Eric Trompier describes the most important factors to be taken into account in order to ensure reliable potentiometric titration measurements and looks at how modern instruments help laboratories achieve them effortlessly.
Potentiometric titration is commonly employed in laboratories to determine the physicochemical parameters of products, which are directly or indirectly used or consumed in our daily life. It is therefore a permanent challenge for all laboratories performing analyses of this type to use a methodology that guarantees the quality of the result obtained and to be able to provide reliable analytical information to any control body that requests it.
First, the expression of the quality of results obtained. This starts with working methods, theso-called aGood Laboratory Practice'. The operator has to keep track of results by relying on his memory and/or a paper procedure at the same time as he operates the instrument. To simplify the operator's task and avoid operating errors, special GLP procedures have been embedded inside TitraLab instruments, making it impossible to forget or misperform operating steps. Second, the ability of the instrument to perform accurate titrations. Reliable stirring and reproducible electrode positioning are crucial here. On TitraLab workstations, stirring is electronically controlled and the speeds are selectable. Magnet stirring starts and stops progressively to avoid a loss of control that could potentially damage electrodes. The bayonet concept of the electrode head allows electrodes and tubing to slot securely in place in one single movement.
Precise burette titrant delivery and electrode signal acquisition also have a direct influence on the accuracy and reproducibility of your measurements. On TitraLab titrators, the burette specification meets ISO8655-3 recommendations for each volume whereas the titrator burette/motor combination allows a resolution as low as 0.1µl to be reached. The electrode signal acquisition offers a ±0.1 mV resolution over a ±2000 mV measuring range. This means that a titration run with TitraLab can reach a few tenths of a µl reproducibility for equivalence point determinations, depending on your application. For even greater measurement accuracy and quality, both electrode inputs and burettes can be calibrated to comply with ISO 9001 and ISO 17025.
Measurement traceability and result archiving is essential to answer key questions: who has done what, when, what was used to obtain each of the specific measurements archived. TitraLab analysers offer a choice of archiving solutions: paper, embedded instrument memory and computer systems. Whatever the solution chosen, all elements required to individually identify each result need to be reported. Results can be expressed according to the specific need, ranging from a detailed report to a concise printout. The permanent embedded result archiving capability is particularly useful in the event of printer problems, as no information is lost. A result archiving capacity encompassing up to 200 individual sample analysis results, 100 reagents and electrode calibrations ensures perfect archiving of large series of samples without the need for a PC. For long-term archiving however, electronic filing is essential and here again TitraLab offers an ideal solution with its dedicated TitraMaster PC software.
When you need to be sure of your results, you need to be sure of the entire analytical path, from the operating interface that guides the operator with clear-text menus to the final result archived with all information related to its acquisition.
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Eric Trompier is TitraLab Product Specialist with Radiometer Analytical SAS, Villeurbanne Cédex, France. www.radiometer-analytical.com
