An environmentally friendly microfluidic paper-based analytical device for simultaneous colorimetric detection of nitrite and nitrate in food products

This study develops an environmentally friendly microfluidic paper-based analytical device (mu PAD) that uses beeswax as a new hydrophobic material for simultaneous measurement of nitrate and nitrite in food products. Screen-printing is used to apply a beeswax emulsion to filter paper to form a hydrophobic barrier that permeates portions of the paper and thereby defining hydrophilic areas. This mu PAD is simple and quick to fabricate, and the device's reproducibility and stability are both high. Functionality of the new mu PAD was optimized for simultaneous colorimetric determination of nitrite and nitrate in food products. The completed device is able to determine both nitrite and nitrate with respective detection limits of 0.1 and 0.4 mg L-1. The respective RSD values for nitrite and nitrate were 1.8-2.9% and 1.2-2.2% (inter-day precision), and 2.1-3.1% and 1.5-2.2% (infra-day precision). The mu PAD was tested for determination of nitrite and nitrate in various food products, and when the results were compared with spectrophotometric results using a paired t-test, there were no significant differences between the two methods at the 95% confidence level. The new beeswax based mu PAD is fast, easy, and inexpensive to fabricate and use, and it represents a useful option for green chemical analysis.