Lower limits of the potentiometric microtitration of chloride with silver ions

The lower levels of the potentiometric titration of chloride with silver ions were investigated. The titrant was 0.001 N acetonic silver perchlorate. The titration media were acetone and acetic anhydride:acetone (4:1). A silver sulfide ion-selective indicator electrode and a double-junction reference electrode were use to monitor emf's. This titration is limited only by the trace amounts of chloride in the reagents used. Satisfactory results and well-defined titration curves were obtained down to 7 μg of chloride per 50 ml of solution (0.2 μmol; 4 × 10^?6N).A small polarization current can be used to enhance the potentiometric breaks of this titration. In an 80% methanolic medium with 0.001 N aqueous silver nitrate and a polarization current of ?0.4 μA, the lower practical limit of this titration was near 22.3 μg of chloride (1.26 × 10^?5N).     

Silver(I) ion-selective membrane based on Schiff base-p-tert-butylcalix[4]arene

A PVC membrane electrode for silver(I) ion based on Schiff base-p-tert-butylcalix[4]arene is reported. The electrode works well over a wide range of concentration (1.0 x 10(-5)-1.0 x 10(-1) mol dm-3) with a Nernstian slope of 59.7 mV per decade. The electrode shows a fast response time of 20 s and operates in the pH range 1.0-5.6. The sensor can be used for more than 6 months without any divergence in the potential. The selectivity of the electrode was studied and it was found that the electrode exhibits good selectivity for silver ion over some alkali, alkaline earth and transition metal ions. The silver ion-selective electrode was used as an indicator electrode for the potentiometric titration of silver ion in solution using a standard solution of sodium chloride; a sharp potential change occurs at the end-point. The applicability of the sensor to silver(I) ion measurement in water samples spiked with silver nitrate is illustrated.     

The mechanism of the platinum indicator electrode in argentometry

A study has been made of the behaviour of platinum and some other inert electrodes in silver nitrate titrations. Where the metal surface has been subjected to a reducing treatment, such as cathodic polarization, before use, the electrode will often function as a silver indicator electrode throughout the titration. It has been shown experimentally that this is due to the formation of a layer of metallic silver upon the electrode by interaction of the surface with silver ions in solution. If the metal surface undergoes such pretreatment that it is oxidized, then its potential normally remains at the oxide value during a silver nitrate titration until the silver ion concentration is sufficiently great for this value to be exceeded by the silver silver ion potential; formation of metallic silver then again takes place and from this point onwards the electrode behaves as a silver electrode. A detailed interpretation of the behaviour of platinum after various pretreatments has been made along these lines.     

Determination of lead(II) by argentimetry

A titrimetric method for determination of lead(II), based on the reaction between plumbite and silver ions, is described. Sodium hydroxide solution is added to the sample until the precipitate of lead hydroxide has redissolved. The solution is then made 0.025M in sodium chloride and titrated with silver nitrate. The titration is monitored with a silver electrode. An error smaller than 0.5% has been obtained for 0.05M lead (II).     

Titrage potentiometrique des thiols en milieu organique a l'aide d'une electrode a monocristal de sulfure d'argent: Comparaison avec une electrode argent-sulfure d'argent classique

The responses of the silver sulfide membrane electrode (the so-called sulfideselective membrane electrode) to different primary and aromatic thiols and to hydrogen sulfide have been studied in an ethanol-benzene mixture. They have not been found in good agreement with the Nernst relationship. However, this electrode can readily be used to follow, by potentiometry, the precipitation of thiols and thiol-hydrogen sulfide mixtures with silver ions. The observed potential breaks are similar to those obtained with a conventional silver-silver sulfide electrode. As it needs neither pretreatment nor maintenance, the silver sulfide membrane electrode is therefore suitable for determining hydrogen sulfide and thiols in petroleum products by potentiometric titration.     

Measurement of surface potential at silver chloride aqueous interface with single-crystal AgCl electrode

The surface potential at the silver chloride aqueous interface was measured by means of a single-crystal silver chloride electrode (SCr-AgCl). The measurements were conducted by titration of the KCl solution with AgNO3, and vice versa. The SCr-AgCl electrode potentials were converted to surface potentials psi(0) by setting zero at the point of zero charge at pCl = 5.2. The psi(0)(pCl) function was linear, with a slope 12% lower with respect to the Nernst equation. It was demonstrated that the surface potential at the silver halide aqueous interface could be interpreted by means of the surface complexation model, originally developed for metal oxides.     

Conductometric titration of thiosulfate using new-type conductivity cells

The conductometric titration of thiosulfate with silver ions using non-conventional conductivity cells is described. For this purpose conductivity cells with different cell constants and electrode constructions, equipped with silver, amalgamated silver, stainless-steel and polished platinum electrodes were used. Two well-resolved break-points were observed at 1:1 and 2:1 silver/thiosulfate stoichiometries. Accurate conductometric determinations can be made, using the second break-points of the titration curves as equivalence points, in the range of thiosulfate concentrations 10(-4)-10(-2) M. Reverse titrations are less accurate.     

Application of silver/sulfide ion-selective electrode for the determination of aliphatic primary and secondary amines

Aliphatic primary and secondary amines were determined utilizing their reaction with carbon disulfide. A potentiometric titration of the formed dithiocarbamates (I) with silver nitrate using a silver/sulfide ion-selective electrode was carried out. The effects of solvent, base, temperature and reaction time were investigated. The optimum conditions for a quantitative formation of (I) requires a minimal amount of 1,4-dioxane, 2 drops of 0.2% sodium hydroxide solution, excess carbon disulfide to stand at room temperature for 15 min. The titration requires prior evaporation of the unreacted carbon disulfide at 46 ° C. An average recovery of 98.5% with a standard deviation of 0.69 was obtained for the analyzed amines.     

Potentiometric titration of cyanide using the cation-sensitive glass electrode as indicator

Summary The argentometric determination of cyanide was re-examined in order to compare the cation-sensitive glass electrode and the silver metal electrode as indicator electrodes for this titration. Contrary to earlier reports, the glass electrode is capable of indicating both titration end points and yields stoichiometric information comparable to or better than that obtained with the silver metal electrode. In the presence of redox interferences, the glass electrode is superior to the silver metal electrode for titration purposes.

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Zusammenfassung Die argentometrische Cyanidbestimmung wurde im Hinblick auf einen Vergleich der kation-empfindlichen Glaselektrode und der Silberelektrode als Indicatorelektroden nochmals untersucht. Im Gegensatz zu früheren Berichten ergab sich, daß die Glaselektrode beide Endpunkte der Titration anzeigen kann und Aussagen über die Stöchiometrie gestattet, die vergleichbar oder besser sind als die mit Hilfe der Silberlektrode erhaltenen. In Gegenwart von Oxydations- oder Reduktionsmitteln erweist sich die Glaselektrode als besser geeignet.

     

The potentiometric and amperometric determination of silver with mercaptophenylthiothiadiazolone and mercaptobenzthiazole

Summary The previously described gravimetric determinations of silver were used for the potentiometric and amperometric determinations of silver in the presence of interfering cations. The potentiometric titration of silver with MFTD (MBT) is a simple matter, if enough complexone is present, in both ammoniacal and neutral solutions. The amperometric determination of silver with MFTD (MBT) is carried out in neutral solution, containing complexone, with rotated platinum electrode and mercury-mercuric iodide half-cell, short-circuited through a microammeter. The only interfering elements are mercury, gold, and some of the platinum metals.     

银电极表面异亮氨酸单分子膜结构和表面性质的表面增强拉曼光谱研究

利用表面增强拉曼光谱(SERS)技术研究了在粗糙化银电极表面吸附的异亮氨酸自组装单层膜结构及其表面性质随溶液酸碱性和电极电位改变的特征.研究结果表明溶液pH值的变化并没有显著改变异亮氨酸分子在银电极表面以去质子化羧基吸附为主的特征.借助于高氯酸根离子这一SERS光谱探针,对异亮氨酸单分子膜的表面酸碱性质进行了表征和分析.而就电位改变对该单分子膜结构的影响而言,在所研究的电位范围内,单分子膜中的异亮氨酸分子是通过去质子化羧基与氨基两个位点而吸附的,且吸附作用随电位负移而呈现有规律的变化.     

Indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim in co-trimazole tablets using copper based mercury film electrode

A simple and rapid indirect potentiometric titration of sulphamethoxazole in the presence of trimethoprim contained in co-trimazole tablets is described. The method is based on the formation of a complex of sulphamethoxazole with a known excess of silver ions and the titration of unreacted silver ion potentiometrically using an inexpensive lab-made copper based mercury film electrode (CBMFE). The titration conditions have been optimized for the determination of 1.0-10.0 mg of sulphamethoxazole in pure and dosage forms. The precision and accuracy of the method have been assessed by the application of lack of fit test and other statistical methods. Overall mean recovery and relative standard deviations obtained were 99.88% and 1.32% (n=7) respectively. No interference was caused by other excipients present in pharmaceutical dosage forms. The application of this method for sulphamethoxazole assay in the presence of trimethoprim in tablets was validated by the comparison of results obtained by the proposed method with that of the British Pharmacopoeia (BP) method using F- and t-statistical tests of significance.     

Mercurous nitrate as a reductimetric reagent: The potentiometric titration of ferric iron in the presence of ions forming highly coloured thiocyanates

The reduction of ferric iron by means of mercurous salts in the presence of an excebs of ammonium, thiocyanate can be predicted on theoretical grounds. By consideration of the oxidation potentials involved it has been shown by calculation that quantitative reduction of the ferric iron is to be expected.—The titration may be effected potentiometrically using a bright platinum indicator electrode in conjunction with a silver/silver chloride electrode or a saturated calomel reference electrode. Ferric iron can be titrated in the presence of ions such as cobalt which form intensely coloured thiocyanate complexes.A possible method for the titration of molybdate by means of mercurous nitrate has been examined. The sensitivity of the method suffers from the instability of potential of the system under titration, but particularly since tungstate does not interfere, the method is worthy of further study.     

Automatic coulometric titration of acids

An apparatus is described for the automatic titration of acids by the constant current coulometric technique. The generator electrodes comprise a platinum cathode and a silver/silver bromide anode. The increase in pH resulting from the reduction of hydrogen ion at the cathode is indicated by a glass electrode, in conjunction with a Beckman Automatic Titrator which automatically monitors the titration and interrupts the generating current when the equivalence point pH is reached. Quantities of hydrochloric acid in the neighborhood of 0.12 millimole in 50 ml were titrated with a mean error of ^-0.07% and an average deviation from the mean of ±0.15%. The technique is applicable to any strong or weak acid, and to acid mixtures, provided that no substance is present which is either reducible at the platinum cathode or reactive in any way at the silver anode.     

A silver electrode in the potentiometric titration of thiols

A silver wire immersed in a thiol solution gives a potential responsive to the thiol concentration, and is a sensitive indicator electrode in the potentiometric titration of thiols with mercury(II) chloride, p-chloromercuryphenyl sulphonate, and silver nitrate at pH 4.5-9.5, 7-9.5 and 9.5 respectively. Titrations of simple thiols such as cysteine or a protein such as albumin are equally successful, but the potential break was smaller for the protein. The end-point could be determined within an increment of titrant equal to 5 nmole of thiol. An inert atmosphere is needed for titration at pH 7.     

2,6-bis-methylsulfanyl-[1,3,5]thiadiazine-4-thione as a Ag+-selective ionophore.

A silver ion-selective electrode was prepared with a polymeric membrane incorporating 2,6-bis-methylsulfanyl-[1,3,5]thiadiazine-4-thione as an ionophore, tri-n-butylphosphate (TBP) as a plasticizer and sodium tetraphenylborate (NaTPB) as an additive. The electrode exhibited a near-Nernstian response of 52 mV/decade over a wide linear concentration range of 1.0 x 10(-5) - 1.0 x 10(-1) M with a lower detection limit of 9.77 x 10(-6) M. The electrode exhibited excellent selectivity for silver ion over many of the alkali, alkaline-earth and transition metal ions. The electrode worked well over a wide pH range of 1.77 - 7.13. The response time of the electrode was less than 20 s. The sensor can be applied as indicator electrode for the potentiometric titration of Ag+ ions with Cl- ions.     

Precise and accurate determination of halogens in organic compounds using an amalgamated gold electrode

Precise and accurate titration of halogens in organic and inorganic materials has been studied. The halogen was titrated with coulometrically generated silver and determined potentiometrically by using an amalgamated gold indicator electrode. An argentometric titration curve using the amalgamated gold indicator electrode showed a large jump in potential at the endpoint as well as in mercurometric determination. Sodium carboxymethyl cellulose (CMC) and aluminum nitrate were added as they are most effective for clarifying the sample solution and eliminating adsorption of the halide ion on the silver halide generated. The electrolytes used were 0.5 M nitric acid containing 0.1% CMC and 0.2 M aluminum nitrate. Approximately 0.2 mmol of chloride, bromide, and iodide ions were titrated with high precision and accuracy. Their standard deviations were 0.03, 0.02, and 0.02%, respectively, with no apparent systematic error. The precise determination of halogens, employing oxygen flask combustion and dissolution of the halide salts in the electrolyte, was carried out with ±0.1% absolute error using samples weighing between 20 and 30 mg.     

Graphite-silver diethyldithiocarbamate as a new potentiometric sensor for titration of some metals,halides, thiols,and sulfonamides

A new simple potentiometric sensor based on the precipitation of AgDDC within a graphite rod is described. The electrode is sensitive for both DDC and silver ions down to 10^?5M and can be used as an indicator electrode for complexometric titration of metallic ions with NaDDC and argentimetric titration of some organic and inorganic compounds. Accurate results are obtained for microdetermination of some metal ions singly or simultaneously (in binary and tertiary mixtures and alloys) and thiols, sulfonamides, and halides in organic compounds.     

Wire-coated silver(I) ion-selective electrode based on 2-mercaptobenzothiazole (MBT) ionophore: application to the determination of silver in real samples.

A new wire-coated silver ion-selective electrode with a wider concentration range (10(-7) M - 10(-1) M) was developed using 2-mercaptobenzothiazole (MBT) as a neutral ionophore. An optimum mixture of PVC, ionophore, dioctylphtalate (DOP) as a plasticizer and sodium tetraphenylborate (NaTPB) as an ion-pairing agent was used in preparing the coatings. The effect of various parameters, such as the electrode bed nature, coating composition and solution pH, on the efficiency of the electrode is described. It has been shown that platinum acts as a more suitable bed for electrode preparation, and exhibits a slope of 59.5 +/- 1 mV over the whole range of studied concentrations. The selectivity coefficient of the electrode towards various interfering cations as well as its reproducibility, response time and lifetime of the electrode were estimated. The developed electrode was successfully used for the determination of trace amounts of silver in human hair and photographic waste as real samples and in the potentiometric titration of halides as an indicator electrode.     

On potentiometric titration curves in complexometry

An equation is given which describes the potential change during complexometric titration of metals with potentiometric end-point detection. The potential of the indicator electrode (e.g., silver or mercury electrode) depends on the equilibrium of the reaction MY + W right harpoon over left harpoon WY + M, where W represents the indicator metal ion, and M the metal ion determined by titration with the ligand Y, forming 1:1 chelates. Introduction of the conditional stability constants and corresponding side-reaction coefficients facilitates the prediction of the limits of application of this type of titration as well as the optimum conditions for the determination.