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k " ADPL`NDIR Le Page e I of ®XYGENo DISSOLVED Azides Modification of Winkler Method' For Water, Sewage and sea Water Introduction This analysis includes the Duret Method and the Digital Titrator Method. The dissolved oxygen test is one of the most important analyses in determining the quality of natural waters. The effect of oxidation wastes on streams,the suitability of water for fish and other organisms and the progress of self-purification can all be measured or estimated from the dissolved oxygen content, in aerobic sewage treatment units,the minimum objectionable odor potential,maximum treatment efficiency and stabilization of wastewater are dependent on mAntenance of rdequatc dissolved Oxygen.Fraquent dissolved oxygen mcasure- ment is essential for adequate process cont A. The Azide Modification of the Winkler Method is the standard test for dissolved oxygen and is offered with two major improvements.The sodium thiosulfate titrant has been packaged in s Digits!Titrator titration cartridge for easy and precise dispensing.The other test reagents havebeen formulated into dry,premeasured powder pit- low form for increased stability and convenience-The standard APHA reagents in solution form also are avail- able as described in Note E of the dissolved oxygen procedure. An Iodate-lvd'ade Standard Solution, If)mgtL as dissolved Oxygen,is available from Hach for checking the strength of the titrating soluti-)r" - � Sampling and Storage Collect samples in a clean DOD bottle as descriixd in procedure Step 1. if storage is necessary run Steps ater seal at 10 to 20T.. through 4 of the procedure and store in the dark at the temperature of the water source or w Samples preserved in this manner can be held four to eight hours.Begin with procedure Step 5 when running the analysis. f WARNING Some of the chemicals used in this procedure may be hazardous to the health end safery of the uscrifinapproprinfelyhandledoraccidenrallymisused•Pleasemadallwarningsonthere gent labels end rrad the safety section of this manual-Hazardous substances appear in italic type- tacx when they aric used in the tesrand deserve extra carr in handling.Itis alwaysgaad practice to.wear safety glasses when handling chemicals. wash thoroughly if anY contact Ocetus. Follow instructions carefully procedure for Digital Titmtor Method i. Collect a water sample in a clean 30Q-mL glass-stoppered BOD bottle by allowing the sample to over- flow the bottle for two or three minutes.This ensue is thereare ano air bubbles trapped in the bottle. 2. Add the contents of one Manganous Sulfate Powder Pillow and one Alkaline Iodide-AzideReagent E Powder Pillow. 3. Immediately insert the stopper so that no air is trapped in the bottle and invert several times to mix.A 1 flocculent precipitate will form.it will be brownish-orange if dissolved Oxygen is present or white if oxygen is absent. i 4. . Allow the sample to stand until the floc has sallied and leaves the top half of the solution clear.Again in- vert the bottle several times to mix and let stand until the upper half of the solution is Blear.See Note C. T 5. Remove the stopper and add the contents of one Sulfamic Acid Powder Pillow. Replace the stopper, -- beim careful not to trap any air bubbles in the bottle,and invert several times to mix.Thefloc will tits- salve and leave a yellow color if dissolved oxygen is present. 3