859 Titrotherm Thermometric titration – the ideal complement to potentiometric titration What is thermometric titration? 02 Titration is the oldest and most widespread method used Every chemical reaction is accompanied by a change in in analytical chemistry. For a long time now, potentio-enthalpy (ΔH). The following equation applies. metric sensors (indicator electrodes) have been used to cover a wide range of titrimetric applications. As a result, ΔH = ΔG + TΔS, where potentiometric titration has become firmly established ΔG = change in free reaction energy and features in many standards. T = absolute temperature ΔS = change in reaction entropy However, a suitable indicator electrode is not always available for an existing problem. There may be no suitAs long as the reaction takes place, this results in either able sensor for the analyte at hand or the sample matrix an increase (exothermic reaction) or decrease (endother-can either interfere with the indicator electrode or even mic reaction) in the temperature of the sample solution. render it unusable. For a simple reaction this means that the increase or reduction in temperature depends on the converted However, the electrochemical potential is only one of the amount of substance. possible ways of following a chemical reaction. A far more universal parameter is the reaction enthalpy. The result is that in a thermometric titration a change in temperature can only be observed as long as the added titrant reacts with the analyte in the sample solution. Schematic of a thermometric titration curve. Advantages of thermometric titration • Proven method 03 • Easy learning and easy carrying-out of thermometric titration through incorporation of the method in the tiamo TM titration software • Problem solver for difficult samples that cannot be titrated potentiometrically • Rapid results • No sensor calibration required • Maintenance-free sensor • Robust method for routine work • Well suited for aggressive media • One sensor for all applications • No membrane or diaphragm problems Titrotherm 859 – can you feel the heat? The 859 Titrotherm combines innovative sensor techno-04 859 Titrotherm – latest USB technology for perfect logy with Metrohm’s unique know-how in titration. ease of use The 859 Titrotherm’s easy operation becomes apparent even during installation. Thanks to advanced USB technology the instrument is recognized automatically by the tiamo TM titration software when it is connected to the PC and does not have to be manually configured. The same applies to the Dosing Units, stirrers and sensors connected to the Titrotherm. tiamo TM – everything at a glance, everything under control The universal, clearly laid-out tiamo TM software allows The endpoints are determined by calculating the first and 05 the titration parameters to be adapted quickly to the second derivatives of the titration curve; by means of particular method and thus provides rapid, effective additional optimization parameters, the reproducibility method development and also fast and easy generation can be improved even further. For report generation, the of results. titration data can be exported manually or automatically into a freely arranged, method-specific report template. 06 Automation pays dividends! Increasing sample numbers, time-consuming sample It’s amazing: You simply connect the sample changer to pre paration steps and unattended overnight operation the Titrotherm’s USB port and the world of automation are good reasons for using sample changers. The 859 opens up to you. Titrotherm comes with the necessary intelligence to con trol sample processors. Together with the 814 USB Sample Processor and 815 Robotic USB Sample Processor XL, the 859 Titrotherm offers a high degree of automation at low investment costs. Thermoprobe – quick, precise and robust Thermoprobe, a temperature sensor based on semicon-07 ductor technology (thermistor), has a response time of only 0.3 s and a resolution of 10–5 K. This makes the Thermoprobe the ideal sensor for thermometric titration, as it can follow any change in temperature quickly and accurately. The housing made of glass provides the sensor with outstanding resistance to many organic solvents and aggressive media. Dosino technology – precise and simple dosing Metrohm’s Dosino technology has defined a new standard for volumetric titration. The Dosing Unit with its drive motor is mounted on the reagent bottle and thus guar-antees maximum precision with minimum space requirements. The titrator and two burets require hardly more bench space than a sheet of DIN A5 paper! 08 Scope of thermometric titration Thermometric titration is a very versatile determination It is particularly suitable for applications method and an ideal complement to potentiometric • for which no suitable potentiometric sensor is available titration. In principle it is suitable for any reaction that • for which no suitable reference electrode is available produces a sufficiently large temperature change in the • in which the sample affects the indicator electrode or sample solution. destroys it • for which no solvent is available that is suitable for potentiometry Typical applications for thermometric titration: Analyte Matrix Titrant Sodium Salts, process solutions, foodstuffs Al (NO ) / KNO -solution 3 3 3 FFA (free fatty acids) Edible oils and edible fats KOH in isopropanol (2-propanol) TAN (Total Acid Number) Mineral oil products, edible oils, biodiesel KOH in isopropanol (2-propanol) Caustic, aluminum, carbonate Bayer Liquor (aluminum production) HCl, KNaC H O ·4H O, KF 4 4 6 2 Acid mixtures (HF, H SO , HNO ...) Electroplating baths (containing HF) NaOH 2 4 3 An overview of other applications can be found at www.titrotherm.com Application example 1: Direct determination of sodium in foodstuffs, using Al3+ + Na+ + 2K+ + 6F– ←→ NaK AlF ↓ 2 6 ketchup as an example Reagents: Because direct determination of sodium by means of Titrant: mixture of 0.5 mol/L Al(NO ) , 3 3 atomic absorption spectroscopy (AAS) or inductively cou-1.1 mol/L KNO solution 09 3 pled plasma mass spectroscopy (ICP-MS) is a very expen-Complexing reagent: 300 g/L NH F·HF 4 sive and time-consuming process, also requiring a large amount of investment in the infrastructure, the method Procedure: frequently adopted is indirect determination by way of Add 5 mL complexing reagent (NH F·HF solution) to 4 quantitative analysis of chloride. However, this can lead 5 - 10 g ketchup (depending on sodium content), make to very inaccurate results, since the sodium in foodstuffs up to 35 - 40 mL with deionized water, stir for approx. can also be present in the form of sodium benzoate or 60 seconds, and then titrate thermometrically to the EP. monosodium glutamate. The chloride can also be present in large quan tities as potassium iodide, so a molar 1:1 ratio of chloride ions to sodium ions cannot be assumed. This application shows how sodium can be determined directly, at relatively low cost in terms of time and money, using thermometric titration. Here, the homogenized sample is titrated thermometrically in the presence of ammonium hydrogen difluoride at ~pH 3 with a stand-ardized, aluminum-containing solution, which contains a stoichiometric excess of potassium ions. This produces an exothermic reaction with the formation of insoluble NaK AlF (elpasolite): 2 6 Application example 2: Analysis of an acid mixture comprising phosphoric acid and Application: nitric acid Measure 0.7 mL (about 1 g) of the acid mixture from the fertilizer production process exactly into a clean, dry titration This acid mixture from the production process for artificial vessel. Add 30 mL of the 180 g/L NaCl solution and allow fertilizers can only be analyzed if the third endpoint – which to stand for about 30 min, so the whole of the hexa-is entirely due to the third proton of the phosphoric acid – fluor osilicic acid contained in it is hydrolyzed. Titrate with can be unequivocally determined. Using a normal pH elec-c(NaOH) = 2 mol/L. trode in aqueous solution, this would be impossible, as the electrochemical dissociation potential is too low. Thermometric titration, in contrast, allows the determination of the third endpoint very easily – and above all very rapidly. The individual acid concentrations can then be calculated from the separations between the endpoints. Reagents: Titrant: c(NaOH) = 2 mol/L Solvent/conditioning solution: 180 g/L NaCl solution (to hydrolyze the hexafluorosilicic acid) Titration rate: 5 mL/min 10 Catalytically enhanced thermometric titration At very low sample concentrations or with low molar case the addition of a small amount of paraformaldehyde reaction enthalpies, the temperature change during the makes it easier to detect the endpoint, for as soon as the reaction is often inadequate for the reliable determina-endpoint is reached (i.e. as soon as excess hydroxide ions tion of the endpoint. With a clever trick it is possible to are present) the base-catalyzed hydrolysis of the parafor-obtain a proper «jump» in such reactions. An example is maldehyde starts. This strongly endothermic reaction the determination of very small amounts of organic acids now provides a well marked endpoint. with the titrant c(KOH) = 0.1 mol/L in isopropanol. In this Catalytically enhanced thermometric titration: after the endpoint has been reached, the excess hydroxide ions catalyze the endothermic hydrolysis of the added paraformaldehyde. Ordering information Titrotherm 859 11 2.859.1010 USB-enabled thermometric titrator with two measuring inputs for Thermoprobe. Four MSB connections for 800 Dosinos and stirrer. Including 6.9011.020 Thermoprobe 2.800.0010 Dosino 2.802.0010 Rod stirrer 2.804.0010 804 Titration stand without stand rod 6.3032.210 Dosing Unit 10 mL 6.2151.000 Cable USB A – mini-DIN 8 pins 6.1414.010 Titration vessel lid SGJ 6.1415.210 Titration vessel 10 - 90 mL 6.2026.010 Stand rod with base plate 6.2013.010 Clamping ring 6.2021.020 Electrode holder 6.6056.231 tiamo TM 2.3 light CD: 1 license Optional accessories 6.9011.040 HF-resistant Thermoprobe 6.2061.010 Bottle holder for 800 Dosino 6.2065.000 Rack for 846 Dosing Interface 6.1450.210 PFA titration vessel 10 - 90 mL 6.3032.120 Dosing Unit 2 mL 6.3032.150 Dosing Unit 5 mL 6.3032.220 Dosing Unit 20 mL 6.3032.250 Dosing Unit 50 mL System requirements for titration software tiamoTM 2.3 or higher Processor Pentium 4; clock frequency 1 GHz RAM 1 GB (WindowsTM 2000 / WindowsTM XP) 2 GB (WindowsTM Vista) Free hard disk Program: 500 MB memory Data: 2 GB (for approx. 5’000 determinations) Operating system WindowsTM 2000 SP4 WindowsTM XP Professional SP2 WindowsTM Vista WindowsTM 7 Connections free USB connection www.metrohm.com td., CH-9100 Herisau ohm L witzerland by Metr , printed in S SW Subject to modifications Layout by Ecknauer+Schoch A 8.859.5004EN – 2012-07