Green Chemistry: A Simple Manual Apparatus for Potentiometric and Conductometric Micro-Titration of Small Samples for the Educational Laboratory

Abstract

A simple manual micro-titration method is proposed for the potentiometric and conductometric titration of 200 to 800 µL of liquid samples. The sample to be titrated is dispensed into the titration chamber; the bottom section of a plastic test tube that is glued to the center of a small stirring magnet. After inserting the sensing probe and the tip of the titrant delivery tip into the titration chamber, the chamber-stirring magnet assembly is spun at low speed using a conventional magnetic stirrer. Titrant is delivered (with 0.2 µL resolution) from the submerged tip of a 100-µL capacity micro-pipette by rotating the plunger with the locking ring unlocked. The apparatus has been used for potentiometric titration and conductometric titration of acids and bases usually encountered in educational laboratories. Compared with macro-scale titrations, the obtained accuracy was between +2.2% and -3.9% relative error and the precision ranged between 1.6% and 2.9% relative standard deviation. The proposed procedure cuts the reagent consumption to 1% or less compared with conventional macro-scale titrations.