The Quality Control Index on the Dichromate Method for the Analysis of COD in Water

On the basis of a large number of monitoring data from many laboratories nationwidely,we analyzed the quality control index of the COD,and compared with the QC index in GB /T 11914-1989 and ISO 6060.The purpose of which was to provide the QC reference and QC index for the people in the monitoring area.Studies indicate that the within-laboratory relative standard deviation control limit of standard samples was less than 3.5%,that of actual samples wan less than 5.5%.The between-laboratory standard deviation control limit ranges beween 3.0 and 6.0 mg /L,RSD′ can be ranged beween 3% and 10% according to the concentration and the data qulity objectives.The relative error of the standard samples was about 10%,at high concentration level,it can be limited in range of 20%,at low concentration,of 5%.The correspounding recovery rates was less than 98%～110%.