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sample aliquot taken for analysIs should be neutralized and aerated before beginning 5. Instrument Parameters (General) 5.1 Drying Time and Temp 30 sec- 125°C 5.2 Ashlng Time and Temp 30 sec- 10000 C 5.3 Atomizing Time and Temp 10 sec-27oooC 5.4 Purge Gas Atmosphere Argon 5.5 Wavelength 367 9nm 5 6 Other operating parameters should be as specified by the particular Instrument manufacturer 7 4 Nltnc ACid, conc Distilled reagent grade or eqUivalent to spectrograde quality 7 5 AcetiC ACid, Glacial ACS reagent grade 7 5 1 AcetiC ACid, 10% (v/v) Dilute 10 mL glacial acetic aCid to 100 mL With deionized distilled water 7 6 AmmOnium HydrOXide, 10% (v/v) Dilute 10 mL conc ammonium hydrOXide, NH40H (analytical reagent grade), to 100 mL With deiOnized distilled water 7 7 Hydrogen PerOXide, 30% ACS reagent grade 7 8 Potassium Dichromate Standard Solution Dissolve 2 8286 grams of dried potassium dichromate, K2Cr207 {analytical reagent grade}, In deionized distIlled water and dilute to 1 liter 1 mL =1 mg Cr (1000 mg/L) 7 9 Trivalent Chromium Working Stock Solution To 50 mL of the potassium dichromate standard solution (7 8) add 1 mL of 30% H202 (77)and1mLconc HN03 (74)and dilute to 100 mL With deIOnized distilled water 1 mL =0 5 mg Cr3+ Prepare fresh monthly or as needed Record the volume of aCid added and adjust the final result to account for the dilution Note Care must be exerCIsed not to take the pH below 3 If the pH IS Inadvertently lowered to < 3, 10% NH40H (7 6) should be used to ialse the pH to above 3 9 2 Pipet a 10 mL aliquot of the adjusted sample Into a centnfuge tube (6 1 2) Add 100jJL of the lead nitrate solution (7 1), stopper the tube, mix the sample and allow to stand for 3 min 6. 6 1 Special Apparatus Glassware 9 4 To prOVide adequate lead sulfate for copreclpltatlon add 100 mL ammonium sulfate solution (7 2), stopper and mix 9 5 Place the stoppered centnfuge tube In the centnfuge, making sure that the tube IS properly counterbalanced Start the centrifuge and slowly Increase the speed to 2000 rpm In small Increments over a penod of 5 min Centrifuge the sam- ple at 2000 rpm for 10 min Note 2 The speed of the centrifuge must be Increased slowly to Insure complete copreclpltatlon 9 6 After centrifuging remove the tube and draw off the supernate uSing the apparatus detailed In Figure 1 As the pasteur pipet IS lowered Into the tube the supernate IS sucked Into the filtering flask With care the supernate can be Withdrawn to Within approximately 0 1 mL above the preCipitate 9 7 To the remaining precipitate add o5 mL conc HN03 (7 4), 100jJL 30% H2 0 2 (7 7) and 100jJL calCium nitrate solution (7 3) Stopper the tube and mix uSing a vortex mixer to disrupt the preCipitate and solubilize the lead chromate Dilute to 10mL, mix and analyze In the same manner as the calibration standard (8 2) 9 8 For the general furnace procedure and calculation, see Furnace Procedure part 9 3 of the AtomiC Absorption Methods section of thiS manual 10 Verification 10 1 For every sample matrix analyzed venflcatlon IS necessary to determine that neither a redUCing condition nor a chemical Interference affecting preCipitation IS present ThiS 6.1 1 Filtering flask, heavy wall, 1 hter capaCIty 6.1.3 Pasteur pIpets, borOSIlicate glass, 6 ~ Inches 6 2 Centrifuge any centnfuge capable of reaching 2000 rpm and acceptmg the centrifuge tubes described In 6 1 2 may be used 6 3 pH Meter a Wide variety of Instruments are commerCially available and sUItable for this work 6 4 Test Tube Mixer any mixer capable of thorough vortex IS acceptable 6.1 2 Centrifuge tubes, heavy duty, oonlcal, graduated, glass stoppered, 10 mL capacity 7. Reagents 7.1 33 1 grams of lead nitrate, Pb(N03}2 (analYtical reagent grade), In cfelonlzed distllled water and dIlute to 100 mL 7.2 AmmoOlum Sulfate Solution Dissolve 2 7 grams of ammonium sulfate, (NH~}2S0~(analytical reagent grade), In deionized distilled water and dilute to 100 mL 7 3 CalCium Nitrate Solution Dissolve 11 8 grams of calcium nitrate, Ca(NO.:J12 4H20 (analYtical reagent grade), in deionized distilled wateranddiluteto100mL 1mL= 20 mg Ca. Lead Nitrate Solution Dissolve 8 Calibration At the time of analYSIS prepare a blank and a series of at least four calibration standards from the Cr3+ working stock (7 9) that Will adequately bracket the sample The normal working range covers a concentration range of 5 to 100 ug Cr/L Add to the blank and each standard 1 mL 30% H202(7 7), 5 mL CONC HNOa (7 4), and 1 mL calCium nitrate solution (73) for each 100 mL of prepared solution before diluting to final volume These calibratIOn standard should be prepared fresh weekly or as needed 8 2 The listed Instrumental conditions (5 ) and the stated calibration concentratIOn range are for a Perkin-Eimer HGA-2100 based on the use of a 20jJL injection, contlnous flow purge gas and non-pyrolytlc graphite The use of Simultaneous background correction IS reqUired for both calibration and sample analYSIS 8 1 9 Procedure Transfer a 50 mL portion of the filtered sample to a 1OOmL Gnffln beakerandadjusttopH35±03by adding 10% acetic aCid dropwlse 9 1 Dec 1982 2185-2 9 3 After the formation of lead 3 chromate, retam the Cr + complex In solution by addition of 0 5 mL glaCial acetic aCid (7 5) Stopper and mixPDF Image | Methods for Chemical Analysis of Water and Wastes
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