George H. Vickers

Developments in plasma source/mass spectrometry

Abstract The field of plasma source/mass spectrometry is critically reviewed and its current status assessed. An overview of PS/MS applications is provided and a discussion is offered of key problem areas that currently exist in the field. Areas that are now receiving strong research attention are outlined and a view is offered for future prospects of plasma source/mass spectrometry as a technique for the determination of elements.

Reduction of Mass-Dependent Interferences in Inductively Coupled Plasma-Mass Spectrometry by using Flow-Injection Analysis

The use of flow-injection analysis to reduce mass-dependent interferences in inductively coupled plasma-mass spectrometry has been assessed. Results are presented which demonstrate nearly complete elimination of analyte-signal suppression under operating conditions where dispersion (D) is approximately 25. Furthermore, results obtained with flow-injection analysis exhibit greater precision, take less time, and suffer only a 40% reduction in sensitivity, compared to continuous-flow analysis.

Ionization Temperatures in the Inductively Coupled Plasma Determined by Mass Spectrometry

Ionization temperatures in the inductively coupled plasma are determined with the use of the ionization fraction for iodine obtained by mass-spectral sampling. Temperatures profiled at different heights and different positions across the plasma are between 6900 and 7800 K at relatively low heights. Power increases raise the measured ionization temperature, while changes in nebulizer gas flow and the addition of an easily ionized element to the plasma have no measurable effect. Desolvation of the sample aerosol causes a decrease of about 500 K in the ionization temperature.

Spatial dependence of ion concentrations in inductively coupled plasma mass spectrometry

Abstract Spatially resolved measurements of ion kinetic energies and densities have been obtained in an inductively coupled plasma (ICP) by mass spectrometry (MS). Because of changes in the plasma potential, ion kinetic energies varied as the ICP was sampled in different locations. These changes were found to be similar to those reported by others, but caused problems in the interpretation of the measured ion densities. Nevertheless, spatial profiles compared favorably to those obtained by laser-excited fluorescence in the ICP, and axial distributions of BaOH+, BaO+, Ba+ and Ba2+ correlated well with the behavior of ICP-MS signals that occur when the inner gas flow rate is varied.

Spectral and physical interferences in a new, flexible inductively coupled plasma mass spectrometry instrument

Different types of interferences in inductively coupled plasma mass spectrometry have been studied on a non-commercial instrument and compared with those reported by other workers. Spectral interferences from plasma and matrix background ions are similar, although relative intensities differ. The extent of formation of oxide and doubly charged ions is quite different from those reported in the literature. Chemical and physical interferences seem not to be present on the new instrument.

Analytical characteristics of an inductively coupled plasma-mass spectrometer

Abstract A new instrument is described for inductively coupled plasma-mass spectrometry. The instrument has features which make it useful for both fundamental studies of plasmas and for analytical elemental analysis. Analytical characteristics of the instrument such as the background mass spectrum, the abundance sensitivity, presence of doubly charged and oxide ions, detection limits and analytical calibration curves are presented. Some interference effects commonly seen in atomic emission spectroscopy are evaluated, and comparisons are made between the performance of the new instrument and that of other inductively coupled plasma-mass spectrometers.

Time-resolved fluorescence with an optical-fiber probe

Abstract Time-resolved fluorescence measurements are made with an optical-fiber probe approximately 16 m long. Fluorescence lifetimes for 1.00 μM solutions of rhodamine-B and rose bengal in ethanol were found to be 2.78 ± 0.04 ns and 0.77 ± 0.07 ns, respectively, similarin accuracy and precision to values obtained with conventional techniques. Calculations are used to investigate the limitations in remote determinations caused by temporal broadening. Results indicate that fiber lengths approaching 1 km can be used without significant loss in accuracy or precision.

Characterisation of a 9-mm torch for inductively coupled plasma mass spectrometry

A 9-mm torch and a 40.68-MHz radiofrequency power supply were evaluated for use in inductively coupled plasma mass spectrometry (ICP-MS). With this system, an analytically useful plasma can be supported at 850 W applied r.f. power and 8.7 l min–1 total argon flow-rate. The effects of operating parameters (nebuliser gas flow-rate, r.f. power, sampling depth and ion-lens voltages) on the analyte ion signals were determined. The 9-mm source exhibits greater independence of the ion-optic bias potential on relative atomic mass than do conventional-sized torches. Further, the 9-mm system produced similar sensitivities, detection limits, doubly charged ion ratios and oxide ion ratios to the conventional plasma but with lower power and argon consumption. However, the proper placement of the discharge under the interface was found to be critical to obtain maximum signal levels.

Comparison of 27- and 40-MHz plasmas in inductively coupled plasma mass spectrometry

The analytical characteristics of a 27.12- and a 40.68-MHz inductively coupled plasma (ICP) are compared as ion sources for use in inductively coupled plasma mass spectrometry. The background spectra produced by the two sources are similar; however, there is evidence of greater entrainment of air in the higher frequency discharge. Calibration graphs are linear over 6–7 orders of magnitude with both operating frequencies, although the 40.68-MHz ICP suffers a factor of 2–5 loss in sensitivity. Accordingly, detection limits are also slightly worse at the higher operating frequency, as is the precision. Interference effects are independent of operating frequency, but the extent of doubly charged, oxide and hydroxide ion formation might be affected by a more significant orifice-linked discharge with the 40.68-MHz ICP.

Novel Techniques for the Determination of Fluorescence Lifetimes

Abstract: Two novel techniques for the measurement of fluorescence lifetimes are discussed. The first method operates in the frequency domain, selectively amplifying the signals generated by the mode beats of a cw laser with a UHF television tuner. The second approach measures the fluorescence with simultaneous temporal and spectral resolution to simplify the characterization of complex samples.