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Simple Chip Electrophoresis Titration of Neutralization Boundary with EDTA Photocatalysis for Distance-Based Sensing of Melamine in Dairy Products

Li, Wen-Lin, Kong, Fan-Zhi, Zhang, Qiang, Liu, Wei-Wen, Kong, Hao, Liu, Xiao-Ping, Khan, Muhammad-Idrees, Wahid, Amir, Saud, Shah, Xiao, Hua, Cao, Cheng-Xi, Fan, Liu-Yin
Analytical chemistry 2018 v.90 no.11 pp. 6710-6717
EDTA (chelating agent), anodes, color, electric field, electrophoresis, hydrogen peroxide, infant formulas, malachite green, melamine, milk, neutralization, photocatalysis, protein content, titration, ultraviolet radiation
Melamine was sometimes adulterated to dairy products for false protein content increase in developing countries. However, a portable sensor has not been developed for on-spot determination of melamine in dairy products yet. Herein, a distance-based sensor was advanced for the quantification of melamine in dairy products based on chip electrophoretic titration (ET) of moving neutralization boundary (NB) and EDTA photocatalysis. In the chip sensor, EDTA, H₂O₂, and leucomalachite green (LMG) were added in the anode well. Under UV light, EDTA photocatalyzes H₂O₂ and colorless LMG as H₂O and color malachite green (MG) with one positive charge. When applying an electric field, the MG in the anode well migrated into the channel and was neutralized with the base in the channel, resulting in colorless MG-OH and NB. If the melamine-content dairy sample was added into the EDTA-H₂O₂-LMG system, H₂O₂ reacts with melamine, leading to the decrease of MG. Thus, the higher the melamine content in dairy products, the shorter the distance of NB migration under the given time, implying a distance-based sensor of melamine. A series of experiments manifested the validity of ET-NB sensor for detection of melamine. Moreover, the results revealed the numerous merits of ET-NB sensor, such as good selectivity, high sensitivity (LOD down to 0.20 μM for milk and 0.10 μM for infant formula vs the FDA safety limits of 20 μM for milk and 8.0 μM for infant formula), good repeatability and recoveries (87–108% for milk, 90–107% for formula). Particularly, the cell phone-like sensor was portable, simple (no any pretreatment), rapid (within 15 min), as well as low cost, to evaluate the quality of dairy products. The developed sensor has great potential in on-spot detection of melamine in dairy products as well as other analytes, at which we are testing in our lab.