Development of direct microwave desorption/gas chromatography mass spectrometry system for rapid analysis of volatile components in medicinal plants

A new direct microwave desorption–gas chromatography‐mass spectrometry method was developed for the analysis of the essential oils of medicinal plants. A homemade direct microwave desorption system was fabricated and used for the desorption of volatile components of medicinal herbs. The desorbed volatiles are transferred directly into the gas chromatography injector for analysis in a one‐step process. Approximately 0.3 g of the herb was needed for the desorption of samples in 60 s. In this study, more than 53 volatile compounds were identified and quantified for Echinophora platyloba DC as model herb sample. The results were found to be in good agreement with the conventional hydrodistillation extraction data. The described results show that direct microwave desorption is fast, simple, and easy to automate and requires only a small amount of sample. The results indicate that essential oil components valuable for varietal identification and characteristic of each variety analyzed when direct microwave desorption–gas chromatography‐mass spectrometry was used for analysis.     

Kinetic analysis of temperature-programmed surface reactions on porous catalysts

By means of model calculations it could be shown for an irreversible surface reaction of 1st order that the determination of the activation energy of the desorption of the reactant or, respectively, of the surface reaction is possible by application of the method of variation of the heating rate to the desorption curve of the reactant, according to circumstances whether the ratio of the activation energy of the surface reaction and of the desorption of the reactant is greater or smaller than one.The possibilities of the kinetic evaluation are applied to the isomerization of cyclopropane on a NaX-zeolite catalyst. The resulting heat of adsorption of cyclopropane and the activation energy of the reaction agree well with the values of literature obtained by isothermal measurements in a pulse reactor.

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Zusammenfassung Mit Modellrechnungen für eine irreversible Oberflächenreaktion 1. Ordnung konnte gezeigt werden, daß durch Anwendung der Methode der Variation der Heizgeschwindigkeit auf die Desorptionskurve des Ausgangsstoffes die näherungsweise Bestimmung der Aktivierungsenergie der Desorption des Ausgangsstoffes bzw. der Oberflächenreaktion möglich ist, je nachdem ob das Verhältnis der Aktivierungsenergien für die Oberflächenreaktion und der Desorption des Ausgangsstoffes größer oder kleiner als eins ist.Die Möglichkeiten der kinetischen Auswertung werden auf die isomerisierung von Cyclopropan an einem NaX-Zeoliten angewendet. Die erhaltene Adsorptionswärme für Cyclopropan und die Aktivierungsenergie für die Reaktion stimmen gut mit Literatur-werten von isothermen Messungen im Impulsreaktor überein.

     

Ganglioside analysis by thin-layer chromatography matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry

Metastable decomposition of ions generated in matrix-assisted laser desorption/ionization (MALDI) mass spectrometers complicates analysis of biological samples that have labile bonds. Recently, several academic laboratories and manufacturers of commercial instruments have designed instruments that introduce a cooling gas into the ion source during the MALDI event and have shown that the resulting vibrational cooling stabilizes these labile bonds. In this study, we compared stabilization and detection of desorbed gangliosides on a commercial orthogonal time-of-flight (oTOF) instrument with results we reported previously that had been obtained on a home-built Fourier transform mass spectrometer. Decoupling of the desorption/ionization from the detection steps resulted in an opportunity for desorbing thin-layer chromatography (TLC)-separated gangliosides directly from a TLC plate without compromising mass spectral accuracy and resolution of the ganglioside analysis, thus coupling TLC and oTOF mass spectrometry. The application of a declustering potential allowed control of the matrix cluster and matrix adduct formation, and, thus, enhanced the detection of the gangliosides.     

Direct surface analysis of fungal species by matrix-assisted laser desorption/ionization mass spectrometry

In this study various methods of sample preparation and matrices were investigated to determine optimum collection and analysis criteria for fungal analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Intact spores and/or hyphae of Aspergillus niger, Rhizopus oryzae, Trichoderma reesei and Phanerochaete chrysosporium were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The fungal samples were applied to the MALDI sample target as untreated, sonicated, or acid/heat treated samples, or blotted directly from the fungal culture with double-stick tape. Ferulic acid or sinapinic acid matrix solution was layered over the dried samples and analyzed by MALDI-MS. Statistical analysis showed that simply using double-stick tape to collect and transfer to a MALDI sample plate typically worked as well as the other preparation methods, and required the least sample handling.     

Gas chromatography/tandem mass spectrometry analysis of alkylresorcinols in red blood cells

Erythrocyte alkylresorcinols (5‐alkyl‐1,3‐dihydroxybenzenes) are potential biomarkers of wholegrain wheat and rye intake. However, their high‐throughput quantitative analysis by gas chromatography/mass spectrometry (GC/MS) is hindered by the time‐consuming sample preparation and, more importantly, by interfering compounds that still remain after sample cleanup. In the present work we describe a gas chromatography/tandem mass spectrometry (GC/MS/MS) method for the rapid and reliable quantification of alkylresorcinols in erythrocyte samples. The performance of the GC/MS/MS method is compared with that of GC/MS. The main characteristics of the method are: lower limits of detection: 2–10 µg/L standard solution; lower limits of quantification: 6–30 µg/L standard solution; linearity coefficients: 0.9611–0.9888; linear ranges: 2–20 µg/L in erythrocytes; and intra‐day precisions (n = 6): 4–13% at endogenous analyte levels in non‐spiked erythrocytes. Tandem mass spectrometry showed greatly improved selectivity over single‐stage mass spectrometry in the case of erythrocyte samples, eliminating all interferences detectable in single‐stage MS and enabling simple peak integration for quantification. Moreover, increased selectivity resulted in GC separation speeded up by a factor of two, allowing the duplicate analysis of over 40 samples per day. This GC/MS/MS method is suggested as an improved alternative to GC/MS for the quantification of alkylresorcinols in erythrocytes for assessing wholegrain wheat and rye intake. Copyright © 2008 John Wiley & Sons, Ltd.     

Gas phase ion/molecule reactions in laser desorption mass spectrometry

The desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process.     

Multiphoton ionization spectroscopy in surface analysis and laser desorption mass spectrometry

The application of resonance-enhanced multiphoton ionization (REMPI) spectroscopy for the ultrasensitive detection of molecules originating from laser desorption experiments performed on a variety of substrates is reviewed. Laser-induced desorption from surfaces is capable of producing intact gas-phase molecules, even from polar, non-volatile, high-molecular-weight and thermally labile substances. REMPI is a highly efficient and optically selective ionization method, which, coupled with laser desorption allows the direct chemical analysis of complex mixtures, without the need for previous sample purification and separation steps. The use of REMPI spectroscopy is discussed in two contexts: (1) for the direct chemical analysis of complex mixtures, e.g., environmental samples, by laser desorption/laser postionization mass spectrometry and (2) for measurements of internal state distribution of molecules laser-desorbed from sub-monolayers surface films to gain insight into the laser desorption mechanism.Presented at the 13th International Symposium on Microchemical Techniques (ISM), held in Montreux, Switzerland, May 16–20,1994     

Gas chromatography electrospray ionization mass spectrometry analysis of trimethylsilyl derivatives

A method based on the analysis of trimethylsilyl (TMS) derivatives by capillary gas chromatography electrospray ionization mass spectrometry (GC–ESI/MS) was proposed. To improve separation, analytes were derivatized to their TMS derivative. During ESI analysis, TMS derivatives may hydrolyze back to their polar native form and are thus suitable for ESI analysis. Several types of analytes were studied to investigate the potential of the approach. Not all TMS derivatives hydrolyzed back to their native form as anticipated. Incomplete hydrolysis was observed for TMS‐organic acids and TMS‐nonchlorinated phenols. For TMS‐chlorophenols, the observation of only the [M ? H]^? ion suggested that these phenols were hydrolyzed back to their native form. For TMS‐beta agonists, the hydrolysis rate was low; therefore, the hydrolysis product was not detected. Both TMS‐chlorophenols and TMS‐beta agonists provide a sensitivity in the range of low parts per billion (0.25–5 ng/ml and 0.5–10 ng/ml respectively). Copyright © 2016 John Wiley & Sons, Ltd.     

Positive secondary-ion mass spectra and thin-layer chromatography/mass spectrometry of phenothiazine drugs

The positive secondary-ion mass spectra of phenothiazine drugs contain abundant protonated molecules and structurally informative fragment ions that are characteristic of the N-substituent. Because the secondary-ion current is carried by a few characteristic ions, selected-ion monitoring is used with chromatographic separation for the determination of these drugs in mixtures. Drugs are extracted in situ from thin-layer chromatograms, and the secondary-ion mass spectra are obtained without destruction of the chromatograva. The spectra are dependent upon the solvent used and not the nature of the underlying chromatographic matrix. Spatially-resolved selected-ion monitoring of the protonated molecule provides the x-y spatial profiles of the sample in the chromatogram. Extended irradiation leads to a beam-induced tailing that alters the profile.     

Gas chromatography/mass spectrometry analysis of the cuticular hydrocarbons from parasitic wasps of the genus Muscidifurax

Parasitic Hymenoptera can be difficult to identify by conventional taxonomic techniques. Examination of the cuticular hydrocarbons (CHCs) provides a basis for chemotaxonomic differentiation, which may lead to the discovery of pheromones, and can be a means of examining colonies for species cross-contamination. The parasitic wasps examined were Muscidifurax raptor, M. zaraptor, M. uniraptor, and the gregarious form of M. raptorellus. Species within the genus Muscidifurax, as well as the sex, can clearly be differentiated by examining the gas chromatograms of the CHCs. Identification of the alkanes by mass spectrometry shows uncommon dimethylalkanes and trimethylalkanes for members of the genus. The methyl branched cuticular hydrocarbons of these insects are rare compared to those found on insects reported in the literature, but are present in significant amounts on these insects. Additionally, sexual dimorphism is observed in long chain alkanes (C₂₁–C₃₉) present on male and female cuticular surfaces for these species. Females tend to have cuticular hydrocarbons with methyl branches located externally on the carbon backbone chain for dimethyl-, trimethyl-, and tetramethylalkanes, whereas males tend to have dimethyl- and trimethylalkanes located internally on the hydrocarbon backbone chains. Mass spectra of novel and rare methyl branched compounds identified on these parasitoids are presented.     

Gas chromatography/mass spectrometry analysis of triacetone triperoxide (TATP) degradation products

Interest in the analysis and detection of triacetone triperoxide (TATP) and other organic peroxides has increased in recent years. Also of interest is the degradation and decomposition of the peroxides, not only to gain more detailed chemical information from organic peroxide samples, but also to investigate possible new procedures or mechanisms for chemical neutralisation. This report investigates the chemical degradation products of TATP after it has been treated with different acids within a sealed system over a period of 14 days. The samples were collected and analysed by solid-phase microextraction (SPME) and direct liquid injection gas chromatography/mass spectrometry (GC/MS). The results of the experiments indicate that the rate of chemical degradation of TATP and the products formed are dependent on the type of acid. The observed differences enables the type of acid used in the degradation process to be determined, provide complementary information to identify the presence of TATP, and possibly indicate new pathways that may be used to chemically neutralise TATP.     

Analysis of hair components by nanoparticle-assisted laser desorption/ionization mass spectrometry imaging

Using a vertical hair-slice section, we compared the components of normal and damaged hair regions using two ionization methods, matrix-assisted laser desorption/ionization and nanoparticle-assisted laser desorption/ionization (Nano-PALDI) mass spectrometry. Nano-PALDI is useful for small-molecule and high spatial resolution (5 μm) analyses due to the lack of noise. Thus, clear images were obtained from thin hair samples. In Nano-PALDI mass spectrometry imaging, cystine and 18-methyleicosanoic acid as endogenous hair components localized in the cuticle and cortex and cuticle of normal hair, respectively. In contrast, both components were absent in damaged hair.     

Direct analysis of polychlorinated biphenyls in heavily contaminated soils by thermal desorption/gas chromatography/mass spectrometry

A robust analytical method is presented for the direct determination of polychlorinated biphenyls in soil samples by thermal desorption/gas chromatography/mass spectrometry. The method is simple to perform (thermal desorption and analysis are performed in-line employing a limited amount of sample, 2?mg) and eliminates the need for any solvent and time-consuming extraction. The analytical procedure was optimized using a soil sample spiked with Aroclor 1254 and Aroclor 1260 and validated with a certified industrial soil sample for which the concentration of thirteen PCB congeners are known. Limits of detection were sensitive to matrix effects and varied substantially among analytes. The matrix effect resulted in a reduction of the limits of detection by 1.5–10 times. However, it was found that the matrix effect is not due to ion suppression but to the increase of the noise of selected ion monitoring (SIM) traces, indicating that no limitation exists with using a single surrogate standard. By employing a 13C-labelled PCB internal standard, limits of detection in the range of 0.8 to 10?µg?g^?1 of soil were obtained. The obtained experimental results demonstrated that the proposed analytical method can be conveniently applied for screening a large number of heavily contaminated soil samples thus avoiding the employment of harmful solvents and time-consuming extraction procedures.     

A method to calculate density distribution of adsorption centers from temperature-programmed desorption spectra

A new method to calculate the function of density distribution of adsorption centers according to the activation energies of desorption by using temperature-programmed desorption curves is suggested. The application of this method is exemplified by toluene desorption from ZSM-5 zeolite.

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Oligonucleotide analysis by nanoparticle-assisted laser desorption/ionization mass spectrometry

We analyzed oligonucleotides by nanoparticle-assisted laser desorption/ionization (nano-PALDI) mass spectrometry (MS). To this end, we prepared several kinds of nanoparticles (Cr-, Fe-, Mn-, Co-based) and optimized the nano-PALDI MS method to analyze the oligonucleotides. Iron oxide nanoparticles with diammonium hydrogen citrate were found to serve as an effective ionization-assisting reagent in MS. The mass spectra showed both [M - H](-) and [M + xMe(2+)- H](-) (Me: transition metal) peaks. The number of metal-adducted ion signals depended on the length of the oligonucleotide. This phenomenon was only observed using bivalent metal core nanoparticles, not with any other valency metal core nanoparticles. Our pilot study demonstrated that iron oxide nanoparticles could easily ionize samples such as chemical drugs and peptides as well as oligonucleotides without the aid of an oligonucleotide-specific chemical matrix (e.g., 3-hydroxypicolinic acid) used in conventional MS methods. These results suggested that iron-based nanoparticles may serve as the assisting material of ionization for genes and other biomolecules.     

Small-molecule analysis by surface-assisted laser desorption/ionization mass spectrometry

In order to meet the challenges facing modern chemistry, biology, and medicine, methods are required capable of performing rapid and reliable analysis of both individual compounds and complex mixtures at the molecular level. Matrix-assisted laser de-sorption/ionization mass spectrometry meets these requirements; however, some limitations complicate its application for the analysis of small molecules. Recently, small-molecule analysis has greatly progressed owing to development of surface-assisted laser desorption/ionization mass spectrometry involving approaches which combine the unique properties of nanostructured surface chemistry and morphology. This review examines such approaches and their specific application in small-molecule mass analysis.     

Rapid analysis of abused drugs using nanostructured silicon surface assisted laser desorption/ionization mass spectrometry

This study developed a rapid, sensitive, and matrix-free method for the determination of amphetamine (AMP), methamphetamine (MA), codeine (COD), morphine (MOR), and ketamine (KET) using nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (nSi-MS). The nanostructured silicon (nSi) chip used in this study was created by employing the metal-assisted etching process. Drug standard tests were applied to the nSi chip platform to evaluate the nSi-MS performance, including detection sensitivity, limit of detection, linearity, and repeatability. Real urine samples obtained from drug addict detainees were directly applied to the nSi chip for drug analysis. By observing the nSi-MS spectra, the target drug peaks can be identified; and an antibody pull-down assay was performed to confirm the specificity of the detected targets. nSi-MS drug quantification was assayed, yielding comparable results with those from using the GC-MS approach. The advantages of applying nSi-MS to analyze AMP, MA, COD, MOR, and KET in the urine of addicts are simple, extremely small urine volumes (～10 μL), and a fast analysis procedure (<15 minutes).     

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry of polychlorinated biphenyls

A sample mixture of polychlorinated biphenyls (PCBs) was measured by gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) using four types of laser sources. When a fourth harmonic emission (266 nm) of a picosecond Nd:YAG laser (1064 nm) was utilized, highly chlorinated PCBs larger than hepta-CBs were not observed. A fifth harmonic emission (213 nm) of the picosecond Nd:YAG laser allowed the measurement of PCBs from di-CBs to octa-CBs, and the limit of detection (LOD) was several pg for each component of PCBs. The LOD for the total amount of PCBs, which was calculated using the protocol provided by the Ministry of the Environment, Japan, was 1000 pg. The signal intensity of the congeners with chlorine atoms at the ortho positions (non-coplanar PCBs) was enhanced by using the fifth harmonic emission. When the fourth harmonic emission remaining after fifth harmonic generation was simultaneously used, the LOD for total PCBs was improved to 667 pg. The PCB sample was also measured using a third harmonic emission (267 nm) of a femtosecond Ti:sapphire laser (800 nm), providing an LOD of 677 pg. Thus, the two-color beam (266/213 nm) of a picosecond Nd:YAG laser had a comparable, or even slightly superior, performance to the more expensive femtosecond Ti:sapphire laser.