Paper-based Analytical Device (PAD) for the Determination of Borax, Salicylic Acid, Nitrite, and Nitrate by Colorimetric Methods

Abstract

Borax, salicylic acid, nitrite, and nitrate have been used as food additives during processing for preserving, coloring, and stabilizing food. These four chemical food additives impact consumer health, e.g., liver cancer and gastric cancer. To maintain the high quality of food and to comply with food safety, a paper-based analytical device (PAD) coupled with a colorimetric method is proposed to simultaneously determine these four chemical food additives in this work. The Griess reaction can be used for the determination of nitrite, and nitrate was reduced to nitrite on the PAD in the section with a hydrophilic channel coated with zinc dust prior to detection by the Griess reaction. Borax and salicylic acid were determined using the complexation reactions with curcumin and FeCl₃, respectively. This work presents the development of colorimetric methods on a PAD for the simultaneous determination of borax, salicylic acid, nitrite and nitrate in food samples. Limits of detection were (mg/L) 10 for borax, 35 for salicylic acid and 0.4 for nitrite and nitrate. Our PAD with a colorimetric method was also used for the determination of borax, salicylic acid, nitrite and nitrate in real food samples. Our detection limits were 3−5 times lower than those of commercial test kits, and the results from the real food samples were not statistically significantly different from those obtained via UV-Vis spectrophotometry at the 95% confidence level (t-test paired samples). Our proposed PAD can rapidly determine four chemical food additives in food with a high sensitivity and is an instrument-free technique.