The effect of gas flow entrainment on the gas sampling, ion sampling, and ion detection processes in inductively coupled plasma mass spectrometry (ICP-MS) has been investigated. Isolated, single droplets of sample from a monodisperse dried microparticulate injector (MDMI) were used in conjunction with time-resolved ICP-MS, photographs of ion cloud movement, and time-gated imaging using a gateable, intensified charge-coupled device (ICCD) detector mounted on an imaging spectrometer. The results indicate that gas flow entrainment into the sampling orifice can have a significant effect on the plasma gas velocities as far as 7 mm from the sampling orifice. The effects are most pronounced within 3 mm of the sampling orifice. The trends in these results are consistent with theoretical calculations. Photographic images show that plasma gas initially as far as 3 mm off axis adopts a curved path into the sampling orifice. Time-resolved emission images of Sr+ ion clouds approaching the sampling orifice demonstrate the entrainment process and significant distortion of the ion cloud as it flows into the sampling orifice. Spatial maps of La+ ICP-MS signals were acquired as a function of distance from the vaporization point and distance from the plasma axis. The results suggest that gas entrainment has a significant effect on the spatial path of ions in the plasma and that accurate radially resolved spatial mapping of plasmas using mass spectrometry may not be possible. The widths of radially resolved La+ ICP-MS signal peaks do not change significantly when ions are sampled 2 mm from the vaporization point compared to 5 mm away. In contrast, ICP-MS signals measured on axis as a function of time clearly show broadening due to diffusion. These observations suggest that some detected ions may have originated from off-axis locations in the plasma.

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The excitation spectra associated with the 7F0↦5D0 transition of Eu+3 has been used to examine the binding sites on cell wall fragments of Datura innoxia. Both native and esterified cell wall fragments were each examined at pH 5 and pH 2 to determine the contributions to metal ion sorption from both the carboxylate and sulfonate functional groups. The excitation spectra have been de-convoluted into the individual groups responsible for metal ion uptake. At least four unique binding sites can be described as being responsible for metal ion uptake. The higher affinity sites involve carboxylates in the binding of Eu+3 in a tridentate (3:1 ligand-to-metal ratio) configuration.

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