.9907–0.9952, correspondingly. The prepared GONR-coated SPME fiber shows larger extraction yield in comparison to pristine MWNTs and commercial PDMS SPME fibers. Furthermore, real sample analysis showed that there is no significant matrix effect for evaluation of PEs from environmental water samples and proposed method could be used for evaluation and determination of PEs from aqueous samples in a precise and accurate manner. The existence of functional groups, π–π interactions, as well as hydrogen bonding between adsorbent phase and PE analytes could be the reason for observing such a high extraction yield. [ABSTRACT FROM AUTHOR]

In this work, a novel calix[4]resorcinarene-based ionic liquid (C4RA-2IL) was synthesized, structurally characterized, and statically coated on capillary column as stationary phase for capillary gas chromatography (GC). The column efficiency of the C4RA-2IL column is 3345 plates m−1, which are determined by n-dodecane at 120 °C. Based on its McReynolds constants, the C4RA-2IL column showed moderate polarity. Particularly, the C4RA-2IL column show high separation performance for a wide range of analytes and some difficult separation of meta/para-isomers. Moreover, it exhibited excellent selectivity for critical aromatic isomers of chloroaniline, bromaniline, iodoaniline, toluidine and xylidine isomers and shows advantageous separation capability over the commercial polysiloxane stationary phase. This work presents a promising future of calixarene-based ionic liquid as a new type of stationary phase in GC separations. [ABSTRACT FROM AUTHOR]

Liquid nonbeverage alcohol products including flavors/flavorings, dietary supplements, medicines, etc. can be complex mixtures of flavor chemicals, adjuvants, and solvents. Ethanol and propylene glycol (PG) are common solvents used in the manufacture of nonbeverage alcohol products and the quantification of these analytes is important for both regulatory and quality control purposes. Presented here is a simple and robust gas chromatography-flame ionization detector (GC-FID) method which simultaneously quantifies ethanol and PG in liquid nonbeverage alcohol samples. The linear range is 0.4–95% v/v for ethanol and 1–99% v/v for PG with r2 of > 0.999. The limit of detection for ethanol was 0.025% v/v and for PG was 0.05% v/v. The limit of quantification was calculated to be 0.075% v/v for ethanol and 0.15% v/v for PG. The method reproducibility was < 2.9%-RSD and < 3.2%-RSD for ethanol and PG, respectively. Spike recoveries for various matrices tested were between 98 and 107% at three different spike concentrations. [ABSTRACT FROM AUTHOR]

Porous organic cages (POCs) are an emerging class of porous molecular materials which self-assembled by discrete, shape-persistent, cage-like molecules and have recently received intensive interest in diverse fields. In this work, a hydroxyl-functionalized homochiral POC was synthesized by [4 + 6] condensation of 2-hydroxy-1,3,5-triformylbenzene with (1R, 2R)-diaminocyclohexane and coated on a capillary column for gas chromatography (GC) separations. Forty-one pairs of enantiomers belonging to various classes have been resolved on the column, including alcohols, diols, esters, lactones, halohydrocarbons, ethers, epoxides, ketones and sulfoxides. Compared with β-cyclodextrin derivative-based commercial β-DEX 120 column, previously reported chiral POCs- (CC9 and CC10) based columns, there are 12, 27 and 19 pairs of studied enantiomers cannot be resolved on β-DEX 120 column, CC9 column and CC10 column, respectively. Besides, both separation factors and resolution values of some racemates are higher on this column than those on β-DEX 120 column, CC9 column and CC10 column. The results demonstrate that the column exhibits good chiral recognition complementarity or superior chiral resolution capability to those columns which used for comparison, and the introduction of hydroxyl group enhances hydrogen-bonding interaction to some racemates, leading to better enantioselectivity. The column also shows excellent separation performance toward positional isomers of dichlorobenzene, dibromobenzene, nitrotoluene, chlorotoluene, nitrobromobenzene and nitrochlorobenzene. The retention time and selectivity of analytes have no significant changes after more than 500 injections and 260 °C conditioned for 6 h, showing the good repeatability and thermal stability of the column. This work indicates the promising prospect of POCs for GC separation, especially for the separation of enantiomers and also demonstrates the significance of design and synthesis of more functionalized chiral POCs for GC enantioseparation that broaden the enantiomer separation scope and applicability of POCs-based columns through their chiral recognition complementarities. [ABSTRACT FROM AUTHOR]

Trimellitic anhydride (TMAn) is an essential starting material of the chemical manufacturing industry; it is widely used in saturated polyester resins (SPR) manufacturing to produce plasticizers for different purposes. TMAn was recently added, as a new substance of very high concern, to the candidate list by the European Chemicals Agency, since it can lead to sensitization, respiratory tract irritation and lung disease. Any substance from the list of candidates if present in manufactured products at concentrations above 0.1% (w/w) obliges the manufacturer to communicate this to customers down the supply chain and to consumers. We propose here a method that allows the fully automated determination of TMAn in SPR samples by using large volume injection (LVI), with programmed temperature vaporization (PTV) injection, in a gas chromatographic (GC) system equipped with ion trap mass spectrometer (IT) operating in tandem mass spectrometry (MS/MS). The method optimization was obtained by a chemometric model, using the experimental design. Introducing the use of short chromatographic column, triethyloxonium tetrafluoroborate (TEO) as derivatization agent and IS granted specificity, sensitivity and robustness. The detection and quantification limits for TMAn were 0.01% and 0.03% w/w, respectively. Trueness (between 94 and 98%) and precision (RSD lower than 10%, n = 6) were also assessed. [ABSTRACT FROM AUTHOR]

Room-temperature ionic liquids (RTILs) have proven to be efficient polar or highly polar stationary phases for GC. Nevertheless, the thermal stability of monocationic RTILs limits their use in high-temperature GC. To improve the thermal stability, an RTIL based on a 1-methylimidazolium derivative was anchored in a three-dimensional network using the sol–gel process. Three different strategies were compared: using the derivative pure, in combination with a polymer or copolymerised with diethoxydimethylsilane. This last method allowed for the preparation of hybrid stationary phases with satisfactory efficiency (3500 plates per meter determined by the injection of n-tetradecane at 80 °C, k = 8.19) and very good thermal stability up to 340 °C using the NTf2 counter ion. The stationary phases demonstrated a good ability to separate positional isomers and polycyclic aromatic hydrocarbons. Polarity and molecular interactions with analytes were characterized by calculating the Rohrschneider–McReynolds constants and Abraham system constants. A classification of the polarity of the new stationary phases relative to 44 stationary phases, including commercial and non-commercial ones, was performed based on the RTILs using principal component analysis. Finally, the maximal operating temperature of these new stationary phases was compared with those of the most thermally stable conventional or RTIL-based stationary phases, demonstrating that the sol–gel process is an efficient way to enhance the thermal stability of GC stationary phases. [ABSTRACT FROM AUTHOR]

In this work, polybenzimidazole (PBI) was used as extraction phase for solid-phase microextraction (SPME) combined with thermal desorption and gas chromatography–mass spectrometry (SPME/TD–GC–MS) to detect triazine herbicides in environmental waters. PBI with high thermostability (up to 370 °C) was coated on the quartz bar by the immersion–precipitation phase transformation method. Key parameters including extraction temperature, stirring rate, pH value, ionic strength, extraction time, desorption temperature and desorption time were optimized. The SPME/TD–GC–MS method showed the advantages of wide linearity (0.05–20 μg L−1) with good correlation coefficients (> 0.99), good precision (RSDs < 8.7%), low detection limits (0.0013–0.010 μg L−1), good reproducibility among SPME bars (< 8.8%), and long lifetime of more than 30 extraction/desorption cycles. Finally, the method was applied to determine triazines in real water samples including tap water, pond water, and river water. The relative recoveries were between 70.5 and 103.5% with RSDs ranging from 0.1 to 8.7%. These results indicate that PBI is a promising candidate for SPME extraction phase, especially for the determination of polar analytes combined with TD–GC–MS. [ABSTRACT FROM AUTHOR]

An increasing number of researchers are focusing on short-chain fatty acids (SCFAs), which are closely related to various aspects of the human body. This study presented a pretreatment method for mouse feces that combined acidification and extraction. Then, a direct injection process into gas chromatography was developed. The limits of detection using this method are 0.5–0.8 mg L−1, and the corresponding sample contents are 0.015–0.024 mg g−1. The limits of quantification are 0.8–1.0 mg L−1, and the corresponding sample contents are 0.024–0.030 mg g−1. The linear relationship of the calibration curve is good and has a correlation coefficient of > 0.999. The recovery rate of the spiked standard is 80–102%. This method had been successfully applied to analysing and determining SCFAs in biological samples. [ABSTRACT FROM AUTHOR]

A novel miniaturized gas chromatography–flame photometric detection device built within a titanium platform (Ti µGC–FPD) is presented. The 7.5 cm × 15 cm monolithic Ti device contains both an OV-101 coated separation column (5 m × 100 µm i.d.) and a shielded cavity to house the hydrogen-rich detector flame. The FPD employs a micro counter-current flame (about 250 µm in diameter) that is stabilized by opposing relatively low flows of oxygen and hydrogen (7–10 mL/min O2 and 40 mL/min H2). Under optimal conditions, the minimum detectable limits are about 70 pg S/s for sulfur and 8 pg P/s for phosphorous. The natural (i.e., unfiltered) selectivity for these responses over carbon is near 104.3 for S/C and 105 for P/C. Even greater selectivity over hydrocarbons can further still be obtained by employing conventional interference filters. Overall, good separations with stable and sensitive detector performance are obtained with the device, and its sturdy Ti structure supports robust operation. Results indicate that this Ti µGC–FPD device may be a useful alternative approach for incorporating selective FPD sensing in µGC analyses. [ABSTRACT FROM AUTHOR]

In this work, we synthesized ethyl carbazole-grafted polysiloxanes, namely, ECP-9 and ECP-18, which possessed ethyl carbazole contents of 9% and 18%, respectively. The results of thermogravimetric analysis showed that ECP-9 and ECP-18 polymers lost 2% of weight at 365 °C and 380 °C. The minimum allowable operating temperature for the ECP-9 and ECP-18 was 40 °C. In addition, the ECP-9 and ECP-18 columns were thermally stable at 340 °C and 360 °C. The column average efficiencies of ECP-9 were 2306-3090 plates m−1 for a 10 m column and 2594-3438 plates m−1 for a 30 m column. The column efficiencies of ECP-18 were 2497-3428 plates m−1 for a 10 m column and 2829-3700 plates m−1 for a 30 m column. ECP-9 and ECP-18 as stationary phases exhibited moderate polarity based on the McReynolds constants. Given its specific dipole-dipole, dipole-induced dipole, π-π stacking interactions, and hydrogen bond force with solutes, the ECP stationary phases achieved excellent separation for aromatic isomers, substituted benzenes, polycyclic aromatic mixtures, polycyclic aromatic hydrocarbons, and fatty acid esters with satisfactory peak shapes. [ABSTRACT FROM AUTHOR]

Volatile amines are usually problematic compounds in sampling, sample pretreatment and gas chromatographic analysis due to their chemical characteristics (polarity, basicity and reactivity). Headspace solid-phase microextraction (SPME) Arrow sampling of aqueous samples were proven to be complicated since moisture in the headspace was also sorbed into the SPME sorbent and resulted in distorted or split peaks for the volatile amines. This was the case especially with old used sorbents not so much with the new ones. Volume of the water sample, sampling conditions, quality of the SPME sorbent and desorption conditions greatly influenced the concentration of water in the headspace and in the sorbent phase. This, in turn, affected the length of the water film in the column which determined the degree of peak splitting and distance between the split amine peaks (water film trapped part of the amine molecules). Addition of the salt to the sample solution and additional drying of the SPME sorbent after the sampling were shown to effectively decrease the amount of water in the headspace and in the sorbent phase. This combined effect of salt addition and drying step resulted in much better peak shapes and intensities for the amines. In the best cases, the peak splitting for the volatile amines could in this way be completely avoided. [ABSTRACT FROM AUTHOR]

Abstract: A rapid method is introduced, which facilitates the selective gas chromatography-flame photometric detection (GC-FPD) analysis of thiols. The method uses lead oxide particles or plumbite solution to complex thiols into a solid lead thiolate moiety that can be physically separated from complex sample matrices and then reconstituted as the original thiol in a simple replacement solvent for analysis. While both red or yellow forms of lead oxide are found to remove thiols from sample solutions, the latter does so about 10 times faster than the former. Comparatively, though, plumbite solution is most rapid in this regard and is still 10 fold faster than solid yellow lead oxide. For example, 98 ± 1% (n = 3) of a 1-butanethiol standard in hexane (600 ng µL− 1) was extracted after only 2 min of contact with a 0.06 M plumbite solution. The method allows thiols to be selectively isolated from co-eluting peaks and other sulfur species, which can simplify their determination. It also allows thiols to be removed from complex hydrocarbon matrices for analysis, which can greatly reduce interference from signal quenching when using a conventional FPD. For instance, analysis of a thiol standard in a commercial gasoline by this method showed that the FPD sulfur signal increased from 16 to 97% of its expected value by removing the quenching hydrocarbon interference. Accordingly, results indicate that this method could be a useful alternative approach for the selective analysis of such thiol-containing samples.Graphical Abstract: [ABSTRACT FROM AUTHOR]

For the first time in this work, two methods of modification of poly(1-trimethylsilyl-1-propyne) (PTMSP) and the possibilities of its application for the determination of catalytic reaction products are described. Aging of PTMSP is determined by three mechanisms: physical, chemical and mechanical effects. Free volume decreases, texture characteristics change, and partial oxidation of the polymer takes place in the structure of PTMSP. The chromatographic behavior of PTMSP, which was used for 18 months, differs significantly from the properties of the freshly prepared polymer. Thermal stability and chemical inertness are the main requirements for chromatographic materials. Therefore, two methods were used to stabilize the aging process. The first method consisted of preparing a mixed phase by adding disubstituted polyacetylene poly(1-phenyl-1-propyne) (PPP) to PTMSP. The resulting sorbent Chromosorb Р NAW + 10 wt% (97% PTMSP + 3% PPP) is efficient for solving a wide range of chromatographic tasks such as simultaneous analysis of hydrocarbons and sulfur-containing inorganic gases, analysis of chlorine-substituted methanes in CCl4 and thiophene in benzene, separation of hydrocarbons and aromatic compounds. It should be noted, the low selectivity of separation of oxygen-containing components on this sorbent. A second method of PTMSP modification, namely the oxidation treatment with nitrous oxide, is proposed. It was shown that the polymer is oxidized by means of its C=C double bond with the formation of ketone, carbonyl and hydroxyl groups. The increase in number of those groups in the polymer changed the polarity of PTMSP. The change in polarity of polymer led to the selectivity of separations, including oxygen-containing substances. Examples of separations of aliphatic and aromatic hydrocarbons, oxygen- and halogen-containing substances are presented. Chromatographic characteristics of the sorbent Chromosorb P NAW + 10 wt% (97% PTMSP + 3% PPP) and PTMSP oxidized by nitrous oxide are stable in the temperature range from 30 to 220 °C for at least 1.5 years of continuous operation.Graphical Abstract: [ABSTRACT FROM AUTHOR]

We report on the synthesis of Fe3O4@SiO2 nanoparticles incorporated poly(divinylbenzene) monolithic column via in situ polymerization. The monolith had larger specific surface area and relatively uniform porous structure and was characterized by scanning electron microscopy, nitrogen adsorption-desorption, and Fourier transform infrared spectroscopy. The monolith was then applied for the evaluation of gas chromatography separation properties. Here, an electromagnetic induction heating technique was employed to control the column temperature with the thermal effect of eddy current in ferromagnetic materials Fe3O4. The monolith offered good separation efficiency for benzene and toluene and a higher column efficiency was obtained up to 4481 and 9216 plates per meter, respectively. In addition, the injection volume and column capacity of the proposed system are as much as 5 µL and 100 ng. This makes it possible to use a UV detector. The fabricated Fe3O4@SiO2 nanoparticles incorporated poly(divinylbenzene) monolithic column has been shown to be very promising for gas chromatography separation.Graphical Abstract: [ABSTRACT FROM AUTHOR]

A highly efficient ultrasonic-assisted dispersive liquid-liquid microextraction (UA-DLLME) procedure coupled with gas chromatography-mass spectrometry was developed for simultaneous analysis of multiclass herbicides with endocrine-disrupting properties in environmental water samples. The parameters affecting the method’s extraction efficiency, such as the types and volumes of the extractant and dispersive solvents, sample pH, and salt concentration, were systematically optimized by response surface methodology based on central composite design to achieve excellent recoveries for multiclass herbicides. The final UA-DLLME protocol involved 115.6 µL of chloroform (extractant), 861.5 µL of ethanol (dispersive solvent), 5.0 mL of water samples, pH 10.0, and 4.3% NaCl solution. The performance of the developed UA-DLLME was compared with that of conventional solid-phase extraction (SPE). Under optimal extraction conditions, UA-DLLME exhibited a higher enrichment factor and greater sensitivity than SPE, with limits of detection and limits of quantification of 0.004-0.024 and 0.013-0.079 µg L−1, respectively, for seawater samples. The accuracy and precision of UA-DLLME were satisfactory for seawater samples spiked at three levels (0.2, 2.5, and 5.0 µg L−1). Average recoveries ranging from 82.3 to 101.8% were achieved, with relative standard deviations lower than 12.8%. The proposed analytical method was successfully applied to the simultaneous determination and quantification of 17 herbicides in environmental river and seawater samples. [ABSTRACT FROM AUTHOR]

Abstract: In this study, magnesium/aluminum-layered double hydroxide (Mg/Al-LDH) was prepared with the hydrothermal method and the morphological features of Mg/Al-LDH were characterized. The as-prepared Mg/Al-LDH was employed as a coating material and coated on the stainless steel wire to construct a solid-phase microextraction fiber. To evaluate the extraction performance of the fiber, four phthalate esters including benzyl butyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate and bis (2-ethylhexyl) phthalate were selected as model compounds. Several experimental parameters affecting the extraction efficiency, such as extraction temperature, extraction time and ionic strength, were optimized. Under the optimum conditions, linear ranges of 1-400 μg L−1 for di-n-butyl phthalate, 10-500 μg L−1 for di-n-octyl phthalate and 10-400 μg L−1 for two other compounds were observed. The limits of detection and limits of quantification ranged from 0.24 to 2.31 μg L−1 and 0.81 to 7.69 μg L−1, respectively. The intra-day and inter-day precision are less than 15.3 and 8.7%. The relative standard deviation of fiber to fiber reproducibility ranged from 8.3 to 16.7%. Finally, the established method was satisfactorily applied to the determination of phthalate esters in the Yangtze River water samples and the recoveries were 76.1-110.6%.Graphical Abstract: [ABSTRACT FROM AUTHOR]

A novel method of on-line pyrolytic methylation-gas chromatography was developed for the rapid analysis of fatty acid composition in Polysorbate 80 without any tedious pre-treatment steps. Fatty acids in Polysorbate 80 were converted into their corresponding fatty acid methyl esters in the presence of trimethylsulfonium hydroxide with a vertical microfurnace pyrolyzer at 300 °C. The premixing procedure of sample and organic alkali reagent was necessary before the on-line pyrolytic methylation to improve the repeatability. The relative standard deviations for peak areas of fatty acids in Polysorbate 80 were over the range of 0.3-9.1% (n = 5). Six Polysorbate 80 samples, consisting of three samples of pharmaceutical grade and three samples of non-pharmaceutical grade, were analyzed to evaluate the feasibility of the proposed method. The relative percentages (%) of fatty acids for samples of pharmaceutical grade meet the Chinese Pharmacopoeia requirements with the amount of oleic acid varying from 78.4 to 89.3%. On the other hand, the relative percentages (%) for palmitic acid and stearic acid in samples of non-pharmaceutical grade were out of the specification limits, with the amount of oleic acid varying from 62.0 to 63.5%. The quantitative results determined by on-line pyrolytic methylation were in agreement with those obtained by off-line methylation. The result proved that gas chromatography with on-line pyrolytic methylation technique is of great value for rapid screening analysis of Polysorbate 80 samples in bulks. [ABSTRACT FROM AUTHOR]

Aromaticity has been used as a criterion to explain the gas chromatographic (GC) retention of cata-condensed polycyclic aromatic sulfur heterocycles (PASHs) C12H8S, C16H10S, C20H12S; and peri-condensed PASHs C18H10S, in a GC column with 50% phenyl/50% dimethyl silphenylene polymer. To establish the aromaticity, nucleus-independent chemical shifts at the level of the molecular plane, NICS(0), and at 1 Å above the surface of the molecular plane, NICS(1), have been used. It has been found that the GC retention of cata-condensed PASHs C12H8S, C16H10S, and C20H12S is satisfactorily defined by the aromaticity of the entire molecule, and the GC retention of peri-condensed PASHs C18H10S is satisfactorily defined by the local aromaticity in the sulfur pentagonal ring. In addition, the positive slope between GC retention and NICS(0) of the entire molecule for cata-condensed PASHs, C12H8S and C16H10S, and by NICS(1) in the pentagonal ring for peri-condensed PASHs, C18H10S, is explained by the interaction between the electrons of the heterocycle molecule and the positive pole of the silicon atom in the GC column, as suggested with PAHs. In contrast, the negative slope between GC retention and aromaticity for cata-condensed C20H12S is explained by the presence of bay, cove, or fjord regions in the vicinity of the sulfur atom that generates either higher GC retention and lower aromaticity or lower GC retention and higher aromaticity. [ABSTRACT FROM AUTHOR]

A fast and sensitive analytical method for the determination of jiahuangxianjunzuo (JHXJZ) using gas chromatography equipped with nitrogen-phosphorus detector was developed and validated for the analysis of Goji berry which is grown in Qinghai Plateau of China. This method employs modified QuEChERS followed by detection. JHXJZ was extracted by alkaline acetonitrile [containing 1% (v/v) NH·HO] and partitioned with a mixture of NaCl and MgSO, and then cleanup was done with 30 mg GCB and 100 mg MgSO. With this modified QuEChERS procedure, the linearity over a concentration range 0.01-5 μg mL was good with a correlation coefficient ( r) > 0.9999. Recovery at three different fortification levels was 90.40-100.9%, respectively, with a relative standard deviation < 5% for all analytes. The limits of detection and the limits of quantification were 0.003 and 0.01 mg kg, respectively. JHXJZ was detected on three Goji berry food products; all positive samples showed JHXJZ contents below the legal limit established by the EU for other analogous berry-based products. These results can be used to help establish appropriate application frequencies and harvest intervals for JHXJZ on Goji berry. Graphical abstract: [ABSTRACT FROM AUTHOR]

The objective of this research was to develop a solidification of floating organic drop liquid phase microextraction coupled with gas chromatography (GC) and apply it to simultaneous enrichment and determination of five fatty acids, including palmitic acid, stearic acid, oleic acid, linoleic acid and α-linolenic acid, in Zanthoxyli Semen. Several parameters influencing the extraction efficiency or enrichment factor, such as the volume of the extraction solvent ( n-dodecanol), extraction time, stirring rate, salt concentration and sample phase volume, were carefully selected. Under the optimum conditions, linearities were 5.09-120.48 μg mL for palmitic acid ( r = 0.9984), 10.13-120.00 μg mL for stearic acid ( r = 0.9993), 4.18-99.12 μg mL for oleic acid ( r = 0.9990), 1.32-132.00 μg mL for linoleic acid ( r = 0.9990) and 1.62-161.72 μg mL for α-linolenic acid ( r = 0.9991), respectively. Detection limits were in the range of 0.12-0.16 μg mL. Satisfactory precision (2.6-9.6%) and accuracy (90.2-109.1%) were also achieved. Compared with traditional liquid-liquid extraction with GC, the determination results of α-linolenic acid, one of the active ingredients in Zanthoxyli Semen, had no significant difference (95% confidence level) in accuracy and precision, and the proposed procedure exhibited low solvent consumption, simple steps, a short extraction time and low LOD. [ABSTRACT FROM AUTHOR]

In this research, a novel nanocomposite based on incorporation of graphene oxide (GO) into polyamide (PA) was prepared by solvent blending method and subsequently it was coated on stir bar substrate through solvent exchange method. The morphology and surface characteristic of PA- and GO/PA-coated stir bars were investigated using scanning electron microscopy (SEM). The prepared GO/PA nanocomposite-based stir bar was applied as an extraction device for stir bar sorptive extraction (SBSE) of organophosphorous pesticides (OPPs) including chlorpyrifos, ethion, and phosalone in fruit juice and vegetable samples followed by gas chromatography-flame ionization detector (GC-FID) detection. The effect of GO doping level into the nanocomposite on the extraction capability of the coating was investigated. Important factors influencing the extraction and desorption processes including extraction time, salt content, sample volume, pH, desorption solvent, its volume, and desorption time were studied and optimized applying central composite design (CCD). Limits of detection (LOD) and linear dynamic ranges of the method were in the range of 0.3-1 ng mL and 1-1000 and 3-1000 ng mL, respectively. The method precision (RSD%) with four replicate determinations was in the range of 6.2-9.1% for distilled water at the concentration level of 100 ng mL. The developed method was successfully applied to various fruit juices and vegetable samples, while the relative recoveries (RR %) were found to be in the range of 82.0-95.6%. Graphical abstract: [ABSTRACT FROM AUTHOR]

An acidic water stationary phase is used for the analysis of carboxylic acids in capillary gas chromatography (GC). Under regular pH 7 operating conditions, these analytes are largely ionized and elute poorly, if at all, from the water phase. However, by adjusting the phase to pH 2, it is found that various acids are neutralized and can be readily eluted and separated in the system. Sulfamic acid is found to provide a stable pH for the water phase over time, whereas hydrochloric acid and other more volatile additives quickly evaporate from the column. Under optimal low pH conditions, the acidic analytes yield good peak shape and are readily observed for masses investigated down to 5 ng on-column. By comparison, on a conventional non-polar capillary GC column, the same analytes display threefold more peak tailing and are not detected for masses below 30 ng on-column. Through altering the phase pH, it is found that the selectivity between certain analytes can be potentially enhanced depending on their respective p Ka values and/or ionizability. The analysis of various different samples containing carboxylic acids is demonstrated and the results indicate that this approach can possibly offer unique and beneficial selectivity in such determinations. [ABSTRACT FROM AUTHOR]

Methanol in insulating oil has been proposed as a new marker for condition assessment of the solid insulation system of power transformers. In the current work, as a first step of using the new marker, an analytical static headspace gas chromatography/mass spectrometry method has been developed, optimized, and validated to measure methanol and ethanol contents in the insulating mineral oil. The analyzing setup consists of a 6890 N gas chromatograph equipped with a 5973 network mass spectrometer (MS) in the absence of a costly headspace autosampler, and the chromatography separation was performed on a 60 m × 320 µm × 0.5 µm VF-WAXms GC column. Calibration curves have been provided using several concentrations of the alcohols, and also limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation percentage (RSD%) have been determined. [ABSTRACT FROM AUTHOR]

A titanium miniature gas chromatography device with an on-board micro-flame ionization detector (Ti µGC-FID) is presented. The design is based on a counter-current method that establishes a stable flame (~240 µm diameter) inside a 1.44 mm circular cavity within the Ti tile. The width of this cavity is found to have a significant impact on flame stability and detector performance. Through polarizing the conductive Ti tile body and situating a collector adjacent to the cavity, useful µFID response is obtained from the flame. The 7.5 cm × 15 cm rectangular monolithic Ti device contains a serpentine column layout (5 m long × 100 μm wide) coated with OV-101 stationary phase that is directly integrated with the on-board μFID. The column produces reasonable analyte peak symmetry and separation performance with a plate height of 1.5 mm for dodecane. Under optimized conditions, the Ti μGC-FID device yields a detection limit of 9 × 10 gC s, a linear response over 3 orders of magnitude, a sensitivity of 60 mC gC, and a signal reproducibility within 5% RSD ( n = 10). Some samples are analyzed using the Ti µGC-FID device and results indicate that this approach can potentially provide a useful alternative means of achieving sensitive and stable μFID performance within a robust, integrated miniaturized GC platform. Graphical Abstract: [ABSTRACT FROM AUTHOR]

A miniaturized QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Save) approach combined with gas chromatography-tandem mass spectrometry (GC-MS/MS) has been developed for the simultaneous determination of nine pesticides (Cyflufenamide, Difenoconazole, Dimethomorph, Fluopicolide, Fluopyram, Metrafenone, Myclobutanil, Quinoxyfen, and Tebuconazole) in insects, snails, and spiders. In contrast to the original QuEChERS approach, only 500 mg of dried and homogenized sample matrix, mixed with 1.0 mL ethyl acetate and 250 mg MgSO:NaCl (4:1), is required for this novel 'micro-QuEChERS' protocol. The organic phase was cleaned using dispersive solid-phase extraction (dSPE) with 75 mg MgSO:PSA sorbent (4:1). The method was validated according to SANCO/12571/2013 and applied to real samples ( n = 7). Fluopicolide was the only detectable pesticide in real samples from vineyards. In two samples, the Fluopicolide levels were between the determined LOD and LOQ (0.15-1.00 mg kg), and in one sample a concentration of 1.68 mg kg was detected. [ABSTRACT FROM AUTHOR]

In this study, a dynamic headspace liquid-phase microextraction method is reported for the extraction and preconcentration of pyridine as a decomposition product in some pharmaceuticals before its determination by gas chromatography-flame ionization detection. In the practical procedure, 5 µL of dimethyl sulfoxide (extraction/collection solvent) containing 1-pentanol (internal standard) is placed into a liner-shaped extraction vessel. The vessel is passed through the septum of a vial containing the sample solution. Then it is placed into a water bath thermostated at 70 °C. After a predetermined time, 1 µL of the extraction/collection solvent is removed and injected into the separation system. The factors influencing the extraction efficiency including extraction/collection solvent kind and its volume, ionic strength, extraction time, extraction temperature, and pH were investigated and optimized. Under optimum extraction conditions, the method showed a wide linear range between 0.012 and 500 mg L. Enrichment factor and extraction recovery were obtained as 314 and 94%, respectively. Limit of detection was calculated as 0.004 mg L in solution and 0.08 mg kg in solid. Relative standard deviation for the extraction of 0.05 mg L of the analyte was obtained as 4 and 6% for intra -day ( n = 6) and inter -day ( n = 4) precisions, respectively. Finally, the target analyte was determined in ceftazidime and mouthwash solution by the proposed method. Graphical Abstract: [ABSTRACT FROM AUTHOR]

A quantitative structure-retention relationship (QSRR) study was performed to correlate descriptors representing molecular structures to the Kováts retention indices of polycyclic aromatic hydrocarbon compounds. The complete set of 37 compounds was divided randomly into a training set of 26 compounds and a test set of 11 compounds. In the pool of descriptors calculated using Dragon and Hyperchem software, the modified Harary index ( $$ H^{\prime\prime} $$ ) developed by our team was added. The best selected descriptors by genetic algorithm to build the three linear models were: the first-order Randić connectivity index ( $$ {}^{1}\chi $$ ), $$ H^{\prime\prime} $$ and the third-order valence connectivity index ( $$ {}^{3}\chi_{p}^{v} $$ ). The selected model was compared with the one built with $$ {}^{1}\chi $$ , the first Harary index (implanted in Dragon H) and $$ {}^{3}\chi_{p}^{v} $$ . Statistical analysis showed that the model with modified Harary index ( R = 99.25, SD 5.82, F = 1517.74) produces better correlation with Kováts retention indices than the one implanted in Dragon ( R = 98.20, SD 9.02, F = 626.09). The final QSRR was internally and externally validated. The leave-one-out, cross-validation, bootstrapping, and y-randomization test indicated that the final model is robust and has no chance correlation. The external validations indicated that the model with modified Harary index showed a good predictive power. The mechanistic interpretation of QSRR model was carried out according to the definition of descriptors. Therefore, the result meets the five principles recommended by the Organization for Economic Co-operation and Development for validation of QSRR model. [ABSTRACT FROM AUTHOR]

A new technique, namely dynamic headspace liquid-phase microextraction, has been developed for the extraction of 1,4-dioxane in cosmetic and hygiene samples followed by gas chromatography-flame ionization detection. In this method, the sample is mixed with acetone as a diluent solvent. Then, a few microliters of n-octanol are added into a home-made extraction vessel placed in the headspace of the sample. By heating, the target analyte is transferred to the headspace of the sample and then extracted into n-octanol. Under the optimized conditions, the method showed a good linearity in the range of 3.24-1000 μg kg with a coefficient of determination 0.998. Figures of merit such as enrichment factor of 375, extraction recovery of 94 %, limits of detection and quantification 0.97 and 3.24 μg kg, respectively, and relative standard deviation 4.7 % ( n = 6, C = 30 μg kg) of the proposed method were satisfactory for determination of the target analyte. Finally, the method was successfully applied in determination of 1,4-dioxane in various cosmetic and hygiene samples including shampoo, toothpaste, lotion, washing liquid, and dishwashing liquid. [ABSTRACT FROM AUTHOR]

For the first time, centrifuge-less emulsification microextraction using effervescent CO tablet (EME-ECT) coupled with gas chromatography-mass spectrometry (GC-MS) is presented for the preconcentration and determination of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. In this method, after injection of a mixture of extraction and disperser solvents into the sample with volume of 90 mL, an effervescent tablet containing the effervescence precursors (sodium bicarbonate as carbon dioxide source and sodium dihydrogen phosphate as proton donor) was applied for phase separation. Thanks to the in situ generation of carbon dioxide, as a consequence of the effervescence reaction, the dispersed extraction solvent was collected at the surface of the aqueous sample and then was narrowed to the capillary part of a special home-made extraction cell for facile retrieval. The experimental variables, including volume of extraction and disperser solvents, ionic strength and weight of effervescent tablet, were investigated and optimized by a central composite design. Under the optimal conditions, the limits of detection were at the range of 0.01-0.1 µg L and preconcentration factors were varied between 134 and 406 for different PAHs. As can be seen here, there is no need for centrifugation or a special apparatus for the proposed emulsification microextraction method and it can easily be applied for the analysis of large volumes of samples. Taking these advantages to account, EME-ECT has the most promise for becoming a quick, simple and economical approach to reduce transportation costs after water sampling in the field. [ABSTRACT FROM AUTHOR]

1-Methyl- 1H-1,2,4-triazole (MTA) is the most stable and abundant transformation product of dimethylhydrazine-based rocket fuel. Concentrations of MTA in soils affected by rocket fuel spills are regularly monitored using a number of available methods mainly based on GC-MS. Complex, time and labor intensive sample preparation makes quantification of MTA quite costly and unsuitable for on-site measurements. The goal of this study was to develop a new method for fast determination of MTA in soil samples based on solvent extraction and GC-MS. MTA extraction effectiveness using known polar organic solvents varies from 30 to 95 % for different soils. Isotope dilution method involving (1-trideuteromethyl)- 1H-1,2,4-triazole (MTA-d3) provides efficient matrix effect control and analyte recovery in the range of 70-130 % for all tested solvents-acetone, methanol and acetonitrile. Any of the tested solvents may be used for the method depending on their affordability and accessibility in the lab. Addition of 3 g of 4Å molecular sieves to acetone extracts from soils removes 98 % of water and does not affect MTA/MTA-d3 concentrations ratio. Compared to the competitive SPME-based method, the developed approach does not require long-time equilibration of soils at elevated temperatures. The developed method is more suitable for determination of concentration at a level above 300 mg kg. MTA concentration in soils taken from the site of accidental 'Proton' rocket crash in 2013 reached 600 mg kg. According to the method validation, its reproducibility and accuracy are below 9 and 23 %, respectively. Detection limit is below 2 mg kg for all studied samples. [ABSTRACT FROM AUTHOR]