Titer determination in potentiometry - Metrohm

Application Bulletin 206/4 eTiter determination in potentiometryOf interest to:General analytical laboratoriesA L 1SummaryThis Bulletin provides an overview of the potentiometrictiter determination in common volumetric solutions.Many publications only describe methods with colorindicators. However, the titration conditions chosen forthe titer determination should resemble those used forthe actual analysis as closely as possible.The tables below contain suitable titrimetric standardsubstances and electrodes for selected titrants as wellas additional information. Following this, a procedurefor titer determinations is described.Instruments and accessoriesVarious instruments or combinations of instrumentscan be used:• pH meter und Dosimat for manual titrations• Titrando, Titrino or Titroprocessor with Dosimats orDosinos for automatic recording and evaluation ofthe titration curves and calculation of the results• Titrators as listed above, combined with a samplechangerThe instruments for automatic titrations offer the possibilityof transmitting the data to a PC using the VESUVor TiNet Metrodata software.Titrimetric standard substancesTitrimetric standard substances have the followingcharacteristic features: Their content remains virtuallyunchanged, they have a defined, high degree of purity,they can be dried and they can be directly traced backto standard reference materials (e.g. from NIST =National Institute of Standards and Technology, USA).Some examples of such recommended titrimetric standardsubstances or secondary standards are:• Fluka No. 11099, arsenic trioxide• Merck No. 102400, potassium hydrogen phthalate• Fluka No. 60357, potassium hydrogen phthalate• Merck No. 102408, tris(hydroxymethyl)-aminomethane• Fluka No. 93440, tris(hydroxymethyl)-aminomethane• Merck No. 102406, sodium chloride• Fluka No. 71387, sodium chloride• Merck No. 102407, sodium oxalate• Fluka No. 71804, sodium oxalate• Fluka No. 60350, potassium hydrogen diiodate• Merck No. 102403, potassium dichromate• Merck No. 102401, benzoic acid• Fluka No. 21067, calcium carbonate• Riedel-de Haën No. 34849, HYDRANAL WaterStandard• Riedel-de Haën No. 34803, sodium tartrate dihydrateRemarksThe weight of titrimetric standard substance dependson the concentration of the titrant and the buret volumeused.For accuracy reasons, the sample weight must not betoo small. A sample weight >100 mg normally yieldsgood analytical results. However, the minimum weightvaries considerably, depending on the substance, thebalance used and the required accuracy.In order to increase the measuring accuracy, it may bea good idea to prepare a stock solution instead ofweighing the titrimetric standard substance directly intothe titration vessel.Literature• G. Jander, K. F. JahrMassanalyse, Theorie und Praxis der Titrationenmit chemischen und physikalischen IndikationenWalter de Gruyter & Co., 2003ISBN 3-11-017098-1• Metrohm Monograph No. 8.015.5003Electrodes in potentiometryMetrohm Ltd., 2001• Metrohm Monograph No. 8.016.5003Practical aspects of modern titrationMetrohm Ltd., 2001• Various Metrohm Application Bulletins• LaborpraxisBirkhäuser, 1996ISBN 3-7643-2528-3• Merck «Spektrum», Sonderheft Titration und Elektrochemie• HYDRANAL-Praktikum, Wasserreagenzien nachEugen Scholz für die Karl-Fischer-TitrationRiedel-de Haën AG, 1996

Application Bulletin 206/4 eTiter determination in potentiometryPage 2/4Electrodes and titrimetric standard substances for determiningthe titer of different titrantsTable 1: Acid-base titrations (acidimetry, alkalimetry)Complexometric/chelatometric titrationsTitrant Titrimetric standard Electrode RemarksAqueous acidsHCl, H 2 SO 4Aqueous basesNaOHPerchloric acid HClO 4in glacial acetic acidTrifluoromethanesulfonicacid CF 3 SO 3 Hin glacial acetic acidTrifluoromethanesulfonicacid CF 3 SO 3 Hin isopropanolTetrabutylammoniumhydroxide in isopropanolAlcoholic KOHCyclohexylamineC 6 H 11 NH 2 in methanolEDTA (Komplexon III,Titriplex III or IdranalIII)Tris(hydroxymethyl)-aminomethane(CH 2 OH) 3 CNH 2 (TRIS)(105 °C)Potassium hydrogenphthalate C 8 H 5 KO 4(105 °C)Potassium hydrogenphthalate C 8 H 5 KO 4 orTRIS(105 °C)Potassium hydrogenphthalate C 8 H 5 KO 4 orTRIS(105 °C)Potassium hydrogenphthalate C 8 H 5 KO 4 orTRIS(105 °C)Benzoic acidC 6 H 5 COOHBenzoic acidC 6 H 5 COOHBenzoic acidC 6 H 5 COOHCalcium carbonateCaCO 3(105 °C)Combined pH electrode,e.g. 6.0259.100Combined pH electrode,e.g. 6.0259.100Solvent: waterSolvent: water6.0229.100 Solvotrode Solvent: glacial acetic acidReference electrolyte: c(LiCl) = 2 mol/Lin ethanol (6.2312.010)6.0229.100 Solvotrode Solvent: glacial acetic acidReference electrolyte: c(LiCl) = 2 mol/Lin ethanol (6.2312.010)6.0229.100 Solvotrode Solvent: glacial acetic acidReference electrolyte: c(LiCl) = 2 mol/Lin ethanol (6.2312.010)6.0229.100 Solvotrode Solvent: isopropanolReference electrolyte: c(TEABr) =0.4 mol/L in ethylene glycol(6.2320.000)6.0229.100 Solvotrode Solvent: ethanolReference electrolyte: c(TEABr) =0.4 mol/L in ethylene glycol(6.2320.000)6.0229.100 Solvotrode Solvent: methanolReference electrolyte: c(TEABr) =0.4 mol/L in ethylene glycol(6.2320.000)6.0504.100 calcium ISEor6.0502.140 copper ISE;6.0726.107 referenceelectrode (filled withc(KCl) = 3 mol/L)Suspend CaCO 3 in water, dissolve inHCl and add buffer pH = 10.0(NH 3 /NH 4 OH).For titrations with the Cu ISE, add1 mL c(Cu-EDTA) = 0.05 mol/L to thesample solution (see also Metrohm ABNo. 101).The indicated electrodes are meant as a suggestion. It is often also possible to use other electrodes or electrodesystems.

Application Bulletin 206/4 eTiter determination in potentiometryPage 3/4Table. 2:Precipitation titrations (argentometry)Redox titrations (cerimetry, iodometry, permanganometry, ferrometry, Karl Fischer titration)Titrant Titrimetric standard Electrode RemarksSilver nitrate AgNO 3Lanthanum nitrateLa(NO 3 ) 3Cerium(IV) in H 2 SO 4 orHClO 4Sodium chloride NaCl(110 °C)Sodium fluoride NaF(110 °C)Arsenic trioxide As 2 O 3(105 °C)Iodine solution KI 3 Arsenic trioxide As 2 O 3(105 °C)Potassium permanganateKMnO 4Sodium thiosulfateNa 2 S 2 O 3Iron(II) solution(NH 4 ) 2 Fe(SO 4 ) 2Sodium oxalateNa 2 C 2 O 4(105 °C)Potassium hydrogendiiodate KH(IO 3 ) 2(100 °C)Potassium dichromateK 2 Cr 2 O 7(105 °C)6.0450.100 combinedAg ring electrode (referenceelectrolyte: KNO 3saturated) or6.0430.100 Ag Titrode6.0502.150 fluoride ISE;6.0726.107 referenceelectrode (filled withc(KCl) = 3 mol/L)6.0451.100 combined Ptring electrode or6.0431.100 Pt Titrode6.0451.100 combined Ptring electrode or6.0431.100 Pt Titrode6.0451.100 combined Ptring electrode or6.0452.100 combinedAu ring electrode6.0451.100 combined Ptring electrode or6.0431.100 Pt Titrode6.0452.100 combinedAu ring electrodeSodium nitrite NaNO 2 Sulfanilic acid 6.0452.100 combinedAu ring electrodeKarl Fischer reagentSodium tartrate dihydrateC 4 H 4 Na 2 O 6 x2 H 2 O orwater standards inampoules (Riedel-deHaën)6.0338.100 polarizeddouble Pt electrodeDissolve NaCl in 40 mL water, thenadd 2 mL c(HNO 3 ) = 2 mol/L and possibly2 mL 0.2% polyvinyl alcohol solution.(Dissolve polyvinyl alcohol (Merck No.114266) in warm water.)Dissolve NaF in 50 mL water, add10 mL acetate buffer pH = 6.0 andtitrate slowly (see also Metrohm ABNo. 82).Dissolve As 2 O 3 in 10 mL c(NaOH) =1 mol/L, then add 6 mL c(H 2 SO 4 ) =1 mol/L and 2 g NaHCO 3 (see alsoMetrohm AB No. 52).Dissolve As 2 O 3 in 10 mL c(NaOH) =1 mol/L, then add 6 mL c(H 2 SO 4 ) =1 mol/L and 2 g NaHCO 3 .Dissolve Na 2 C 2 O 4 in 40 mL water, thenadd 5 mL concentrated H 2 SO 4 and 1 gMnSO 4 .Stock solution: Dissolve KH(IO 3 ) 2 inwater and make up to 100 mL; use10 mL of this solution, dilute with40 mL water, then add 1 g KI and 4 mLc(HCl) = 1 mol/L.Dissolve K 2 Cr 2 O 7 in 40 mL water, thenadd 3 mL concentrated H 2 SO 4 .Dissolve sulfanilic acid in 50 mL water,add 30 mL w(HBr) = 20% and titrateimmediately using the MET mode(0.10 mL, 25 s).Fill methanol or KF solvent into thetitration vessel and condition. As soonas a steady drift is attained, add thestandard and titrate with the KF reagent.The titer is specified in mg H 2 O / mLKF reagent (documentation availablefrom Riedel-de Haën or Merck).The indicated electrodes are meant as a suggestion. It is often also possible to use other electrodes or electrodesystems.

Application Bulletin 206/4 eTiter determination in potentiometryPage 4/4Example of a procedure for titer determinations using the799 GPT TitrinoSummaryDetermination of the titer of c(HCl) = 0.1 mol/L usingthe 799 GPT Titrino.The titration is carried out in the DET or MET mode.Tris(hydroxymethyl)-aminomethane is used as titrimetricstandard substance.Instruments and accessories• 799 GPT Titrino• 2.728.0040 Magnetic Stirrer• 6.3026.220 Exchange Unit 20 mL• 6.0259.100 Unitrode (reference electrolyte: c(KCl)= 3 mol/L)• 6.2104.020 electrode cableReagents• Tris(hydroxymethyl)-aminomethane (TRIS) (titrimetricstandard substance), Merck No. 102408 orFluka No. 93440• Distilled water (free from carbonate)AnalysisThe TRIS is dried in a flat bowl for 2 h at 105 °C, thenallowed to cool down in a desiccator and stored there.Using an analytical balance, approx. 0.15 g of the driedTRIS is weighed exactly into a 100 mL beaker. Afteraddition of 40 mL carbonate-free water, the solution isstirred until the titrimetric standard substance hasdissolved, then titration is performed using the followingparameters:Parameters MET:Titration parametersV step0.10 mLdos.ratemax. mL/minsignal drift50 mV/minstart V:rel.faktor 50Stop conditionsstop V:rel.stop V 120CalculationTiter = C00 / (C01 * C02 * EP1)C00 = weight of TRIS in mgC01 = 121.14 (molar mass of TRIS in g/mol)C02 = 0.1 (concentration of the titrant in mol/L)EP1 = titrant consumption in mLRemarksThe titer determination is carried out five times.Using the Titrino’s statistics function, the mean valueas well as the absolute and relative standard deviationcan be calculated.The mean value can be automatically stored as commonvariable (C3X). This makes it possible to directlyuse the current titer in other titration methods.Parameters DET:Titration parametersmeas.pt.density 4min.incr. 10.0 µLsignal drift50 mV/minstart V:rel.faktor 50Stop conditionsstop V:rel.stop V 120