A simple homemade light emitting diode based photometer for chromium speciation

A simple spectrophotometric method utilizing a homemade light emitting diode (LED) based photometer is developed for chromium (VI) and total chromium determination in water samples. The photometer is composed of an LED (white color) as light source and a programmable light-to-frequency converter (three arrays of photodiodes each with a red, green or blue filter) as a detector. The chromium speciation is based on the complex formation reaction of Cr(VI) with 1,5-diphenylcarbazide. Considering the maximum absorption wavelength of the complex, the determination was performed using green filter detector. Prior to the total chromium determination, Cr(III) was oxidized to Cr(VI) with Ce(IV). Cr(III) concentration was calculated from the difference between total Cr and Cr(VI) concentrations. Under the optimum conditions, the calibration graph was linear in 10-200 μg L−1 chromium concentration range. The relative standard deviation (n = 5) and the limit of detection was calculated to be 2.45 and 2.99 μg L−1 respectively. The proposed method was successfully applied to chromium speciation in spiked water samples.