Sensitive Determination of Hexavalent Chromium Using a μPAD

Chromium has diverse oxidation states, the charges of +3 and +6 for chromium occur the most commonly within chromium compounds. Trivalent chromium (Cr(III)) is not toxic and is essential for living organisms. On the other hand, hexavalent chromium (Cr(VI)) is known to has the strong ability to oxidize and to be a carcinogen. Therefore, it is important selectively to determine of Cr(VI) for the analysis of chromium due to the difference of toxicity between Cr(III) and Cr(VI). 1, 5-Diphenylcarbazide (DPC) is a reagent which selectively reacts with Cr(VI) to color violet complex. We have developed a simple and sensitive analysis of Cr (VI) using a micro fluidic paper-based analytical device (μPAD) with the DPC colorimetric reaction. The fabrication of μPADs was carried out by melting wax with an oven after the pattern was printed with a wax printer. The detection spots were dropped DPC solution and dried. Then, the sample solution was dropped into the sampling spot and wicked to the detection spots. μPAD was scanned with a scanner, the color intensity for the detection spots was analyzed by an image analysis software. The RGB intensity of the images was analyzed, and the highest sensitivity was obtained when G-intensity was used. The detection limit of this device for the Cr(VI) analysis was 26.2 μg/L, the sensitivity for present method has been enhanced compared to the previous method (30 mg/L).