Filtern
Dokumenttyp
Sprache
- Englisch (3)
Referierte Publikation
- ja (3)
Schlagworte
- ICP (1)
- Matrix effects (1)
- Microdroplets (1)
Analyte atomization in an inductively coupled argon plasma is studied with spatial and temporal resolution by simultaneous side- and end-on emission spectroscopy. The samples are either introduced as single monodisperse microdroplets of analyte solution or in form of spherical nano- or microparticles with narrow size distributions embedded in microdroplets. While end-on spectroscopy provides quantitative information on the total atomization process during the transport through the ICP of a single injection event, side-on measurements deliver the spatial positions of the processes. It is shown that there are significant spatial shifts of the position of analyte atomization in dependence on injector gas flow, droplet size, analyte mass, and the mass of accompanying elements. These shifts have direct influence on the size of the analyte clouds at a particular position in the ICP, e.g., at the position of the sampler of a mass spectrometer in ICP-MS, and, therefore, on the detection efficiency of this technique. Furthermore, the dynamic processes of analyte ionization as well as element dependent diffusion were studied with spatial and temporal resolution.
End-on inductively coupled plasma optical emission spectrometry (ICP-OES) of the relative mass distributions in ensembles of spherical SiO2 particles with small and large size variations is presented. The particles are introduced into the ICP by injection of monodisperse microdroplets generated from diluted particle suspensions. The spectroscopic signals, taking into account the peak or the integrated intensities of the Si 288.16 nm line, are compared with mass distribution measurements of corresponding SiO2 particle ensembles performed by Scanning Electron Microscopy (SEM). It is found that the relative mass distributions measured by ICP-OES are in good agreement with SEM measurements if the spectroscopic signal to noise ratio is sufficiently large indicating that intensity variations due to different particle trajectories in the ICP are less important than expected.
An inductively coupled plasma (ICP) is analyzed by means of experiments and numerical simulation. Important plasma properties are analyzed, namely, the effective temperature inside the central channel and the mean flow velocity inside the plasma. Furthermore, the effect of torches with different injector diameters is studied by the model. The temperature inside the central channel is determined from the end-on collected line-to-background ratio in dependence of the injector gas flow rates. Within the limits of 3% deviation, the results of the simulation and the experiments are in good agreement in the range of flow rates relevant for the analysis of relatively large droplets, i.e., ~ 50 µm. The deviation increases for higher gas flow rates but stays below 6% for all flow rates studied. The velocity of the gas inside the coil region was determined by side-on analyte emission measurements with single monodisperse droplet introduction and by the analysis of the injector gas path lines in the simulation. In the downstream region significantly higher velocities were found than in the upstream region in both the simulation and the experiment. The quantitative values show good agreement in the downstream region. In the upstream region, deviations were found in the absolute values which can be attributed to the flow conditions in that region and because the methods used for velocity determination are not fully consistent. Eddy structures are found in the simulated flow lines. These affect strongly the way taken by the path lines of the injector gas and they can explain the very long analytical signals found in the experiments at low flow rates. Simulations were performed for different injector diameters in order to find conditions where good analyte transport and optimum signals can be expected. The results clearly show the existence of a transition flow rate which marks the lower limit for effective analyte transport conditions through the plasma. A rule-of-thumb equation was extracted from the results from which the transition flow rate can be estimated for different injector diameters and different injector gas compositions.