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AlumInum, berylhum, banum and strontmm also do not react wIth APDC While the APDC·MIBK chelatmg-solvent system can be used satIsfactonly, It IS possIble to expenencedIfficulties (SeeNote9) NOTE 9: CertaIn metal chelates, manganese-APDC In partlCular, are not stable In MIBK and will redIssolve Into the aqueous phase on standIng The extractIOn of other metalsISsensItivetobothshakIngrateandtime AswIthcadmmm,prolongedextractIOn beyond 1 mInute, will reduce the extractIOn efficIency, whereas 3 mInutes of vIgorous shakIng IS reqmred for chrommm Also, when multIple metals are to be determIned eIther larger sample volumes must be extracted or IndIVIdual extractIOns made for each metal beIng determIned The aCId form of APDC-pyrrohdIne dlthIOcarbamlc aCId prepared dIrectly In chloroform as descnbed by Lakanen, [AtomIc AbsorptIOn Newsletter 5, p 17 (1966)], (see 7 7 1) has been found to be most advantageous In thIS procedure the more dense chloroform layer allows for easy cOmbInatIOn of multiple extractIOns whlCh are carned out over a broader pH range favorable to multielement extractIOns PyrrohdIne dlthIOcarbamlc aCId In chloroform IS very stable and may be stored m a brown bottle In the refngerator for months Because chloroform IS used as the solvent, It may not be aspIrated Into the flame The followmg procedure IS suggested 9 2 1 ExtractIOn chloroform procedure wIth pyrrohdIne dlthIOcarbamlc aCId (PDCA) In Transfer 200 ml ofsample Into a 250 ml separatory funnel, add 2 drops bromphenol blue IndlCator solutIOn (7 7 3) and mIX Prepare a blank and sufficIent standards m the same manner and adjust the volume of each to approxImately 200 ml wIth deIOnIzed dlstdled water All of the metals to be determIned may be combIned Into SIngle solutIOns at the appropnate concentratIOn levels ' Adjust the pH by addItIOn of 2N NH40H solutIOn (7 7 2) untd a blue color persIsts Add HCI (774) dropWlse until the blue color Just dIsappears, then add 2 0 ml Hel (7 7 4) m excess The pH at thIS pomt should be 2 3 (The pH adjustment may be made WIth a pH meter .nstead of USIng mdlCator ) Add 5 ml of PDCA-chloroform reagent (7 7 1) and shake vIgorously for 2 mInutes Allow the phases to separate and draIn the chloroform layerIntoa100m1beaker (SeeNOTE10) NOTE 10: If hexavalent chrommm IS to be extracted, the aqueous phase must be readjusted back to a pH of 2 3 after the addItion of PDCA-chloroform and maIntaIned at that pH throughout the extractIOn For multielement extractIOn, the pH may adjusted upward after the chrommm has been extracted 9 2 1 1 9 2 1 2 9 2 1 3 9214 r MET ALS-ISPDF Image | Methods for Chemical Analysis of Water and Wastes
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