| Summary: | 碩士 === 正修科技大學 === 化工與材料工程研究所 === 98 === The closed reflux colorimetric method, which can run with different analysis conditions targeting diverse the chemical oxygen demand (COD) concentration range, can result in accurate determination of COD. Moreover, by contrast with the closed reflux titrimetric method, the COD value from the closed reflux colorimetric method has good recovery.
The method used in Taiwan area for testing is the closed reflux potassium dichromate titration method. However, the samples and digestion solutions for titration are more costly, and the EPA, APHA and HACH methods all use the reactant six price chromium or the resultant three price chromium to digest the extinction under the different wave length. Thus, the colorimetric method would become the major means of determining the COD in Taiwan on coming days.
This paper is primarily to study how the differences and disturbance between the closed reflux colorimetric and titrimetric methods affect the colorimetric analysis. Also, by refer to the closed reflux potassium dichromate titration method, HACH and APHA 5220D, it is to compare the dissimilarities between the result from the colorimetric and titrimetric methods and to show that how the differences of wavelengths, optical path lengths and concentrations of potassium dichromate solution influence the colorimetric analysis.
By the findings, it shows that when the COD concentration is in between 20 to 500 mg/L , the best measurements comes with 0.03475 M potassium dichromate solution, the wavelength 600 nm, and light path 5 cm. Furthermore, if COD concentration is in the range of 10 to 200 mg/L, it is better to use 0.008333 M potassium dichromate solution, the wavelength 420 nm and light path 1 cm. Also, if COD concentration is in between 2 to 50 mg/L, the best results are to use 0.002083 M potassium dichromate solution, wavelength 350 nm, and light path 1 cm. If there is Cr6+ interference, to avoid impacts of the Cr6+ on the analysis is better to use the optical wavelength of 600 nm diameter 5 cm.
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