Comparison of three optimized digestion methods for rapid determination of chemical oxygen demand: Closed microwaves, open microwaves and ultrasound irradiation
Claudia E. Dominib, Montserrat Hidalgoa, Frank Markenc, Antonio Canalsa,∗ a Departamento de Qu´ımica Anal´ıtica, Nutrición y Bromatolog´ıa, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain b Departamento de Qu´ımica, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bah´ıa Blanca, Argentina c Department of Chemistry, University of Bath, Bath BA2 7AY , UK
Received 21 October 2005; received in revised form 10 January 2006; accepted 10 January 2006
摘要：
Abstract
In the present work, experimental design was used for the fast optimization of three kinds of sample digestion procedures with the final aim of obtaining the COD value of wastewater samples. The digestion methods evaluated were “closed microwave-assisted” (CMWD), “open microwave-assisted” (OMWD) and “ultrasound-assisted” (USD). Classical digestion was used as reference method. The optimum values for the different variables studied in each method were: 90 psi pressure, 475W power and 4min irradiation time (CMWD); 150 ◦C temperature and 4 min irradiation time (OMWD); 90% of maximum nominal power (180W), 0.9 s(s −1)cycles and 1 min irradiation time (USD). In all cases, interference concentration that produces a deviation of 10% in COD values is 13.4, 23.4, 21.1 and 2819 mg/L for S 2−, Fe2+,NO2− and Cl−, respectively. Under optimum conditions, the proposed digestion methods have been successfully applied, with the exception of pyridine, to several pure organ compounds and COD recoveries for 10 real wastewater samples were ranged between 88 and 104% of the values obtained with the classical (op reflux) method used as reference, with R.S.D. lower than 4% in most cases. Thus, the use of ultrasound energy for COD determination seems be an interesting and promising alternative to conventional open reflux and microwave-assisted digestion methods used for the same purpose sin the instrumentation is simpler, cheaper and safer and the digestion step faster than the ones used for the same purpose.
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