Question

LAB: Determination of iron in multivitamin tablets by colorimetry and verification of consistency between two batches of tablets

Briefly describe how you will use this method to determine the relative concentration of different Fe species (ie Fe (II) and Fe (iii) oxidation states in the same solution), for example in lake water to monitor environments oxido- reduction.

Answer 1

This method can be exploited for spectrophotometric determination of the relative concentrations of different Fe species ( Fe (II) and Fe (iii) oxidation states in the same solution).

This can be done in two steps : we can take 2 samples of a given solution ,

1. one sample can be treated in same manner as in case of total iron determination in multivitamin tablet , in this all Fe is forms complex as Fe(II) and we get , Total Fe = Fe (II) + Fe (III)

2. 2nd sample is treated for complex formation without reduction of Fe(III) to Fe (II) by ascorbic acid , in this case both Fe species forms complexes but absorbs at different wavelengths, we determine concentration of Fe (II) in sample by absorbance of Fe(II)-complex at its characteristic wavelength. ( as in 1) , Fe = Fe (II)

Fe (III) = Total Fe - Fe (II)

we can use information from 1 and 2 to  determine the relative concentrations of different Fe species.