Investigation of probe insertion effects on plasma excitation conditions in direct sample insertion-inductively coupled plasma atomic emission spectrometry
Abstract of thesis entitled
INVESTIGATION OF PROBE INSERTION EFFECTS ON
PLASMA EXCITATION CONDITIONS IN DIRECT SAMPLE
INSERTION-INDUCTIVELY COUPLED PLASMA ATOMIC
CHEUNG WAIKWONG ANDY
for the degree of Doctor of Philosophy
at The University of Hong Kong
in October 2005
Direct sample insertion (DSI) is an alternative sample introduction method for inductively coupled plasma-atomic emission spectrometry (ICPAES). Insertion of a sample probe into the ICP, however, changes the plasma excitation conditions significantly. It has been shown that the excitation temperature of the plasma reduces by 2000 to 3000 K and the electron number density reduces by 2 or 3 orders of magnitude upon sample probe insertion. The weakened plasma excitation conditions could be a limitation of DSI-ICPAES measurements.
In this thesis, the effects of probe insertion position and the size and material of the sample probe on plasma excitation conditions of the ICP were presented.
Testing elements (Fe, Zn and Mg) were introduced into the ICP for excitation temperature and electron number density measurement. Three methods of testing element introduction were used. A steady flow of laser-sampled testing elements was introduced into the ICP via an in-torch capillary or a hollow probe. Testing elements were also vaporized directly from the sample probe. The vertical emission profiles of the testing elements were measured using a charge-coupled device (CCD) imaging spectrometer.
The study shows that the extent of reduction in plasma excitation temperature and electron number density increases with probe insertion position and probe size for all observation position. The probe effects also strongly depend on the relative distance of the observation position to the tip of the probe. The probe effects are strongest near the tip of the probe and are reduced at observation position further away from the tip. The effects of the probe material on the plasma excitation conditions are minor.
The vertical emission profiles of the testing elements are dependent on the excitation and ionization characteristics of the emission lines, but are independent on the original form of the elements. Atomic emission intensity increases quickly from the tip of the probe, reaches the maximum at a few mm above the tip, and reduces quickly at higher position of the plasma. Ionic emission intensity increases slowly and reaches the maximum at approximately 15 mm above the tip of the probe. Signal-to-background ratios (SBR) of the testing elements follow the same pattern. The temporal profiles of emission intensity are also broadened as the probe insertion position increases. Criteria for the optimization of probe size, probe insertion position and observation position were discussed.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:inductively coupled plasma atomic emission spectrometry spectroscopy
Date of Publication:01/01/2005