RU2295121C1 - Method for fluorometric determination of copper(ii) in solutions - Google Patents

Abstract

FIELD: analytical methods.

SUBSTANCE: method comprises adding complexing reagent to test solution and registrations of changes in fluorescence intensity value. Complexing reagent utilized can be aqueous solution of β-arylaminopropionyl-N,N-di(2-carboxyethyl)-3,4-xylidine or aqueous solution of β-arylaminopropionyl-N-(2-carboxyethyl)-o-aminobemzoic acid, which is irradiated with light having wavelength range 210-220 nm to induce fluorescence. Fluorescence intensity is registered within wavelength range 350-370 nm or 400-440 nm, respectively, while maintaining pH 6.0 with the aid of acetate buffer solution.

EFFECT: selectivity and sensibility of copper(II) determination in presence of accompanying components without preliminary separation thereof.

2 dwg, 4 tbl

Description

The invention relates to the field of analytical chemistry, in particular to a fluorimetric method for determining the concentration of copper (II) ions in solutions using aromatic amino-β-propionic acids (β-AAPC) - N, N-di (2-carboxyethyl) -3,4 -xylidine (reagent I) or N- (2-carboxyethyl) -o-aminobenzoic acid (reagent II). The method is based on recording changes in the fluorescence intensity of β-AAPC solutions when adding an analyte solution containing copper (II) ions to them. The quenching of fluorescence of β-AAPK solutions during their formation of complexes with copper (II) ions is proportional to the concentration of the quencher ion.

Several methods for the fluorimetric determination of copper are known (Golovina A.P., Levshin L.V. Chemical luminescent analysis of inorganic substances - M: Chemistry, 1978 - 248 p. [1], Stolyarov KP, Grigoryev NN Introduction to luminescent analysis of inorganic substances. L .: Chemistry, 1967. 364 p. [2], Bozhevolnov EA. Luminescent analysis of inorganic substances. M: Chemistry, 1966. 416 p. [3]). A brief description of some of them is presented in table 1.

From table 1 it follows that the existing fluorimetric methods are either low-selective or require the use of organic solvents. The determination of copper (II) concentration is impeded by the presence of nickel (II), cobalt (II), iron (III) ions, etc. in the analyzed solutions, which makes it necessary to separate the accompanying components from the solution by precipitation of their water-insoluble compounds and the introduction of additional complexing reagents, or carrying out the extraction of their complexes using organic solvents. These additional procedures significantly increase the time spent on the analysis, its complexity, and the use of toxic solvents makes the measurements unsafe.

Closest to the claimed method is (prototype) - a method for fluorimetric determination of the mass concentration of copper in water samples using a solution of lumocupferon (substituted benzylidene-benzoyl-aminoacetic acid) in acetone (Methodological guidelines for measuring the mass concentration of copper by fluorimetric method in samples of drinking water and water surface and underground sources of water use // Collection of guidelines. Measurement of the mass concentration of chemicals by luminescent methods in the facility environment. M .: Russian Ministry of Health, 1997. S.67-76). The method is based on the catalytic effect of copper ions on lumokupferon, which in their presence forms a fluorescent dimer when the solution is heated for 15 minutes at pH 10. The dimer formation reaction is stopped by binding copper to a strong complex with Trilon B. The fluorescence intensity of the solution is directly proportional to the amount of copper in the solution . The method allows to determine copper in the concentration range of 0.005-0.2 mg / dm ³ without diluting the sample.

The disadvantages of this method are:

- the need to dilute the test samples if the copper concentration in them exceeds 0.5 mg / dm ³ , which introduces an additional error in the analysis results and lengthens it;

- an interfering effect on the analysis results of more than 3-fold molar excesses of iron ions, more than 7-fold molar excesses of aluminum, cobalt and nickel ions;

- the need to work with a toxic solvent.

The objective of the proposed technical solution is to develop a fluorimetric method for determining the concentration of copper (II) in solutions with higher selectivity and environmental friendliness due to the exclusion of work with organic solvents.

The technical result of the present invention is expressed in increasing selectivity, which allows the determination of copper (II) in solutions against the background of related components without prior separation. The method does not provide additional operations during sample preparation.

The solution of this problem is achieved by the fact that in the method of fluorimetric determination of the copper (II) content in solutions, which includes introducing a complexing reagent into the test solution and recording changes in the fluorescence intensity value, according to the invention, an aqueous solution of aromatic amino-β-propionic acid is used as a complexing reagent ( β-AAPC) -N, N-di (2-carboxyethyl) -3,4-xylidine (reagent I) or an aqueous solution of β-AAPC - N- (2-carboxyethyl) -o-aminobenzoic acid (reagent II), which irradiate light with a wavelength in the range of 210-220 nm, register the intensity of the resulting fluorescence at a wavelength in the range of 350-370 nm, or in the range of 350-370 nm, or in the range of 400-440 nm, respectively, while maintaining an acetate buffer pH equal to 6.0.

Reagents I and II dissolve in water when heated to 70 ° C for several minutes, are able to form complex compounds with copper (II) ions (Melkozerov V.P., Neudachina L.K., Vshivkov A.A. Spectrophotometric and potentiometric studies states of N-aryl-3-aminopropionic acids // Journal of General Chemistry. 1997. T. 67, No. 1. P.98-103; Skorik Yu.A., Neudachina L.K., Vshivkov A.A., Yatluk Yu.G., Gert N.V. N, N-di- (2-carboxyethyl) -3,4-xylidine: synthesis, protolytic equilibria, complexation with copper (II) ions // Zh. Phys. Chemistry. 1999 T.73., Issue 12. S.2269-2271). Spectrophotometric data are known (Neudachina L.K., Osintseva E.V., Skorik Yu.A., Vshivkov A.A. N-aryl-3-aminopropionic acids - selective reagents for the determination of copper in metallurgical products // J. Anal. Chemistry. 2005, T.60, No. 3. P.271-277) on the high selectivity of the complexation reaction, the formation of a complex with copper does not interfere with N-fold molar excesses: for reagent I - N = 1000 for K ⁺ , Na ⁺ , NH ₄ ⁺ , Ba ²⁺ , Cd ²⁺ , N = 750 for Co ²⁺ , N = 500 for Ni ²⁺ , Mn ²⁺ , Mg ²⁺ , N = 250 for Ca ²⁺ , N = 200 for Zn ^{2 +} ; for reagent II - N = 1000 for K ⁺ , Na ⁺ , NH ₄ ⁺ , Ba ²⁺ , N = 25 for Cd ²⁺ , N = 10 for Co ²⁺ , Ni ²⁺ , Mn ²⁺ , Mg ²⁺ , N = 50 for Zn ²⁺ , N = 20 for Ca ²⁺ . The effect of chromium (III) ions, aluminum (III), iron (III), and a number of rare-earth elements was also tested. Thousand molar excesses of chloride, acetate, sulfate and carbonate ions, 25-fold excesses of nitrate ion do not interfere with the determination of copper using reagents I and II.

The solutions of reagents I and II have the ability to fluorescence under the influence of UV radiation, the fluorescence intensity decreases as the complexation reaction proceeds.

In FIG. Figures 1 and 2 show the fluorescence registration spectra of solutions of reagents I and II at different acidities.

As can be seen from FIG. 1, two bands are observed in the fluorescence detection spectrum of reagent I solution, with peaks at registration wavelengths of 280 and 360 nm. Tests have shown that a band with a maximum of 360 nm decreases its intensity with increasing concentration of copper (II) ions in solution, while the intensity of a band with a maximum of 280 nm remains unchanged. Therefore, to develop a fluorimetric method for determining the concentration of copper (II) ions in solutions using reagent I, a wavelength of 360 nm was chosen to record the fluorescence intensity (the maximum signal sensitivity coefficient is observed at maximum).

From FIG. Figure 2 shows that the reagent II solution has one band in its fluorescence recording spectrum, the maximum of which shifts toward shorter wavelengths with increasing pH, at a pH of 6 (optimal for the complexation of reagent II and copper (II) ions), the maximum fluorescence intensity is observed at 411 nm. Therefore, in the fluorimetric method for determining the concentration of copper (II) ions in solutions using reagent II, it is this fluorescence detection wavelength that is used to achieve the maximum possible signal sensitivity.

Example 1. β-AAPC - reagents for fluorimetric determination of copper

Quenching of the fluorescence of solutions of reagents I and II is proportional to the concentration of the quencher ion, which makes it possible to determine the concentration of the quencher ion in the solution. The optimal conditions for the determination of copper (II) using reagents I and II by the fluorimetric method were established (table 2).

As can be seen from table 2, the fluorimetric method using reagent I allows the determination of copper (II) in the concentration range of 0.05-5.0 mg / dm ³ , creating a pH of 6 with an acetate buffer solution, and the determination can be made 20 minutes after adding the reagents . The method using reagent II requires maintaining the solution for 60 minutes (the optimum pH of 6 is also created by acetate buffer solution), but has a larger range of detectable copper concentrations - 0.005-5.0 mg / dm ³ , which is also wider than the range of the fluorimetric method with using lumocupferon (0.005-0.2 mg / dm ³ ).

Tests showed high selectivity of the fluorimetric method for determining the concentration of copper using β-AAPK. Fluorimetric determination of copper concentration is not impeded by N-fold molar excesses of the following ions:

Definition with reagent I:

N-2000-K ⁺ , Na ⁺ , Ca ²⁺ , Mg ²⁺ , SO 4 ^2- , Zn ²⁺ ;

N = 1000-NH ₄ ⁺ , Cl ^- , CH ₃ COO ^- , F ^- ,

N = 500-Mn ²⁺ , Ba ²⁺ ; N = 300-PO ₄ ^3- ;

N = 100-Ni ²⁺ , Co ²⁺ ;

N = 10-HCO ₃ ^- , Al ³⁺ , Cr ³⁺ ;

N = 1-Fe ²⁺ ;

N = 0.5-NO ₃ ^- , Fe ³⁺ ;

Definition with reagent II:

N = 1000-K ⁺ , Na ⁺ , NH ₄ ⁺ , SO ₄ ^2- , Cl ^- , СН ₃ СОО ^- , BO ₄ ^3- , F ^- , Zn ²⁺ ;

N = 200-Ba ²⁺ ;

N = 100-Ca ²⁺ , Mg ²⁺ ;

N = 50-Fe ²⁺ , Mn ²⁺ , F ^- ,

N = 10-HCO ₃ ^- , Cd ²⁺ ;

N = 3-Co ²⁺ ;

N = 2-Al ³⁺ , NO ₂ ^- ;

N = 0.5-Cr ³⁺ , S ^2- .

The absence of the interfering effect of a number of metal and non-metal ions under the conditions of luminescent determination of copper allows the analysis of various environmental objects, such as surface water of land, sewage, drinking water, as well as technological solutions.

Example 2. Fluorometric method for the determination of copper using reagents I and II

The method allows to determine copper in surface water, as well as drinking, waste water and technological solutions with a pH of not more than 3.0 in the range of copper concentrations from 0.005 to 5.0 mg / dm ³ without diluting the sample. Sample dilution at a copper concentration of 5.0-50.0 mg / dm ³ is allowed.

Preparation of 0.2 M acetate-ammonia buffer solution with a pH of 6.

To 52 ml of concentrated acetic acid with a concentration of 2 mol / dm ³ add 50 cm ^{3 of} aqueous ammonia of the same concentration and dilute with bidistilled water to the mark in a flask with a capacity of 1000 cm ³ , controlling the pH value using an ionomer.

Preparation of standard solutions of copper ions

A solution of copper (II) ions with a concentration of 500 mg / dm ³ (solution A) is prepared by dissolving a weighed portion of 0.1964 g of copper sulfate pentahydrate CuSO ₄ · 5H ₂ O in 100 cm ³ bidistilled water. A solution of copper (II) ions with a concentration of 50 mg / dm ³ (solution B) and 5 mg / dm (solution C) is prepared by successive dilution of 10 cm ^{3 of} solution A (or B respectively) in a volumetric flask with a capacity of 100 cm ³ to the mark with double-distilled water . Solutions A and B are suitable for 2 weeks, solution B is prepared on the day of use.

Preparation of solutions of reagent I with a concentration of 6 mmol / dm ³ , 0.6 mmol / dm ³ and 0.06 mmol / dm ³ .

A portion of 0.3180 g of reagent I is dissolved in bidistilled water when heated in a water bath and the volume is adjusted to 200 cm ³ in a volumetric flask. The solution is stored in a cool dark place for 3 weeks. Solutions with a concentration of 0.6 and 0.06 mmol / dm ³ are prepared by diluting 5 cm ^{3 of} solutions of 6 mmol / dm ³ and 0.6 mmol / dm ^3, respectively, in a volumetric flask with a capacity of 50 cm ³ . Solutions are prepared before use.

Spectrofluorimeter graduation

When the copper content in the test samples exceeds 0.5 mg / dm ³ in a number of volumetric flasks with a capacity of 50 cm ³ , solutions are prepared containing 0, 0.5, 1, 2, 3 cm ³ of a copper solution B, 5 cm ³ of a reagent solution I s a concentration of 0.6 mmol / dm ³ , 5 cm ^{3 of a} buffer solution with pH = 6 and bidistilled water to the mark.

When the copper content in the studied samples is from 0.05 to 0.5 mg / dm ^3, calibration solutions are prepared similarly, but using a standard solution of copper B and a solution of reagent I with a concentration of 0.06 mmol / dm ³ .

The fluorescence intensity of calibration solutions is measured on a Fluorat-02-Panorama spectrofluorimeter with a maximum PMT sensitivity, a fluorescence excitation wavelength of 215 nm and a fluorescence detection of 360 nm (the signal is averaged over 250 measurements). Measurements for each of the solutions are repeated 3 times, calculating the arithmetic mean, and build a graph in the coordinates of I _fluorescence = f (C _copper ).

Preparation of assay solutions

Into a flask with a capacity of 50 cm ^3, 25 cm ^{3 of a} pre-filtered assay sample containing copper, 5 cm ³ of reagent I solution, 5 cm ^{3 of a} buffer solution with pH 6, and bidistilled water are added to the mark. The concentration of the reagent solution (0.6 mmol / dm ³ or 0.06 mmol / dm ³ ) is selected based on the expected value of the concentration of copper in the analyzed sample. Measurements are carried out under the same conditions as for calibration solutions. Measurements are repeated 3 times, the arithmetic mean is calculated. The concentration of copper in the solution for measuring C _x is determined by the calibration curve. To determine the concentration of copper in the analyzed sample, the obtained value is doubled: C _pr = 2 · C _x . The determination of the concentration of copper in the analyzed solution is repeated twice, the arithmetic mean is taken as the result of the analysis.

When the copper content in the test sample in the range of 0.005-0.5 mg / dm ³ , an analysis is carried out according to a similar procedure, but using a reagent II solution with a concentration of 6 · 10 ^-6 mol / dm ³ , a standard copper solution with a concentration of 0.5 mg / dm ³ and the corresponding determination conditions (see table 2 for reagent II). In this case, a solution of 0.6 mmol / dm ^{3 of} reagent II is prepared by dissolving, while heating in a water bath, a sample of 0.0125 g in 100 cm ^{3 of} bidistilled water. An aliquot of 5 cm ^{3 is} diluted to the mark with double-distilled water in a volumetric flask with a capacity of 500 cm ³ , obtaining a solution of reagent II with a concentration of 6 · 10 ^-6 mol / dm ³ .

When the content of fluorescent organic impurities and ions in the analyzed sample is established in amounts exceeding the concentrations in which they do not interfere with the determination of copper (see above), it is possible to use a variant of the additive method (Bulatov M.I., Kalinkin I.P. Practical Guide to Photometric Methods of Analysis - 5th ed., - L .: Chemistry, 1986. - 432 pp.), In which the difference in fluorescence intensity ΔI = I of _reagent -I of the _{sample is} examined and its dependence on concentration obavki standard copper solution.

The results of the comparative determination of the copper content in the wastewater sample of a metallurgical plant containing nickel ions by the fluorimetric method using a reagent solution II and the atomic absorption method are shown in table 3.

The results of determination of copper (II) ions in an artificial mixture prepared on the basis of natural drinking water containing Ca ^{2+ ions} (30-100 mg / dm ³ ), Mg ²⁺ (<50 mg / dm ³ ), HCO ₃ ^- (150 -300 mg / dm ³ ) and other components (total mineralization 300-600 mg / dm ³ ), to which a standard solution of copper (II) ions was added so that the copper content is 1.27 mg / cm ³ , are given in table 4.

Thus, as can be seen from tables 3 and 4, the proposed fluorimetric method allows satisfactory accuracy to determine copper in complex solutions without the use of toxic organic solvents.

The effect obtained from the use of the invention lies in the ability to determine the concentration of copper (II) ions in the presence of high concentrations of other ions, including transition metal ions, and also in the ability to determine the concentration of copper (II) ions without dilution in a wide range. Compared with the spectrophotometric method for determining the concentration of copper (II) ions in solutions using the same reagents (Neudachina L.K., Osintseva E.V., Skorik Yu.A., Vshivkov A.A. N-aryl-3-aminopropionic acids - selective reagents for determining copper in the products of metallurgical production // Journal of Analytical Chemistry. 2005, T.60, No. 3. P.271-277) the described method allows you to work in a lower range of copper concentrations (linearity range of the calibration graph of 0.005 -5.0 mg / dm ³ compared to 3-25 mg / ^dm3) and is more sensitive Stew (sensitivity factor ε is equal to 2 × 10 ⁵ -3 10 ⁷ l / mole · cm compared with 1700-3300 liters / mole cm), which can be used for environmental monitoring (MAC copper in drinking water and surface water sushi is 1 mg / dm).

Table 1
Comparative characteristics of some fluorimetric methods for determining the concentration of copper (II) Reagent λ, nm The range of determined concentrations, mg / DM ³ Conditions Ions that interfere with the determination Liter. Benzoin 422 0.002-0.06 C ₂ H ₅ OH Ag ⁺ , Co ²⁺ , Ni ²⁺ 1,2 Luminol 0.02-0.2 H ₂ O ₂ , pH> 6.0 Fe ³⁺ , Co ²⁺ , Ni ²⁺ , Cr ³⁺ , F ^- , Ag ⁺ , Al ³⁺ , Mn ²⁺ , etc. 1.3 Thiamine 650 0.1-30 C ₂ H ₅ OH, NH ₂ OH, pH 7 one 1,1,3-tricyano-2-amino-1-propene 500 0.015-0.6 Imidazole pH 7.5-8.9 one Eosin, 1,10-phenanthroline 580 0.01-0.1 CHCl ₃ , (CH ₃ ) ₂ CO up to 50%, pH 9 one

Table 3
The results of the determination of copper (II) in wastewater containing 20 mg / cm ³ Nickel (II) No. p / p Reagent II fluorimetric method Atomic absorption method one 2.04 2,35 2 2,36 2,30 3 2.11 2.26 four 2,38 2.29 5 2.29 2.20 6 2.21 2.25 7 2.15 2,30 Average 2.24 2.28 SKO 0.13 0.05 The result of the analysis, P = 0.95 2.24 ± 0.12 2.28 ± 0.05 Table 4
The results of the determination of copper (II) in drinking water
according to TU 9185-004-41645795-01 (introduced copper concentration of 1.27 mg / dm ³ ) No. p / p The concentration of copper found, mg / DM ³ one 1.25 2 1.39 3 1.18 four 1,61 5 1.29 6 1.66 7 1.16 8 1.34 Average 1.36 SKO 0.19 The result of the analysis, P = 0.95 1.36 ± 0.16

Claims (1)

A method for fluorimetric determination of copper (II) content in solutions, comprising introducing a complexing reagent into the test solution and registering a change in the fluorescence intensity value, characterized in that an aqueous solution of β-AAPC - N, N-di (2-carboxyethyl) is used as a complexing reagent -3,4-xylidine or an aqueous solution of β-AAPC - N- (2-carboxyethyl) -o-aminobenzoic acid, which is irradiated with light with a wavelength of 210-220 nm, record the intensity of the resulting fluorescence at a wavelength of 350-370 nm or 400 -440 m, respectively, while maintaining the acetate buffer pH 6.0.

Images