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7. 6 8 Workmg Mercury SolutlOn Make succeSSIve dilutlOns of the stock mercury solutlOn to obtam a workmg standard contammg 0 1 ug per ml ThIS workmg standard and the dl1utlOns of the stock mercury solutlOn should be prepared fresh dally ACIdIty of the workmg standard should be mamtamed at 015% mtnc aCId ThIS aCId should be added to the flask as needed before the addItion ofthe ahquot CalibratlOn 8 Procedure 71 Transfer 0, 05, 10, 20, 50 and 100 ml ahquots ofthe workmg mercury SolutIon contammg0to 10 ugofmercurytoasenesof300mlBODbottles AddenoughdIstIlled water to each bottle to make a total volume of 100 ml MIX thoroughly and add 5 ml of conc sulfunc aCId (6 1) and 2 5 ml of conc mtnc aCId (6 2) to each bottle Add 15 mlof KMn04 (6 5) solutlOn to each bottle and allow to stand at least 15 mmutes Add 8 mlof potassmm persulfate (6 6) to each bottle and heat for 2 ho~r~m a water bath mamtmed at 95°C Cool and add 6 ml of sodmm ch1onde-hydroxyl~me sulfate SolutIon (64) to reduce the excess permanganate When the SolutIon has been decolonzed walt 30 seconds, add 5 ml of the stannous sulfate solutlOn (63) and ImmedIately attach the bottle to the aeratlOn apparatus fOrming a closed system At thIS pomt the sample IS allowed to stand qUietly WIthout manual agitatiOn The clrculatmg pump, WhICh has prevIously been adjusted to a rate of 1 hter per mmute, IS allowed to run contmuously (See Note 4) The absorbance WIll mcrease and reach maXlffium wlthm 30 seconds As soon as the recorder pen levels off, approXlffiately 1 mmute, open the bypass valve and contmue the aeratlOnuntlltheabsorbancereturnstoItSmmlmumvalue(seeNote5) Closethebypass valve, remove the stopper and fnt from the BOD bottle and contmue the aeration Proceed WIth the standards and construct a standard curve by plottmg peak heIght versus mIcrograms ofmercury NOTE 4: An open system where the mercury vapor IS passed through the absorptlOn cell only once may be used mstead ofthe closed system ' NOTE 5: Because ofthe tOXiC nature ofmercury"vapor precautlOn must be taken to aVOid ItS mhalatlOn Therefore, a bypass has been mcluded m the system to eIther vent the mercury vapor mto an exhaust hood or pass the vapor through some absorbmg medIa, such as a) equal volumes of0 1M KMn04 and 10% H2S04 b) 025% lOdme m a 3% KI solutlOn A specIally treated charcoal that wlll adsorb mercury vapor IS also aval1able from Bamebeyand Cheney, E 8th Ave and N CassIdy St , Columbus, OhlO 43219, Cat #580-13 or #580-22 8 1 Transfer 100 ml, or an ahquot dlluted to 100 ml, contammg not more than 10 ug of mercury, to a 300 ml BOD bottle Add 5 ml of sulfunc aCId (6 1) and 25 ml of conc mtnc aCId (62) mlxmg after each addItion Add 15 ml of potassmm permanganate solution (6 5) to each sample bottle For sewage samples additlOnal permanganate may be reqUired Shake and add addItIonal portlOns of potassmm permanganate SolutIon, If nece~sary, untIl the purple color persIsts for at least 15 mmutes Add 8 ml ofpotassmm persulfate (6 6) to each bottle and heat for 2 hours m a water bath at 95°C Cool and add 6 245 1-4PDF Image | Methods for Chemical Analysis of Water and Wastes
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