RU2484452C1 - Method for x-ray fluorescence determination of trace elements with preliminary concentration thereof from ultra-small samples of water and aqueous solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves preliminary concentration of trace elements from ultra-small samples of water and aqueous solutions. A microgranule of hydrophilic material is placed on a stretched radiotransparent hydrophobic film, a droplet of the analysed solution is collected and then deposited on said film to coat said microgranule. Said droplet is evaporated and the microgranule is then analysed by an X-ray fluorescent microanalyser with a focusing X-ray lens. Before placing the microgranule, the film is smeared with a liquid surfactant which is insoluble in water and aqueous solutions. 1-5% concentrated nitric acid or chloric acid is added to the droplet of the analysed solution or said droplet is taken from the analysed solution to which nitric acid or chloric acid has been added until achieving concentration thereof of 1-5%.

EFFECT: fewer analytical errors.

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Description

The invention relates to the field of instrumental chemical analysis, and more specifically to a method for X-ray fluorescence determination of trace elements with their preliminary concentration from ultralight samples of water and aqueous solutions.

A number of methods are known for analyzing water and aqueous solutions by X-ray spectral methods, in which, in order to eliminate interfering effects when recording the corresponding spectra, as well as to reduce the detection limits of analytes, the determined components are transferred in one way or another to the solid phase with their simultaneous concentration. For example, they use combined solution analysis schemes, including sorption concentrated microelements and their subsequent determination in the sorbent phase (Yu.A. Zolotov, G.I. Tsizin, S.G. Dmitrienko, E.I. Morosanova. Sorption concentration of microcomponents from solutions. Application in inorganic analysis, M., "Science", 2007, p.320 [1]; O. B. Mokhodoeva, G. V. Myasoedova, I. V. Kubrakova. Sorption concentration in combined methods for the determination of noble metals, J. Analytical Chemistry, 2007, Vol. 62, No. 7, pp. 679-695 [2]; R.Kh. Khamizov, A.N. Gruzdeva, M.G. Tokmache c, G.I. Tsizin, N. A. Tikhonov, M. A. Kumakhov Highly sensitive x-ray fluorescence analysis of solutions using a sorption storage microsystem, J. Analytical Chemistry, 2009, V.64, No. 9, p. 939-943 [3]; KVOskolok and OVMonogarova. X-Ray Fluorescence and Atomic Emission Determination of Cobalt in Water Using Polyurethane Foam Sorbents, Moscow University Chemistry Bulletin, 2011, Vol.66, No.3, p.179-183 [4] ) Methods of controlled evaporation of the liquid phase on special surfaces are also used (Takao Moriyama. Trace heavy element analysis for wastewater and river water by X-ray fluorescence spectrometry. Examples for ppm to sub ppm level analysis of heavy elements. // The Rigaku J., 2009 , Vol.25, No.1, p.13-14, [5]).

Among the known methods, it is worth highlighting the methods of X-ray spectral microanalysis, in which through the use of a focused electron beam in the emission X-ray spectral method or a focused primary X-ray radiation in the X-ray fluorescence method, it is possible to determine elements from the analyzed samples (targets) of a microscopic scale (S.G. Prutchenko, G. A. Grigorieva, Y. Tomashpolsky, Method for determining the content of impurity chemical elements in natural and industrial waters dah and sampler device RF Patent No. 2152614, published July 10, 2000 [6]; APMorovov, LD Danilin, VVZhmailo, VNFunin, Yu.V. Ignat'ev, NVPilipenko, MGVasin, VVNazarov, VVChulkov Thin film sorbents for TXRF analysis, Advances in X-Ray Analysis, 2000, V. 42, p. 119-125 [7]; A.A. Bolotokov, M.A. Kumakhov, A.N. Gruzdeva, R. Kh. Khamizov, E.B. Podgornaya, On the Possibility of X-Ray Fluorescence Microanalysis of Solutions with Pre-Concentration, Sorption and Chromatographic Processes, 2011, T.11, Issue 1, pp. 88-99 [8]).

In particular, in accordance with the method [6], the elements to be determined are concentrated on ion exchangers not containing these elements and masking impurities in the form of 1-5 granules with a size of 10-1000 μm by pumping the analyzed solutions through a special cassette (sampler) with the indicated granules, and then conduct an electron probe x-ray microanalysis of individual ion exchanger granules. This method is characterized by the following disadvantages: the need to use such expensive and inaccessible devices as electron probe raster microscopes with X-ray spectral analyzers: laborious sample preparation, relatively large samples of the initial analyzed solutions; analytical errors related to the difficulty of recalculating the content of elements determined in the solid phase to their content in the initial analyzed solution in the absence of quantitative extraction during sorption concentration; long times for the implementation of a full chemical-analytical cycle, including sample preparation and measurement: more than one hour.

In the method [7], the determined elements are concentrated from the analyzed solutions on sorption materials made in the form of thin films, and then their X-ray fluorescence analysis is carried out using a total external reflection X-ray analyzer (TXRF) equipped with an X-ray optical unit including monochromatic mirrors from multilayer heterostructures. The method allows to reduce the sample volume of the initial solution to one drop, however, all the remaining disadvantages of the above method [6] are inherent in the method [7].

Closest to the proposed one is a method of X-ray fluorescence determination of trace elements with their preliminary concentration from ultra-small samples of water and aqueous solutions [8]. In accordance with this method, a microgranule of hydrophilic material and a drop of the analyzed solution of a very small volume (from one to several microliters) are placed on an X-ray hydrophobic film so that it covers the specified microgranule. The droplet is evaporated naturally or with the help of special devices, for example, an infrared lamp, and the microgranule covered with the remnants of the droplet is analyzed using an X-ray fluorescence microanalyzer, the X-ray optical scheme of which is assembled on the basis of focusing X-ray lenses - Kumakhov’s lenses (MAKumakhov. Capillary optics and their use in X-ray analysis, X-ray Spectrom., 2000, V.29, p. 343-348 [9]). The method [8] is based on the effect discovered by its authors and that a drop of an aqueous solution, when it evaporates on a hydrophobic surface, “shrinks” around this microbead so that the determined components are ultimately almost completely transferred to the hydrophilic surface of this microbead. If, for example, a microbead with a diameter of 10 μm and a volume of less than 1 nl is taken, and a drop has a volume of 1 μl, the degree of concentration exceeds three orders of magnitude. Another feature that defines one of the advantages of this method is that it achieves high sensitivity by eliminating background x-ray radiation. To do this, a single microbead placed on a previously stretched, for example on the end face of a hollow cylinder, X-ray transparent hydrophobic film is subjected to irradiation with a primary X-ray beam. The method [8] is carried out using a special device — an X-ray fluorescence microanalyzer, which includes an X-ray optical unit with a sharp focus low-power X-ray tube and a multicapillary lens, a semiconductor detector with ADC and access to a personal computer, a stage, and an optical unit that provides adjustment of the target stage for positioning the target (microbeads) to the desired point for irradiation with the primary x-ray beam. The method can also be implemented on other x-ray fluorescence devices after they are additionally equipped with an x-ray optical unit with a focusing lens. The main condition is to ensure that it is easy to monitor on a computer monitor all the manipulations, including placing a microbead on a film, applying a drop of a solution to it and positioning a target, as well as tracking the drying process of a drop and the trace left by it. In addition to simplifying and reducing the cost of instrumentation and reducing the volume of the analyzed solution to one drop, the method [8] can significantly facilitate sample preparation and reduce the analysis time to 30 minutes or less.

However, this method, when used to analyze a number of solutions, has errors inherent in the quantitative transfer of the elements being determined from the initial liquid phase to (or into) the solid phase directly irradiated with an X-ray beam. Two factors lead to this:

- if the analyzed solution contains water-soluble surfactants, then analytically significant amounts of the determined elements remain in the wake of the evaporation of the droplet on the hydrophobic film;

- if the analyte solution contains sparingly soluble substances, then during evaporation they can precipitate in the form of microcrystals in the “field” of the trace of a drop before this drop completely evaporates and “pulls” all the contents around the hydrophilic microgranule. Then, these microcrystals, also possessing certain hydrophilic properties, themselves begin to serve as additional centers of concentration of the components contained in the initial drop. This leads to the loss of part of the components for their analytical determination.

Both of these factors are characteristic of natural waters; therefore, the method [8] has limitations in the analysis of natural waters.

The present invention is aimed at achieving a technical result, which consists in reducing analytical errors due to both of these factors.

The method of X-ray fluorescence determination of trace elements with their preliminary concentration from ultra-small samples of water and aqueous solutions according to the invention, as well as the closest known method [8], includes the steps of:

- placing the microbeads of hydrophilic material on a pre-stretched x-ray transparent hydrophobic film,

- taking a drop from the analyzed solution and

- applying it to the specified film so that the specified microbead is covered with the analyzed solution,

- evaporation of the specified droplet and analysis of the microbead using an x-ray fluorescence microanalyzer with a focusing x-ray lens.

To achieve the above technical result in the proposed method, in contrast to the specified closest known to it, the specified film is lubricated with a liquid surfactant insoluble in water and aqueous solutions and placed into the specified drop of the analyzed solution from 1 to 5% concentrated nitric or perchloric acid, or take this drop from the test solution into which nitric or perchloric acid is previously introduced until reaching its concentration is from 1 to 5%.

Lubrication of an X-ray transparent hydrophobic film with a liquid surfactant insoluble in water and aqueous solutions prevents the adsorption of the components of the analyzed solution, and the use of nitric or perchloric acid, which concentrates during the evaporation of the droplet, allows two results to be achieved simultaneously: to destroy the water-soluble surfactants contained in the initial the analyzed solution, and not to allow micro- and nanocrystals of sparingly soluble impurities to settle on the film surface.

These acids do not contain elements that interfere with determination. In this case, the use of nitric acid is preferable, since it contains only light elements that are not determined by the method of energy dispersive x-ray fluorescence analysis.

As the X-ray transparent hydrophobic film, any films for X-ray fluorescence analysis can be used, for example, from the following materials: lavsan (Mylar), fluoroplast (Teflon), polycarbonate.

As insoluble surfactants, it is preferable to use any of the homologous series of fatty organic acids from pentanoic (valerianic) acid to nonanoic (pelargonic) acid). These acids are completely insoluble in water, which is a necessary condition for their use in the proposed method.

The invention is illustrated by examples 1-4 and figures 1-8, which show:

- figure 1 is a photograph of an X-ray fluorescence spectrometer MX-10 used in the examples described below;

- figure 2 is a diagram of a fluorescence spectrum from a microgranule of a hydrophilic material using an MX-10 device;

- figure 3 is a photograph of a microgranule of a hydrophilic material with a drop of the analyzed solution applied to it;

- figure 4, relating to example 1, the trace after evaporation of a drop of the analyzed solution deposited on a granule of hydrophilic material;

- figure 5 is a fluorescence spectrum of a microbead of hydrophilic material in the case illustrated by figure 4;

- in Fig.6, relating to example 2, the trace after evaporation of a drop of the analyzed solution, in which nitric acid was previously introduced;

- in Fig. 7, relating to example 3, the trace after evaporation of a drop of the analyzed solution upon preliminary lubrication of the place under the drop with an insoluble in water and aqueous solutions liquid surfactant and the addition of nitric acid to the analyzed solution from which the drop was taken;

- in Fig. 8, relating to examples 3 and 4, the fluorescence spectrum in the case illustrated in Fig. 7, and a case different from it in that nitric acid is applied directly to a drop of the analyzed solution.

To obtain the fluorescence spectrum in examples 1-4, we used the MX-10 X-ray fluorescence spectrometer manufactured by Institute of Physical Optics LLC (Moscow, www.xrayoptic.ru) with a focal spot 26 microns in size. The photograph of figure 1 shows the x-ray tube 1 included in this device, an x-ray lens (Kumakhov lens) 2, a semiconductor detector 3 of x-ray fluorescence radiation, a digital microscope 4 and a stage 10.

This device implements the method of energy dispersive x-ray fluorescence analysis.

The main technical characteristics of the MX-10 device are presented in the table:

X-ray source X-ray tube with copper anode Tube voltage, kV Up to 35 Tube current, μA Up to 200 Tube power, W Up to 5 Cooling Aerial Locality, microns 10-30 Analysis time, sec From 10 Optical zoom 90 × Weight, kg 3 Sizes, mm 200 × 200 × 400 Analyzed Elements From Al to U Detection limit of elements (depending on the element),% 0.003 ÷ 100 Interfaces USB Control Software

In all the examples described below, the scheme for obtaining the fluorescence spectrum from the microgranule of a hydrophilic material shown in FIG. 2 was used.

This figure shows the sample holder 5, the X-ray transparent hydrophobic film 7 stretched on the holder 5, placed on the film 7 of a microgranule 8 of a hydrophilic material with a drop of the analyzed solution applied to it, and also the X-ray lens 2 (Kumakhov lens) included in the MX-10 device focusing radiation on the microsphere 8 and the detector 3 of x-ray fluorescence radiation.

We used a holder of 5 samples made of fluoroplastic in the form of a hollow cylinder 5.1 with a height of 20 mm and a diameter of 30 mm and a shorter cylinder 5.2 put on it. Both cylinders have identical coaxial holes 6.1, 6.2 with a diameter of 10 mm at the end. Between these cylinders during assembly, as shown in FIG. 2, an X-ray hydrophobic film 7 of a thickness of 6 μm made of Mylar was pulled. The holder 5 was placed on a stage 10 (figure 1).

A microgranule 8 of a hydrophilic material, the Sac8 sorbent used as the sorbent, was placed on the film portion 7 above the opening 6.1.

The following operational parameters of the MX-10 device were used: tube voltage - 30 kV, tube current - 100 μA, analysis time - 300 sec.

Example 1 (by the closest known method [8] for comparison with him proposed)

A. Microgranule 8 of the indicated sorbent was fixed in the focus of a digital microscope 4, following all the manipulations on a computer screen.

B. Using an analytical microsyringe, a microbead was coated with 8 drops of an analyzed model solution of 1 μl tap water containing the same amounts of microcomponents (0.2 mg / l each): iron, manganese, cobalt and nickel, when they were present together. In figure 3, the drop 9 applied to the microgranule 8 is shown with a 90-fold increase.

C. The droplet was evaporated naturally for 20 minutes.

D. Microgranule 8 was analyzed using an MX-10 X-ray fluorescence microanalyzer while focusing on it the radiation of X-ray tube 1 using lens 2.

After evaporation on the film 7 under the conditions of example 1, there remained a trace of 11 drops surrounding microgranule 8 (see micrograph in figure 4). It can be seen that this trace is “smeared” over the entire initial area of the drop, and it does not “contract” around the microgranule 8.

Figure 5 presents the fluorescence spectrum of microgranules 8 obtained by performing paragraph D of example 1. It practically does not have peaks corresponding to trace elements introduced into the model solution.

Example 2

The process was carried out according to paragraphs A, B, C, D of example 1, except that before the implementation of paragraph B, a test solution of 1 ml was taken and 0.1 ml of nitric acid qualification of special grade compounds with a concentration of 30% was added to it, after mixing, a drop was taken using a microsyringe and covered microbead 8.

Figure 6 shows the result of evaporation of a droplet with a volume of 1 μl after performing step B under the conditions of Example 2 (trace 12 drops after its evaporation).

It is seen that the addition of nitric acid made it possible to reduce the trace from the evaporation of water in comparison with figure 4, but, as in the previous case, the trace was smeared randomly.

The spectrum obtained when performing point D is practically the same as in Fig. 5, i.e. as in the conditions of example 1 for the closest known method [8].

Example 3

The process was carried out as described in example 2 (i.e., according to points A, B, C, D of example 1, taking into account the above differences from example 2), however, before the implementation of point A, film 7 was lubricated with liquid insoluble in water and aqueous solutions surfactant, which was used pelargonic acid.

Fig. 7 shows the result after performing step B under the conditions of example 3 (trace 13 drops after its evaporation), and Fig. 8 shows the fluorescence spectrum obtained by performing step D. Peaks of trace elements contained in the model solution are clearly visible.

Example 4

The process was carried out as described in example 3, with the difference that after the implementation of paragraph B, nitric acid with a concentration of 30% was not added to the test solution from which a drop was taken, but it was added in an amount of 0.1 μl directly to the drop.

The result after performing step B under the conditions of example 4 and the fluorescence spectrum obtained by performing step G almost coincide with those shown in Figs. 7 and 8 for example 3. Peaks of trace elements contained in the model solution are clearly visible on the resulting spectrum.

It should be noted that the use in experiments of a specific instance of the MX-10 device, which has an x-ray tube with a copper anode, did not allow the analysis of a model solution with the introduction of heavier elements into it. It is quite obvious that in the presence of a tube, for example, with a molybdenum anode, such elements, for example, Cu and Zn, would also be successfully determined.

A comparison of the data obtained in the described examples shows that the joint use of the features of the proposed method, namely, the lubrication of the place of “drop-off” of a drop of pelargonic acid and the addition of nitric acid to the analyzed solution, ensure the achievement of the technical result mentioned above before describing the essence of the invention. A drop of the analyzed solution, evaporating, is pulled together to a point around the microgranule 8, due to which the X-ray fluorescence spectrum has clearly visible peaks of the elements being determined. High sensitivity is achieved in the analysis of natural waters and industrial solutions, including industrial wastewater, for environmental, technological or other purposes, combined with the simplicity and expressness of the method.

Information sources

1. Yu.A. Zolotov, G.I. Tsizin, S.G. Dmitrienko, E.I. Morosanova. Sorption concentration of microcomponents from solutions. Application in inorganic analysis, M., "Science", 2007, p.320.

2. O.B. Mokhodoeva, G.V. Myasoedova, I.V. Kubrakova. Sorption concentration in combined methods for the determination of noble metals, J. analyt. Chemistry, 2007, Vol. 62, No. 7, pp. 679-695.

3. R.Kh. Khamizov, A. N. Gruzdeva, M. G. Tokmachev, G. I. Tsizin, N. A. Tikhonov, M. A. Kumakhov. Highly sensitive x-ray fluorescence analysis of solutions using a sorption storage microsystem, J. analyt. Chemistry, 2009, Vol. 64, No. 9, pp. 939-943.

4. K.V. Oskolok and O.V. Monogarova. X-Ray Fluorescence and Atomic Emission Determination of Cobalt in Water Using Polyurethane Foam Sorbents, Moscow University Chemistry Bulletin, 2011, Vol.66, No. 3, p. 179-183.

5. Takao Moriyama. Trace heavy element analysis for wastewater and river water by X-ray fluorescence spectrometry. Examples for ppm to sub ppm level analysis of heavy elements. // The Rigaku J., 2009, Vol.25, No. 1, p.l3-14.

6. S.G. Prutchenko, G.A. Grigorieva, Yu.Ya. Tomashpolsky. A method for determining the content of impurity chemical elements in natural and industrial waters and a sampler device. RF patent No. 2152614, publ. 07/10/2000.

7. A.P. Morovov, L.D. Danilin, V.V. Zhmailo, V.N. Funin, Yu.V. Ignat'ev, N.V. Pilipenko, M.G. Vasin, V.V. Nazarov, V.V. Chulkov. Thin film sorbents for TXRF analysis, Advances in X-Ray Analysis, 2000, V. 42, p. 119-125.

8. A.A. Bolotokov, M.A. Kumakhov, A.N. Gruzdeva, R.Kh. Khamizov, E.B. Podgornaya. On the possibility of X-ray fluorescence microanalysis of solutions with preliminary concentration. Sorption and chromatographic processes, 2011, T.11, Issue 1, pp. 88-99.

9. M.A. Kumakhov. Capillary optics and their use in X-ray analysis, X-ray Spectrom., 2000, V.29, p. 343-348.

Claims (3)

1. The method of x-ray fluorescence determination of trace elements with their preliminary concentration from ultra-small samples of water and aqueous solutions, comprising placing a microbead of hydrophilic material on a pre-stretched X-ray transparent hydrophobic film, taking a drop from the analyzed solution and applying it to the specified film coated with the specified microbead, evaporating the specified drop and analysis of the specified microbeads using x-ray fluorescence microanalyzer with a focusing x-ray lens, excellent which means that the said film is coated with hydrophilic material insoluble in water and aqueous solutions, and the surface-active substance is insoluble in water and aqueous solutions, and 1 to 5% concentrated nitric or perchloric acid is introduced into the drop of the analyzed solution, or this drop is taken from the analyzed solution , in which nitric or perchloric acid is previously introduced until its concentration reaches from 1 to 5%. 2. The method according to claim 1, characterized in that as a radiolucent hydrophobic film using a film from the group of materials: Mylar, fluoroplastic, polyethylene, polycarbonate. 3. The method according to claim 1 or 2, characterized in that as an insoluble in water and aqueous solutions of a liquid surfactant using any of the homologous series of fatty organic acids from pentanoic acid to nonanoic acid.

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