Determination of Trace Amount of Lead in Paint by Differential Potentiometric Stripping Analysis

The paint sample in a porcelain crucible was first dried in an oven at 105 ℃ to expel organic solvents,then charred by heating on a hot plate and finally ignited in a muffle furnace at 475-500 ℃ for 1 h.The residue was dissolved in dil.HNO3,and used for the differential potentiometric stripping analysis.Lead ion in the sample solution (HNO3 medium of pH 0.5,containing 1 mol·L-1 KNO3) was reduced and amalgamated at the Hg-film-rotary glassy carbon disk electrode at the potential of -1.10 V (vs.SCE) for 40 s.Lead ion was then stripped from the working electrode by the action of oxidant and the differential stripping potential curve in the potential range of -0.10--0.90 V was recorded and the stripping potential peak of Pb2+ was observed at -0.46 V (vs.SCE).Content of lead in the sample was found from a working curve perpared in the same way with standard Pb2+ solution.Linear relationship between values of the peak height and mass concentration of Pb2+ was obtained in the range of 4-500 μg·L-1,with its detection limit (3S/N) of 1 μg·L-1.