Gas analysis device

Abstract

The invention relates to a gas analysis device, comprising: • - a gas-tight enclosure (300), under vacuum or containing an inert atmosphere; • - at least one detector (100, 101, 102) such as an NGD (nano-gravimetric detector) or a TCD (thermal conductivity detector), also referred to as a katharometer, arranged in the enclosure (300); • - a fluidic circuit (110a, 110b, 111a, 111b, 112a, 112b) configured to circulate a gas to be analysed through the detector; • - a cooling interface (200) in thermal contact with the detector (100, 101, 102), the interface being thermally coupled to a cooling device (201) so as to cool the detector by thermal conduction.

Description

[0001] GAS ANALYSIS DEVICE

[0002] TECHNICAL FIELD

[0003] The present invention relates to a gas analysis device.

[0004] STATE OF THE ART

[0005] Gas analysis devices comprise a fluid circuit adapted to circulate a sample of a gas through a detector.

[0006] Among the detectors, NGD type detectors (acronym for the English term "Nano Gravimetric Detector") are particularly advantageous because they allow the design of compact and easily transportable analysis devices. These detectors use nano-electromechanical systems, known by the acronym NEMS (for "Nano ElectroMechanical System"). NGD detectors can optionally be combined with TCD detectors (acronym for the English term "Thermal Conductivity Detector", also called a catharometer).

[0007] Detection of trace species in a gas mixture is difficult to implement in known gas analysis devices.

[0008] Under normal operating conditions, NGD detectors can detect heavy molecules, with a molecular weight greater than or equal to that of hexane (C6), at concentrations down to an order of magnitude lower than ppm (parts per million).

[0009] NGD detectors, on the other hand, are less efficient at detecting light molecules, particularly hydrocarbons with a molecular weight less than or equal to that of pentane (C5), such as methane, CO2, H2S or hydrogen. TCD detectors can detect such molecules with a concentration down to approximately 1 ppm.

[0010] However, certain applications, particularly those linked to biomethane and hydrogen, require the ability to detect light molecules down to the ppb (parts per billion) scale.

[0011] A first issue is the sensitivity of the detector with respect to the species to be detected, that is to say the concentration from which the detector is able to detect said species. Each type of detector has an intrinsic sensitivity with respect to a given species. To improve the sensitivity of a detector, it is known to carry out a preconcentration step of the sample, in order to increase the concentration of the species in the sample. However, such a preconcentration step is complex and it is therefore desirable to do without it.

[0012] A second issue is the specificity of the detector, that is to say its capacity to provide a response specific to the target species compared to other species contained in the gas mixture.

[0013] Since the sensitivity of NGD and TCD detectors increases inversely with temperature, it may be possible to consider cooling them in order to increase their sensitivity.

[0014] However, such cooling is likely to disrupt the operation of the analysis device. Indeed, species contained in the gas to be analyzed, particularly water, are likely to condense under the effect of this cooling. Such condensation can, on the one hand, disrupt detection and, on the other hand, cause short circuits in the detector's electrical circuit.

[0015] SUMMARY OF THE INVENTION

[0016] An aim of the invention is therefore to design a gas device which makes it possible to detect one or more species in the form of traces in a gas.

[0017] To this end, the invention proposes a gas analysis device, comprising:

[0018] - a gas-tight enclosure, under vacuum or containing an inert atmosphere,

[0019] - at least one NGD or TCD type detector arranged in the enclosure,

[0020] - a fluid circuit configured to circulate a gas to be analyzed through the detector,

[0021] - a cooling interface in thermal contact with the detector, said interface being thermally coupled to a cooling device so as to cool the detector by thermal conduction.

[0022] Thanks to this device, the temperature of the detector can be controlled to optimize its sensitivity to the species to be detected, over a wide range of temperatures.

[0023] Placing the detector in a vacuum enclosure or one with an inert atmosphere prevents condensation of water or, where applicable, other species contained in the gas. The operation of the detector is therefore not affected by low temperatures.

[0024] According to other advantageous characteristics of the invention, considered alone or in combination:

[0025] - the enclosure is provided with bulkheads ensuring a sealed passage of the fluid circuit through the wall of the enclosure;

[0026] - the wall of the enclosure is provided with at least one waterproof electrical connector ensuring an electrical connection with the detector;

[0027] - the enclosure is under vacuum and the fluid circuit includes a vent opening into the enclosure downstream of the detector;

[0028] - the device further comprises a vacuum pump fluidly connected to the enclosure and / or to an outlet of the fluid circuit;

[0029] - the fluid circuit includes a source of pressurized gas upstream of the detector;

[0030] - the device further comprises a heating element configured to heat the detector;

[0031] - the cooling device is selectively movable relative to the cooling interface between:

[0032] (i) an active position in which the cooling device is thermally connected to the cooling interface, and

[0033] (ii) a neutral position in which the cooling device is thermally decoupled from the cooling interface;

[0034] - the device comprises an NGD detector and a TCD detector arranged in the enclosure in the same fluid circuit; - the device comprises two NGD detectors arranged in the enclosure in two separate fluid circuits;

[0035] - the cooling device comprises a Stirling engine or a Joule-Thomson engine, and a cold finger thermally connecting said engine to the cooling interface;

[0036] - the motor is arranged outside the enclosure, the cold finger passing through the wall of the enclosure, the wall of the enclosure being provided with a seal around the cold finger;

[0037] - the cooling device comprises a Peltier element;

[0038] - the device further comprises a chromatography column arranged in the fluid circuit upstream of the detector;

[0039] - the chromatography column is in thermal contact with the cooling interface;

[0040] - the fluid circuit includes an impurity trap arranged in the enclosure in thermal contact with the cooling interface upstream of the detector.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the annotated drawings, in which:

[0043] - Figure 1 is a schematic diagram of an NGD detector;

[0044] - Figure 2 shows different values ​​of the detection limit of the NGD detector as a function of temperature for different species;

[0045] - figure 3 illustrates a first embodiment of the gas analysis device;

[0046] - figure 4 illustrates a second embodiment of the gas analysis device;

[0047] - Figure 5 illustrates a third embodiment of the gas analysis device.

[0048] For reasons of readability of the figures, the elements of the device are not necessarily represented to scale.

[0049] DETAILED DESCRIPTION OF EMBODIMENTS

[0050] The gas analysis device comprises an acquisition chain comprising at least one NGD or TCD type detector, a fluid circuit adapted to circulate a gas to be analyzed in said detector, and a cooling device configured to cool the detector to a temperature below ambient temperature. In the present text, ambient temperature is defined as being of the order of 25°C and atmospheric pressure is defined as being of the order of 10 5 Pa.

[0051] In the following text, unless otherwise indicated, the term "detector" refers indifferently to an NGD detector or a TCD detector. An advantage of NGD and TCD detectors is that they allow non-destructive measurement, which allows them to be arranged in series in the same fluid circuit. The gas analysis device can thus include both an NGD detector and a TCD detector.

[0052] Acquisition chain

[0053] The acquisition chain comprises at least one NGD and / or TCD type detector, a power supply for activating the detector and a processor electrically connected to the detector to receive the output signal from the detector and implement processing of said signal to measure a variation in behavior linked to an interaction of the detector with one or more species contained in the gas mixture.

[0054] NGD Detector

[0055] In a manner known per se, the NGD detector comprises at least one NEMS resonator.

[0056] The resonator is in the form of a beam, at least one main surface of which is covered with a functional layer that has a chemical affinity with the species of interest. Depending on the intended applications, the functional layer can be polar or apolar.

[0057] Optionally, the detector may comprise several resonators, comprising the same functional layer or a different functional layer, chosen according to the species of interest.

[0058] The beam is suspended relative to a substrate at one of its ends (the other end of the beam being free), or at both of its ends.

[0059] For purely indicative purposes, the dimensions of the beam of such a resonator are of the order of a few micrometers in length, a few hundred nanometers in width, and a hundred nanometers in thickness. Thus, according to an embodiment given as an example, the beam has a length of 1 to 100 pm, a width of 50 to 500 nm or even a few pm and a thickness of 50 to 500 nm.

[0060] The resonator is controlled by an electronic reading device configured to drive the beam into vibration at its resonant frequency and to measure a variation in said resonant frequency under the effect of the adsorption or desorption of a species by the functional layer.

[0061] When a species of interest is adsorbed on the functional layer (or desorbed), the effective mass of the beam is modified, which causes a variation in the resonant frequency of the resonator. Thus, measuring the variation in the resonant frequency by the reading system makes it possible to measure the variations in the mass of the resonator and to deduce the concentration of the species in the gas mixture.

[0062] The manufacture of a NEMS resonator is known in itself and therefore does not need to be described in detail in this text. Reference may in particular be made to documents [Mile2010], EP 2 008 965, WO 2012 / 034990 and WO 2012 / 034951, which describe NEMS resonators capable of being implemented in a detector according to the invention.

[0063] It will be noted that, instead of a single NEMS resonator, the detector may comprise one or more NEMS resonator arrays. Reference may be made to WO 2014 / 053575 for the description of an NEMS resonator array that can be implemented in a detector according to the present invention. In the case where several NEMS resonator arrays are used within the detector, it is possible to functionalize these arrays with a functional layer that differs from one array to another.

[0064] Although the term “NEMS resonator” is used in the following text in the singular, it is understood that the description also applies to a plurality of NEMS resonators, whether or not arranged in an array. Figure 1 is a scanning electron microscope view of a NEMS resonator capable of being implemented in an NGD 100 detector.

[0065] Said resonator is advantageously formed on a semiconductor substrate 1, for example silicon. The substrate 1 is advantageously covered with an electrically insulating layer (for example, silicon oxide) and a silicon layer, to form a silicon-on-insulator (SOI) type substrate.

[0066] The resonator comprises a beam 2.

[0067] The beam 2 is suspended relative to the support substrate 1, being embedded at its ends 2a, 2b in a part of the substrate projecting relative to the plane of the substrate which extends under the beam.

[0068] In a manner known per se, such a beam can be formed in the silicon layer, by means of etching to delimit the beam and eliminate the part of the electrically insulating layer located under the beam, in order to release it.

[0069] On either side of the beam extend two strain gauges 3, for example piezoresistive, which are also suspended relative to the substrate 1.

[0070] Advantageously, said gauges are, like the beam, etched in the SOI substrate and have at least one plane in common with the beam. These gauges are advantageously made of doped semiconductor material, preferably having a dopant concentration greater than 10 19 atoms / cm3 . Preferably, said doped semiconductor material is doped silicon.

[0071] The intersection between each of the gauges and the beam is at a determined distance from the beam embedment region, chosen to maximize the stress exerted on the gauge during beam deflection.

[0072] Each of the gauges 3 is connected to an electrode 30, said electrodes allowing the application respectively of constant potentials of opposite signs.

[0073] In other embodiments of the resonator, it is possible to use only a strain gauge made of doped semiconductor material.

[0074] The resonator further comprises a device for electrostatic actuation of the beam which, as shown here, may comprise two electrodes 4 extending in the same plane as the beam and arranged on either side of the latter, at a determined distance.

[0075] The electrodes 4 are intended to receive respectively an electrical excitation signal and a signal of opposite sign, and therefore constitute two inputs of the resonator.

[0076] Under the application of an electrical signal having a frequency corresponding to the no-load resonant frequency of the beam, the beam is driven into vibration in a plane parallel to the substrate. By no-load resonant frequency of the beam is meant the resonant frequency of the beam in the absence of the gas mixture to be analyzed.

[0077] According to one embodiment, the measurement of the variation in electrical resistance of the piezoresistive gauges is carried out between the embedded end of the beam and the junction between the beam and the gauges. The output signal of the resonator is thus supplied to a connection electrode 5 located at each embedded end of the beam, for the purpose of reading said signal.

[0078] This measurement method is not, however, exclusive and the output signal can be provided by other means; for example, it is possible to apply a polarization voltage to the electrode and measure the voltage across the two gauges to deduce the variation in their electrical resistance.

[0079] The person skilled in the art will therefore be able to adjust the design of the polarization of the strain gauge(s) and the measurement of their response without departing from the scope of the present invention. Furthermore, another actuation mode may be used without departing from the scope of the invention.

[0080] Particularly advantageously, the NEMS resonator can be formed on a chip a few millimeters on each side, said chip being able to be embedded on a printed circuit as will be described in detail below.

[0081] The resonator is arranged in the fluid circuit so as to be exposed to the gas to be analyzed.

[0082] The adsorption of one or more molecules of a given species has the effect of increasing the mass of the resonator and consequently of decreasing its resonance frequency, which is measured by strain gauges.

[0083] The sensitivity of such a detector is all the greater as the number of carbon atoms in the species to be analyzed is large.

[0084] The sensitivity of the detector is also greater the lower the temperature to which it is exposed.

[0085] The response of the NGD detector to a given species can be modeled by the formula: where A p is the area of ​​the peak of the species considered, C mj M wis the mass concentration of the species in the sample, a is a constant related to the geometry of the NGD detector and the sample flow rate, AH° is the standard adsorption enthalpy for a given solute, AS 0 is the standard entropy of adsorption for a given solute, T is the temperature and R is the universal ideal gas constant.

[0086] Figure 2 illustrates the detection limit LD (expressed in mol) of the NGD detector in Figure 1 for different molecules with 3 to 6 carbon atoms, including linear alkanes (n-C4, n-C5, n-C6) and branched alkanes (i-C4, i-C5), as a function of temperature T (°C), extrapolated from measurements carried out at a temperature of 50°C. The dotted line indicates the detection limit of a TCD detector.

[0087] It is observed that the detection limit of the NGD detector decreases with temperature for all species, which shows the interest of strongly cooling the NGD detector to improve its sensitivity to light species.

[0088] This allows detection of certain species down to a concentration of the order of ppb.

[0089] TCD Detector In a manner known per se, a TCD detector comprises an electrically conductive wire traversed by an electric current which heats it by the Joule effect. The TCD detector which is placed in the fluid circuit to expose the heated wire to the flow of gas to be analyzed.

[0090] The sensitivity of the TCD detector is also temperature dependent. Cooling the detector increases the thermal gradient between the thermal mass of the detector and the conductive wire heated by the electric current. This increases the variation in the electrical conductivity of the wire depending on the species present in the gas flow to which the wire is exposed.

[0091] Pregnant

[0092] The enclosure represents a hermetically sealed, gas-tight volume, of dimensions suitable for containing the detector(s) to be cooled.

[0093] Due to the compactness of the NGD and TCD detectors, the enclosure can have reduced dimensions, for example a volume of the order of a few cm 3 or tens of cm 3 , which allows it to be integrated into a portable measuring device.

[0094] The enclosure includes through passages for the fluid circuit and for the electrical connections of the acquisition chain, these passages being made gas-tight by suitable sealing devices.

[0095] For this purpose, the wall of the enclosure is provided with bulkheads allowing the gas supply pipe to pass to the detector and, where applicable, the gas outlet pipe from the detector.

[0096] Furthermore, the wall of the enclosure is provided with waterproof electrical connectors enabling an electrical connection to be ensured between the part of the electrical circuit arranged inside the enclosure and the part of the electrical circuit arranged outside the enclosure.

[0097] In some embodiments, the enclosure may be evacuated, down to a pressure of the order of 1.10' 4Pa to 0.01 Pa. The vacuum can be applied permanently, with the detector enclosed in the enclosure during manufacture and sealed to maintain the vacuum. Alternatively, the vacuum can be applied temporarily, while the analysis device is in use. In this case, the enclosure is fluidically connected to a vacuum pump that is operated during the analysis phases.

[0098] In other embodiments, the enclosure contains an inert atmosphere, for example, argon or nitrogen.

[0099] The use of a vacuum or an inert atmosphere makes it possible in particular to avoid trapping water molecules or other species likely to condense during the cooling of the detector.

[0100] Fluidic circuit

[0101] The fluid circuit is arranged so as to pass the gas to be analyzed through the detector. To do this, a pressure difference must be ensured between the inlet and outlet of the detector, the pressure upstream of the detector having to be higher than the pressure downstream of the detector.

[0102] Such a pressure difference can be achieved by various means. When the enclosure is under vacuum, the detector outlet can open directly into the enclosure through a vent.

[0103] When the enclosure is not under vacuum, the detector outlet can be fluidically connected to a vacuum pump to suck out the gas.

[0104] Alternatively or additionally, the gas to be analyzed may be a pressurized gas or be carried by a pressurized carrier gas.

[0105] Whether or not a carrier gas is used depends on the gas mixture to be analyzed.

[0106] In some embodiments, the carrier gas may be an inert gas, such as argon, nitrogen, or helium.

[0107] In other embodiments, the carrier gas may be ambient air, present outside the enclosure.

[0108] Preferably, the carrier gas is pure. This avoids disturbing the measurement with the adsorption of impurities on the cooled NGD detector, which generates background noise in the detector response signal.

[0109] However, as discussed below, even if the carrier gas (especially when it is ambient air) contains water or impurities, it is possible to filter or trap these impurities before they enter the detector.

[0110] Cooling chain

[0111] The cooling chain includes a cooling device capable of reaching temperatures low enough for optimal detector sensitivity, an interface in contact with the detector to cool it by thermal conduction, and a thermal connection between the cooling device and the cooling interface.

[0112] The cooling interface is, for example, in the form of a tray on which the detector is placed. The cooling interface can form part of the enclosure wall or be entirely included in the enclosure.

[0113] The cooling device is designed to bring the detector to a temperature of up to -100°C or less, preferably -150°C or less, and more preferably -200°C or less.

[0114] Various cooling devices, which are known in themselves, can be used. The choice of cooling device can be made according to the temperature to be reached and / or the space available to install said cooling device.

[0115] According to a first embodiment, the cooling device comprises one or more Peltier elements in thermal connection with the cooling interface. For example, if the interface is in the form of a thermally conductive plate, the Peltier element(s) may be arranged so that their cold face is in contact with the face of the plate opposite the detector, or with a lateral face. According to a second embodiment, the cooling device comprises a Stirling-type engine. The thermal connection between the engine and the cooling interface is then ensured by a cold finger.

[0116] According to a third embodiment, the cooling device comprises a Joule-Thomson type motor. The thermal connection between the motor and the cooling interface is then ensured by a cold finger.

[0117] For example, if the interface is in the form of a thermally conductive plate, the cold finger may be in contact with the face of the plate opposite the detector, or a side face.

[0118] In some embodiments, the thermal bond may be permanent.

[0119] In other embodiments, the thermal connection may be selectively interrupted. To this end, the analysis device comprises a mechanism for decoupling the cooling interface from the cooling device. For example, such a mechanism may comprise an actuator for moving the Stirling or Joule-Thomson engine and / or the cold finger relative to the cooling interface, so as to create a free space between the cold finger and the cooling interface. The cooling device then comprises an active position in which the cooling interface is in thermal connection with the cooling device, and a neutral position in which the cooling device is thermally decoupled from the cooling interface.

[0120] To minimize the volume of the enclosure, the cooling device is advantageously located outside the enclosure. In particular, in the case where the cooling device comprises a Stirling or Joule-Thomson engine, the engine is arranged outside the enclosure and the cold finger passes through the wall of the enclosure. The sealing of the enclosure is ensured by a seal arranged around the cold finger at the level of its passage through the wall.

[0121] Heating element

[0122] Particularly advantageously, the analysis device further comprises a heating element adapted to heat the detector. The heating element can be arranged in the enclosure, as close as possible to the detector.

[0123] Such heating can be useful, for example, for cleaning the detector after an analysis, the heating making it possible to desorb the species adsorbed on the detector in order to evacuate them from the fluid circuit by sweeping a flow of inert gas.

[0124] Furthermore, the heating element provides greater versatility to the analysis device by allowing measurements to be carried out at temperatures above room temperature. The analysis device therefore has a wide temperature range, making it suitable for detecting a large number of different species and / or species with different concentrations.

[0125] When such a heating element is present, the thermal connection between the cooling device and the cooling interface is advantageously reversible. Indeed, the cooling device is likely to be damaged by heat and it is therefore preferable to keep it away from the heating element during operation of the latter.

[0126] Differential detection

[0127] Besides the effective mass of the resonator, the resonant frequency of the NEMS resonator also depends on the detector temperature, the carrier gas flow rate, and other exogenous factors.

[0128] As a result, the baseline of the measurement signal varies with temperature. There is therefore an overlap between the signal useful for the measurement (i.e. variations in the resonant frequency of the NEMS resonator linked to adsorption / desorption of the gas) and a background signal (temperature variation of the NEMS resonator, and other exogenous factors varying the resonant frequency of the resonator) which is not useful.

[0129] Advantageously, a so-called differential reading of the NEMS resonator is therefore implemented, which makes it possible to reduce these variations independent of the mass variation created by adsorption of a species of interest and to highlight only the variations in the resonance frequency of the NEMS resonator by adsorption / desorption of the gas.

[0130] For this purpose, two NGD detectors (or, if a TCD detector is associated with the NGD detector, two pairs each formed by an NGD detector and a TCD detector) can be placed in the enclosure, in order to simultaneously measure, during the same analysis phase, the variation in resonance frequency of two differential resonators. Thus, one NGD detector is arranged on an analysis channel and therefore measures the additive combination of the different species peaks and any other exogenous phenomenon. The other NGD detector is arranged on a reference channel in which the gas to be analyzed does not circulate and therefore only measures exogenous phenomena. The reference detector can be at the pressure of the enclosure or at atmospheric pressure (i.e. the pressure outside the enclosure), via capillaries opening outside the enclosure.Thanks to electronics differentiating the measurement signals from the two detectors, only the signals from the adsorption / desorption of the different gas peaks are retained.

[0131] Optimization of detector specificity

[0132] In the case of simple gas mixtures, the detector may have sufficient specificity with respect to the species to be detected so as not to require separation before introduction into the detector. In this case, it is therefore not necessary to include a preliminary step of separation of the constituents of the mixture.

[0133] In other situations, particularly in the case of complex mixtures, it may be advantageous to separate the species contained in the gas mixture to increase the specificity of the detector. A particularly effective separation is chromatographic separation. For this purpose, at least one chromatographic column is placed in the fluid circuit upstream of the detector.

[0134] Chromatography column The chromatography column can be any commercially available column suitable for the constituents of interest in the mixture.

[0135] The column may be made on a substrate, for example silicon, into which a path for the gas to be analyzed is etched. This type of column allows miniaturization and a particularly compact arrangement. Alternatively, the column may be a capillary chromatography column, for example a fused silica capillary column having a functional coating (usually called 'stationary phase') on its inner surface. The column may be wound on itself, for example in the form of a coil, to provide suitable compactness.

[0136] The chromatography column can be arranged in the same enclosure as the detector. In particular, the column can be arranged in thermal contact with the cooling interface. Indeed, cooling promotes the adsorption of species in the column and thus allows for better separation.

[0137] The chromatography column can also be arranged outside the enclosure. In this case, the chromatography column can be brought to a suitable temperature by an independent heating or cooling device.

[0138] Dirt trap

[0139] When the gas circulating in the fluid circuit contains water, which is likely to condense due to the low temperatures to which the detector is exposed, or impurities likely to be adsorbed by the detector and affect the accuracy of the measurements, it is advantageous to trap the water and / or these impurities upstream of the detector.

[0140] For this purpose, the fluid circuit may include a trap configured to retain, in particular by adsorption or condensation, impurities or undesirable species.

[0141] The trap advantageously has as large an exchange surface as possible exposed to the gas mixture circulating in the fluid circuit. To optimize the compactness of the trap while providing a sufficiently large exchange surface, the trap can be in the form of a channel arranged in a serpentine pattern.

[0142] Particularly advantageously, the trap is arranged in contact with the cooling interface. Thus, the trap promotes the condensation of impurities on the exchange surface.

[0143] This makes it possible to use a carrier gas with low purity, such as ambient air. In particular, the trap makes it possible to eliminate the humidity generally present in ambient air and which can significantly impact gas analyses.

[0144] In the case where the species to be detected are in low concentration in the gas to be analyzed, the trap advantageously makes it possible to reduce the concentration of impurities to a level at least one order of magnitude lower than the concentration of the species to be detected.

[0145] Such a trap can be replaced by or combined with a suitable filter to retain impurities upstream of the detector.

[0146] Conclusion - Features of the gas analysis device As explained above, the cooling device is used at least to cool the detector, which helps to increase its sensitivity.

[0147] However, it can advantageously perform additional functions in the gas analysis device. These functions are optional and can be implemented separately or in combination depending on the elements present in the gas device, in particular with a view to increasing the specificity of the detector:

[0148] - cooling of the chromatography column;

[0149] - formation of the cold trap to trap water or impurities by adsorption upstream of the detector.

[0150] Since cooling the detector can cause non-reversible adsorption of certain species which can thus accumulate in the detector, the cooling device is advantageously combined with the heating element which promotes the desorption of the species. The desorbed species can be evacuated from the fluid circuit by circulating a carrier gas, preferably pure, in the fluid circuit, between successive analyses.

[0151] Heating therefore allows the analysis device to be periodically reconditioned.

[0152] In some applications, the device according to the invention can be used autonomously. In other applications, the device according to the invention can be coupled or integrated with another gas analysis device, for example comprising a chromatography column, an NGD detector and / or a TCD detector. For this purpose, a fluid connection must be provided, for example in the form of capillaries, to connect the inlet of the detector of the device according to the invention to the outlet of the chromatography column.

[0153] Having several NGD and / or TCD detectors, of which at least a first NGD detector is cooled by the cooling interface in the enclosure according to the invention, and at least a second NGD detector or a TCD detector is outside the enclosure and thermally decoupled from the first NGD detector, makes it possible to exploit the performance of these sensors for a wide variety of species, by optimizing the sensitivity of each detector as a function of the temperature for each species to be detected.

[0154] Naturally, the different embodiments and examples described in this text can be combined according to the specificities of the analysis to be carried out.

[0155] Examples

[0156] Figure 3 illustrates a first embodiment of the gas analysis device configured to allow differential analysis.

[0157] Two NGD detectors 101, 102 are arranged on a printed circuit 103. Each detector is fluidically connected to an inlet capillary 111a, 112a and an outlet capillary 111b, 112b in order to circulate the gas to be analyzed through one of the detectors and an inert gas through the other detector. The printed circuit 103 is placed in contact with a plate 200 forming the cooling interface. The plate is thermally connected to a Stirling engine 201 via a cold finger 202.

[0158] The tray supporting the detectors is arranged in a gas-tight enclosure 300. During an analysis, the enclosure is evacuated by a vacuum pump P with which it is fluidically connected.

[0159] The inlet capillaries 111a, 112a of the detectors are in fluid connection with a source of pressurized gas (not shown) arranged outside the enclosure 300, and the outlet capillaries 111b, 112b open outside the enclosure 300. The capillaries 111a, 112a, 111b, 112b pass through the wall of the enclosure by means of bulkheads 113 mounted in a sealed manner in a respective opening of the enclosure.

[0160] The electrical power supply for the detectors and the processing system (not shown) are arranged outside the enclosure 300. The electrical connection between the detectors and the elements of the acquisition chain outside the enclosure is provided by an electrical connector 400 arranged in a sealed manner in an opening of the enclosure and connected to the detectors 101, 102 by an electrical connection 401.

[0161] The Stirling engine 201 is arranged outside the enclosure 300. The enclosure is provided with an orifice for the passage of the cold finger 202. A seal 203 is arranged between the cold finger and the wall of the enclosure to ensure the gas-tightness of the enclosure.

[0162] Figure 4 illustrates a second embodiment of the gas analysis device configured to allow differential analysis.

[0163] Compared to the device in Figure 3, the detector outlet capillaries open directly into the enclosure. Thus, the gas to be analyzed and the neutral gas are sucked from the inlet of the fluid circuit by the vacuum pump. It is therefore not necessary to use a source of pressurized gas to circulate the gases through the detectors.

[0164] This principle also simplifies the assembly of the device since it is not necessary to provide bulkheads for the passage of the outlet capillaries.

[0165] The other elements of the device are identical to those of the device of Figure 3 and are therefore not described again.

[0166] Figure 5 illustrates a third embodiment of the gas analysis device.

[0167] The NGD detector 100 is formed in a silicon substrate 1. The substrate is in integral contact with a heat-conducting plate 200 forming the cooling interface. Said plate further forms a part of the enclosure 300 in which the detector is arranged.

[0168] The NEMS resonator 2 intended to be brought into contact with the gas to be analyzed is arranged on a first side of the substrate 1. The resonator is located in a first volume 302 delimited by the substrate 1 and a glass cover 301. The glass cover 301 is sealed to the silicon substrate 1, for example by an adhesive seal. The cover is gas-tight and forms a good thermal insulator in order to thermally insulate the interior volume. The first volume comprises a gas inlet 110a and a gas outlet 110b and thus forms part of the fluid circuit 110. The gas inlet 110a and outlet 110b can be fluidically connected to capillaries (not shown) for conveying and discharging the gas to be analyzed.

[0169] The substrate 1 further comprises electrical connections 402 for electrically powering the detector 100. The electrical connections 402 are connected by cables 401 to sealed electrical connectors 400 arranged in the wall of the enclosure 300.

[0170] A second volume 303, fluidically isolated from the first volume 302, surrounds the electrical connections 402, the cables 401 and the inner face of the electrical connectors 400. The second volume 303 is evacuated during the manufacture of the device and then hermetically sealed. Alternatively, the second volume is filled with an inert gas during the manufacture of the device and hermetically sealed. The arrangement of the electrical elements 400, 401, 402 under vacuum or under an inert atmosphere makes it possible to avoid condensation of moisture on these elements during the cooling of the detector 100 and the plate 200. This makes it possible to avoid electrical short circuits.

[0171] Naturally, the examples presented above are provided for illustrative purposes only and are not limiting.

[0172] REFERENCES

[0173] [Mile2010] E. Mile, G. Jourdan, I. Bargatin, S. Labarthe, C. Marcoux, P. Andreucci, S. Hentz, C. Kharrat, E. Colinet, L. Duraffourg, In-plane nanoelectromechanical resonators based on silicon nanowire piezoresistive detection, Nanotechnology 21, (2010) 165504

[0174] EP 2 008 965

[0175] WO 2012 / 034990

[0176] WO 2012 / 034951

[0177] WO 2014 / 053575

Claims

CLAIMS 1. Gas analysis device, comprising: - a gas-tight enclosure (300), under vacuum or containing an inert atmosphere, - at least one nanometric gravimetry detector (NGD) (100, 101, 102) and / or a thermal conductivity detector (TCD) arranged in the enclosure (300), - a fluid circuit (110a, 110b, 111a, 111b, 112a, 112b) configured to circulate a gas to be analyzed through the detector, - a cooling interface (200) in thermal contact with the detector (100, 101, 102), said interface being thermally coupled to a cooling device (201) so as to cool the detector by thermal conduction.

2. Device according to claim 1, in which the enclosure is under vacuum and the fluid circuit comprises a vent opening into the enclosure downstream of the detector.

3. Device according to one of claims 1 or 2, further comprising a vacuum pump fluidly connected to the enclosure and / or to an outlet of the fluid circuit.

4. Device according to one of claims 1 to 3, in which the fluid circuit comprises a source of pressurized gas upstream of the detector.

5. Device according to one of claims 1 to 4, further comprising a heating element configured to heat the detector.

6. Device according to one of claims 1 to 5, wherein the cooling device is selectively movable relative to the cooling interface between: an active position in which the cooling device is in thermal connection with the cooling interface, and a neutral position in which the cooling device is thermally decoupled from the cooling interface.

7. Device according to one of claims 1 to 6, comprising an NGD detector and a TCD detector arranged in the enclosure in the same fluid circuit.

8. Device according to one of claims 1 to 7, comprising two NGD detectors arranged in the enclosure in two separate fluid circuits.

9. Device according to one of claims 1 to 8, wherein the cooling device comprises a Stirling engine or a Joule-Thomson engine (201), and a cold finger (202) thermally connecting said engine to the cooling interface (200).

10. Device according to one of claims 1 to 9, wherein the cooling device comprises a Peltier element.

11. Device according to one of claims 1 to 10, further comprising a chromatography column arranged in the fluid circuit upstream of the detector.

12. Device according to claim 11, wherein the chromatography column is in thermal contact with the cooling interface.

13. Device according to one of claims 1 to 12, in which the fluid circuit comprises an impurity trap arranged in the enclosure in contact with the cooling interface upstream of the detector.

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