Gas Chromatographic Peaks Research Articles

A hyper-fast gas chromatograph coupled to an ion mobility spectrometer with high repetition rate and flow-optimized ion source to resolve the short chromatographic peaks

By combining the high selectivity of a gas chromatograph (GC) with the high sensitivity and decent selectivity of an ion mobility spectrometer (IMS), GC-IMS have become increasingly popular in many applications. However, most GC suffer from long analysis times. In contrast, an hyper-fast GC allows for extremely fast analysis in the tens of seconds while reaching comparably high resolution. In turn, coupling such hyper-fast GC with IMS requires sufficiently high repetition rate of recording full IMS spectra to resolve the short GC peaks. Therefore, we present a drift tube IMS with 100 Hz repetition rate. Key is a small effective detector volume combined with short drift length. Therefore, the ion source of the IMS combines a small reaction region with an extended field-switching ion shutter and optimized gas flows. To resolve even the shortest GC peaks with a full width at half maximum of 100 ms, a short drift length of just 41 mm was used, achieving a measurement time of 10 ms per spectrum and hence ten data points across the shortest GC peak. To avoid condensation of the sample, the entire IMS was heated isothermally to 120 °C. Despite short drift times and high temperatures, the IMS still reaches high resolving power of Rp = 60. The hyper-fast GC-IMS reaches low detection limits in the low ppbV range. For demonstration, ketone mixes and three different hop varieties were analyzed in <30 s.

Characterization of Pyrolysis Oil Extracted from High Lignocellulosic Groundnut Shell Biomass

&lt;div&gt;Fossil fuel reserves are swiftly depleting when consumer demand for these fuels continues to rise. In order to meet the demand and diminish the pollution derived through conventional fuels, it is crucial to employ cleaner fuels made from substitutes such as waste biomass. Also, converting waste biomass to fuel can lower usage of landfills. There are many biomass resources that are suitable for fuel production, out of which groundnut is also a potential feedstock. Groundnut shell biomass was chosen for this study, as it is a waste leftover during shelling of groundnuts for various commercial applications. The procured groundnut shells were converted to oil using pyrolysis process and was distilled. Both the pyrolysis oil and the distilled oil were analyzed using Fourier transform infrared instrument wherein the presence of functional groups such as alcohols, amines, and carboxylic acids were identified. Further analysis of the distilled oil using gas chromatography and mass spectrometry indicates that major peaks correspond to phenolic groups. Acetic groups such as vaccenic acid and dicarboxylic acid were also identified in the distilled oil. Physiochemical property tests of distilled oil reveal that the overall qualities were inferior when compared to diesel. Further studies on using groundnut shell distilled oil as a fuel for combustion engine can be done using blend strategy.&lt;/div&gt;

Component composition and biological activity of essential oil of plant Zinnia elegans

By the method of steam distillation, samples of essential oil were obtained from a plant cultivated in the East Kazakhstan region. The essential oil was obtained with a yield in terms of air-dry raw materials. The method of gas-liquid chromatography carried out a quantitative analysis of the components of the essential oil. The quantitative content of essential oil components was calculated from the areas of gas chromatographic peaks without using correction factors. The main components of Zinnia elegans essential oil are α-terpineol, β-myrcene, myrtenal and camphene. Terpineol has a pleasant, lilac-like odor and is a common ingredient in perfumes, cosmetics, and fragrances. Pleasant smelling oily liquid. Myrcene has a large number of beneficial properties for the body, whether pure or in aromatherapy through the essential oils that contain it: Sedative and muscle relaxant, anti-inflammatory, interferon inhibition, gastric and duodenal ulcers, antalgic and antinociceptive, reduces sensitivity to pain by self-healing endogenous derivatives of morphine. Myrtenal - has an anti-inflammatory, resolving effect on acne, infiltrates. Increases the protective barrier of the epidermis. Antioxidant, rejuvenating. Camphene components are effective in the treatment of fungal, viral and bacterial infections that affect the respiratory system.

Automated Gas Chromatography Peak Alignment: A Deep Learning Approach using Greedy Optimization and Simulation.

The clinical significance of volatile organic compounds (VOC) in detecting diseases has been established over the past decades. Gas chromatography (GC) devices enable the measurement of these VOCs. Chromatographic peak alignment is one of the important yet challenging steps in analyzing chromatogram signals. Traditional semi-automated alignment algorithms require manual intervention by an operator which is slow, expensive and inconsistent. A pipeline is proposed to train a deep-learning model from artificial chromatograms simulated from a small, annotated dataset, and a postprocessing step based on greedy optimization to align the signals.Clinical Relevance- Breath VOCs have been shown to have a significant diagnostic power for various diseases including asthma, acute respiratory distress syndrome and COVID-19. Automatic analysis of chromatograms can lead to improvements in the diagnosis and management of such diseases.

Investigating volatile semiochemical production from Bos taurus and Bos indicus as a novel phenotype for breeding host resistance to ixodid ticks

Ticks and tick-borne diseases cause significant loss in livestock production with about 80% world's cattle at risk. The cost of chemical control is high and there is an ever-increasing tick resistance to chemical acaricides. Genetic selection as alternative long-term control strategy is constrained by laborious phenotyping using tick counts or scores. This study explored the use of host volatile semiochemicals that may be attractants or repellents to ticks as a phenotype for new tick resistance, with potential to be used as a proxy in selection programmes. Approximately 100 young cattle composed of Bos indicus and Bos taurus were artificially infested with 2,500 African blue tick, Rhipicephalus decoloratus larvae, with daily female tick (4.5 mm) counts taken from day 20 post-infestation. Volatile organic compounds were sampled from cattle before and after tick infestation by dynamic headspace collection, analysed by high-resolution gas chromatography (GC) and subjected to multivariate statistical analysis. Using 6-day repeated measure analysis, three pre-infestation GC peaks (BI938 - unknown, BI966 - 6-methyl-5-hepten-2-one and BI995 – hexyl acetate) and one post-infestation GC peak (AI933 – benzaldehyde / (E)-2-heptenal) were associated with tick resistance (P < 0.01 and P < 0.05 respectively). The high correlation coefficients (r = 0.66) between repeated records with all volatile compounds support the potential predictive value for volatile compounds in selective breeding programmes for tick resistance in cattle.

STUDY OF THE CHEMICAL COMPOSITION OF STACHYS PALUSTRIS L. ESSENTIAL OIL PRODUCING IN THE ASTRAKHAN REGION

Samples of essential oil from the ground part of Stachys palustris L., which grows wild in the Astrakhan region, were obtained by hydrodistillation, and the dependence of its yield on the growing season of the plant was studied. The duration of the hydrodistillation process was set experimentally to study the dynamics of changes in the results of essential oil over time. The yield of essential oil is observed in % when converted to the weight of absolutely dry raw materials. The highest yield of essential oil was obtained from plants in the flowering phase (0.19–0.20%). Quantitative analysis of the main components of Stachys palustris L. essential oil was carried out by GC-MS method. The quantitative content of essential oil components was calculated from the areas of gas chromatographic peaks without using correction factors. It was found that the composition of the essential oil of Stachys palustris L. was very specific. 47 compounds belonging to various classes have been identified. It has been established that the composition of the essential oil of the Stachys palustris L. is very specific. 47 compounds corresponding to the class were identified. Compound classes include fatty acids and acid esters (36.23%), carbonyl compounds (14.25%) and oxygenated basic sesquiterpenes (12.90%), phenols (5.85%). Among the sesquiterpenoids, the predominant component of the essential oil is hexahydrofarnesylacetone (7.5%). The oil also contains (Z)-phytol (6.78%), thymol (4.2%), β-ionone (3.36%) and β-caryophyllene (2.87%). Nonspecific components of the essential oil of the taxon Stachys palustris growing in the Astrakhan region are coumarin (10.27%) and coumaran (0.36%).

Influence of modulator injection width on comprehensive two-dimensional gas chromatography peak dimensions.

This study examines how the height and width of peaks exiting the secondary column of a comprehensive two-dimensional gas chromatography (GC × GC) separation are affected by the width of the pulse introduced to the secondary column. A flow-modulated GC × GC apparatus was assembled that allowed input pulse widths to be controlled precisely over a range of 10 to 70ms. GC × GC chromatograms were obtained using secondary columns containing a polyethylene glycol stationary phase with internal diameters of 0.25 and 0.32mm. The area, height, and width of peaks emerging from the secondary column were found to be accurately modeled by the convolution of a rectangular function with a Gaussian distribution. The rectangular function represents the input pulse, and the Gaussian distribution represents the broadening that occurs in the secondary column. The minimum peak width that could be produced by the secondary column was determined for a wide range of compounds. Injection pulse widths that matched a compound's minimum peak width produced peaks that were 25% wider than the minimum width and had heights that were 76% of the maximum possible peak height. Increasing the injection width significantly above the minimum width yielded substantially broader peaks with only a modest increase (< 25%) in peak height.

The significance in detecting and determining out-of-scope findings for volatile organic compounds in forensic casework

To provide an appreciation for identifying unknown peaks in headspace gas chromatography and a process for reporting additional information for volatile organic compounds (VOCs) in cases. VOCs are frequently abused as inhalants (gases or solvents). They are often abused due to their accessibility and low cost. VOCs are used in a variety of products including household and commercial items such as gasoline, compressed air duster products, nail polish, glues, paints, and varnishes. They are abused because they can be inhaled or insufflated. Abusing these substances can lead to serious health problems including the possibility of death due to chemical asphyxia and/or central nervous system depression. Routine testing procedures can be used to identify many such compounds. Cases for which VOCs were detected that were not in the routine scope of testing were identified during 2020 to 2022. The samples (all blood except for one gastric case) were originally analyzed using either headspace gas chromatography with flame ionized detection (GC/FID) and/or headspace gas chromatography/mass spectrometry (GC/MS). Where possible, if laboratory testing was performed in addition to volatile testing, volatile testing was performed first to limit evaporation of volatile compounds. Based on the results the sample either had further testing performed or an experienced forensic toxicologist was consulted to determine the next course of action. Unknown peaks identified through volatile toxicological testing include 1,1-Difluoroethane (DFE), Chlorodifluoromethane (Freon22), and components found in gasoline such as butane, pentane, benzene, etc. It is important to establish a process to determine when additional peak identification is needed. Frequently, this is provided through case history, but that is not always readily available. Depending on the sample matrix, the detected analytes, and their volatility, results were reported either qualitatively or quantitatively. Case reports for select samples will be discussed further to demonstrate the inherent value of this approach. Challenges exist with the use of headspace gas chromatography in the identification of unknown peaks. These peaks can provide vital information about a case. It is important to be vigilant when assessing such data since these peaks can often be missed or overlooked due to limits in the method. Identified unusual peaks in the chromatography should be interpreted with caution and additional case information needs to be sought. The significant findings from the out-of-scope headspace gas chromatography analysis can provide key toxicological information in cases when no other additional results are found.

Methods and limitations of stable isotope measurements via direct elution of chromatographic peaks using gas chromotography-Orbitrap mass spectrometry

The Thermo Scientific™ QExactive Orbitrap™ mass spectrometer combined with a Thermo Scientific™ Trace™ 1310 GC enables high-mass-resolution measurements of molecular isotopic structure (e.g., molecular-average, position-specific, and multiple substitution measurements), but thus far has employed non-traditional, slow sample introduction methods and long integrations lasting minutes or tens of minutes to optimize measurement precision. This study examines the performance of the Orbitrap for isotope ratio measurements of analytes eluting directly from the gas chromatograph (GC) as traditional GC peaks — i.e. eluting over a period of seconds and with rapidly varying signal intensities. Such a measurement holds potential for simultaneous compound identification and isotope ratio measurement of numerous analytes separated by GC within a single acquisition. We applied this “direct elution” measurement strategy to molecular and fragment ions of para-xylene, serine, and a mixture of polycyclic aromatic hydrocarbons (PAHs) at natural isotope abundances. We built a mathematical model and used a Monte Carlo simulation to evaluate how variations in data processing decisions and GC peak characteristics (e.g., peak shape and elution timing) affect the accuracy of the resulting absolute isotope ratios and sample-standard comparisons (δ values). These case studies inform our recommendations for applying direct elution measurements. The method is appropriate for systems with large position-specific, molecular, or multiply-substituted isotopic anomalies (e.g., isotopically labelled or extraterrestrial compounds), and for compounds that produce strong molecular ions. Precisions improve when experiments are designed to (1) target ions with relatively high mass spectral intensities, (2) optimize the number of ions and range of masses admitted into the Orbitrap, and (3) minimize the nominal resolution settings while still separating relevant isobars.

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

Incorporating Sulfur Atoms into Palladium Catalysts by Reactive Metal–Support Interaction for Selective Hydrogenation

An in situ gas chromatograph with automatic detector switching between PTR- and EI-TOF-MS: isomer-resolved measurements of indoor air

Abstract. We have developed a field-deployable gas chromatograph (GC) with thermal desorption preconcentration (TDPC), which is demonstrated here with automatic detector switching between two high-resolution time-of-flight mass spectrometers (TOF-MSs) for in situ measurements of volatile organic compounds (VOCs). This system provides many analytical advances, including acquisition of fast time–response data in tandem with molecular speciation and two types of mass spectral information for each resolved GC peak: molecular ion identification from Vocus proton transfer reaction (PTR) TOF-MS and fragmentation pattern from electron ionization (EI) TOF-MS detection. This system was deployed during the 2018 ATHLETIC campaign at the University of Colorado Dal Ward Athletic Center in Boulder, Colorado, where it was used to characterize VOC emissions in the indoor environment. The addition of the TDPC-GC increased the Vocus sensitivity by a factor of 50 due to preconcentration over a 6 min GC sample time versus direct air sampling with the Vocus, which was operated with a time resolution of 1 Hz. The GC-TOF methods demonstrated average limits of detection of 1.6 ppt across a range of monoterpenes and aromatics. Here, we describe the method to use the two-detector system to conclusively identify a range of VOCs including hydrocarbons, oxygenates, and halocarbons, along with detailed results including the quantification of anthropogenic monoterpenes, where limonene accounted for 47 %–80 % of the indoor monoterpene composition. We also report the detection of dimethylsilanediol (DMSD), an organosiloxane degradation product, which was observed with dynamic temporal behavior distinct from volatile organosiloxanes (e.g., decamethylcyclopentasiloxane, D5 siloxane). Our results suggest DMSD is produced from humidity-dependent heterogeneous reactions occurring on surfaces in the indoor environment, rather than formed through gas-phase oxidation of volatile siloxanes.

An Off-Line DPPH-GC-MS Coupling Countercurrent Chromatography Method for Screening, Identification, and Separation of Antioxidant Compounds in Essential Oil.

Essential oils are an important source of natural antioxidants and multiple methods have been established for evaluation of their overall antioxidant activity, however, the antioxidant activities of their compounds are less investigated. In the present study, the hyphenation of 2,2′-diphenyl-1-picrylhydrazyl (DPPH)-gas chromatography (GC)-mass spectrometry (MS) offline and high-speed countercurrent chromatography (HSCCC) is established for efficient screening, identification, and isolation of antioxidants from essential oils and applied to the essential oil of Curcuma wenyujin Y.H. Chen et C. Ling. Five compounds are preliminarily screened as antioxidants using DPPH-GC according to the reduction of GC peak areas of each compound after reaction with DPPH and then identified as eucalyptol (7.66%), camphor (2.34%), δ-elemene (1.15%), β-elemene (7.10%), and curzerene (15.77%) using GC-MS. Moreover, these five compounds are isolated by HSCCC using two solvent systems, n-hexane-acetonitrile-ethanol (5:3:2, v/v) and n-hexane-acetonitrile-acetone (4:3:1, v/v), and subjected to DPPH scavenging assay. Camphor, δ-elemene, and β-elemene show weak DPPH scavenging activity, while curzerene and eucalyptol show moderate DPPH scavenging activity. Notably, a significant synergistic effect on DPPH scavenging is found between curzerene and eucalyptol. The result demonstrated that off-line DPPH-GC-MS coupling CCC is an efficient method for screening, identification, and separation of antioxidant compounds in essential oil

Quantitative analysis of adsorption and desorption of volatile organic compounds on reusable zeolite filters using gas chromatography.

In this study, we propose a method to quantitatively analyze the concentration of VOCs adsorbed on zeolite filters via gas chromatography (GC). The sampled VOCs from the filters with ethanol as a solution were characterized using GC to determine the concentration of the adsorbed VOCs by comparing the areas of GC peaks of the detected VOCs and ethanol. The proposed method also enabled determination of the desorption (regeneration) conditions of the zeolite filters according to heating temperature and time for various VOCs. Repeated adsorption and desorption of VOCs on zeolite filters and GC analyses allow us to evaluate the durability and reusability of the filter and could help predict the lifetime of zeolite filters in practice.

Polymerization of organoalkoxysilanes: Kinetics of the polycondensation progress and the effect of solvent properties and salts addition

The kinetics and the produced oligomer patterns of organoalkoxysilanes (AS) were investigated under different conditions by using gas chromatography (GC), because the degree of the polymerization and the siloxane conformations have an effect on the polymer applications. GC peaks were assigned to AS monomers and oligomers by using a mass detector. The pattern of the produced oligomers depended on the catalysts, time, and the solvent, while the kinetics of hydrolysis, re-esterification, condensation, and progress depended on the solvent and type of catalyst. The methoxy and hydrolyzed monomers of trimethylethoxysilane (TMES) were in equilibrium in alkaline and fluorinated media, while the monomers were completely converted to dimers in acidic media. An investigation of the effect of solvent properties (e.g. dielectric constant and viscosity) on the hydrolysis reaction revealed that there was no change in the polarity of the activated complex during spontaneous hydrolysis, and that the reaction was not diffusion controlled.

Chemical Compositions of the Essential Oils and Headspace Volatiles of Seseli peucedanoides Plant Parts

The chemical compositions of the essential oils of Seseli peucedanoides (M.Bieb.) Koso-Pol. inflorescences and leaves, isolated by hydrodistillation, and headspace volatiles, obtained by the static headspace method, were analyzed in detail by gas chromatography (GC) and GC/mass spectrometry (MS). In total, 74 constituents were identified, representing more than 98% of the observed GC peaks. The number of identified essential oil components obtained from the inflorescences was 63 while for the leaf essential oil it was 46. A much smaller number of compounds, 26 for inflorescences and 21 for leaves, were detected in the headspace samples. In both essential oils the most abundant compounds were the same, ( E)-caryophyllene and germacrene D, only in different proportions. The main components in the headspace specimens were α-pinene and ( E)-β-ocimene with ( E)-caryophyllene and ( Z)-3-hexen-1-ol also determined in significant percentages. The major class of compounds identified in the investigated essential oils was hydrocarbon sesquiterpenes with a share of over 80%, while the most dominant class of the headspace volatiles was hydrocarbon monoterpenes, which contribute slightly less than 80% of the total.

Facile Approach for Calculation of Second Dimensional Retention Indices in Comprehensive Two Dimensional Gas Chromatography with Single Injection

In the present work, a novel and simple approach to generate isovolatility curves for alkane series was established, which serves to calculate the second dimension (2D) retention indices (2 I) for peaks in comprehensive two-dimensional gas chromatography (GC×GC). The approach is applicable to routine GC×GC results without requiring multiple injections of alkanes or requiring internal and external standards under different oven temperature conditions which might be normally required in other approaches. A proposed relationship between 2 I values and first dimension (1D) and 2D retention times (1 tR and 2 tR) of compounds can be simplified to an equation with four constants. Values of the four constants can be obtained by fitting the proposed equation with experimental 1 tR and 2 tR data of standard compounds obtained from a single injection of a standard mixture or by using data of known compounds in an analyzed sample. The effect of selected compound sets on calculation of the four constants and derivation of 2 I using the established approach was investigated. The approach was evaluated by comparison with the traditional method based on multiple injections in calculating 2 I values of compounds in a frankincense sample. With a suitable set of chosen standard compounds well-spread over the first and second dimension (2D) space, the potential of the present concept allows simple and reliable calculation of 2 I. This approach should facilitate application of 2 I for compound identification in GC×GC, which is somewhat underutilized largely due to the tedious and time-consuming approach presently used in construction of isovolatility curves, based on multiple injections.

STUDYING THE CHEMICAL COMPOSITION OF ESSENTIAL OIL RECEIVED FROM FRUITS OF PRANGOS ODON-TALGICA WILD-GROWING IN ASTRAKHAN REGION

The chemical composition of Prangos odontalgica (Pall.) Herrnst. et. Heyn essential oil, which grows wild in the Astrakhan region, has not been practically studied, unlike other species of the genus Prangos, growing in Iran, Turkey and Uzbekistan. To obtain the essential oil, all parts of the plant (roots, stems, flowers, leaves, fruits) are used, as well as various methods of isolation (hydrodistillation, supercritical fluid extraction, solid-phase microextraction, and others). Essential oil from the fruit of Prangos odontalgica we obtained by the method of hydrodistillation. The duration of the hydrodistillation process, established experimentally on the basis of a study of the dynamics of change in the yield of essential oil over time, was 3 hours. The yield of essential oil in mass% by volume in terms of absolutely dry raw materials according to the results of a threefold determination is 0.07 ± 0.01%. The method of gas-liquid chromatography carried out a quantitative analysis of the main components of the essential oil Prangos odontalgica. The quantitative content of the components of the essential oil was calculated by the areas of gas chromatographic peaks without the use of correction factors. Qualitative analysis was performed by comparing linear retention indices. In the Prangos odontalgica essential oil, 38 substances were identified (88.4%). It contains sesquiterpenes (31.48%), terpenoids (19.2%), hydrocarbons (15.39%), carboxylic acids and their esters (10.86%), alcohols, phenols (8.84%). Among sesquiterpenes, the predominant components are γ-elemen (9.84%), bisabolol (9.41%), and among terpenoids – trans-nerolidol (3.90%) and linalyl isobutyrate (3.41%).

Microbial degradation of Pyrazine Compounds in Wastewater and cow dung SouthwestNigeria.

Wastewater samples, industrial effluents from food industry and cow dung were obtained aseptically and the physico-chemical properties were determined following standard procedures. Serial dilution technique was used in isolating native pyrazine - degraders from composite wastewater and cow dung samples obtained from Agbara and Apapa wastewater treatment plant (WTP) as well as Agege and Agbara Abattoirs respectively. Nutrient agar and Mineral salt medium supplemented with (3%) Pyrazine-2-carboxamide were used for enrichment for the isolates. Standard and conventional methods were used for the characterization and identification of pyrazine degraders. Gas chromatography (GC) flame ionization detector (FID) was used to determine the degree of mineralization of pyrazine. The mean pyrazine-degrader count from wastewater samples was 1.1×106 cfu/ml while that of cow dung was 9.7×105 cfu/ml. The GC peaks revealed that the initial quantity of pyrazine (15mg/l) was mineralized leaving behind (0.175mg/l) residues after 21 days of its introduction. The bacterial genera found utilizing pyrazine as source of C and N energy includes; Bacillus sp.,Flavobacterium sp.,Corynebacterium sp., Pseudomonas sp.,Streptococcus sp. and Staphylococcus sp. The biodegradability of pyrazine by tropical indigenous bacterial consortium was established and the convincing evidence of its mineralization was with gas chromatography. The objectives of the current study was to isolate and identify indigenous pyrazine-degraders from tropical wastewater and cow dung.

Picomolar-scale compound-specific isotope analyses.

We report modifications to compound-specific isotope analyses (CSIA) to enable high-precision isotopic analyses of picomoles of carbon for intact organic molecules. This sample size is two orders of magnitude below the amounts required for commercial systems. The greatly enhanced sensitivity of this system expands molecular isotope studies and applications previously prohibited by low concentrations and small samples. We utilize the resolving power and low volumetric flow rates of narrow-bore capillary gas chromatography to improve sample transfer efficiency while maintaining narrow peak widths. Post-column peak broadening is minimized using a micro-fluidic valve for solvent diversion, capillary combustion reactor, narrow-bore capillary transfer lines, and cryogenic water trap. The mass spectrometer was fitted with collector amplifiers configured to 25ms response times and a data logger board with firmware capable of rapid data acquisition. Carbon dioxide gas was introduced directly into the ion source to evaluate the dynamic range of the system and accuracy and precision of carbon isotope ratio (δ13 C value) measurements. The accuracy and precision for combusted compounds were evaluated using a suite of n-alkanes. For ≥30 pmol carbon introduced directly into the ion source, the mean difference between the measured and expected δ13 C values is 0.03‰ (1σ, n = 57) and the standard deviation of replicate measurements is 0.11‰ (1σ). The CO2 peak widths generated by the exponential dilution flask were 250ms and the peak widths produced by combusting n-alkanes were ca 500ms, less than 25% the width of conventional gas chromatography peaks. For a mixture of 15 n-alkanes (n-C16 to n-C30 ), the accuracy is 0.3‰ (1σ) and precision is 0.9‰ (1σ) for replicate δ13 C measurements with 100pmol carbon per compound on column. The pico-CSIA method described here offers improved chromatographic resolution and reduces sample size requirements by two orders of magnitude. These advances significantly broaden the available analytical window for CSIA in research areas frequently hindered by sample size limitations, such as forensics, paleoclimate, astrobiology, and biochemistry.

Characterization of thermal desorption with the Deans-switch technique in gas chromatographic analysis of volatile organic compounds

This study presents a novel application based on the Deans-switch cutting technique to characterize the thermal-desorption (TD) properties for gas chromatographic (GC) analysis of ambient volatile organic compounds (VOCs). Flash-heating of the sorbent bed at high temperatures to desorb trapped VOCs to GC may easily produce severe asymmetric or tailing GC peaks affecting resolution and sensitivity if care is not taken to optimize the TD conditions. The TD peak without GC separation was first examined for the quality of the TD peak by analyzing a standard gas mixture from C2 to C12 at ppb level. The Deans switch was later applied in two different stages. First, it was used to cut the trailing tail of the TD peak, which, although significantly improved the GC peak symmetry, led to more loss of the higher boiling compounds than the low boiling ones, thus suggesting compound discrimination. Subsequently, the Deans switch was used to dissect the TD peak into six 30s slices in series, and an uneven distribution in composition between the slices were found. A progressive decrease in low boiling compounds and increase in higher boiling ones across the slices indicated severe inhomogeneity in the TD profile. This finding provided a clear evidence to answer the discrimination problem found with the tail cutting approach to improve peak symmetry.Through the use of the innovated slicing method based on the Deans-switch cutting technique, optimization of TD injection for highly resolved, symmetric and non-discriminated GC peaks can now be more quantitatively assessed and guided.