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SpectrosenseTechnical specificationsHousingWidthHeightDepthWeightMaterial50 mm63 mm (withoutshaft and withoutcable)20 mm120 gAluminumApplication examplesDetermination of the total hardness of tap water by means of a photometric titrationwith Titrando and 610 nm SpectrosenseTitrant:c(EDTA) = 0.1 mol/LBuffer solution: NH 3/NH 4Cl, pH = 10Color indicator: Eriochrome black TShaftDiameterLength without mirrorTotal lengthShaft materialOptical path lengthMaterial of mirror frameOperational rangesPhotometricDark voltageBright voltage12 mm129 mm145 mmPEEK22 mmStainless steel50...1000 mVmax. 50 mVmax. 1200 mV(in dist. water)Wavelength6.1109.100 523 nm, greenblue6.1109.110 610 nm, orangeResult block and titration curve for the determination of the total hardness in tap water.Ambient conditionsHousing 0...45 °CMirror 0...80 °CRelative humidity category «Sensors»Result block and titration curve of a sulfate determination.22 Metrohm Information Issue 2/2005
DIN EN 14480New DIN/EN standard for determining anionic surfactants by meansof potentiometric two-phase titrationThe determination of the content of surface-active agents (surfactants) plays animportant role in many sectors – from wastewater analysis up to quality controlin production processes. A method that is still in widespread use is the socalledEpton titration according to ISO 2271, a complicated and time-consumingmanual titration. The new DIN EN 14480 standard now describes an alternativedetermination method that is much simpler and faster: potentiometric two-phasetitration.Classical Epton titration – the appearance is deceptive!In this manual titration the anionic surfactant is precipitated by a cationic surfactantin an Erlenmeyer flask containing a two-phase mixture of water and chloroform. Theion pair formed must be extracted into the solvent phase by vigorous shaking. Thetitration endpoint is then determined visually using a color indicator. This method isnot only complicated, it also suffers from the following serious disadvantages:• Use of the toxic solvent chloroform• Very time-consuming determination as after each titrant addition a waiting periodfor phase separation is required• Inaccurate visual endpoint recognition• Cannot be automatedPotentiometric two-phase titration according to DIN EN 14480:more precise, faster and much healthier!The solution of the anionic surfactant is pipetted into a titration vessel, to which atwo-phase mixture of water and methyl isobutyl ketone/ethanol 1 : 1 and an emulsifierare added. Under vigorous stirring the emulsion formed is titrated with a cationicsurfactant, in this case benzethonium chloride (Hyamine 1622). The ion pairformed, which is insoluble in water, is extracted immediately into the organic phase.The determination of the equivalence point does not take place visually, but potentiometricallyusing surfactant-sensitive electrodes. The Surfactrodes from Metrohm(Surfactrode Resistant or Surfactrode Refill, see photo at right) are used for thispurpose; they have a high affinity for surface-active agents. In comparison with theEpton titration you profit from the following advantages:• Use of unproblematic solvents instead of chloroform• Short determination times: only a few minutes per titration• Objective, computer-supported determination of the equivalence point and thereforeimproved precision• Can easily be automatedIn an extensive Europe-wide interlaboratory test the potentiometric two-phase titrationwas compared with the Epton method and was found to yield the same analyticalresults with a better repeatability. A detailed evaluation of the interlaboratory testcan be found in the appendix of DIN EN 14480.The Metrosensor Surfactrodes for potentiometric twophasetitration: 6.0507.130 Surfactrode Resistant (right)and 6.0507.140 Surfactrode Refill with paste and fillingtool.Metrohm Information Issue 2/2005 23
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