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METHYLENE BLUE ACTIVE SUBSTANCES (MBAS) Method 425.1 (Co~orimetric) STORET NO. 38260 1 Scope and ApphcatlOn 11 ThIS method IS apphcable to the measurement of methylene blue actIve substances (MBAS) m dnnkmg waters, surface waters, domestIc and mdustnal wastes It IS not apphcable to measurement ofsurfactant-type matena1s m sahne waters 12 It IS not possIble to dIfferentIate between hnear alkyl sulfonate (LAS) and alkyl benzene sulfonate (ABS) or other Isomers of these types of compounds However, LAS has essentlally replaced ABS on the surfactant market so that measurable surfactant matenals WIll probably be LAS type matenals 13 The method IS apphcable over the range of0 025 to 100 mg!l LAS 2 Summary of Method 2 1 The dye, methylene blue, m aqueous solutlOn reacts wIth amomc-type surface actIve matenals to form a blue colored salt The salt IS extractable wIth chloroform and the IntenSIty ofcolor produced IS proportIonal to the concentratlOn ofMBAS 3 Comments 31 Matenals other than man-made surface actIve agents WhIch react With methylene blue are orgamcally bound sulfates, sulfonates, carboxylates, phosphates, phenols, cyanates, thiocyanates and some morganlc Ions such as mtrates and chlondes However, the occurrence of these matenals at Interference levels IS relatIvely rare and WIth the exceptlOn of chlofldes may generally be dIsregarded 32 Chlondes at concentratlOn of about 1000 mg!l show a pOSItIve mterference but the degree of mterference has not been quantIfied For thIS reason the method IS not apphcable to bnne samples 33 Naturally occurnng orgamc matenals that react WIth methylene blue are relatIvely InsIgmficant Except under hIghly unusual CIrcumstances, measurements of MBAS In fimshed waters, surface waters and domestIc sewages may be assumed to be accurate measurements of man-made surface actIve agents 4 PreCISIon and Accuracy 41 On a sample offiltered flver water, spIked WIth 294 mg LAS!hter, 110 analysts obtaIned ameanof298mg!lWIthastandarddeviatlOnof ±O272 42 On a sample oftap water spIked WIth 048 mg LAS/hter, 110 analysts obtaIned a mean of a49 mg!l WIth a standard devIatlOn of ±O 048 43 On a sample of dIstIlled water spIked WIth 0 27 mg LAS!hter, 110 analysts obtamed a mean of0 24 mg!l WIth a standard deVIatIOn of ±O 036 44 AnalytIcal Reference SerVIce, Water Surfactant No 3, Study No 32, (1968) Approved for NPDES Issued 1971 425 1-1PDF Image | Methods for Chemical Analysis of Water and Wastes
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