Differentiation of types of crude oils in polluted soil samples by headspace-fast gas chromatography-mass spectrometry

The coupling of a headspace sampler to a fast gas chromatography system with mass spectrometry detection is proposed as a method for the identification of the sources of contamination in soils due to the presence of hydrocarbons derived from petroleum. The samples are subjected to the headspace generation process, with no prior treatment, and the volatiles generated are separated by fast gas chromatography. The total time of the chromatogram per sample is less than six minutes. Chemometric treatments, such as hierarchical cluster analysis (HCA), principal component analysis (PCA), and soft independent modelling of class analogy (SIMCA) were applied to the signals obtained for the different samples. The variables used for the chemometric treatments include m/z ratios characteristic of linear and branched saturated hydrocarbons, alkyl cyclohexanes, benzene, toluene, xylenes, C3-benzenes, naphthalene and methyl-naphthalenes. The results obtained show clear differentiated clusters for the different crude oils and correct predictions when SIMCA is applied, thus allowing the differentiation of types of crude oils contaminating soils in a rapid and reliable manner.     

Direct screening and confirmation of priority volatile organic pollutants in drinking water

A screening tool was proposed for the rapid detection of eight priority volatile organic pollutants according to European standards in drinking water. The method is based on the direct coupling of a headspace sampler with a mass spectrometer, using a chromatographic column heated to 175 degrees C as an interface. The water sample was subjected to the headspace extraction process and the volatile fraction was introduced directly into the mass spectrometer, without prior chromatographic separation, achieving low detection limits (0.6-1.2 ng/ml) for all compounds. The mass spectrum resulting from the simultaneous ionization and fragmentation of the mixture of molecules constitutes the volatile profile of each sample. An appropriate chemometric treatment of these signals permitted them to be classified, on the basis of their volatile composition, as contaminated or uncontaminated with respect to the legally established concentration levels for these compounds in drinking water, and providing no false negatives. A conventional confirmation method was carried out to analyze positive water samples by using the same instrumental setup as in the screening method, but using an appropriate temperature program in the chromatographic column to separate, identify and quantify each analyte.     

Fast screening method for determining 2,4,6-trichloroanisole in wines using a headspace–mass spectrometry (HS–MS) system and multivariate calibration

The system based on coupling a headspace sampler to a mass spectrometer (HS-MS), which is considered one kind of electronic nose, is an emergent technique for ensuring and controlling quality in industry. It involves injecting the headspace of the sample into the ionization chamber of the mass spectrometer where the analytes are fragmented. The result is a complex mass spectrum for each sample analyzed. When several samples are analyzed the data matrix generated is processed with chemometric techniques to compare and classify the substances from their volatile composition, in other words, to compare and classify their flavor. So far, information from electronic nose applications has mainly been qualitative. In this paper we present a quantitative study that uses a multivariate calibration. We analyzed several white wines using HS-MS to determine 2,4,6-tricholoranisole (TCA). This is an off-flavor that is a serious problem for the wine industry. The method is simple because it does not require sample preparation, only addition of sodium chloride being necessary for sample conditioning. Also, it provides a fast screening (10 min/sample) of the quantity of TCA in wines at ultratrace (sub microg L(-1)) levels.     

Chiral separation of amino acids by capillary electrophoresis with octyl-beta-thioglucopyranoside as chiral selector

In the present work, we propose the use of direct coupling of a headspace sampler to a mass spectrometer for the detection of adulterants in olive oil. Samples of olive oils were mixed with different proportions of sunflower oil and olive-pomace oil, respectively, and patterns of the volatile compounds in the original and mixed samples were generated. Application of the linear discriminant analysis technique to the data from the signals was sufficient to differentiate the adulterated from the non-adulterated oils and to discriminate the type of adulteration. The results obtained revealed 100% success in classification and close to 100% in prediction. The main advantages of the proposed methodology are the speed of analysis (since no prior sample preparation steps are required), low cost, and the simplicity of the measuring process.     

Headspace mass spectrometry methodology: application to oil spill identification in soils

In the present work we report the results obtained with a methodology based on direct coupling of a headspace generator to a mass spectrometer for the identification of different types of petroleum crudes in polluted soils. With no prior treatment, the samples are subjected to the headspace generation process and the volatiles generated are introduced directly into the mass spectrometer, thereby obtaining a fingerprint of volatiles in the sample analysed. The mass spectrum corresponding to the mass/charge ratios (m/z) contains the information related to the composition of the headspace and is used as the analytical signal for the characterization of the samples. The signals obtained for the different samples were treated by chemometric techniques to obtain the desired information. The main advantage of the proposed methodology is that no prior chromatographic separation and no sample manipulation are required. The method is rapid, simple and, in view of the results, highly promising for the implementation of a new approach for oil spill identification in soils. Figure PCA score plots illustrate clear discrimination of types of crude oil in polluted soil samples (e.g. results are shown for vertisol)     

On-line coupling of liquid chromatography,capillary gas chromatography and mass spectrometry for the determination and identification of polycyclic aromatic hydrocarbons in vegetable oils

Summary An on-line combination of liquid chromatography, gas chromatography and mass spectrometry has been realized by coupling a quadrupole mass spectrometer to an LC-GC apparatus. Liquid chromatography was used for sample pretreatment of oil samples of different origin. The appropriate LC fraction, containing polycyclic aromatic hydrocarbons, was transferred to the gas chromatograph using a loop-type interface. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were introduced into the mass spectrometer for detection and identification. The GC column was connected to a short piece of deactivated fused silica that protruded into the ion source. The total analytical set-up allowed the direct analysis of oil samples after dilution in n-pentane without any sample clean-up. Detection limits are about 40 pg in the full scan mode and about 1 pg with selective ion monitoring, i.e. 20 ppb and 0.5 ppb respectively.     

Headspace–Mass Spectrometry with Alternative Chromatographic Separation Using a Column Switching System for the Screening and Determination of BTEX and Styrene in Comestible Oil

A headspace–mass spectrometry with alternative chromatographic separation using a column switching system was developed for the screening and confirmation of BTEX and styrene in comestible oils. According to the position of the switching valve, the chromatographic column can be bypassed and the volatile sample constituents are transferred directly from the headspace sampler to the mass spectrometer providing a global, non resolved, signal in less than 1 min after injection. In this way, a set of samples can be rapidly processed in order to determine if they are (or not) contaminated with BTEX and styrene. Subsequently, only the samples with positive response in the previous screening can be processed by gas chromatography–mass spectrometry in the same analytical system by switching the position of the valve, thus confirming the presence of the analytes in the sample.

The method presents good analytical features and it is applicable to the analysis of real samples. Detection limits were lower than 0.1 ng mL^?1, and recoveries were between 97 and 105% with relative standard deviations lower than 4%.

Analysis of real comestible oils showed the presence of toluene, benzene, and styrene in some samples packed in plastic bottles.     

The characterization of closely related polymeric materials by thermogravimetry—mass spectrometry

The potential of a new technique in forensic science, thermogravimetry—mass spectrometry, is illustrated by its application to the examination of acrylic fibres and white alkyd gloss paints, small samples of which are difficult to differentiate even by a combination of current techniques. A simple interface allowing the coupling of a magnetic sector mass spectrometer to a thermobalance is described. This combination allows up to five experimental parameters to be determined simultaneously either for classification of the material under investigation or for the detailed direct comparison of samples. The thermobalance allows the temperatures at which weight losses occur and their relative proportions to be determined; the basic parameter obtained from the mass spectrometer is the total ion current trace. From this, single qualitative mass spectra may be chosen for examination and ions, whose presence or absence may be diagnostic or which vary characteristically throughout the analysis, can be selected. The variations of these ions may then be examined by computer-generated mass thermograms (analagous to mass chromatograms in g.c.—m.s.) or, if computer facilities are not available, by multiple ion detection. The residue from the analysis can be used for trace element analysis, e.g. by energy-dispersive x-ray fluorescence spectrometry.     

Investigation of different crude oils applying thermal analysis/mass spectrometry with soft photoionisation

A variety of crude oil samples have been investigated by the combined methods of thermal analysis and mass spectrometry by means of a newly developed prototype of a thermogravimetry—single photon ionisation time-of-flight mass spectrometer coupling (TG-SPI-TOFMS). Single photon ionisation (SPI) was conducted utilising a novel electron beam pumped argon excimer lamp (EBEL) as photon source, and a TOFMS with orthogonal acceleration has been applied for the detection of the mass to charge signals. The advantage of the soft SPI technique over EI for the analysis of such complex samples could be clearly demonstrated, as the aliphatic hydrocarbons present in crude oil may be detected via their respective molecular ion signals, not showing the intense fragmentation typical for EI spectra of this substance class. The application of SPI revealed furthermore two distinct decomposition regions, dominated by evaporation and pyrolysis processes, respectively. Moreover, different crude oils could be distinguished by TA/SPI mass spectra due to their unique molecular signatures.     

Automated analysis of 13C/12C ratios in CO2 and dissolved inorganic carbon for ecological and environmental applications

Stable carbon isotope ratios (13C/12C) are a valuable tool for studying a wide range of environmental processes, including carbon cycling and subsurface microbial activity. Recent advances in automated analysis provide the opportunity to increase greatly the ease and consistency of isotopic analysis. This study evaluated an automated headspace sampler linked to a commercially available CO2 preconcentration system and continuous flow isotope ratio mass spectrometer. Field sampling and analysis methods are illustrated for delta13C of soil respired CO2, from both tracer and natural abundance experiments, and dissolved inorganic carbon from contaminated groundwater. The automated system demonstrated accuracy, precision, and linearity, with standard errors below 0.1 per thousand for replicate gas standards run at concentrations varying five-fold. It measured 40 samples per 10-hour run, with concentrations ranging from ppb to percentage levels. In the field, gas samples were injected into nitrogen-filled autosampler vials, thereby allowing use of small sample volumes, control of analyte concentration, and direct analysis by the automated system with no further preparation. A significant linear relationship between standard concentrations and peak area allows for accurate estimates of sample CO2 concentration from the mass spectrometric data. The ability to analyze multiple small-volume samples with minimal off-line preparation should enhance the application of isotopes to well-replicated field experiments for process-level studies and spatial and temporal scaling.     

Rapid determination of short chain carnitines in human plasma by electrospray ionisation-ion trap mass spectrometry using capillary electrophoresis instrument as sampler

A capillary electrophoresis apparatus was used as sampler for flow injection analysis (FIA) in tandem mass spectrometry of L-carnitine and its acetyl- and propionyl-metabolites in human plasma. The capillary electrophoresis instrument was coupled to the ion trap mass spectrometer by an electrospray ionization coaxial sheath liquid interface. The electrophoresis capillary introduced the sample directly into the source by applying a prolonged sample injection. The use of the capillary electrophoresis apparatus miniaturised the FIA procedure, substantially reducing the quantities of solvents and samples used, and allowed rapid automated sequential analyses. The method was optimised and validated using a dialyzed human plasma matrix. The plasma samples were analysed after a simple, rapid deproteinisation procedure with acetonitrile and diluted 70 times before direct injection into the mass spectrometer for product ion scan MS/MS analysis in positive ionisation. The total analysis time was 5 min, including capillary preconditioning and acquisition time (3 min). The method was sensitive, allowing the determination of L-, L-acetyl- and L-propionyl-carnitines at 140, 14 and 3.6 nM concentrations (injected values) corresponding to lower limit of quantitation values in plasma of 10, 1 and 0.25 microM, respectively. The method was processed for full validation and applied to the analysis of L-carnitine and its short chain derivatives in human plasma samples.     

Application of headspace-mass spectrometry for differentiating sources of olive oil

In the present work we propose the use of headspace-mass spectrometry (HS-MS) for the characterisation of monovarietal olive oils, an issue of interest when the origin of an oil has to be determined. The HS-MS procedure involves the direct introduction of the sample into a vial, headspace generation and automatic injection of the volatiles into a mass spectrometer. The results were compared with those obtained using more conventional approaches, including chromatographic, spectrophotometric and other types of analysis. Linear Discriminant Analysis (LDA) was applied to the data obtained with both analytical methodologies to achieve the differentiation of the three types of samples. The proposed method is faster and cheaper than those usually employed for edible oil analysis and no sample preparation is required. Additionally, the measuring process is simple and the results obtained from chemometric treatment are 100% correct as regards classification and prediction, making it an appropriate method for routine control.     

Screening for sarin in air and water by solid-phase microextraction-gas chromatography-mass spectrometry.

A method of screening air and water samples for the chemical-warfare agent Sarin is developed using solid-phase microextraction (SPME)-gas chromatography (GC)-mass spectrometry (MS). The SPME field kit sampler is ideal for collecting air and water samples in the field and transporting samples safely to the laboratory. The sampler also allows the sample to be introduced into the GC-MS system without further sample preparation. Results of the tests with Sarin using the SPME technique indicate that a sample collection time of 5 min is sufficient to detect 100 ng/L of Sarin in air. For water samples, Sarin is detected at a concentration of 12 microg/mL or higher. This method is ideal for screening samples for quick response situations.     

On-line measurement of the absolute humidity of air, breath and liquid headspace samples by selected ion flow tube mass spectrometry

We describe how selected ion flow tube mass spectrometry (SIFT-MS) can be used to determine the absolute humidity of air, breath and liquid headspace samples. This involves the determination of the relative count rates of the H3O+ ions and those H3O+.(H2O)(1,2,3) hydrate ions that inevitably form in the helium carrier gas when humid samples are being analysed by SIFT-MS using H3O+ precursor ions. This requires an understanding of the kinetics of hydrated hydronium ion formation, the involvement of mass discrimination in the analytical quadrupole mass spectrometer and the decreased diffusive loss of the heavier hydrates along the flow tube. Thus, we show that the humidity of breath and liquid headspace samples, typically at the few percent level, can be directly obtained on-line to the SIFT-MS instrument along with the concentrations of trace gases, which are present at much lower levels. We emphasise the value of parallel humidity measurements in ensuring good real-time sampling of breath and liquid headspace and the value of such measurements to trace gas analysis using SIFT-MS.     

Thermal analysis/mass spectrometry using soft photo-ionisation for the investigation of biomass and mineral oils

The combined analytical methods of thermal analysis and mass spectrometry have been applied in form of a newly developed prototype of a thermogravimetry — single photon ionisation time-of-flight mass spectrometer coupling (TG-SPI-TOFMS) to investigate the molecular patterns of evolved gases from several biomass samples as well as a crude oil sample. Single photon ionization (SPI) was conducted by means of a novel electron beam pumped argon excimer lamp (EBEL) as photon source. With SPI-TOFMS various lignin decomposition products such as guaiacol, syringol and coniferyl alcohol could be monitored. Furthermore, SPI allows the detection of aliphatic hydrocarbons, mainly alkenes, carbonylic compounds such as acetone, and furan derivatives such as furfuryl alcohol and hydroxymethylfurfural. More alkaline biomass such as coarse colza meal show intense signals from nitrogen containing substances such as (iso-)propylamine and pyrrole. Thermal degradation of crude oil takes place in two steps, evaporation of volatile components and pyrolysis of larger molecular structures at higher temperatures. Due to the soft ionisation, homologue rows of alkanes and alkenes could be detected on basis of their molecular ions. The obtained information from the thermal analysis/photo ionisation mass spectrometry experiments can be drawn on in comparison to the investigation of the primary products from flash pyrolysis of biomass for production of biofuels and chemicals.     

Current applications of capillary electrophoresis-mass spectrometry for the analysis of biologically important analytes in urine (2017 to mid-2021): A review

Capillary electrophoresis coupled online with mass detection is a modern tool for analyzing wide ranges of compounds in complex samples, including urine. Capillary electrophoresis with mass spectrometry allows the separation and identification of various analytes spanning from small ions to high molecular weight protein complexes. Similarly to the much more common liquid chromatography-mass spectrometry techniques, the capillary electrophoresis separation reduces the complexity of the mixture of analytes entering the mass spectrometer resulting in reduced ion suppression and a more straightforward interpretation of the mass spectrometry data. This review summarizes capillary electrophoresis with mass spectrometry studies published between the years 2017 and 2021, aiming at the determination of various compounds excreted in urine. The properties of the urine, including its diagnostical and analytical features and chemical composition, are also discussed including general protocols for the urine sample preparation. The mechanism of the electrophoretic separation and the instrumentation for capillary electrophoresis with mass spectrometry coupling is also included. This review shows the potential of the capillary electrophoresis with mass spectrometry technique for the analyses of different kinds of analytes in a complex biological matrix. The discussed applications are divided into two main groups (capillary electrophoresis with mass spectrometry for the determination of drugs and drugs of abuse in urine and capillary electrophoresis with mass spectrometry for the studies of urinary metabolome).     

Fast characterization of foodstuff by headspace mass spectrometry (HS-MS)

The field of the rapid characterization of products by HS-MS is reviewed. The general principle of HS-MS systems consists of introducing volatile components present in the HS of a sample without prior chromatographic separation into the ionization chamber of a mass spectrometer. The spectrum resulting from simultaneous ionization and fragmentation of the mixture of molecules introduced constitutes a “fingerprint” that is characteristic of the product being analyzed. Exploitation of this spectral information allows one determine the composition of the sample.     

Electrospray ionization mass spectrometry of phosphopeptides isolated by on-line immobilized metal-ion affinity chromatography

Electrospray ionization mass spectrometry (ESI/MS) affords a rapid and sensitive technique for determining peptides produced by the enzymatic digestion of phosphoroteins. When coupled with on-line immobilized metal-ion affinity chromatography (IMAC), the combmation allows separation and mass spectrometric identification of phosphorylated and nonphosphorylated peptides. In this study, the feasibility and general applicability of on-line IMAC/ESI/MS is investigated by using immobilized ferric ions for selective chelation of several phosphotyrosine and phosphoserine peptides. The sensitivity and practicality of the technique for phosphoproteins are demonstrated via the analysis of 30 pmol (～0.7 μg) of bovine β-casein purified by sodium dodecylsulfate-polyacrylamide gel electrophoresis, electroblotted onto a polyvinylidene difluoride membrane, and digested in situ with trypsin. It is observed that on-line IMAC/ESI/MS suffers less from sample losses than experiments performed off-line, suggesting that the limiting factors in sensitivity for this technique are the purification procedures and sample handling rather than the IMAC and mass spectrometry. Thus, the ability to inject the tryptic digest of an electroblotted protein directly onto the column without buffer exchange and to analyze the eluent directly via on-line coupling of the IMAC column to the mass spectrometer greatly reduces sample losses incurred through sample handling and provides a convenient method for analyzing phosphopeptides at low levels.     

A radiofrequency glow-discharge-time-of-flight mass spectrometer for direct analysis of glasses

A radiofrequency (rf) glow-discharge (GD) ion source coupled to a commercial on-axis time-of-flight mass spectrometer (TOFMS) has been developed for the direct analysis of non-conducting samples. Different instrumental configurations of the rf-GD source, including the optional use of a sampler cone and the possibility of allowing electrical floating of the discharge, were evaluated first with a conducting sample. Higher ion signals were obtained when the GD was electrically floating and no sampler cone was used. A homogeneous glass was then analyzed using two different rf-GD configurations—with a sampler cone and discarding the use of the sampler cone. The atomic mass spectra obtained with the TOFMS using both configurations were compared. Analyte signals were systematically higher for the latest mode which avoids the sampler cone. The analytical capability of the proposed rf-GD–TOFMS system for the analysis of thick glasses, up to 6 mm, has been investigated in terms of sensitivity, isotopic ratio accuracy, and mass-resolving power. Different homogeneous glasses (including glasses as thick as 6 mm) have been analyzed and major and minor elements were detected. Isotope ratio accuracies of about ±1% and mass resolving powers of about 700 were observed.     

Detection of perfluorocarbons in blood by headspace solid-phase microextraction combined with gas chromatography/mass spectrometry.

A new method of detection of perfluorocarbon molecules (PFCs) in blood sample has been established. After an extraction and pre-concentration step performed by headspace solid-phase microextraction (HS-SPME), the PFCs are detected by gas chromatography-mass spectrometry (GC/MS) with an ion trap mass spectrometer in MS and MS/MS modes. The influence of different parameters on the SPME process is discussed. The limit of detection and the linearity of the procedure have been determined for two PFCs.