Construction And Application Of Gallic Acid Molecular Imprinting Sensor

At present,there are some problems in the determination of gallic acid,such as poor sensitivity and expensive instrument.Therefore,it is great significance to establish an economical and efficient method for the determination of gallic acid.Electrochemical detection technique,molecular imprinting technique?MIP?,polypyrrole materials,metal-organic framework materials and nano-materials were combined in this paper.Fe₃O₄@ZIF-67/Au was prepared by the interaction of cobalt ion chelated magnetic beads(Fe₃O₄@Co²⁺)with 2-methylimidazole on gold electrode?Au?.Then,polypyrrole was polymerized on the surface of Fe₃O₄@ZIF-67/Au to construct a molecular imprinted electrochemical sensor?MIP/Fe₃O₄@ZIF-67/Au sensor?for detecting gallic acid.The preparation parameters,detection parameters,properties of the sensor and the feasibility of detection in practical samples were investigated.The main contents of the study are as followed.?1?The peak current value and?i were taken as indexes.The single factor experiments were used to optimize the eluent type,elution time and polymeric electric quantity during the preparation of molecular imprinted polymer membrane.The morphology and peak current of MIP/Fe₃O₄@ZIF-67/Au were characterized by scanning electron microscopy and differential pulse voltammetry.The results showed that the optimum conditions for preparation of molecularly imprinted polymer membrane were that the eluent was anhydrous ethanol and 0.01mol/L NaOH mixed solution?1:1,V:V?,the elution time was 200 min and polymeric electric quantity was2.0×10^-33 C.The surface morphology and peak current of MIP/Fe₃O₄@ZIF-67/Au at each modification stage had their own changes and verified each other which confirmed that the sensor was successfully fabricated,and the MIP/Fe₃O₄@ZIF-67/Au sensor after elution had the ability for detecting gallic acid.?2??i was taken as index,single factor experiments were used to optimize the adsorption time,pH,pulse period and pulse width of MIP/Fe₃O₄@ZIF-67/Au sensor for the detection of gallic acid.The detection limit,selectivity,reproducibility and stability of the method were also investigated.The results showed that the optimal parameters for the detection of gallic acid by this sensor were the adsorption time of90 min,pH=2.0,the pulse duration of 0.3 s and the pulse width of 0.03 s.The detection limit of gallic acid was 0.297 pmol/L and the method had good anti-interference effect on gallic acid structure analogues.The relative standard deviation of 600 pmol/L gallic acid was detected by MIP/Fe₃O₄@ZIF-67/Au sensor was 4.35%.When stored at 4°C for 20 days,the response current of MIP/Fe₃O₄@ZIF-67/Au sensor for 600 pmol/L gallic acid was still 87.97%of the initial value.Compared with other analytical techniques,this method was more suitable for trace determination of gallic acid.?3?MIP/Fe₃O₄@ZIF-67/Au sensor were used to detect gallic acid content in distilled water,mineral water,tap water,black tea and green tea.The results showed that the recovery rate of gallic acid in different water types were 90.8¹13.8%and the recovery rate of gallic acid in black tea and green tea were 89.5¹18.4%and111.3¹16.7%respectively.The relative standard deviations of each experiment were within acceptable range.