RU2229109C2 - Procedure of selection and analysis of samples to establish degree of contamination of surfaces by metallic mercury - Google Patents

Abstract

FIELD: analytical chemistry, specifically, procedures taking and processing mercury samples by Polezhaev's method. SUBSTANCE: according to invention samples of mercury are taken by means of wads with weight 300±50 mg from area of 100-150 cu cm wetted in solution of iodine in potassium iodide and its subsequent reaction with compound solution with formation of colored complex Cu₂(HgI₄). Samples are taken from surfaces at least twice by two wads. First wad with mass 300±50 is wetted in absorption solution and examined surface is rubbed clean with it. Second dry wad with mass 100±20 collects residues of absorption solution. Thereupon both wads are transferred into test tube with absorption solution and wads are rubbed over in solution at temperature 35-40 C. Wrung out wads are treated in similar way till negative reaction for mercury is obtained with summation of results. Absorption solution is centrifuged at 3000 rpm in the course of 3.0 min to separate contaminants from it. EFFECT: ensured selection and analysis of mercury samples taken from surfaces. 6 dwg

Description

The invention relates to the field of analytical chemistry, in particular to methods for the selection and processing of mercury samples by the Polezhaev method.

Currently known and described are the following methods for the collection and processing of mercury samples by the Polezhaev method from various media that are analogues of the invention.

a) Determination of mercury in air by the Polezhaev method [1].

The essence of the method is the interaction of mercury vapor with iodine in the presence of KI with the formation of the complex compound K ₂ (HgI ₄ )

and its subsequent interaction with a solution of copper sulfate with the formation of a colored complex Cu ₂ (HgI ₄ ). The mercury content is determined colorimetrically by pink color against a white suspension of CuI ₂ . The sensitivity of the method is 0.01 mg / m ³ .

The reagents used in this method are prepared as follows:

- iodine crystalline sublime (sublimation of crystalline iodine is carried out on an electric stove in a glass beaker, where about 10 grams of iodine are added.) The glass is closed with a watch glass or Petri dish, onto which cotton wool moistened with cold water is placed. In the process of sublimation, iodine vapor settles on a cold surface, forming violet crystals. At the end of the sublimation, the crystals are scraped off into the bottle. Sublimation is carried out under traction;

- iodine, 0.1 n. a solution in a 3% solution of potassium iodide;

- potassium iodide - 3% aqueous solution;

- absorption solution (2.5 g of iodine iodine and 30 grams of potassium iodide are dissolved in a small amount of water and the volume is adjusted to 1 liter with distilled water);

- sodium sulfite Na ₂ SO ₃ · 7H ₂ About 3 N. solution;

- copper chloride CuCl ₂ · 2H ₂ O, 7% solution or copper sulfate CuSO ₄ · 5H ₂ O, 10% solution;

- reactive solution (1 volume of a 10% solution of copper sulfate and 5 volumes of a 3N sodium sulfite solution are added to the graduated cylinder). The mixture is shaken until the precipitate is dissolved. The solution is prepared before analysis);

- standard mercury solution (0.0135 g of mercury chloride is dissolved in 100 ml of an absorption solution). Then 1 ml of the prepared solution is diluted to 100 ml with an absorbing solution (the standard solution contains 1 μg of mercury ion Hg ^{+ 2} in 1 ml);

Sampling for analysis is as follows. 30-40 l of test air at a speed of 40 l / h is pulled through two sequentially connected absorption devices of Polezhaev containing 2 ml of absorption solution (Fig. 1). In the process of sampling, iodine is carried away from the solution, while the color of the absorption solution becomes pale. The initial color of the solution is restored to 0.1 N. a solution of iodine in a 3% solution of potassium iodide, which is added dropwise to restore the original color. The entrainment of iodine is especially large if heated air is analyzed.

The determination of mercury in the sample is as follows. In a centrifuge tube make 1 ml of absorbent solution from each device, add 1-2 drops of 0.1 N. iodine solution to restore the original color of the absorption solution and 0.8 ml of the reaction solution is introduced. The liquid is shaken, left for 15-20 minutes until sedimentation of the suspension, then the color of the latter is compared with a standard scale (Fig. 2), (Table 1). Doubling of all reaction components by volume is possible.

The calculation of the concentration of mercury in the air is carried out according to the formula

Where

V is the total volume of the test solution, ml;

a - the amount of substance found in the analyzed volume of the solution, mcg;

V ₁ - the volume of the test solution taken for analysis, ml;

V ₀ - the volume of the investigated air, l

This method is applicable only for air analysis. The difference between the proposed method and the analogue lies in a fundamentally different method of sampling.

So the actual sampling is carried out by wiping the contaminated surface with wet and dry swabs. A centrifugation method is used to eliminate the interfering effect of dirt collected simultaneously from the surface. To increase the degree of extraction of mercury from the sample, the sample is processed at elevated temperatures (35–40 ° C). To ensure reliability, tampons and the surface are treated to a negative reaction to mercury.

b) Another analogue of the invention is the determination of mercury in protective clothing [3]. Soaking of the studied clothing by this method is carried out in 5 liters of an absorbing solution. Analyzed 0.1 ml of the obtained extract. The disadvantage of this method is the absence of any operations to clean the absorption solution from dirt, which can distort the results of the analysis. In addition, overalls may contain mercury in a metallic form, which is not completely recovered when treated once with an absorbent solution.

The proposed method, in addition to the actual sampling, is characterized by the presence of repeated processing of the test surface and sampling means - cotton swabs, as well as centrifugation of the absorption solution in order to separate the dirt.

c) Another analogue of the invention is a method for determining mercury in various materials [2].

The method, like both the previous ones, is based on the extraction of mercury from materials with a solution of iodine in potassium iodide, however, the actual mercury extraction is achieved by heating the sample, thermal desorption of mercury and subsequent determination of the mercury ion.

A sample of plaster, cement, concrete is taken in different places of the room at different depths (2-6 cm). Scraping from the walls, floor and various objects is taken from the surface (5-10 cm ² ).

Samples are ground in a mortar, the tree is cut into small pieces. For analysis, 5-10 g of the sample is placed in a flask with a ground stopper, filled with a 0.5% iodine solution so as to cover its surface, and left for 2-3 hours, occasionally shaking. If the iodine is discolored, an 8% iodine solution is added in small portions until the discoloration ceases. Then the sample is filtered through a paper filter, previously washed with 5% iodine solution and distilled water. Measure the volume of the filtrate and determine the mercury ion. In cases where extraneous colored compounds are mixed with the sample, which complicates the colorimetry, the extraction of mercury from the sample is carried out by thermal desorption. A portion of the crushed material is placed in a glass tube and about 20 l of pure, mercury-free air is pulled through it when heated to about 150 ° C. The mercury vapors released during this process absorb 10 ml of mercury absorption solution.

A control experiment is preliminarily carried out, for which 20 liters of clean air are pulled through the tube into an absorption device with 10 ml of absorption solution (0.02 N iodine solution in KI). For analysis, 1 and 5 ml of the sample 5 ml from the control solution is transferred to centrifuge tubes; 1 ml of the sample was adjusted to 5 ml with an absorbent solution. At the same time preparing a scale of standards.

If the sample is colored less intensely than the solutions on the scale, then add 1-2 drops of an 8% iodine solution until the colors are equalized. Then, 1 ml of a composite solution (10% CuSO ₄ + Na ₂ SO ₃ (1: 5)) is added to the test tubes and samples. 15-20 minutes after the complete sedimentation of the suspension to the bottom of the tubes, the color intensity of the sediment is compared with the standard scale.

The mercury content X (mg / g material) is calculated by the formula

where a is the amount of mercury in the analyzed sample volume, mcg;

V is the sample volume taken for analysis, ml;

V ₀ - total sample volume, ml;

g - hitch, g.

This method is an analogue of the invention and it has the same differences from the proposed method: the sampling is fundamentally different, the analogue in question claims that the mercury in the sample after contact with a solution of iodine in potassium iodide is completely removed. However, it is not. In experiments, it was shown that for reliable extraction of mercury, multiple processing of the sample is necessary. The exposure time given in the procedure for 3 hours is very short. When analyzing such samples as wood, plastics, scraping paint, exposure to 3 hours is not enough. A more complete extraction of mercury from porous materials is achieved when the test sample is in the absorption solution for about a day. To exclude the interfering effect of a finely dispersed sample on the absorption solution in the prototype, the filtering method is used. However, in this case, the results of the analysis can be greatly distorted due to dilution of the sample on the filter. In the proposed method, the cleaning is carried out by centrifugation.

The prototype of the invention is “Methodology for measuring the mass concentration of mercury in the filtrate of washes from surfaces on a mercury analyzer RA-915 + with the prefix RP-91” [4].

In the prototype, sampling is carried out using the Polezhaev method with a cotton swab weighing 300 mg soaked in an absorption solution with an area of 150 cm ² . The test surface is wiped with a cotton swab, then the swab is poured with the volume of an absorbing solution of 5 ml, the swab is squeezed out, the resulting solution is filtered on a paper filter. Subsequent processing of the results is carried out by the method of "cold steam" on the analyzer RA-915 + with the prefix RP-91. The main disadvantages of the prototype method are:

- processing with a swab of surfaces is carried out only once. This is due to the use of this method for the analysis of contaminants only up to 0.05 μg of mercury in a sample (a sample taken from a surface of 150 cm ² ). Impurities of this order are possible during depressurization of mercury fluorescent lamps. In other cases of contamination, the method will yield a deliberately incorrect result;

- separation of dirt from the absorption solution is carried out by the filter method on the filter, which leads to losses of mercury on the filter;

collection of the remaining part of the absorption solution in an area of 150 cm is not performed. Meanwhile, up to 20-30% of the solution containing mercury, which is lost, remains on it.

The essence of the invention lies in the combination of essential features that are in a causal relationship and ensure the achievement of the claimed result: selection and analysis of samples of mercury on surfaces:

- sampling is carried out with two cotton swabs. The first tampon with a mass of 300 ± 50 mg is moistened with an absorbent solution, slightly wrung out, and a surface of a certain area is rubbed with tweezers, after which the tampon is transferred to a test tube with an absorbent solution. The second dry swab of less weight 100 ± 20 mg from the same surface collects the remains of the absorption solution. After collecting them, the swab is placed in the same tube. The mass of tampons is optimal for the sizes of the area of 100-150 cm ² from which the sample is taken, and for the volume of the absorbing solution 1-2, ml in which the analysis takes place;

- tampons in the absorption solution are carefully rubbed with a glass rod, and then squeezed on the side of the tube and transferred to another tube for re-analysis;

- centrifugation of the contents of the tube at 3000 rpm for 3 minutes. Taking swabs (“smears”) from the surface is always accompanied by contamination of swabs with an absorbent solution that come in contact with the test surface. In some cases, the cotton moistened with the absorption solution can be very heavily contaminated with sand, dust, soot, old paint, etc. After pressing the cotton, the absorption solution becomes opaque, changes color and contains a suspension (Fig. 3). When conducting the actual analysis, the resulting white precipitate of copper iodide interferes with the dirt, and it is impossible to get any results at all. Two methods are used to separate the dirt from the solution: filtration and the proposed one - centrifugation.

The filtration method consists in filtering the studied absorption solution through a filter pre-moistened with an absorption solution. However, in this case, the concentration in the sample is distorted due to the loss and dilution of mercury on the filter.

The centrifugation method allows you to easily and without loss to separate the suspension from the solution. When centrifuged at a speed of 3000 rpm for 3 minutes, the suspension is reliably separable from the absorption solution. After centrifugation, the initial color of the absorption solution is restored. With large accelerations and centrifugation time of about 10 minutes, the cake is caked so that even when it is poured into another tube, “sedimentation” of the cake does not occur. When centrifuging, cotton wool must be placed on the bottom of the centrifuge seat. If this is not done, then the centrifuge may break the bottom of the tube.

- processing tampons is carried out several times until a negative reaction to mercury with a summation of the results;

- treatment of one test surface contaminated with mercury is carried out at least two times;

- in order to reduce the number of tampon treatment cycles, the extraction of mercury from tampons with an absorbent solution is carried out at a temperature of 35-40 ° C. In this case, a higher degree of extraction from tampons of mercury by an absorption solution is achieved with a single treatment. At higher temperatures of 50 ° C and higher, a decrease in the intensity of staining of the Cu ₂ (HgI ₄ ) complex is observed, which leads to a distortion of the analysis results.

To assess the degree of surface contamination with mercury, the following methodology is proposed. Flushing is carried out from a surface of 100 cm ² (square 10 × 10). For this purpose, a stencil is made, the boundaries of which are applied on the surface to be examined with a simple pencil (Fig. 4).

The absorption solution is applied to this surface with tweezers using a cotton swab weighing approximately 300 mg. To do this, a cotton swab is wetted in an absorbent solution, slightly wrung out, and the surface is wiped with parallel horizontal and then vertical movements. After that, the swab is placed in a test tube and poured 2 ml of the absorption solution (figure 5).

The remaining portion of the absorption solution is collected by a second dry cotton swab weighing approximately 100 mg. After collecting the absorption solution, the swab is placed in the same tube. Both swabs are carefully rubbed with a glass rod in the solution, then squeezed out on the side surface of the tube and removed from it (for possible re-processing) (Fig.6).

The contamination of the surfaces during the drop strait of mercury is quite large. Therefore, the range of the scale for an indicative assessment of pollution increases. To obtain sufficiently reliable data, two scales are built: approximate and accurate. To build an indicative scale, it is necessary to use a mercury solution with a concentration of 0.1 mg / ml. An indicative scale is shown in Table 2. It has a "step" concentration of approximately 10 μg. An accurate scale is constructed after a rough assessment of the level of contamination with a "step" of 0.2 μg.

The possibility of implementing the method is confirmed by the following examples.

Example 1

In a glass jar was a plate of polyethylene with an area of 100 cm ² , which was in contact with mercury vapor for 5 days at a temperature of 20 ° C.

After that, two successive rinses were made from her with tampons according to the proposed method (the first tampon wiped and wetted the surface of the polyethylene plate, and the second wiped its surface to dryness).

After sampling the mercury, both swabs were placed in an absorption solution and kneading for 1 minute, after which the cotton wool was squeezed out, the solution was centrifuged and the absorption solution was poured again.

As a result of the experiment, the first flush with two swabs gave a positive result - the presence of mercury of approximately 1 μg in the sample (0.02 μg / cm). Repeated treatment of the cotton with an absorbent solution showed the presence of mercury as low as about 0.3 μg in the sample. The third treatment was negative.

The second flush from the surface gave the following results:

The first treatment is 0.3 μg in the sample. The second is negative.

Conducted for control purposes, the third wash was negative during the first treatment of the swab. Thus, the total surface contamination was 1 μg + 0.3 μg + 0.3 μg = 1.6 μg on a surface of 100 cm ² . A significant increase in contamination with an increase in the contact time of the polyethylene plate with mercury vapor up to 10 days did not occur. The average level of pollution remained the same.

Example 2

The purpose of the experiment is to detect mercury contamination of the glass surface at high concentrations of mercury.

To do this, a glass surface S = 100 cm ^{2 was} rubbed with a wet swab and then a dry swab, after passing a drop of mercury on the surface.

To assess the degree of contamination, the first wash with two swabs was treated with an absorbent solution in accordance with the claimed method.

Results:

1 treatment of tampons - mercury content of 20 μg in the sample;

2 treatment of tampons - mercury content of 20 μg in the sample;

3 treatment of tampons - mercury content of 10 μg in the sample;

4 treatment of tampons - mercury content of 8 μg in the sample;

5 treatment of tampons - mercury content of 6 μg in the sample;

6 treatment of tampons - mercury content of 3-4 μg in the sample;

7 treatment of tampons - mercury content of 1 μg in the sample;

8 treatment of tampons - mercury content of 0.2 (traces) μg in the sample;

Processing the second flush with two cotton swabs gave the following

results:

1 treatment of tampons - mercury content of 6 μg in the sample;

2 treatment of tampons - mercury content of 3 μg in the sample;

3 treatment of tampons - mercury content of 1.5 μg in the sample;

4 treatment of tampons - mercury content of 0.2 μg in the sample;

5 treatment of tampons is negative.

Processing the third wash with two cotton swabs gave the following results:

1 treatment - mercury content of 1.5 μg in the sample;

2 processing - mercury content of 0.3 μg in the sample;

3 treatment is negative.

Processing the fourth wash gave a negative result.

Thus, when using the method of taking swabs from surfaces with large contaminants with mercury, tampons should be processed until a negative result for mercury is obtained.

The total surface mercury contamination was 81.7 μg in the sample (20 + 20 + 10 + 8 + 6 + 4 + 1 + 0.2 + 6 + 3 + 1.5 + 0.2 + 1.5 + 0.3) .

Sources of information

1. Peregud EA et al. Chemical analysis of air in industrial enterprises. - L .: Chemistry, 1973.

2. Peregud EA Chemical analysis of air. - L .: Chemistry, 1976

3. Mercury. Normative and methodological documents. Directory. - SPb., 1991, Appendix No. 3, p. 62.

4. Mercury. Normative and methodological documents. Directory. - SPb., 1991, p. 170.

Claims (1)

A method of sampling and processing samples to determine the contamination of surfaces with metallic mercury and its compounds, which consists in sampling mercury with swabs weighing (300 ± 50) mg from an area of 100-150 cm ² moistened with a solution of iodine in potassium iodide, and its subsequent reaction with a compound solution with the formation of a colored complex Cu ₂ (HgI ₄ ), characterized in that the sampling from the surfaces is carried out at least two times with two cotton swabs: the first swab with a mass of (300 ± 50) mg is moistened with an absorbent solution and the test surface is wiped with it b, the second - a dry swab with a mass of (100 ± 20) mg, residues of the absorption solution are collected from the surface, after which both swabs are transferred to a test tube with the absorption solution, grinding the swabs in the solution is carried out at a temperature of 35-40 ° C, squeezed swabs are treated in a similar manner until a negative reaction to mercury with a summation of the results obtained, and to separate the dirt from the absorption solution, it is centrifuged at 3000 rpm for 3 minutes

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