Effect of excess sodium on the excitation of potassium in an air-acetylene flame: a steady state kinetic model which takes into account collisional excitation

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The effects of excess Na on the ionization and excitation of K in an air-acetylene flame were studied using absorbance signal and emission signal ratios, A′/A and E′/E respectively, as probes, where A′ and E′ are the line absorbance and line emission readings in the presence of excess Na interferent, and unprimed quantities represent readings in the absence of the interferent. An emission signal enhancement which increases exponentially as the ratio of interferent to analyte increases (up to about 2000), was observed irrespective of whether measurements were made from the primary or secondary reaction zones of the flame, while a similar line absorbance signal enhancement was observed only when measurements were made from the primary reaction zone. For both line emission and line absorbance, the maximum enhancements observed are in excess of those predicted on the basis of complete suppression of ionization of analyte atoms as a result of the increased partial pressure of electrons. A steady state kinetic model is presented, which takes into account radiative recombination collisional excitation of K+ ions and collisional charge transfer between the heavy particles, and whose predictions are consistent with the observed interference effects.