|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1994 : ¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1993 : ¥1,200,000 (Direct Cost : ¥1,200,000)
A high power (1.5 kW,2.45 GHz) atmospheric pressure helium microwave-induced plasma for trace elemnt analysis was produced using a Okamoto cavity (J.Anal.At.Spectrom., 7 (1991) 283-289) operated in a surface wave mode. The fundamental analytical features of the plasma (annular-shaped) ware examined by measuring the emission and mass intensities.
The cavity, nonresonant and with no cooling, consists of two parts. One section is a reduced flat rectangular waveguide (thickness : 6.4 mm, width : 109.2 mm). The other section is a mode transfer which consists of an inner conductor and an outer cylindrical conductor terminated by a front plate. The distance between the front plate and the front edge of the inner conductor, gap, is 5 to 10 mm. The surface wave is excited in the gap.
Spatial profiles of the emission spectra for helium obtained from 200 to 850 nm. Emissions from the helium plasma were He I (587.6 nm, 23.0 eV), He I (388.9 nm, 23.0 eV) and He I (667.8 nm, 23.1 eV) et al. The domina
nt peak was He I (587.6 nm) Weak background peaks obtained for OH (306.4 nm, 4.1 eV) and O I (777.6 nm, 10.7 eV).
Gas sample (100 ppm) ; argon (Ar, ionization potential : 15.8 eV) or nitrogen (N_2,15.5 eV) introduced into the helium plasma and Ar I (811.5 nm) or N I (746.8nm) emission could be detected. The plasma is a sesitive ionization source.
Solution sample (Fe : 1000 ppm) was introduced into the plasma through the inner tube using an ultra sonic nebulizer without a desolvation system (laboratory built). Using a pneumatic nebulizer of an Ar ICP,the plasma became unstable.
The Fe I excitation temperatue was obtained from the Boltzmann plot of emission intensities vesus the energy of the upper state in the transition. The excitation temperature of 5500 K was obtained and electron density of 10^<14>/cm^3 was calculated at the microwave power of 1kW.These values show that the plasma is the most useful excitation and/or ionization source for trace element analysis.
More details of this work and its application for mass spectrometry are currently being investigated in our laboratory and willbe published in the near feature. Less