Thermoresponsive polymer-mediated extraction for graphite furnace atomic absorption spectrometric determination of trace metals in high purity iron

A thermoresponsive polymer-mediated extraction was designed for the selective separation of traces metal ions from high purity iron solutions. Traces metals were extracted into the coagulum of a thermoresponsive polymer, poly(N-isopropylacrylamide) as their dibenzyldithiocarbamate chelates, while Fe(III) matrix remained in the bulk aqueous solution as its water-soluble tartrate chelate. The coagulum was readily collected from the solution and then dissolved with a small amount of N,N-dimethylformamide for the introduction to a graphite furnace of atomic absorption spectrometer. The use of 0.5 g l−1 poly(N-isopropylacrylamide), 2.0 mM sodium dibenzyldithiocarbamate, and 0.6 M diammonium tartrate (pH 10.7) allowed nearly complete (>99.9%) collection of Co(II), Ni(II), Cu(II), Cd(II), Pb(II), and Bi(III) with reducing Fe(III) concentration from 50 mg ml−1 to 14 ± 1 μg ml−1 being lower than the tolerance limits for the determination of traces of metals. Because of effective elimination of iron matrix, six metals at fractional μg g−1 levels were successfully determined with high reproducibility. The accuracy and precision were evaluated by analyzing certified reference materials of high purity iron.