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利用V(Ⅴ)-BrO_3~--铬变酸体系催化动力学方法测定钒已有报道,但该方法对分光光度计要求较高,其样品室需有恒温装置。我们利用草酸根离子对此反应的抑制作用,建立了催化动力学固定时间法,仅用恒温水浴及普通分光光度计等简单设备即可测定水溶液中痕量的钒。本方法快速、简便、灵敏度高。检测下限可达5ng/ml。16ng钒(Ⅴ)10次测定的相对标准偏差为4.4％。分析原理:对于溴酸钾氧化铬变酸的反应,钒(Ⅴ)是有效的催化剂。在溴酸钾过量的条件下,反应对钒(Ⅴ)和铬变酸皆为一级反应,如固定铬变酸的浓度,则反应速度与钒(Ⅴ)的浓度呈线性关系。因此,通过测定反应后生成的铬变酸氧化产物的浓度即可求得钒的浓度。
Vanadium has been reported for its catalytic kinetics using the V (Ⅴ) -BrO_3-chromic acid system. However, this method requires a high level of spectrophotometer, and the sample chamber needs a thermostat. We use oxalate ions to inhibit this reaction and set up a catalytic kinetic fixed time method. The trace amounts of vanadium in aqueous solution can be determined only by simple equipment such as constant temperature water bath and ordinary spectrophotometer. The method is fast, easy and sensitive. Detection limit of up to 5ng / ml. The relative standard deviation of 16 ng vanadium (V) 10 determinations was 4.4%. Analysis principle: For the reaction of potassium bromate chromic acid, vanadium (V) is an effective catalyst. Under the condition of excess potassium bromate, the reaction is a first-order reaction for both vanadium (Ⅴ) and chromium (Ⅴ). For example, when the concentration of chromium is fixed, the reaction rate has a linear relationship with the concentration of vanadium (Ⅴ). Therefore, the concentration of vanadium can be determined by measuring the concentration of chromic acid oxidation product formed after the reaction.