Study of traces of Au and Ag atoms by resonant laser stepwise ionization spectroscopy

Abstract

New effective stepwise excitation schemes for gold (An) and silver (Ag) atoms are proposed and experimentally studied with different wavelengths: lambda(1) = 267.6 nm, lambda(2) = 294.0 nm and lambda(1) = 267.6 nm, lambda(2) = 306.0 nm for gold and lambda(1) = 328.1 nm, lambda(2) = 282.0 nm and lambda(1) = 328.1 nm, lambda(2) = 272.0 nm for silver. By using these excitation schemes, we also studied the efficiency of resonance ionization. Two types of atomizers, a rod-flame and a graphite furnace, were used for investigations. The analytical potentiality of laser-enhanced ionization (LEI) spectrometry was demonstrated by determining the gold and the silver contents in diluted nitric acid solutions. The maximum ionization signals of An atoms were observed for the principal quantum numbers n = 8 and n = 9. In the case of Ag atoms, the transitions at the wavelengths 272.0 nm and 282.0 nm from 5p(2) P-3/2 states were shown to have two strong auto-ionization states. Also the selective ionization signal in the stepwise excitation was several orders higher than it was in one step excitation. The lower limits of detection for An and Ag were 5 pg/ml and 0.2 pg/ml, respectively, in a graphite furnace. Investigations of highly excited states of An and Ag atoms were also carried out with a laser photo-ionization spectrometer under optimum conditions.