Studies on the Development of Methods for Determining 10(-6)% of Certain Inorganic Impurities in Solutions Simulating Biological Objects
Abstract Generated abstract
This study examines the extension of amalgam polarographic analysis to solutions simulating biological materials and food industry objects for trace determination of inorganic impurities. Using a film cathode, saturated calomel reference electrode, nitrogen deaeration, controlled acidity, and selected accumulation potentials, the authors investigated simultaneous determination of Zn, Pb, Cu, Sb, and Bi in physiological solutions, sodium chloride, hydrochloric acid, and ethanol mixtures. The work reports linear relationships between anodic peak heights and both analyte concentration and accumulation time, with no observed mutual interference among the elements studied. Procedures based on standard additions are proposed for these matrices, achieving a reported sensitivity of 1 x 10^-6 percent with advantages of simplicity, speed, and avoidance of evaporation.
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Studies on the Development of Methods for Determining \(10^{-6}\%\) of Certain Inorganic Impurities in Solutions Simulating Biological Objects
A. A. Kaplin, V. F. Yankauskas, A. S. Zharkikh
(Presented at the scientific seminar of the Department of Physical and Colloid Chemistry)
This work was undertaken with the aim of extending the field of application of the APA method to biological objects and to objects simulating materials used in the food industry.
The possibility was investigated of the simultaneous amalgam-polarographic determination of \(10^{-6}\%\) Zn, Pb, Cu, Sb, and Bi in solutions (simulating food and biological objects) of the following composition:
1) physiological solution \((\mathrm{pH}=8,\ \mathrm{pH}=5)\);
2) \(0.8\%\ \mathrm{NaCl}\);
3) \(0.5\%\ \mathrm{HCl}\);
4) ethyl alcohol of various concentrations \((10\%,\ 25\%,\ 40\%\) and \(96\%)\).
In the work an electrolyzer with replaceable cups was used; the cathode was a film electrode \((S=0.04\ \mathrm{cm}^2)\), and the reference electrode was a saturated calomel electrode. For stirring the solution and removing oxygen from it, gaseous nitrogen with an oxygen content of not more than \(0.2\text{--}0.5\%\) was used. In the course of developing the method, the mutual influence of the elements being determined was studied. The absence of such an influence was shown.
The dependences of the heights of the anodic peaks of the elements being determined on their concentration in solution (Table 1) and on the accumulation time (Table 2) were studied. These dependences are linear.
On the basis of the investigations carried out, methods were proposed for the simultaneous determination of Zn, Pb, Cu, Sb, and Bi for each of the above-mentioned solutions.
Their essence consists in creating, for each of the elements being determined, the most favorable acidity of the medium, by acidifying and neutralizing the medium with hydrochloric acid and an \(\mathrm{NH_4OH}\) solution, respectively. In addition, to separate the peaks of copper and antimony, an accumulation potential \((-0.4\ \mathrm{V})\) is selected at which one of the elements (Cu) is not reduced.
Alcohol Mixtures
Procedure of analysis. \(3\ \mathrm{ml}\) of the solution under investigation is purged with purified nitrogen for \(5\ \mathrm{min}\) to remove oxygen and is polarographed for the content of lead and copper at an accumulation potential of \(-1.0\ \mathrm{V}\). Then the solution is acidified with three drops of \(12\mathrm{N}\ \mathrm{HCl}\), and the anodic peaks of antimony and bismuth are recorded (accumulation potential \(-0.45\ \mathrm{V}\)).
Table 1
Dependence of the heights of the anodic peaks of antimony and copper on their concentration in various backgrounds
| $C$, $1\cdot10^{-8}\ \mathrm{g/ml}$ | 0.5% HCl, $h$ mm | 0.8% NaCl, $h$ mm | Complex mixture, pH = 5 | 10% alcohol, $h$ mm | Experimental conditions |
|---|---|---|---|---|---|
| 0.03 | 14 | 10 | 5 | 10 | $\tau=5$ min. |
| 0.06 | 28 | 21 | 8 | 28 | $V=3$ ml |
| 0.09 | 42 | 32 | 16 | 42 | $i=1\cdot10^{-8}$ A/mm |
| 0.12 | 57 | 43 | 20 | 56 | $\varphi_{\mathrm{el}}=-1.5$ V |
| 0.15 | 72 | 52 | 26 | 70 | |
| 0.18 | 85 | 65 | 29 | 85 | |
| 0.21 | — | — | 34 | — |
Table 2
Dependence of the peak heights of antimony and copper on electrolysis time
(for experimental conditions, see Table 1)
| Electrolysis time, min. | 0.5% HCl, $h$ mm | 0.8% NaCl, $h$ mm | pH = 5 complex mixture, $h$ mm | 10% alcohol, $h$ mm |
|---|---|---|---|---|
| 3 | 4 | 5 | 5 | 6 |
| 5 | 8 | 10 | 12 | 10 |
| 7 | 10 | 13 | 19 | 14 |
| 9 | 12 | — | 28 | 18 |
| 10 | 15 | 18 | — | 20 |
| 11 | — | — | 44 | — |
| 12 | — | 21 | 50 | 23 |
| 15 | — | 27 | 52 | 30 |
The solution is neutralized with 3 drops of a concentrated ammonia solution, after which the anodic zinc peak is recorded. The concentrations of all elements were determined by the method of additions of standard solutions.
Using all the above-listed procedures, other mixtures can be analyzed in an analogous manner (HCl solution, complex mixture pH = 5, 0.8% NaCl).
The results of analysis of a 0.8% NaCl solution for the content of Cu, Sb, Bi, Pb, and Zn impurities are given in Table 3.
Table 3
Results of analysis of a 0.8% NaCl solution for the content of impurities Cu, Bi, Sb, Pb, and Zn (experimental conditions, see Table 1)
$(n=11;\ \alpha=0.95;\ t_{0.95}=2.23)$
| Elements | $\bar{x}\cdot10^{6}$ % | $S_{\bar{x}}\cdot10^{6}$ % | $\pm\varepsilon=S_{\bar{x}}t_{\beta}(0.95)$ | $\pm\varepsilon$ % |
|---|---|---|---|---|
| Zn | 17.3 | 0.141 | 0.31 | 1.7 |
| Pb | 11.3 | 0.165 | 0.36 | 3.1 |
| Cu | 14 | 0.145 | 0.11 | 0.8 |
| Sb | 8.1 | 0.135 | 0.30 | 3.7 |
| Bi | 28.5 | 0.207 | 0.56 | 1.9 |
The sensitivity of the developed methods is $1\cdot10^{-6}\%$.
The merits of the method are the absence of evaporation, simplicity, and rapidity of analysis.