Coulometric determination of sulfur speciation in natural waters

A systematic analytical method for the species of trace sulfur in water has been developed by using electrochemically coulometric titration in combination with several separation and concentration techniques.Based on the reaction of iodine with sodium azide,the studies were carried out on the catalytically coulometric determination of ppb levels of ionic or molecular sulfides,thiosulfates and hydrogen sulfide in wateri constant current coulometric determination of sulfites;and indirect coulometric determination of sulfate salts and esters.Coupled with the determination of the content of total sulfur,the scope of distribution of the species of inorganic sulfur(including trace sulfur compounds in labile state)and organic sulfur in water was given.The method thus developed was found to be featured by being easy and reliable to operate with a higher sensitivity and reproducibility and to be applicable to the analysis of sulfur species in water.

STUDY ON DETERMINATION OF DIC IN SEAWATER BY COULOMETRIC METHOD

The complete analytical procedure using coulometric titration to determine dissolved inorganic carbon (DIC) in seawater consists of studying the setup of the coulometric titration, the solution composition of the coulometer cell. conrrectly judging the titration end-point, and establishing(and evaluating the accuracy of) the DIC determination system.

Application of Polyaniline Incorporated Carbon Particles Coated Platinum Electrode in Coulometric Titration to Determination of Polyisoprene Alcohol

The feasibility of using electrodes modified with polyaniline incorporated carbon particles films for improving the precision of coulometric titration is demonstrated. The problem of large deviation produced during determining polyisoprene by coulometric titration with direct titration technique(double Pt electrodes indicating electrode) has been solved. In the titration process, polyisoprene alcohol, an electro-inactive species, is adsorbed on the surface of the bare Pt electrode, which inhibits the electrode reaction of Br - and Br 2. Therefore, when the titration reaches the end-point, the detected current will slowly change with time, which can make the repeatability of end-point poor. The atomic force microscopic images show the morphology of the electrode surface of adsorbing polyisoprene alcohol. The application of the chemically modified electrode instead of the bare Pt electrode to indicating the end-point has been investigated. The results show that the Pt electrode coated with polyaniline incorporated carbon particles films is an excellent indicator electrode. This electrode has advantages that the indicating signals are sharp and repeatable at end-point. The precision and the accuracy of the determination of polyisoprene alcohol are satisfactory.

COULOMETRIC TITRATION OF MYLIS

A method for the determination of Mylis by coulometric titration was developed.The titration was carried out in a mixture of 1 mol/L KBr-2 mol/L HCl(1:1)and bromine was generated at the anode, Mylis reacted with one mole of bromine with a n value of 2. The advantages of this method are simple and rapid,it can be used to analyze small amount of sample.

Application of Coulometric Titration for the Certification of Primary Reference Materials of Pure Substances

In this article, the block scheme and metrological characteristics of the State primary standard of the mass (molar) fraction and mass (molar) concentration of the component in the liquid and solid substances and materials based on coulometric titration GET 176-2010 are given. Primary reference materials certified by coulometric titration in the Ural Scientific and Research Institute for Metrology include eight certified reference materials (CRMs) of pure solid substances (mostly salts of sodium or potassium) and one hydrochloric acid solution CRM. The metrological characteristics of these reference materials and the scheme of their application in titrimetric analysis are shown. The expanded uncertainty of the certified value (mass fraction for the solid substances or molar concentration for the solution) is in the range from 0.018% to 0.05%. Information about two primary reference materials of high purity iron and lead nitrate certified by controlled-potential coulometry with expanded uncertainty from 0.04% to 0.07% is also given.

Coulometric Response of H-Selective Solid-Contact Ion-Selective Electrodes and Its Application in Flexible Sensors+

The analytical performance of H+-selective solid-contact ion-selective electrodes(SCISEs)based on solid contact polyaniline doped with chloride(PANI(Cl))and poly(3,4-ethylenedioxythiophene)doped with poly(styrene sulfonate)(PEDOT(PSS))was characterized by a developed coulometric signal transduction method.PEDOT(PSS)solid contact is covered by PVC based H+-selective membrane.The obtained coulometric signal demonstrates that the cumulated charge can be amplified by increasing the capacitance of solid contact.SCISEs covered with spin-coated membrane behave faster amperometric response than electrodes with drop-cast mem-brane.In contrast to earlier works,the amperometric response and impedance spectrum demonstrates H+transfer through SCISEs is independent from the thickness of membrane.The exceptional behavior of PANI(Cl)H+-SCISEs shows that the capacitance estimated from impedance spectrum at low frequency 10 mHz and coulometric signal of PANI(Cl)based SCISEs is influenced by the applied po-tentials,whereas PEDOT(PSS)solid contact is independent from the chosen applied potentials.Furthermore,preliminary investiga-tions of coulometric signal transduction on flexible pH sensor implies its potential applications in wearable sensors for sweat ion concentration detection.

Selective DNA detection at Zeptomole level based on coulometric measurement of gold nanoparticle-mediated electron transfer across a self-assembled monolayer

A selective DNA sensing with zeptomole detection level is developed based on coulometric measurement of gold nanoparticle （AuNPs）-mediated electron transfer （ET） across a self-assembled monolayer on the gold electrode. After immobilization of a thiolated hairpin-structured DNA probe, an alkanethiol monolayer was self-assembled on the resultant electrode to block [Fe（CN）6]3-/4 in a solution from accessing the electrode. In the presence of DNA target, hybridization between the DNA probe and the DNA target breaks the stem duplex of DNA probe. Consequently, stem moiety at the 3＇-end of the DNA probes was removed from the electrode surface and made available for hybridization with the reporter DNA-AuNPs conjugates （reporter DNA-AuNPs）. The thiolated reporter DNA matches the stem moiety at the 3＇-end of the DNA probe. AuNPs were then en- larged by immersing the electrode in a growth solution containing HAuCI4 and H202 after the reporter DNA-AuNPs bound onto the electrode surface. The enlarged AuNPs on the electrode restored the ET between the electrode and the [Fe（CN）6]3 -/4-, as a result, amplified signals were achieved for DNA target detection using the coulometric measurement of Fe（CN）63- elec- tro-reduction by prolonging the electrolysis time. The quantities of ET on the DNA sensor increased with the increase in DNA target concentration through a linear range of 3.0 fM to 1.0 pM when electrolysis time was set to 300 s, and the detection limit was 1.0 fM. Correspondingly, thousands of DNA （zeptomole） copies were detected in 10-μL samples. Furthermore, the DNA sensor showed excellent differentiation ability for single-base mismatch.

Coulometric determination of dissolved hydrogen with a multielectrolytic modified carbon felt electrode-based sensor

A multielectrolytic modified carbon electrode （MEMCE） was fabricated by the electrolytic-oxidation/reduction processes. First, the functional groups containing nitrogen atoms such as amino group were introduced by the electrode oxidation of carbon felt electrode in an ammonium carbamate aqueous solution, and next, this electrode was electroreduced in sulfuric acid. The redox waves between hydrogen ion and hydrogen molecule at highly positive potential range appeared in the cyclic voltammogram obtained by MEMCE. A coulometric cell using MEMCE with a catalytic activity of electrooxidation of hydrogen molecule was constructed and was used for the measurement of dissolved hydrogen. The typical current vs. time curve was obtained by the repetitive measurement of the dissolved hydrogen. These curves indicated that the measurement of dissolved hydrogen was finished completely in a very short time （ca. 10 sec）. A linear relationship was obtained between the electrical charge needed for the electrooxidation process of hydrogen molecule and dissolved hydrogen concentration. This indicates that the developed coulometric method can be used for the determination of the dissolved hydrogen concentration.

Development of a new ferulic acid certified reference material for use in clinical chemistry and pharmaceutical analysis

This study compares the results of three certified methods, namely differential scanning calorimetry (DSC), the mass balance (MB) method and coulometric titrimetry (CT), in the purity assessment of ferulic acid certified reference material (CRM). Purity and expanded uncertainty as determined by the three methods were respectively 99.81%, 0.16%; 99.797, 0.16%; and 99.81%, 0.26% with, in all cases, a coverage factor (k) of 2 (P=95%). The purity results are consistent indicating that the combination of DSC, the MB method and CT provides a confident assessment of the purity of suitable CRMs like ferulic acid. (C) 2015 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.