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42 4 3 44 Copper has also been reported to mterfere, however, copper concentratiOns as high as 10 mg/l had no effect on recovery ofmercury from spiked samples Sea waters, bnnes and mdustnal effluents high m chlondes reqUire additiOnal permanganate (as much as 25 ml) Dunng the OXidation step, chlondes are converted to free chlonne which w111 also absorb radiatiOn of 253 nm Care must be taken to assure that free chlonne IS absent before the mercury IS reduced and swept mto the cell ThiS may be accomphshed by usmg an excess of hydroxylamme sulfate reagent (25 ml) In addition, the dead air space m the BOD bottle must be purged before the additiOn of stannous sulfate Both morgamc and orgamc mercury spikes have been quantitatively recovered from sea water usmg thiS techmque Interference from certam volatl1e orgamc matenals which w111 absorb at thiS wavelength IS also pOSSible A prehmmary run Without reagents should determme If thiS type of mterference IS present (see AppendiX 11 1) 5. Apparatus 51 AtomiC AbsorptiOn Spectrophotometer (See Note 1) Any atomIC absorptiOn umt havmg an open sample presentatIOn area m which to mount the absorptiOn cell IS SUitable Instrument settmgs recommended by the partICular manufacturer should be followed Note 1 Instruments designed speCifically for the measurement of mercury usmg the cold vapor techmque are commercially available and may be substituted for the atomic absorptiOn spectrophotometer 5.2 Mercury Hollow Cathode Lamp Westmghouse WL-22847, argon filled, or eqUivalent 53 Recorder Any multi-range vanable speed recorder that IS compatible With the UV detection system IS SUitable 54 Absorption Cell Standard spectrophotometer cells 10 cm long, havmg quartz end wmdows may be used SUitable cells may be constructed from plexiglass tubmg, 1" 0 D X 4-112" The ends are ground perpendicular to the longltudmal aXIs and quartz wmdows (1" diameter X 1116" thickness) are cemented m place The cell IS strapped to a , burner for support and ahgned m the hght beam by use of two 2" by 2" cards One mch diameter holes are cut m the middle ofeach card, the cards are then placed over each end of the cell The cell IS then posItioned and adjusted vertically and honzontally to give the maximum transmittance 5.5 Air Pump Any penstaltlc pump capable of dehvenng 1 hter of air per mmute may be used AMasterflexpumpWithelectromcspeedcontrolhasbeenfoundtobesatisfactory 56 Flowmeter Capableofmeasunnganairflowof1hterpermmute 57 Aeration Tubmg A straight glass fnt havmg a coarse porosity Tygon tubmg IS used for passage ofthe mercury vapor from the sample bottle to the absorptiOn cell and return 58 Drymg Tube 6" X 3/4" diameter tube contammg 20 g of magnesIUm perchlorate (see Note 2) The apparatus IS assembled as shown m Figure 1 NOTE 2: In place of the magnesIUm perchlorate drymg tube, a small readmg lamp With 60W bulb may be used to prevent condensatiOn of mOisture mSlde the cell The lamp IS posItioned to shme on the absorptiOn cell mamtammg the air temperature m the cell about IOGCaboveambient 245 1-2 II IIIPDF Image | Methods for Chemical Analysis of Water and Wastes
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