Highly selective and sensitive detection of 2,4,6-trinitrotoluene by means of fluorescence enhancement using UV-induced photoreaction with anions

Abstract

A method for detecting an analyte comprising 2,4,6-trinitrotoluene in a sample comprising: providing an indicator solution, comprising a cation and an anion; bringing in contact and/or interacting the indicator solution and the sample comprising the analyte; photocatalytically induced forming of an anionic TNT sigma complex, comprising the analyte and the anion, by means of exposure of the indicator solution and the sample brought in contact with one another; fluorescence optically detecting the formed anionic TNT sigma complex.

Claims

1. A method for detecting an analyte comprising 2,4,6-trinitrotoluene, comprising: —providing an indicator solution, comprising a cation, an anion and a polar solvent; —interacting the indicator solution with the analyte; —photocatalytically induced forming of a complex, comprising the analyte and the anion, by means of UV exposure of the indicator solution interacting with the analyte; and fluorescence optically detecting the formed complex.

2. The method according to claim 1, wherein the cation is selected from: a tetraalkylammonium cation, a trialkylammonium cation, and a dialkylammonium cation.

3. The method according to claim 1, wherein the anion is selected from: an acetate anion; a propionate anion; a butyrate anion; a carboxylate anion including a number of carbon atoms from 4 to 15; a phosphate anion; a hydrogen phosphate anion; a dihydrogen phosphate anion; a benzoate anion; a phenylacetate anion; a phenolate anion; a cyanide anion; a fluoride anion; a carbonate anion; a hydrogen carbonate anion; and a formate anion.

4. The method according to claim 1, wherein the indicator solution comprises a polar, non-fluorescent solvent.

5. The method according to claim 1, wherein, wherein the tetraalkylammonium cation is selected from a tetrabutylammonium cation, a tetrahexylammonium cation and a tetraoctylammonium cation, and the anion is selected from an acetate anion, a benzoate anion or a phosphate anion.

6. The method according to claim 4, wherein the polar, non-fluorescent solvent is selected from: N,N-diethylformamide, N,N-dipropylformamide, N,N-dimethylformamide, N,N-dibutylformamide, 1-formylpyrrolidine, dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, dibutyl sulfoxide, tetrahydrothiophene 1-oxide, acetamide, N,N-dimethylacetamide, N,N′-diformyl-N,N′-dimethylethylendiamine, N,N-diethylacetamide, 1,4-piperazine dicarboxaldehyde, diformamide derivatives, 1,3,5-triazine-1,3,5(2H,4H,6H)-tricarboxaldehyde, triformamide derivatives, a polyamide, a polyvinylpyrrolidon, a polyformamide, a polyacrylamide, a poly(N,N-dimethylacrylamide) and a polyethylene glycol, or a mixture of at least two of these.

7. The method according to claim 1, wherein the photocatalytically induced formation of the complex comprises an exposure of the indicator solution interacting with the analyte in a wavelength range of 255 to 300 nm.

8. The method according to claim 1, wherein the fluorescence optical detection includes an excitation of a fluorescence of the formed complex at an excitation wavelength in a range of 400 nm to 500 nm, and a detection of a magnitude of a fluorescence in a range of 550 nm to 700 nm.

9. The method according to claim 8, wherein the magnitude of the fluorescence includes a fluorescence intensity and/or a fluorescence quantum yield.

10. The method according to claim 8, wherein the recorded magnitude of the fluorescence is assigned to a known quantity or concentration of the analyte, so that a calibration of the method takes place; the recorded magnitude of the fluorescence is attributed to a known quantity or concentration of the analyte in a solution, so that an at least semi-quantitative determination of the analyte takes place in a sample having an initially unknown concentration of the analyte, wherein the solution is obtained by an extraction of the sample or is the sample itself.

11. The method according to claim 1, wherein a concentration of the anion in the indicator solution is between 20 and 220 mM.

12. The method according to claim 1, wherein the interaction of the indicator solution with the analyte is preceded by an enrichment of the analyte from a sample on a hydrophobic carrier material.

13. The method according to claim 12, wherein the hydrophobic carrier material is selected from: a polybenzyl methacrylate, a polystyrene, a hydrophobized cellulose or a hydrophobized silica material, for example a chromatographic carrier, and Teflon or another hydrophobic material, it being immaterial whether the polybenzyl methacrylate, the polystyrene, the hydrophobized cellulose, the hydrophobized silica material or the other hydrophobic material is present in crosslinked or noncrosslinked form with or without a crosslinking agent.

14. The method according to claim 1, wherein the complex, comprising the analyte and the anion, is a fluorescent anionic TNT sigma complex.

15. Use of UV light for the catalytic formation of an anionic sigma complex, comprising TNT and an anion, selected from an acetate anion, a benzoate anion and a phosphate anion.

16. Use of an anionic sigma complex, comprising TNT and an anion, for the fluorescence optical detection or for the fluorescence optical quantification of TNT in a sample, and in particular in an environmental sample.

17. The use according to claim 16, wherein the anion is selected from: an acetate anion; a propionate anion; a butyrate anion; a carboxylate anion including a number of carbon atoms from 4 to 15; a phosphate anion; a hydrogen phosphate anion; a dihydrogen phosphate anion; a benzoate anion; a phenolate anion; a phenylacetate anion; a cyanide anion; a fluoride anion; a carbonate anion; a hydrogen carbonate anion; and a formate anion.

18. A sensor for fluorescence optical detection of TNT in a fluid, comprising a sensor layer arranged on a substrate, wherein the sensor layer comprises an indicator solution containing a cation, an anion, and at least one polar solvent, wherein the sensor layer is arranged on the substrate, and wherein a complex comprising the analyte and the anion is formed by photocatalytically induced formation, such that the fluid presumably containing TNT is able to interact with the sensor layer and a fluorescence signal resulting from this interaction is optically measurable.

19. The sensor according to claim 18, wherein the cation is selected from: tetraalkylammonium cation, a trialkylammonium cation, and a dialkylammonium cation.

20. The sensor according to claim 18, wherein the anion is selected from: an acetate anion; a propionate anion; a butyrate anion; a carboxylate anion including a number of carbon atoms from 4 to 15; a phosphate anion; a hydrogen phosphate anion; a dihydrogen phosphate anion; a benzoate anion; a phenylacetate anion; a phenolate anion; a cyanide anion; a fluoride anion; a carbonate anion; a hydrogen carbonate anion; and a formate anion.

21. The sensor according to claim 18, wherein the at least one polar solvent is selected from: N,N-diethylformamide, N,N-dipropylformamide, N,N-dimethylformamide, N,N-dibutylformamide, 1-formylpyrrolidine, dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, dibutyl sulfoxide, tetrahydrothiophene 1-oxide, acetamide, N,N-dimethylacetamide, N,N′-diformyl-N,N′-dimethylethylendiamine, N,N-diethylacetamide, 1,4-piperazine dicarboxaldehyde, diformamide derivatives, 1,3,5-triazine-1,3,5(2H,4H,6H)-tricarboxaldehyde, triformamide derivatives, a polyamide, a polyvinylpyrrolidon, a polyformamide, a polyacrylamide, a poly(N,N-dimethylacrylamide) and a polyethylene glycol, or a mixture of at least two of these.

22. The method according to claim 1, further comprising the step of assigning a fluorescence signal recorded during the fluorescence optical detection to a quantity or to a concentration of the analyte.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further description of the invention follows, with reference to the attached drawings, wherein:

(2) FIG. 1 shows standardized absorption and fluorescence spectra of TNT (in 7.3 μL chloroform, c=0.22 mM) in a TOAA/DEF solution (100 μL, c=220 mM) before (dashed) and after (solid and dotted) UV irradiation at 275 nm lasting 5 minutes;

(3) FIG. 2 shows fluorescence spectra of the reaction batches with TNT in TOAA/DEF without TNT (dotted) and with TNT after UV irradiation at 275 nm for 5 min (solid) and for another 5 min (dashed); dot-dash: 5 min irradiation at 425 nm;

(4) FIG. 3 shows the relative fluorescence intensity I/I.sub.0 plotted against the amount of TNT that, dissolved in a volume of 7.3 μL chloroform, was introduced into a TOAA/DEF solution (100 μL, c=55 mM) after 5 minutes of UV irradiation at 275 nm;

(5) FIG. 4 shows the absorption spectra of the TNA reaction batch in TOAA/DEF without irradiation (dotted), after 25 min of UV irradiation at 275 nm (solid), and of the TNB reaction batch without UV irradiation in TOAA/DEF (dashed);

DETAILED DESCRIPTION

(6) FIG. 1 shows standardized absorption and fluorescence spectra of TNT (in 7.3 μL chloroform, c=0.22 mM) in a TOAA/DEF solution (100 μL, c=220 mM) before (dashed) and after (solid and dotted) UV irradiation at 275 nm lasting 5 minutes. A denotes absorption (relative units), F denotes fluorescence (relative units), and λ denotes the respective wavelength (nm).

(7) The formation of the TNT TOAA complex caused the strongest increase in fluorescence in DEF. As a result of the irradiation of a TNT TOAA solution in anhydrous DEF with UV light (275 nm), an acceleration of the reaction was observed within 5 minutes, which resulted in a decrease in the pronounced absorption bands of the charge transfer complex and a simultaneous amplification of a new absorption peak at 426 nm and fluorescence enhancement (λ.sub.max=577 nm) (see FIG. 1).

(8) The compounds show the greatest fluorescence in the emission wavelength range described above (see FIG. 1).

(9) FIG. 2 shows fluorescence spectra of the reaction batches with TNT in TOAA/DEF without TNT (dotted) and with TNT after UV irradiation at 275 nm for 5 min (solid) and for another 5 min (dashed); dot-dash: 5 min irradiation at 425 nm. The ordinate designation F denotes the fluorescence intensity.

(10) In particular, FIG. 2 shows that the fluorescence of the TNT/TOAA reaction batch in DEF has a decreasing fluorescence intensity (dashed) with further UV irradiation (275 nm). It was possible to dramatically enhance this decrease when irradiation (5 min) was carried out at the absorption maximum (at 425 nm), which indicates that the anionic sigma complexes in the reaction batch are not photostable (dot-dash).

(11) In all other indicator solutions, the concentration is likewise 20 to 220 mM. Using an indicator solution amount of 100 μL, it is possible to use or detect 0.1 to 1000 μL TNT solutions in aprotic organic solvents and 0.1 to 20 μL TNT water samples.

(12) FIG. 3 shows the relative fluorescence intensity I/I.sub.0 plotted against the amount of TNT that, dissolved in a volume of 7.3 μL chloroform, was introduced into a TOAA/DEF solution (100 μL, c=55 mM) after 5 minutes of UV irradiation at 275 nm. From the progression of the calibration curve results the option of reliably detecting TNT up to an absolute amount of 0.2 ng for the conditions described here.

(13) FIG. 4 shows the absorption spectra of the TNA reaction batch in TOAA/DEF without irradiation (dotted), after 25 min of UV irradiation at 275 nm (solid), and of the TNB reaction batch without UV irradiation in TOAA/DEF (dashed).

(14) The gist of the invention relates to the highly selective and sensitive detection of TNT using a non-fluorescent indicator solution, which forms fluorescent anionic TNT sigma complexes in the reaction mixture in the presence of TNT after UV irradiation. Due to the high specificity of the photoreaction between TNT and the anions in the polar solution, an increase in fluorescence is only observed in the case of TNT under these measuring conditions. Thus, a differentiation of TNT from mononitroaromatics, dinitroaromatics and other trinitroaromatics is possible even in a complex mixture.

(15) Advantages of the proposed method and of the use of the described indicator solution are, in particular, high selectivity and sensitivity. Moreover, low costs are characterizing since additionally the complex synthesis of conjugated polymers, dyes, antibodies, etc. can be dispensed with. The method is easy to validate and can also be used by untrained staff for the highly selective and sensitive detection of TNT. It is suitable for the long-term monitoring of military facilities, the long-term monitoring of water lines, (offshore), and for the search for contaminations, for example based on analyses of groundwater.

(16) In summary, a method for detecting an analyte comprising 2,4,6-trinitrotoluene is proposed. TNT can be present in dissolved form in an aqueous or organic solvent. The method comprises: providing an indicator solution. The indicator solution comprises a cation, an anion and a polar solvent. The cation is selected from: a tetraalkylammonium cation; a trialkylammonium cation; and a dialkylammonium cation. The anion is selected from: an acetate anion; a propionate anion; a butyrate anion; a carboxylate anion including a number of carbon atoms from 4 to 15; a phosphate anion; a hydrogen phosphate anion; a dihydrogen phosphate anion; a benzoate anion; a phenolate anion; a phenylacetate anion; a cyanide anion; a fluoride anion; a carbonate anion; a hydrogen carbonate anion; and a formate anion. The method further comprises the interaction of the indicator solution and TNT, for example the interaction of the indicator solution and a solution containing the analyte, and the subsequent photocatalytically induced formation of an anionic sigma complex, which comprises the analyte and the anion. The fluorescent anionic sigma complex is formed by exposure of the indicator solution and analyte having started to interact (interacting) with one another. This is followed by the fluorescence optical detection of the formed anionic sigma complex. Thereafter, a fluorescence signal recorded during the detection is optionally assigned to a quantity of the analyte or to a concentration of the analyte. Preferably, the fluorescence signal is assigned to a concentration of the analyte in a solution. This solution can be a sample extract, for example, wherein the extracted sample can be a soil sample or a water sample, for example.

(17) Briefly summarized, the invention can be characterized as follows:

(18) 1. simple preparation of the TNT indicator solution

(19) 2. UV-induced photoreaction of TNT with anions

(20) 3. detection of TNT by means of fluorescence enhancement

(21) 4. highly selective detection of TNT

(22) 5. quantitative detection of TNT

(23) 6. sensitive detection of TNT

(24) 7. selective detection of TNT in a complex mixture of dinitroaromatics and trinitroaromatics

(25) 8. detection of TNT in the air, in a solution and as a swipe sample

(26) 9. option of internal referencing

(27) Even though specific embodiments have been shown and described herein, it is within the scope of the present invention to suitably modify the shown embodiments, without departing from the scope of protection of the present invention. The following claims represent a first, non-binding attempt to define the invention in general terms.