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AOAC Official 965.15 Dithiocarbamates in Pesticide ulations Carbon Disulfide

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AOAC Official 965.15 Dithiocarbamates in Pesticide ulations Carbon Disulfide Evolution First Action 1965 Final Action 1966_AOAC.rar,AOAC Official 965.15 Dithiocarbamates in Pesticide ulations Carbon Disulfide

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7.3.09AOAC Official Method 965.15Dithiocarbamatesin Pesticide FormulationsCarbon Disulfide Evolution MethodFirst Action 1965Final Action 1966(Applicableonlytoconcentratesorformulationscontainingferbam,maneb, nabam, zineb, or ziram and free from interfering sub-stances.)A. PrincipleDithiocarbamates decompose on heating in acid medium.Evolved CS2is passed through Pb(CH3COO)2solution traps to re-moveH2SandSO2formedfromproduct impurities.WashedCS2isreacted with methanolic KOH, and xanthate formed is titrated withI2solution.B. ApparatusCarbon disulfide evolution apparatus.See Figure 965.15.Available from Lurex Scientific, No. JE-1000-0000.C. ReagentMethanolic potassium hydroxide.2M. Dissolve 112 g KOHpelletsin500mLanhydrousmethanol,filterthroughcotton,andaddadditional 500 mL anhydrous methanol.D. DeterminationAdd 20 mL 10% Pb(CH3COO)2solution (w/v) to eachPb(CH3COO)2trapandpipet50mL2MmethanolKOHsolutionintomethanolKOH absorber (Figure 965.15). (Absorber must be dry attimeofadditionandkeptat251C.)Add50mLH2SO4(1+4)tore-actionflaskandheatacidtoboiling.Adjustaspirationrateto1bub-ble/s through methanolKOH solution, using stopper in reactionflask.Weigh 5 g test portion (containing 0.10.3 g dithiocarbamates)into small filter paper cone and fold cone to prevent test portion loss.Remove stopper from reaction flask, insert wrapped test portion, andimmediately stopper flask. Adjust air flow if necessary and maintainsteady, moderate boil. Do not let acid solution enter air inlet tube.Some dust formulations react vigorously and require special care toprevent ejection of hot acid. As reaction proceeds, adjust system sothat rates of boiling and aspiration are almost in equilibrium, produc-ingonlyveryslowrateofbubblingthroughmethanolKOHsolution.Continue boiling 1.5 h. Disconnect methanolKOH absorber and 2000 AOAC INTERNATIONALFigure 965.15Carbon disulfide evolution apparatus.食品伙伴网rinsecontentsinto500mLErlenmeyer,usingca250mLH2O.(Tore-move absorber contents, apply slight air pressure to top of absorberand force solution through side arm. Rinse with 4 ca 25 mL portionsH2O, forcing out rinse H2O in same manner with air pressure.)Add 3 drops phenolphthalein, and titrate with 30% CH3COOH(v/v)untilredjustdisappears.Immediatelytitratewith0.1MI2;nearend point, add 5 mL starch indicator solution, 922.03A(f) (see7.1.05), and titrate to faint but definite color change.Determine blank (usually 0.10.2 mL 0.1M I2) by diluting 50 mLmethanolKOH solution with 250 mL H2O, neutralizing with 30%CH3COOH and titrating as above.Calculate as follows:Dithiocarbamate, % = (test solution titration blank)(I2molarity) (equivalent weight dithiocarbamate)/(g test por-tion 10)Equivalent weights (12MW) of zineb, maneb, ziram, nabam, and(13MW) ferbam are 137.87, 132.65, 152.91, 128.18, and 138.82, re-spectively.References: JAOAC 48, 562(19