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1.
A system is presented that demonstrates the principle of on-line and on-chip post-column derivatisation reactions in micro-high-performance liquid chromatography (micro-HPLC) hyphenated to electrospray time-of-flight mass spectrometry (ESI-TOFMS). In this micro-HPLC-chip-MS set-up, the analytes are separated using gradient micro-HPLC and subsequently derivatised on-chip and detected. One of the major limitations of MS detection is its dependency on the degree of ionisation, which is widely variable and compound-specific. Optimising and controlling the degree of ionisation in a simple manner would allow MS detection to be truly generic. One way of achieving this is by pre-ionisation of analytes using simple derivatisation procedures that are both rapid and quantitative. Performing this in situ on the system described here overcomes issues of sample handling and efficiency losses when time-consuming "bench chemistry" is necessary prior to analysis. The power of the system is demonstrated by the separation of primary and secondary amines, which are subsequently derivatised with a positively charged phosphonium complex and detected in an enhanced manner. Typically, molecular cations (M(+)) are detected showing that the ionisation process is dominated by the phosphonium species, leading to more constant ionisation for a variety of compounds. In addition, stable isotopically labelled ((12)C/(13)C)-phosphonium reagent is used for the reactions, allowing for inherent signal/noise (S/N) improvement and automated data processing using cluster analysis. A similar reaction scheme is used for the derivatisation of ketones and aldehydes, also demonstrating dramatic increases in sensitivity, especially with increasing temperature. Minimal loss in chromatographic fidelity in terms of retention times is observed by the introduction of the micromixer chip into the system. Optimal flow rates in micro-HPLC and ESI-MS are compatible with flow rates for the chip as well as a multitude of in-line optical detectors including UV and fluorescence. In addition, the micromixer chip can be positioned pre-column if preferred. The system is robust, easily fully automated and applicable to a wide variety of reactions. The system has a major advantage in its simple robust connection to the "normal scale" outside world.  相似文献   

2.
The on-line application of mass spectrometry (m.s.) includes analysis of the fermentor gas phase by using a capillary inlet and analysis of the liquid phase by using membrane probes. Gas-phase measurements with a capillary inlet are fast and accurate for all gases of interest (O2, N2, CO2, H2, etc.). Liquid-phase measurements are done with steam-sterilizable membrane inlet probes, permitting direct analysis of dissolved gases and various volatiles. With these two inlets, automatic measurement of both the liquid and gas phases is possible when a microcomputer is used. This was applied to the batch fermentation of Bacillus subtilis. A further application of the membrane probe is evaluation of fermentation process state; this involves measuring the spectra of all detectable volatiles and correlating this information with the process state (e.g., product formation). Sufficient characteristic volatiles were found in various industrial fermentation samples. When mass spectra are treated by factor analysis, useful correlations are found with the product concentrations measured off-line. Calibration depending on the process conditions is necessary for this method, but it is widely applicable and allows automatic monitoring.  相似文献   

3.
Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is one of the most prominent analytical techniques owing to its inherent selectivity and sensitivity. In LC/ESI-MS/MS, chemical derivatization is often used to enhance the detection sensitivity. Derivatization improves the chromatographic separation, and enhances the mass spectrometric ionization efficiency and MS/MS detectability. In this review, an overview of the derivatization reagents which have been applied to LC/ESI-MS/MS is presented, focusing on the applications to low molecular weight compounds.  相似文献   

4.
This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.  相似文献   

5.
Heparin and low molecular mass heparin (LMMH) consists of complex mixtures of sulphated linear oligosaccharides that are difficult to analyse. An on-line size exclusion chromatographic/electrospray ionization (ESI) mass spectrometric method that allows the determination of more than 60 components in an LMMH preparation is presented. The experimental setup includes on-line cation exchange in order to prevent massive adducting in the ESI interface.  相似文献   

6.
The analysis of intact neutral oligosaccharides by on-line liquid chromatography/thermospray mass spectrometry is described. Molecular-weight information on oligomers up to a degree of polymerization of 10 is obtained using an aqueous mobile phase containing 10(-4) mol/L sodium acetate, which was found to be compatible with thermospray interfacing and ionization. Ions due to sodiated and disodiated oligosaccharides are observed under these conditions without fragmentation. The aqueous 10(-4) mol/L sodium acetate mobile phase is demonstrated to be applicable in the separation of mixtures of oligosaccharides on a reversed-phase octadecyl-modified silica column.  相似文献   

7.
Daniel JM  Ehala S  Friess SD  Zenobi R 《The Analyst》2004,129(7):574-578
A new technique is presented for the coupling of atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) mass spectrometry with liquid delivery systems. Mass measurements of polymers and peptides are demonstrated using a co-dissolved matrix, e.g. alpha-cyano-4-hydroxycinnamic acid (HCCA). Improvements in terms of sensitivity are achieved by optimizing the shape und control of the exit capillary and by using a laser (355 nm) at a 1 kHz repetition rate. Two calibration experiments promise a good applicability of the presented coupling method for quantitative measurements. The limit of detection achieved so far is 500 nM for peptides in methanol solution containing 25 mM HCCA.  相似文献   

8.
Matrix-assisted laser desorption/ionization (MALDI) was used for the on-line analysis of single particles. An aerosol was generated at atmospheric pressure and particles were introduced into a time-of-flight (TOF) mass spectrometer through a single-stage differentially pumped capillary inlet. Prior to entering the mass spectrometer, a matrix was added to the particles using a heated saturator and condenser. A liquid matrix, 3-nitrobenzyl alcohol (NBA), and a solid matrix, picolinic acid (PA), were used. Particles were ablated with a 351 nm excimer laser and the resulting ions were mass-separated in a two-stage reflectron TOF mass spectrometer. Aerosol particles containing the biomolecules erythromycin and gramicidin S were analyzed with and without the matrix addition step. The addition of NBA to the particles resulted in mass spectra that contained an intact molecular ion mass peak. In contrast, PA-coated particles did not yield molecular ion peaks from matrix-coated particles.  相似文献   

9.
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is a powerful tool for the measurement of low molecular mass compounds of biological interest. The limitations for this method are the volatility of many analytes, possible interference with matrix signals or bad ionization or desorption behavior of the compounds. We investigated the application of well-known and straightforward one-pot derivatization procedures to circumvent these problems. The derivatizations tested allow the measurement and the labeling of alcohols, aldehydes and ketones, carboxylic acids, alpha-ketocarboxylic acids and amines.  相似文献   

10.
After 7 years of continuous development, LC/MS has attracted considerable attention. Those who have not yet used it believe that LC/MS will solve nearly every analytical problem. The few current users are not so optimistic; instrumental difficulties are still severe, but new techniques are being developed to overcome these.  相似文献   

11.
This work evaluated derivatization procedures for detecting both natural and synthetic estrogenic chemicals by gas chromatography/mass spectrometry (GC/MS). Different silylating agents, mainly trimethylsilylating (TMS) agents, were compared, and the roles of various content of trimethylchlorosilane (TMCS, as a stimulator) were investigated. The difference in the abundances of the derivatives was caused by the steric hindrance of multiple hydroxyl groups and ethynyl groups in the structures of estrogenic chemicals. The use of TMCS produces an increase in the derivatization yield, especially for the compounds with multiple hydroxyl groups (i.e., 17beta-estradiol (E(2)) and estriol (E(3))). Mass spectra of O-TMS derivatives and tentative fragmentation profiles are proposed. Molecular ions were the base peaks for all the derivatives, and were used as the quantitation ions to obtain maximum detection sensitivity and specificity. Sample enrichment was achieved by Oasis HLB solid-phase extraction cartridges. The quantitation limits of these compounds ranged from 5 to 10 ng/L in 1000-mL water samples. Recovery of the estrogenic chemicals in spiked various water samples ranged from 78 to 102% while relative standard deviation (RSD) ranged from 1 to 15%.  相似文献   

12.
The interaction of copper ions with peptides was investigated by electrospray mass spectrometry. Two electrospray micro-emitters were compared, the first one with a platinum electrode using a copper(II) electrolyte solution containing a peptide sample, and the second one with a sacrificial copper anode in a water/methanol solution containing only a peptide (i.e., angiotensin III, bradykinin, or Leu-enkephalin). The former yielded mainly Cu(2+) complexes either with histidine residues or with the peptide backbone (Cu(+) complexes can be also formed due to gas-phase reactions), whereas the latter can generate a mixture of both Cu(+) and Cu(2+) aqueous complexes that yield different complexation patterns. This study shows that electrospray emitters with soluble copper anodes enable the study of Cu(I)-peptide complexes in solution.  相似文献   

13.
A single droplet generator was coupled with a rotating ball inlet matrix-assisted laser desorption/ionization (MALDI) time of flight (TOF) mass spectrometer. Single droplets with 100 picoliter volume were ejected by a piezoelectric-actuated droplet generator and deposited onto a matrix-coated rotating stainless steel ball at atmospheric pressure. The single droplet deposit was transported to the vacuum side of the instrument where ionization was accomplished using a UV pulsed laser. Using this on-line interface, it was possible to obtain protonated molecule signal from as little as 10 fmol analyte.  相似文献   

14.
Gliotoxin is produced by non-ribosomal peptide synthesis and secreted from certain fungi, including Aspergillus fumigatus. It is an epipolythiodioxopiperazine that contains an intact disulphide bridge and is the focus of intense research as a consequence of its negative immunomodulatory properties. Gliotoxin detection is generally enabled by reversed-phase–high-performance liquid chromatography (RP-HPLC), with absorbance detection (220–280 nm), or liquid chromatography-mass spectrometry, yet detection is not readily achievable by matrix-assisted laser desorption ionisation–time-of-flight mass spectrometry (MALDI-ToF MS). We have developed a single-pot derivatisation strategy which uses sodium borohydride-mediated reduction of gliotoxin followed by immediate alkylation of exposed thiols by 5′-iodoacetamidofluorescein to yield a stable product, diacetamidofluorescein-gliotoxin (GT-(AF)2), of molecular mass 1103.931 Da ((M + H)+). This product is readily detectable by RP-HPLC and exhibits a 6.8-fold increase in molar absorptivity compared with gliotoxin, which results in a higher sensitivity of detection (40 ng; 125 pmoL). GT-(AF)2 also fluoresces (excitation/emission, 492:518 nm). Unlike free gliotoxin, the product (>800 fmol) is detectable by MALDI-ToF MS. Sporidesmin A can also be detected by RP-HPLC and MALDI-ToF MS (>530 fmol) using this strategy. We also demonstrate that the strategy facilitates detection of gliotoxin (mean ± SD = 3.55 ± 0.07 μg 100 μL−1; n = 2) produced by A. fumigatus, without the requirement for organic extraction of culture supernatants and associated solvent removal. GT-(AF)2 is also detectable (150 ng; 460 pmol) by thin-layer chromatography.  相似文献   

15.
On-line electrochemistry/liquid chromatography/mass spectrometry (EC/LC/MS) was employed to mimic the oxidative metabolism of the fungicide boscalid. High-resolution mass spectrometry and MS/MS experiments were used to identify its electrochemical oxidation products. Furthermore, the introduction of a second electrochemical cell with reductive conditions provided important additional information on the oxidation products. With this equipment, hydroxylation, dehydrogenation, formation of a covalent ammonia adduct, and dimerization were detected after initial one-electron oxidation of boscalid to a radical cation. On-line reaction with glutathione yielded different isomeric covalent glutathione adducts. The results of the electrochemical oxidation are in good accordance with previously reported in vivo experiments, showing that EC/LC/MS is a useful tool for studying biotransformation reactions of various groups of xenobiotics.  相似文献   

16.
The use of pseudostationary phases (PSPs) in capillary electrophoresis provides powerful separation systems of high efficiency, selectivity and flexibility. Such electrokinetic chromatographic (EKC) systems are particularly useful for chiral analysis or for the analysis of samples containing a broad range of compounds. As the availability of mass and/or structural data on (unknown) sample constituents is increasingly important, the on-line coupling of EKC and mass spectrometry (MS) has gained attention. However, commonly used PSPs, such as micelles and cyclodextrines, may strongly interfere with electrospray ionization (ESI), making on-line EKC–MS quite a challenging task. This review covers the various approaches that have been proposed and developed to combine EKC and MS. A distinction is made between methodologies that prevent the PSP from entering the MS system, and methodologies that allow introduction of PSPs into the ion source. Various approaches such as partial filling of the separation capillary with PSP, use of reverse-migrating PSPs, employment of volatile PSPs, and alternative ionization modes, are outlined. Specific applications are described and overview tables are provided. It is concluded that there is no general solution for EKC–MS available yet, but new ionization techniques like atmospheric pressure photoionization may offer attractive perspectives for achieving full compatibility.  相似文献   

17.
18.
Naphthenic acids (NAs) are partially uncharacterised complex mixtures of carboxylic acids, resulting from the microbial oxidation of petroleum hydrocarbons. They are associated with the fouling of pipelines and process equipment in oil production and with corrosion in oil refineries. As by-products of the rapidly expanding oil (tar) sands industries, NAs are also pollutants and have proved to be toxic to a range of organisms. They also have important beneficial uses as fungicides, tyre additives and, paradoxically, also in the manufacture of corrosion inhibitors. These features make the characterisation of NAs an important goal for analytical chemists. Here we describe the synthesis of amide derivatives of NAs for characterisation by liquid chromatography/electrospray ionisation multistage mass spectrometry (LC/ESI-MS(n)). The method was applied to commercially available carboxylic acids, novel synthetic NAs, commercial NAs refined from crude oils, crude oil NAs and Athabasca oil sands NAs. In addition to confirming the number of alicyclic rings and length of alkyl side chain substituents (confirming information from existing methods), the MS(n) results provided further structural information. Most important of these was the finding that bi- to polycyclic acids containing ethanoate side chains, in addition to alkyl substituents, were widespread amongst the oil and oil sands NAs. The latter NAs are known end members of the beta-oxidation of NAs with even carbon number alkanoate chains. Since such NA mixtures are toxic, they should be targets for bioremediation. Bioremediation of NAs can also be monitored better by application of the methods described herein.  相似文献   

19.
It was found that in the chemical ionization (isobutane) mass spectra of some asymmetric secondary alcohols and α-amino acids, when a pair of enantiomers (such as R- and S-2-phenyIbutyric anhydride, R- and S-mandelic acid, R- and S-2-methylbutanoic acid or R- and S-α-phenyl ethyl amine) were used as reaction reagents, the relative abundances of characteristic ions formed by the stereoselective reaction between sample and reagent of the same configuration were much higher than those ions formed by the sample and a reagent of a different configuration. The absolute configuration of the sample molecule may be predicted by examination of mass spectra of the sample measured with R- and S-reagent respectively. This approach proved to be a convenient way for determination of the absolute configurations of organic molecules on a micromole level by mass Spectrometry.  相似文献   

20.
The decomposition products of hexabromocyclododecane (HBCD), a widely used brominated flame retardant, were investigated by gas chromatography/mass spectrometry (GC/MS). HBCD thermal degradation was conducted under a moderate heating rate (10 degrees C/min) in a batch reactor using both inert and oxidizing atmospheres. GC/MS analysis allowed the identification of substances derived from the primary pyrolysis process at the moderate heating rates used. The presence of oxygen seems to have a negligible influence on the degradation products obtained in HBCD decomposition, at least at moderate heating rates. Based on the identified products, the main pathways of HBCD thermal degradation were assessed and a mechanism for HBCD decomposition was proposed. The results obtained indicate that hexa-, penta- and tetrabrominated polyaromatic structures seem not to be primary products of HBCD decomposition, and may only be obtained by secondary bromination reactions.  相似文献   

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