Rapid-scanning Quadrupole Research Articles

Chemical characterisation of Piper amalago (Piperaceae) essential oil by comprehensive two-dimensional gas chromatography coupled with rapid-scanning quadrupole mass spectrometry (GC×GC/qMS) and their antilithiasic activity and acute toxicity.

Piper amalago has a distribution from Mexico to Brazil; their aerial parts have been used in folk medicine to treat diuretic and kidney diseases. The purpose of this study was to obtain a deeper understanding of the chemical composition of essential oils (EOs) extracted from both the leaves and stems of P. amalago, compare them, and evaluate their antilithiasic activity and acute toxicity. Extraction was performed by hydrodistillation, whereas chemical characterisation by two-dimensional gas chromatography coupled with rapid-scanning quadrupole mass spectrometry (GC×GC/qMS). The antilithiasic activity was evaluated by the effect of the EOs on calcium oxalate crystallisation in vitro. The turbidity index and the number of crystals formed were determined and used as an estimative of the activity. In the acute toxicity assay, the effects of a single oral dose of the EOs in Wistar rats were determined. General behaviour, adverse effects, and mortality were determined. A total of 322 compounds were identified in the EOs. The sesquiterpenes displayed the highest contribution in leaves EOs among which included bicyclogermacrene and δ-cadinene. Sesquiterpenes and oxygenated sesquiterpenes displayed the highest contribution in EOs from stems, among which included bicyclogermacrene and α-cadinol. The EOs demonstrated an excellent action on the crystals growth inhibition, and the oral dose tested did not induce significant changes in the parameters for acute toxicity. The oils have a high chemical complexity, and there are differences between their compositions, which could explain the observed differences in antilithiasic activity. The findings support the use of this plant in folk medicine to treat kidney diseases.

James Douglas Morrison 1924–2013

Jim Morrison was born in Scotland in 1924 and completed his PhD studies in X-ray crystallography at the University of Glasgow before taking up a position with CSIRO in Melbourne in 1949. There he became expert in the construction and operation of mass spectrometers, mainly for the study of ion physics. In 1967, he became the Foundation Professor Physical Chemistry at the new La Trobe University in Melbourne where he continued his work in mass spectrometry but was also involved in university leadership that included a period as head of a residential college.Together with his students, he developed the use of compact, rapid-scanning quadrupole mass spectrometers, linking them in series to allow secondary studies (including photochemistry) of particular ions, but also taking advantage of the speed of the quadrupoles to link them to gas chromatographs for the study of mixtures of organic compounds. In all of this he was a pioneer in the use of computers with spectroscopic instruments. Internationally he was a recognized expert, speaking at conferences, establishing collaborations, and spending periods of leave at the University of Utah. After his retirement in 1990 he spent a long period as Emeritus Professor before his death in 2013.

Valorization of coffee silverskin industrial waste by pyrolysis: From optimization of bio-oil production to chemical characterization by GC × GC/qMS

Coffee bean tegument (silverskin) is a by-product derived from the coffee roasting process. This residue has been discarded, which constitutes a serious environmental problem. The depletion of oil reserves and environmental issues promoted by the combustion of fossil fuels has generated interest in the use of biomass to obtain fuel and chemicals products. The liquid product obtained by biomass pyrolysis is commonly called bio-oil. Bio-oil is a complex mixture of compounds, and its detailed chemical characterization is necessary to prospect its potential uses. Therefore, this study optimized the final temperature of pyrolysis and N2 flow rate parameters for the pyrolysis of silverskin in a fixed bed reactor, by using a central composite design and response surface. The bio-oil chemical composition was evaluated by comprehensive two-dimensional gas chromatography coupled to rapid-scanning quadrupole mass spectrometry (GC × GC/qMS), combined with the use of standards and linear temperature-programmed retention indices (LTPRI). The optimal values ​​calculated were 560 °C for the final pyrolysis temperature and 49 mL min−1 for the N2 flow rate. The organic phase yield was 15.2% under these conditions. At the optimal conditions, 228 compounds were identified (90.1% of the sample chromatographic volume) in the organic phase. The major chemical class, in terms of volume percentage, were the phenols (26.70%), followed by nitrogen compounds (18.51%). In addition, it is worth mentioning the high representability of the saturated hydrocarbons (8.28%), unsaturated aliphatic (6.69%), and aromatics (7.77%), which together account for 22.74% of the sample chromatographic volume. These results showed that the silverskin bio-oil may have the potential use as a source of chemical inputs.

Selective Identification of Organic Iodine Compounds Using Liquid Chromatography–High Resolution Mass Spectrometry

A method to selectively and sensitively detect organic iodine compounds and identify their structures has been developed using liquid chromatography-high resolution mass spectrometry (LC-HRMS). Using extracted ion chromatograms of product ions (iodine ion) collected on a rapid scanning quadrupole orbitrap mass spectrometer, the retention times of the unknown organic iodine compounds were determined, and the structural information were acquired according to the MS/MS experiments and the matching with reference standards. We have demonstrated the application of this method by identifying unknown organic iodine compounds in seaweed. A total of 28 possible organic iodine peaks were discovered, among them, the accurate mass and element composition of the corresponding precursor ions were identified for 12 peaks, and molecular structures were confirmed for 4 peaks, which were 3-iodo-L-tyrosine, 3,5-diiodo-L-tyrosine, 4-iodophenol, and 2-iodobenzoic acid. This method is expected to lead to the future discovery of new organic iodine compounds via LC-HRMS in different environmental samples, which is crucial for understanding the iodine biogeochemical cycling.

Comprehensive two-dimensional gas chromatography with mass spectrometry applied to the analysis of volatiles in artichoke (Cynara scolymus L.) leaves

Artichoke (Cynara scolymus L.) is well known due to its medicinal properties and, as a result, a large number of studies have been conducted to determine the chemical constituents produced by the plant. However, investigations were mainly focused on the non-volatile compounds, while the volatile constituents remained largely neglected. This study was aimed at obtaining a deeper understanding of the volatile composition of artichoke. For this propose, comprehensive two-dimensional gas chromatography coupled to a rapid scanning quadrupole mass spectrometer (GC×GC/qMS) and retention indices were used to improve the chemical characterization of volatiles from leaves. A total of 130 compounds were found, 109 of which are reported for the first time in C. scolymus L., including oxygenated monoterpenes, sesquiterpenes, oxygenated sesquiterpenes, norisoprenoids, lactones, alcohols, ketones and aldehydes. The major compounds were 1-octen-3-one (3.85%), (E)-2-hexenal (3.75%), benzene acetaldehyde (2.90%), 2,2-dimethyl-4-pentenal (2.81%), β-ionone (1.94%), furfural (1.65%), (E)-β-damescenone (1.59%), α-methyl-γ-butirolactone (1.53%), benzaldehyde (1.47%) and dihydroactinidiolide (1.44%). The comprehensive GC×GC/qMS approach enabled a greater number of analytes to be identified, approximately four times higher than that obtained for GC/qMS. Additionally, the results imply that artichoke leaves are a potential source of volatile bioactive compounds.

Gas velocity at the point of re-injection: An additional parameter in comprehensive two-dimensional gas chromatography optimization

The present research is focused on the introduction of a new optimization parameter in the field of comprehensive 2D GC (GC×GC), herein defined as “gas velocity at the point of re-injection”. GC×GC experiments were performed using a loop-type cryogenic modulator and a rapid-scanning quadrupole mass spectrometer, as detection system. All experiments were performed using a 30m×0.25mm ID apolar primary column, and a 1m×0.10mm ID medium-polarity secondary one. With regards to the modulator loops, three types of uncoated columns were used, namely with a 0.25, 0.18, and 0.10mm ID. It was found that under the same second-dimension analytical conditions (modulation, oven temperature, gas velocity) the quality of the GC×GC separation was dependent on the gas velocity at the moment of re-injection. For a loop-type modulator, the re-injection point is located at the downstream cooling/heating point of the delay loop. It was found that the GC×GC performance gradually improved when the ID of the modulator loop decreased (and the re-injection gas velocity increased), and reached its best when the 0.10mm ID uncoated column was used. GC×GC experiments were performed on a C14 n-alkane (to evaluate the efficiency of band re-injection, in terms of peak widths) and on an essential oil sample (to evaluate peak widths, resolution and the overall separation performance). The results herein reported are valid for practically any type of cryogenic modulator.

Elucidation of the volatile composition of Marsala wines by using comprehensive two-dimensional gas chromatography

The present contribution describes a research work focused on the elucidation of the composition of the headspace of Marsala wine. Four sample-types, of different ageing (“fine”, “superiore secco”, “superiore riserva”, “vergine”) were subjected to headspace solid-phase microextraction-comprehensive 2D GC analysis. At the outlet of the second GC dimension, the eluting analytes were split between a flame ionisation detector (for relative quantification purposes) and a rapid-scanning quadrupole mass spectrometer (for compound identification). Over 500 peaks were detected in each application, with a total of 128 compounds tentatively-identified considering the four sample types (mainly esters, alcohols, ketones, and aldehydes). The results attained open a door on the highly complex nature of the Marsala headspace; furthermore, they also demonstrated that the use of one-dimensional GC technologies, for the untargeted analysis of complex aroma profiles (e.g., dessert wines), is often too much of an analytical challenge.

Use of Narrow Mass-Window, High-Resolution Extracted Product Ion Chromatograms for the Sensitive and Selective Identification of Protein Modifications

Protein modifications, including oxidative modifications, glycosylations, and oxidized lipid-protein adducts, are becoming increasingly important as biomarkers and in understanding disease etiology. There has been a great deal of interest in mapping these on Apo B100 from low density lipoprotein (LDL). We have used extracted ion chromatograms of product ions generated using a very narrow mass window from high-resolution tandem mass spectrometric data collected on a rapid scanning quadrupole time-of-flight (QTOF) instrument, to selectively and sensitively detect modified peptides and identify the site and nature of a number of protein modifications in parallel. We have demonstrated the utility of this method by characterizing for the first time oxidized phospholipid adducts to LDL and human serum albumin and for the detection of glycosylation and kynurenin formation from the oxidation of tryptophan residues in LDL.

Evaluation of comprehensive two-dimensional gas chromatography coupled to rapid scanning quadrupole mass spectrometry for quantitative analysis

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful technique that provides excellent separation and identification of analytes in highly complex samples with considerable increase in GC peak capacities. However, since second dimension analyses are very fast, detectors with a rapid acquisition rate are required. Over the last years, quite a number of studies have discussed the potential and limitations of the combination GC×GC with a variety of quadrupole mass spectrometers. The present research focuses on the evaluation of qMS effectiveness at a 10,000-amu/s scan speed and 20-Hz scan frequency for the identification (full scan mode acquisition-TIC) and quantification (extracted ion chromatogram) of target pesticide residues in tomato samples. The following MS parameters have been evaluated: number of data points per peak, mass spectrum quality, peak skewing, and sensitivity. The validated proposed GC×GC/qMS method presented satisfactory results in terms of repeatability (coefficient of variation lower than 15%), accuracy (84–117%), and linearity (ranging from 25 to 500ng/g), while significant enhancement in sensitivity was observed (a factor of around 10) under scan conditions.

Performance evaluation of a rapid‐scanning quadrupole mass spectrometer in the comprehensive two‐dimensional gas chromatography analysis of pesticides in water

The performance of a novel rapid-scanning (20,000 amu/s) quadrupole mass spectrometer (qMS) has been evaluated in the comprehensive 2-D gas chromatography (GC×GC) analysis of pesticides contained in water. Analyte extraction was performed by using direct solid-phase microextraction (SPME). The MS system was operated using a rather wide m/z 50-450 mass range and a 33 Hz spectral production rate, a frequency which was found sufficient for reliable quantification. The qMS performance was evaluated considering: (i) number of data points per peak, (ii) mass spectral quality, (iii) extent of peak skewing, and (iv) consistency of retention times. Seven-point calibration curves (external calibration) were constructed for 28 pesticides over the limit of quantification range of 100 μg/L (1, 5, 10, 25, 50, and 100 μg/L). The solid-phase microextraction-GC×GC-qMS method was validated by calculating limits of detection and quantification, intraday peak area precision, accuracy, and intraday retention-time precision. A series of tap water samples were subjected to analysis, fortunately giving negative results.

Evaluation of a Rapid-Scanning Quadrupole Mass Spectrometer in an Apolar × Ionic-Liquid Comprehensive Two-Dimensional Gas Chromatography System

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful technique which can enable a great increase in GC peak capacities. However, since secondary-column separations are very rapid, detectors with a fast acquisition rate are mandatory. Such a requirement has certainly limited the use of the quadrupole mass spectrometer in the GC×GC field. The present research is focused on the evaluation of a novel rapid-scanning quadrupole mass spectrometry (qMS) detector, characterized by a 20,000 amu/s scan speed and a 50 Hz scan frequency, using a 290 amu mass range (40-330 m/z). The performance of the MS system was assessed by analyzing mixtures of 24 allergens, as well as a perfume sample, through GC×GC/qMS. The MS parameters evaluated at different acquisition rates (50, 33, and 25 Hz), as well as in the (simultaneous) scan/selected ion monitoring (SIM) mode, were the number of data points per peak, mass spectrum quality, peak skewing, and sensitivity. Two GC×GC/qMS methods, using the 50 Hz acquisition rate and the scan/SIM mode, were validated. Both methods provided similar results in terms of repeatability, accuracy, and linearity, while a great increase in sensitivity was observed (ca. a factor of 10) under scan/SIM conditions. The validated method proved to be suitable for the analysis of perfume allergens, according to the requirements of Directive 2003/15/EC.

Analysis of Fresh and Aged Tea Tree Essential Oils By Using GCxGC-qMS

The present research is focused on the qualitative elucidation of the chemical profile of fresh tea tree essential oil and an oxidized, aged (circa 1984) counterpart by using the most powerful analytical tool available today for volatile analysis, namely comprehensive two-dimensional gas chromatography (GCxGC) in combination with a mass spectrometer (MS). The rapid-scanning quadrupole (q) MS system employed generated a sufficient number of spectra/s (20/s) for the reliable identification of the high-speed GCxGC peaks. The total ion current GCxGC-qMS chromatogram of the fresh product was characterized by the presence of approximately 130 unknowns. Among these, 61 peaks were assigned with spectral similarities > or = 90%, while 28 components presented MS library matches in the 80-89% range. With regards to the oxidized essential oil, about 180 volatiles were visible on the 2D plane with 63 of these characterized by library "hits" > or = 90% and 45 presenting similarities within the 80-89% range. The use of the enhanced-resolution 3D methodology enabled the full separation of the samples analyzed and, hence, a clear distinction between the essential oils.

Characterization of the yerba mate (Ilex paraguariensis) volatile fraction using solid‐phase microextraction‐comprehensive 2‐D GC‐MS

The present research is focused on the use of a solid-phase microextraction-comprehensive 2-D GC methodology, in the analysis of the volatile fraction of yerba mate. Yerba mate is used for the generation of a tea-like beverage, widely consumed in South America. A rapid-scanning quadrupole mass spectrometer (qMS), employed as a detection system and operated at a 25 Hz scanning frequency, supplied high-quality mass spectra. The effectiveness of the 3-D comprehensive 2-D GC-qMS experiment was compared to that of GC-qMS analysis on the same sample. Peak identification, in both applications, was achieved through MS library matching, with the support of linear retention index data. Apart from a great increase in the number of analytes separated (approx. by a factor of 5) and identified (approx. by a factor of 3.5), the comprehensive 2-D GC-qMS approach enabled the determination of a high number of hazardous contaminants (aliphatic hydrocarbons, polycyclic aromatic hydrocarbons, and plasticizers), barely visible in the GC-qMS analysis.

Micro-bore Column Fast Gas Chromatography-Mass Spectrometry in Essential Oil Analysis

The present research is focused on the use of micro-bore column fast gas chromatography in combination with rapid-scanning quadrupole mass spectrometry for mediumly-complex essential oil analysis. A basil essential oil sample was initially subjected to conventional GC-MS (analysis time: 25 min) under optimum analytical conditions. Peak identification was carried by using a dual-filtered MS library search procedure: the first filter deleted “hits” with a less than 90% spectral similarity, while the second filter eliminated matches with a linear retention index (LRI) outside a pre-defined LRI window. The same essential oil sample was analyzed under optimized fast GC-MS conditions by using a micro-bore column, with the same aforementioned MS library search process (analysis time: 5.3 min). Resolution was altogether similar in both applications, with the same number of compounds reliably-identified, namely fifty-nine. The experiment demonstrated the usefulness of the rapid GC approach in this type of experiment.

Identification, quantitation and method validation for the analysis of suspected allergens in fragrances by comprehensive two-dimensional gas chromatography coupled with quadrupole mass spectrometry and with flame ionization detection

The first part of this study first aims at validating a method to identify suspected allergens limited by EU regulations in fragrances by comprehensive two-dimensional gas chromatography (GC × GC) coupled with rapid scanning quadrupole MS (GC × GC-qMS). The effectiveness of the quadrupole MS operating at different scanning speed (1000 and 11,111 amu/s) was evaluated in identifying (full scan mode acquisition – TIC) and in quantifying (single ion monitoring – SIM) the target analytes in complex mixtures. In full scan acquisition mode the mass range was reduced to 40–240 amu to increase the scan acquisition rate while in SIM mode the influence of different dwell-times (40, 10 and 5 ms) was tested. The number of scans for each single modulated chromatographic GC × GC peak and the total number of scans for the 2D peak, together with half height peak width (referred to apex) of each allergen in the standard mixture in both TIC and SIM modes were determined. Moreover, the match quality of the spectra obtained by GC/MS at 1000 and 11,111 amu/s and by GC × GC–MS at 11,111 amu/s were compared and the occurrence of spectral skewing verified. In the second part of this work quantitative methods by GC × GC-SIM/qMS and GC × GC-FID were validated on the basis of Eurachem/CITAC protocols through which the following performance parameters were determined: confirmation of identity, selectivity and specificity, limit of detection (LOD), limit of quantitation (LOQ), linearity (working and linear range), precision and accuracy and uncertainty. Suspected allergens were spiked in a concentration range between 2 and 25 ppm (μg/mL) on a Test fragrance taken as a reference, while 1,4 dibromo-benzene and 4,4′-dibromodiphenyl were used as internal standards.

Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC × GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90 Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC × GC–ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10–150 fg injected) and CDD/Fs (10–700 fg injected) in the selected ion monitoring mode.

Comprehensive two-dimensional gas chromatography in combination with rapid scanning quadrupole mass spectrometry in perfume analysis

Single column gas chromatography (GC) in combination with a flame ionization detector (FID) and/or a mass spectrometer is routinely employed in the determination of perfume profiles. The latter are to be considered medium to highly complex matrices and, as such, can only be partially separated even on long capillaries. Inevitably, several monodimensional peaks are the result of two or more overlapping components, often hindering reliable identification and quantitation. The present investigation is based on the use of a comprehensive GC (GC × GC) method, in vacuum outlet conditions, for the near to complete resolution of a complex perfume sample. A rapid scanning quadrupole mass spectrometry (qMS) system, employed for the assignment of GC × GC peaks, supplied high quality mass spectra. The validity of the three-dimensional (3D) GC × GC–qMS application was measured and compared to that of GC–qMS analysis on the same matrix. Peak identification, in all applications, was achieved through MS spectra library matching and the interactive use of linear retention indices (LRI).

Comprehensive two-dimensional gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer: principles and applications

The principles, practicability and potential of comprehensive two-dimensional (2D) gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer (GC × GC–qMS) for the analysis of complex flavour mixtures in food, allergens in fragrances and polychlorinated biphenyls (PCBs) were studied. With a scan speed of 10,000 amu/s, monitoring over a mass range of up to 200 atomic mass unit (amu) can be achieved at an acquisition frequency of 33 Hz. Extending this mass range and/or increasing the data acquisition frequency results in a loss of spectral quality. Optimal parameter settings allow, next to unambiguous identification/confirmation of target compounds on the basis of high-quality mass spectra, fully satisfactory quantification (three to four modulations per peak) with linear calibration plots and detection limits in the low-pg level. The potential of time-scheduled data acquisition to increase the effective mass range within one GC × GC run was also explored. The analyses, with baseline separation of the flavours, allergens and PCB target compounds, took less than 30 min.

Comprehensive two-dimensional gas chromatography-mass spectrometry analysis of Pelargonium graveolens essential oil using rapid scanning quadrupole mass spectrometry

The analysis of Pelargonium graveolens essential oil is reported using comprehensive two-dimensional gas chromatography with quadrupole mass spectrometric detection (GC×GC-qMS). A spectral acquisition rate of 20 Hz was achieved by using a reduced mass scan range of 188 u. 65 components were identified within the two-dimensional separation space based upon retention index and mass spectral matching with literature data. Very high quality mass spectra were obtained, which facilitated accurate library matching, without the need for background correction. High efficiency in the short, fast-GC second dimension column was achieved by applying the principles of vacuum-GC. It is demonstrated that facile determination of the key citronellol : geraniol ratio and the amount of 10-epi-γ-eudesmol in geranium essential oils using GC×GC will be possible. The method should be generally suited to the analysis of similar essential oil samples.