Determination of chemical oxygen demand employed manganese as an environmentally friendly oxidizing reagent by a flow injection method based on microwave digestion and speciation coupled to ICP-OES

A novel flow injection (FI) system for chemical oxygen demand (COD) determination is evaluated. Manganese (VII) is used as oxidant. FI microwave solid phase extraction system by activated carbon (AC) was employed. FI system involves a digestion circuit, placed in a home MW oven, coupled to inductively coupled plasma-optical emission spectrometry. Manganese (II) was determined after the reduction of Mn (VII) and eluted from AC with nitric acid (1% v/v) at pH 4. Doehlert experimental design has been used to speed up the optimization of assisted digestion methods and the optimum values obtained for different experimental variables studied. The method can give a high throughput of about 22 samples per 60 min. Under optimum conditions, the evaluated assisted digestion methods have been successfully applied to several pure organic compounds and real samples. A large linear range of 2.6-850 mg O-2 L-1 with an excellent detection limit of 1.25 mg O-2 L-1 was obtained with a correlation coefficient of 0.998. The interference by high chloride concentration was studied, and values below 3000 mg Cl- ions L-1, is not interfering in the estimation of COD load without any masking agents. COD values for various types of wastewater samples were well correlated with those obtained by standard manual methods. Thus, the FI-MW-SPE method seems to be an interesting and promising alternative to conventional COD digestion methods since it is faster and reduces reagent volume, hazardous emission and external contamination with a good reproducibility and accuracy. (C) 2012 Elsevier B.V. All rights reserved.