The oxygen inductively coupled plasma discharge for spectrochemical analysis

• Main Author: Yang, Pengyuan
• Language: ENG
• Published: ScholarWorks@UMass Amherst 1987
• Subjects: Analytical chemistry
• Online Access: https://scholarworks.umass.edu/dissertations/AAI8805980

An low-power oxygen ICP discharge has been investigated theoretically and experimentally. Temperature and flow fields have been calculated by computer simulations. The electron temperature and density, intensity ratio of ion line to atom line, and excitation temperature have been measured and compared with the LTE values. The analytical features also are evaluated. The low-power oxygen ICP discharge has been converted from a pre-running argon plasma. The torch used in the normal argon plasma is applied without modifications. The whole procedure is simplified to two steps, with a total conversion time of 1 minute. A new computer simulation method developed for an industrial plasma has been modified and applied to the analytical plasma. The two-dimensional electromagnetic field and the swirl force effect have been included in the computation. The oxygen plasma operated at the high frequency and low power now can be simulated at various operating conditions. The electron temperature for the low-power oxygen plasma has been measured and are in good agreement with the one predicted by the computer simulation. The excitation temperature has been calculated from the measurement of Boltzmann distribution of Fe I population levels and are found to be close to the electron temperature. The distribution of electron number density has been measured from the H alpha line width. The experimental results for the ratio of intensities of Ca II to Ca I and of Cd II to Cd I are in good agreement with the ones predicted by a LTE model, which confirms the oxygen plasma is close to LTE. In addition to LTE properties, the charge transfer from oxygen ions has been confirmed as an important excitation mechanism process. The detection limits for thirty eight elements have been measured and are generally 10 times poorer than in an argon plasma, but are still better than in an air or nitrogen plasma. BaO powder sample has been analyzed. A more than 10 times improvement has been observed for the signal to background ratio of Ba II line when compared to those in argon plasma.