将铅笔芯电极(PCE)置于含有0.01 mol·L-1亚甲基蓝(MB)、pH 5.0的0.1 mol·L-1磷酸盐缓冲溶液和0.2 mol·L-1氯化钾的混合溶液中,用循环伏安法以100 mV·s-1速率扫描50圈,使亚甲基蓝通过电聚合在PCE表面形成薄膜.由此制得聚亚甲基蓝修饰的铅笔电极(简写作PMB/PCE),在此电极的循环伏安图可见一对氧化还原峰,其峰电位(Ep)随溶液pH值升高而负方面移动,且其Ep与溶液的pH值在pH 1.90~pH 8.52之间呈线性关系.更为准确地说,其线性范围应分为两段,一段从pH 1.90至pH 6.76,另一段从pH 6.76至pH 8.52.应用此方法测定了橙子、菠萝及黄瓜3种样品液汁的酸度,所得的pH值的准确度与精密度均优于用常规的pH计(用玻璃电极作指示电极)或用精密pH试纸所测得的值.

Polymethylene blue modified pencil core electrode (PMB/PCE) was prepared by electropolymerization of methylene blue (MB) onto the surface of PCE through scanning cyclic-voltammetrically for 50 cycles at a rate of 100 mV·s-1 in a solution containing 0.01 mol·L-1 MB in 0.1 mol·L-1 PBS of pH 5.0 and 0.2 mol·L-1 KCl solution.A pair of redox peaks was observed in the cyclic voltammogram under above mentioned condition,and the values of peak potantial (Ep) were shifted negatively as the pH-values of the solution were increased,and linear relationship was kept in the pH range of pH 1.90 to pH 8.52,or more precisely in 2 segments,one from pH 1.90 to pH 6.76 and the other from pH 6.76 to pH 8.52.Acidity of sample juices of orange,pineapple and cucumber were determined cyclic voltammetrically by using PMB/PCE as indicator electrode,platinum wire as opposite electrode and Ag/AgCl electrode as reference electrode.It was shown that more accurate and precise results were obtained by the present method as compared with those found by conventional pH-meter using glass indicator electrode or by the precise pH-paper.