A highly sensitive spectrophotometric method has been developed for the determination of trace amounts of BPO based on the oxidation of I- to I3- by BPO and the further reaction of I3- with Methylene Blue to form the ion-association complex in phosphoric acid solution. In the AES,the association was transparent blue-purple. The λmax of the absorption spectrum is at 530nm against reagent blank. It was discovered that the absolute value of the λmax is proportional to the BPO concentration. Beer's law was obeyed in the range of 2.0 × 10-4 ～ 8.0 × 10.3 mg· mL-1. The apparent molar absorption coefficient was ε530 = 1.82 × 104 L · mol-1· cm-1. The BPO detection limit by this method was 1.72 × 10-5mg · mL-1. The spike recoveries were between 92.0％ ～ 101％ ,and the RSD were between 1.75％ ～ 3.56％. The method has been applied to the determination of in wheat flour with satisfactory results.%在磷酸介质中,过氧化苯甲酰(BPO)氧化I<'->离子形成I<'-><,3>络阴离子,I<'-><,3>络阴离子进一步与亚甲基蓝形成离子缔合物,在烷基聚氧乙烯醚硫酸钠(AES)中,缔合物呈清亮的蓝紫色溶液,以试剂空白为参比,最大吸收波长位于530nm,吸光度A与过氧化苯甲酰浓度呈线性关系,BPO含量在2.0×10<'-4>～8.0×10<'-3>mg·mL<'-1>服从比耳定律,表观摩尔吸光系数ε<,530>=1.82×10<'4>L·mol<'-1>·cm<'-1>,方法的检出限为1.72×10<'-5>mg·mL<'-1>,加标回收率为92.0%～101%,RSD为1.75%～3.56%.该方法用于面粉中BPO测定,结果令人满意.
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