用1B铅笔芯制成聚甲基丙烯酸甲酯包裹的铅笔芯电极。将此电极置于pH 2.20磷酸盐缓冲溶液中,在-1.5~+2.0 V(vs.SCE)电位区间,以0.1 V·s-1扫描速率连续扫描30圈使其活化。试验表明:在pH 4.8的乙酸盐底液中,核黄素在此电极上产生还原峰,其峰电位在-0.300 V(vs.SCE)。其峰电流的导数与核黄素的质量浓度在1.88×10-4~0.376 mg·L-1范围内呈线性关系,其检出限(3S/N)为4.42×10-5mg·L-1,应用此方法测定了维生素B2片剂中核黄素的含量,所得测定值与其标示值相符。在此样品的基础上做加标回收试验,测得回收率在96.5%~111%之间,测定值的相对标准偏差(n=5)为2.5%。

A polymethylmethacrylate enveloped pencil lead electrode was prepared on the base of pencil lead of a 1B pencil, and it was activated by scanning for 30 cycles in the potential range from -1.5 V to +2.0 V (vs.SCE) at a scanning rate of 0.1 V·s-1, in a PBS of pH 2.20. In a base solution of pH 4.8 acetate buffer, a reduction peak at the peak potential of -0.300 V (vs.SCE) given by riboflavin at this electrod was observed, with the derivative of its peak current keeping linear relationship with mass concentration of riboflavin in the range from 1.88×10-4 to 0.376 mg·L-1, and with the detection limit (3S/N) of 4.42×10-5mg·L-1. Riboflavin in vitamin B2 tablets was determined by this method, giving results in conformity to the labelled value. Test for recovery was made by standard addition method, values of recovery were found in the range from 96.5% to 111%. Value of RSD (n=5) found was 2.5%.