Simultaneous preconcentration and speciation of iron(II) and iron(III) in water samples by 2-mercaptobenzimidazole-silica gel sorbent and flow injection analysis system Original Research Article

2-Mercaptobenzimidazole, loaded on silica gel (MBI-SG) was used for preconcentration and speciation of iron(II) and iron(III) in water samples. The speciation is based upon selective retention of iron(III) on MBI-SG sorbent and quantitatively passing iron(II) ions. This type of sorbent was not only capable of separating theses two ions but also could concentrate them. The adsorbed iron(III) on MBI-SG was desorbed from the column by an SCN− solution and transferred to the detection device. The effluent, then, was treated with hydrogen peroxide to oxidize iron(II) into iron(III) and subsequently was pumped through the MBI-SG column. A home-made flow injection system was coupled with a UV–VIS and an atomic absorption spectrometer, simultaneously. This method was applied to four different water samples and sub-ppb detection limit, high accuracy (>99% recovery), good precision (R.S.D.<5%), and good potential for automation were observed.