The effect of different matrix anions in the solution on the intensity of metal atomic lines was investigated. A significant increase in intensity was found for chloride anions compared with nitrate and sulfate anions. This effect was even greater when the appropriate acids were applied. A further enhancement of the metal line intensities could be observed when HCl was used in the solution phase and simultaneously elemental chlorine was mixed with atmospheric air at levels up to 6-10 vol.%. This double effect was especially high for the Cu, Ni and Pb resonant atomic lines at higher chlorine-to-air ratios in the gas phase, and the W-anode tip was destroyed by chemical burning. The application of volatile organic chlorine compounds (carbon tetrachloride and chloroform) in the gas phase, even without any acidification, also caused an enhancement of the metal line intensities. The experimental results can be attributed to the different rates of the ion-ion (positive metal ion-negative chloride ion) and the positive metal ion-electron recombination processes taking place in the cathode dark space of the discharge plasma, yielding neutral metal atoms for excitation. This study is important for the on-line measurement of heavy metals in liquids.