Ionophore-Based Titrimetric Detection of Alkali Metal Ions in Serum

Abstract

While the titrimetric assay is one of the most precise analytical techniques available, only a limited list of complexometric chelators is available, as many otherwise promising reagents are not water-soluble. Recent work demonstrated successful titrimetry with ion-exchanging polymeric nanospheres containing hydrophobic complexing agents, socalled ionophores, opening an exciting avenue in this field. However, this method was limited to ionophores of very high affinity to the analyte and exhibited a relatively limited titration capacity. To overcome these two limitations, we report here on solvent based titration reagents. This heterogeneous titration principle is based on the dissolution of all hydrophobic recognition components in a solvent such as dichloromethane (CH 2 Cl 2 ) where the ionophores are shown to maintain a high affinity to the target ions. HSV (hue, saturation, value) analysis of the images captured with a digital camera provides a convenient and inexpensive way to determine the end point. This approach is combined with an automated titration setup. The titrations of the alkali metals K + , Na + , and Li + in aqueous solution are successfully demonstrated. The potassium concentration in human serum without pretreatment was precisely and accurately determined as 4.38 mM ± 0.10 mM (automated titration), which compares favorably with atomic emission spectroscopy (4.47 mM ± 0.20 mM).

Ionophore‐based Heterogeneous Calcium Optical Titration

“…While in previous work we referred to the optode response function in order to simulate the theoretical titration curves for monovalent ions , the equation became much more complicated for a divalent ion system. Here, we provide a theoretical simulation based on a simpler scheme, which was adopted for previous ionophore‐based titrations involving solvatochromic dyes and originally borrowed from ISE membranes .…”

Colorimetric ionophore-based coextraction titrimetry of potassium ions

“…Recently, the titrimetric analysis of potassium was demonstrated with a two-phase solvent system, using valinomycin as selective molecular probe in the organic solvent that also contains a lipophilic cation-exchanger. 22 Any potassium will then quantitatively ion-exchange with the original counter ion of the cation-exchanger in the organic solvent. Endpoint detection was achieved by a lipophilic pH indicator in the organic phase: after exhaustive ion-exchange of the original counter ion, the more tightly bound hydrogen ion is expelled, again by ion-exchange with potassium.…”

“…The approach was demonstrated to be sufficiently selective for the titration of serum samples. 22 However, the titrant is either the sample solution or the organic phase containing the selective reagents. The former is not practical as it requires a large sample volume and a complicated assay that is prone to cross-contamination.…”

An Ionophore‐Based Anion‐Selective Optode Printed on Cellulose Paper

“…Such optodes typically rely on use of an organic plasticizer, plasticizer-polymer mixture, or self-plasticized polymer as a medium to dissolve the sensing ingredients, and may be employed in different configurations, including films, micro/nano-particles, or liquid to satisfy requirements of different applications. [3, 4] …”

“…Metalloporphyrin, metallophthalocyanines, metal-salophen complexes, and other organometallic compounds have been used for sensing anions such as Cl − , NO 2 − , PO 43 − , F − , I − , and salicylate. [3,4,8,9] Herein, a fluoride-selective optode based on Al(III) octaethylporphyrin (Al[OEP]) as the ionophore [9] is employed to demonstrate the new paper-based ISO concept.…”