Determination of lead and tin by stripping voltammetry ... - Metrohm

Application Bulletin 176/4 eDetermination of lead and tin by anodic stripping voltammetryPage 6/65 0STIR 20.06 SWEEP 25.6 U.start -800 mV U.step 4 mVU.end -300 mV Sweep rate 20 mV/s7 0MEAS U.standby mV8 ENDMethod: AB176_1bCALCULATIONmax. 15 lines--------------------------------------------------------------------------------Quantity Formula (R##, C##, A##) Res.unit Sig.dig.------------ ---------------------------------------- -------- --------Sn R1000=MC:Sn #g/L 5Pb R1001=MC:Pb #g/L 5Method 2: Determination of lead and tin withmethylene bluePrincipleTraces of Sn and Pb can be determined in oxalatebuffer in presence of methylene blue. Interferences byCd or Tl can be eliminated by modifying the pH andan intermediate electrolysis procedure.The detection limit of Sn and of Pb is 1 µg/L.ReagentsAll of the used reagents must be of purest qualitypossible (analytical grade or suprapur). Only ultrapurewater should be used.• Hydrochloric acid, suprapur, w(HCl) = 30%• Di-ammonium oxalate monohydrate, puriss. p. a.,CAS 6009-70-7• Ammonium chloride, suprapur, CAS 12125-02-9• Methylene blue, C.I. 52015, CAS 61-73-4• Sn standard stock solution, β(Sn 4+ ) = 1 g/L,commercially available• Pb standard stock solution, β(Pb 2+ ) = 1 g/L,commercially availableReady-to-use solutions:Base electrolytemethylene bluesolutionPb standardsolutionc(oxalate) = 0.14 mol/Lc(Ammoniumchlorid) = 0.17mol/Lc(HCl) = 0.15 mol/LpH = 1.619.2 g ammonium oxalate and9.2 g ammonium chloride aredissolved in ultrapure water.15.8 mL hydrochloric acid areadded. The solution is made upto 500 mL with ultrapure water.β(methylene blue) = 1g/L0.1 g methylene blue are dissolvedin 100 mL ultrapure water.The solution is stable for oneweek.β(Pb 2+ ) = 1 mg/LSn standardsolutionAnalysisβ(Sn 4+ ) = 1 mg/LThe solutions are diluted withc(HCl) = 0.01 mol/L. They arestable for max. 1 week.5 mL (diluted) sample+ 5 mL base electrolyte+ 0.05 mL methylene blue solutionThe pH of the solution should be 1.8.The voltammogram is recorded with the followingparameters:Working electrodeHMDEStirrer speed2000 rpmModeDPdrop size 4Purge time300 sCleaning potential (deposition) -800 mVCleaning time90 sDeposition potential-580 mV(intermediate electrolysis)Deposition timeEquilibration timePulse amplitudeStart potentialEnd potentialVoltage stepVoltage step timeSweep ratePeak potential (Sn)Peak potential (Pb)20 s10 s50 mV-800 mV-250 mV4 mV0.2 s20 mV/s-540 mV-400 mVThe concentration is determined by standard addition.