Ionophore‐based Heterogeneous Calcium Optical Titration

Abstract

Recently, the field of complexometric titration significantly progressed with the advent of ionophore‐based titration reagents. We present here for the first time an ionophore‐based heterogeneous optical titration method for calcium. The all‐in‐one reagent was composed of chromoionophore, ion‐exchanger and calcium ionophore in dichloromethane (DCM). The endpoint of this reverse titration scheme was determined by the color change of the DCM phase (blue to red). The ion‐exchange theory borrowed from ISE membranes was used to simulate the titration curve in a simplified manner. The phase separation speed during titration was found much faster at and beyond the endpoint. A mechanism was proposed for this phenomenon, with zeta‐potential measurements on ion‐selective nanospheres to support the hypothesis. Calcium titration in a urine sample was also successfully demonstrated and compared with EDTA titration with potentiometric ion‐selective electrodes as endpoint indicator. The proposed reagent serves as an alternative to the classical EDTA.

Chemiluminescent Ion Sensing Platform Based on Ionophores

“…The ionophore, cation exchanger TFPB, and LG 2+ are dissolved in a water immiscible organic phase, which could be a PVC-DOS film or as simple as dichloromethane (DCM). While plasticized PVC films were widely employed for ion-selective electrodes and optodes, DCM was also recently used for ionophore-based sensing and titration. , When the organic phase contacts the aqueous sample, the ion-exchange between the target ion (M n + ) and LG 2+ will occur according to eq , where L is the ionophore, LM n + is the complex formed between L and M n + , and aq and org represent the aqueous phase and the organic phase, respectively. Notice that LG 2+ is a divalent organic cation, the exchange stoichiometry is different compared with previous ion-selective optodes that involve H + chromoionophores or monovalent solvatochromic dyes. − The overall equilibrium constant K ex1 is expressed in eq , with the concentrations in the organic phase expressed with brackets, a M n + and a LG 2+ being the activity of M n + and LG 2+ in the aqueous phase, respectively.…”

“…The results shown above were collect with the sensing components dissolved in DCM, but sometimes the liquid DCM is not favored by the users since it is quite volatile, although the preparation with DCM was very convenient. , Therefore, DCM was replaced with a DOS plasticized PVC film. The PVC-DOS films were drop cast on glass slides and inserted into the samples for 30 min.…”

“…While plasticized PVC films were widely employed for ion-selective electrodes and optodes, DCM was also recently used for ionophore-based sensing and titration. 30,31 When the organic phase contacts the aqueous sample, the ion-exchange between the target ion (M n+ ) and LG 2+ will occur according to eq 1, where L is the ionophore,…”

Response Patterns of Chromoionophore-Based Bulk Optodes Containing Lipophilic Electrolytes: Toward Background-Independent pH-Sensing

“…Nevertheless, there is no such general solution for optodes. Existing approaches to address the problem of optical response cross-sensitivity include titration of the sample with a nanoparticle sensor phase, implementation of redox systems, development of new classes of fluoroionophores, , and solvatochromic − and electrochemiluminescent dyes. , Reference introduces promising K + - and Ca 2+ -selective optodes based on polyoctylthiophene nanospheres containing two neutral ionophores: one selective to the analyte ion and the other selective to H + . Novel fluoroionophores are capable of changing their optical properties by binding to target ions (e.g., lithium or potassium cations), thus allowing direct optical read-out.…”

Distance and Color Change Based Hydrogel Sensor for Visual Quantitative Determination of Buffer Concentrations

“…On the other hand, portable sensors with visual readout (including color and distance) are becoming increasingly more welcome for onsite and in situ applications. − The cost of the sensors will be significantly reduced if the sensor signals are acquired in instrumentation-free ways. Visual readouts have been reported for a number of sensors which monitored signals including the change of color, distance, volume, and pressure. − Previously, we have introduced ion-selective hydrogels that contain highly selective ionophores for Na + , K + , Ca 2+ , and Pb 2+ . , The hydrogel interacted dynamically with the sample, and the results could be conveniently obtained by analyzing the change of distance and color (within the gel or in the sample solution).…”