Indirect determination of zinc by thiol complexation and iodine coulometric titration with photocell detection

Mercado, Jeralyne B. Padilla; Konkolewicz, Dominik; Bretz, Stacey Lowery; Danielson, Neil D.

doi:10.1016/j.microc.2017.05.013

Cited by 2 publications

(3 citation statements)

References 10 publications

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“…Certainly, extensions of the coulometry student experiment can be envisioned. The indirect determination of zinc after thiol complexation at alkaline pH and then titration by iodine using this same coulometry instrument, a second research chapter in ref , has been recently published by us . Students could be involved in a redesign of the circuit to gain experience working with operational amplifiers.…”

Section: Discussionmentioning

confidence: 99%

Iodine Coulometry of Various Reducing Agents Including Thiols with Online Photocell Detection Coupled to a Multifunctional Chemical Analysis Station To Eliminate Student End Point Detection by Eye

et al. 2018

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Multifunctional chemical analysis (MCA) systems provide a viable alternative for large scale instruction while supporting a hands-on approach to more advanced instrumentation. These systems are robust and typically use student stations connected to a remote central computer for data collection, minimizing the need for computers at every student workspace. MCA networks offer multiple measurement capabilities; however, constant-current coulometry is still an uncommon MCA option. The characterization of an assembled teaching coulometry instrument for online data acquisition using an MCA system is described. A constantcurrent source connected to nonisolated Pt electrodes in a 150 mL beaker serving as the reaction cell caused the iodine titrant to be electrochemically generated for subsequent reaction with the analyte reducing agent. A photoresistor mounted on the stir plate below the beaker monitored the darkening of the solution due to formation of the starch−iodine complex. The change in voltage from an operational amplifier circuit permitted this titration curve to be stored by the MCA system for subsequent graphical analysis by Excel. Characterization of the instrument for direct analyte determination is performed with ascorbic acid, thiols, thiosulfate, and bisulfite. The number of electrons per mole of thiol for iodine titration of glutathione and N-acetylcysteine varied differently as a function of pH, indicating different reaction pathways. Ascorbic acid and the thiols are determined in dietary supplements with a recovery of 90−100%, and % RSDs of triplicate measurements ranged from 0.7% to 5%.

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Section: Discussionmentioning

confidence: 99%

Iodine Coulometry of Various Reducing Agents Including Thiols with Online Photocell Detection Coupled to a Multifunctional Chemical Analysis Station To Eliminate Student End Point Detection by Eye

et al. 2018

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“…Around thirty related articles were referenced as an indication of the usefulness of the constant-current coulometry. In the last six years, some articles based on the use of coulometry, from the analytical point of view, were published describing the application to the detection and quantification of a variety of compounds from metals, pharmaceuticals, water, antioxidants, gases, and certified materials [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Furthermore, numerous papers on coulometry have been published in education journals due to their instructional character (see recent papers on coulometry for chemical education [ 19 , 20 , 21 ] and the references therein).…”

Section: Introductionmentioning

confidence: 99%

“…Notwithstanding its versatility, the implementation of the spectrophotometric technique is generally more expensive. A possible way around such budgetary constraints resulting from using spectrometry without a big loss in flexibility can be resolved by the use of a colorimeter for the visible detection [ 10 , 20 , 25 ]. In this work, a simple colorimeter was developed based on a RGB LED as a light emitter, coupled to a visible light detector as a photo resistor (LDR/photodiode).…”

Section: Introductionmentioning

confidence: 99%

Coulometer from a Digitally Controlled Galvanostat with Photometric Endpoint Detection

González-Arjona

González

López-Pérez

et al. 2022

Sensors

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In this work, a coulometer was developed from a digitally controlled galvanostat. A simple colorimeter based on a RGB LED was used as a light emitter coupled to light detectors, while light dependent resistance (LDR) and photodiodes have been developed as endpoint detectors. Both hardware and software have been adapted from the original galvanostat design. Regarding the hardware, new electrical signal conditioners (filters and voltage dividers) were included to optimize the working system. The software was developed based on an open source Arduino UNO microcontroller. The different variables that control the titration process are managed by an add-in module for Excel data acquisition software that is freely available. A study of the possible variables that influence the titration process has been carried out. The system was tested with two classical coulometric titrations such as iodometry (thiosulfate, ascorbic acid) and acid/base (potassium acid phthalate as standard). The developed system is versatile as different endpoint color indicators can be employed (starch and phenolphthalein for the investigated reactions). Different experimental arrangements have been studied: the nature of the electrodes (Pt, Ag), type of cells (two separate compartments or a single compartment), and light detectors (LDR, photodiode). The influence of several experimental parameters (both electrical, light, and integration time) was studied and chosen to obtain the best performance of the complete system. Reproducibility results below 1% can be obtained under controlled conditions. In the case of acid/base titrations, the presence of atmospheric carbon dioxide was detected, whose interference was mainly affected by the stirring rate and the titration time.

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Indirect determination of zinc by thiol complexation and iodine coulometric titration with photocell detection

Cited by 2 publications

References 10 publications

Iodine Coulometry of Various Reducing Agents Including Thiols with Online Photocell Detection Coupled to a Multifunctional Chemical Analysis Station To Eliminate Student End Point Detection by Eye

Iodine Coulometry of Various Reducing Agents Including Thiols with Online Photocell Detection Coupled to a Multifunctional Chemical Analysis Station To Eliminate Student End Point Detection by Eye

Coulometer from a Digitally Controlled Galvanostat with Photometric Endpoint Detection

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