RU2324169C1 - Electrochemical method of mercury definition by modification of graphitized electrode by ionic liquid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: mercury concentrating from liquid samples according to the invention is carried out by means of the aqueous delaminating system containing derivant of pyrazyl ketone and organic acid. Delaminating in system is carried out due to chemical interaction of "pharmaceutical" antipyrine and salicyl-sulphonic acid with unique dissolvent - water. At delaminating the bottom phase of ionic organic liquid is formed, which put in microliter quantities on a graphitized electrode surface. Then it is put in a three-electrode mesh with HCl about 0.1 mole/l, it is submitted voltage potential of mercury accumulation - 1.4 W within 30 seconds and then in a mode of anodic scan voltamperegram is displayed with peak of the mercury anodic oxidation, observed at potential within 0.00-0.10 W and linearly depending on mercury concentration in an ionic liquid, in a mode of direct current at a scanning speed of 80 mW/sec over the range from -1.2 to 1.0 W.

EFFECT: reduction in price of the analysis procedure.

1 tbl, 2 dwg

Description

The invention relates to the field of analytical chemistry of environmental objects determination of mercury by voltammetric method.

A known method of electrochemical determination of mercury in the quantitative chemical analysis of food products [E.A. Zakharova, V.M. Pichugin, N.P. Pikula. Methods for quantitative chemical analysis of alcoholic and non-alcoholic drinks for mercury content by inversion voltammetry. MU 08-47 / 037. Tomsk TPU 1995. - 25 p.]. The technique (analogue) is based on inversion-voltammetric measurements without accumulation with a linear sweep of a potential of 30 ... 40 mV / s in constant current mode of recording the anode current in the form of a peak with a maximum in the range +0.55 ... + 0, 65 V relative to silver chloride electrode. Preparation of a working graphite electrode before the analytical procedure includes the step of electrodeposition of gold from its 100 mg / dm ³ aqueous HClO ₄ solution (1: 1) at a potential of 0.00 V for 5 minutes. In the case of natural waters and other liquid samples, the prototype uses a long, about one hour, and laborious preparation of an analytical sample, including wet oxidation with nitric acid, hydrogen peroxide, ultraviolet with a photocatalyst - titanium dioxide, can take up to two hours, depending on the availability in a sample of organic matter.

The working life of the working gold-graphite electrode is limited, special conditions for its storage are required, a special program for the formation of gold on the surface of graphite, the authors note the interfering effect of silver ions.

Of the known technical solutions, the closest in purpose and technical essence to the claimed object is a method for the separation of mercury from aqueous solutions (as.with. 1357759) / B.I. Petrov, S.I. Rogozhnikov, T.V. Sukhneva. // B.I. 1987, No. 45 — by extraction of mercury from aqueous solutions using an exfoliating system including a pyrazolone derivative and an organic acid, with the end of the analytical procedure by atomic emission analysis of the extract after applying it to a plasma torch graphite electrode (prototype) in milliliter amounts (0.5 ml or 500 μl). Common to the prototype and the claimed invention is the use of an exfoliating system: water, a pyrazolone derivative and an organic acid.

The disadvantages of the prototype include:

- the use of an emission spectrometer that does not provide the necessary sensitivity for determining mercury in natural waters and snow water (precipitation); the detection limit of mercury by the inductively coupled plasma emission method is about 50 μg / L. Decrease in determined concentrations is achieved with the help of hydride generators, which in combination with high temperatures serve as additional sources of danger;

- despite the possibility of determining several elements in one act of chemical analysis, the emission method with inductively coupled plasma (modern version) or with graphite electrodes (prototype) remains very costly and expensive.

The essence of the invention

The proposed electrochemical method for determining mercury by modifying a graphite electrode with an ionic liquid, which consists in extracting mercury from an aqueous exfoliating system containing a pyrazolone derivative and an organic acid, characterized in that 1.5-2.0 mmol is added to extract mercury from the acid chloride aqueous solution “Pharmacopeia” antipyrine and 0.7-1.0 mmol of 2-aqueous sulfosalicylic acid, retaining a total volume of 10 ml, after vigorous 5-minute shaking, 15-minute settling at room temperature At 25 ° C and 5-10 minutes centrifugation, the lower phase of the ionic organic liquid is formed, which is applied in an amount of 1 microliter on the surface of the graphite electrode, then placed in a three-electrode cell with 10 ml of 0.1 mol / L HCl, the storage potential is applied without delay a mercury of -1.4 V for 30 s and then in the anode scan mode, a voltammogram is recorded with a peak of anodic oxidation of mercury observed at a potential for oxidation of mercury on graphite in the range of 0.00-0.10 V and linearly dependent on the concentration of mercury in the ionic liquid in constant current mode at a scan speed of 80 mV / s in the range from -1.2 to 1.0 V.

The proposed method differs from the prototype in that it reduces the cost of the analysis due to the use of much simpler and cheaper equipment that does not have sources of increased danger for the analyst, eliminates the stage of high-temperature decomposition of the analyte with the aim of atomization. Electrochemical analyzers are easier to automate, much smaller in size and weight, and electrochemical methods make it possible to further concentrate the analyte on the surface of the working electrode in a voltammetric cycle. Field-based voltammetric analyzers allow you to control mercury directly at the site of water sampling.

The implementation of the invention

A method for the electrochemical determination of mercury by modifying a graphite electrode with an ionic liquid is to extract mercury from the liquid aqueous phase into the organic component of the water-antipyrine-sulfosalicylic acid exfoliating system. Concentration of mercury occurs from a liquid sample (for example, snow water) in an “in situ” mode, that is, during the formation of the lower phase of the stratified system. In a glass tube for concentration with a total volume of 10 ml dry powdered substances are introduced - chemical reagents:

1.5-2.0 mmol of "pharmacopeia" antipyrine (gross formula C ₁₁ H ₁₂ N ₂ O, melting point 113 ° C, molecular weight 188.23 g / mol),

0.7-1.0 mmol of 2-aqueous sulfosalicylic acid (GOST 4478-78, gross formula C ₇ H ₆ O ₆ S × 2H ₂ O, molecular weight 254.21 g / mol),

the rest is up to 10 ml, the only solvent is water.

Upon dissolution of the antipyrine reagent and organic acid (solid) in the object of analysis (an aqueous solution containing trace amounts of mercury), an acid-base interaction occurs between the protonated antipyrine and the anions of the organic acid. The resulting organic component, consisting of an ionic associate of an organic salt, antipyrinium sulfasalicylate and antipyrine, has an acidic reaction and extracts mercury hydroxochlorides from acidic chloride solutions due to the formation of a complex metal complex with an ionic in nature and organic in composition liquid. The volume of the organic component (lower phase) in the presented range of chemical reagent compositions varies from 1 to 3 ml, and a change in the molar amounts of reagents for the indicated composition interval leads to a violation of the conditions of liquid-phase separation and the formation of monotectic phases of variable composition (transparent crystals, isotherm solubility). The closed region of the compositions in the upper part of the concentration triangle on the solubility isotherm corresponds to the optimal composition of the components in the water - antipyrine - organic sulfonic acid system. In this region, limited by the field of saturated solutions, delamination occurs into the lower yellow phase (ionic organic liquid) and the upper aqueous phase of lower density. In the claimed invention, the optimal range of compositions of such a system with another (sulfosalicylic) organic acid in the formula is presented in millimoles for a certain total volume of the system [B.I. Petrov, S.A. Denisova, A.E. Lesnov, G.E. Shestakova. Interphase distribution of some elements in the water-antipyrine-naphthalene-2-sulfonic acid system // News of universities. Chemistry and Chem. technology. 1999. T.42, N 1. S.21-23], Fig.1.

The proposed method for determining mercury differs from the known determination in the method for preparing an ionic conductive fluid. Since the mercury content in natural objects is low, a model model is used for concentration of the exfoliating exfoliating system water - antipyrine - sulfosalicylic acid. Previously, the degree of mercury extraction by this system from model aqueous solutions (table) with GSO 7263-69 additives of the composition of mercury ions 0.95-1.05 mg / ml, introduced into the system by the method of sequential dilution, was determined by the introduced-found method. Model exfoliating systems are prepared from 2 mol / L solutions of antipyrine and sulfosalicylic acid. The optimal ratio of the volumes of such solutions of antipyrine and sulfosalicylic acid is 2: 1. The total volume of the system is 10 ml, the volume of the organic component is 1 ml. The degree of extraction of mercury in the organic component is 96.5%; 95.0%; 97%, which allows the use of an extract of the above system to extract mercury from natural snow water. The mercury signal obtained for the aqueous phase of the system is commensurate with the signal of the control (blank) experiment in the cold vapor method (about 0.01 ngHg / ml).

The results presented in the table for the organic component of the system (1 ml) were obtained by atomic absorption method with the restoration of all forms of mercury with an alkaline 3% sodium borohydride solution (1 ml) against a background of 0.1 mol / L HCl (1 ml) followed by atomization mercury in a quartz furnace (140 ° C) in a stream of argon. In the future, the AA method of cold steam is used as independent for the calibration of the inventive electrochemical method.

The organic component of the exfoliating system, which forms in the lower phase when exfoliating in the form of a yellow ionic liquid, is used to modify the graphite electrode. Before each determination, the surface of the graphite electrode is updated, polished with filter paper and washed in boiling distilled water to remove excess oxygen from its surface. On a dry graphite surface, 1 μl of ionic liquid was applied using a MS – 1 M chromatographic syringe, uniformly distributing along the end surface of the electrode (geometric area 0.5 cm ² ). Such a film electrode is placed in a three-electrode cell with 10 ml of 0.1 HCl (as a background solution). Further, without delay, the potential for accumulation of mercury of -1.4 V is supplied for 30 s. Then, in the anode scan mode, a voltammogram is recorded. The peak of the anodic oxidation of mercury is recorded at a potential in the range of 0.00-0.10 V (the oxidation potential of mercury on graphite) in constant current mode at a sweep speed of 80 mV / s in the range from -1.2 to +1.0 V. The observed anode peak in height linearly depends on the concentration of mercury in the ionic liquid. Figure 2 shows the calibration dependence of the limiting diffusion current on the concentration of mercury. Voltammograms were recorded using a TA-2 voltammetric analyzer (NPP Tekhnoanalit, Tomsk, TU 4215-000-36304081-95).

When mercury was extracted from snow water, the minimum detectable mercury concentration was 0.0084 ± 0.0002 μg / L in the AAS method, and these results relate to conditionally background snow cover samples. The results of the determination of mercury in the same three samples of snow water by the IVA method amounted to 0.0115 ± 0.0003. Comparison of these two independent methods satisfies t (0.57 <2.45) and F (2.46 <4.15) statistical criteria, and the difference in the results of both methods is statistically insignificant. The minimum concentrations of mercury determination thus established of 0.008-0.012 μg Hg in a liter of snow water are representative, determined in 10 ml of the object and correspond to volume concentration up to 10 times.

Metrological characteristics of the stratified extraction system water - antipyrine - sulfosalicylic acid Introduced Hg, mcg Found Hg, mcg R% D 0.00250 0.00240 96.5 248 0,00237 95.0 171 0,00243 97.0 291 <value> ± ε _α 0.00240 ± 0.0001 96 ± 4 240 ± 150 Note: ε _α is the confidence interval; R is the degree of extraction, D is the distribution coefficient, the total volume of the system is 10 ml, the volume of the organic component (lower phase) is 1 ml.

Claims (1)

An electrochemical method for determining mercury by modifying a graphite electrode with an ionic liquid, which involves extracting mercury from an aqueous exfoliating system containing a pyrazolone derivative and an organic acid, characterized in that 1.5-2.0 mmol of antipyrine and 0 are added to extract mercury from the aqueous solution , 7-1.0 mmol of 2-aqueous sulfosalicylic acid, while maintaining a total volume of 10 ml, is vigorously shaken, settled at 25 ° C and centrifuged to form the lower phase of the ionic organic liquid, which applied in an amount of 1 μl for modification to the surface of a graphite electrode, then it is placed in a three-electrode cell with 0.1 mol / L HCl, the accumulation potential of -1.4 V mercury is applied without delay for 30 s, and then a voltammogram is recorded in the anode scan mode with a peak of anodic oxidation of mercury, observed at a potential in the range of 0.00-0.10 V and linearly dependent on the concentration of mercury in the ionic liquid, in a constant current mode at a sweep speed of 80 mV / s in the range from -1.2 to 1 , 0 V.

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