gas phase chemical analysis process

Abstract

The present invention relates to a chemical analysis method, enabling in particular the detection and quantification of a chemical species in a liquid solution (for example aqueous). More particularly, the present invention relates to a method for analyzing a chemical species X present in two different forms. Species X may be present, in the liquid solution, in the form of a first compound A and in the form of a second compound B. The analysis method according to the present invention is, in this respect, suitable for enabling a discriminatory analysis of the first compound A and the second compound B under the action of a single reactive agent. Figure 1

Description

Title of the invention: gas phase chemical analysis method FIELD OF THE INVENTION

[0001] The invention relates to the field of chemical analyses and more particularly to gas-phase chemical analyses. In particular, the present invention relates to a method for the sequential analysis of a chemical species present in two different compounds. The invention is, in this respect, particularly suitable for the detection and measurement of nitrogen compounds likely to be present in water, and in particular wastewater. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] The field of water treatment, and in particular wastewater treatment, is a field in which chemical analysis techniques play a vital role. These techniques are, in this respect, implemented to detect, and where appropriate quantify, the presence of chemical elements or species in the solution in question.

[0003] Indeed, given increasingly strict environmental regulations or simply for reasons of toxicity of certain chemical elements, it is necessary to use analysis techniques with increased sensitivity and selectivity.

[0004] In this respect, the detection and quantification of nitrate ions and nitrite ions during water treatment is essential. Indeed, these two species, recognized for their toxicity, both for the environment and for humans, cannot be present, beyond a regulatory concentration threshold, in the treated water at the time of its discharge into nature.

[0005] The detection of these two species is today essentially implemented by liquid means and can notably involve colorimetry and / or potentiometry techniques.

[0006] However, wastewater is likely to be colored, and to have significant turbidity and salinity which can impair the performance of these techniques.

[0007] An aim of the present invention is to provide a chemical analysis method less sensitive to turbidity and the presence of interfering elements.

[0008] Another aim of the present invention is to propose a chemical analysis method having increased sensitivity compared to the methods known from the state of the art. BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method for analyzing a chemical element X present in a liquid solution S in the form of a first compound A and a second compound B different from the first compound A, the first compound A being capable of forming a compound G, in gaseous form and which comprises the chemical element X, by reaction with a reagent R, while the second compound B is only capable of forming the compound G, in gaseous form, by reaction with the reagent R when the temperature T is higher than a temperature T1, the method comprising the following steps:

[0010] a) a first conversion step which comprises adding to the liquid solution S the reagent R and maintaining said liquid solution S at a temperature lower than the temperature T1 so as to convert only the first compound A into compound G in gaseous form;

[0011] b) a first step of spectroscopic measurement of the quantity of compound G formed at the end of step a);

[0012] c) a second conversion step which comprises raising the temperature to a temperature higher than the temperature T1 so as to convert, under the effect of the reagent R, the second compound B into compound G in gaseous form;

[0013] d) a second step of spectroscopic measurement of the quantity of compound G formed at the end of step c).

[0014] According to one embodiment, the chemical element X is in a first oxidation state in the first compound A, and in a second oxidation state, different from the first oxidation state, in the second compound B.

[0015] According to one embodiment, the chemical element X comprises nitrogen.

[0016] According to one embodiment, the first compound A comprises a nitrite ion, the second compound B comprises a nitrate ion, and compound G comprises nitric oxide.

[0017] According to one embodiment, the reagent R comprises vanadium chloride and hydrochloric acid. According to one embodiment, the temperature T1 is greater than 35°C, advantageously greater than 40°C, even more advantageously greater than 90°C.

[0018] According to one embodiment, said analysis method is implemented by means of an ampoule in which the first conversion step a) and the second conversion step b) are implemented, said ampoule being in fluid communication with a circulation cell and cooperating with ultraviolet spectroscopy measuring means.

[0019] According to one embodiment, the temperature increase of step c) is implemented by means of a system allowing the heating of the liquid present in the bulb.

[0020] According to one embodiment, step a) is preceded by a sequence making it possible to measure the quantity of ammonium ions likely to be present in the liquid solution S.

[0021] According to one embodiment, the sequence comprises on the one hand a step of converting ammonium ions into ammonia in gaseous form by means of a basic species, and a step of spectroscopic measurement of the quantity of gaseous ammonia formed during the conversion step.

[0022] According to one embodiment, said method further comprises the execution of a step a1) interposed between step a) and step b) which comprises cooling of the compound G formed during step a).

[0023] According to one embodiment, said method further comprises the execution of a step cl) interposed between step c) and step d) which comprises cooling of the compound G formed during step c). Brief description of the drawings

[0024] Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figure in which:

[0025] [Fig-1] [Fig.l] is a schematic representation of an analysis device capable of implementing the analysis method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention relates to a chemical analysis method, enabling in particular the detection and quantification of a chemical species in a liquid solution (for example aqueous). More particularly, the present invention relates to a method for analyzing a chemical species X present in two different forms. Species X may be present, in the liquid solution, in the form of a first compound A and in the form of a second compound B. The analysis method according to the present invention is, in this respect, suitable for enabling a discriminatory analysis of the first compound A and the second compound B under the action of a single reactive agent.

[0027] Thus, the invention relates to a method for analyzing a chemical element X present in a liquid solution S in the form of a first compound A and a second compound B different from the first compound A, the first compound A being capable of forming a compound G, in gaseous form and which comprises the chemical element X, by reaction with a reagent R, while the second compound B is only capable of forming the compound G, in gaseous form, by reaction with the reagent R when the temperature T is higher than a temperature TL

[0028] From the above, it should be understood that the first compound A can be converted into compound G, by reaction with the reagent R, regardless of the temperature, while that the second compound B can be converted into G, by reaction with the reagent R, only when the temperature is higher than the temperature Tl. In other words, the invention forms the gaseous compound G selectively from the first compound A or from the second compound B. This selection occurs by an appropriate choice of temperature.

[0029] Thus, the method comprises the following steps:

[0030] a) a first conversion step which comprises adding to the liquid solution S the reagent R and maintaining said liquid solution S at a temperature lower than the temperature T1 so as to convert only the first compound A into compound G in gaseous form;

[0031] b) a first step of spectroscopic measurement of the quantity of compound G formed at the end of step a);

[0032] c) a second conversion step which comprises raising the temperature to a temperature higher than the temperature T1 so as to convert, under the effect of the reagent R, the second compound B into compound G in gaseous form;

[0033] d) a second step of spectroscopic measurement of the quantity of compound G formed at the end of step c).

[0034] In this regard, the present invention can in particular be implemented by means of an analysis device 10 shown in [Fig.l].

[0035] The analysis device 10 comprises at least one bulb 20 of generally elongated shape in a vertical direction.

[0036] The remainder of the statement defines terms qualified as "top", "high", or "bottom", "low". These qualifiers are defined in relation to the vertical direction. It is understood that if it were a question of defining a horizontal direction the terms "left" and "right" would have replaced the terms "top" and "bottom".

[0037] The ampoule 20 is provided on a first lower part 20a with means for injecting a liquid sample (for example a liquid sample taken from a liquid solution to be analyzed). The injection means may in particular comprise an injection inlet 21 through which the liquid sample passes for its injection into the lower part of the ampoule 20. The ampoule 20 may also comprise in its first lower part 20a a purge outlet 21b.

[0038] The bulb 20 also comprises in its first upper part 20b (opposite the lower part) an outlet 22.

[0039] The analysis device 10 further comprises a circulation cell 30 also of elongated shape in the vertical direction. The circulation cell 30 is further terminated at each of these two ends, called respectively the lower end 31a and the upper end 31b, by two windows, called respectively the lower window 32a and the upper window 32b. The upper window 32b and the lower window 32a have optical properties suitable for the implementation of a measurement by optical spectroscopy which will be mentioned in the remainder of the statement. In particular, these two windows 32a and 32b are transparent in a predetermined range of optical wavelengths. For example, when it comes to implementing the analysis device for measurements by optical spectroscopy in an ultraviolet range (hereinafter “UV”), said windows 32a and 32b considered are transparent in said UV range.

[0040] The first lower part 20a of the bulb 20 is fluidically connected, by a lower fluid channel 40a, to a second lower part 30a of the circulation cell 30, while the first upper part 20b of the bulb 20 is fluidically connected, by an upper fluid channel 40b, to a second upper part 30b of the circulation cell 30.

[0041] The lower fluid channel 40a may comprise a pump 50 configured to allow the extraction of a gas from the circulation cell 30 to the bulb 20.

[0042] The upper fluid channel 40b may comprise a three-way valve 51 allowing the passage of a gas from the outlet 22 to the second upper part 30b, or the injection of air via a channel 52 into the upper part of the circulation cell 30, for example, to purge the latter.

[0043] In addition, the analysis device 10 comprises a light source 60 as well as a spectrograph 61. In particular, the light source 60 and the spectrograph 61 are arranged to measure the absorption of the light radiation likely to be emitted by said source by a gas circulating in the circulation cell 30. In this respect, the light source 60 can be opposite the lower window 32a while the spectrograph 61 can be arranged opposite the upper window 32b.

[0044] The light source 60 may be configured to emit UV light radiation. The spectrograph 61 may comprise a slit, a diffraction grating intended to disperse light radiation in wavelength and redirect it towards a detection means, for example a CMOS bar.

[0045] The analysis device 10 may also comprise heating means 70 configured to allow a rise in temperature of a liquid present in the first lower part 20a of the bulb 20. The heating element 70 may comprise a heating lamp, or even an electrical resistor.

[0046] The method according to the present invention can be implemented by means of the analysis device 10 described above. Nevertheless, and even if only reference will be made to this analysis device in the remainder of the description, the invention should not be limited to this aspect alone.

[0047] Thus, the analysis method according to the present invention allows in particular the detection and / or quantification of a chemical element X present in at least two different compounds called, respectively, first compound A and second compound B.

[0048] By way of example, and without however limiting the invention to this single aspect, the chemical element X may be in a first oxidation state in the first compound A, and in a second oxidation state, different from the first oxidation state, in the second compound B.

[0049] Thus, the chemical element X may comprise the element nitrogen (N) while the first compound A and the second compound B may comprise, respectively, the nitrite ion (NO2) and the nitrate ion (NO3).

[0050] According to the present invention, the first compound A is capable of forming a compound G, in gaseous form and which comprises the chemical element X, by reaction with a reagent R.

[0051] Equivalently, the second compound B is capable of forming the compound G, in gaseous form, by reaction with the reagent R only when the temperature T is higher than a temperature T1.

[0052] Thus, advantageously, and since the first compound A comprises the nitrite ion and the second compound B comprises the nitrate ion, the reagent R may comprise a combination of vanadium trichloride (VC13) and hydrochloric acid (HCl). In this respect, the vanadium trichloride as well as the hydrochloric acid may be in aqueous solution in well-defined molar proportions. In particular, the molar ratio of vanadium trichloride to hydrochloric acid may be between 10% and 40%, for example be equal to 25%.

[0053] The reagent R comprising vanadium trichloride and hydrochloric acid reacts chemically with nitrite ions (NO2) to form nitrogen monoxide (NO) in particular at room temperature (the room temperature being for example between 15°C and 28°C, advantageously between 18°C and 22°C).

[0054] Equivalently, the reagent R comprising vanadium trichloride and hydrochloric acid reacts chemically with nitrate ions (NO3) to form nitrogen monoxide (NO) as soon as the temperature is higher than the predetermined temperature Tl. In the present example, the temperature Tl can be equal to 90°C.

[0055] Thus, the principles presented above are advantageously implemented for the detection and / or the dosage of the chemical element X in the first compound A on the one hand and then in the second compound B on the other hand.

[0056] In this regard, the analysis method may comprise a step of taking a liquid sample (also called “liquid solution S”) from a reservoir comprising a liquid. This tank may contain wastewater in particular, for which the nitrogen element content is to be determined.

[0057] The liquid solution can be analyzed in the analysis device of [Fig. 1].

[0058] More particularly, the liquid solution is mixed with the reagent R, and is maintained at a temperature lower than the predetermined temperature in the first lower part 20a of the ampoule 20 in order to carry out a first conversion step a).

[0059] In particular, during the first conversion step a), the first compound A reacts with the reactant R to form the compound G in gaseous form, while, to the extent that the temperature remains below the predetermined temperature T1, the second compound B remains inert.

[0060] The compound G formed during step a) is then conducted, for example by means of a draining gas, into the circulation cell and in which a first step of spectroscopic measurement b) of the quantity of compound G formed at the end of step a).

[0061] The spectroscopic measurement notably implements illumination, with the light source 60, of the compound G in gaseous form, and light detection of an absorption spectrum by means of the spectrograph 61.

[0062] Step b) is followed by a second conversion step c). The second conversion step c) comprises a temperature increase to a temperature higher than the predetermined temperature TL. This temperature increase of the liquid solution in the first lower part can in particular implement the heating means 70.

[0063] As soon as the temperature exceeds the predetermined temperature Tl, the second compound B present in the liquid solution reacts with the reagent R to form the compound G in gaseous form.

[0064] This is followed by the implementation of a step d) of spectroscopic measurement according to terms equivalent, or even identical, to step b), in order to detect the compound G formed in gaseous form during step c).

[0065] Thus, and according to a particularly advantageous embodiment, the analysis method according to the present invention makes it possible to discriminate, on the one hand, the nitrogen present in the form of nitrite, and on the other hand, the nitrogen present in the form of nitrate.

[0066] Furthermore, it is understood that steps b) and d) which make it possible to determine the quantities of nitrogen monoxide formed respectively during steps a) and c) may implement calibration curves and / or calibration processes which are known to those skilled in the art and which are therefore not described in the present description.

[0067] These determinations may involve mathematical processing such as regression or processing by Fourier analysis (for example Fast Fourier Transform calculations: FFT).

[0068] In particular, step a) makes it possible to convert a first compound A made of nitrite into nitrogen monoxide, then by carrying out step b), to detect the nitrogen monoxide formed during step a) and, where appropriate, to deduce the quantity.

[0069] Equivalently, step c) makes it possible to convert a second compound B made of nitrate into nitrogen monoxide, then by carrying out step d), to detect the nitrogen monoxide formed during step c) and, if necessary, to deduce the quantity.

[0070] Advantageously, a purge of the circulation cell can be carried out between steps b) and c) in order to eliminate any trace of nitrogen monoxide formed during step a).

[0071] Still advantageously, step a) is preceded by a sequence making it possible to measure the quantity of ammonium ions likely to be present in the liquid solution S.

[0072] In this respect, the sequence comprises on the one hand a step of converting ammonium ions into ammonia in gaseous form by means of a basic species (for example NaOH or KOH), and a step of spectroscopic measurement of the quantity of gaseous ammonia formed during the conversion step.

[0073] Thus, the method according to the present invention makes it possible to sequentially measure the quantity of nitrite ions on the one hand, and the quantity of nitrate ions on the other hand, present in a liquid solution. In particular, this measurement is carried out in the gas phase and therefore remains insensitive to problems relating to possible turbidity of the liquid solution.

[0074] The analysis method according to the present invention is advantageously implemented for the measurement of total nitrogen in a liquid solution.

[0075] Advantageously, the method further comprises the execution of a step a1) interposed between step a) and step b) which comprises cooling of the compound G formed during step a).

[0076] Still advantageously, the method further comprises the execution of a step cl) interposed between step c) and step d) which comprises cooling of the compound G formed during step c).

[0077] These two steps al) and cl) make it possible to limit condensation in the circulation cell.

[0078] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. A method for analyzing nitrogen present in a liquid solution S in the form of a first compound A which comprises a nitrite ion and a second compound B which comprises a nitrate ion, the first compound A being capable of forming nitrogen monoxide, in gaseous form, by reaction with a reagent R, while the second compound B is capable of forming nitrogen monoxide, in gaseous form, by reaction with the reagent R only when the temperature T is higher than a temperature Tl, the method comprising the following steps: a) a first conversion step which comprises adding to the liquid solution S the reagent R and maintaining said liquid solution S at a temperature lower than the temperature Tl so as to convert only the first compound A into nitrogen monoxide in gaseous form; b) a first step of spectroscopic measurement of the quantity of nitrogen monoxide formed at the end of step a);c) a second conversion step which comprises a temperature increase to a temperature above the temperature Tl so as to convert, under the effect of the reagent R, the second compound B into nitrogen monoxide in gaseous form; d) a second step of spectroscopic measurement of the quantity of nitrogen monoxide formed at the end of step c); step a) is preceded by a sequence making it possible to measure the quantity of ammonium ions likely to be present in the liquid solution S, the sequence comprises on the one hand a step of conversion of the ammonium ions into ammonia in gaseous form by means of a basic species, and a step of spectroscopic measurement of the quantity of gaseous ammonia formed during the conversion step.;

2. The analysis method of claim 1, wherein the chemical element X is in a first oxidation state in the first compound A, and in a second oxidation state, different from the first oxidation state, in the second compound B.

3. An analysis method according to claim 1 or 2, wherein the reagent R comprises vanadium chloride and hydrochloric acid.

4. Analysis method according to one of claims 1 or 3, in which the temperature T1 is greater than 35°C, advantageously greater than 40°C, even more advantageously greater than 90°C.

5. Analysis method according to one of claims 1 to 4, wherein said analysis method is implemented by means of an ampoule in which the first conversion step a) and the second conversion step c) are implemented, said ampoule being in fluid communication with a circulation cell and cooperating with ultraviolet spectroscopy measuring means.

6. Analysis method according to claim 5, wherein the temperature increase of step c) is carried out by means of a heating means cooperating with the bulb.

7. Analysis method according to one of claims 1 to 6, wherein said method further comprises carrying out a step a1) interposed between step a) and step b) which comprises cooling the compound G formed during step a).

8. Analysis method according to one of claims 1 to 7, wherein said method further comprises carrying out a step cl) interposed between step c) and step d) which comprises cooling of the compound G formed during step c).

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