Improvement of the potentiometric method for toxic elements specification on the basis of lead, cadmium and copper

The results of analysis of possibility to define ions of cadmium (II), lead (II) and copper (II) with potentiometric standard addition methods, ionometry and potentiometric titration within concentration limits outside the lower bound of electrodes sensitivity declared by the producer, with the use of reference solutions of defined ions, and reference solutions of defined ions against each other, and against stirring ions, with their following removal corresponding to such parameters as simplicity of execution are given in the article. The extension of the methods of analysis as well as new methods of analytical chemistry lead to structural changes of applied physical and chemical methods and the increase of the scope of research performed by the laboratories to implement new rapid methods of toxic elements specification guaranteeing the accuracy of measurements in the concentration of defined elements in the studied object and the assessment of food stock safety indexes in particular. Within preliminary analysis the necessity of sensitivity increase for ion-selective electrodes and decrease in a minimum limit of detection, introduction of masking agents or processes contributing to the removal of stirring substances as well as concentration of specified substances without use of complex separation and concentration methods is revealed. The authors prove that the accuracy index of calibration dependence approxiamtion is close to the unity which proves the possibility to apply direct potentiometry method as well as standard addition method at small concentration of a defined ion. The options to increase the accuracy of specification by means of silver chloride electrode replacement with nitrate selective electrode which excludes potential change because of changes in concentration of background elements are given. The authors provide options for removal of such stirring ions as iron (III) ion the influence of which is reduced with solution boiling with the following filtering, there is no effect on concentration of defined ions because of boiling, and the effect of copper (II) ions which is reduced with standard solution of sodium thiosulphate addition to the studied solution, there is no effect of thiosulphate on the concentration of a specified ion. The research is performed under Agreement "Development of Technologies, Technical Solutions and Software in the Sphere of Informational and Telecommunication Systems, Electronics Medicine, Mechanical Engineering, New Materials and New Types of Food Stock Production", concluded within the "Participant of Youth Scientific and Innovative Competition" program organized by the Fund of assistance to development of small enterprises in scientific and technical spheres.