USER COMInformation for users ofMETTLER TOLEDO Titration and pH Systems,Density Meters and Refractometers 3

DL-TIP

Fast yet Accurate: IdealParameters for your TitrationMETTLER TOLEDO titrators are easy to use !Built-in standard parameters for each titrationtype, METTLER methods or even a learn titrationprovide time saving and easy method develop-ment for most titrations. Occasionally howeverit is necessary to manually improve the param-eter setting of the titrator. These parameter aredivided into three categories : Control-, recogni-tion- and evaluation parameters. In this issue ofthe USERCOM the control parameters arediscussed.

Contents

DL-TIP• Fast yet Accurate:

Ideal Parameters for your Titration

New in the sales program• Two-phase titration beaker:

automation with the DL58 titrator• DS500 surfactant sensitive

electrode• The new applications brochure

no. 22 “Surfactant titration”

Applications• Techniques in surfactant titration• Surfactant Content by Two-Phase

Titration: Determination Limit• Mixtures of alkaline earth metals• The DL38 Titrator in a practical

Test

Guest article• METTLER TOLEDO LiquiSystems -

Liquid Handling Redefined

Questionnaire• Tell us what you think and win a

Swatch

Dear Reader“The times they are a changing” asthe famous tune goes. Was it notonly yesterday, when we had the glasstubes and the Erlenmeyer flask toperform the daily analysis ? Todaycomputerized instruments are usedto perform the most traditional of allchemical analysis. Any improve-ment ? We believe yes, and are de-lighted to present to you anotherUSERCOM full of valuable informa-tion for the analytical chemists. Maywe draw your attention to the ques-tionnaire in this issue ? We verymuch appreciate your feedback !

Control parameters instruct the in-strument as to how the titrant shouldbe added. Incremental, dynamic orcontinuous titrant addition are pos-sible, the choice depends mainly onthe characteristics of the chemicalreaction or of the sensor used for in-dication.

Incremental titration, as the mosttraditional technique involves theaddition of fixed volume incrementsthroughout the course of the titra-tion. It results in rather slow titra-tions with limited data points aroundthe equivalence point because theparameter for incremental titration

EQP

E

V∆Vfix

Figure 1: Incremental addition

∆Vfix is always a bit of a compromisebetween speed and accuracy. It stillhas its applications for titrationswith steep and sudden jumps, orwhen the signal is somewhat un-stable. Typical applications for incre-mental titrant additions are REDOXor COMPLEXOMETRIC titrations aswell as certain non aqueous acid/base titrations.

2

For endpoint titrations, where titrantis added until a preset potential isreached, we can apply the so calledcontinuous titrant addition. Here,titrant is added at continuous highspeed until a preset control band isreached. From this point on incre-ments are reduced in size by the in-strument to get to the endpoint asquickly as possible yet without over-shooting. The DL5x titrators even ap-ply “Fuzzy logic”, a modern controlmethod aiming at highest speed andaccuracy. The control band and theminimal increment have to be speci-fied.

Nowadays more common is the dy-namic titrant addition, where incre-ment size is matched to the shape ofthe titration curve, resulting in largeincrements in the flat area of thecurve and small increments in thevicinity of the equivalence pointwhere the curve is steep. This followsvery much a human like approachand enhances the speed as well asthe accuracy of the titrations. To pre-vent the titrator from adding toolarge increments, we limit the maxi-mum increment size with ∆Vmax. Inorder to avoid unnecessary long ti-trations we specify the minimumwith ∆Vmin . The potential difference,the titrator should aim for with eachincrement is set as ∆E(set). Dynamicaddition results in fast and accuratetitration for most applications. Ex-ceptions being those mentioned un-der incremental titrant addition. InMETTLER TOLEDO we take pride inthe fact, that our instruments werethe first to apply this technique!

nal is measured and thereforematches both the speed of the chemi-cal reaction and the electrode re-sponse. Here the instrument is in-structed as to how stable the signalshould be, given as a maximum drift∆E/∆t. In case the titration does notreach an equilibrium, a maximumwaiting time is defined by tmax and inorder to avoid too quick addition wehave a tmin. Equilibrium measuredvalue acquisition is the best tech-nique apart from very few exceptionsmentioned above.

How to know if the parameters areideal? Print out the table of mea-sured values and check the valuesagainst the preprogrammed param-eters of your titration method!

With a bit of practice you will be-come an experienced titration spe-cialist. Our comprehensive book“Fundamentals of Titration” pro-vides additional information (see lit-erature list).

Figure 4: Poor equilibrium

E

t

E

t

Figure 5: Equilibrium reached

Figure 3: Continuous addition

E

V

Cont

rol b

and

Figure 2: Dynamic addition

EQP

E

V∆Vmin

∆Vmax

∆Eset

Beside the manner of titrant addi-tion, the measured value acquisitionalso has to be programmed for eachtitration method. This will tell thetitrator as to at which point the po-tential should be recorded and thenext increment added. Fixed time in-tervals are possible, where the instru-ment always waits for a preset timeperiod ∆t before adding the next in-crement. It is used for unstable con-ditions (non aqueous titrations). Thesecond technique, called equilibriumcontrolled, involves the instrumentwaiting until a stable electrode sig-

3

Control parameters/Titration addition What Cause Solution

Incremental INC Poor accuracy Increment too large Decrease increment sizeSignal change per increment:steady increase to a maximum Noisy signal Increment too small Increase increment sizeand decrease away from EQP

Dynamic DYN Flat part of curve: Max. increment too Increase maximumSignal change per increment: ∆E(set) not achieved small incrementapproximately equal to ∆E(set)

Steep part of curve: Minimum increment too Reduce minimumFirst derivative signal: ∆E(set) exceeded large incrementsmooth increase up to a maximumand smooth decrease away again.

Increment size:steady decrease down to (or close)to the minimum increment

Continuous Poor accuracy due to Control band too small Larger control bandovertitration

Excessive titration time Minimum increment too Increase minimumsmall or control band incrementtoo large

Control parameters/Measured value acquisition What Cause Solution

Fixed Time Interval FIX Results much higher/lower ∆t too short Increase fixed time interval

Lower result due to excess Reaction slower than rate Increase fixed time intervalof titrant of titrant addition

Higher result due to late Electrode response slower Increase fixed time intervalindication of the EQP than rate of titrant addition

Equilibrium EQU High/low results Titration rate too high due to Decrease ∆E/∆t orCheck: 1) set drift being too high, or increase t(max)DL20/DL50 titrators have an analog 2) t(max) too low.output. Connect chart recorder to recordsignal versus time curve. After each Signal change and increment Equilibrium has not been Decrease ∆E/∆t and/orincrement addition the potential jumps size values are oscillating reached before addition of increase t(max)and slowly returns to original value. next incrementCurve should flatten out prior to the nextaddition (see figure 4 and 5). Successive increments with t(min) too short Increase t(min)

very small signal changesand sudden large changeafter one increment

Table 1a: Influence of control parameters for the titrant addition on the results and titration curve

Table 1b: Influence of control parameters for the measured value acquisition on the results and titration curve

4

Two-phase surfactant titration:easily automated with the DL58 titrator

Surfactants are widely used in daily life: soaps, detergents andwashing powders are well-known examples. Their analysis hasbecome more relevant, in particular with respect to optimizationof production processes and environmental monitoring. Auto-mated two-phase titration with the DL58 titrator, a special two-phase titration vessel and the DP550/660 Phototrode allowefficient, accurate and reproducible results. How to titrate aspecific sample? Titration brochure No. 22 helps you to find theright solution for your analysis.

Titration is a standard method forthe quantitative analysis of surfac-tants. The classical two-phase analy-sis according to Epton [1] is a widelyapplied technique for the titration ofionic surfactants. It is still a refer-ence method approved by various or-ganizations such as ASTM, DIN andBSI. Briefly, in Epton titration thecontent of e.g. anionic surfactants ina sample is determined by titrationwith a cationic surfactant in a water/chloroform system. The endpoint isdetected by a color change of a mixedindicator in the organic phase [2].Its major drawback is mainly repre-sented by the strictly manual proce-dure. In addition, the endpoint de-tection is strongly dependent on theskills and experience of the operator.But this was yesterday: after showingthat the classical two-phase titrationcan be automated [3], the introduc-tion of the METTLER TOLEDO DL58titrator has completely changed thesituation. In fact, this titrator caneasily automate the analysis se-quence by the special function “Two-phase titration”, in combinationwith an appropriate photometric sen-sor, i.e. the DP550 phototrode [3, 4].After addition of a titrant increment,the sample is stirred vigorously dur-ing a defined time period to allowreaction of the titrant with theanalyte and its extraction into the

References[1] S.R. Epton, Nature 160 (1947), 795.[2] a) V.M. Reid, G.F. Longman,

E. Heinerth, Surfactant Surf. 4, 1967, p. 292.b) J.T. Cross, Analyst 90, 1965, p. 315.

[3] Ch. M. Walter, C.A. De Caro, “Tenside titra-tion: a practical discussion”, in “Proceedingsof the 4th World Surfactants Congress”, 3-7June 1996, Barcelona, Spain, p. 432-445.

[4] C. A. De Caro, Riv. Ital. Sostanze Grasse 75,197-205 (1998).

Figure 1: Titration of an anionic surfactant by two-phase titration

Pink Pink

H2O

CHCl3

Titrant addition Stirring Data acquisition

Pink Blue

H2O

CHCl3

Before EQP EQP After EQP

organic phase (chloroform). Thestrong stirring is stopped and the twophases separate. This cycle is per-formed until a titrant excess leads toa clear color change in the organicphase [3, 4].

Anionic surfactant

5

New! Two-phase titration beaker :more comfort in surfactant titration

During automated two-phase titra-tion, water bubbles can coat the mir-ror and the window of the phototrodeaffecting the signal acquisition. Toavoid this, the special two-phase ti-tration beaker (ME-51107655) hasnow been introduced. This beakerhas a lateral port where the photo-trode is mounted. A black plasticsupport holds the Phototrode withoutthe need for further tools. Waterbubbles can therefore escape fromthe detection system of the Photo-trode. The formation of waterbubbles is reduced considerably andthe Phototrode can detect the colorchange in the organic phase withoutinterferences.

Potentiometric titration of surfactants :the new DS500 surfactant sensitive electrode

Surfactant titration has experienceda remarkable development by the in-troduction of surfactant sensitiveelectrodes for the potentiometric ti-tration of surfactants. The newDS500 surfactant sensitive electrode(ME-51107670) by METTLERTOLEDO is now available together

with an accessory spare membranekit (ME-51107669). The DS500 elec-trode has an S7 screw cap and can beeasily connected to the titrators ofthe DL5x and DL7x series with thecable ME-89601. In combinationwith an InLab 301 reference elec-trode (ME-52000128), this new elec-

Following our tradition: the new applicationsbrochure No. 22, “Surfactant titration”

trode allows the potentiometric titra-tion of ionic surfactants in aqueoussolutions. In addition, aqueous so-lutions containing nonionic surfac-tants can also be titrated after addi-tion of a specific activator.

Titration stand of the DL58 with two-phase titration beaker and phototrode

Applications brochures contain com-prehensive information on specifictitration procedures. The collectionof different applications on a specificsubject in one brochure representsindispensable support since all pre-sented methods have been developedand tested by applications chemists.Following a well-known tradition at

METTLER TOLEDO, a brochure onsurfactant titration (No. 22, ME-51725015) is available as of May1999, adding a new chapter in theseries of titration applications bro-chures. In this detailed brochure dif-ferent titration methods are pre-sented, described and compared.

6

Back to basics: Overview of techniquesin surfactant titration

Two-Phase Titration (2P)To determine the anionic (or cat-ionic) surfactant content in a water/chloroform two-phase medium, thecolor change of a mixed indicator ismonitored in the organic phase witha phototrode. The analyte is titratedwith a counter ionic surfactant, e.g.anionic surfactants are titrated withcationic surfactants. An anionic-cationic ion-pair is formed which isthen extracted into chloroform. After

each increment addition, the mix-ture is stirred vigorously and thenallowed to separate.

This sequence can be easily achievedwith the function “Two-phase titra-tion” of the DL58. An additional pos-sibility is to skip the separation ofthe phases by measuring under con-tinuous stirring (Mixed two-phasetitration). The equivalence point isdetermined by a color change in theorganic phase or the mixed phases.The curve is evaluated with the“Standard” evaluation.

This technique is still the referencemethod in surfactant titration. Itsmain advantage is the extraction ofthe titrant-analyte ion-pair into theorganic phase: matrix effects, i.e. in-terferences due to additional compo-nents present in the sample, cangenerally be avoided. This method isparticularly suited for the analysisof anionic and cationic surfactants.Methods for the 2P-titration of non-ionic surfactants containing ethyleneoxide units and of amphoteric sur-factants are also described in the lit-erature. In classical two-phase titra-tion, the phase separation is alwaysthe time-consuming step. For someionic surfactants, the mixed two-phase titration can be used, since thephase separation can be completelyavoided and therefore the analysistime can be reduced considerably.

Turbidimetric TitrationThe turbidity of an aqueous or mixedphase sample solution is measuredusing a phototrode. This sensor mea-sures the light transmission throughthe sample. Near the equivalencepoint, a precipitate between titrantand analyte is formed, and the solu-tion becomes turbid. The equivalencepoint is at the minimum in lighttransmission (Evaluation: “Mini-mum”).However, if the signal does not showa clear minimum and is noisy, thecurve is evaluated at the largestchange in turbidity (Evaluation:“Standard”). In this case, the curveobtained from the standardizationof the titrant must also be evaluatedwith the standard evaluation.

The phototrode does not need condi-tioning and maintenance is reducedto the minimum. The use of organicsolvents is also avoided. On the otherhand, there is no extraction of thecomplex into the organic phase as inthe classical Epton titration, andtherefore interferences can become aserious problem. This method ismost suited for ionic surfactants. Inaddition, nonionic surfactants (rawmaterials) and a pure solution of be-taines (amphoteric surfactants) weretitrated using sodium tetraphenyl-borate as a titrant (see brochure 22,“Surfactant titration”,ME-51725015).

Titer determination of Hyamine with SDS

Titer determination of SDS with CPC

7

Potentiometric Titration:Surfactant sensitive electrodeand non-aqueous titrationPotentiometric titrations are indi-cated with a surfactant sensitiveelectrode (SSE). Generally, an SSEhas a PVC membrane containing anion carrier. The potential is formedby interaction between the ion car-rier and the analyte in the samplesolution, and is measured against areference electrode. During titration,the surfactant forms an ion-pairwith the titrant, which leads to a po-tential resulting in S-shaped titra-tion curves, easily evaluated with the“Standard” procedure.The titration of ionic surfactants bySSE is rather straightforward. Thissensor is suitable for the analysis ofall types of surfactants, but appro-priate conditioning and carefulmaintenance of the SSE become veryrelevant. Thorough cleaning of theSSE membrane is crucial, since itcan be coated by the precipitate, inparticular when titrating nonionicsurfactants. A further technique isthe potentiometric titration in non-aqueous solution by a pH-combina-tion electrode. With this method thecontent of betaines was determinedin a shampoo (Brochure 22, “Sur-factant titration”).

Titration with the DN100Infratrode photometric sensorA DN100 sensor dipping into the ti-tration beaker can indicate turbiditychanges, refractive index changes orboth effects. This sensor has been es-pecially developed for anionic con-tent determination in lubricants andis limited to this application. Sincethese samples are usually milky afteraddition of water, the determinationis hardly possible with the photo-trode. Due to its robustness and re-duced maintenance, the DN100 isparticularly suited for routine analy-sis with a high sample throughput.

CommentsAll techniques are based on the for-mation of an ion-pair betweenanalyte and titrant, which precipi-tates in the solution. To achieve cor-rect results, the following parametersmust be considered:• Solubility and stability : The pre-

cipitation must be complete andthe complex must be insoluble.

• Reaction speed: How long does ittake to form the precipitate? Thesignal acquisition must considerthe kinetics of the precipitation re-action, i.e. the appropriate controlparameters must be selected (seeDLTip).

There is no general titration methodwhich can be used for all possibleformulations and products. When thesample consists of one pure surfac-tant component, e.g. in raw materi-als, the determination is usuallystraightforward. In the case of for-mulated products, i.e. products con-taining various surfactants and addi-tional components, a specific methodwith appropriate detection techniquemust be chosen, developed and opti-mized taking into account:• Additional surfactant components

present in the sample;• Appropriate pH values;• Additional components such as

salts, abrasive particles, fra-grances.

METTLER TOLEDO offers you com-petent support in surfactant titration:a comprehensive application bro-chure, potentiometric and photomet-ric sensors, automated two-phase ti-tration, and special titration vessel.These enable you to select the opti-mum method. You now have thechoice.

METTLER TOLEDO offering in Surfactant titration

Analysis Sensor Titrator

Automated two-phase titration DP550, DP660 Photometric sensors DL58, DL77Two-phase Titration beaker Accessory

Turbidimetric titration DP550, DP660 Photometric sensors DL5x, DL7x

Potentiometric titration (SSE) DS500 Surfactant sensitive electrode DL5x, DL7x

Anionic surfactant in lubricants DN100 Photometric sensor DL5x, DL7x

Potentiometric titration DG113 Combined pH-electrode DL5x, DL7xin non-aqueous media

8

How low can we go?Determination Limit for Two-Phase Titration

Determination LimitIt is considered that the minimumacceptable relative standard devia-tion srel for this kind of low contentsample is 3%. Thus, it can be seenfrom the plot, that the correspondingdetermination limit is 0.015 mmol ofSPS per sample aliquot.

Titration and AutomationThe titration of surfactants is a wellestablished procedure. It is used forresearch as well as quality control,monitoring the contents of surfac-tants in soaps, cleaners, shampoos,technical solutions such as coolingliquids or moistening agents andmany other products.For years the titration in two phasesaccording to Epton has proven as ref-erence method for many applica-tions. Unfortunately, it was accessibleto manual titration only or requestedquite an extravagant instrumentalsetup for its automation. Now theDL58 titrator of METTLER TOLEDOoffers a very convenient, simple butfully automated Epton method. TheDL58 automatically adds the titrantin increments, stirs for good mixing,waits for the separation of the twophases and then measures the colorchange. This cycle is repeated untilthe equivalence point is detected.

ExampleSince manufacturers and industrialusers of surfactants nowadays alsohave to check waste and effluents,the titration of surfactants is also ap-plied to samples of low concentra-tion. In this context it is importantto know the determination limit of amethod as it is described in the Ap-plication Brochure Nr 16, Validationof Titration Methods.Series of samples containing variousamounts of surfactants have been ti-trated and statistically evaluated.The example surfactant was a mix-ture designated as sodium petroleumsulfates (SPS) with sodium dodecylbenzene sulfonate (SDBS) as itsmain component.

ResultsA series of 4 to 8 sample aliquotshave been titrated. The results andthe corresponding repeatability assrel are plotted.

References[1] Epton, Nature 160, (1947) 795.[2] Mettler-Toledo GmbH, Application Brochure

No. 16, ME-51724912 (1996)[3] Mettler-Toledo GmbH, Application No. M652,

in preparation

Amount of SPS [mmol] srel [%]

0.0034 7.560.0057 5.670.0120 3.010.0182 1.140.0253 0.46

8

7

6

5

4

3

2

1

00 0.005 0.01 0.015 0.02 0.025 0.03

srel

[%

]

Amount of substance [mmol]

Determination limit for srel = 3%

9

Calcium and Barium inOne Shot

Amongst the most powerful applica-tions of ion selective electrodes(ISEs) is their use in complexomet-ric titrations. By using the multiplesensor inputs available for allMETTLER TOLEDO titrators from theDL53 upwards, with a combinationof appropriate ISEs, it is possible totitrate a mixture of ions in the samesample aliquot. Mixtures of alkalineearth metals, such as calcium andmagnesium or calcium and barium,are particularly amenable to this ap-proach using EGTA as a titrant. Addi-tion of more than ten new ISEs (seeUSERCOM 2), including magnesiumand barium, to the METTLERTOLEDO range of electrodes meansour customers are better equipped toanalyze ion mixtures.

The ProblemA common titrimetric problem in thewater industry has been to determinecalcium and magnesium with onetitration without mutual interfer-ence, as the stability constants of themagnesium and calcium EDTA com-plexes only differ by two orders ofmagnitude. Compounds of bariumare used as additives in productsranging from drilling muds to con-crete and determination of bariumwithout interference from its ubiqui-tous associate calcium is equally dif-ficult as the stability constants of theEDTA complexes of these metals alsodiffer by less than two orders of mag-nitude. It has been suggested [1]that for the “one pot”, one titrant,complexometric titration of two met-als to be successful - without selec-tive masking - requires the stabilityconstants of the complexes formed todiffer by 5 to 6 orders of magnitude.

Method CaBa Calcium + Barium Version 06-Apr-1999 15:02

Title Method ID . . . . . . . . . . . . . CaBa Title . . . . . . . . . . . . . . . Calcium + Barium Date/time . . . . . . . . . . . . . 06-Apr-1999 15:02Sample Number samples . . . . . . . . . . . 5 Titration stand . . . . . . . . . . Stand 1 Entry type . . . . . . . . . . . . . Weight m Lower limit [g] . . . . . . . . . 0.075 Upper limit [g] . . . . . . . . . 0.125 ID1 . . . . . . . . . . . . . . . . Molar mass M . . . . . . . . . . . . 1 Equivalent number z . . . . . . . . 1 Temperature sensor . . . . . . . . . ManualStir Speed [%] . . . . . . . . . . . . . 50 Time [s] . . . . . . . . . . . . . . 10Titration Titrant . . . . . . . . . . . . . . EGTA Concentration [mol/L] . . . . . . 0.01 Sensor . . . . . . . . . . . . . CaISE Unit of meas. . . . . . . . . . . mV Titration mode . . . . . . . . . . . EQP Predispensing 1 . . . . . . . . . mL Volume [mL] . . . . . . . . . 0.5 Titrant addition . . . . . . . . DYN ∆E(set) [mV] . . . . . . . . . 6.0 Limits ∆V . . . . . . . . . . Absolute ∆V(min) [mL] . . . . . . . 0.01 ∆V(max) [mL] . . . . . . . 0.075 Measure mode . . . . . . . . . . EQU ∆E [mV] . . . . . . . . . . . 0.5 ∆t [s] . . . . . . . . . . . . 1.0 t(min) [s] . . . . . . . . . . 5.0 t(max) [s] . . . . . . . . . . 10.0 Threshold . . . . . . . . . . . . 15.0 EQP range . . . . . . . . . . . . Yes Limit A . . . . . . . . . . . 1000 Limit B . . . . . . . . . . . -1000 Maximum volume [mL] . . . . . 10.0 Termination after n EQPs . . . . Yes n = . . . . . . . . . . . . . 1 Evaluation procedure . . . . . . StandardCalculation Result name . . . . . . . . . . . . Calcium Formula . . . . . . . . . . . . . . R=Q[1]*4.008/m Constant . . . . . . . . . . . . . . Result unit . . . . . . . . . . . . % Decimal places . . . . . . . . . . . 2Record Output unit . . . . . . . . . . . . Printer+Computer Results last sample . . . . . . . . Yes E - V curve . . . . . . . . . . . . Yes ∆E/ ∆V - V curve . . . . . . . . . . YesTitration Titrant . . . . . . . . . . . . . . EGTA Concentration [mol/L] . . . . . . 0.01 Sensor . . . . . . . . . . . . . BaISE Unit of meas. . . . . . . . . . . mV Titration mode . . . . . . . . . . . EQP Predispensing 1 . . . . . . . . . mL Volume [mL] . . . . . . . . . 1.0 Titrant addition . . . . . . . . DYN ∆E(set) [mV] . . . . . . . . . 6.0 Limits ∆V . . . . . . . . . . Absolute ∆V(min) [mL] . . . . . . . 0.01 ∆V(max) [mL] . . . . . . . 0.15 Measure mode . . . . . . . . . . EQU ∆E [mV] . . . . . . . . . . . 0.5 ∆t [s] . . . . . . . . . . . . 1.0 t(min) [s] . . . . . . . . . . 3.0 t(max) [s] . . . . . . . . . . 30.0 Threshold . . . . . . . . . . . . 15.0 EQP range . . . . . . . . . . . . Yes Limit A . . . . . . . . . . . 1000 Limit B . . . . . . . . . . . -1000 Maximum volume [mL] . . . . . 10.0 Termination after n EQPs . . . . Yes n = . . . . . . . . . . . . . 1 Evaluation procedure . . . . . . Standard Stop for reevaluation . . . . . . Yes Condition . . . . . . . . . . neq=0Calculation Result name . . . . . . . . . . . . Barium Formula . . . . . . . . . . . . . . R2=(Q[2]+QEX[1])*C2/m Constant . . . . . . . . . . . . . . C2=137.3/10 Result unit . . . . . . . . . . . . % Decimal places . . . . . . . . . . . 2

Output unit . . . . . . . . . . . . Printer+Computer All results . . . . . . . . . . . . Yes E - V curve . . . . . . . . . . . . Yes ∆E/ ∆V - V curve . . . . . . . . . . Yes

Figure 1: Titration method

10

The SolutionThe stability constant of the EGTAcomplex of calcium exceeds that ofthe magnesium complex by almostsix orders of magnitude. As a conse-quence calcium and magnesium canbe titrated successively with EGTA onthe same sample aliquot [1]. The ad-dition of a magnesium ISE to theMETTLER TOLEDO range of ISEsnow means that magnesium and cal-cium in (for example) water samplescan be reliably determined in asingle titration with EGTA, even forsamples with very high calcium tomagnesium ratios.Although the stability of the EGTAcomplexes of barium and calciumonly differ by 2.5 orders of magni-tude [2] the formation kinetics ofthe barium complex appears to besuch that it has proven possible todetermine calcium and barium witha single EGTA titration. For simpleinorganic mixtures of calcium andbarium it was possible to use a cal-cium-selective electrode to detectboth the calcium and the bariumequivalence points (the first and sec-ond equivalence points respectively).However, chemically complex prod-ucts such as mixed ligno-sulfonates– used as concrete additives – do notalways yield two clear equivalencepoints with a single calcium elec-trode. For these applications we haveused a calcium ISE to detect the cal-cium equivalence point and abarium ISE to detect the bariumequivalence point.A METTLER TOLEDO DL70ES autoti-trator has been used for these appli-cations. Dynamic addition of theEGTA titrant and the detection andanalysis of the two equivalencepoints was controlled by the programpresented as figure 1. This methodcouples two titration functions - thefirst controlling the titration of cal-cium using a calcium ISE and thesecond controlling the (continuing)

Figure 2a and 2b: Titration curves for Calcium

Figure 3a and 3b: Titration curves for Barium

11

References[1] Vogel’s Textbook of Quantitative Chemical

Analysis, 5th Edition, Editors - G.H.Jeffery,J.Bassett, J.Mendham and R.C. Denney,Longman Scientific and Technical, 1989

[2] Atlas of Metal-Ligand Equilibria in AqueousSolution, J.Kragten, Ellis Horwood Limited,John Wiley and Sons, 1990

titration of the barium using abarium ISE. Note that the secondcalculation function corrects for thesmall volume of titrant added in ex-cess of the equivalence point at theend of the first titration (QEX[1]).This method can be run, with slightmodification, on any METTLER TO-LEDO DL53, 55 or 58 fitted with anextra sensor option.

The ResultsTypical titration curves for a mixedcalcium/barium compound are pre-sented as figures 2a and b (E-V and1st derivative curves for calcium)and figures 3a and 3b (E-V and 1stderivative curves for barium).A statistical summary of results ob-tained from replicate analyses of thiscompound are presented as figure 4.

Repeatability for barium is good,with a relative standard deviation of0.4%. The lower precision of the cal-cium determination is thought to bea consequence of the relatively lowcalcium content and the highbarium/calcium ratio.

What You NeedAny METTLER TOLEDO autotitratorin the DL67/70 range or a DL53, 55or 58 (if fitted with an additionalsensor option).• DX240 METTLER TOLEDO calcium

ISE• DX337 METTLER TOLEDO barium

ISE• DX200 METTLER TOLEDO double

junction reference electrode

Sample Ca [%] Ba [%] Mean x srelCa Ba Ca Ba

1 0,51 8,832 0,51 8,843 0,50 8,84 0,50 8,86 2,6 0,44 0,48 8,905 0,51 8,90

Figure 4 : Results for mixed barium/calcium compound

12

The DL38 Karl Fischer Titrator in a Practical Test :Fast and precise titrations

plicable to samples of low moisturecontent which previously have beenthe realm of the coulometric methodonly.

TestA customer in China PRC has tocheck the moisture content of or-ganic solvents such as alcohols andhydrocarbons on a frequent andregular basis. The concentrationranges from the ppm to the percentlevel. Because the KF titrator shouldbe used by several operators andaround the clock, the customer askedfor a test to verify the suitability ofthe new DL38 Karl Fischer titrator ofMETTLER TOLEDO.

ResultsSpeed and Accuracy5 samples of methanol containingapproximately 2% moisture havebeen analyzed by 4 different opera-tors, using single component KF re-agent using default or modified con-trol parameters.The relative standard deviation srelas measure for repeatability or repro-ducibility is compared with the timerequired to complete the titration.

srel [%]srel [%]srel [%]srel [%]srel [%] time [s]time [s]time [s]time [s]time [s] control parameterscontrol parameterscontrol parameterscontrol parameterscontrol parameters0.69 120 by default0.38 120 by default0.21 220 for slower titration0.11 130 by default

The test proves that reproducible re-sults can be obtained in about 2minutes titration time without priormodification and streamlining of thetitrator settings.

Moisture AnalysisThe determination of moisture is oneof the most frequent and ubiquitousanalyses known to everybody. Severaltechniques are applied depending onthe purpose, quality requirements orlegal aspects. Amongst these tech-niques Karl Fischer titration is a fa-vorite thanks to its universal applica-tion and, thus, is of widespread usein labs all over the world. It is esti-mated that some 500’000 KarlFischer titrations are performed perday in spite of the aggressive iodinecontaining KF reagents.

Automatic KF TitrationAutomatic titrators since the times ofthe METTLER TOLEDO DL18 limitthe manual handling of the unpleas-ant and toxic reagents to a veryminimum. Now the new KF titratorsDL38 and DL31 even further ease theproceeding of KF titrations. Besidesthe Hello Program, which leads new-comers smoothly through the setupand operation of the titrator, an al-most absolutely tight titration cellprevents ambient moisture from in-terfering and also reagents fromevaporating.The most advanced titration controlprinciples of the built-in FuzzyLogic, fully compatible with all kindsof KF reagents and enjoyed by the ex-perts, allow for fast and accurate re-sults. The old dilemma of speed orprecision is overcome.Furthermore, this new control prin-ciple of KF titration in combinationwith the high resolution of the bu-rette system of the DL38/DL31 alsomakes the volumetric technique ap-

References[1] Mettler-Toledo GmbH, Application Brochure

26, ME-51 709 855 (1998)[2] E. Scholz, Karl Fischer Titration, Springer-

Verlag Berlin (1984)

Low Moisture5 different operators were analyzingtoluene samples 3 to 6 times (4 dif-ferent batches).Operators B and E analyzed the samebatch from the same container.One component KF reagent. Controlparameters by default.

mean [ppm]mean [ppm]mean [ppm]mean [ppm]mean [ppm] srel [%]srel [%]srel [%]srel [%]srel [%] OperatorOperatorOperatorOperatorOperator114 8.8 A103 4.9 B167 2.9 C129 2.1 D98 7.3 E

Also low moisture samples runsmoothly on the DL38 by differentoperators. Note that the results ofOperators B and E show a very goodagreement.

13

METTLER TOLEDO LiquiSystems –Liquid Handling Redefined

Measuring and transferring liquidvolumes in the mL and µL range hasbecome one of the most frequenttasks in scientific and medical labo-ratories. Carrying out this task ex-actly and rapidly is an indispensableprerequisite for successful work. Inview of the large number of advan-tages they offer, modern air-cushionpipettes are used for most of thesetasks. They are the ideal instrumentsfor effectively measuring smallquantities of liquids. Using pipettesof this type conforming to the high-est quality standards enables thework to be carried out with high pro-ductivity and corresponding timesavings.Trends in research, such as workingwith smaller and smaller volumes ofever more costly reagents in the lifesciences field, and the increasing

number of samples needing to beprocessed when using methods ofcombinatorial chemistry, havecaused the demands placed on pi-pettes in recent years to become in-creasingly exacting.To take account of these trends, andto provide users with instrumentswhich match their needs, METTLERTOLEDO has decided to develop acomplete range of pipettes, tips,boxes, and accessories. Because thedemanding requirements can only bemet by fully compatible instruments,and this philosophy has served as theguiding principle for development ofthe entire product line, all METTLERTOLEDO liquid handling productswill be marketed under the name ofLiquiSystems.LiquiSystems includes a completerange of seven sizes of single-channel

air-cushion pipettes (VoluMate),which cover the volume range from0.1 µL to 5,000 µL. In addition to ful-filling the usual expectations in rela-tion to extreme precision and accu-racy, the main development objectiveswere ease of operation and a previ-ously unattained level of ergonomics.This simplifies repetitive pipettingand minimizes errors due to incorrectoperation. The MultiMate multi-channel pipette has identical ergo-nomics to the single channel pipetteand is also operated identically. It isavailable in three volume ranges be-tween 0.5 µL and 250 µL, with both 8-and 12-channel versions for eachrange.The precision and accuracy of a pi-pette depend absolutely on the tipused. Only pipette tips which aremanufactured to the highest qualitystandards give the desired results.This is the reason why the METTLERTOLEDO LiquiSystems line includesmatching tips for all the single andmulti-channel pipettes. From the2.5 µL tip for molecular biology, tothe 5,000 µL tip for classical chemis-try, and sterile filter tips for microbi-ology and pharmacy - the renownedMETTLER TOLEDO quality is as-sured.METTLER TOLEDO has also com-pletely re-conceived and newly devel-oped one of the most-used articles inthe laboratory - the boxes for storingand handling pipette tips. The newcreation is a ruggedly constructedbox which can be used with onehand, is not easily knocked over, hasa removable lid, and which - need-less to say - is also autoclavable.Easy, ergonomic handling rightdown to the last detail. Refilling the

Sampling of a DL38 Karl-Fischer Titrator with a pipette

14

box is made much faster by pre-filledtrays which can be replaced in oneoperation, and which prevent touch-ing and possibly contaminatingloose tips. But of course, for less de-manding tasks METTLER TOLEDOcan also supply you with any size oftip packed loose in bags for use asstandard.Fast, intuitive selection of the correcttip was never so simple as now. Thedurable and attractively shaped standfor safely storing the LiquiSystemsVoluMate and LiquiMate pipettes en-sures that the color coding on the pi-pettes is visible from all sides.

Regular gravimetric checks, and ad-justment of the pipette if necessary,are important requirements of mod-ern quality assurance systems. Reli-able and efficient checking requireshigh quality balances, supportingsoftware, and perfectly matching ac-cessories. Together with the pipettesand tips, all of these items todayform an inseparable system in whichthe weakest link determines thequality of the chain.Thanks to LiquiSystems, METTLERTOLEDO is the only single-sourcemanufacturer able to supply all thecomponents in the system.

Tell us what you think and wina Swatch of your choice!

Afric

an B

BQ

Gold

en je

lly

Blue

nite

We started USERCOM last year with the intention of keeping youbetter informed on what is going on in the METTLER TOLEDOworld of Titration. In order to better focus the USERCOM on yourinterests, we ask you to give us your opinion and your titrationneeds by filling out the form below. Don't forget to pick one ofthe three Swatch watches you would like to win. We will giveaway 5 SWATCH watches.

If you want to participate in our SWATCH draw, please tell usbelow where we have to send it in case you are among the fivelucky winners.The draw of the prizes will take place October 1st 1999.

Name

Company

Address

City/Zip

Country

Plea

se s

end

the

fille

d ou

t for

m b

y fa

x or

mai

l to:

Met

tler-

Tole

do G

mbH

, Mar

ketin

g Ti

tratio

nSo

nnen

berg

stra

sse

74CH

-860

3 Sc

hwer

zenb

ach

Fax:

++4

1 1

806

72 7

0

African BBQBlue niteGolden Jelly

Questionnaire

1. How do you perform titrations?

with an automatic titrator manually with a burettemanually with a dispenser I perform no titrations

2. What samples do you analyze using titration and what do youanalyze for?

3. How many samples do you measure approx. per day?

1-3 4-10 11-29 30-99 100-300 >300

4. Is the titration mainly done by chemists?

yes no

5. How many different titration methods do you use?

1 2-3 4-10 11-20 over 20

6. Did you develop your methods yourself/in your lab ?

yes no

7. What are the most important features of a titrator for you ?

ease of use PC connectability/LIMSGLP functions PC Softwareautomation compact formatafter sales support strong method capabilitieshigh sample throughput

8. What brands of titrators do you use?

Metrohm Orion Radiometer OtherMettler Schott Crison None

10. Do you use titrators together with PCs?

yes in the future no

11. Do you use dedicated titration PC Software?

yes in the future no

12. What do you miss most on today’s titrators?

USERCOM

13. Which topics would you expand in future USERCOM?

DL-Tip Applications Tips&HintsNew Products Guest article

14. How many people read your USERCOM (including yourself)?

1 2 3 4 or more

15. Do you keep the USERCOM after you have read it ?

yes no

16. How would you rate the overall quality of the USERCOM?

very good good average bad

Publications

Layout and productionMarket Support AnaChem Schwerzenbach,V. Mahler© 6/99 Mettler-Toledo GmbHPrinted in Switzerland ME-51709963Printed on 100% chlorine-free paper, for the sakeof our environment.

Editorial officeMettler-Toledo GmbH, AnalyticalSonnenbergstrasse 74CH-8603 Schwerzenbach, SwitzerlandTel. ++41 1 806 7711Fax ++41 1 806 7240E-Mail: msganachem@mt.comInternet: http://www.mt.com

C. Gordon, Dr. C. A. De Caro, G. Reutemann,Ch. Walter, Dr. J. Angus, M. Gietenbruch,Dr. Ch. Bircher

The application chemists of theAnaChem market support group haveprepared several publications and aseries of application brochures tosupport customers in their routine

Publications, reprints and applications German EnglishTitration in routine and process investigations 51724658 51724659Basics of Titration 51725007 51725008Fundamentals of Titration 704152 704153Applications Brochure DL70 Customer Methods 724491 724492Applications Brochure DL70 Gold and Silver 724613Applications Brochure 2 Various Methods 724556 724557Applications Brochure 3 TAN/TBN 724558 724559Applications Brochure 4 Electroplating 724560 724561Applications Brochure 5 Determin in Water 51724633 51724634Applications Brochure 6 Direct measurement with ISE 51724645 51724646Applications Brochure 7 Incremental Techniques with ISEs 51724647 51724648Applications Brochure 8 Standardization of titrations I 51724649 51724650Applications Brochure 9 Standardization of titrations II 51724651 51724652Applications Brochure 11 Gran evaluation DL7x 51724676 51724677Applications Brochure 12 Selected Applications DL50 51724764 51724765Applications Brochure 13 Nitrogen Determ. by Kjeldahl 51724768 51724769Applications Brochure 14 GLP in the Titration Lab 51724907 51724908Applications Brochure 15 Guidelines for Result Check 51724909 51724910Applications Brochure 16 Validation of Titration Methods 51724911 51724912Applications Brochure 17 Memory card “Pulp and paper” 51724915Applications Brochure 18 Memory card “Standard. of titrants” 51724916 51724917Applications Brochure 19 Memory card “Determination in Beverages” 51725012 51725013Applications Brochure 20 Petroleum 51725020Applications Brochure 21 O-ST Determination 51725017Applications Brochure 22 Surfactant Titration 51725014 51725015Applications Brochure 26 METTLER TOLEDO Titrators DL31/38 * 51709854 51709855Applications Brochure KF Chemical 724353 724354Applications Brochure KF Food, Beverage, Cosmetics 724477 724478Applications Brochure KF 10 DL35 Applications 724325 724326Applications Brochure DL18 724589 724590Applications Brochure DL12 724521Applications Brochure DL25 724105 724106Applications Brochure DL25 Food 51724624 51724625Applications Brochure DL25 Petro / Galva 51724626 51724627Applications Brochure DL25 Chemical 51724628 51724629

* Also available in French (51709856), Spanish (51709857) and Italian (51709858)

work in the laboratory. Each bro-chure is dedicated either to a particu-lar sector of industry (such as paperand pulp, petroleum and beverages),a particular titrator or a specific

analysis technique. The following listshows all publications, together withtheir order numbers. They are avail-able from your local METTLERTOLEDO marketing organization.