Multi-capillary column-ion mobility spectrometry: a potential screening system to differentiate virgin olive oils

The potential of a headspace device coupled to multi-capillary column-ion mobility spectrometry has been studied as a screening system to differentiate virgin olive oils (“lampante,” “virgin,” and “extra virgin” olive oil). The last two types are virgin olive oil samples of very similar characteristics, which were very difficult to distinguish with the existing analytical method. The procedure involves the direct introduction of the virgin olive oil sample into a vial, headspace generation, and automatic injection of the volatiles into a gas chromatograph-ion mobility spectrometer. The data obtained after the analysis by duplicate of 98 samples of three different categories of virgin olive oils, were preprocessed and submitted to a detailed chemometric treatment to classify the virgin olive oil samples according to their sensory quality. The same virgin olive oil samples were also analyzed by an expert’s panel to establish their category and use these data as reference values to check the potential of this new screening system. This comparison confirms the potential of the results presented here. The model was able to classify 97% of virgin olive oil samples in their corresponding group. Finally, the chemometric method was validated obtaining a percentage of prediction of 87%. These results provide promising perspectives for the use of ion mobility spectrometry to differentiate virgin olive oil samples according to their quality instead of using the classical analytical procedure.     

Evaluation of a differential mobility spectrometer/miniature mass spectrometer system

A planar differential mobility spectrometer (DMS) was coupled to a Mini 10 handheld rectilinear ion trap (RIT) mass spectrometer (MS) (total weight 10 kg), and the performance of the instrument was evaluated using illicit drug analysis. Coupling of DMS (which requires a continuous flow of drift gas) with a miniature MS (which operates best using sample introduction via a discontinuous atmospheric pressure interface, DAPI), was achieved with auxiliary pumping using a 5 L/min miniature diaphragm sample pump placed between the two devices. On-line ion mobility filtering showed to be advantageous in reducing the background chemical noise in the analysis of the psychotropic drug diazepam in urine using nanoelectrospray ionization. The combination of a miniature mass spectrometer with simple and rapid gas-phase ion separation by DMS allowed the characteristic fragmentation pattern of diazepam to be distinguished in a simple urine extract at lower limits of detection (50 ng/mL) than that achieved without DMS (200 ng/mL). The additional separation power of DMS facilitated the identification of two drugs of similar molecular weight, morphine (average MW = 285.34) and diazepam (average MW = 284.70), using a miniature mass spectrometer capable of unit resolution. The similarity in the proton affinities of these two compounds resulted in some cross-interference in the MS data due to facile ionization of the neutral form of the compound even when the ionic form had been separated by DMS.     

Ion trapping at atmospheric pressure (760 Torr) and room temperature with a high-field asymmetric waveform ion mobility spectrometer

A method for the confinement of ions at 760 Torr and room temperature is described. We have recently shown that a cylindrical-geometry high-field asymmetric waveform ion mobility spectrometer (FAIMS), which utilizes an ion separation technique based on the change in ion mobility at high electric fields, focuses ions in two dimensions. This article describes a FAIMS device in which the focusing is extended to three dimensions (i.e. ion trap). Characterization of the ion trap was carried out using a laboratory-constructed time-of-flight mass spectrometer. The half-life of a m/z 380 ion in the trap was determined to be 5 ms.     

Simultaneous sampling and analysis for vapor mercury in ambient air using needle trap coupled with gas chromatography-mass spectrometry

A needle trap (NT) technique for simultaneous sampling and analysis of vapor and particle mercury in ambient air using gold wire filled in a syringe needle has been developed. This NT technique relies on gold amalgamation rather than adsorption/absorption to traditional solid-phase microextraction. Hg trapped by Au-amalgamation NT is thermally desorbed in a hot injection port of a gas chromatograph; desorbed Hg is then determined by the coupled mass spectrometer. This simultaneous sampling and analysis technique were optimized, tested, and used for the collection and accurate determination of elemental Hg in ambient air. Linear calibration curves were obtained for Hg sampling by NT when mass spectrometry (MS) was used for detection; they spanned over 4 orders of magnitude. MS offered excellent sensitivity and selectivity. Selected ion monitor (SIM) mode was used for the linear calibration curves. The selected quantitation ion was m/z 202, since m/z 202 was the strongest isotope of mercury mass spectrum. The method was verified with HgCl(2) spiked solution samples. An excellent agreement was found between the results obtained for the Hg-saturated air samples and HgCl(2) spiked solution samples. The use of the Au-amalgamation gas-sampling needle trap method, for the measurement of Hg in air and Hg(2+) water samples, is described herein.     

Multi-component analysis (sterols, tocopherols and triterpenic dialcohols) of the unsaponifiable fraction of vegetable oils by liquid chromatography-atmospheric pressure chemical ionization-ion trap mass spectrometry

A simple and sensitive method for the analysis of sterols, tocopherols and triterpenic dialcohols from the unsaponifiable fraction from oil samples in a single analytical run using liquid chromatography coupled to mass spectrometry was developed. With this method, the compounds could be detected directly after dissolving the unsaponifiable fraction in acetonitrile without necessity of time-consuming sample pre-treatment or derivatization. Separation of the analytes was carried out at room temperature, by using a C18 column (5 μm i.d. 3.0 mm × 250 mm) with a linear gradient of acetonitrile/water (0.01% acetic acid) at a flow rate of 1.5 mL/min. The full scan mass spectra of the investigated compounds were measured by an ion trap mass spectrometer equipped with an APCI ion source. The optimized methodology was suitable for the identification of 23 compounds belonging to different families present in olive oil and other kinds of oils, as well as for the quantification of 15 analytes (vs. their commercial standards).     

Orthogonal trap time-of-flight mass spectrometer using a collisional damping chamber

We report a new hybrid mass spectrometer, which is a combination of a quadrupole ion trap and an orthogonal time-of-flight (TOF) mass spectrometer. This new configuration consists of a collisional-damping chamber (CDC) inserted between an MSn-capable ion trap and a high-mass-accuracy orthogonal-TOF mass spectrometer. Because the CDC converted an ion packet into an energy-focused and quasi-continuous beam, a high mass resolution of over 10,000 and a high mass accuracy of better than 3 ppm were achieved. Moreover, the ratio of the maximum detectable m/z to the minimum detectable m/z, which is referred to here as the mass window, was improved to more than 10.     

Characterization of isomers of oleuropein aglycon in olive oils by rapid‐resolution liquid chromatography coupled to electrospray time‐of‐flight and ion trap tandem mass spectrometry

In this work, rapid‐resolution liquid chromatography (RRLC) coupled to electrospray ionization time‐of‐flight mass spectrometry (ESI‐TOF‐MS) and ion trap multiple mass spectrometry (IT‐MSⁿ) has been applied to separate and characterize eleven isomers of oleuropein aglycon in fourteen Spanish extra‐virgin olive oils. After the extra‐virgin olive oil sample had been dissolved in hexane and cleaned up by a diol‐bonded phase solid‐phase extraction (SPE) cartridge, the eluting extract was resolved in methanol and analyzed on an Angilent 1200 system with a 4.6 × 150 mm, 1.8 µm Zorbax Eclipse plus C18 column. Mass spectrometry was carried out on a Bruker Daltonics microTOF mass spectrometer and a Bruker Daltonics ion trap mass spectrometer. The characterization of isomers of oleuropein aglycon was based on accurate mass data and the isotope function of characteristic fragment ions in the studied compounds by TOF‐MS, and the fragment ions were further confirmed by IT‐MSⁿ. The fragmentation pathway of oleuropein aglycon was successfully elucidated and all possible transformations among isomers of oleuropein aglycon were suggested. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of volatiles and semivolatiles in drinking water by microextraction and thermal desorption

A new technique to analyze aqueous samples for nanograms per liter levels of volatile and semivolatile compounds using microextraction and thermal desorption into a gas chromatograph/ion trap mass spectrometer (GC/MS) is described. This method is inherently sensitive (50 mL of aqueous sample is extracted prior to each desorption), uses no solvents, and detects volatiles and semivolatiles in the same analysis. Aqueous standards and environmental samples are pumped through a length of porous-layer open-tubular capillary column, which is then thermally desorbed onto a 30 m × 0.25 mm i.d. analytical column interfaced to an ion trap mass spectrometer for subsequent separation and detection. Sharp chromatographic peaks and reproducible retention times (RT) were observed. Replicate injections of surrogates (n = 6) averaged 32.6% R.S.D. Analysis of domestic tap water detected 55 analytes, some at the low-nanograms per liter level, and detected 3 halogenated ethenes, not previously reported in drinking water. Analysis of an aqueous sample from a municipal ground water source detected the presence of numerous semivolatile compounds at trace-levels.     

Determination of water contents in leaves by a near-infrared multispectral imaging technique

The kinetics of water desorption from olive leaves was studied using a near-infrared (NIR) multispectral imaging spectrometer. This imaging spectrometer is capable of sensitively and rapidly recording NIR spectral images of leaves because it was constructed with an acousto-optic tunable filter and an InGaAs focal plane array NIR camera. The high sensitivity and fast scanning ability of the imaging spectrometer make it suitable for kinetic determination. The kinetics of water desorption from olive leaves, determined by this multispectral imaging instrument, show that rate of water desorption is strongly dependent on the environment in which the leaves were stored. Water desorbed from leaves faster when leaves were stored under dry conditions. The rate for leaves stored in 0% humidity environment is 1.5× faster than those stored in 50% humidity.     

A capillary electrophoresis-tandem mass spectrometry methodology for the determination of non-protein amino acids in vegetable oils as novel markers for the detection of adulterations in olive oils

A new analytical methodology based on capillary electrophoresis-mass spectrometry (CE-MS(2)) is presented in this work, enabling the identification and determination of six non-protein amino acids (ornithine, β-alanine, GABA, alloisoleucine, citrulline and pyroglutamic acid) in vegetable oils. This methodology is based on a previous derivatization with butanol and subsequent separation using acidic conditions followed by on-line coupling to an ion trap analyzer for MS(2) detection established through an electrospray-coaxial sheath flow interface. The electrophoretic and interface parameters were optimized obtaining the separation of all compounds in less than 15 min and with resolutions higher than 5. The proposed method was validated by assessing its accuracy, precision (RSD<7% for corrected peak areas), LODs and LOQs (between 0.04-0.19 ng/g and 0.06-0.31 ng/g, respectively) and linearity range (R(2)>0.99), and it was used in order to identify the selected non-protein amino acids in soybean oils, sunflower oils, corn oils and extra virgin olive oils. MS(2) experiments performed the fingerprint fragmentation of these compounds allowing to corroborate ornithine and alloisoleucine in seed oils but not in olive oils. The method was applied to identify and quantify olive oil adulterations with soybean oil detecting in a single run the amino acids in mixtures up to 2% (w/w). The results showed a high potential in using these compounds as novel markers for the detection of adulterations of extra virgin olive oils with seed oils. Thus, the developed method could be considered a simple, rapid and reliable method for the quality evaluation of extra virgin olive oil permitting its authentication.     

Identification of137Cs in an individual microparticle by laser desorption/ionization ion trap mass spectrometer

The detection of radiocesium in microparticles was performed by using an ion trap mass spectrometer coupled with laser desorption and ionization. Pulsed laser desorbed particle and the resulted ions were analyzed by an ion trap mass analyzer. The presence of radiocesium, especially about¹³⁷Cs, in microparticles was verified by single as well as successive particle analysis. The detection limit was reached to ≈ag/particle level with a signal-to-background ratio of 4. The inhomogeneous distribution of particle size and the irregular shapes of particle limit the quantitative evaluation of¹³⁷Cs concentration in the microparticle. But this high sensitivity allows to monitor directly the radiocesium from small amounts of a microparticle sample.     

A New Method for Olive Oil Screening Using Multivariate Analysis of Proton NMR Spectra

A new NMR-based method for the discrimination of olive oils of any grade from seed oils and mixtures thereof was developed with the aim of allowing the verification of olive oil authenticity. Ten seed oils and seven monovarietal and blended extra virgin olive oils were utilized to develop a principal component analysis (PCA) based analysis of ¹H NMR spectra to rapidly and accurately determine the authenticity of olive oils. Another twenty-eight olive oils were utilized to test the principal component analysis (PCA) based analysis. Detection of seed oil adulteration levels as low as 5% v/v has been shown using simple one-dimensional proton spectra obtained using a 400 MHz NMR spectrometer equipped with a room temperature inverse probe. The combination of simple sample preparation, rapid sample analysis, novel processing parameters, and easily interpreted results, makes this method an easily accessible tool for olive oil fraud detection by substitution or dilution compared to other methods already published.     

Detection of volatile organic compounds by temperature-programmed desorption combined with mass spectrometry and Fourier transform infrared spectroscopy

A temperature-programmed desorption (TPD) device connected to a mass spectrometer was used to detect volatile organic compounds from air samples. The main aim was to develop an analytical method, by which both non-polar and polar organic components can be detected in the same run. In TPD, the adsorbed compounds are desorbed from the resin more slowly than in the conventional trapping techniques, such as purge-and-trap technique, in which the resin is flash-heated and the compounds are desorbed at the same time to a cryogenic trap or an analytical column. In TPD, the adsorbent resin acts also as an analytical column. In this way it is possible to obtain more rapid analysis, and also a more simple instrumentation, which can be used on-line and on-site. In this work, a new version of TPD device, which uses a resistor for heating and a Peltier element for rapid cooling, was designed and constructed. Various adsorbent resins were tested for their adsorption and desorption properties of both polar and non-polar compounds. When using a mixture of adsorbent resins, Tenax TA and HayeSep D, it was possible to analyze both polar, low-molecular weight compounds, such as methanol and ethanol, and non-polar volatile organic compounds, such as benzene and toluene, in the same run within 15 min including sampling. The same TPD principle was also tested using a Fourier transform infrared spectrometer as an analytical instrument, and the results showed that it was possible to obtain a separation of similar compounds, such as hexane and heptane, and still retaining the same sensitivity as the original on-line FTIR instrument.     

Direct olive oil authentication: detection of adulteration of olive oil with hazelnut oil by direct coupling of headspace and mass spectrometry, and multivariate regression techniques

Control of adulteration of olive oil, together with authentication and contamination, is one of the main aspects in the quality control of olive oil. Adulteration with hazelnut oil is one of the most difficult to detect due to the similar composition of hazelnut and olive oils; both virgin olive oil and olive oil are subjected to that kind of adulteration. The main objective of this work was to develop an analytical method able to detect adulteration of virgin olive oils and olive oils with hazelnut oil by means of its analysis by a headspace autosampler directly coupled to a mass spectrometer used as detector (ChemSensor). As no chromatographic separation of the individual components of the samples exists, a global signal of the sample is obtained and employed for its characterization by means of chemometric techniques. Four different crude hazelnut oils from Turkey were employed for the development of the method. Multivariate regression techniques (partial least squares and principal components analysis) were applied to generate adequate regression models. Good values were obtained in both techniques for the parameters employed (standard errors of prediction (SEP) and prediction residual error sum of squares (PRESS)) to evaluate its goodness. With the proposed method, minimum adulteration levels of 7 and 15% can be detected in refined and virgin olive oils, respectively. Once validated, the method was applied to the detection of such adulteration in commercial olive oil and virgin olive oil samples.     

Extending the Dynamic Range of the Ion Trap by Differential Mobility Filtration

A miniature, planar, differential ion mobility spectrometer (DMS) was interfaced to an LCQ classic ion trap to conduct selective ion filtration prior to mass analysis in order to extend the dynamic range of the trap. Space charge effects are known to limit the functional ion storage capacity of ion trap mass analyzers and this, in turn, can affect the quality of the mass spectral data generated. This problem is further exacerbated in the analysis of mixtures where the indiscriminate introduction of matrix ions results in premature trap saturation with non-targeted species, thereby reducing the number of parent ions that may be used to conduct MS/MS experiments for quantitation or other diagnostic studies. We show that conducting differential mobility-based separations prior to mass analysis allows the isolation of targeted analytes from electrosprayed mixtures preventing the indiscriminate introduction of matrix ions and premature trap saturation with analytically unrelated species. Coupling these two analytical techniques is shown to enhance the detection of a targeted drug metabolite from a biological matrix. In its capacity as a selective ion filter, the DMS can improve the analytical performance of analyzers such as quadrupole (3D or linear) and ion cyclotron resonance (FT-ICR) ion traps that depend on ion accumulation.

Multivariate analysis of HT/GC-(IT)MS chromatographic profiles of triacylglycerol for classification of olive oil varieties

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories (“extra-virgin olive oil”, “virgin olive oil”, “olive oil” and “olive-pomace” oil), and for the “extra-virgin” category, six different well-identified olive oil varieties (“hojiblanca”, “manzanilla”, “picual”, “cornicabra”, “arbequina” and “frantoio”) and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.     

Coupling Pervaporation-Gas Chromatography for Speciation of Volatile Forms of Selenium in Sediments

Abstract

A method for speciation of dimethylselenide (DMeSe), dimethyldiselenide (DMeDSe) and diethylselenide (DEtSe) in sediments based on a coupling between a pervaporation module, a preconcentration sorptive trap and a gas chromatograph-mass spectrometer is reported. The coupling is performed through a high pressure injection valve which allows two different operational modes: (a) analysis without preconcentration, in which analytes are directly driven from the pervaporation chamber to the injection port of the chromatograph, and (b) analysis with preconcentration in a trap, in which the analytes from the pervaporation chamber are first trapped on a Tenax minicolumn and then thermally desorbed and driven to the GC. This second approach improves the sensitivity compared to the direct coupling, reaching estimated absolute detection limits lower than 0.6 ng Se for each tested species. The method is applied to the determination of volatile organic selenium species in several sediments collected from different areas in the Southwest of Spain.     

Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry

Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths λ?=?213 and 266 nm and pulse energies between 50 and 300 μJ. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1–50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion–molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed.     

Dual buffer gases for ion manipulation in a miniature ion trap mass spectrometer with a discontinuous atmospheric pressure interface

The discontinuous atmospheric pressure interface (DAPI) has been developed to allow a direct transfer of ions from atmosphere into an ion trap mass spectrometer with minimum pumping capability. Air is introduced into the trap with ions and used as a buffer gas for the ion trap operation. In this study, a method of introducing helium as a second buffer gas was developed for a miniature mass spectrometer using a dual DAPI configuration. The buffer gas effects on the performance of a linear ion trap (LIT) with hyperbolic electrodes were characterized for ion isolation, fragmentation and a mass-selective instability scan. Significant improvement was obtained with helium for resolutions of mass analysis and ion isolation, while moderate advantage was gained with air for collision-induced dissociation. The buffer gas can be switched between air and helium for different steps within a single scan, which allows further optimization of the instrument performance for tandem mass spectrometry.     

Environmental analysis of organic compounds in water using solid phase micro extraction

Solid Phase Micro Extraction (SPME) involves exposing a fused silica fiber coated with stationary phase to a contaminated water sample. The organic analytes become partitioned between the stationary phase and the water and when equilibrium is reached the fiber is removed from the solution and the analytes are thermally desorbed in the injector of a gas chromatograph. The fiber is contained in a syringe to facilitate handling. Factors which affect linear range, limit of detection, and total analysis time are discussed with regard to the development of a method for analysis of volatile compounds in environmental water samples. The sensitivity of the method was determined by the thickness of the film of stationary phase; the equilibration time, however, increased with the film thickness, although it can be minimized by use of a cross-shaped stirrer bar. Increasing the thickness of stationary phase in the analytical column enables the cryofocusing temperature to be increased from ?40 to ?15°C. With an ion trap mass spectrometer, detection limits required by the US Environmental Protection Agency are met for all compounds except chloromethane and chloroethane. The method has been applied to environmental water samples.