On-line reaction monitoring by extractive electrospray ionisation

The design and development of a novel extractive electrospray ionisation (EESI) device for on-line reaction monitoring is described. The EESI apparatus uses a secondary, grounded nebuliser to produce an analyte aerosol and a Venturi pump is then used to transfer a sample of the aerosol to an electrospray source where it is ionised. The EESI apparatus was then tested with a variety of small, organic molecules to assess sensitivity, linearity and dynamic range. The performance of the technique will depend on the mass spectrometer used for the experiments; in the configurations used here it has a usable dynamic range of around 3.5 orders of magnitude with a linear range of around 2.5 orders of magnitude and is capable of analysing species present down to low μg/mL with signal-to-noise ratio greater than 2.5. The use of EESI for reaction monitoring was validated using a series of mock reaction mixtures and then used to monitor the base hydrolysis of ethyl salicylate to salicylic acid.     

脉冲电喷雾现象的初步研究

生物质谱方法的发展得益于生物质谱技术的发展,众所周知,电喷雾与基体辅助激光解吸技术的发展,极大地改善了生物质谱的分析性能,对于复杂生命体系的研究,现有的生物质谱面临着新的挑战,复杂体系要求以很少量的样品（nL-μL级）得到功能蛋白质组的许多信息,如各蛋白质的分子量、肽谱、氨基酸序列以及各类转译后修饰结构等,而现有的生物质谱大多要求足够大的样品量（1－10μL）,因此对低流量样品的高通量信息需求是生物质谱分析领域中的难题。     

A simple device for the extraction of TLC spots: direct coupling with an electrospray mass spectrometer

A new device is described which allows the recovery of compounds from thin layer chromatograms in short times, within a small volume, and without contamination. This apparatus can be coupled online to an electrospray mass spectrometer, but can also be used with other detectors or for micropreparations.     

Development of a dual-spray electrospray deposition system for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A new method of matrix-assisted laser desorption/ionization (MALDI) sample preparation using a dual-spray electrospray deposition system is demonstrated and employed for the investigation of gas-phase cationization reactions in the MALDI plume. The dual-spray electrospray system is found to increase the homogeneity of the sample similarly to that of a conventional single-spray electrospray system. The dual-spray electrospray system allows for intimate mixing of separately prepared sample components and results in improved quantitative results. The development of this device also leads to the possibility of mixing sample components prepared in different solvents without the need to be concerned with solvent miscibility.     

Comparison of solid-phase extraction and micro-solid-phase extraction for liquid chromatography/mass spectrometry analysis of pesticides in water samples

Our recent on-line solid-phase extraction (SPE) device for micro-liquid chromatography, known as micro-solid-phase extraction (microSPE), was compared with traditional SPE for the analysis, from aqueous samples, of 4 pesticides belonging to different classes. Two different kinds of adsorbents, C18 and graphitized carbon black, were tested. A 2-stage ion trap mass spectrometer, equipped with homemade microflow electrospray ion (ESI) source, was used. Detection limits with a signal-to-noise ratio of 3:1 for both extraction methods were in the range of 0.1 microg/L for all compounds. However, better recoveries were obtained when microSPE traps were used.     

Micro-electrospray mass spectrometry: Ultra-high-sensitivity analysis of peptides and proteins

A “micro-electrospray” ionization source has been developed that markedly increases the sensitivity of the conventional electrospray source. This was achieved by optimization of the source to accommodate nanoliter flow rates from 300 to 800-nL/min spraying directly from a capillary needle that, for the analysis of peptides, contained C18 liquid chromatography packing as an integrated concentration-desalting device. Thus, a total of 1 fmol of methionine enkephalin was desorbed from the capillary column spray needle, loaded as a 10-μL injection of 100-amol/μL solution. The mass spectrum showed the [M + H]⁺ ion at m/z 574.2 with a signal-to-noise ratio of better than 5:1 from a chromatographic peak with a width of about 12 s. A narrow range (15-u) tandem mass spectrum was obtained for methionine enkephalin from the injection of 500 amol, and a full-scan tandem-mass spectrum was obtained from 50 fmol. For proteins, the average mass measurement accuracy was approximately 100–200 ppm for the injection of 2.5 fmol of apomyoglobin and 20–40 ppm for 200 fmol. Carbonic anhydrase B and bovine serum albumin showed similar mass measurement accuracies.     

Porous polymer monolith assisted electrospray from a glass microdevice

The coupling of a lab-on-a-chip microfluidic device to a nanoelectrospray ionization mass spectrometer has the potential to automate many routine analytical procedures and produce a powerful analytical tool. However, past coupling strategies have relied on complex manufacturing steps including drilling and etching the device to attach a capillary or building a nanospray emitter directly into the device. This study shows that a nanospray emitter can be easily fabricated using a porous polymer monolith (PPM) at the end of a glass microdevice. These devices are able to obtain a stable electrospray at a variety of flow rates (50-500 nL/min) but optimal results are obtained at lower flow rates (50-100 nL/min) compatible with electroosmotic flow processes. The PPM is photo-patterned so that it can be placed in any position within the channel of the device with no dead volume. The porous character and the hydrophobic nature of the PPM both aid in development of a stable electrospray process. Total ion current traces for the constant infusion of leucine-enkephalin and PPG show relative standard errors as low as 4%, and produce mass spectra with good signal-to-noise (S/N 43) from only 2 fmol of material. In addition, multiple experiments in a given day show good repeatability with variability as low as 13%, and the multiple flow paths inherent in the PPM limit sprayer clogging.     

Charge reduction lowers mass resolving power for isotopically resolved electrospray ionization Fourier transform ion cyclotron resonance mass spectra

Electrospray ionization of synthetic or biological macromolecules above ∼1–2 kDa in mass typically produces ions of multiple charge states. Several recent papers have illustrated charge reduction as a means to simplify low-resolution electrospray ionization mass spectra, at the cost of significant loss in signal-to-noise ratio. However, if mass resolving power is sufficiently high (as in Fourier transform ion cyclotron resonance mass spectrometry) to resolve the heavy-atom isotopic distribution, then charge reduction actually lowers mass resolving power by a factor proportional to the ion charge. For proteins or nucleic acids of 10–50 kDa in mass, reducing the charge state to unity thus lowers mass resolving power by a factor of 10–50. In other words, as long as it is possible to resolve the isotopic distributions, charge reduction has no advantages for electrospray ionization mass spectrometry and has the very serious disadvantage of greatly degraded mass resolving power. Copyright © 2001 John Wiley & Sons, Ltd.     

Sheath liquid effects in capillary high-performance liquid chromatography-electrospray mass spectrometry of oligonucleotides

Fused-silica capillary columns of 200 μm inner diameter were packed with micropellicular, octadecylated, 2.3 μm poly(styrene–divinylbenzene) particles and applied to the separation of oligonucleotides by ion-pair reversed-phase high-performance liquid chromatography. Oligonucleotides were eluted at 50°C with gradients of 3–13% acetonitrile in 50 mM triethylammonium bicarbonate. Addition of sheath liquid to the column effluent allowed the detection of oligonucleotides by electrospray ionization mass spectrometry using full-scan data acquisition with a detectability comparable to that obtained with UV detection. The signal-to-noise ratios with different sheath liquids increased in the order isopropanol相似文献   

Fast DNA hybridization on a microfluidic mixing device based on pneumatic driving

A novel fluid mixing strategy was developed which significantly enhanced the efficiency of DNA hybridization. A pneumatic micro-mixing device consisting of two pneumatic chambers and an underneath DNA microarray chamber was built up. The fluid in the array chamber was pneumatically pumped alternately by the two pneumatic chambers. The chaotic oscillatory flow caused by the pumping greatly intensified the fluidic mixing. A homogeneous distribution of the tracer dye solution in the microarray chamber was observed after 2 s mixing with a pumping frequency of 24 Hz. Microarray DNA hybridization was substantially accelerated using this device, and the fluorescence intensity showed a plateau after oscillating 30 s at room temperature. The corresponding signal level of the dynamic hybridization was 12.5-fold higher than that of the static hybridization performed at 42 °C. A signal-to-noise ratio of 117 was achieved and the nonspecific adsorption of the targets to the sample array was minimized, which might be attributed to the strong shearing force generated during the pneumatic mixing process.     

Characterization and application of a self‐aspirating electrospray source with pneumatic‐assisted ionization

A single gas‐assisted electrospray ion source developed for ambient mass spectrometry is introduced in this paper. Simultaneous self‐aspiration and electrospray could be achieved by using a constant sheath gas flow supplied from a mini air pump. A gas dynamic study of the spray module is carried out for structural optimization. The entire device exhibits a simplified design and has been systematically characterized through both simulated and experimental investigations. According to the results, the ion source exhibited satisfactory stability and the ability for quantitative operation in routine electrospray ionization mass spectrometry. Furthermore, the ion source can be operated as a desorption electrospray ionization source to perform direct desorption/ionization of the solid samples. The versatile source described here appears to provide a practical approach to perform ambient mass spectrometry analysis with unrestricted sampling operation, and the extensive gas dynamic studies together with the experimental characterization are believed to be helpful in building self‐aspirating spray devices. Copyright © 2017 John Wiley & Sons, Ltd.     

The effect of ruthenium(III) chloride on the formation of protonated parent ions in electrospray mass spectrometry

We report the use of RuCl3 as an "alkali metal sponge". This is a general and highly efficient method for generating protonated parent ions for a variety of compounds that usually do not show this ion in electrospray mass spectrometry. This technique is demonstrated to be highly useful in "cleaning up" spectra from multiply metallated ions, thereby substantially improving the signal-to-noise ratio.     

Complete large-molecule high-resolution mass spectra from 50-femtomole microvolume injection

For electrospray ionization in Fourier-transform mass spectrometry, direct injection of 5×10^?14 mol (0.5 µL of 100 nM from a microvolume sample valve) of ubiquitin (8565 Da) into the flowing solvent stream yields a spectrum with 85:1 signal-to-noise ratio, 2-ppm mass accuracy, and isotopic resolution. Gated trapping for 100 µs from a 0.15-µL/min injection of 20-µM ubiquitin consumes 5×10^?18 mol, which produces a spectrum with 23:1 signal-to-noise ratio and τ;3×10⁵ resolving power.     

Small angle neutron scattering measurements of synthetic polymer dispersions in matrix-assisted laser desorption/ionization matrixes

Small angle neutron scattering (SANS) is used to measure the size and the dispersion of synthetic polymers in matrix-assisted laser desorption/ionization (MALDI) matrixes. Deuterated polystyrene (DPS) and dithranol in tetrahydrofuran were deposited by electrospray onto a substrate for small angle neutron scattering (SANS) measurements. DPS with 6050 and 27,000 g mol(-1) molecular masses were prepared at mass fractions between 0.2 and 6%. All samples contained large aggregates of DPS with characteristic sizes >200 A that represent hundreds of aggregated chains. Samples of mass fraction 1% DPS (6050 g mol(-1)) in 2,5-dihydroxybenzoic acid, all-trans-retinoic acid, and sinapinic acid also have large zero angle scattering characteristic of large aggregates. The morphological trend obtained from the SANS measurements of the DPS aggregate size in the four matrixes is dithranol > 2,5-dihydroxybenzoic acid > all-trans-retinoic acid > sinapinic acid. These measurements indicate that DPS in dithranol exhibits the most strong phase separation, while DPS in sinapinic acid shows considerable domain mixing. All of these matrixes produce MALDI signal strength under appropriate conditions, suggesting that strong phase separation does not diminish the signal-to-noise ratio. DPS (188,000 g mol(-1)) in biphenyl was used as a model system of a matrix that can be either crystalline or amorphous. SANS data shows that above the biphenyl melting point, a conventional solution is formed that has molecularly dispersed polymers. Upon crystallization, there is strong aggregation of the DPS into large domains. Therefore, the crystalline matrixes commonly used in MALDI measurements probably cause large aggregations of polymers to be present during the MALDI process.     

Simultaneous determination of NOGE-related and BADGE-related compounds in canned food by ultra-performance liquid chromatography–tandem mass spectrometry

An improved analytical method enabling rapid and accurate determination and identification of bisphenol F diglycidyl ether (novolac glycidyl ether 2-ring), novolac glycidyl ether 3-ring, novolac glycidyl ether 4-ring, novolac glycidyl ether 5-ring, novolac glycidyl ether 6-ring, bisphenol A diglycidyl ether, bisphenol A (2,3-dihydroxypropyl) glycidyl ether, bisphenol A (3-chloro-2-hydroxypropyl) glycidyl ether, bisphenol A bis(3-chloro-2-hydroxypropyl) ether, and bisphenol A (3-chloro-2-hydroxypropyl) (2,3-dihydroxypropyl) ether in canned food and their contact packaging materials has been developed by using, for the first time, ultra-performance liquid chromatography coupled with tandem mass spectrometry. After comparison of electrospray ionization and atmospheric pressure chemical ionization in positive and negative-ion modes, tandem mass spectrometry with positive electrospray ionization was chosen to carry out selective multiple reaction monitoring analysis of novolac glycidyl ethers, bisphenol A diglycidyl ether, and its derivatives. The analysis time is only 5.5 min per run. Limits of detection varied from 0.01 to 0.20 ng g(-1) for the different target compounds on the basis of a signal-to-noise ratio (S/N) = 3; limits of quantitation were from 0.03 to 0.66 ng g(-1). The relative standard deviation for repeatability was <8.01%. Analytical recovery ranged from 87.60 to 108.93%. This method was successfully applied to twenty samples of canned food and their contact packaging materials for determination of migration of NOGE, BADGE, and their derivatives from can coatings into food.     

Development of the continuously variable volume reactor for flow injection analysis: Part 1. Design, capabilities and testing

A new apparatus for mixing sample and reagent in flow injection analysis (FIA) is described. The continuously variable volume reactor (CVVR) replaces the conventional mixing coil in a flow injection (FI) manifold to provide mixing and dilution. A linear actuator motor allows control of the chamber volume via LabVIEW software. The chamber volume can be incremented in steps of 1 μl over the range 68-1704 μl. In addition, the chamber has an integral variable-speed stirring unit that is also under computer control. Experiments were performed to evaluate the dispersion characteristics of this new device, evaluate the volume reproducibility, and understand the mixing characteristics. Use of the chamber is shown in the determination of iron(II) in pond water, and in NIST SRM 1643d with excellent results and a detection limit of 3.7 μg/l iron(II). Advantages of the CVVR and future research activities using the device are discussed.     

Comparison of negative and positive ion electrospray tandem mass spectrometry for the liquid chromatography tandem mass spectrometry analysis of oxidized deoxynucleosides

Oxidized deoxynucleosides are widely used as biomarkers for DNA oxidation and oxidative stress assessment. Although gas chromatography mass spectrometry is widely used for the measurement of multiple DNA lesions, this approach requires complex sample preparation contributing to possible artifactual oxidation. To address these issues, a high performance liquid chromatography (HPLC)-tandem mass spectrometric (LC-MS/MS) method was developed to measure 8-hydroxy-2'-deoxyguanosine (8-OH-dG), 8-hydroxy-2'-deoxyadenosine (8-OH-dA), 2-hydroxy-2'-deoxyadenosine (2-OH-dA), thymidine glycol (TG), and 5-hydroxy-methyl-2'-deoxyuridine (HMDU) in DNA samples with fast sample preparation. In order to selectively monitor the product ions of these precursors with optimum sensitivity for use during quantitative LC-MS/MS analysis, unique and abundant fragment ions had to be identified during MS/MS with collision-induced dissociation (CID). Positive and negative ion electrospray tandem mass spectra with CID were compared for the analysis of these five oxidized deoxynucleosides. The most abundant fragment ions were usually formed by cleavage of the glycosidic bond in both positive and negative ion modes. However, in the negative ion electrospray tandem mass spectra of 8-OH-dG, 2-OH-dA, and 8-OH-dA, cleavage of two bonds within the sugar ring produced abundant S1 type ions with loss of a neutral molecule weighing 90 u, [M - H - 90]-. The signal-to-noise ratio was similar for negative and positive ion electrospray MS/MS except in the case of thymidine glycol where the signal-to-noise was 100 times greater in negative ionization mode. Therefore, negative ion electrospray tandem mass spectrometry with CID would be preferred to positive ion mode for the analysis of sets of oxidized deoxynucleosides that include thymidine glycol. Investigation of the fragmentation pathways indicated some new general rules for the fragmentation of negatively charged oxidized nucleosides. When purine nucleosides contain a hydroxyl group in the C8 position, an S1 type product ion will dominate the product ions due to a six-membered ring hydrogen transfer process. Finally, a new type of fragment ion formed by elimination of a neutral molecule weighing 48 (CO2H4) from the sugar moiety was observed for all three oxidized purine nucleosides.     

Quantitative analysis of urinary C-peptide by liquid chromatography-tandem mass spectrometry with a stable isotopically labelled internal standard

We describe the first results of a quantitative LC-tandem mass spectrometry method for urinary C-peptide with the use of [2H14]C-peptide as internal standard. LC was based on gradient elution of a Hypersil PEP C18 column. Mass spectrometry was performed in the negative electrospray ionization mode and by monitoring of the transitions at m/z 1514/1334 ([2H14]C-peptide) and 1507/1320 (C-peptide). For sample preparation, we applied ultrafiltration. The analytical performance of the method in terms of measurement precision gave an RSD of <2% (n=10). The overall imprecision was investigated from independent analysis of two urine samples in six-fold and resulted in an RSD<5%. The limit of detection, expressed as signal-to-noise ratio 3, was approximately 0.15 ng C-peptide injected. Analysis of 10 random urine samples from laboratory volunteers showed interference-free ion chromatograms at a signal-to-noise ratio of approximately 75 on average. The C-peptide concentrations calculated from quantification by the bracketing calibration technique ranged from 32 to 165 ng/ml.     

Simultaneous particle counting and detecting on a chip

This paper reports a lab-on-a-chip device that performs particle detection and number counting by coupling the fluorescent detection and particle counting simultaneously. The particle number counting is realized by a resistive pulse sensor (RPS) and fluorescent particle detection is achieved by a miniaturized laser-fiber optic detection system. By using a single microfluidic channel with two detecting arm channels placed at the two ends of the sensing section, the RPS signal-to-noise ratio is improved significantly. Two-stage differential amplification is used to further increase the signal-to-noise ratio for both the RPS and fluorescent signals. This method is also highly sensitive, so that we were able to realize the RPS and fluorescent detection of 0.9 microm (mean diameter) fluorescent particles. Excellent agreement was achieved by comparing the results obtained by our system with the results from a commercial flow cytometer for a variety of samples of mixed fluorescent and non-fluorescent particles. The method described in this paper is simple and can be applied to develop a compact device without the need of lock-in amplifier or similar bulky supplemental equipment.     

A polymeric microchip with integrated tips and in situ polymerized monolith for electrospray mass spectrometry

We describe the integration of a cyclo-olefin polymer based microchip with a sheathless capillary tip for electrospray ionization-mass spectrometry (ESI-MS). The microchip was fabricated by hot embossing and thermal bonding. Its design includes a side channel for adjusting the composition of the electrospray solution so that analytes in 100% water can be analyzed. The fused silica capillaries, used for sample introduction, and the electrospray tips for MS coupling were directly inserted into the microchannel before thermal bonding of the device. A microfabricated on-chip gold microelectrode was used to apply the electrospray voltage. Annealing the device after thermal bonding increased the pressure resistance of the microchip. The cross section of the microchannel was imaged by scanning electron microscopy to estimate the effects of the annealing step. The relationship between the applied electrospray voltages and MS signal was measured at different flow rates by coupling the device to an ion trap mass spectrometer. The performance of the microchip was evaluated by MS analysis of imipramine in ammonium acetate buffer solution by direct infusion. An alkylacrylate based monolith polymer bed for on-chip sample pretreatment and separation was polymerized in the microchannel and tested for ESI-MS applications.