Simple and green method for direct quantification of hypochlorite in household bleach with membraneless gas-separation microfluidic paper-based analytical device.

This work presents development of a microfluidic paper-based analytical device (µPAD) for direct determination of hypochlorite in household bleach. The recent design of a membraneless gas-separation microfluidic paper-based analytical device (MBL-GS µPAD) was employed to fabricate the hypochlorite-µPAD. Chlorine gas is generated in the µPAD via acidification of an aliquot of sample loaded on to the donor reservoir located at the bottom layer of the μPAD. The liberated chlorine gas diffuses through the air space to oxidize iodide ion previously impregnated in the acceptor reservoir at the top layer of the μPAD, leading to formation of the brown color of the tri-iodide ions. Digital image of the brown zone was captured at exactly 5 min after loading the acid. Image J program is used for analysis of the image for quantification of the hypochlorite in unit of g Cl2 L-1. It was found that employing a relatively large volume of the air space (ca. 270 µL) direct analysis of the high concentration of hypochlorite in the bleach was achieved without prior dilution. The method thus provides a linear working range of 25-100 g Cl2 L-1, which is suitable for most commercial household products. The calibration line has a coefficient of determination of 0.999. The precision of measurements is 0.96% RSD and 0.30% RSD at 30 g Cl2 L-1 and 80 g Cl2 L-1 (n = 10), respectively. Using the paired t-test (P = 0.05, n = 8), the method agreed well with the iodometric titration method. Our μPAD for hypochlorite is portable and cost-effective. The method is also "green" since there is a significant reduction in use of reagents compared to other conventional methods.