Studies on Determination of Ge in Au Alloys by Potassium Iodate Potentiometric Titration Method

The paper presents a new method of determining Ge in gold alloys by potassium iodate potentiometric titration rather than by traditional distillation separation. The influences of conditions such as the reduction acidity, dosage of sodium hypophosphite and reduction time on the determination of Ge were studied. Comparison was made between the influences of end-point indication for potential method and starch method on accruracy and precision of the analysed results, stability and sensitivity of end-point, selectivity of method and so on. The possibility of reaction in an electrochemical way was discussed. Ge in the alloys such as AuGe 12 , AuGeNi 12 2 , AuAgGe 18.8 12.5 and AuAgGeNi 43.8 6 0.2 was measured, respectively, with the relative standard deviation of 0.10%~0.31% and the recoveries of added standard Ge in sample of 99.40%～100.40% when the reduction acidity was 0.40~0.80 mol/L HCl and 3.3 mol/L H 3 PO 4, 15 g sodium hypophosphite and reduction time 40 min. The new method presented is high accuracy and precision in results, good stability and sensibility in end point, easy operation and strong selectivity of determination. When it is applied to analyse actual samples, satisfactory results are achieved.

Counterion Binding in Aqueous Solutions of Poly(vinylpyridines) as Assessed by Potentiometric Titration

The extent to which counterions bind to polyelectrolytes influences a variety of polymer-based applications, including polyelectrolyte enhanced ultrafiltration and forward osmosis using polyelectrolytes as draw agents. Potentiometric titrations of poly (2-vinylpyridine) (P2VP), poly (3-vinylpyridine) (P3VP), and poly (4-vinylpydine) (P4VP) were performed using HBr, HCl, HNO3, and HClO4 in both the presence and absence of added NaCl. Because of the systematic differences among the three polyelectrolytes, titration results provide insight into the role of polymer structure in the relative extents to which various counterions bind. Titration data reveal that ionization properties vary as functions of polymer investigated, titrant used, degree of protonation, and added salt concentration. Acid dissociation constants of the pyridinium moieties were found to generally increase with increasing degree of protonation, though appreciable differences were exhibited among the three polymers investigated. For all three polymers, Cl- demonstrated the lowest affinity for the charged pyridinium residues, while the affinities associated with Br- and NO-3 were nearly identical to each other. The relative extent of binding for CIO-4 varied across the polymers investigated, and was greatest for P4VP.

Determination of Ge in Au alloys using sodium hypophosphite and potassium iodate potentiometric titration method

This paper presents a new method of determining Ge in AuGe alloys by potassium iodate(KIO3)potentiometric titration when Ge(Ⅱ)and Au(0)are simultaneously reduced from Ge(Ⅳ)and Au(Ⅲ)by sodium hypophosphite rather than by distillation separation.The influences of such conditions as the reduction acidity,the dosage of sodium hypophosphite and the reduction time on the determination of Ge were studied.Ge in AuGe alloys such as AuGe_(12),AuGeNi_(12-2),AuAgGe_(18.8-12.5),and AuAgGeNi_(43.8-6-0.2)was measured with the relative standard deviation(RSD)of 0.10%-0.31%and the recoveries of added standard Ge in sample of 99.40%-100.40%under the conditions of 0.40-0.80 mol·L^(-1)HCl,3.3 mol·L^(-1)H^(3)PO^(4),15 g sodium hypophosphite,and reduction time of40 min.The new method presented is of high accuracy in results,good stability and sensibility in end-point,and easy operation and strong selectivity of determination.

Novel Screen-Printed All-Solid-State Copper(II)-Selective Electrode for Mobile Environmental Analysis

Based on poly(vinyl chloride) membranes, a novel miniaturized screen-printed all-solid-state copper(II)-selective electrode has been developed for applications in environmental monitoring. Performance and applicability of the ion-selective electrode (ISE) have been proved by potentiometric investigations. Conducting polymers were used as intermediate layers and as solid contacts between the ion-selective membrane and the graphite transducer. The ion-complexing reagent 2-mercapto-benzoxazole was incorporated into poly(vinyl chloride) membranes. In the concentration range 10-6 - 10-2 mol/L, the ISE exhibited a linear Nernstian potential response to copper(II) with an average slope value of 28 mV/decade. The detection limit was 3 × 10-7 mol/L. The electrode exhibits a short response time (<10 s) and can be used in the range of pH = 3 - 7. Selectivity coefficents against certain interfering ions are investigated. The life time of the electrode under laboratory conditions was approximately 12-month. The electrode was applied in the investigation of different aqueous environmental samples and the electrode characteristics were described. The copper(II) ASS electrode has also successfully been used in potentiometric, complexometric titrations with ethylenediaminetetraacetic acid.

Acid-base and lipophilic properties of peptide nucleic acid derivatives

The first combined experimental and theoretical study on the ionization and lipophilic properties of peptide nucleic acid(PNA)derivatives,including eleven PNA monomers and two PNA decamers,is described.The acidity constants(pKa)of individual acidic and basic centers of PNA monomers were measured by automated potentiometric pH titrations in water/methanol solution,and these values were found to be in agreement with those obtained by MoKa software.These results indicate that single nucleobases do not change their pKa values when included in PNA monomers and oligomers.In addition,immobilized artificial membrane chromatography was employed to evaluate the lipophilic properties of PNA monomers and oligomers,which showed the PNA derivatives had poor affinity towards membrane phospholipids,and confirmed their scarce cell penetrating ability.Overall,our study not only is of potential relevance to evaluate the pharmacokinetic properties of PNA,but also constitutes a reliable basis to properly modify PNA to obtain mimics with enhanced cell penetration properties.

Determination of the dissociation constants of polyepoxysuccinic acid

The dissociation constants of polyepoxysuccinic acid(PESA)were investigated in this study.Based on the potentiometric titration and the BEST program,the dissociation constants of PESA were determined.Considering the complexity of the dissociation of PESA in aqueous solution,several models were constructed to simulate the dissociation process of PESA.By comparison,the dissociation constants of PESA were obtained with model 4.The species distribution of PESA in aqueous solution as a function of pH was also presented according to the experimental and calculation results.It showed that the H_(2)L model with five basic structure units to describe the dissociation of PESA was reasonable,and the relevant constants had less error and better matching between the experimental and calculation data.The corresponding values of pK_(ai) were 4.68 and 4.92,respectively,for H2L at 35℃ with ionic strength of 0.1 mol/L.