The extraction method of preparation of analytical samples

 

(57) Abstract:

The invention relates to the preparation of solid samples environment for the quantitative determination of cadmium by physico-chemical methods. How is that for the extraction of cadmium from the surface and of the volume of natural objects use the dissecting system consisting of thiopurine in the number of 0,002-0,003 mol, trichloroacetic acid number of 1.2 to 1.6 mol, phosphoric acid number of 0.03 to 0.05 mol, and distilled water to 1 liter, which at room temperature of 25 ° C for 30 minutes, treated with natural material. The proposed method ensures maximum extraction of cadmium for a short time at room temperature. table 1.

The invention relates to the preparation of solid samples of environmental objects (solids snow cover, suspended solids rivers and lakes, soil, sediment, and other solid samples) for the quantitative determination of cadmium optical, polarographic or other method of analysis.

Known methods of dry [GOST 26929-94. Raw materials and food products. Preparation of samples. Mineralization for the determination of toxic elements] and wet ed methods of trace metal analysis: Biological and Evironmental Samples/Jon C. Van Loon. 1985/NY/Toronto/Vol.80. - 351 pp] particulate samples of natural objects to retrieve (desorption) of toxic elements such as cadmium, surface and volume of particles in the mixture of mineral acids. As a rule, as extractants of cadmium and heavy metals using a mixture of sulfuric, nitric and concentrated hydrochloric acid in various volume ratios depending on the object of analysis. Sulfuric and nitric acid act on the solid component of the sample as restrukturisasi and oxidizing agents, acid mixture, destroying and oxidizing natural compounds organic and inorganic composition. Hydrochloric acid acts in the acid mixture as complexes cadmium and heavy metals agent that binds heavy metal ions in the chloride complexes. Akin to a "Royal" vodka (a mixture of nitric and hydrochloric acid in a volume ratio of 3:1) on the metal gold when it is dissolved. However, the dry ashing requires careful control over the temperature ashing. So, if you increase the temperature more IS irreversibly lost cadmium and other volatile metals (bismuth, arsenic, mercury, lead, tin). You additionally need expensive refractory quartz ware. MDE wet ashing the mixture of acids requires special care (fume cupboard, individual protective equipment), additional time and labor costs.

The proposed method sample preparation completely eliminates the above mentioned disadvantages, by providing the desired degree of extraction of cadmium, close to 100%.

Known technical solutions closest to destination and technical nature of the claimed object is a method of preparation according to GOST 26929-94. Raw materials and food products. Preparation of samples. Mineralization for the determination of toxic elements. Total for the prototype and the claimed invention are the use of acids for desorption of cadmium in the solution from the surface and bulk solids samples. You should list the main disadvantages of the prototype:

- the use of aggressive mineral acids (sulfuric, nitric, hydrochloric);

- long-term (90 min) heat of analytical samples.

The proposed method differs from the prototype in that aggressive (sulphuric, nitric, hydrochloric) acid is replaced in the application of phosphate (visivel) and trichloroacetic (particulate organic matter) acid. Acid provide a safe extraction of cadmium in the form of a complex with an organic reagent - tipitina (not in PR is anantnag system (water, trichloroacetic and phosphoric acid, thiopyran). In the present method does not require prolonged heating, which can cause irreversible loss of cadmium. Unlike the prototype in the claimed method provides the necessary extraction of cadmium in less time for 30 min at room temperature. While removing cadmium from the solid sample is provided serosoderjaschei organic nitrogenous reagent - tipitina.

The invention consists in that for the extraction of cadmium from the surface and bulk solids natural object (total weight of 0.5-1 gram) with a degree of recovery 98-100% used four stratifying system volume of 10 ml, consisting of reagent - thiopurine (0,00002-0,00003 mol), trichloroacetic acid (0,012-to 0.016 mol), orthophosphoric acid (0,0003-of 0.0005 mol) and distilled water up to 10 ml In contrast to the prototype to achieve a technical result and obtain reliable expert estimates, close to 100%, the process of desorption of cadmium is implemented at room temperature of 25 ° C for 30 minutes the desired degree of extraction of cadmium is achieved by extraction of the metal in the organic phase in a volume of 1 ml, generated in the process rassle the practical definition (atomic absorption, polarography, emission spectrometry, spectrophotometry, and so on).

The implementation of the invention is achieved as follows. The sample weighing 0.5 to 1 gram of natural material, such as solid particles of snow water obtained after filtration through a membrane filter IFA-MA NO. 6 (TU 6-05-1903-81), weighed on an analytical balance with an accuracy of 0.0002 g and placed in a clean extraction tube with a volume of 15 ml, equipped with a glass stopper. The extract is prepared as follows. Mix 4 ml of a 4M solution of trichloroacetic acid (reagent-grade) plus 4 ml of 0.1 M phosphoric acid (reagent-grade) plus 0,4546 g thiopurine plus distilled water to 10 ml of the Prepared sample natural material processed cooked extract for 30 minutes at a temperature of 25 ° C and then defended before the formation of the organic phase (1 ml). Next was collected by pipette 1 ml of the organic phase was diluted with bidistilled water in a volumetric flask of 25 ml and analyzed for total cadmium content by two methods: inversion voltammetry at the mercury film electrode and atomic absorption spectrometry. As a comparative prototype parallel hinge solid components of the snow cover was subjected to wet Aravali.

The table presents comparative data for both methods of preparation of the same samples of snow. The table shows that regardless of the degree of particulate aerosols cadmium concentration of metal desorbed and claimed in a known manner, coincide within the statistical random error analysis. Moreover, the technology of sample preparation more attractive and technologically (pH 2-3, temperature 25 ° C, time: 30 minutes, security, aqueous-organic system with low cost of chemicals, water after extraction of cadmium can be easily cleaned up).

The prototype, which is a mixture of concentrated sulphuric, nitric and hydrochloric acids, requires extra caution and required personal protective equipment for the analyst, and a good exhaust ventilation to remove toxic gaseous emissions: sulfur dioxide and nitrogen oxides generated during the processing of solid particles of natural objects. Preparation of samples in the prototype requires additional heating to 250-300C, heat resistant tubes, provided with check-in refrigerators, time decomposition of the samples more than 5-6 times (2.5-3 hours) compared with extraction, which provides a share of the/P>

The extraction method of preparation of analytical samples of natural objects, namely, that for desorption of cadmium from the particulate nature of the material it is treated with a mixture of acids, characterized in that for metal recovery using aqueous-organic exfoliating system containing reagent thiopyran - 0,002-0,003 mol and organic - trichloroacetic - 1,2-1,6 mol and inorganic phosphoric - 0,03-0,05 mol of acid and distilled water to liters, which at room temperature of 25 ° C for 30 min, treated with natural material.

 

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1 tbl

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2 ex

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2 ex

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