Daniel A. Wilson

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.

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.

Determination of Subnanosecond Fluorescence Lifetimes with a UHF Television Tuner and a cw or Mode-Locked Laser

An inexpensive ultra-high-frequency (UHF) television tuner and an argon-ion laser are employed for the determination of excited-state lifetimes of a series of common fluorophores. Fluorescence lifetimes are determined in the frequency domain; the results are in good agreement with previously reported values and demonstrate the utility of the new approach for subnanosecond measurements. Binary mixtures of rhodamine 6G and rose bengal can also be resolved with the use of this novel instrument design.

Detection of ions by replacement-ion chromatography coupled to a microwave-induced nitrogen discharge at atmospheric pressure

Abstract The capabilities and limitations of replacement-ion chromatography (RIC) using a lithium-based replacement method and a microwave-induced nitrogen discharge at atmospheric pressure as the detector are critically evaluated for the determination of anions and cations. The system, including chromatographic columns, interface, and plasma-emission source, provides detection limits of 30–300 ng for anions and 100–500 ng for cations. Detectability and precision of the instrument are ultimately limited by multiplicative noise sources. The limitations imposed by multiplicative noise on RIC detection are assessed, and guidelines are presented that will allow judicious choice of alternative RIC detectors in the future.

Comparison of the helium/oxygen/acetylene and air/acetylene flames as atom sources for continuum-source atomic fluorescence spectrometry

Abstract The helium/oxygen/acetylene flame is compared to the more widely used air/acetylene flame for its utility as an atom cell for atomic fluorescence spectrometry. Nearly identical experimental arrangements were used for both flames in order to make the comparison valid. With a continuum source used for excitation, fluorescence detection limits in the helium/oxygen/acetylene flame were between 13 and 60 times better (lower) than those determined for the same eight elements in the air/acetylene flame. The improved detection limits are attributable mainly to the higher temperature, increased thermal conductivity and lower quenching in the helium flame. Fluorescence background spectra were obtained for both flames over the wavelength range 185–650 nm, and showed the helium flame to have slightly smaller background fluctuations, but a much larger background because of the more favorable fluorescence conditions in the flame.

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.