GC-MS in space research: decoding complex isothermal chromatograms recovered from space missions

An analytical procedure is described to study GC-MS isothermal chromatograms simulating those recovered from space missions: in fact GC plays a predominant role in space missions devoted to characterizing the chemical composition of extra-terrestrial atmospheres. SIM (selected ion monitoring) detection was used for monitoring selected chemical classes: a simplified chromatogram can be obtained giving information on the chemical composition of the complex mixture. Since only isothermal GC chromatograms are allowed by flight constraints, a time axis transformation is required to make them homogeneous: i.e., constant retention increments for CH2 additions in terms of a homologous series. The order in the linearized chromatogram can be simply singled out with a chemometric approach based on the study of the Autocovariance Function (ACVF) computed on the digitized chromatogram: the plot of the experimental autocorrelation function (EACF) shows well-shaped peaks if constant interdistances are repeated in different regions of the chromatogram. The method was applied to standard mixtures representative of planetary atmospheres--hydrocarbons, nitriles and oxygenated compounds with between 3 and 12 carbon atoms--analyzed in flight simulating conditions. The coupling of the selectivity of SIM detection with the interpretation power of the EACF procedure proves to be a powerful tool for interpreting data recovered from space missions: the chemical composition of the mixture can be identified by handling the raw SIM chromatograms.     

Functional speciation of metal-dissolved organic matter complexes by size exclusion chromatography coupled to inductively coupled plasma mass spectrometry and deconvolution analysis

High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (HP-SEC–ICP-MS), in combination with deconvolution analysis, has been used to obtain multielemental qualitative and quantitative information about the distributions of metal complexes with different forms of natural dissolved organic matter (DOM). High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry chromatograms only provide continuous distributions of metals with respect to molecular masses, due to the high heterogeneity of dissolved organic matter, which consists of humic substances as well as biomolecules and other organic compounds. A functional speciation approach, based on the determination of the metals associated to different groups of homologous compounds, has been followed. Dissolved organic matter groups of homologous compounds are isolated from the aqueous samples under study and their high performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry elution profiles fitted to model Gaussian peaks, characterized by their respective retention times and peak widths. High performance size exclusion chromatography coupled to inductively coupled plasma mass spectrometry chromatograms of the samples are deconvoluted with respect to these model Gaussian peaks. This methodology has been applied to the characterization of metal–dissolved organic matter complexes in compost leachates. The most significant groups of homologous compounds involved in the complexation of metals in the compost leachates studied have been hydrophobic acids (humic and fulvic acids) and low molecular mass hydrophilic compounds. The environmental significance of these compounds is related to the higher biodegradability of the low molecular mass hydrophilic compounds and the lower mobility of humic acids. In general, the hydrophilic compounds accounted for the complexation of around 50% of the leached metals, with variable contributions of humic and fulvic acids, depending on the nature of the samples and the metals.     

Comparison by capillary SFC and SFC-MS of soxhlet and supercritical fluid extraction of hamster feces

Components of hamster feces ranging from low molecular weight fatty acids through the expected range of triglycerides have been eluted in a single SFC run with simultaneous pressure and temperature programming. Temperature programming from 140°C to 240°C was required to provide optimum conditions for separation of the fatty acids and to move the elution region of the sterol esters away from that of the triglycerides. Data from chemical ionization and electron impact mass spectrometry of compounds separated by SFC were used to confirm identities suggested by retention measurements and to provide tentative identities of unknown compounds. SFC with flame ionization detection was used to compare Soxhlet extraction, off-line supercritical fluid extraction (SFE), and on-line SFE of the feces. Although samples obtained by Soxhlet extraction and SFE produced very similar chromatograms, SFE required far less time and consumed much smaller quantities of organic solvent.     

Development of a headspace solid-phase microextraction-gas chromatography-mass spectrometry method for the identification of odour-causing volatile compounds in packaging materials

A method for the identification of volatile organic compounds in packaging materials is presented in this study. These compounds are formed by thermooxidative degradation during the extrusion coating process in the manufacture of packaging. Headspace solid-phase microextraction (HS-SPME) was used as sample preparation technique prior to the determination of the volatile organic compounds by gas chromatography-mass spectrometry (GC-MS). The effects of extraction variables, such as the type of fibre, the incubation temperature, the pre-incubation time, the size of the vial and the extraction time on the amounts of the extracted volatile compounds were studied. The optimal conditions were found to be: carboxen-polydimethylsiloxane 75 microm fibre, 5 min of pre-incubation time, 100 degrees C of incubation temperature, 20-ml vial, and 15 min of extraction time. The chromatograms obtained by HS-SPME and static headspace extraction were compared in order to show that the HS-SPME method surpasses the static headspace method in terms of sensitivity. Twenty-five compounds were identified including carbonyl compounds (such as 3-methyl-butanal, 3-heptanone or octanal), carboxylic acids (such as pentanoic acid or hexanoic acid) known as odour causing compounds and hydrocarbons (such as decane, undecane or dodecane). Finally, the method was applied to different packaging samples (one odour-unacceptable, two odour-acceptable, and three odourless samples) and to the raw materials in order to find out the odour-responsible volatile organic compounds and their source.     

An ultrasonication-assisted extraction and derivatization protocol for GC/TOFMS-based metabolite profiling

Conventional chemical derivatization of metabolites in biological specimens is time-consuming, which limits the throughput and efficiency of metabolite profiling using a gas chromatography/time-of-flight mass spectrometry (GC/TOFMS) platform. We report an ultrasonication-assisted protocol which reduces the derivatization time from hours to about 30 min and significantly enhances the derivatization efficiency prior to a GC/TOFMS analysis. The protocol was evaluated using 40 compounds representing different classes of human metabolites, and demonstrated good analytical precision and accuracy. In comparison with the conventional method, the new protocol was able to increase the intensity of most of the identified peaks (71.0%) in the GC/TOFMS chromatograms of human serum samples. The detected compounds with increased intensity include most amino acids, keto-containing organic acids, carbonyl-containing carbohydrates, and unsaturated fatty acids. We applied this protocol in a metabolomic study of human serum samples obtained from 34 patients diagnosed with hypertension and 29 age- and gender-matched healthy subjects. Metabolite markers associated with hypertension, including glucosamine, D-sorbitol, 1-stearoylglycerol, and homocysteine, were identified and validated by statistical methods and use of reference standards. Our work highlights the potential of this novel approach for the large-scale metabolite profiling of samples generated from plant, animal, and clinical and epidemiological studies.     

Signal processing of GC-MS data of complex environmental samples: characterization of homologous series

Identification and characterization of homologous series by GC-MS analysis provide very relevant information on organic compounds in complex mixtures. A chemometric approach, based on the study of the autocovariance function, EACVF_tot, is described as a suitable tool for extracting molecular-structural information from the GC signal, in particular for identifying the presence of homologous series and quantifying the number of their terms. A data pre-processing procedure is introduced to transform the time axis in order to display a strictly homogenous retention pattern: n-alkanes are used as external standard to stretch or shrink the original chromatogram in order to build up a linear GC retention scale. This addition can be regarded as a further step in the direction of a signal processing procedure for achieving a systematic characterization of complex mixture from experimental chromatograms. The EACVF_tot was computed on the linearized chromatogram: if the sample presents terms of homologous series, the EACVF_tot plot shows well-defined deterministic peaks at repeated constant interdistances. By comparison with standard references, the presence of such peaks is diagnostic for the presence of the ordered series, their position can be related to the chemical structure of the compounds, their height is the basis for estimating the number of terms in the series. The power of the procedure can be magnified by studying SIM chromatograms acquired at specific m/z values characteristic of the compounds of interest: the EACVF_tot on these selective signals makes it possible to confirm the results obtained from an unknown mixture and check their reliability.The procedure was validated on standard mixtures of known composition and applied to an unknown gas oil sample. In particular, the paper focuses on the study of two specific classes of compounds: n-alkanes and oxygen-containing compounds, since their identification provides information useful for characterizing the chemical composition of many samples of different origin. The robustness of the method was tested in experimental chromatograms obtained under unfavorable conditions: chromatograms acquired in non-optimal temperature program conditions and chromatographic data affected by signal noise.     

Creating a fatty acid methyl ester database for lipid profiling in a single drop of human blood using high resolution capillary gas chromatography and mass spectrometry

Capillary gas chromatography (CGC) in combination with mass spectrometry (MS) was optimized for the separation and detection of the fatty acids occurring in the lipid fraction of blood. A fingertip blood sample (ca. 50 microL) was transesterified into the methyl esters and analyzed on a 100 m x 0.25 mm ID column coated with a biscyanopropyl polysiloxane (HP-88) stationary phase. The method was retention time locked. Programmed temperature vaporization injection (PTV) in the solvent venting mode was applied to minimize the sample size, while maintaining high sensitivity. The total analysis time was ca. 60 min. Retention times and both electron impact (EI) and positive chemical ionization (PCI) mass spectrometry were combined to elucidate the fatty acids according to alkyl chain, degree of unsaturation and position of the double bonds. Using extracted ion chromatograms about 100 fatty acids and related compounds were detected in blood samples and most of them were identified. This work resulted in a very large fatty acid methyl esters database, containing retention time and mass spectral information that will be applied to metabolomic studies.     

Thermochemolysis in search for organics in extraterrestrial environments

It has been suggested that extraterrestrial organic material may well represent an important part of the organic material available for the origin of life. It may be expected that early life on Mars was similar to prokaryotic life on Earth and whatever preceded the prokaryotes. Detection of markers of microorganisms on Mars is then a key point in the search for life. The analytical technique has to be robust, sensitive and non-specific due to the large scope of targeted molecules. The main objective of this work is to present the capabilities of a TMAH-PY-GC–MS technique for the in situ analysis of organic matter in extraterrestrial soil samples. Two Martian analogues were analyzed to validate the technique. Biomarkers of microbial and higher plants origin such as lipids (n-alkenes, fatty acids) and carbohydrates were detected in samples. In the two samples, fatty acids had a microbial origin. On the other hand, n-alkenes and n-alkanols were from preserved higher plants biopolymers. TMAH-PY-GC–MS technique presented the advantage to wider the scopes of targeted molecules without adding additional device as pyrolysers are already used in spacecraft.     

The discriminant pixel approach: A new tool for the rational interpretation of GCxGC-MS chromatograms

GCxGC is now recognized as the most suited analytical technique for the characterization of complex mixtures of volatile compounds; it is implemented worldwide in academic and industrial laboratories. However, in the frame of comprehensive analysis of non-target analytes, going beyond the visual examination of the color plots remains challenging for most users. We propose a strategy that aims at classifying chromatograms according to the chemical composition of the samples while determining the origin of the discrimination between different classes of samples: the discriminant pixel approach.After data pre-processing and time-alignment, the discriminatory power of each chromatogram pixel for a given class was defined as its correlation with the membership to this class. Using a peak finding algorithm, the most discriminant pixels were then linked to chromatographic peaks. Finally, crosschecking with mass spectrometry data enabled to establish relationships with compounds that could consequently be considered as candidate class markers.This strategy was applied to a large experimental data set of 145 GCxGC-MS chromatograms of tobacco extracts corresponding to three distinct classes of tobacco.     

Adsorption of simple aromatic compounds on activated carbons

The adsorption of model aromatic compounds (phenol, aniline, nitrobenzene) on modified activated carbons has been investigated. Electrostatic and dispersive adsorbate/adsorbent interactions are involved in this process. Their influence on the uptake of the above mentioned aromatic compounds has been evaluated using different solution pH conditions and activated carbon samples with different surface chemistries. These samples were obtained by modification of a commercial activated carbon by means of chemical treatment with HNO3 (acid sample) and thermal treatment under a flow of H2 (basic sample). The textural properties were not significantly changed after these modifications. The best uptake for all the adsorptives under most of the pH conditions used corresponded to the basic sample, which means that dispersive interactions are the most important in this process. However, electrostatic interactions cannot be neglected, as can be seen from the uptakes for the same sample at different pH. In the case of aniline at pH 2, electrostatic interactions are predominant, and the best uptake corresponds to the acid sample. The influence of textural properties on the adsorption process was also investigated, by comparing with another commercial activated carbon. As expected, for this type of organic compounds the uptake increases with the micropore surface area.     

Chemical derivatization techniques in the determination of functional groups by X-ray photoelectron spectroscopy

The fundamentals of chemical derivatization techniques as applied to the quantitative analysis of ultrathin surface layers of various organic compounds via functional groups were considered. Using X-ray photoelectron spectroscopy as an example of the most informative and almost nondestructive technique for characterization of thin layers, the general requirements imposed on the selective chemical reactions and possible artifacts were discussed. The validity of the technique was illustrated by the examples of analyses of surface layers of organic polymers with known concentrations of surface functional groups, plasma-modified polymers, and carbon fibers. It was noted that selective chemical reactions are successfully used in other techniques for studying material surfaces. The surface analysis of organic materials via functional groups can be performed with a simultaneous increase in the sensitivity of the corresponding spectral technique.     

Multivariate Statistical Analysis for Mutual Dependence Assessment of Selected Polyphenols,Organic Acids and Metals in Cool-Climate Wines

Polyphenols, organic acids and metal ions are an important group of compounds that affect the human health and quality of food and beverage products, including wines. It is known that a specific correlation between these groups exist. While wines coming from the New World and the Old World countries are extensively studied, wines coming from cool-climate countries are rarely discussed in the literature. One of the goals of this study was to determine the elemental composition of the wine samples, which later on, together as polyphenols and organic acids content, was used as input data for chemometric analysis. The multivariate statistical approach was applied in order to find specific correlations between the selected group of compounds in the cool-climate wines and the features that distinguish the most and differ between red and white wines and rosé wines. Moreover, special attention was paid to resveratrol and its correlation with selected wine constituents.     

Automated gas chromatography with cryogenic/sorbent trap for the measurement of volatile organic compounds in the atmosphere

An automated gas chromatographic system was constructed to easily adapt either the cryogenic trap or chemical sorbent trap for preconcentrating ambient levels of volatile organic compounds. Remarkable similarity in chromatograms from C3 to C10 was found between these two enrichment methods, except that the sorbent trap did not quantitatively trap the C2-hydrocarbons. In contrast to cryogenic trapping, the chromatographic conditions for more volatile compounds were substantially improved using the sorbent trap. Water interference on the porous-layer open tubular column was also better managed using the sorbent trap for the continuous analysis of humid room air. The similarity in peak profiles between the GC-flame ionization detection (FID) and a commercial GC-MS system, regardless of concentration levels, facilitated compound identification on the FID chromatograms based on a field mission involving analysis of 106 air samples.     

New approach based on solid-phase extraction for the assessment of organic compound pollutions in so-called pharmaceutically pure water

The application of a new kind of technique involving solid-phase extraction coupled with thermal desorption (SPE-TD) to the qualitative analysis of water used in pharmaceutical products was evaluated. Comparative analyses performed by the purge and trap (PT) technique were also conducted. The application of this SPE-TD technique resulted in the isolation of a large number of compounds from the water sample. The SPE-TD technique is applied to less volatile compounds, whereas the PT technique is used for more volatile and nonpolar ones. These two techniques should be applied in order to achieve complete identification and quantitative determination. Additionally, an attempt to identify organic compounds in pharmaceutical products was also conducted. The compounds present in such products include aldehydes, ketones, hydrocarbons, alcohols, esters. The influence of storage on the quality of water was also investigated. For samples characterized by a longer storage time, qualitatively richer chromatograms were obtained, which confirmed that components were released from the packaging (especially polyethylene) which entered the stored product.     

Chemical Composition and Biological Activity of Argentinian Propolis of Four Species of Stingless Bees

The chemical composition of propolis of four species of stingless bees (SLBs) from Argentina was determined, and its antibacterial and anticancer activity was evaluated on selected types of microbes and cancer cell lines. Volatile secretions of all propolis samples are formed by 174 C₂–C₁₅ organic compounds, mainly mono- and sesquiterpenes and their derivatives. The chromatograms of ether extracts showed 287 peaks, of which 210 were identified. The most representative groups in the extracts of various propolis samples were diterpenoids (mainly resin acids), triterpenoids and phenolic compounds: long-chain alkenyl phenols, resorcinols and salicylates. The composition of both volatile and extractive compounds turned out to be species-specific; however, in both cases, the pairwise similarity of the propolis of Scaptotrigona postica and Tetragonisca fiebrigi versus that of Tetragona clavipes and Melipona quadrifasciata quadrifasciata was observed, which indicated the similarity of the preferences of the respective species when choosing plant sources of resin. The composition of the studied extracts completely lacked flavonoids and phenolcarboxylic acids, which are usually associated with the biological activity and medicinal properties of propolis. However, tests on selected microbial species and cancer cell lines showed such activity. All propolis samples tested against Paenibacillus larvae, two species of Bacillus and E. coli showed biofilm inhibition unrelated to the inhibition of bacterial growth, leading to a decrease in their pathogenicity. Testing the anticancer activity of ether extracts using five types of cell cultures showed that all four types of propolis studied inhibit the growth of cancer cells in a dose- and time-dependent manner. Propolis harvested by T. clavipes demonstrated the highest cytotoxicity on all tested cell lines.     

Surface and wastewater quality monitoring: combination of liquid chromatography with (geno)toxicity detection,diode array detection and tandem mass spectrometry for identification of pollutants

Identification of unknown water pollutants with liquid chromatography and tandem mass spectrometry (LC–MS–MS) is often more complex and time consuming than identification with gas chromatography and mass spectrometry (GC–MS). In order to focus the identification effort on relevant compounds, unknown peaks need to be selected carefully. Based on its frequency of occurrence in the LC–Diode Array Detection (LC–DAD) chromatograms of surface and infiltrated waters, an unknown peak was selected for identification with LC–MS–MS. This compound was identified as hexamethoxymethylmelamine (HMMM), a chemical often used in the coating industry. This is the first time the presence of this chemical in surface waters has been reported. In addition to HMMM, two other structurally related compounds were found to be present in the investigated surface water. A standard mixture of HMMM and its by-products did not exhibit (geno)toxicity under the test conditions applied in this study. In another example, a genotoxic fraction of an industrial wastewater was isolated and examined by LC–MS–MS using a modern quadrupole–orthogonal acceleration-time-of-flight mass spectrometer (Q-TOF). Four compounds were detected. The structures of two compounds present are proposed to be 9-amino-2-hydroxy-acridine and 9-hydroxy-acridine-N-oxide or its structural isomer dihydroxy-acridine. Confirmation with standards could not be carried out, as pure compounds are not available. The other two compounds (structural isomers) could not be identified based on the data available within this study.     

基于气相色谱-质谱联用与液相色谱-质谱联用的非靶向代谢组学用于3类茶叶中化学成分分析（英文）

茶叶中的化学成分是构成其风味特征的物质基础。本研究建立了基于气相色谱-质谱联用和液相色谱-质谱联用的非靶向代谢组学方法。完成预处理及分析条件优化后,使用标准样品考察方法的线性、回收率及重复性,结果表明方法整体稳定且结果可靠。将该方法用于绿茶、乌龙茶和红茶中化学成分的分析。通过超声辅助溶剂提取及气相色谱-质谱联用分析共获得1812个特征峰,而使用加热溶剂提取及液相色谱-质谱联用分析可获得2608个特征峰。结合保留规律及质谱数据库,共定性173种化合物(109种随后经标准样品验证),其中只有9种化合物在上述两类分析中被同时检出,表明方法互补性良好。3类茶叶数据的偏最小二乘判别分析结果表明,三者间存在显著差异。结合模型的变量重要因子(VIP)与非参数检验共筛选出90种化合物,其中包含儿茶素、氨基酸、糖、有机酸和黄酮苷类等众多与茶叶滋味密切相关的化学成分。     

Benzil and Benzoin: General Spray Reagents for the Visualization of Organic Compounds on Thin Layer Chromatograms

Benzil and Benzoin spray reagents have been adopted to detect some organic compounds on thin layer chromatograms (TLC). These reagents were found to visualize sugars, amino acids, dicarboxylic acids and some natural products on thin layer plates. Colors produced with these reagents were shades of the spectrum and characteristic of individual or class of the organic and natural products.     

Application of two-dimensional gas chromatography combined with pixel-based chemometric processing for the chemical profiling of illicit drug samples

The chemical profiling of illicit drugs is a complex process. The results are affected by many different factors such as sample size, the sample processing conditions, the used analytical technique as well as the statistics that are applied. Within this proof-of-concept study, which was done in cooperation with the German Federal Criminal Police Office (Bundeskriminalamt, BKA), the adaptability of comprehensive two-dimensional (2D) gas chromatography (GCxGC) combined with a pixel-based chemometric data processing method is demonstrated. Samples of heroin and cannabis are extracted and analyzed with GCxGC-TOF-MS (time-of-flight mass spectrometry) and GCxGC-FID (flame ionization detection). The obtained second-order data are then used to identify possible marker compounds for the discrimination of the samples according to their chemical profile. The pixel-based chemometric process includes preprocessing steps (background correction, alignment of chromatograms and normalization) followed by an adaptation of hierarchical clustering to identify chemically similar samples, and finally a subsequent calculation of Fisher criterion based on the found clustering in order to identify promising marker compounds. The results of the pixel-based data analysis are compared to a limited peak-based study for cannabis and to a well-established standard method for the chemical profiling of heroin.     

Die Kosmochemie des Mars: Mit Raumsonden und Meteoriten

The chemical composition of Martian surface material is deduced using two different approaches: Direct measurements by the Alpha‐Proton‐X‐Ray Spectrometer (APXS) flown to Mars by the Pathfinder mission, and by analyses of SNC meteorites, which are believed to be rocks from Mars. Several surface rocks of Mars measured by the APXS have different chemical compositions than those of SNC meteorites. Both compositions are also different from the Martian soil found at the Pathfinder landing site. However, this soil, which covers the surface of Mars, seems to be a mixture of local rocks, SNC meteoritic material, and an iron‐rich component. From selected element correlations found in SNC meteorites and Martian surface samples, the bulk chemical composition of the planet is obtained. According to this model, Mars has an iron rich core of about 22 wt.%, which is relatively smaller than the Earth's core of about 33.5 %.