A CONTINUOUS-FLOW COLD VAPOR PROCEDURE FOR MERCURY DETERMINATION BY ATOMIC-EMISSION USING THE REVERSE FLOW-INJECTION APPROACH

An experimental set-up for on-line Hg2+ reduction and determination wa s devised using the reverse flow injection analysis (r-FIA) concept an d the cold vapour (CV) technique, injecting an acidic Sn2+ solution in to the mercury sample line. The elemental mercury generated is separat ed from the reacting mixture by a 100 mi min(-1) helium stream, which passes through a gas-liquid separator connected to a permeation cell. This gas stream is used as the plasma medium. The permeated Hg-o is th en concentrated on a 0.3 g gold foil placed inside a quartz tube conne cted to an 11 W He de discharge plasma chamber. The mercury retained o n the gold surface is released by resistive heating and the emission i ntensity is observed at the 253.7 nm mercury line. For an injection cy cle of 30 s, the calibration graphs are linear up to 50 ng mi(-1) (P = 0.999). An injection frequency of 120 h(-1) is achieved, with negligi ble carry-over. The calculated relative standard deviation of the tran sient peaks is 1.6%. Higher sensitivities can be achieved using longer injection cycles. Samples of Human Hair Certified Reference Material were used to determine the accuracy of the method.