The Determination of Protonation Constants of Some Amino Acids and Their Esters by Potentiometry in Different Media

In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25^∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L⁻¹ using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition on the protonation constants is discussed. The log₁₀ K₂ values of esters generally decreased with increasing ethanol content. However, the log₁₀ K₁ values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content in contrast those of L-lysine and L-histidine esters.     

The Isoelectric Point and the Points of Zero Charge of Fe-Al-Mg Hydrotalcite-like Compounds

The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.     

Effect of External Acidity of Mordenite-Supported Catalysts on the 2,2-Dimethylbutane Content in Hydroisomerization Products of n-Hexane

We have used potentiometric titration with tetrabutylammonium hydroxide to determine the acid center content on the outer surface of dealuminated natural and synthetic mordenites. We have established a symbatic relationship between the 2,2-dimethylbutane content in the hydroisomerization products of n-hexane on dealuminated palladium-containing mordenites and the number of their external acid centers. We have studied the possibility of partial deactivation of such centers during ion-exchange deposition of palladium on the catalysts, using a tetraammine palladium solution.     

二点滴定法研究

就二点滴定法的原理，方法和应用进行了讨论，导出了二点滴定法计算公式。讨论了滴定剂加入量与测定结果准确度的关系。已用本法对标样样液及试样进行了多次测定，测定结果相对误差及相对标准偏差约０．２％。本法简便，快速，准确，且昨达于任何滴定类型的通用方法。     

All-solid-state planar miniature ion-selective chloride electrode

All-solid-state ion-selective electrodes with plastic membrane (poly(vinyl chloride) (PVC), bis(2-ethylhexyl) sebacate (DOS), methyltri-n-tetradecylammonium chloride (MTTACl)), a conducting poly(pyrrole) (PPy) film doped either with chloride ions (PPyCl) or hexacyanoferrate(II) ions (PPyFeCN), and glassy carbon (GC) or screen-printed graphite layer (S-PG) as an inner electric contact were investigated. All the electrodes show close to Nernstian response, but their lifetimes vary. The at least 2-months lifetime of screen-printed electrodes is only achieved for the electrodes containing PPyFeCN (cation-exchanging film). Shorter lifetime of other screen-printed electrodes, i.e. without PPy, or with PPyCl (anion-exchanging film), was attributed to the diffusion of anionic products of the hydrolysis of organic components of the graphite paste used to prepare the electric contact. The properties of miniature, screen-printed electrodes comprising PPyFeCN solid contact, were comparable to those ion-selective electrodes with PPy solid contact (regardless the ion-exchanging characteristic of the polymer) deposited on GC electric contact.     

银微电极微分电位溶出分析法研究

本文首次报道了银微电极微分电位溶出分析法。用化学刻蚀法方便地制作了银微电极，用于ＤＰＳＡ具有背景值低，分辨率好、精密度及灵敏度高，在不搅拌，仅需一定酸度而酸度而无其它介质的条件下就能测试等优点，对人工试样及自来水样分析，结果令人满意。     

Carbon Paste Electrode for the Potentiometric Flow Injection Analysis of Drotaverine Hydrochloride in Serum and Urine

A carbon paste electrode for drotaverine hydrochloride (DvCl) was prepared and fully characterized in terms of composition, life span, usable pH range, response time and temperature. The electrode was applied to the potentiometric determination of drotaverinium ions in pharmaceutical preparations and biological fluids in steady state and flow injection conditions (FIA). The electrode is based on a mixture of two ion exchangers, namely, drotaverinium-silicotungestate and drotaverinium-tetraphenylborate dissolved in tricresyl phosphate as pasting liquid. The modified electrode showed a near-Nernstian slope of 59.34±2mV over the concentration range of 5.0×10^–7–1.0 × 10^–2M. The electrode exhibits good selectivity for DvCl with respect to a large number of inorganic cations, organic cations, sugars and amino acids. Potentiometric titrations of DvCl with several titrants have been monitored using this modified carbon paste electrode as an end-point indicator electrode. The proposed electrode offers the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored samples.     

Utilization of maltodextrin based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-perindopril

Enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins {dextrose equivalent (DE) 4.0-7.0 (I), 13.0-17.0 (II) and 16.5-19.5 (III)} as chiral selectors for the assay of S-perindopril is described. The proposed electrodes could be reliably employed in the assay of S-perindopril raw material and from its pharmaceutical formulation, Coversyl^® tablets. The electrode based on maltodextrin (I) showed the best enantioselectivity and time-stability. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper.     

Ion association in calcium phosphate solutions at 37°C

Ion association in the system Ca(OH)₂–H₃PO₄–KCl–H₂O at 37°C has been studied potentiometrically over a range of pH from 3 to 9. The experimental conditions were optimized for the accurate determination of the association constants for the formation of the ion pairs CaH₂PO ₄ ⁺ , CaHPO₄ and CaPO ₄ ^– which were found to be 27.9±0.1, 591±2, and (1.35±0.02)×10⁶ L-mol^–1, respectively.