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The preliminary validation of a high-performance liquid chromatography particle beam mass spectrometry method (HPLC-PB/MS) with electron impact ionization source for analysis of botanical extracts is presented. The LC-PB/MS system was evaluated for the analysis of ephedrine alkaloids using ephedra-containing National Institute of Standards and Technology dietary supplement standard reference materials (SRMs) 3241 Ephedra Sinica Stapf Native Extract and 3242 Ephedra Sinica Stapf Commercial Extract. The ephedrine alkaloids were separated by reversed-phase chromatography using a phenyl column at room temperature. A linear gradient method with a mobile phase composition varying from 5:95 [MeOH:0.1 trifluoroacetic acid (TFA) in water] to 20:80 (MeOH:0.1 TFA in water) at a flow rate of 1.0 mL/min, with an analysis time of less than 20 min, was used. The source block temperature was evaluated to determine the optimal operating conditions by monitoring the intensities and fragmentation patterns of the ephedrine alkaloids. Ephedrine and N-methylephedrine were taken as a representative of the test alkaloids. The LODs on the sub-nanogram level were achieved, with ephedrine, pseudoephedrine, and methylephedrine in the SRMs quantified by a standard addition method with recoveries of 86 and RSDs of 14 (N = 3).

The monomer fraction of a representative petroleum pitch, M-50, was characterized in terms of both the predominant polycyclic aromatic hydrocarbon (PAH) backbones and their extent of alkylation. Such an identification of individual molecular species and their relative abundance was greatly facilitated by the use of a series of separation processes prior to analysis. In particular, low (up to 270), medium (270−335), and high (335−388) molecular-weight cuts of the monomeric fraction of the M-50 pitch were isolated by dense-gas extraction (DGE). The resultant three cuts were then further fractionated by preparative-scale gel permeation chromatography (prep-scale GPC) to obtain narrow molecular-weight fractions suitable for individual species identification by both matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry and reversed-phase high-performance liquid chromatography with photodiode array detection (HPLC/PDA). Results indicate that the monomer fraction consists of five d...

Factors controlling the depth resolution in radio frequency glow discharge optical emission spectroscopy (rf-GDOES) depth profiling analysis of thin films have been investigated using anodic alumina films of varying thicknesses with delta function marker layers of ∼2 nm width located at various depths from the oxide surface. In rf-GDOES depth profiling analysis, where a relatively large area of ∼4 mm in diameter is analysed, it was found that the depth resolution is determined mainly by the large-scale variation of sputtering rate across the crater. Despite the relatively large area analysed, the uniformity of sputtering rate across the crater was constant to within 1% under the optimum Ar pressure except for near-edge regions of ∼0.4 mm width, where the sputtering rate was ∼6% higher than in the central crater region. Owing to this relatively minor non-uniformity of sputtering rate, the depth resolution degrades approximately linearly with depth. A depth resolution of ∼1.3 nm was realized to depths of ∼25 nm, where the degradation of depth resolution due to the non-uniformity in sputtering rate is insignificant. The depth resolution is close to the ultimate depth resolution in sputter depth profiling, claimed to be 0.7– 1.0 nm, and arises from the minimal atomic mixing associated with film sputtering with Ar+ions of very low energy, ∼50 eV, in rf-GDOES analysis. Copyright © 2001 John Wiley & Sons, Ltd.

The absorbance of Cu atoms sputtered from a Cu cathode in a laboratory-modified radio frequency glow discharge atomizer for atomic absorption spectrometry was measured at different regions within the atomizer chamber for different discharge parameters. The results show that not only the discharge gas flow rate and pressure but also the applied rf power and the degree of extension of the negative glow have significant effects on the atomization and on the distribution of sputtered atoms within the atomizer chamber. The influence of various diameters and thicknesses of the sampling orifice (anode) on the plasma atomization characteristics and the sample weight loss rates has been examined. By increasing the diameter of the sampling orifice, a larger area of the cathode surface (Cu) was allowed to be sputtered, thereby generating a larger number of atoms (higher absorbance) in the analysis volume, where the sputtered atoms were studied by atomic absorption spectrometry. The absorbance of Cu atoms was inverse...

The design and preliminary operating characteristics of a particle beam/hollow cathode atomic emission spectrometry (PB/HC-AES) device is described. By use of a high-efficiency thermal-concentric nebulization system coupled to a particle beam LC/MS interface, analyte particles originating in aqueous solution are introduced into a heated hollow cathode glow discharge for subsequent vaporization and excitation. Helium and argon are evaluated as discharge gases over a range of pressures and discharge currents, with He chosen as the most appropriate for subsequent analytical studies. Nebulization temperature, liquid (solvent) flow rate, and vaporization temperature are evaluated in order to determine their effects on analyte emission characteristics. Optimized sample introduction and He plasma operation conditions are employed to study the analytical characteristics of the PB/HC-AES system. Subsequent studies of cesium at ppm levels in diluted (1000 [times]) simulated nuclear waste solutions (5.0 M NaNO[sub 3] and 0.1 M KOH) indicated that the addition of excess chloride as a counterion, rather than nitrate, greatly enhances detectability. 26 refs., 7 figs.

A radio-frequency- (rf-) powered glow discharge has been interfaced to a double-focusing mass spectrometer. This type of discharge allows direct analysis of nonconducting, as well as conducting, solids. The rf discharge source and electrical system overcome several problems which have inhibited success in prior efforts. Problems of inadequate rf shielding, maintaining the necessary dc bias potential on the sample surface, preventing rf modulation of ion energies, and coupling of the accelerating potential to the discharge are resolved. Representative spectra of glass, soil, and brass matrices are presented. Preliminary relative sensitivity factors for conducting and non-conducting matrices show relatively small differences in ion yields across the periodic table. 31 refs., 9 figs., 2 tabs.

Compositional depth profiles have been obtained on chemical solution deposited lead zirconate titanate (PZT) thin films using radio-frequency glow discharge atomic emission spectroscopy. The technique is very rapid, requiring less than one minute for complete multi-element depth profiling of films and multilayer substrates. In the present study, the method was employed to obtain compositional profiles of the various metallic (Pb, Zr, Ti, Si) and organic-related (C, H, O) species that are present in the films and underlying device. Preliminary results using this relatively new technique are reported for PZT films deposited by an aqueous acetate process and heat treated at temperatures ranging from 300 and 700°C. The initial results from these investigations suggest that Pb volatilization occurs at temperatures as low as those typically encountered during the pyrolysis step. Significant interdiffusion of the Pb into the underlying Pt electrode at this temperature is also suggested. Effects of modifying ligand on film thickness and organic decomposition behavior were also observed.

The effects of discharge conditions on the sputtering, spatial distributions and transport patterns of sputtered atoms in a demountable, radiofrequency (r.f.) glow discharge (GD) atomizer, were investigated. Results obtained for sputtering of oxygen-free hard copper indicate that the GD plume is constricted by an increase in the Ar gas pressure and disturbed by Ar gas/vacuum flow. It is shown that the glow is an inhomogeneous medium and that most of the sputtered Cu atoms are localized in the front of the sampling orifice. Independent control of flow rate and pressure of the sputtering gas (Ar) is critical in determining the spatial distribution of analyte atoms within the atomizer chamber. Both the flow rate and the pressure of the Ar gas affect the removal of ground-state atoms from the analysis volume. The plasma location at different discharge parameters was also investigated in this study. The results show that the r.f. GD source is able to sustain a stable plasma which enables the sequential atomic absorption analysis and depth profiling of samples such as metal alloys.

The glow discharge is a simple, yet effective device which has found application in atomic absorption, atomic emission, and elemental mass spectrometry. It takes the form of a low-pressure gas discharge wherein rare gas ions are attracted to a sample cathode and efficiently sputter atoms from the surface. Figure 1 shows the essential components of the source. The discharge has been powered by dc, pulsed dc, and rf supplies, usually operating in a low power regime, with optimum currents and voltages determined by such factors as source configuration, discharge gas, and pressure. Nearly all the discharge voltage is dropped across the cathode dark space, serving to accelerate the argon ions onto the cathode, which is formed directly from the sample or compacted from a sample/matrix mixture. The glow discharge approach is simple, inexpensive, and shows relatively few matrix effects. Sensitivity in the ppb range is seen for most elements. A disadvantage of the technique is that the gas discharge produces certain background species which can create interferences for some elements, if alternative isotopes are not available.

The glow discharge is a simple, yet effective device which has found application in atomic absorption, atomic emission, and elemental mass spectrometry. It takes the form of a low-pressure gas discharge wherein rare gas ions are attracted to a sample cathode and efficiently sputter atoms from the surface. Figure 1 shows the essential components of the source. The discharge has been powered by dc, pulsed dc, and rf supplies, usually operating in a low power regime, with optimum currents and voltages determined by such factors as source configuration, discharge gas, and pressure. Nearly all the discharge voltage is dropped across the cathode dark space, serving to accelerate the argon ions onto the cathode, which is formed directly from the sample or compacted from a sample/matrix mixture. The glow discharge approach is simple, inexpensive, and shows relatively few matrix effects. Sensitivity in the ppb range is seen for most elements. A disadvantage of the technique is that the gas discharge produces certain background species which can create interferences for some elements, if alternative isotopes are not available.