RU2486500C1 - Method of determining osmium by stripping voltammetry in natural and man-made material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of determining osmium by stripping voltammetry in natural and man-made material involves transferring osmium (VIII) into a solution in form of volatile osmium tetraoxide and conducting catalytic, voltammetric determination, wherein osmium ions are accumulated on a soot electrode in a stirred solution in the presence of hydrogen peroxide for 60-120 s, followed by recording anodic peaks of electrocatalytic decomposition of hydrogen peroxide on an OsO₂ precipitate with potential sweep rate of 80-120 mV/s at electrolysis potential of minus 0.2 V on a background electrolyte of 0.05-0.1 M CH₃COOH; concentration of osmium ions is determined from the height of the anodic reverse peak of catalytic decomposition of hydrogen peroxide on the current-voltage curve in a potential range from plus 0.1 V to plus 0.3 V relative a saturated silver chloride electrode by standard addition.

EFFECT: invention enables to reduce the limit and lower bound of determined osmium content based on the peak of electrocatalytic decomposition of hydrogen peroxide, obtained after electroconcentration of OsO₂ on a soot electrode by stripping voltammetry.

2 ex, 2 tbl, 2 dwg

Description

The invention relates to analytical chemistry, namely to the analysis of objects of natural and technogenic origin by the method of inverse voltammetry to determine osmium ions, and can be used to determine it in the presence of dissolved oxygen in objects of natural and technogenic origin.

K. and Csányi L.J. On the polarographic study of the system hydrogen peroxide-osmium tetroxide // Acta Chimica Hungaricae, 1963. Т.38, №3, р.193-202]. Недостатком данного метода является то, что для исследуемых растворов осмия наблюдается смещение потенциала максимума в область положительных потенциалов и максимум осмия раздваивается. Одновременно нарушается пропорциональная зависимость между величиной тока и концентрацией осмия в растворе. Для устранения этих недостатков авторы предлагают использовать буферные растворы с pH ~ 9-10 с добавкой тиосульфата для стабилизации растворов, содержащих осмий.The electrochemical behavior of osmium in the presence of hydrogen peroxide on various background electrolytes was studied: acid solutions, neutral and buffer solutions. The possibility of determining osmium by the polarographic method with a content of up to 1 · 10 ^-7 M. [

K. and Csányi LJ On the polarographic study of the system hydrogen peroxide-osmium tetroxide // Acta Chimica Hungaricae, 1963. Vol. 38, No. 3, pp. 193-202]. The disadvantage of this method is that for the studied solutions of osmium, a maximum potential shift to the region of positive potentials is observed and the maximum osmium bifurcates. At the same time, the proportional relationship between the magnitude of the current and the concentration of osmium in the solution is violated. To eliminate these shortcomings, the authors propose using buffer solutions with a pH of ~ 9-10 with the addition of thiosulfate to stabilize solutions containing osmium.

A known method for the determination of osmium on a platinum or graphite rotating electrode. The reference electrode served us. feces electrode, electrolysis time of 10 minutes at an electrolysis potential of 0.0 V (for a graphite electrode). The range of the determined contents is (1.2-4.0) · 10 ^-5 g-ion / l (25 ml - 2-7.6 μg / ml). In the case of dilute solutions, a platinum electrode is used, the electrolysis time is 30 minutes at a potential of minus 0.3 V. The interval of the determined contents is (2.0-8.0) · 10 ^-6 g-ion / l [Usatenko Yu.N., Shvydka L.F., Tolubara A.I. and Tulupa F.M. Film polarography with the concentration of osmium on solid electrodes. // Proceedings of universities. Series: Chemistry and Chemical Technology. - 1969, T. 12, No. 12, p. 1654-1657]. The disadvantage is the problem of manufacturing a platinum electrode for other modifications of the devices used. Low sensitivity even in the application of increased electrolysis time (from 10 to 30 minutes). A decrease in the anode current is observed when acetate, chloride ion, and citric acid are introduced into the solution. Ruthenium also has an effect with a triple excess.

A technique was developed using a mixed background of 0.1 M KCl + xM KOH (pH 9-10). A graphite or platinum microdisk electrode is used. The electrolysis potential is minus 0.7 V and the accumulation time is 6 minutes. The minimum detectable concentration is 1 · 10 ^-7 M [Bardin MB, Gorcharenko VP and Bolotskaya F.Z. Determination of small amounts of osmium by film voltammetry. // Journal of analytical chemistry. - 1970, v.25, issue 11, pp. 2160-2166]. The disadvantage is that the pH of the solution is strictly maintained (10, since the sensitivity decreases at pH 4-8, and at pH> 12 the current-voltage curves are distorted and the maximum bifurcates, which leads to a violation of the proportionality between the concentration of osmium in the solution and the maximum current value. For this, the authors recommend use buffer solutions with a pH of 9-10 with the addition of thiosulfates, oxalates or tartrates, which makes the background solution multicomponent, and also indicates the interfering effect of ruthenium, which leads to distortion of the current-voltage curves.

A known method for the determination of osmium by the method of IV using a graphite electrode, acetate buffer solution with a pH of 4.6. The technique was developed for copper-nickel sulfide ores. The lower limit of the determined contents was 5 · 10 ^-6 %. [Kolpakova N.A., Shvets L.A. Determination of osmium by the method of inverse voltammetry in mineral raw materials. // Journal of analytical chemistry, - 1983, vol. 38, issue 8, p. 1858-1862]. The disadvantage is that thiosulfate is used to stabilize the solutions and the determination of osmium is possible with no more than 25 times the amount of ruthenium. HClO _{4 is} used in distillation, which upon decomposition forms HCl, which leads to the formation of volatile chlorides (AsCl ₃ , SbCl ₅ , BiCl3, etc.), which interfere with the determination of osmium and distort the shape of the current-voltage curves.

A technique was developed using graphite as an indicator electrode, and calomel was used as a reference electrode. The background was formic acid with a concentration of 0.01 M. The lower boundary of the determined osmium contents was 2 · 10 ^-8 M [Shvets L.A., Kolpakova N.A. Determination of osmium by inversion voltammetry in technological products. // Journal of analytical chemistry, - 1983, vol. 38, issue 8, p. 1858-1862]. The disadvantage is that they purge the analyzed solution with nitrogen. In this case, volatilization of OsO ₄ and underestimation of the results of the analysis occur. As a result, the appropriate accumulation time is selected depending on the osmium content in the technological product from 1 to 10 minutes.

A hybrid version of the inversion voltammetry method has been developed - the kinetic method of inversion voltammetry (Kin-IV). The method is implemented by the example of determination of osmium. It was found that during electrooxidation of Os + OsO ₂ , which was previously deposited on the surface of a graphite electrode, inverse electrolytes are observed in acidic electrolytes and in the presence of hydrogen peroxide on the anode current-voltage curves. It was shown that the determination of osmium by the Kin-IV method can be carried out in complex matrices without separation. The lower boundary of the determined osmium contents against a background of 0.1 M sulfuric acid at a concentration of hydrogen peroxide of 30% is 8 · 10 ^-10 mol / l [Kolpakova N.A., Kaminskaya O.V., Yagovkina E.V. “Determination of osmium in mineral raw materials by the method of kinetic inversion voltammetry” // Factory Laboratory. Diagnostics of materials. - 1997, t. 64, No. 4, p. 9-12]. The main disadvantage is the interfering effect of silver and 10 ^5- fold excesses of base components. Without separation of osmium, distillation is interfered with by all noble metals as well as some components of the sample (Fe, Se, Te, As, etc.).

For the inversion voltammetric determination of osmium in natural and industrial facilities, a technique was developed [Kolpakova N.A., Kropotkina S.V., Sukhomlinova O.V. Copyright certificate No. 1746285, 07.07.1992, Bull. No. 25 // Inversion voltammetric method for determining osmium in natural and industrial facilities] (prototype). The determination of osmium is carried out according to the following procedure. To determine osmium, a graphite electrode was used as a working electrode, and a calomel electrode was used as a reference electrode. The background electrolyte was 0.01 M formic acid. The electrolysis potential was 0.0 V at an electrolysis time of 1 minute. The potential of the inverse maximum was recorded in an acidic medium and in the presence of 10 ^-3 - 30% hydrogen peroxide from 0.4 to 0.5 V at a sweep speed of 50 mV / s. The disadvantage of this method is that the current of the inverse maximum strongly depends on the concentration of hydrogen peroxide. Low sensitivity of determination of osmium in poor foods with a content of 10 ^-7 -10 ^-6 %. Silver has a very strong effect, distorting the shape of the current-voltage curve.

The task was set to reduce the limit and lower limit of the determined osmium (VIII) contents by the peak of the electrocatalytic decomposition of hydrogen peroxide obtained after electroconcentration of OsO ₂ on a carbon black electrode (SE) by the IV method.

The task is achieved by the fact that osmium (VIII) ions are electrochemically concentrated on the surface of various types of carbon black electrodes in the form of OsO ₂ , followed by decomposition of hydrogen peroxide on the precipitate and registration of anode current-voltage curves with a reverse peak. Osmium ions are accumulated on the carbon black electrode in a stirred solution in the presence of hydrogen peroxide for 60-120 seconds, followed by registration of the anode peaks of the electrocatalytic decomposition of hydrogen peroxide on the OsO ₂ precipitate at a potential sweep rate of 80-120 mV / s at electrolysis potentials of minus 0.2 The background electrolyte at 0.05-0.1 M CH ₃ COOH, osmium ion concentration is determined by the height of the anodic peak inverse catalytic decomposition of hydrogen peroxide current-voltage curve in the potential range of from 0.1 to plus pole of 0.3 V relative to the saturated silver chloride electrode method certified mixtures of additives.

New in the method is that to obtain a useful signal, which depends on the concentration of osmium (VIII), an excess of hydrogen peroxide is used to complete the catalytic reaction of its decomposition on the precipitate obtained during electroconcentration of Os from solution.

In the proposed method, the ability of the osmium precipitate to decompose hydrogen peroxide on the surface of various types of carbon black electrodes is established. SE was used as an indicator (a graphite electrode was used in the prototype). The use of such electrodes is due to the high chemical and electrochemical stability of soot, a wide range of working potentials, as well as the simplicity of mechanical surface renewal and safety requirements. The analysis does not use mercury, as mercury is toxic. The lower limit of the determined contents by this method was 1 · 10 ^-4 mg / dm ³ (in the prototype 1 · 10 ^-3 mg / dm ³ ).

The results of the determination of osmium (VIII) on the solar cells are shown in table 1 and table 2. As can be seen from table 1, the maximum measurement error is about 15.8%, in standard samples it was ~ 40%. Determination of the determined concentrations of osmium is carried out according to the method of "entered-found."

Osmium (VIII) ions are accumulated on the surface of the carbon black electrode in a mixed solution in the presence of hydrogen peroxide for 60-120 s at an electrolysis potential of minus 0.2 V. A further decrease in the electrolysis potential causes a decrease in the osmium peak (VIII), which reduces the sensitivity of determination. The measurements were carried out against a background of 0.05-0.1 M CH ₃ COOH, followed by registration of the anode peaks in the storage mode and shooting voltammograms at a scan speed of 80-120 mV / s. The concentration of osmium (VIII) ions is determined by the height of the anode inverse peak of the decomposition of hydrogen peroxide in the potential range from plus 0.1 to plus 0.3 V relative to the saturated silver chloride electrode (chemical grade). Figure 1 presents the current-voltage curves of the electrocatalytic decomposition of hydrogen peroxide on the precipitate OsO ₂ pre-electrodeposited on the surface of the carbon black electrode against a background of 0.1 M CH ₃ COOH. Curve 1 - background 0.1 M CH ₃ COOH + 1 ml 30% H ₂ O ₂ , curve 2 - C _{Os (VIII)} is 0.002 mg / dm ³ , curve 3 - C _{Os (VIII)} is 0.004 mg / dm ³ .

Thus, the established conditions made it possible for the first time to quantify the content of osmium (VIII) ions based on the catalytic decomposition of hydrogen peroxide with the release of oxygen on the surface of the carbon black electrode.

The proposed voltammetric method has significantly improved the metrological characteristics of the analysis of osmium (VIII); increase the sensitivity of the determination (1 · 10 ^-4 mg / DM ³ ), which is an order of magnitude lower compared to the prototype.

Case Studies

Example 1. The measurements were carried out on artificial mixtures (figure 1). 10 ml of background electrolyte (0.1 M CH ₃ COOH) is placed in a quartz glass and 1 ml of 30% H ₂ O _{3 is} added. Without stopping mixing, the solution is electrolyzed, at E _e = -0.2 V and at τ _e = 60 sec, the current-voltage curve of the electrocatalytic decomposition of hydrogen peroxide is measured at a sweep speed of 100 mV / s. The absence of peaks on the current-voltage curve in the range from plus 0.1 to plus 0.3 V indicates the purity of the background. Then add a certified solution of osmium (VIII) 0.02 ml of 0.1 mg / DM ³ and conduct electrochemical concentration of the precipitate under similar conditions. On the current-voltage curve in the range from plus 0.1 to plus 0.3 V, a peak of electrocatalytic decomposition of hydrogen peroxide appears. An addition of a standard solution of osmium (VIII) of 0.02 ml of 0.1 mg / dm ^{3 was} added and the analytical signal was recorded again with an accumulation potential of -0.2 V. The concentration of osmium in the solution was calculated from the difference in the peak currents of the catalytic decomposition of hydrogen peroxide. The peak of the current of catalytic decomposition of hydrogen peroxide on the OsO ₂ precipitate, previously electrodeposited on the surface of the carbon black electrode, was recorded in the potential range from plus 0.1 to plus 0.3 V (rel.

Example 2. Measurements of osmium were carried out after its isolation from the sample (figure 2). 1 g of the sample is mixed with a five-fold excess of sodium peroxide. Put in a muffle furnace and alloy at a temperature of from 550 to 700 ° C for 30 minutes After cooling the crucible, the sample is leached with water and quantitatively transferred to a distillation flask. Concentrated sulfuric acid is added until the alkaline solution is completely neutralized. Then add from 3 to 5 ml of 30% hydrogen peroxide. The flask is placed on a tile preheated to 115 ° C and osmium is distilled off in the form of OsO ₄ . During the distillation, 1 ml of 30% hydrogen peroxide is periodically added. The distillation time is 30 minutes. After distillation from the receivers, the resulting solution is collected.

10 ml of background electrolyte (0.1 M CH ₃ COOH) is placed in a quartz glass and 1 ml of 30% H ₂ O _{2 is} added. Without stopping mixing, the solution is electrolyzed, at E _e = -0.2 V and at τ _e = 60 sec, the current-voltage curve of the electrocatalytic decomposition of hydrogen peroxide is measured at a sweep speed of 100 mV / s. The absence of peaks on the current-voltage curve in the range from plus 0.1 to plus 0.3 V indicates the purity of the background. Then add 1 ml of the solution obtained after distillation, and conduct the electrochemical concentration of the precipitate under similar conditions. On the current-voltage curve in the range from plus 0.1 to plus 0.3 V, a peak of electrocatalytic decomposition of hydrogen peroxide appears. If a peak does not appear on the current-voltage curve, then add another aliquot of the test solution. Then, an additive of a standard solution of osmium (VIII) of 0.02 ml of 1 mg / dm ^{3 is} added and the analytical signal is recorded again at an electroconcentration potential of 0.2 V. The concentration of osmium in the sample was calculated from the difference in the peak currents of the catalytic decomposition of hydrogen peroxide. The peak of the current of catalytic decomposition of hydrogen peroxide on the OsO ₂ precipitate, previously electrodeposited on the surface of the carbon black electrode, was recorded in the potential range from plus 0.1 to plus 0.3 V (rel.

Thus, the ability to quantitatively analyze osmium by the peaks of catalytic electrooxidation of hydrogen peroxide on a pre-electroconcentrated precipitate in the form of OsO ₂ on the surface of a carbon black electrode against the background of 0.1 M CH ₃ COOH was first established. The proposed method is simple, mercury is not used due to its toxic effect. The method can be applied in any chemical laboratory having computerized analyzers such as CTA, TA or a polarograph.

The proposed method can be used to determine osmium in objects of natural and technogenic origin.

Method for determination of osmium by inversion - voltammetric method in natural and technogenic raw materials

Table 1 Introduced C _Os , mg / dm ³ Found C _Os , mg / dm ³ n Sr (t _0.95 ) ε,% 0.02 0.019 ± 0.003 5 0.001 15.8 0.2 0.19 ± 0.01 5 0.002 5.3 2.0 1.94 ± 0.19 5 0,067 9.8

table 2 Object of study (ore) Os content in CO, mg / kg Found Os, mg / kg Sr (t _0.95 ), n = 3 XO1 GSO 1703-79 0.014 ± 0.003 0.0136 ± 0.0062 0.0014 KN-1 GSO 1702-79 0.06 ± 0.04 0.063 ± 0.041 0.0096 MBCh-5 GSO 7966-2001 4 ± 0.56 3.6 ± 0.98 0.23

Claims (1)

The method of determining osmium by the inversion voltammetric method in natural and man-made raw materials, which consists in the fact that osmium (VIII) is transferred in solution in the form of volatile osmium tetroxide and a catalytic, voltammetric determination is carried out, characterized in that the accumulation of osmium ions on the carbon black electrode in the mixed solution in the presence of hydrogen peroxide for 60-120 s followed by registration of the anode peaks of the electrocatalytic decomposition of hydrogen peroxide on the OsO ₂ precipitate at a sweep speed of a potential of 80-120 mV / s with electrolysis potentials of minus 0.2 V on the background electrolyte 0.05-0.1 M CH ₃ COOH, the concentration of osmium ions is determined by the height of the anode inverse peak of the catalytic decomposition of hydrogen peroxide on the volt-ampere curve in the potential range from plus 0.1 to plus 0.3 V relative to a saturated silver chloride electrode by the method of additives of certified mixtures.

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