化学需氧量在线自动监测仪示值误差的检定

介绍化学需氧量(COD)在线自动监测仪示值误差的检定方法及注意事项。选取基准试剂邻苯二甲酸氢钾,依次配制零点溶液和质量浓度分别为50,150,500 mg/L的COD标准物质溶液,用于检定COD maxⅡ型在线监测仪的示值误差。直接配制溶液为100 mg/L的COD标准溶液,与相同浓度的标准物质溶液GBW(E)082219进行比较,结果符合检定规程JJG 1012–2006的要求。检定结果表明:以重铬酸钾为氧化剂时,邻苯二甲酸氢钾的COD氧化值呈线性关系,可直接配制100 mg/L的COD标准溶液;检定COD maxⅡ型在线监测仪,每次需要的标准溶液体积为100 m L,综合考虑,进行示值误差检定时,每种浓度至少配制500 m L。作为还原性标准物质用于检定仪器示值误差,邻苯二甲酸氢钾可能无法准确反映水体中有机物的真实还原情况,具有一定的局限性。

Verification of Indication Error of On-line Automatic Determinator of Chemical Oxygen Demand

The method and attentions for verifation of on-line automatic determinator of chemical oxygen demand (COD) were introduced. Potassium hydrogen phthalate was selected to prepared zero solution and standard solution.Some standard solutions with 50, 150 and 500 mg/L mass concentrations were used to calibrate indication error of monitoring instruments on-line of COD max Ⅱ type. Compared with standard material solution GBW(E) 082219, the result of laboratory prepared standard solution (100 mg/L) conformed to the requirements of the regulations JJG 1012-2006. It indicated that by the verification results the oxidation value of potassium hydrogen phthalate had a linear relationship and it could be used to prepare 100 mg/L standard solution directly; 100 mL volume should be needed each time and 500 mL should be prepared each level for the indication error verification. As a reducing standard material to verify the indication error of COD on-line automatic determinator, potassium hydrogen phthalate showed limitations for not precisely reflecting the reduction degree of organic compounds in water.