Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.

The design and implementation of two different interfaces for capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) are described. These interfaces will allow for on-line analysis of CE effluents with ICP-MS detection. One interface is based on a concentric tube nebulizer and the other on a standard cross-flow nebulizer. These systems were investigated in parallel and their performances, under various experimental conditions, were compared. Each interface possesses a unique set of advantages and shortcomings. Recognizing that typical sample flow rates for ICP-MS are of the order of ml min 21 and that the flow rates for CE are a few nl min 21 , some difficulties in flow compatibility are encountered. Aspects discussed include interface considerations, flow compatibility and the influence of flow rates on the overall sensitivity. Several guidelines are provided for workers interested in implementing a CE-ICP-MS instrument for elemental speciation. The Cd detection limits in rabbit metallothionein were 2.36 and 0.21 mg ml 21 for the concentric and cross-flow nebulizers, respectively.

No abstract

No abstract

No abstract

A millisecond pulsed glow discharge is used as a versatile ion source for time-gated generation of elemental, structural, and molecular ions. The utility of this ion source for comprehensive chemical analysis of a series of aromatic and halogenated hydrocarbons is illustrated in this manuscript. To highlight the analytical utility of this transient ion source, it was connected to a gas chromatograph for the mass spectrometric determination of mixtures containing benzene, toluene, o-xylene, cymene, tert-butylbenzene, carbon tetrachloride, chloroform, chlorobenzene, tetrachlorethane, and dichlorobenzene. Explicit chemical analysis was accomplished by introducing the GC eluent into a pulsed glow discharge operating at a rate of 100 Hz with a 50% duty cycle. Using three independent digitizers for time-gated acquisition in three separate time regimes, nearly concurrent collection of elemental, structural, and molecular information was accomplished. In general, elemental information was obtained during the first 0.015 ms after the plasma onset; structural information, as ascertained from molecular fragmentation, was obtained during the plateau time regime when the plasma pulse is at a steady state, whereas molecular M(+) and MH(+) ions were obtained during the afterpeak time regime, that is, after the cessation of the plasma power pulse.

The glow discharge ionization source operated in the trace levels is becoming the major area of interest in analytical pulsed (or modulated ) power mode offers unique characchemistry. Therefore, any new analytical technique that is teristics not available from its steady state counterpart. It applied to these problems must be extremely sensitive. Other has been well established that higher instantaneous power applications that require molecular mass and elemental comdensities are obtainable without compromising the sample position characterization include clinical analysis, materials integrity when pulsed plasmas are implemented. This chemistry and pharmaceuticals. It is well known that the operating parameter affords higher sputter yields and oxidation state and the chemical form of hazardous materials lower limits of detection relative to the steady state play a vital role in their actual toxic effects on biological plasmas. Of special interest are the discrete temporal systems and the environment in general.7,11,12 In the near regions associated with the modulated plasma. The presfuture, these criteria will play an increasingly important role ence of these time regimes offers temporal selectivity, in measuring and classifying hazardous sites. Subsequently, it allowing the collection of analytical data in a region where is becoming paramount to identify the molecular forms of the contribution from background and contaminant these elements and their corresponding concentrations in species is minimized. These regions are characterized by environmental samples. strikingly different ionization mechanisms. Acquisition of At present, the acquisition of both elemental and molecular data during each of these temporal regimes provides both molecular and elemental information. In this work the information requires mutually exclusive techniques.13 potential use of the pulsed glow discharge for collecting Although this manner of analysis is possible and indeed works concurrent molecular and elemental information was fairly well, it suffers from a number of disadvantages. The explored. This task was accomplished using time-of-flight most apparent shortcomings of using two independent techmass spectrometry ( TOFMS). TOFMS has a significantly niques involve the time needed to complete an analysis and high throughput and duty cycle, making it ideally suited the amount of sample required. Unfortunately, time and for rapid acquisition of spectra. This characteristic allows sample size are two very important factors when considering data acquisition during each of these temporal regions for a potential new technique. Hence, it is apparent that a technique each discharge pulse power cycle, affording concurrent that could limit analysis time and sample size requirements elemental and molecular detection. p-Xylene was used as could fill a niche that has so far eluded us. a test molecule for these studies.Currently, there are many mass and optical spectrometry based systems that are well suited for each particular type of analysis. T...

Through proteolysis and peptide mass determination using mass spectrometry, a peptide mass map (PMM) can be generated for protein identification. However, insufficient peptide mass accuracy and protein sequence coverage limit the potential of the PMM approach for high-throughput, large-scale analysis of proteins. In our novel approach, nonlabile protons in particular amino acid residues were replaced with deuteriums to mass-tag proteins of the S. cerevisiae proteome in a sequence-specific manner. The resulting mass-tagged proteolytic peptides with characteristic mass-split patterns can be identified in the data search using constraints of both amino acid composition and mass-to-charge ratio. More importantly, the mass-tagged peptides can further act as internal calibrants with high confidence in a PMM to identify the parent proteins at modest mass accuracy and low sequence coverage. As a result, the specificity and accuracy of a PMM was greatly enhanced without the need for peptide sequencing or instrumental improvements to obtain increased mass accuracy. The power of PMM has been extended to the unambiguous identification of multiple proteins in a 1D SDS gel band including the identification of a membrane protein.