SIMULTANEOUS SPECTROPHOTOMETRIC MEASUREMENT OF FE(II) AND FE(III) IN ATMOSPHERIC WATER

A new analytical method employing di-2-pyridyl ketone benzoylhydrazone (DPKBH) as a colorimetric chelating agent for the simultaneous determination of iron(II) and iron(III) in cloudwater has been developed. A spectrophotometric detection limit of 4 nM for both Fe(III) and Fe(II) with a linear response from 4 nM to 0.1-mu-M was established for samples extracted with CHCl3-H2O. DPKBH chelation without CHCl3 extraction showed a linear response from 0.1 to 30-mu-M. The molar extinction coefficients of the Fe(II)-bis(DPKBH) (epsilon-2) and Fe(III)-bis(DPKBH) (epsilon-1) complexes are epsilon-1 and epsilon-2 = 3.6 x 10(4) L mol-1 cm-1 at 370 nm and epsilon-2 = 1.1 x 10(4) L mol-1 cm-1 at 660 nm. Analytical interference studies on the possible changes in the oxidation state of iron with S(IV), oxalate, and other potential electron donors have also been carried out. This analytical method has been used to determine iron(II) and iron(III) simultaneously in cloudwater samples collected within the Los Angeles basin airshed. The concentration of Fe(II) varied from 0.3 to 5-mu-M, and the concentration of Fe(III) varied from 0.6 to 1.4-mu-M during several stratus cloud events.