Colorimetric ionophore-based coextraction titrimetry of potassium ions

Abstract

Potassium ion concentration can be successfully determined volumetrically by moving the titration from a homogeneous phase to a two phase solvent system. This is because potassium can be readily complexed in a selective and thermodynamically stable manner by ionophores such as valinomycin. Previous work demonstrated the successful titration of potassium by ion-exchange into an organic phase containing valinomycin, but the sample itself served as titrant, which is not sufficiently practical for routine applications. This problem is overcome here by a co-extraction based approach, with the sodium salt of the water soluble lipophilic anion tetraphenylborate as titrant. The extraction of potassium tetraphenylborate must be preferred over that of the hydrogen ion-tetraphenylborate pair, which is used to indicate the endpoint by the presence of a lipophilic indicator in the organic phase. This is controlled by the sample pH, which for the conditions chosen here is around 7 for optimal sharpness and accuracy of the endpoint. The approach is demonstrated in a colorimetric detection approach, by use of a tethered digital camera and subsequent automated analysis of the resulting image files. The potassium analysis in a variety of samples is successfully demonstrated, including blood serum.

Conjugated molecules for colourimetric and fluorimetric sensing of sodium and potassium

“…Optical sensors are generally characterised by a slightly simpler operation over ion-selective electrochemical sensors which require careful calibration, temperature and pH control. 7 Typically, solution phase optical sensors for Na + and K + and other metal ions have been based on size-selective heteroatomcontaining macrocycles such as the crown ether, 8,9 azacrown, 10,11 cryptand 12 or calixarene 13,14 as the binding unit. The binding unit is covalently bonded to a chromophore or fluorophore which exhibits a change in absorbance or fluorescence properties as a result of the binding event.…”

Towards Green Titration: Batchwise Titration with Reusable Solid Sorbed Indicators

“…Previously, some studies on micro-batchwise titration have been reported. 4,5 This study aims to develop an alternative and cost-effective approach to make the reagent reusable in conventional batch titration towards a green chemical analysis. Moreover, natural reagents were also of interest as alternatives to commercial synthesized chemicals.…”