RESUMO
In this paper a new method for the silica gel H phase-diffuse reflectance spectrophotometric determination of iron(III) with piperonal fluorine (PIF) has been developed. In the presence of cetyltrimethyl ammonium bromide and in a NH4 Cl-NH3.H2O medium at pH 9.6-10.3, iron(III) reacts with PIF to form a stable blue complex which is absorbed by silica gel H with a diffuse reflectance absorption peak at 640 nm. The calibration curve is linear over the concentration range 0-25 ng of iron(III) in 1 mL. The linear regression equation is AR = 0.022 1c-0.005,5(r = 0.999,7), where c is expressed as ng per 1 mL. The method has high analytical speed and sensitivity. The effect of a number of foreign ions has been studied by carrying out determining of 200 ng.(10 mL)-1 of iron (III), 1 mg K+, Na+, F-, Cl-, NO3-, PO(4)3-, 0.6 mg Ca2+, Mg2+, 35 micrograms Sr2+, 20 micrograms Cr(III), 6 micrograms Mn2+, 4 micrograms Pb2+, 3.5 micrograms Cd2+, 2.5 micrograms Cu2+, Ag+, 1.5 micrograms Cr(VI), 1 microgram Ni2+, 0.75 microgram Zn2+, Sn4+ et al don't interfere with the measurement. The method has been applied to the determination of microamount iron in magnesium oxide with satisfactory results.
