Barbara S. Ross

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.

Alteration of the ion-optic lens configuration to eliminate mass-dependent matrix-interference effects in inductively coupled plasma-mass spectrometry

Abstract The ion-optic lens configuration can have a substantial influence on mass-dependent matrix effects in inductively coupled plasma-mass spectrometry (ICP-MS). A laboratory-constructed instrument is used to study the influence of Sr, Ba, W, Pb and U (10 mM) on signals from Sc, Zn, Y, Ag and Cs (10 μM). Instrumental arrangements which did not utilize second-stage ion lenses were found to eliminate the matrix effects. With additional modifications to the third-stage lens system, the analytical utility of the system is maintained.

Fundamental studies of the sampling process in an inductively coupled plasma mass spectrometer: III. Monitoring the ion beam

Abstract The influence of gas dynamic and electrostatic forces on the ion beam that passes through an ICP-MS interface has been studied. Results from these experiments show that electrostatic forces overpower gas-kinetic processes in the molecular-flow regions of the interface. Because ion movement in these regions cannot be predicted by gas dynamic theory alone, optimal skimming conditions must be determined on an empirical basis. Those parameters that were found to influence ion-beam formation are first-stage pressure, solvent load, and inner-gas flow rate. Also studied was the influence of atomic mass on dispersion within the ion beam. Elements of mass greater than the bath-gas species (argon) were found to travel with the ion beam, whereas lighter elements tended to be dispersed off axis. Importantly, however, dispersion of these lighter ions could be eliminated by reducing ion-beam space charge

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.

The Investigation of a 13-mm Torch for Use in Inductively Coupled Plasma-Mass Spectrometry

A 13-mm torch is evaluated for use in inductively coupled plasma-mass spectrometry (ICP-MS). With this system, an analytically useful plasma can be supported at 1.35 kW applied rf power and 9.35 L/min total argon flow. The effect of operating parameters (nebulizer flow rate, rf power, sampling depth, and ion-lens voltages) on analyte ion signals was examined, also. The optimal nebulizer-gas flow rate, sampling depth, and power for the 13-mm torch were found to be comparable to those used for the standard (18-mm) torch. Similar trends were seen between the two systems when these parameters were varied. Under optimal operating conditions, the 13-mm torch was found to produce comparable sensitivities, oxide-ion ratios, and doubly charged ion ratios. The most significant difference exhibited between the two torches was the independence of the doubly charged ion ratio on plasma parameter settings for the 13-mm torch.

Comparison of center-tapped and inverted load-coil geometries for inductively coupled plasma-mass spectrometry

Abstract A non-commercial inductively coupled plasma-mass spectrometry (ICP-MS) instrument is used to compare a center-tapped ICP load-coil geometry with the standard inverted-coil arrangement. This direct comparison on the same ICP-MS unit shows that the load coil exerts only a minor influence on analytical characteristics such as sensitivity, doubly charged ion and oxide-ion ratios, and detection limits. The influence of operating parameters (nebulizer flow rate, sampling depth, generator rf frequency and applied power) on analyte-ion signals and oxide-ion ratios similarly appears to be independent of the load coil. However, the load-coil geometry is found to dictate the particular nebulizer flow rate, sampling depth, and biaspotential setting that are optimal and how these parameters affect doubly charged ion ratios and backgroundion signal magnitudes. Also, there is a greater loss in sensitivity for higher-mass elements with the center-tapped unit.

Selection of solvent load and first-stage pressure to reduce interference effects in inductively coupled plasma-mass spectrometry.

In inductively coupled plasma-mass spectrometry the first-stage pressure and solvent characteristics can strongly influence spectral and nonspectroscopic interference effects. By manipulating the pressure and solvent load, one can regulate the degree of analyte signal suppression observed in the presence of high concentrations (> 10 mM) of concomitants. Importantly, the same operating conditions that eliminate the matrix effects maintain the analytical utility of the system. However, for some interferent-analyte combinations, the identity of the concomitant anion and subsequent pH of the solution determine whether the interference effects can be eliminated entirely. The first-stage pressure does not appear to significantly affect the oxide-ion and doubly charged ion ratios; the solvent characteristics are the dominant factors that dictate these ratios.

Fundamental and Applied Investigations in Plasma-Source Mass Spectrometry for Elemental Analysis

The current status of plasma source-mass spectrometry (PS-MS) is reviewed. An overview of interference effects that exist, alternative plasma sources available, and mass spectrometer interface studies is provided. A discussion of current and future development areas in plasma source mass spectrometry is also included.

Characterization of a 23-mm torch for use in inductively coupled plasma mass spectrometry

A 23-mm-i.d. torch is described and evaluated for use in inductively coupled plasma mass spectrometry. The plasma operates optimally at 1.50 kW forward power and 19.2 L/min total argon flow. The effect of the customary operating parameters (nebulizer flow rate, rf power, sampling depth, and ion-lens voltages) on analyte signals is discussed. Detection limits, oxide-ion ratios, and doubly charged ion ratios have been measured and are compared with those produced by an 18-mm-i.d. low-flow MAK torch. When compared to the conventional torch, the 23-mm system exhibits comparable detection limits for low-mass ions but better detection limits for high-mass ions (Pb and U). Oxide-ion ratios are lower in the larger torch, but doubly charged ion ratios are higher. Because optimal sampling depths in the larger torch are higher, entrained air in the tail flame causes instability and results in increased ArO+ and ArN+ background signals.