The prospect of using Shewhart control charts in assessing the quality of ionometric measurements by the method of adding a sample to a standard

Modern methods of quantitative physical and chemical measurements should necessarily include procedures for quality control of research results. Recently, the procedure for quality control of measurements using control charts is gaining particular popularity in the practice of analytical measurements. To date, the methods of potentiometric studies operating in the territory of the Russian Federation, in most cases, do not include quality control using this control procedure. However, despite the complexity of the implementation and interpretation of its results, it is the use of control charts that allows you to control the quality of ionometric measurements. This is especially important for potentiometric determinations based on the addition method, since the instability of the slope of the electrode function and its deviation significantly contribute to the uncertainty of the measurement results. This article presents the main results of evaluating the use of the Shewhart control chart method for monitoring the repeatability and accuracy of measurement results. The measurement results have been obtained using an improved method of quantitative potentiometric determination of high concentrations (more than 1 gm/cdm) of ammonium ions by the method of adding a sample to the standard. In addition, an experimental substantiation of the fact that the value of the slope of the electrode function significantly affects the accuracy of measurements by the addition method has been presented. It has been revealed that when the angular coefficient of the electrode function is more than 62 mV/pNH4+ at (25±5)°C, deviations of the measurement results from the control standard by more than 50% are observed. It has been found that at (25±5)°С the most accurate results of quantitative determination are achieved when the angular coefficient of the electrode function is from 54 mV/pNH4+ to 62 mV/pNH4+ inclusive.

Theoretical description of the ligand function for ionoselective electrodes reversible to metal anion complexes. 3. Modeling of the electrode response in ligand and foreign ions solutions using the multi-species approach model

A description for the ligand function of the tetrathiocyanatozincate selective electrode, has been proposed, using a multi-species approach model. This model takes into account simultaneous phase-boundary, diffusion-controlled, processes of ion exchange between tetrathiocyanatozincate, thyocyanate and foreign ions unable to form zinc complexes, as well as distribution of the neutral zinc complex between phases, partial decomposition of quaternary ammonium tetrathiocyanatozincate salt and stepwise complex formation processes in water phase. The model is based on solving the system of equations describing several interphase and intraphase equilibria, assuming that diffusion flows of all membrane and solution components at the phase boundary are stationary. It provides the adequate description of tetrathiocyanatozincate selective electrode in solutions of the ligand, foreign ions and mixed solutions of the above, and predicts the effect of zinc chloride concentration in the sample solution upon electrode function slopes, lower detection limits and selectivity coefficients.

Potentiometric sensor for lead ions determination

One of the sensitive and inexpensive methods used for the analysis of water bodies is the ionometry, the development of which is associated with the introduction of new ion-selective electrodes into the practice of potentiometric analysis. An optimized composition of the membrane for the manufacturing of a zinc-selective electrode based on polyvinyl chloride modified with 2-mercaptobenzthiazole (MPVC) is proposed with the following ratio of ingredients (in wt. %): Polyvinyl chloride - 31.7; dioctyl sebacate - 66.3; potassium tetra-p-chlorophenylborate - 0.5; MPVH - 1.5. The working range of pH was established with a minimum potential drift, which was 1.5 - 3. The slope of the electrode function was calculated as 30.1 ± 0.3 mV. According to the dependence of the electrode potential for the selected composition of the membrane on the logarithm of the zinc ion concentration, it was found that the proposed model of the electrode operates in the concentration range of 1∙10-5 - 1∙10-1 mol / L, with a detection limit of 0.65 mg / l. The stabilization time of the potential within 1 mV was 15 - 20 s. The potentiometric coefficients of the selectivity of the zinc selective electrode with respect to various ions have been determined. The conditions for the determination of zinc using the obtained sensor in alloys and wastewater were proposed. The electrode with the membrane based on polyvinyl chloride modified with 2-mercaptobenzthiazole can be used as an alternative to the industrial electrode XC-Zn-001 for the determination of zinc ions in various objects. The obtained experimental data was close in accuracy to the results obtained by the atomic absorption methods, as well as the ionometry using the industrial electrode. In conclusion, the electrode with the membrane based on polyvinyl chloride modified with 2-mercaptobenzthiazole can be used as an alternative to XC-Zn-001.

Potentiometric Sensor For Analgin Determination In Pharmaceutical Formulations

Ion associates (IA) of butylrodamine C with triiodide and iod bromide have been synthesized. Their thermal behavior is investigated. Thermolysis synthesized by IA BR+I3¯ passes through a number of intermediate stages, since the C4H9 radical, which is part of the dye, has a significant effect on the process of thermolysis of the ionic associate. IA BR+I3¯ begins to decompose significantly at a temperature higher than 140 єC with an endothermic effect at 240 єC and two small exothermic effects with a maximum at 282 єC and 355 єC (corresponding to the release of 2NH3, 8C2H4, 2HI). In the range of 380–720 єC, the exothermic effect of the IA combustion occurs at a temperature of 485 єC with significant mass loss. The obtained IAs are stable under normal conditions. An I3¯ and I2Br¯ sensor containing butyrodromine C associate of butylrodamine C with triiodide and iodum bromide was developed. The working interval of the pH of the triiodide sensor is 2 - 12, and for iodum bromide, the pH is 2 - 10, respectively. The linearity interval of the electrode function is in the range 9 ∙10-6 - 1 ∙10-1 mol L-1, the slope is 65 mV/pC for the triiodide, and for the iodine bromide - 1 ∙10-5 - 1 ∙10-1 mol L-1, the slope 68 mV/pC. The technique of potentiometric determination of analgin in medicines is developed.

IONOMETRICAL DETERMINATION OF IRON (III) IN VEGETABLES AND FRUITS

The ability of iron (III) ionometric determination in a form of its thiosulfate complex was shown. Conditions of analysis were optimized. The obtained anionic electrode function E=f(pCFe(III) obeys to the Nernst equation in the range of 2.0 to 5.0 unit of MS and has a slope equals to 56±2 mV/pC. The determination selectivity in the presence of a number of cations and anions was studied by the “mixed” solutions method. The method was applied for the analysis of iron (III) content in some fruit and vegetables.