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Several operating parameters for single-droplet analysis by inductively coupled plasma‐atomic emission spectrometry were investigated and optimized. Two plasma observation modes, both of which measure the plasma side-on, were compared. In the “whole-vertical” mode, the entire vertical emission pattern of the center portion of the central channel was spatially integrated, whereas in the “lateral” mode emission from a thin horizontal slice of the vertical plasma image was measured. The limits of detection (LOD) as well as measurement precision attainable by these two observation modes were found to be practically identical. However, the lateral mode is preferred because emission is then more insensitive to a small drift in carrier-gas flow than in the vertical mode. Precision was found to degrade at carrier-gas flows that yield maximum sensitivities in both observation modes. As a result, the best precision and lowest LODs cannot be achieved under the same plasma operating conditions and a compromise is needed. In this study, precision was given a higher priority than LOD because each individual droplet is regarded as a new sample in single-droplet analysis and each such sample can be measured only once. For best precision, the observation region should be 3 mm downstream of the atomization site to avoid the adverse local plasma cooling effect of the vaporizing particle. Under optimized conditions, the best precision is about 3–4% and the absolute detection limits for eleven elements (Ag, B, Ca, Cd, Cu, Fe, Mg, Ni, Pb, Sr, and Zn) range from sub-single to hundreds of femtograms, which corresponds to 106 to 109 atoms for single-droplet analysis. In addition, a new synchronization trigger method for droplet analysis was developed. This method is based on Hα emission collected between the first and second lowest turns of the load coil. This trigger signal fires while the droplet is still intact, resides inside the lowest portion of the load coil, and is typically around 1 to 2 ms ahead of the atomization event. Jitter between this trigger signal and analyte emission is typically less than 100 μs, and is precise enough for correct timing for signal acquisition and integration.

A mathematical model for the desolvation of solvent droplets has been used in conjunction with an existing code for simulation of ICP fundamental parameters. The combination has been used for the calculation of droplet histories and desolvation behavior along the central channel of an ICP. Calculations have been performed for droplets of various sizes and under a variety of ICP operating conditions. As central-channel gas flow rate increases, the point of complete desolvation of the droplet shifts upward in the plasma, away from the load coil. This relationship is fairly linear. As forward power increases, the point of complete desolvation moves down in the discharge, closer to the load coil. This is approximately an inverse relationship. Finally, simulation of behavior for a log-normal size distribution of a large number of droplets (10 8 ) shows that the number of surviving droplets falls sigmoidally with height above the load coil. For most nebulizer/spray chamber systems, the desolvation process is complete at a well-defined height in the plasma.

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.

The power delivered to an inductively coupled plasma (ICP) is repetitively switched off and on to add the dimension of time to fundamental studies of the ICP's behavior. Described are time- and space-resolved measurements of emission intensities from argon and calcium that were recorded with two primary objectives. The first is the identification of the means by which energy is transported from the load coil and transferred to the analyte in the normal analytical zone. The second is the identification of regions where and times when the study of non-emitting species will be most productive. The data suggest that analyte excitation depends on species created 1–2 ms earlier and lower in the plasma. Emission data alone are insufficient for identification of the energy carrying species, but they suggest other types of measurements will be most effective during the 200 μs decay period. Spatial shifts in the plasma structure emphasize the need for caution in the interpretation of single-point, time-resolved measurements.

Spatially resolved, radial electron number density (ne) profiles have been measured at rf power settings of 1.00, 1.25, 1.50, 1.75 and 2.00 kW, and vertical heights of 4, 8, 12, 16 and 20 mm above the load coil. These profiles have been condensed and presented as electron density contour plots for each input power. The precision of the method was evaluated by doing ten replicate measurements of electron density. The relative standard deviation varied between 2 and 10 % with the maximum at the plasma centre. Electron density was measured with and without the presence of the easily ionizable element—Cs, and no significant difference was observed.

A vertically movable horizontal slit driven by a computer-controlled stepping motor was placed close to the front of the entrance slit of a monochromator. The axial channel of the plasma being imaged onto the entrance slit, the observation height was scanned by slicing the image of the plasma with the horizontal slit. Excitation and gas temperature profiles were calculated under various operating conditions from emission profiles of Fe I and OH lines, respectively. From the axial emission and temperature profiles, two excitational regions governed by different excitation mechanisms were postulated along the axis of the plasma. In the first region from 0 to 8 mm above the load coil, low-energy lines were predominantly excited and their emission profiles were controlled mainly by the dissociation rate of molecules. In the second region from 10 to 20mm above the load coil, high-energy lines were predominant and volatilization interferences were small.

Spatially resolved, radial electron density ( n e ) profiles were measured at rf power settings of 1.25 and 1.75 kW and vertical heights of 4, 8, 12, 16 and 20 mm above the load coil with and without water vapor in the nebulizer gas. The removal of water vapor from the aerosol gas resulted in a decrease in electron density. The greatest change in n e , a decrease of 1.0 × 10 15 cm −3 , was observed at 4 mm above the load coil in the annular region. The differences in electron density became smaller with increasing height above the load coil. Electron density was also measured with no aerosol gas flow into the plasma. Electron density significantly increased when aerosol gas was eliminated.

Spatially resolved, radical excitation temperature distributions experienced by analyte species injected into the axial channel of a toroidally shaped, inductively coupled argon plasma are presented. Typical axial temperatures experienced by the thermometric species (FeI) ranged from 6500 K to 5500 K in the analytical zone of 15–25 mm above the load coil. A comparison of temperatures calculated with different sets of transition probabilities is also given.