Improvement of analytical performance of liquid cathode glow discharge for the determination of bismuth using formic acid as a matrix modifier

The bismuth in natural water samples and drugs was successfully determined by liquid cathode glow discharge (LCGD) with formic acid as a matrix modifier. It was found that adding formic acid (3%, V/V ) could enhance the emission intensity of Bi over 23-fold. The possible signal enhancement mechanism was discussed. The Cu 2+ , Cl − , Br − and I −   ions seriously interfered with the analysis of bismuth, and the interferences from Cl – , Br – and I – ions were effectively eliminated with the addition of formic acid. After adding 3% formic acid, the sensitivity of Bi was improved above 51-fold, limit of detection (LOD) was arrived at 0.092 mg L −1   which enhanced by 9.0-fold, and the energy consumption was as low as 40 W. The relative standard deviation (RSD, n  = 11) of 2 mg L −1 Bi was reduced from 7.2% without formic acid to 1.8% with adding formic acid. The measured results of Bi in natural water samples by the proposed method were in agreement well with the spiked values, and the satisfactory recoveries between 106% and 113% were obtained. There was no significant different of Bi in drug samples by the proposed method with the verified values obtained by ICP-AES at the 95% confidence level. All results suggested that determination of Bi by LCGD with formic acid possesses   merits   of   low LOD and power consumption, high sensitivity and stability, and good   precision   and   accuracy.