Microanalyzer for pollutants and associated process

Abstract

Title: Pollutant Microanalyzer and Associated Process The invention relates to a device for analyzing a pollutant contained in a gaseous phase, comprising: - sampling means capable of sampling said gaseous phase and generating a flow stream, - capture means capable of allowing said gaseous phase and the trapping liquid solution to flow on either side of a porous membrane, and of transferring said gaseous pollutant to the trapping solution, reaction means connected to the capture means, capable of reacting the enriched trapping solution with the pollutant, to generate a reaction product, - means for analyzing the reaction product capable of analyzing said reaction product in solution and deducing therefrom a measurement of the concentration of said pollutant in the gaseous phase.The device is characterized in that it also comprises: - a reference gas inlet connected to the capture means and capable of supplying the capture means with a flow of reference gas, and - a valve device such as a three-way valve disposed upstream of the capture means to supply the capture means alternately with said gaseous phase comprising the pollutant, or with said reference gas. Figure for the abbreviation: Fig. 1,

Description

Title of the invention: Pollutant microanalyzer and associated method technical field

[0001] The present invention relates to a microfluidic device for the dynamic analysis of a pollutant contained in a gaseous phase, and a method associated with this device.

[0002] The invention relates more specifically to the measurement of a pollutant soluble in a solvent or a mixture of solvents. A preferred application of the invention is the measurement of formaldehyde in the air. A preferred application of the invention involves the use of water as the solvent. STATE OF THE ART

[0003] French patent FR 3097967 discloses a microfluidic analysis device for the quantification of water-soluble gaseous pollutants. This small-sized device is thus a microanalyzer.

[0004] This device makes it possible to measure the concentration of a gaseous pollutant in the air - and in particular the concentration of formaldehyde.

[0005] The present invention aims to provide an improvement to existing microanalyzers.

[0006] In particular, the invention aims to provide a robust and easy-to-use device. SUMMARY

[0007] To achieve these objectives, the invention proposes, according to a first aspect, a microfluidic device for the dynamic analysis of a pollutant contained in a gaseous phase, the device comprising: • sampling means capable of sampling said gaseous phase containing the pollutant, and of generating a flow of said gaseous phase, • a gas phase supply line, connected to the sampling equipment, • capture means connected to the sampling means by said gaseous phase supply circuit, said capture means comprising: • means for admitting said flow of said gaseous phase, • means for admitting a liquid trapping solution comprising a derivative agent, said solution being capable of trapping said pollutant initially contained in the gaseous phase, said capture means being capable of allowing said gaseous phase and the liquid trapping solution to flow on either side of a porous membrane, and of transferring said gaseous pollutant to the trapping solution, • Reaction means connected to the capture means, said reaction means being capable of reacting the trapping solution enriched with the pollutant, to generate a reaction product, • Means of analyzing the reaction product capable of analyzing said reaction product in solution and deducing a concentration measurement of said pollutant in the gaseous phase, the device being characterized in that it also includes: • a reference gas outlet connected to the capture means and capable of supplying the capture means with a reference gas flow, and • a valve device such as a three-way valve disposed upstream of the capture means to supply the capture means alternately with said gaseous phase comprising the pollutant, or with said reference gas.

[0008] Preferred but not limiting aspects of this device are as follows: • The device includes means for regulating the gas phase flow rate to maintain the gas phase flow rate at a setpoint value for the gas phase, and means for regulating the reference gas flow rate to maintain the reference gas flow rate at a setpoint value for the reference gas. • The device includes synchronization means capable of synchronizing the analysis means with said valve device so that the analysis of said reaction product is carried out during time intervals corresponding to the phases of supplying the capture means with said gaseous phase comprising the pollutant, • the capture means comprise a chamber and a microporous tube passing through the chamber, the microporous tube having a tube inlet connected to the means for admitting the trapping solution and a tube outlet to allow the exit of the trapping solution enriched with the pollutant, the chamber comprising an internal space through which the microporous tube passes and the chamber comprising a chamber inlet consisting of the means for admitting the gas phase flow and a chamber outlet, • The means of reaction include means of heating, • The means for analyzing the reaction product include a fluorescence cell, a photomultiplier or a photodiode and means for processing the signal from the photomultiplier or the photodiode.

[0009] According to a second aspect, the invention also proposes a method for the dynamic analysis of a pollutant contained in a gaseous phase, with a device microfluidic analysis as mentioned above, said process comprising the steps of: • Supply the capture devices alternately with the gas phase flow and with the reference gas. • To trigger a reaction in order to cause the trapping solution, in which the pollutant initially in the gaseous phase was trapped, to react and generate a reaction product. • Analyze the product of said reaction, and deduce from this analysis a measurement of the concentration of said pollutant in the gaseous phase.

[0010] Preferred but not limiting aspects of this process are as follows: • The analysis of the product of said reaction includes the analysis of a fluorescence signal of the reaction product, • The pollutant is formaldehyde, • the reference gas is substantially free of the pollutant to be measured, • The reference gas is dry air, nitrogen, argon, helium, or any inert gas, • The analysis includes the processing of signals generated by the alternating phases of supplying the capture devices with the flow of the gaseous phase containing the pollutant, and the phases of supplying the capture devices with the reference gas, • These signals generally have the shape of Gaussian peaks, • said treatment includes determining the area of ​​said signals and determining the concentration of pollutant in the gas stream from said area. BRIEF DESCRIPTION OF THE FIGURES

[0011] The aims, objects, features and advantages of the invention will be apparent better than a detailed description of a method of implementation of the latter, which is illustrated by the following accompanying drawings in which:

[0012] [Fig. 1] Fig. 1 is a diagram of the device according to the invention, illustrating its main components,

[0013] [Fig.2] Fig.2 is a two-dimensional diagram showing a permeation modulus that can be used in the capture means of the invention,

[0014] [Fig.3] [Fig.3] is a three-dimensional view of an example module as shown in [Fig.2],

[0015] [Fig.4] Figure 4 is a graph showing the evolution of the intensity of the signal measured with a device according to the invention, for different measurement durations.

[0016] [Fig.5] Figure [Fig.5] shows a signal measured with a prior art device,

[0017] [Fig. 6] Figure 6 illustrates a configuration of the invention in which the device according to the invention comprises two means of capture.

[0018] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. DETAILED DESCRIPTION

[0019] Fig. 1 shows a microfluidic device D for analyzing a pollutant contained in a gaseous phase according to the invention.

[0020] This device provides a dynamic analysis of a pollutant contained in a gaseous phase. Indeed, this analysis can be performed at any time in real time by sampling a portion of this gaseous phase. As will be seen, the device makes it possible to characterize the concentration of the pollutant in the gaseous phase and to monitor the evolution of this quantity over time.

[0021] This device includes sampling means 10 suitable for sampling said gaseous phase comprising the pollutant, and for generating a flow of said gaseous phase.

[0022] The sampling means include for this purpose a gas phase sampling line 101 comprising a gas phase inlet 102 for admitting a gas phase. The sampling means also include a pump 103 which is mounted on the gas phase sampling line to generate a flow of this phase.

[0023] The general direction of gas phase flow is from left to right on [Fig.1].

[0024] A flow regulator 1020 is mounted in series with the pump on the line 101. The regulator 1020 shown in [Fig. 1] can be a mass flow regulator that measures the mass of the gas phase flow to ensure that the pump flow rate corresponds to a desired flow rate. This mass flow controller can be replaced by any suitable flow control means for regulating the gas phase flow rate.

[0025] The gaseous phase inlet is connected to a volume which contains a gaseous phase of which one of the components is to be characterized.

[0026] In an alternative configuration, the pump 103 and the regulator 1020 can be placed at the outlet of the gaseous phase of the capture means which will be described later in this text.

[0027] In a preferred application, the gas phase inlet is placed in a room whose indoor air is to be analyzed, or outdoors to analyze the ambient outdoor air, or even in an industrial environment. In this preferred application, We wish to characterize the concentration of a particular pollutant in this air. The gaseous phase is thus the air in the room in question or the ambient outdoor air. In other applications of the invention, the gaseous phase is not limited to air, but can be any type of gas, including gases at pressures higher or lower than atmospheric pressure.

[0028] The invention makes it possible to detect pollutant concentrations ranging from a few tens of ppt (parts per trillion in English, or parts per thousand billion in French), up to several hundred ppm (parts per million).

[0029] The pollutant may be formaldehyde. Analyzing the concentration of formaldehyde in ambient air is indeed a preferred (but not limiting) application of the invention, which will be described in more detail in this description.

[0030] The device also includes a gas phase supply line 104 which is connected to the sampling means, and collection means 20 connected to the sampling means by the gas phase supply line 104.

[0031] The capture means include means 21 for admitting the flow of said gaseous phase, to receive the gaseous phase flow from the gaseous phase supply line.

[0032] The capture means also include means 22 for admitting a liquid trapping solution comprising a derivatizing agent. The trapping solution is capable of trapping said pollutant contained in the gaseous phase. The derivatizing agent enables the reaction which will be described later in this text and which takes place in reaction means 30.

[0033] In the preferred example described here, this trapping solution is an aqueous solution of acetylacetone enabling the formation of fluoral-p, which reacts specifically with formaldehyde.

[0034] The capture means are adapted to allow the gas phase and the trapping solution to flow on either side of a porous membrane, and to transfer the pollutant contained in the gas phase—formaldehyde in the example described here—into the trapping solution and through the membrane, thus forming an enriched solution containing the pollutant. These capture means will be described later in this text.

[0035] The device also includes reaction means 30 located downstream of the capture means and connected to them by a conduit 31, to receive the solution enriched in pollutant.

[0036] The reaction means are suitable for reacting the pollutant-enriched trapping solution with the derivatizing agent to generate a reaction product. In the example described here, the reaction means include heating means 32 for this purpose. to heat the pollutant-enriched solution - for example to a temperature of 65 degrees Celsius in the preferred example.

[0037] The device also includes means 40 for analyzing the reaction product. The analysis means 40 are connected by a conduit to the outlet of the reaction means 30.

[0038] These analytical means are suitable for analyzing the reaction product and deducing a concentration measurement of the pollutant in the liquid phase and consequently in the gaseous phase. These means and the main steps of the analysis will also be described later in this text.

[0039] The device also includes a reference gas outlet (or inlet) 11. This reference outlet is connected to the collection means 20 by a reference gas line 111.

[0040] The reference gas supply is continuously supplied by a pressurized reference gas source in a preferred configuration. In an alternative configuration, ambient air drawn in by a pump, cleaned and dried, can replace this reference gas. Reference gas flow control means 1110 are provided on the reference gas line 111. These means are capable of regulating the reference gas flow rate to a desired setpoint. These control means can be of any known type.

[0041] On [Fig. 1], the reference gas line 111 joins the gas phase supply line 104 upstream of the capture means, following the direction of the gas phase flow.

[0042] In a preferred configuration, a three-way valve 1040 is disposed at the junction of the pipes 111 and 104. This valve is controlled to direct to the gas phase flow means 21 either the gas phase from the gas phase inlet 102, or the reference gas from the inlet 11. This three-way valve is an example of a valve device ensuring the circulation of fluid between a first pipe (the pipe 104 which supplies the capture means) and either of two pipes 101 and 111.

[0043] The device includes controllers, not shown in the figures, for: • Regulate the reference gas flow to a desired flow rate, via the control means 1010, • Regulate the gas phase flow rate to a specified flow rate, using the control means 1020 and the pump 103, • Regulate the flow rate of the trapping solution, • Control the operation of the 1040 three-way valve, to supply the means of capturing 20 in reference gas which is preferably dry, or in gaseous phase to be analyzed.

[0044] For this purpose the controllers are connected respectively to the control means 1010, to the control means 1020, to the valve 1040, to the pump 103, to the pump 105, and they control their operation.

[0045] It is also possible that the control means 1010, the control means 1020, the pump 105 and / or the pump 103 operate autonomously, with their own control.

[0046] In all cases, the capture means can be supplied either by the gaseous phase or by the reference gas.

[0047] Indeed, a controller controls the operation of the valve 1040 to supply the capture means selectively with reference gas, or in gaseous phase.

[0048] More specifically, the controller controls the operation of valve 1040 to supply the collection means alternately with reference gas or in gaseous phase. The alternation of supplying the collection means with reference gas and in gaseous phase constitutes a supply cycle that is controlled by the controller.

[0049] The controller is connected to the analysis means and is able to transmit to them in particular the state of the three-way valve, and in any case it is able to transmit to them the start-up times of each power supply phase of the capture means.

[0050] A feeding cycle is preferably a sequence of a reference gas feeding phase, followed by a gaseous phase feeding, followed by a second reference gas feeding phase. In one example, the total cycle time is 20 minutes, each of the two reference gas feeding phases lasts 7 minutes, and the gaseous phase feeding phase lasts 6 minutes.

[0051] The reference gas does not react with the trapping solution in the capture means, because this reference gas does not contain the gaseous pollutant that one seeks to detect in the gas phase. This reference gas contains, in fact, no or extremely little of the pollutant that one seeks to measure in the gas phase (preferably the concentration of pollutant in the reference gas is less than at least one hundredth of the concentration of pollutant in the gas phase).

[0052] The reference gas is also a gas which is preferably a dry gas - in this text a dry gas is for example a gas whose relative humidity is low, preferably less than 30%, and particularly preferably less than 5%.

[0053] In general, this reference gas can thus be pure dry air, pure nitrogen, pure argon, pure helium or any other pure and inert gas.

[0054] The pipes and means arranged upstream of the capture means may have a different configuration from that shown in [Fig. 1]. In all cases these The pipes and means, and the controller which commands their operation, are capable of supplying the capture means alternately with the gaseous phase including the pollutant, or with the reference gas only.

[0055] The analysis means receive from the controller the start-up times of each supply phase (whether in gaseous phase or reference gas), and the operation of the analysis means is continuous and this operation includes the different supply phases.

[0056] In a preferred embodiment, the trapping solution circulates continuously at a controlled flow rate through the capture means (the trapping solution being then possibly enriched with pollutant), through the reaction means (the trapping solution being then possibly enriched with reaction product), and through the analysis means.

[0057] It is specified that, as an alternative, it is possible to provide that the trapping solution does not circulate continuously and that its circulation is interrupted during controlled time intervals which allow the pollutant to be concentrated in said solution at the level of the capture means.

[0058] The reference gas, and the gaseous phase comprising the pollutant, circulate alternately in the capture means - being in contact with the surface of the microporous tube which will be described below.

[0059] Alternating the supply of the capture means with phases of supply in gaseous phase including the pollutant, and phases of supply in reference gas only, is advantageous.

[0060] This makes it possible in particular to eliminate measurement drifts during the reference gas supply phases, drifts which could exist due to the enrichment of the trapping solution (which is stored in its tank 106) by the pollutant contained in the ambient air where the device is placed.

[0061] This also prevents condensation in the device (particularly in the capture means), since the reference gas is dry. Such condensation could interfere with pollutant measurement, especially in the case of a pollutant that is highly soluble in water.

[0062] As illustrated in Figures 2 and 3, which show a non-limiting example of the implementation of the capture means, the capture means comprise a chamber 200 and a microporous tube T passing through the chamber. The microporous tube is an example of a membrane exchange module that can be implemented in the capture means.

[0063] The microporous tube has a tube inlet 220 which is connected to the means 22 for the intake of the trapping solution, and a tube outlet 221 (see [Fig. 2]). The trapping solution is directed by a pump 105 (see [Fig. 1]) to the tube microporous in which it circulates, and exits this microporous tube through outlet 221 after trapping a fraction of the pollutant that was contained in the gaseous phase and which passed through the wall of the tube to join the trapping solution.

[0064] In a preferred configuration, the gas phase flow rate is controlled so that the quantity of trapped gas molecules is maximized.

[0065] The pump 105 pumps the trapping solution contained in the reservoir 106 and regulates the flow rate of the trapping solution so that this flow rate is fixed at a desired value.

[0066] The pump 105 is visible in [Fig.1], as well as the trapping liquid reservoir 106 from which the pump 105 draws the trapping liquid to inject it into the inlet of the tube 220.

[0067] The chamber comprises an internal space 201 through which the microporous tube passes (see [Fig.2]). This chamber comprises a chamber inlet 210 which is connected to the means 21 for admitting the gas phase flow (see [Fig.1]), and a chamber outlet 211 through which the gas is discharged after having circulated in the chamber and thus having been in contact with the surface of the microporous tube.

[0068] Depending on the state of the valve 1040 (see [Fig.1]), the gas entering the chamber consists of the gaseous phase including the pollutant, or of the reference gas.

[0069] The reference gas and the gaseous phase comprising the pollutant are thus injected alternately into the chamber of the capture means, and said chamber is traversed by the microporous wall tube in which, in a preferred embodiment, the aqueous trapping solution (the acetylacetone solution in the preferred example described here) circulates continuously.

[0070] In the example illustrated in Figures 2 and 3, the gas injected into the chamber and the aqueous trapping solution flow in opposite directions. It is also possible to configure the capture means so that the gas injected into the chamber and the aqueous trapping solution flow in the same direction. In all cases, the gas flow and the aqueous trapping solution flow are separated by a porous membrane so that any pollutant contained in the gas can migrate to the trapping solution through the membrane wall.

[0071] Indeed, during the phases of feeding the capture means with the gaseous phase, when the gas entering the chamber is the gaseous phase including the pollutant, at least a part of this pollutant joins the trapping solution through the wall of the microporous tube, and a part of this pollutant is transferred into the trapping solution.

[0072] Circle C in [Fig. 2] is a partial enlarged view of a portion of the microporous wall of tube T. The partial enlarged view shown in this circle illustrates the migration of some of the pollutant molecules M through the microporous wall. P of the tube. This migration causes pollutant molecules to reach the trapping solution circulating inside the tube, enriching this solution with the pollutant.

[0073] The capture methods may differ from the example just described.

[0074] After leaving the capture means via exit 221, the trapping solution The pollutant-enriched solution is directed via conduit 31 to the reaction means 30.

[0075] These reaction means cause the enriched solution to react (under the effect of heat) to generate a reaction product. In the preferred example described here, the reaction product is 3,5-diacetyl-1,4-dihydrolutidine (which will be referred to as DDL in the remainder of this text), which is formed via a Hantzsch reaction.

[0076] Thus, in the preferred example described here in detail, the reaction means include heating means for heating the trapping solution to 65 degrees Celsius (which is an optimal temperature), and when exposed to this heating, the formaldehyde (which is the pollutant in the preferred example described here) dissolved in the trapping solution reacts with fluoral-p to form a reaction product which is DDL.

[0077] Alternatively, the reaction means include a light source capable of emitting light enabling the reaction in the trapping solution to form a reaction product.

[0078] Upon exiting the reaction means, the solution containing the reaction product is then directed to the reaction product analysis means 40.

[0079] In a preferred embodiment, these analysis means comprise a fluorescence cell 41, a photomultiplier 42, and means 43 for processing the signal from the photomultiplier. They also comprise lighting means 44 for illuminating the solution in the fluorescence cell to induce fluorescence of the reaction product. The analysis means may also include optical filters for selecting wavelengths from the lighting means and / or the fluorescence light.

[0080] The reaction product is excited under irradiation from this lighting by the lighting means 44, in the fluorescence cell. Its de-excitation induces the emission of photons by fluorescence.

[0081] The detection cell 41 is therefore the location where the fluorescence of the reaction product under the effect of this excitation light is induced and detected, and the photons emitted by the fluorescence of the reaction product are collected by the photomultiplier, which induces a quantifiable electrical signal, namely a current or a voltage. This signal is amplified and then analyzed by the processing means 43, which include, in particular, a processor.

[0082] The fluorescence observed is proportional to the concentration of the reaction product in the solution.

[0083] The photomultiplier can alternatively be a photodiode, or any type of photon detector.

[0084] The analytical means are thus able to subject the reaction product to radiation whose wavelength allows the excitation of the fluorescence of the reaction product, and to detect the fluorescence emitted in response to this excitation.

[0085] In the preferred example described here in which the reaction product is DDL, the analytical means are suitable for subjecting the DDL to radiation with a wavelength of 415 nm (nm meaning nanometer), thereby exciting the DDL and detecting the fluorescence emitted in response to this excitation in a wavelength range of 530 ± 40 nm.

[0086] When the reference gas is used to supply the capture means, the analysis means can subject the trapping solution - which has not become enriched in pollutant during its passage through the capture means while these capture means are supplied only with reference gas - to the same exposure and fluorescence detection as during the phases of supply with the gaseous phase.

[0087] Thus, alternating the supply of the capture means with a gaseous phase containing the pollutant and with a reference gas only allows the detection of a reference fluorescence signal during the phases when the reference gas is used only. This reference signal is stable and constant because the reference gas has a controlled quality to ensure consistency, specifically in that this gas does not contain the gaseous pollutant.

[0088] During the gas phase feeding of the capture means, the detected fluorescence signal increases due to the detection of the fluorescence of the reaction product.

[0089] The intensity of the fluorescence observed is indeed proportional to the concentration of the product, which is a fluorophore excited by the radiation from the lighting means 44.

[0090] Fig. 4 shows the evolution over time of the intensity of the fluorescence signals observed during the feeding phases of the capture means with the gaseous phase, and this for different measurement durations.

[0091] As shown in [Fig. 4], this increase forms, in the preferred case, a Gaussian peak for gas-phase feeding times less than 7.5 minutes. For gas-phase feeding times greater than this value, the intensity of the observed fluorescence signals stabilizes at a constant level after an initial increase.

[0092] The fact that the fluorescence measurement covers the feeding phase of the gas-phase capture means, said phase being followed and preceded by two phases respective supply of the means of capture in reference gas only, produces in effect such a peak of Gaussian shape.

[0093] Figure 4 illustrates the fluorescence signal detected in a wavelength range of 530 ± 40 nm, for a reaction product which is DDL, excited at 415 nm. In this example, the acquisition frequency of the fluorescence signal is typically 2 to 10 seconds.

[0094] Several peaks are shown in this figure, each peak corresponding to a different gas-phase supply duration. The durations of the different gas-phase supply phases are respectively: 1 minute, 2.5 minutes, 5 minutes, 7.5 minutes, 10 minutes, and 12.5 minutes. Before and after each gas-phase supply phase, a reference gas supply phase, preferably lasting 7 minutes, is provided. This reference gas supply duration can be increased.

[0095] The area under each peak was calculated by the processor and stored in a memory of the analysis means. For a fixed gas phase supply time and a constant trapping efficiency, this area is proportional to the formaldehyde concentration in the sampled gas phase.

[0096] It is observed that the peaks obtained generally have a Gaussian shape (see [Fig.4]).

[0097] Obtaining a signal in the form of a Gaussian peak whose peak area is proportional to the pollutant concentration in the aqueous phase and therefore to that of the gaseous concentration (the trapping efficiency being constant), makes the quantification of this gaseous phase concentration easy and rapid, without the need for complex reprocessing. The process according to the invention is thus fully automated.

[0098] Moreover, with such a signal shape which is Gaussian, and with gas-phase supply phase durations on the order of a few minutes, the quantification of the detected signal is of very good quality - with in particular a ratio (signal detected during the gas-phase supply phases / signal detected during the reference gas supply phases) which is particularly high.

[0099] Figure 4 shows that beyond a certain measurement duration, the fluorescence intensity no longer increases. For measurements longer than this duration, the signal takes the form of a plateau, for a stable pollutant concentration. In this respect, and in one alternative, the analysis of any signal variations on the plateau makes it possible to characterize, in real time, the variations in the pollutant concentration in the gas phase.

[0100] The time required for the signal to reach a plateau, from the beginning of a gas-phase feeding phase, corresponds to the time required to renew the volume of the fluorescence cell with the enriched trapping solution.

[0101] The sensitivity of the analysis is related to the peak height, since this sensitivity is derived from the signal height divided by the measurement noise – said noise being measured on the signals obtained during the reference gas supply phases, i.e., before or after the peak. Maximum sensitivity is therefore obtained with a signal of maximum height.

[0102] Moreover, a measurement duration greater than the shortest duration which allows obtaining a signal of maximum height, and which would therefore generate a signal plateau, would provide limited benefit.

[0103] Preferably, the device is calibrated to determine the shortest measurement time that allows the signal with a maximum peak height to be reached, and then the three-way valve 1040 ([Fig.l]) is controlled to carry out the gas phase supply phases with this measurement time.

[0104] In the example illustrated in detail in this text, pollutant detection is carried out by fluorescence. Alternatively, this pollutant detection could be carried out by any other liquid-phase detection device such as a device using colorimetry or conductimetry.

[0105] When analyzing a pollutant in the gaseous phase (for example in the air), the invention makes it possible to obtain a measurement signal (for example fluorescence) that is easily integrable.

[0106] Furthermore, and as will be detailed with reference to [Fig. 5], the drift of the fluorescence measurements observed in [Fig. 4] during the supply of reference gas (before and after the peak) is negligible during the measurement time corresponding to an integrable peak, which is on the order of a few minutes in a preferred embodiment. This distinguishes the invention from known systems in which interpolation between two measurement blanks separated by 12 or 24 hours is sometimes difficult. These known systems generally require data reprocessing by an expert and are likely to introduce uncertainties and errors in the measured concentrations.

[0107] Thanks to the alternation with a dry reference gas, the invention also makes it possible to avoid any condensation of water in the components of the device - including in the capture means - which makes the device particularly robust.

[0108] In particular, the signal analyzed by the analytical means is not influenced by any alteration in the pollutant measurement that would be caused by water condensation forming around the microporous tube due to the humidity of the gas phase. Indeed, the supply of dry air (or, more generally, a dry reference gas) allows the moisture-capturing means to be purged of any moisture they may contain, thus preventing the accumulation of condensation. This purging of the capture means It also helps to avoid undesirable memory effects between two measurements on the gas phase.

[0109] The combination of the absence of measurement drift and the absence of condensation also makes the operation of the device particularly simple, this operation being able to be carried out autonomously (i.e. with a minimum of intervention on the part of an operator).

[0110] The sensitivity (i.e., the ability to measure low concentrations of pollutants) obtained with the invention, particularly for measuring formaldehyde in air, is characterized by a detection limit on the order of 0.1 to 0.2 ppb (ppb is the acronym for "parts per billion"). This is approximately 5 to 10 times lower than the sensitivity of known methods.

[0111] This very good sensitivity is favored by the efficiency, repeatability and homogeneity of the transfer of the molecules of interest (the pollutant molecules) between the gaseous phase and the liquid phase, as well as by the alternation between the supply phases of reference gas and gaseous phase, allowing the obtaining of a signal in the form of a Gaussian peak which allows simple, precise and reproducible signal processing.

[0112] The following paragraphs give some additional details about the preferred example of implementation of the invention, for the measurement of formaldehyde in air. This example is in no way limiting.

[0113] The aqueous solution of acetylacetone (0.01M) was injected with different fixed flow rates located between 14.1 and 25.1 microlitres per minute, using a peristaltic micropump (RP-TX Series, Takasago Electric), into a hydrophobic microporous tube made of polytetrafluoroethylene (PTFE) (tube supplied by the company Chromatotec, Saint-André-de-Cubzac, France).

[0114] The microporous tube was 5 cm long and had an external diameter of 0.0669 inch (1.70 mm). The tube was mounted around and concentrically to a stainless steel tube with an external diameter of 1 mm, this stainless steel tube being connected to the fluidic circuit of the trapping solution (aqueous acetylacetone solution), the microporous tube being connected to the gas inlet by a Teflon tube having a diameter of one quarter inch.

[0115] The reference gas was dry air containing less than 5% relative humidity. The optimal flow rate of this dry air was 250 millilitres per minute.

[0116] Ambient air possibly containing formaldehyde was pumped by a Teflon diaphragm pump of type SP570.ECBLa, Schwarzer Precision, Essen, Germany, and its pumping rate was regulated between 22 and 400 milliliters per minute by a mass flow controller. Different gas-phase supply times, from 1 to 12.5 minutes, were implemented.

[0117] The invention provides access, as described in this text, to advantages of robustness and ease of use. It also provides access to concentration measurements with very good sensitivity.

[0118] The invention also makes it possible to obtain excellent performance in terms of the limit of quantification (i.e., the lowest measurable concentration with a low error, for example, an error of 5%). This limit is approximately 3 ppb (3 parts per billion, or 3.7 micrograms per cubic meter) with known systems. The limit of quantification observed in the case of the example described above is 0.4 ppb. It should be noted that this limit of quantification is related to sensitivity.

[0119] Furthermore, the robustness achieved with the invention is also evident in the significantly longer maintenance cycle (i.e., the time between two maintenance operations required, particularly on the data collection means, to ensure the proper functioning of the device). In the case of the invention, this cycle is annual, whereas it is shorter—by a few days—in the case of some known systems.

[0120] Fig. 5 shows a fluorescence signal obtained with a known device, in which alternation between supply by the gaseous phase to be analyzed and by a reference gas is not provided, unlike the case of the invention.

[0121] This figure shows two periods of "blanks" (corresponding to the first and last signal plateaus on the graph in this figure). These blanks correspond to measurements during periods when the device is not supplied with gaseous phase but with reference gas.

[0122] The signal between these two blanks corresponds to pollutant measurement phases in a gaseous phase. During these measurements, the pollutant concentration is deduced from the difference between the measured signal and the signal value when the known device is supplied with reference gas (blank).

[0123] It is therefore necessary to have an applicable "white" signal value while the device is supplied with gas. This is obtained by interpolating between the white preceding and the white following the gas supply.

[0124] However, the time and quality of processing are linked to this interpolation, which is time-consuming for the user.

[0125] Furthermore, it generally takes between one and a half and two hours to perform such a "blank". Performing a blank thus prevents the measurement of formaldehyde concentration during these periods, which is a drawback of these known devices.

[0126] Furthermore, measurement drift is possible and the measured level for several whites may be different. This is all the more true, and this drift can be all the more more importantly, the time separating two blanks is long - and in known devices this time can be on the order of 12 hours or even more.

[0127] Interpolation is therefore subject to a certain level of uncertainty. Furthermore, it is necessary to involve an expert to perform this interpolation between two blanks.

[0128] Finally, as mentioned above, during these periods of inactivity no operational measurement is possible. These periods typically involve two two-hour periods in a day, which limits the system's operational measurement capabilities.

[0129] The invention makes it possible to overcome these drawbacks. It does not require such "gaps" nor the involvement of an expert to reprocess the data - the processing being, in the case of the invention, automatable by a microcontroller.

[0130] And in the case of the invention, the measurement is continuous and it allows for example three to four measurements per hour (i.e. a time step of 15 to 20 min) and does not suffer from long periods of interruption which would be due to periods of blanks.

[0131] Fig. 6 illustrates a configuration of the invention, which can be implemented with all the variants and embodiments described above in this text, in which the device (D' on Fig. 6) comprises two capture means 2001 and 2002 arranged in parallel.

[0132] The capture means 2001 and 2002 are both connected to a gas phase outlet 102', as well as to a reference gas outlet 11'.

[0133] The gaseous phase is brought to the capture means by a pump 103', the operation of which is regulated by control means 1020'.

[0134] A three-way valve 1041 is controlled to alternately supply the collection means 2001 with reference gas, or in gaseous phase, according to predetermined supply phases and for example as described above.

[0135] A three-way valve 1042 is controlled to alternately supply the collection means 2002 with reference gas, or in gaseous phase, according to predetermined supply phases and for example as described above.

[0136] The capture means 2001 and 2002 are also connected to a reservoir 106' of trapping solution, the flow of which is regulated by a pump and a regulator 105'.

[0137] The fluidic outlets of the two capture means 2001 and 2002 join to supply reaction means 30', via a three-way valve 2010. The trapping solution flows are thus directed by fluidic outlets to the capture means 2001 and 2002 and then to the reaction means, in which the trapping solution undergoes a reaction as described above in this text, and then to the analysis means 40'.

[0138] The three-way valve 2010 is controlled to selectively direct the flow of trapping solution from the capture means 2001, the flow of trapping solution from the capture means 2002, towards the reaction means 30'.

[0139] The trapping solution, having thus undergone a reaction, is directed to analytical means 40' as described above.

[0140] Alternatively, two separate devices may be provided downstream of each of the capture means, each device receiving the trapping solution from the respective capture means 2001, 2002, and each device comprising reaction means and possibly also separate analysis means.

[0141] In this configuration, it is possible to operate the two capture means in parallel and alternately, by supplying them alternately with the gaseous phase or with the reference gas.

[0142] This mode of operation allows the number of measurements to be doubled. In this case, the valve 2010 is, for example, controlled to alternately direct the flows of trapping solution from means 2001 and 2002 respectively to the reaction means 30', then to the analysis means 40'.

[0143] In another mode of operation, it is also possible to measure the concentrations of two different pollutants contained in the gaseous phase.

[0144] In this mode of operation, the first capture means 2001 can be designed to trap a first pollutant, while the second capture means 2002 can be designed to trap a second pollutant.

[0145] In this mode of operation and to measure the concentrations of two pollutants, it is also possible to control the operation of the reaction means 30' to make the trapping solution flows from means 2001 and 2002 react differently. This can be achieved, for example, by controlling the heating temperature of the reaction means differently when these reaction means are traversed by the trapping solution flow from means 2001, and when these reaction means are traversed by the trapping solution flow from means 2002.

[0146] It is also possible, following the same principle, to provide for more than two means of capture in parallel.

[0147] The principal field of application of the invention is the analysis of gases, and in particular air. Non-limiting examples of applications of the invention include the measurement of formaldehyde in air, or in hydrogen, or in town gas. The invention can also be used to evaluate in real time the performance of an air pollution control system (or any other gas control system), by analyzing the air quality before and after pollution control with the device according to the invention.

Claims

1. Demands Microfluidic device (D) for the dynamic analysis of a pollutant contained in a gaseous phase, the device comprising: • sampling means (10) capable of sampling said gaseous phase comprising the pollutant, and of generating a flow of said gaseous phase, • a gas phase supply line (104), connected to the sampling means, • means (20) for capturing and connected to the sampling means by said gaseous phase supply circuit, said capturing means comprising: • means for admitting said gaseous phase flow, • means for admitting a liquid trapping solution comprising a derivative agent, said solution being capable of trapping said pollutant initially contained in the gaseous phase, said capture means being capable of allowing said gaseous phase and the liquid trapping solution to flow on either side of a porous membrane, and of transferring said gaseous pollutant to the trapping solution, • reaction means (30) connected to the capture means, said reaction means being capable of reacting the trapping solution enriched with the pollutant, to generate a reaction product, • means (40) for analyzing the reaction product capable of analyzing said reaction product in solution and deducing therefrom a measurement of the concentration of said pollutant in the gaseous phase, the device being characterized in that it also includes: • a reference gas outlet (11) connected to the capture means and capable of supplying the capture means with a flow of reference gas, and • a valve device such as a three-way valve (1040) disposed upstream of the capture means to supply the capture means alternately with said gaseous phase comprising the pollutant, or with said reference gas.

2. Device according to the preceding claim characterized in that the device includes means for regulating the gas phase flow rate to maintain the gas phase flow rate at a gas phase setpoint value, and means for regulating the reference gas flow rate to maintain the reference gas flow rate at a reference gas setpoint value.

3. Device according to the preceding claim characterized in that the device includes synchronization means capable of synchronizing the analysis means with said valve device so that the analysis of said reaction product is carried out during time intervals corresponding to the phases of supplying the capture means with said gaseous phase comprising the pollutant.

4. Device according to any one of the preceding claims characterized in that the capture means comprise a chamber and a microporous tube passing through the chamber, the microporous tube having a tube inlet connected to the means for admitting the trapping solution and a tube outlet to allow the exit of the trapping solution enriched with the pollutant, the chamber comprising an internal space through which the microporous tube passes and the chamber comprising a chamber inlet constituted by the means for admitting the gas phase flow and a chamber outlet.

5. Device according to any one of the preceding claims characterized in that the reaction means comprise heating means.

6. A device according to any one of the preceding claims, characterized in that the means for analyzing the reaction product comprise a fluorescence cell, a photomultiplier tube, or a photodiode and means of processing the signal from the photomultiplier or photodiode.

7. A method for the dynamic analysis of a pollutant contained in a gaseous phase, with a microfluidic analysis device according to any one of the preceding claims, said method comprising the steps of: • Supplying the capture means alternately with the flow of the gaseous phase, and with the reference gas, • Inducing the reaction to cause the trapping solution in which the pollutant initially in the gaseous phase was trapped to react, to generate a reaction product, • Analyzing the product of said reaction, and deducing from this analysis a measurement of the concentration of said pollutant in the gaseous phase.

8. A method according to the preceding claim characterized in that the analysis of the product of said reaction comprises the analysis of a fluorescence signal of the reaction product.

9. A process according to the preceding claim characterized in that the pollutant is formaldehyde.

10. A method according to one of the two preceding claims characterized in that the reference gas is substantially free of the pollutant to be measured.

11. A method according to the preceding claim characterized in that the reference gas is dry air, nitrogen, argon, helium or any inert gas.

12. A method according to one of the four preceding claims characterized in that the analysis includes the processing of the signals generated by the alternation of the feeding phases of the capture means with the flow of the gaseous phase containing the pollutant, and of the feeding phases of the capture means with the reference gas.

13. Method according to the preceding claim characterized in that said signals have the general form of Gaussian peaks.

14. A method according to one of the two preceding claims characterized in that said treatment comprises determining the area of ​​said signals and determining the concentration of pollutant in the gas stream from said area.

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