Web Date: November 15, 2011
Overthrowing a Titrant
Titration, the stalwart procedure for figuring out the amount of a chemical dissolved in a sample, usually requires the precise determination of volume. Now, researchers have developed a simplified approach that uses a tracer instead of volume measurements (Anal. Chem., DOI: 10.1021/ac2025656).
Since measuring volume during hand titrations is tedious, scientists sometimes use mechanical pumps to automatically perform titrations, says Michael DeGrandpre of the University of Montana. The problem, DeGrandpre says, “is that pumps are expensive, and can be unreliable.” Plus, the equipment isn’t easily portable, so researchers often must haul environmental samples to a laboratory for analysis.
To make titrations simple and field-friendly, DeGrandpre and his team turned to a tracer. The tracer is any substance that, when added to a titration reagent, or titrant, in a known quantity, allows researchers to quickly determine how much titrant has been added to a sample. The chemists picked tracers that they could follow easily using simple, automated measurements with portable devices such as spectrophotometers.
The researchers tested the tracer approach on an acid-base titration. First, they added blue food coloring as the tracer to a solution of sodium hydroxide, the titrant, both in known concentrations. Then, they titrated a solution of hydrochloric acid with the tracer-laced base until it reached a neutral pH. The researchers then measured the final concentration of blue dye with a spectrophotometer, determining how diluted it had become after mixing with the acid. The researchers could then calculate the concentration of acid in the solution using only the tracer’s dilution factor, the reaction stoichiometry, and the titrant concentration.
The researchers performed two other test titrations, each with different titrants and tracers. In all three cases, the measurements agreed with results from conventional titrations, says DeGrandpre, demonstrating the method’s versatility.
- Chemical & Engineering News
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