RU2478944C1 - METHOD OF DETERMINING BISMUTH IN AQUEOUS SOLUTIONS BY STRIPPING VOLTAMMETRY ON SELECTIVE ELECTROOXIDATION PEAKS OF BISMUTH FROM INTERMETALLIC COMPOUND Au2Bi - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of determining bismuth in aqueous solutions by stripping voltammetry on peaks for selective electrooxidation of bismuth from an intermetallic compound Au₂Bi according to the invention involves transferring bismuth (III) from a sample to a solution and conducting voltammetric determination, which is characterised by that bismuth is accumulated on polyethylene-impregnated graphite electrodes in a mixed solution in the presence of gold ions for 60-120 s, followed by detection of selective electrooxidation peaks of bismuth (III) from the intermetallic compound Au₂Bi, at a potential sweep rate of 60-100 mV/s and electrolysis potential from -0.3 to -1.1 V on backgrounds: 0.5-1.0 M HNO₃ or 0.5-1.0 M HCl. Concentration of bismuth (III) ions is determined from the value of area under voltage versus current curves at potential ranging from +0.05 V to +0.20 V relative a saturated silver chloride electrode using a certified mixture addition technique.

EFFECT: determining bismuth in aqueous solutions by stripping voltammetry.

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Description

The invention relates to analytical chemistry, and in particular to methods for determining the content of metal ions for determination in drinking and natural waters, industrial plums by inverse voltammetry (IVA).

A known method for the determination of Bi, in which, as a background, a mixture of 0.1 M sodium tartrate + 0.05 M acetic acid + 0.05 M sodium acetate with pH = 4.75, which makes it possible to determine bismuth in an amount of 1 mg / ml, is proposed. Against this background, the potential of the half-wave Bi is -0.27 V [Kryukova T.A., Sinyakova S.I., Arefieva T.V. Polarographic analysis. - M .: State. scientific and technical .: Chem. lit. - 1959. - 772 p.]. The disadvantage of this technique is the use of a multi-component background with a certain pH value. Low sensitivity for the determined bismuth contents and the use of metallic mercury in the polarography method.

There is a known method for determining Bi on a mercury-film electrode; we served as a reference electrode. calomel electrode. The film was applied electrolytically in a saturated solution of Hg ₂ (NO ₃ ) ₂ for 2 min at a current of 1 mA. Background 0.2 M HCl, electrolysis time 20 min, E _nak = -1.1 V. The error in determining the concentration of bismuth of the order of 10 mol / l does not exceed 25% [Kamenev AI, Vinogradova EI On the reproducibility of the determination of bismuth on a film electrode in the method of amalgam polarography with accumulation. // Journal of analytical chemistry. - 1966. - T.21, issue 3, S.320-322]. The disadvantage of this method is its low sensitivity for the determined bismuth contents and the use of mercury salts in the method.

A known method of determining Bi on a mercury-graphite electrode. The reference electrode was Polarograms were taken at a potential change rate of 200 mV / min, the minimum detectable bismuth concentration was 1 · 10 ^-8 mg / ml at an electrolysis time of 2 min and a potential of -1.0 V, then the potential was reduced to -0.6 V and electrolysis was performed for 15 min . The peak potential under these conditions is -0.2 V [Malkov E.M., Fedoseeva A.G., Stromberg A.G. Determination of nanogram amounts of antimony and bismuth by amalgam polarography with accumulation after their extraction separation. // Journal of analytical chemistry. - 1970 - T.25 - issue 9 - p. 1748-1751]. The disadvantage of this method is the duration of electrolysis, the use of mercury and its salts.

A known method for the determination of Bi on a disk microelectrode made of graphite impregnated with epoxy resin ED-6 with polyethylene polyamine. The reference electrode served us. calomel. Used 0.5; 1.0 and 3.0 M HCl solutions. E _e = -0.5 V, electrolysis time 5 min, E _max = -0.2 V, sweep speed 125 mV / s. The dependence of the maximum current of the electrochemical oxidation of bismuth on the concentration of metal ions in the solution remains proportional in the concentration range 1 · 10 ^-9 -1-10 ^-7 g-ion / l [Brainina X.3., Neiman E.Ya., Trukhacheva L. N. Inversion voltammetry of bismuth. // Plant. lab. - 1972.V. 38, No. 1. - S.12-16]. The disadvantage of the proposed method is the manufacture of a disk microelectrode, for which it is possible only to electrochemically update the surface, often not giving complete background purity, as well as the use of mercury salts.

A known method for determining bismuth by the method of anodic inverse differential pulsed voltammetry on a hanging mercury drop, the silver chloride served as the reference electrode, the platinum auxiliary electrode. Preconcentration is carried out by sorption of a complex of bismuth (III) with 2- (5-bromo-2-pyridylazo) -5-diethylaminophenol on Amberlite XAD-2 resin at pH 2.0 ... 3.0. Desorption is carried out with 10 ml of a 2M HCl solution. Polarograms were recorded from -0.15 to +0.05 V. Bismuth was precipitated at a potential of -0.8 V for 60 seconds while stirring the solution. Sweep speed 15 mV / s with a pulse amplitude of 50 mV. The minimum detectable bismuth concentration is 0.15 μg / L [Taher, Mohammad Ali. Anodic stripping voltammetric determination of bismuth after solid-phase extraction using amberlite XAD-2 resin modified with 2- (5-bromo-2-pyridylazo) -5-diethylaminophenol. // Talanta. - 2004. - V.63, No. 3. - P.797-801]. The disadvantage of this method is the use of metallic mercury.

A known method for determining Bi on a disk carbon-metal electrode modified with mercury. The detection limit of bismuth (III) 5 · 10 ^-8 M [Kamenev A.I., Katenaire R., Ishenko A.A. Inversion voltammetric determination of copper and bismuth on a mercury-film carbon-metal electrode. Kamenev A.I., Katenaire R., Ischenko A.A. // Vestn. Moscow State University. Ser. 2. - 2004. - T.45 - No. 4. - S.255-257]. The disadvantage of the proposed method is the complexity of manufacturing carbon-metal disk electrodes, for which it is possible only to electrochemically update the surface, often not giving complete background purity. Low detection sensitivity, as well as the use of mercury salts.

A known method for the determination of Bi on a solid carbon-containing electrode modified with organic modifiers, for example sodium huminate, allows to determine 4.78 · 10 ^-8 mol / dm ³ bismuth (III) [Wang C, Sun Q., Li N. Voltammetric behavior and determination of bismuth on sodium humate modified carbon paste electrode. // Electroanalysis. - 1997 - V.9. - No. 8. - P.645-649]. The disadvantage of this method is the low sensitivity of the determination of bismuth, and the process is complicated by the modification of the organic components of the electrode surface.

A known method for determining bismuth in high purity indium, which is carried out using a mercury-film electrode in the range of potentials from -0.45 to -0.02 V in an electrolyzer with an inserted quartz glass on a background of 1.5 M HCl [A.A. Kaplin , B.F. Nazarov, R.D. Tresnitskaya, M.S. Zakharov. Accelerated determination of copper and bismuth in india. M .: Nauka, 1966 - 299 p.]. The disadvantage of this method: it is possible to determine bismuth in the sample only with comparable quantitative ratios of bismuth and copper.

In [Wang Lei, Ding Hai-yu, Li Yi-jun, He Xi-wen. // Fenxi ceshi xuebao = J. Instrum. Anal. - 2005. - V.24 - No. 6. - P.89-95] (prototype) studied the behavior of bismuth on a glassy carbon electrode coated with an in-situ copper film. The mutual influence of copper and bismuth is eliminated through the use of a multi-component background of -0.1 M H ₂ SO ₄ +0.4 M KNO ₃ +0.05 M KSCN. Peak separation is achieved due to the formation of a sparingly soluble CuSCN compound, while the bismuth peak does not shift and the sensitivity of the method does not change. It is noted that a copper film, like mercury, can significantly reduce the limit of determination of bismuth (III), which is 2 · 10 ^-6 g / dm ³ , a linear dependence is observed in the range 1 · 10 ^-5 -4 · 10 ^-3 g / dm ³ . The disadvantage of this method is the use of a multicomponent background, the difficulty in updating the working surface of the glassy carbon electrode, the high toxicity of cyanide ions, as well as the low sensitivity of the determined bismuth contents.

The objective of the invention is to reduce the limit and lower boundary of the determined contents and increase the range of determined bismuth (III) contents by peaks of selective bismuth electrooxidation from the Au ₂ Bi intermetallic compound obtained after electroconcentration of a gold-bismuth binary precipitate on a graphite electrode by the IV method.

The problem is achieved by the fact that they accumulate bismuth on impregnated polyethylene graphite electrodes in a stirred solution in the presence of gold ions for 60-120, followed by recording peaks of selective electrooxidation of bismuth (III) from the intermetallic compound Au ₂ Bi, at a potential sweep speed of 60 -100 mV / s and electrolysis potentials from -0.3 to -1.1 V, on the background: 0.5-1.0 M HNO ₃ or 0.5-1.0 M HCl, the concentration of bismuth ions (III) determined by the size of the areas under the current-voltage curves in the range of potentials about t of 0.05 to +0.20 V relative to a saturated silver chloride electrode by the method of additives of certified mixtures. New in the method is that to obtain a useful signal, depending on the concentration of bismuth (III), the process of selective electrooxidation of bismuth from gold IM with bismuth is used.

In the proposed method, for the first time, the ability of a gold precipitate with bismuth to oxidize on impregnated graphite electrodes (IGE) was established (in the prototype a glassy carbon electrode with a copper film was used). The use of such electrodes is due to the high chemical and electrochemical stability of graphite, a wide range of working potentials, as well as the simplicity of mechanical surface renewal and safety requirements. The analysis does not use copper ions, rhodanide - and cyanide ions, because they are toxic.

The maximum value of the recorded current is observed at the electrodes of the IGE and SUE.

Proposed in the claimed invention backgrounds of 0.5-1 M HCl or 0.5-1 M HNO ₃ can determine the low content of bismuth ions (III) with good reproducibility. The highest sensitivity coefficient was observed on the background of 0.5-1 M HNO ₃ or 0.5-1 M HCl. The lower boundary of the determined contents by this method was 5 · 10 ^-7 g / dm ³ (in the prototype 2 · 10 ^-6 g / dm ³ ).

The results of using electrodes on various backgrounds are shown in table 1. The table shows that the IGE electrodes have the highest sensitivity coefficients.

Carry out electroconcentration of bismuth (III) ions on the surface of the IGE in a mixed solution in the presence of gold (III) ions for 60-120 s at electrolysis potentials from -0.3 to -1.1 V on the background: 0.5-1 M HCl or 0.5-1 M HNO ₃ with subsequent registration of the anode peaks with a linear change in potential at a speed of 60-100 mV / s. The concentration of bismuth (III) ions is determined by the area under the current-voltage curves, taken in the range of potentials from +0.05 to +0.2 V relative to the saturated silver chloride electrode (n.h.e.). Figure 1 presents the current-voltage curves of electrooxidation of the precipitate Au ₂ Bi from the surface of the impregnated graphite electrode. Curve 1 - background, 1M HCl containing C _{Au + 3} equal to 0.01 g / DM ³ ; curve 2 - C _Bi equal to 0.01 mg / DM ³ ; curve 3 - C _Bi is 0.02 mg / dm ³ .

Thus, the established conditions for the first time made it possible to quantitatively determine the content of bismuth (III) ions based on the reaction of selective electrooxidation of bismuth from the intermetallic compound (IMC) Au ₂ Bi obtained at the stage of preliminary electroconcentration (figure 2).

The proposed voltammetric method has significantly improved the metrological characteristics of the analysis of bismuth (III); increase the sensitivity of the determination (5 · 10 ^-7 g / dm ³ ), which is almost an order of magnitude lower compared to the prototype, the analysis time does not exceed 120 s (table 2).

Examples of specific performance.

Example 1. The measurements were carried out on a model solution. 10 ml of 1 M HCl background electrolyte is placed in a quartz glass. Without stopping stirring, electrolysis of the solution is carried out on the IHE under the condition: E _e = -0.300 V, τ _e = 100 s. The background current-voltage curve of the electrooxidation is taken at a sweep speed of 80 mV / s, starting from the potential E _nach = -0.100 V. The absence of peaks indicates the purity of the background. Then add 0.1 ml of a certified solution of gold ions (III) with a concentration of 100 mg / DM ³ and conduct electrochemical concentration of the precipitate under similar conditions. The peak of gold of the indicated concentration of the substance is recorded in the potential range from +0.70 to +1.0 V (relative to H.s.). The absence of other peaks indicates the purity of the background.

Then add 0.01 ml of a certified solution of bismuth (III) ions with a concentration of 1 mg / dm ³ , conduct the electrochemical concentration of the precipitate under similar conditions. The volt-ampere curve of the selective bismuth electrooxidation from IC with gold is recorded in the potential range from +0.05 to +0.2 V (relative to n.h.e.).

An additive of 0.01 ml of a certified solution of bismuth (III) ions with a concentration of 1 mg / dm ^{3 is} introduced into the analyzed solution and the analytical signal is recorded again. By the difference in the areas under the anode peaks of the selective electrooxidation of bismuth from the Au ₂ Bi IC, the concentration of bismuth (III) ions in the solution is calculated.

Example 2. Measurements were carried out in tap water.

In 100 ml of the test solution, 1 ml of nitric acid is added and evaporated to a dry residue. A cup of sediment is calcined in a muffle at 450-500 ° C. Add 10 ml of 1 M HCl of background electrolyte to the glass and transfer the precipitate to the solution with gentle heating of the glass. Cool the glass with contents to room temperature.

Check the electrodes for cleanliness. The absence of peaks indicates a clean background. In a chilled glass add 0.1 ml of a solution of gold ions (III) with a concentration of 100 mg / DM ³ and placed in the device. Without stopping stirring, electrolysis is carried out on the IHE solution under electroconcentration conditions: E _e = -0.300 V, τ _e = 100 s. The volt-ampere curve of the selective bismuth electrooxidation from IC with gold is recorded at a sweep speed of 80 mV / s, starting from potential E _beg = -0.100 V. The peak of bismuth of the indicated concentration of the substance is recorded in the potential range from +0.05 to +0.2 V (relative to us.h.e.). Then add 0.02 ml of a certified mixture of bismuth (III) ions with a concentration of 1 mg / DM ³ and conduct the electrochemical concentration of the precipitate under similar conditions. The peak of the selective oxidation of bismuth from the intermetallic compound Au ₂ Bi of the indicated concentration of the substance is recorded in the potential range from 0.05 to +0.20 V (relative to nc). The concentration of bismuth (III) ions in the solution is calculated from the difference in the area of the IM ₂ Au ICs.

Thus, for the first time, the ability of quantitative analysis of bismuth by peaks of selective electrooxidation of bismuth from the intermetallic compound Au ₂ Bi was established.

The proposed method is simple, mercury is not used due to its negative physiological effect. The method can be applied in any chemical laboratory having computerized analyzers such as CTA, TA or polarograph. The proposed method can be used to determine bismuth in drinking, natural and wastewater.

Table 1 Method for determination of bismuth in aqueous solutions by inverse voltammetry by peaks of selective bismuth electrooxidation from intermetallic compound Au ₂ Bi Electrode Sensitivity factors of various 1 M background electrolytes H ₂ SO ₄ HNO ₃ Hcl HclO ₄ Glassy carbon 0.02 0.30 0.28 0.20 Impregnated Graphite 0.09 0.37 0.32 0.27

table 2 Object of study Introduced, C _{Bi (III)} , mg / L Found, C _{Bi (III)} , mg / l Sr, (t _0.95 ) n = 5 Tap water 0.01 0.009 ± 0.005 0.002

Claims (1)

A method for determining bismuth in aqueous solutions by inversion voltammetry according to the peaks of selective bismuth electrooxidation from an intermetallic compound Au ₂ Bi, which consists in transferring bismuth (III) from a sample to a solution and performing a voltammetric determination, characterized in that bismuth is accumulated on impregnated polyethylene graphite electrodes in a stirred solution in the presence of gold ions, for 60-120 s followed by registration of peaks of selective bismuth (III) electrooxidation and h intermetallic compound Au ₂ Bi, at a potential sweep speed of 60-100 mV / s and electrolysis potentials from -0.3 to -1.1 V, on the background: 0.5-1.0 M HNO ₃ or 0.5- 1.0 M HCl, the concentration of bismuth (III) ions is determined by the area under the volt-ampere curves in the potential range from 0.05 to 0.20 V relative to the saturated silver chloride electrode by the method of additives of certified mixtures.

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