DOE Method Ra-04-RC

 In the FIA-CL hyphenated method, a wide COD concentration of 4–4000 mg L− 1 with detection limit of 2 mg L− 1 was observed which took only 1.5 min for complete analysis. Cation ion-exchange column was adopted on the sampling system to remove the interference of excess MnO4− with the luminol CL system.26 However, the oxidation efficiency observed by this method was very low. To solve this shortcoming, a flow injection-microwave solid phase extraction (FI-MW-SPE) methodology was adopted in which COD of the sample was determined by ICP-OES.31 High throughput of 18 h− 1 and detection limit of 0.94 mg L− 1 were obtained in linear range of 2.78–850 mg L− 1.

A systematic representation of the instrumentation set up for FIA based ICP-OES system has been clearly shown in Fig. 4. Using this method, no chloride interference was observed below 3000 mg L− 1. However, the method involved K2Cr2O7 as oxidizing agent and thus the problem of environmental pollution existed. To overcome this, a FIA method based on microwave digestion was employed where manganese was employed as oxidant in place of K2Cr2O7.32