Combination of a smart phone based low-cost portable colorimeter with air-assisted liquid-liquid microextraction for speciation and determination of chromium (III) and (VI)

Abstract

In this study, a simple, cheap and rapid technique has been developed for speciation analysis of chromium in different water samples using air-assisted liquid-liquid microextraction and digital image decomposition into the primary colors Red (R), Green (G) and Blue (B). In the proposed method, Cr(VI) was mixed with 1,5 diphenyle carbazid (DPC) in an HCl medium and then formed an ion pair with sodium dodecyl sulfate (SDS). The obtained ion pair was extracted into 350 µL of chloroform and then digital image of extraction phase was obtained by a smartphone and converted to the RGB-values using a free application. Considering the color of extraction phase, the value of G channel was taken as analytical signal. Total chromium is subjected to a similar extraction procedure after oxidation. Then Cr(III) has been calculated by subtracting.Cr(VI) from the total chromium. The effects of different parameters influencing the extraction efficiency were investigated in detail. Under the optimal conditions, the limit of detection (LOD) and quantitation (LOQ) were 0.9 and 3 µg L−1, respectively. Also the relative standard deviation for five replicate determinations of 100 μg L−1 Cr(VI) was 3.2%. The developed method was validated by recovery experiment and independent analysis by Graphite Furnace Atomic Absorption Spectrometry technique and successfully applied to speciation of Cr(III) and Cr(VI) in environmental water samples.