COMPLEXOMETRIC TITRATIONS Introduction The complete applications package At Radiometer Analytical, we put applications first. When you order one of our new gen- eration of titration workstations with a dedicated application package, you have every- thing you need to get started right away: electrodes, specific accessories, standards, maintenance solutions and, of course, methods and application notes. Application booklets Complexometric titrations are generally run in order to determine divalent cations. The most important appli- cations are the titration of calcium and magnesium for example for water hardness and the determination of nickel, zinc, copper and cobalt for the plating industry. Certain modifications may be needed to take into account the composition of specific baths or standards in force in certain industries. The equivalence point was and still is frequently deter- mined using a colorimetric method but ion specific electrodes can also be used as measuring electrodes. In addition to dedicated application booklets, Radiometer Analytical also produces tech- nique-based applications. Ask your local representative for the following booklets: Technique Part No. Acid-base titrations D41T009 Precipitation titrations D41T010 Redox titrations D41T012 Dedicated Part No. Food and beverage analysis D41T004 Plating bath analysis D41T005 Water and environmental analysis D41T006 Chemical industries D41T007 Our Applications Laboratory is continually developing new applications. For the latest updates visit us at www .titr ation.com.
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COMPLEXOMETRIC TITRATIONSIntroduction
The complete applications package
At Radiometer Analytical, we put applications first. When you order one of our new gen-eration of titration workstations with a dedicated application package, you have every-thing you need to get started right away: electrodes, specific accessories, standards,maintenance solutions and, of course, methods and application notes.
Application booklets
Complexometric titrations are generally run in order todetermine divalent cations. The most important appli-cations are the titration of calcium and magnesium forexample for water hardness and the determination ofnickel, zinc, copper and cobalt for the plating industry.Certain modifications may be needed to take intoaccount the composition of specific baths or standardsin force in certain industries.The equivalence point was and still is frequently deter-mined using a colorimetric method but ion specificelectrodes can also be used as measuring electrodes.
In addition to dedicated application booklets, Radiometer Analytical also produces tech-nique-based applications. Ask your local representative for the following booklets:
Inflection Point Titration ManagerOperational Qualification
Introduction
The operational qualification pro-cedure demonstrates that an in-strument runs according to theoperational specifications in theselected environment. For a titra-tion manager using automaticinflection point determination, thisoperation can consist of two steps:
- Calibration and checking of a pHmeasurement electrode system,
- Titration of anhydrous sodiumcarbonate standard using a com-mercial standard solution of HCl.
Principle
The reaction has 2 steps corre-sponding to 2 different inflectionpoints:
Na2CO
3 + HCl � NaHCO
3 + NaCl
NaHCO3 + HCl � CO
2 + H
2O + NaCl
The operational qualification takesinto account the second equiva-lence point (close to pH 4.00)
corresponding to the completeneutralisation of sodium carbonate.
The Titration Manager settingsallow the complete titration curveto be seen.
ResultsResults by: cumulateNumber of result: 1Acceptation criteria: YES
Result 1Result unit: %Molar weight: 105.99Reaction: 1 smp + 2 titrCalculate with IP: 2Minimum value: 99Maximum value: 101
Procedure
Electrode calibration andcheckingIf the electrode is new, condition itby immersion in distilled water forat least 1 hour.Connect the pHC2011-8 electrodeand the T201 Temperature SensorUsing the above-mentioned set-tings, RUN an electrode calibra-tion with 2 or more cycles.At the end of the last cycle, cali-bration results should be acceptedEnsure that the temperature of thestandards does not differ by morethan 2°C.
Operation qualification in con-tinuous IPFit the burette of the titration man-ager with HCl 0.1 M as titrant andinstall the titrant
Preparation of Na2CO3As indicated, dry approximately5 g of anhydrous sodium carbon-ate in an oven for 4 hours at250°C. Let it cool to room tem-perature in a desiccator with P
2O
5or another humidity adsorber.
Notes
To determine the necessaryamount of sodium carbonate
With a 25 ml burette capacity
Weigh exactly approximately85-90 mg of Na
2CO
3
This weight corresponds to
1.6-1.8 meq or 16-18 ml of HCl0.1M. Use a maximum volumeclose to 20/22 ml
With a 10 ml burette capacity
Weigh exactly approximately 40 mgof Na
2CO
3. Use a maximum vol-
ume of 10 ml
With a 5 ml burette capacityWeigh exactly approximately 20 mgof Na
2CO
3. Use a maximum vol-
ume of 5 ml
Dissolve the weighed sodium car-bonate quantitatively in the titra-tion beaker with 50 to 80 ml offreshly distilled water.
Immerse the electrode and thedelivery tip in the solution.
Using the above-mentioned set-tings, run a titration on 3 differenttests or replicates. Results shouldbe accepted between 99 and 101%.
Inflection Point Titration Manager Operational Qualification
Calculations are programmed togive a result according to the de-livered titrant volume at the inflec-tion point situated in the accept-ance range 2.80-6.00 pH
Dynamic IP Titrationsettings
This application note can be usedwith incremental addition of titrant(Dynamic IP)
These settings were tested with a10 ml burette. The others settingsare unchanged.
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Determination of Hardness in Water(ISO 6059 and Standard methods for water 18th edition 2.36 2340C)
Introduction
Hardness of water measures thesum of calcium and magnesiumions present in the water. Theabove-mentioned standard laysdown a titration with EDTA atpH 10.00, using a NH
4Cl /NH
4OH
buffer and a colorimetric detectionof the equivalent point.This application note also usesEDTA titration with a potentio-metric determination of theequivalent point by means of aCalcium ion-selective electrode.Instead of the NH
4Cl /NH
4OH
buffer, we use a mixture of TRISand acetylacetone. This buffersolution allows separation betweenCalcium and Magnesium when aCalcium selective electrode isused as measuring electrode.
Principle
The titrant EDTA reacts with Ca2+
or Mg2+ according to the reaction
Me2+ + H2Y2- MeY + 2H+
Where Me2+ represents Ca2+ or Mg2+
and H2Y2- the di-sodium salt of EDTA
1 mole of EDTA corresponds to1 mole of Ca2+ or Mg2+
The EDTA concentration is 0.02 mol/lThe results are generally expressedas mg/l of CaCO
Results: (see notes)Results by: cumulateNumber of results: 2
Result 1Result unit: mmol/lReaction: 1 smp + 1 titrCalculate with IP: 1
Result 2Result unit: mmol/lReaction: 1 smp + 1 titrCalculate with IP: 2
Procedure
This procedure is suitable for sur-face waters, tap water and drinkingwaters.
Prepare and fill the ISE25Ca Ion-Selective Electrode as indicated inthe operating instructions and storeit in CaCl2 for one hour prior to thefirst use.
Install electrodes and titrant
Pipette the necessary amount ofwater (generally 50 or 100 ml)
Add 20 ml of the buffer solution
Dip electrodes and delivery tip inthe beaker
Run the titration.
Results
Depending on the ratio betweenconcentration of Ca2+ and Mg2+,the titration curve can show one ortwo inflection points.
For one inflection pointIt corresponds to the cumulate
(Ca2+ + Mg2+) or Ca2+ if there is noMg2+ in the water or if the ratioCa2+/Mg2+ between relative con-centrations of these 2 elements istoo high.For two inflection pointsThe first one corresponds to Ca2+
The difference between the firstand the second corresponds toMg2+
The total volume delivered to thesecond equivalent point correspondsto the cumulate (Ca2+ + Mg2+)
Results are generally expressedin mmol/l or mg/l of CaCO3 forthe cumulate (Ca2+ + Mg2+)
R (mmol/l) = V(titr) * C(titr) / V(smp)
R (mg/l CaCO3) = V(titr) * C(titr) * 100 / V(smp)
- V(titr) = Total volume of titrantused in ml
- C(titr) = Concentration of titrant inmmol/l
- V(smp) = Sample volume in ml
- 100 = molecular weight of CaCO3
For 5 determinations on a min-eral waterMean: 3.25 mmol/l
or 325 mg/l CaCO3
Standard deviation: 0.03 mmol/lRel standard deviation: 0.9%
Working range
For 100 ml of sample and a 20 mlburette volume, a titrant volumebetween 1 and 18 ml correspondsto a working range between 0.2and 3.6 mmol/l or 20 and 360 mg/lof CaCO
3 (see above formulas).
Notes
Note regarding the inflectionpoints ordinates
The above-mentioned values cor-respond to the curve ordinates
Determination of Hardness in Water (ISO 6059 and Standard methods for water 18th edition 2.36 2340C)
generally observed for normal tapwater
For the first inflection point (Cal-cium determination), the inflectionpoint is often close to 80/90 mVand for the second (Magnesiumdetermination), it is close to 15/30 mV
Note regarding the result
Result expressed in mg/l ofCaCO3The above-mentioned settingsallow a result in line with thestandard (total hardness expressedin mmol/l) whether the titrationcurve presents one or two inflec-tion points.
If a result expressed in mg/l ofCaCO
3 is needed, use the follow-
ing settings.
Result unit: mg/lMolar weight: 100Reaction: 1 smp + 1 titr
Results expressed separately inmg/l of Ca2+ and Mg2+ and totalhardnessIf the titration curve presents 2inflection points, the first pointcorresponds to the Calcium andthe second to Magnesium.The results can then be modifiedas follows:
Results by: Difference
Result 1Result unit: mg/lMolar weight: 40.1
(molar weight of Ca)Reaction: 1 smp + 1 titrCalculate with IP: 1
Result 2Result unit: mg/lMolar weight: 24.31
(molar weight of Mg)Reaction: 1 smp + 1 titrCalculate with IP: 2
Note regarding titrant calibrationIf necessary, the EDTA solutioncan be calibrated using 0.01 mol/lCa2+ solution. To calculate the ti-trant concentration, enter the Ca2+
standard concentration in mol/land ask for a result in mol/l with areaction corresponding to 1 smp +1 Titr.
Note regarding Calcium ion-selective electrode maintenancePrepare and use the Calcium ion-selective electrode according tothe operating instructions.
During experiments, store theelectrode in a 0.01 mol/l Ca2+ solu-tion.
For long-term storage, empty theelectrode and store it in its box.
Determination of Hardness in Water (ISO 6059 and Standard methods for water 18th edition 2.36 2340C)
Curve
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Nickel in Nickel Plating Solutions(EDTA Titration)
Introduction
Nickel is commonly used as plat-ing in surface treatment or prepa-ration industries. In some cases,especially for bright plating, thebath is a mixture of boric acid andnickel salt. It is possible to deter-mine boric acid and nickel contentwith an acid-base titration (seenote TTEP01.07PLA), but as ageneral rule, nickel determinationis performed using NiEDTA com-plex formation.A typical nickel concentration innickel plating baths is around50-80 g/l of but some baths havegreater concentrations (e.g. 400 g/l).The molar weight of nickel is58.71 g/mole.
Principle
A two-step back titration is used.First step:
Addition of an excess of EDTAthat reacts with Ni2+ formingNiEDTA complex, 1 mole of EDTAreacting with 1 mole of Ni2+ ionaccording to
Ni2+ + H2Y2- NiY + 2H+
Second step:Titration of the excess EDTA witha copper solution according to
Cu2+ + H2Y2- CuY + 2H+
The two reactions must take placein buffered media (for example apH around 4.5 with acetic buffersolution). The measuring electrodeis a Cu2+ selective electrode.
REF201 Red Rod ReferenceElectrode (part no. E21M001)
EDTA solution 0.10 mol/l
The molecular weight of Na2EDTAis 372.24 g/mol.Dissolve 37.224 of Na2EDTA in1000 ml of water using a volumetricflask.This solution is also commerciallyavailable.
Sodium acetate buffer solution
Dissolve 85 g of sodium acetate(CH3COONa) in water, add 60 mlof glacial acetic acid and dilute to1000 ml with distilled water. Thissolution contains approximately1 mole of CH3COOH and 1 moleof CH3COONa per litre.
Titrant: 0.1 mol/l Cu2+ solution:dissolve 24.968 g of CuSO4, 5H2Oin 1000 ml of distilled water usinga volumetric flask.Note that it is possible to use an-other copper salt (Cu(NO3)2 forexample).
Molar weight: 58.71(for a result expressed in g/l of Ni2+)Excess: 1 smp + 1 excReaction: 1 Exc + 1 Titr
Procedure
Connect the ISE25Cu electrode tothe E1 electrode input by meansof the CL114 cable
Connect the REF201 electrode tothe reference electrode input
Fill the titration burette with the0.1 mole/l copper solution
Sample preparationAs nickel concentration can covera wide range, it is important toensure the sample solution con-tains an excess of EDTA beforetitration.
Nickel in Nickel Plating Solutions (EDTA Titration)
This table takes into account con-centrations of 0.1 mol/l for EDTAand Copper solution.To simplify the table, the molarweight of Ni is taken as 60 g/mol(true value 58.71 g/mol).Other figures may be specified inlaboratory regulations.
Add 10 ml of acetate buffer solu-tion and the necessary amount ofEDTA solution to the samplealiquot.Depending on the composition ofthe bath, the volume of the acetatebuffer solution may need to beincreased.If necessary, add distilled waterStart method by pressing the RUNkey.
Results
Generally expressed in g/l ofNickel (MW = 58.71 g/mol)The titration is a back titration ofexcess EDTA using Cu2+ as titrantAs indicated before, 1 Ni2+ and1 Cu2+ react with 1 mole of EDTA,then the result is
CNi =(Vexc * Cexc – Vtitr * Ctitr) * 58.71 / Vsmp
Vexc = Volume of EDTA added in mlCexc = Concentration of the EDTAsolution in mol/lVtitr = Volume of titrant (Cu2+ solu-tion) used for titration in mlCtitr = Concentration of the titrantin mol/l
Ni conc. Sample vol. Total dil. Vol. Aliquot EDTA added Titrant vol.g/l ml ml ml ml ml
60 10 200 10 10 5
120 10 200 10 20 10
240 5 200 10 20 10
480 5 200 5 20 10
Vsmp = Sample volume in mlpresent in the titration beaker58.71 = Molar weight of Nickel
For results in g/lWith the settings indicated above,the Titration Manager gives a resultaccording to the above formulataking into account the sampledilution.
Three determinations on thesame bathNickelMean: 53.5 g/l nickelStandard deviation:
0.70 g/l boric acidRelative standard deviation: 1.3%
A Nickel/boric acid bath is used inthis application.
Notes
ElectrodesTo avoid reference electrode con-tamination, it is recommended touse a REF251 double junctionreference electrode (part no.E21M001) instead of the REF201reference electrode (part no.E21M009).Do not leave the ISE25Cu selec-tive electrode in a solution contain-ing excess EDTA for too long.When the titration is finished, rinsethe electrodes and store theISE25Cu in a solution containingapproximately 10-3 mol/l of Cu2+ indistilled water.Refer to the electrode operatinginstructions.
As a guideline, refer to the following table
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Nickel in Nickel Plating Solutions (EDTA Titration)
Titration automationAddition of EDTA solution can beautomated using a bi-buretteworkstation.Install the second burette with avolume corresponding to 10 or20 ml.Create and install the EDTA rea-gent with a 0.1M concentration onthis burette.Change the method settings to
Back Titration: AUTOMATICExcess reagent: EDTA 0.1MExcess volume: 10 ml
This automatic addition of EDTAimproves accuracy and reproduc-ibility of the results.
Start and end potentialsDepending on the bath composi-tion, the start and end potentialsmay change, but the titrationalways increases the measuredpotential and the potential jumpduring the titration is close to100 mV.
Modifying the procedureWith some Nickel baths, especiallyNickel/boric acid, it is possible touse an ammonium buffer solutioninstead of the acetic buffer solution.
NH4Cl and NH4OH buffer solutionDissolve 50 g of ammonium chlo-ride (NH4Cl) in 200 ml of distilledwater, add 250 ml of concentratedammonia (NH4OH 30%), completeto 1000 ml with distilled water.
The measured potential during thetitration changes.Use the following settings as ex-perimental values:
Copper in Electroless Copper Baths(EDTA Titration)
Introduction
Chemical copper baths, used inparticular in the manufacture ofprinted circuits, contain coppersalts, sodium hydroxide stabilisingagents and formol.The sodium hydroxide concentra-tion of the bath is generally be-tween 8 and 12 g/l. Formol con-centration is between 3 and 8 g/l.Copper concentration is around 3 g/l.HCHO and NaOH concentrationscan be determined as indicated inapplication notes TTEP01.04PLAand TTEP01.05PLA.According to bath manufacturer'sprocedures, copper concentrationdetermination uses either a redoxreaction (with iodide) or a complexo-metric reaction with E.D.T.A as inthis application note.
Principle
The titrant EDTA reacts with Cu2+
according to the reaction
Cu2+ + H2Y2- CuY + 2H+
Then 1 mole of EDTA correspondsto 1 mole of Cu2+
The EDTA concentration is gener-ally 0.1 or 0.2 mol/lAs for every complexometric titra-tion, the reaction occurs in a pHbuffered solution; in this case pH10.0 with a mixture of NH4Cl andNH4OH.The indicating electrode should bea Cu2+ selective electrode.
REF251 Red Rod ReferenceElectrode (part no. E21M001)
EDTA titrant 0.10 mol/l (or 0.2 mol/l)
The molecular weight of Na2EDTAis 372.24 g/mol.Dissolve 37.224 (or 74.448 g for a0.2 mol/l concentration) of Na2EDTAin 1000 ml of water using a volu-metric flask.This titrant is also commerciallyavailable.
NH4Cl and NH4OH buffer solution
Dissolve 50 g of ammonium chlo-ride (NH4Cl) in 200 ml of distilledwater, add 250 ml of concentratedammonia (NH4OH 30%), completeto 1000 ml with distilled water.
Distilled water
Inflection DetectionSettings
CONTINUOUS ADDITION MODE
Stirring speed: 550 rpm
Stirring delay: 20 sBurette volume: 10 ml
(see working range)Maximum volume: 10 mlStop point: -350 mV (see notes)Smoothing parameter: 6Inflection point number: 1Minimum speed: 0.2 ml/minMaximum speed: 4 ml/minDirection: Decreasing mVStop at last IP: YES
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InflectionMin. ordinate: -270 mV (see notes)Max. ordinate: -140 mV
Sample unit: mlSample amount: 10
Results:Number of results: 1
Result 1Result unit: g/lMolar weight: 63.5 (see notes)Reaction: 1 smp + 1 titr
Procedure
Connect the ISE25Cu electrode tothe E1 electrode input by meansof the CL114 cable.
Connect the REF201 electrode tothe reference electrode input.
Pipette 10 ml of bath.
Add 50 ml of NH4Cl and NH4OHbuffer solution and, if necessary,distilled water.
Dip electrodes and delivery tip inthe solution.
Start method by pressing the RUNkey.
Results
Generally expressed as mg/l ofcopper (Cu with a molar weightof 63.5 g/mol)
RCu = Vtitr * Ctitr * 63.5 / Vsmp
RCu = result in g/l of CuVtitr = delivered volume of titrant toreach the inflection point in mlCtitr = exact concentration of titrantin mol/l63.5 = molar weight of CuVsmp = Current sample amount in ml
With the settings indicated above,the Titration Manager gives a resultaccording to the above formula.
Copper in Electroless Copper Baths (EDTA Titration)
3 determinations on the samebathMean: 3.02 g/lStandard deviation: 0.01 g/l
Working range
As the copper determination isconducted according to automaticinflection point detection, it is rec-ommended to have 2 ml of titrantbefore and after the equivalencepoint.With a sample amount of 10 ml anda titrant concentration of 0.1 mol/l,see the following table:
For other copper concentrationschange the sample amount and/ortitrant concentration.
Notes
Note regarding electrodesTo avoid reference electrode con-tamination, it is recommended touse a REF251 double junctionreference electrode (part no.E21M001) instead of the REF201reference electrode (part no.E21M009).Do not leave the ISE25Cu selec-tive electrode in a solution contain-ing excess EDTA for too long.When the titration is finished, rinsethe electrodes and store theISE25Cu in a solution containingapproximately 10-3 mol/l of Cu2+ indistilled water.Refer to the electrode operatinginstructions.
Note regarding stop point andordinate valuesThese values vary depending onthe chemical composition of thecopper bath. The indicated valuescorrespond to an electroless cop-per bath containing NaOH andHCHO. The titration always de-creases the measured potentialand the potential jump during thetitration is close to 150 mV.
Note regarding result unitThe result unit used in the applica-tion note corresponds to g/l ofcopper (molar weight 63.5 g/mol).Some local rules use g/l of
CuSO4, 5H2O with amolar weight of249.5 g/mol as re-sult unit. In thiscase, change themolar weight in theresult screen andrefer to the table forthe correspondingworking range.
Note regarding other copperbathsThis application note is also appli-cable to other copper baths suchas acid baths containing copperions and sulphuric acid.With this kind of bath, it is neces-sary to neutralise the sample be-fore buffer solution addition (pHclose to 8.00/9.00).
Dynamic IncrementalAddition of the Titrant
(Dynamic IP)
It is possible to work with dynamic IPDynamic dose: 10Maximum dose: 0.30 mlBurette speed: 20.00 ml/minStabilisation: 3 mV/minAcceptation: 10 sFilter: 1I.P. reject: 50
Other settings are the same as forContinuous IP
Burette Delivered vol. CuSO4, 5H20 Coppervolume volume conc. in g/l conc. In g/l
10 ml2 ml 4.95 1.268 ml 19.8 5.04
25 ml2 ml 4.95 1.26
23 ml 57 14.6
50 ml2 ml 4.95 1.26
48 ml 119 30.5
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Copper in Electroless Copper Baths (EDTA Titration)
