Accuracy, Reproducibility, and Walk-Away Operation
Titrators are basic laboratory tools that add solutions of one reagent to solutions of another with varying degrees of precision. Labs employ titrators mostly in analytic mode to measure concentrations of analytes.
Titrators are basic laboratory tools that add solutions of one reagent to solutions of another with varying degrees of precision. Labs employ titrators mostly in analytic mode to measure concentrations of analytes. Labs also use titration to prepare reagents and stock solutions tightly controlled for pH or some other characteristic. Vital components of modern titrators are electrodes or detectors that monitor the desired property—pH, oxidation, or alkalinity, for example.
Titration end points and how they are determined may be based on almost any chemical state or interaction. The most prevalent are pH, chemical complexation, oxidation reduction, and Zeta potential. Each technique requires a separate detector, and assays involving more than one quantity require multiple electrodes.
Lab Manager Magazine’s 2012 survey of end users reflects how end users acquire and employ titration systems. Half those polled had at least one titrator in their labs, suggesting that titration remains a specialized technique even in quality control environments, which comprised eight percent of workplaces surveyed. Potentiometric (47 percent) and Karl Fischer (coulometric 22 percent; volumetric 27 percent) made up the lion’s share of titration modes. Sample preparation techniques were common and varied, reflecting the diverse nature of titration assays. Forty-eight percent of users employed an autosampler, 12 percent used a homogenizer, and 32 percent required some form of drying (evaporation 11 percent; oven 21 percent). Not surprisingly, 98 percent of respondents cited “accuracy” as the number one characteristic they looked for in a titrator.
Those who took high school chemistry recall using a manually operated burette and separate pH meter to quantify acid or base concentrations. Measurements were only as good as the operator’s eye and acumen in plotting graphs of volume versus pH or whatever quantity was being measured. Today’s titrators are automated, typically sold with the detector(s) of choice, perform basic calculations unattended, and provide a level of accuracy unheard of in the “old days.”
“I have often thought about colorimetric acid-base titrations that we did in high school with indicators like bromthymol blue and phenolphthalein red,” muses John MacFarlane of JM Science. “I’m certain I always over-titrated. Not anymore!”
Titration, in particular Karl Fischer titration, is a mature lab technique used in many industries that rely on “wet” analysis. With liquid dispensing reduced to settled engineering, most improvements in recent years have centered on automation, software, and user interface.
Automatic and accurate endpoint determinations, color touch screens, built-in printers, enhanced storage data handling capabilities, and compatibility with existing lab data networks are now relatively common. Titration software now stores methods, automatically calculates end points, and adheres to regulatory guidelines for both operation and audit purposes.
Technical instrument improvements tend to be incremental. For example, Japan’s Hiranuma Company, whose instruments JM distributes in the United States, has developed a background compensation method that suppresses the production of interfering substances on the anode electrode for coulometric Karl Fischer titration. This results in improved determination and precision for ultra-trace moisture determinations (lower than 10μg). “They have also improved the AC polarization current detection method for volumetric Karl Fischer determinations, which is now userselectable to match specific applications,” MacFarlane says.
Robert Menegotto, president of Mantech (Guelph, ON), claims his company is the only remaining North American manufacturer of titrators. Automated titrators,he says, provide accuracy, precision, labor savings, automatic reporting to LIMS or data networks, error-free data transcription, and elimination of user bias. “The smallest drop from a burette is 250 microliters. Our instruments get down to less than one microliter. They allow you to pinpoint the end point.”
Automation has transformed titration, he says, and not just in the traditional sense of robotics. Through automated functions, users can schedule sampling and calibrations, initiate unattended quality checks through the software, and of course dispense reagents with superhuman accuracy. Moreover, these functions may be deployed at or near a process line with minimal human intervention.
Automated titration has also contributed, albeit modestly, to the “greening” of laboratory operations. Systems can operate on very small samples, which means extremely low reagent consumption and much less waste. Some systems can measure three or more quantities— for example, pH, alkalinity, chloride, and hardness—from the same sample, provided the instrument has the right detectors or electrodes. Newer capabilities for quantifying such things as fluoride, conductivity, and turbidity—not traditional titration measurements— further reduce the time and reagents required to set up separate measurements.
Fairfax Water (Herndon, VA) uses automated titrators to measure alkalinity, conductivity, total hardness, and calcium hardness. The latter two tests use a colorimetric monitoring probe. The public utility has also recently acquired an ammonia ion-sensitive electrode.
Lab supervisor Craig Rice describes titrators as one of the most difficult equipment purchases. “Titrators are so modular, especially for a lab running as many tests as we do.” Mr. Rice concedes that other instruments offer many options, “but by the time you figure out what you require in an autotitrator, determine the modules you need, and consider the varied approaches different vendors take, comparing ‘apples to apples’ becomes difficult. It would be easier if we were just doing alkalinity.”
One would think that mixing and matching titrators with detectors would be a simple matter. Not so, says Mr. Rice. Depending on the vendor and model, instruments may require extra ports to accommodate all those electrodes. Autosampler and liquid handling capabilities may also require upgrades, depending on the number of reagents demanded by typical workflows. “Some reagents and buffers may require precisely monitored piston-operated dispensing, while some will get by with a peristaltic pump. Plus you need enough room on the autosampler head.”
Overall, says Mr. Rice, vendors are “working very hard” to find the proper balance between satisfying a wide range of users and providing instruments at reasonable cost. “The technology is improving, moving in the right direction.”
For additional resources on titrators, including useful articles and a list of manufacturers, visit www.labmanager.com/titrators