MAGNETIC FIELD TAILORING OF ELECTRICALLY VAPORIZED THIN FILM PLASMAS FOR ATOMIC EMISSION SPECTROSCOP

An external magnetic field of a few kG is used to alter significantly the radiative properties of atmospheric pressure plasmas generated by the capacitive discharge vaporization of thin Ag films. The magnetic field is generated by the plasma current in a large inductor surrounding the plasma. Peak magnetic field strength of 2.7 kG is obtained with a peak discharge current of 2.7 kA. The magnetic field is oriented normal to the electric field in the plasma. This orientation results in a drift motion of the plasma normal to the plane established by the electric and magnetic field vectors. The drift motion of the plasma is directed toward the plastic substrate on which the Ag film and a powder or solution residue sample are originally located. This increases plasma-sample interaction.;Time integrated, spatially resolved photographic spectra and spatially resolved photoelectric radiation profiles show that with the magnetic field, the continuum background radiation is confined to a relatively narrow region (0.5-1 cm) near the substrate surface. This results in significantly larger analyte line-to-background intensity ratios in the region 1-2 cm above the substrate surface.;Particle-size studies show a reduction in particle-size dependent radiation when a 30 (mu)F, 6 kV, 105 (mu)H discharge is used with a magnetic field. Particle-size independent emission for particles under 30 (mu)m in diameter is observed under these conditions after the second current half-cycle (0.34 ms) of the discharge. Faster vaporization rates of the sample are also evident with the magnetic field.;Delayed integration of radiation techniques are used to generate analytical curves for the direct determination of V, Pb, Cr and Mn in seven NBS solid powder standard reference materials. Excellent results are obtained in the NBS analyses with an average relative error of 10.8% for the 15 determinations. A single set of discharge conditions is used for all analyses. Readily available salts are used for aqueous standard solutions. No matrix matching is required and the only sample pretreatment is grinding to reduce sample particle size to under 30 (mu)m in diameter.