Significant sensitivity improvement of alternating current driven-liquid discharge by using formic acid medium for optical determination of elements

A method has been developed to improve the performance of alternating-current electrolyte atmospheric liquid discharge (ac-EALD) optical emission spectrometry for the determination of elements. Significant enhancement of emission intensity was achieved by adding organic substance into the nitric acid electrolyte solutions. Under the optimized conditions, 3% (v/v) formic acid in nitric acid (pH 1.0) produced 13 times enhancement for Ag and 7% (v/v) formic acid resulted in 17 times enhancement for Cd. The emission of Pb was even enhanced 78 times in the presence of 3% formic acid. In addition, the signal stability was also improved compared with that in the absence of organic substances. Repeatability was 0.8% for 0.1 mg L−1 Ag, 0.7% for 0.2 mg L−1 Cd and 2.6% for 1 mg L−1 Pb standard solutions (n=5). The limits of detection of Ag, Cd and Pb were 1, 17 and 45 μg L−1, respectively. The accuracy of the method was demonstrated by determination of elements in simulated natural water samples (GBW(E)080402 and GBW(E)080399).