Although titrations have been in the standard repertoire of laboratory chemists for at least a couple of centuries, scientists began to innovate and optimize new methods in the first half of the twentieth century for the oil industry, to quantify impurities or calibrate pH in petroleum products and make decisions about adapting the refining process. In a standard titration, one adds a solution (the titrant) containing a known concentration of a reactive compound to a sample (the analyte) containing an unknown amount of corresponding substrate. As the titrant is added volumetrically via burette, the reaction consumes it until an equivalence point denoted by a characteristic change in the analyte, such as a change in color or pH, is reached. Volume is a surrogate to calculate the unknown in the analyte.
There is a multitude of titration types, and extensive guides to performing them to standardized specifications, assembled by ASTM International over the course of more than 100 years. Although the fundamental principle of dispensing titrants with a burette is immutable, automation has optimized procedures to exert much finer control, with piston-driven burettes capable of delivering sub-microliter amounts.
Automated systems have also moved beyond unreliable and subjective indicators dependent on the user’s acuity and training to electrodes and sensors that measure, record, and store precise endpoints and associated data. Therefore, a pH electrode mediates acid-base titrations, a silver electrode resolves precipitation assays, ion-selective electrodes or conductivity cells gauge electrical conductivity, and so on.
A Karl Fischer titration (KFT) determines the amount of water in a substance via oxidation of sulfur dioxide to sulfuric acid by iodine. Fischer’s original formulations were directed toward quantifying water in crude oil; addition of pyridine catalyzed the reaction, resulting in a cloying odor and oxidation of iodine to an indicative brown color. Subsequent amendments included incorporation of the base imidazole in KF reagent mixtures, and substitution of platinum electrodes; KFT can thus be performed either volumetrically or coulometrically, in which water is calculated from charge passed between two electrodes. In both principle and practice, the method can determine water content in materials from petroleum to pasta. Food scientists and culinary strategists employ KFT to choose stay-fresh packaging, and to finely calibrate the degree of crunch consumers associate with their favorite snack foods.
Although automation has removed some user-introduced confounding variables and has streamlined procedures, the variety of protocols, electrodes, and reagents calls for a modular approach to titration, where one system can provide a high degree of variability.
Mettler Toledo offers the Excellence series of titrators, whose modularity and array of accessories allow for a wealth of “plug-and-play” titrations, which can be executed potentiometrically, conductometrically, or complexometrically. The Excellence T7 can be upgraded to the T9 model; both can be adapted to fit previous and future attachments to diversify titration options, and driven to higher throughput via InMotion autosamplers, integrating robotic arms with sample carousels.
The Metrohm OMNIS is a dedicated high-throughput titration unit that can perform parallel operations via integration with small, medium, or large sample robots. The inherent scalability means that laboratories can accommodate industrial titration workloads while obviating many errors in operation and recording, improving safety, and maintaining data standards that meet the rigorous compliance expectations of audit trails.