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What wavelength for reading COD test? (Read 245 times)

remember0505 YaBB Newbies Offline I love Water and Wastewater.com Posts: 24 Ho Chi Minh City Gender: Company or Organization: VITTEP	What wavelength for reading COD test? Jul 22^nd, 2011, 12:57am Hi everybody! I'm testing for COD by Standard Method 5220D. I'm using HACH DR890 to measure the absorbance but it's not support in 600nm, it's only support in 610nm. Can i measure the absorbance of sample in 610nm? Excuse for my english skill!! Thanks for help!
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Re: What wavelength for reading COD test?
Reply #1 - Jul 22^nd, 2011, 9:44am

The method says that you should use 600. Now, I've run different methods with a slightly different wavelength and been able to get good results. I would try it at 610 and see if you can get acceptable QC. If it passes and anyone ever asks why you do 610 instead of 600, tell them you had to optimize the wavelength for your instrument's performance.

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Re: What wavelength for reading COD test?
Reply #2 - Jul 22^nd, 2011, 11:33am

The DR890 has four, fixed wavelengths (420/520/560/610 nm). The program you enter (17 for COD, High range and high range+) selects the proper wavelength (in this case, 610), and the internal curve is used to determine what conc.

You can always verify with standards to be sure that a 100 mg/L reads as 100 mg/L (or whatever conc matters to you).

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