WO2020250086A1 - Système d'analyse chimique au moyen d'une séparation par chromatographie en phase gazeuse et d'une spectroscopie photoacoustique de mélanges d'échantillons - Google Patents

Système d'analyse chimique au moyen d'une séparation par chromatographie en phase gazeuse et d'une spectroscopie photoacoustique de mélanges d'échantillons Download PDF

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Publication number
WO2020250086A1
WO2020250086A1 PCT/IB2020/055226 IB2020055226W WO2020250086A1 WO 2020250086 A1 WO2020250086 A1 WO 2020250086A1 IB 2020055226 W IB2020055226 W IB 2020055226W WO 2020250086 A1 WO2020250086 A1 WO 2020250086A1
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Prior art keywords
valves
concentrator
gas
photoacoustic
separation column
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PCT/IB2020/055226
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English (en)
Inventor
Stefano ZAMPOLLI
Ivan ELMI
Fulvio MANCARELLA
Sandro Mengali
Nicola Liberatore
Roberto Viola
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Consiglio Nazionale Delle Ricerche
Consorzio C.R.E.O.
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Priority to EP20735453.1A priority Critical patent/EP3980768A1/fr
Publication of WO2020250086A1 publication Critical patent/WO2020250086A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/62—Detectors specially adapted therefor
    • G01N30/76—Acoustical detectors

Definitions

  • the present invention relates to the field of miniaturized systems for pre-concentration and chemical analysis by means of (gas) chromatographic separation and spectrometry of sample mixtures.
  • infrared absorption spectroscopy allows to identify not only known illicit substances, but also similar substances, having the same functional groups, but specially modified so as not to be recognizable (“designer drugs") .
  • designer drugs designer drugs
  • no portable GC-IRAS instruments are available, since conventional IRAS analyzers (both of the dispersive and of the Fourier transform type) operate with analysis cells of significant volume, which may not be coupled with miniaturized GC columns.
  • existing GC systems also have limits, which often affect the final measurement of the spectrometers.
  • pre-concentration systems of the "purge&trap" type are known, used to increase the concentration of a sample before injecting it into a gas-chromatographic (GC) columns for separating and detecting the analytes contained therein.
  • GC gas-chromatographic
  • These as well are implemented almost exclusively in laboratory measurement systems, and generally consist of tubes (made of metal or glass) filled with specific absorbent materials which, at room temperature or cooled down, retain the molecules of interest (analytes) from the flow of sample.
  • This sampling and pre-concentration step may even be long (tens of minutes), so as to absorb a large quantity of sample.
  • the tube is generally heated (and therefore, the contained absorbent material) , releasing the trapped molecules (thermal desorption) inside a flow of carrier gas. An attempt is made to perform this release in the shortest possible time, so that the molecules absorbed are released inside a possibly reduced volume of carrier gas, thus increasing the concentration of the sample.
  • a pre-concentrator samples 10 liters of air within a few minutes, and then releases the absorbed material inside a volume of only 100 milliliters.
  • the concentration factor is ideally lOOx.
  • MEMS (on-chip) injection systems for gas-chromatography exist, also referred to for micro-gas-chromatography (pGC) , which are based on pressure-actuated membrane valves made of polymeric materials (generally Kapton) (for example, MEMS injectors [2]) .
  • pGC micro-gas-chromatography
  • mini-GC miniaturized/portable "mini-GC” system [3], based on the pre-concentration in a MEMS (therefore not in a glass or metal tube) , on the injection into a MEMS GC column, and on a detector (which may be of different types) .
  • This system allows to perform the GC analysis of some low concentration samples by means of the pre-concentration step.
  • the pre-concentrator allows, for example, to analyze benzene up to concentrations of ppb fractions
  • the MEMS pre-concentrator may be heated very quickly, with ramps up to > 50°C/s, thus allowing a rapid pre-concentrated injection without the need for cryogenic traps, i.e., devices adapted to focus on the sample at the head of the GC column by means of rapid thermal cycles: capture of the sample at cryogenic temperature (generally with the aid of liquid nitrogen or expansion of compressed gas) and subsequent injection into the column by means of rapid heating.
  • cryogenic traps i.e., devices adapted to focus on the sample at the head of the GC column by means of rapid thermal cycles: capture of the sample at cryogenic temperature (generally with the aid of liquid nitrogen or expansion of compressed gas) and subsequent injection into the column by means of rapid heating.
  • the mini-GC system which was developed as a device highly specific for the application in the analysis of benzene in air, has, although, the main disadvantage that the injection circuit is implemented using commercial miniature solenoid valves, characterized in that they have :
  • Patent application WO2017180933A1 uses a pre concentrator and a separation column, but it is not easily miniaturizable and the injection is carried out with conventional valves, therefore it is not possible to heat them up to measure low volatile compounds, and, additionally, the dead volumes of the valves used thereby are too high.
  • Patent application US 4028932 A [7] describes an improved photoacoustic cell to be used in the analysis of solid and quasi-solid samples.
  • the cell includes a sample containment chamber having a wall made of a clear transparent material.
  • the sample containment chamber is connected to a microphone by means of a thin tube which makes the cell, which includes the chamber tube and the microphone, an acoustic resonant structure with a frequency within the response features of the microphone.
  • the cell is mounted with respect to a support structure so that different portions of the sample may be related, so that the cell may be advantageously used to analyze plates, paper or the like, originating from chromatographic techniques.
  • the gas in US 4028932 A is however used as a transducer means of an acoustic signal generated by the sample which is stationary. Therefore, there is no movement of analyte packets as there are in gas-chromatography, and therefore the issues of the latter technique, which instead requires temporal and spatial separation between packets and sufficient concentration thereof, are not there .
  • Figure 1 shows a diagrammatic representation of the combined (gas-) chromatographic and photoacoustic system according to an embodiment of the present invention
  • Figure 2 shows a side section of the QEPAS photoacoustic cell according to an embodiment of the present invention
  • Figure 3 shows a vertical front section of the same cell in Figure 1;
  • Figure 4 shows a horizontal section of the same cell in Figures 2 and 3;
  • Figure 5 shows a side section diagram of an embodiment of the GC device in accordance with the invention.
  • Figure 6 shows a simplified side section diagram, with indication of the flows, of the device in Figure 1;
  • Figure 7 shows a more detailed three-dimensional view of the device in Figures 5 and 6;
  • Figure 8 shows a detailed functional diagram of the device according to Figure 7, in a first pre concentration operating state;
  • Figure 9 shows a detailed functional diagram of the device according to Figure 7, in a second GC analysis operating state
  • Figure 10 shows the flow directions in an open (b) and closed (a) microvalve in an embodiment of the device according to the invention
  • Figure 11 shows in (a) a chromatogram of the integral absorbance of the simulant of the nerve agent dimethyl-methylphosphonate and of the simulant of the blistering agent methyl salicylate in ethanol (a) and the IR spectra of the two eluted compounds in 80s (b) and 120s (c) , in an experiment with an embodiment of the system in Figure 1; and
  • Figure 12 shows the IR spectra measured by an embodiment of the GC-QEPAS system in Figure 1: 10 ppm of 2-methoxyethanol (EGME) sampled for 60s (a) and 2 ppm of dipropylene glycol methyl ether (DPGME) sampled for 120s (b) .
  • EGME 2-methoxyethanol
  • DPGME dipropylene glycol methyl ether
  • the present embodiment relates to a (portable) chemical analysis system capable of identifying illicit or toxic trace substances (sub-ppm concentrations) by virtue of the two-dimensional selectivity obtained from a specific combination between the Gas-Chromatographic (GC) separation technique and the photoacoustic (PA) infrared (IR) analysis technique, in particular, but not exclusively, in the implementation thereof referred to as Quartz Enhanced Photo Acoustic Spectroscopy (QEPAS) .
  • GC Gas-Chromatographic
  • PA photoacoustic
  • IR infrared
  • the photoacoustic PA infrared technique generates very similar spectra (in shape and contained structural information) to the IRAS spectra, exploiting the pressure wave generated by a gaseous sample which, by absorbing the IR radiation, warms up and then expands generating an acoustic signal, which is then acquired by a special transducer, such as, for example, a microphone or a piezoelectric tuning fork.
  • the photoacoustic technique may be implemented with solutions which allow to analyze gaseous samples of infinitesimal volume.
  • the GC module is preferably implemented as a MEMS device of the FAST type, capable of separating, with reduced thermal budgets and very short elution times (a few minutes), even complex and low-volatile samples.
  • the GC module may be any, and therefore not necessarily having the features of the embodiment described below.
  • the GC module 100' may comprise a valve (for example, a 6-way or 10-way one) 104, to which a pump for the sample 101, the carrier gas tank 103, a MEMS pre-concentrator 160 (constructed, for example, as in the embodiment of the GC illustrated below) and the actual GC column 150 are connected. From this GC column the gas packets pass to the QEPAS module 200, which comprises a piezoelectric fork (also referred to as a "tuning fork”) 230 with a quartz resonator and an infrared source 260.
  • a piezoelectric fork also referred to as a "tuning fork”
  • the fork 230 allows a particularly effective coupling with the GC, both by virtue of the extremely small query volume thereof (approx. 1 microliter) which allows to solve the equally small peaks eluted by the GC, and by virtue of the fork, being much more rigid than a membrane, not being affected by the disturbance due to the passage of the analyte packet in the flow or the variations in the flow (within certain determinable limits, for example, up to a few tens of seem) .
  • a pre-concentrator 300 in a stage preceding the GC module may also be present.
  • Such pre-concentrator uses a sample inlet 310, and a reversible pump 330 to pre-concentrate the sample itself in 320 and supply it to the GC stage 100' .
  • the QEPAS module 200 comprises, according to an aspect of the invention:
  • an inner volume 210 of the cell 200 (e.g., the entire inner volume of the cell) ;
  • micro-resonator 220 (or, in general, resonator means) ;
  • piezoelectric fork 230 (or, in general, transducer means) which transduces the photoacoustic signal
  • a photoacoustic cell 200 of the prior art with a GC column (also known per se) 100', the Inventors were able to observe an excessive dilution of the sample packets.
  • known photoacoustic cells have an inner volume (in which to convey the sample packet to be analyzed) which ranges from 100 to 1000 times the volume of a conventional sample packet ranging from 10 to 100 microliters.
  • the packets exiting the GC column (eluted) vary by less than one order of magnitude, and therefore the packet would, in any case, be strongly diluted and mixed with the following packets eluted from the column, which would cancel any measurement of the peaks, as shown below in concrete cases .
  • the Inventors were instead capable of determining that, if the cell volume reaches 10 times the volume of a packet, then this does not happen, and the peaks may still be measured and therefore the appropriate analyzes may be provided. Even better is the situation in which the cell volume reaches up to 5 times the packet volume, with a preference for the sub-range which reaches up to 2 times, with which it is actually possible to process, with high sensitivity and excellent selectivity, even very small vapor flows, such as those supplied by a FAST- GC column.
  • One of the main applications of the present invention is aimed at identifying multiple substances not known a priori, whereby the basic concept is that the smaller the inner volume of the cell is, the better. Therefore, if the cell is not small enough, the measured peaks are too close and mix again. Instead, the smaller the cell is with respect to the sample packet, the more the cell makes multiple acquisitions following the peak. Ideally, the multiple acquisitions would constitute a quantitative measure with regard to the detected substances, and not only qualitative about the presence or not thereof. Since however the main application is to detect the mere presence in the field, there is only one upper limit to the size of the cell, experimentally verified and reported above, and there is no lower limit thereof .
  • the concentration and the separation of the chromatographic peaks is maintained inside the analysis chamber without dilution or mixing, thus allowing a high sensitivity and identification of each component of the sample mixture.
  • the Inventors have identified a further issue generated by the photoacoustic cells known in some cases.
  • the sample packets of high-boiling substances or, in general, low-volatile substances
  • the simple coupling of the two devices of the prior art would degrade the measurement making the overall system unusable.
  • This issue was solved by providing the photoacoustic cell with means for heating the inner volume thereof, as well as, optionally, with heating control means.
  • the present embodiment therefore achieves an original and particularly effective coupling between separation and analysis devices and techniques, and gives rise to a new family of trace sensors for field use which are distinguished by portability and response speed.
  • the core of the QEPAS detector is a heated detection chamber with a minimum dead volume.
  • a laser beam is focused inside the chamber between the prongs of a standard commercial quartz tuning fork (QTF) which resounds at 32,768 Hz, by means of a 25 mm focal length external lens.
  • QTF quartz tuning fork
  • a micro-resonator consisting of two small steel tubes with a 0.9 mm I.D. and a 4.6 mm length is positioned close to the QTF to amplify the photoacoustic signal.
  • the outlet of the GC column is connected to the chamber, which is heated to avoid condensation of less volatile compounds eluted from the column.
  • Another criticality detected by the Inventors during the tests for coupling the two apparatuses is the distance between the capillary outlet from which the packets of the GC column outlet and the point where the laser is focused, between the two branches of the photoacoustic detector fork.
  • the Inventors have tried a coupling in this reduced range both in the case of analysis volumes 100-1000 times the volume of the packets, and in the case of analysis volumes which do not exceed 10 times the volume of the packets.
  • the result is that, in the first case (of the prior art), there is still no measurement, while in the second case the measurements are obtained and are excellent.
  • exclusively changing the fork capillary distance does not solve alone the dilution issue described above.
  • the QEPAS sensor uses an external cavity quantum cascade laser (EC-QCL) , from Monolux Pranalytica (USA) , as a tunable high-brightness IR source, from 8.8 pm to 9.9 pm, in which different dangerous compounds have their characteristic spectrum.
  • E-QCL external cavity quantum cascade laser
  • the optical head of the QEPAS sensor, (laser, focusing lens and QEPAS cell) , is integrated with the electronics for reading the signal and the thermal control and with a mini-PC, which allows to manage the module even remotely .
  • the injection valve may be a 10-way commercial valve (VICI-Valco) housed inside a small thermally insulated oven, and all the tubes and transfer lines are heated by inserting them into polyimide tubes equipped with external stainless steel braids, which have been used as electrical resistors (Microlumen Inc., Oldsmar FL, USA) .
  • VICI-Valco 10-way commercial valve housed inside a small thermally insulated oven, and all the tubes and transfer lines are heated by inserting them into polyimide tubes equipped with external stainless steel braids, which have been used as electrical resistors (Microlumen Inc., Oldsmar FL, USA) .
  • the present embodiment may be well combined with the first embodiment set out above (although the combination is possible with any GC module) , as the Inventors were able to ascertain with the results described below.
  • the invention relates to a miniaturized gas- chromatographic system, based on MEMS components for analyzing trace gaseous samples by means of purge&trap pre-concentration with thermal desorption, in which the features illustrated below may be understood individually as well as in any combination, respecting the technical concept of the invention.
  • the gas-chromatographic device 100 in a first embodiment according to the invention, comprises a chromatographic column unit 150 and a pre-concentrator 160 (also referred to as a "thermal desorption trap") . Mounted (for example, bridged) between the two, there is an injector unit 140. The mounting preferably occurs by means of O-rings 180 which are pressed between two rigid parts so as to form fluidic connections (more generally, any joint or fluidic connection, even using means other than O-rings, may be used) .
  • a fluidic head 170 preferably made of steel, faces the injector unit 140. Again, preferably, there is no direct contact between the fluidic head 170 and the injector unit 140, but the contact occurs by means of O-Rings 180.
  • the separation column is a column preferably comprised in the group which includes: packed micro- fabricated GC columns, semi-packed micro-fabricated GC columns, micro-fabricated capillary GC columns, micro- fabricated multi-capillary GC columns, porous-layer tubular GC columns and micro-fabricated GC columns based on ionic liquids .
  • the thermal desorption trap 160 may be filled with a suitable absorbent comprised in the set of porous polymers, graphite carbons, molecular sieves, zeolite molecular sieves, or multiple-bed sorbent traps based on sequences of any one of the aforementioned sorbents.
  • both the thermal desorption trap and the chromatographic separation column are filled with graphite carbons with different specific surfaces, therefore, they are adapted for high-temperature ramps in the presence of oxygen in the carrier gas, thus allowing the use of purified air as carrier gas .
  • a first layer 130 is preferably made of aluminum and acts as a structural reinforcement and as a protection for a second layer 120 which is made of a thermally insulating material, so that the solenoid valves 110 do not heat up in contact with the injector unit 140.
  • the fluid flows inside the device 100 of the invention are shown.
  • the overpressure +dP of the carrier gas the overpressure +dP of the carrier gas
  • the underpressure -dP of the pump which sucks in the sample (or other sample movement means)
  • the outlet flow towards the detector in this case meant to be a photoionization detector "PID”.
  • the overpressure +dP pushes the carrier gas into the gas-chromatographic column 150, gas which then passes into the injector unit 140 and finally into the detector (one or more, not shown) .
  • This circuit is operated by means of the use of the solenoid valves 110 which, however, open and close other pressure-actuated on/off valves, better illustrated below.
  • 173 indicates the inlet of the sample, 171 the overpressure +dP and 172 the underpressure -dP, 174 the outlet towards the detector.
  • the actuation pressure inlet channel 125 is made.
  • Two other channels 135 are there between the solenoid valves 110 and the injector unit 140, which are channels for actuating the device (for the valves V1-V5, see below), which receive pressure from the channel 125.
  • the channels 171-174 are advantageously constructed in the fluidic head 170, and this is preferably made of steel: in fact, this material has a high degree of passivation (i.e., it is possible to passivate the surface of the channels, for example, with vitrification processes, so that they become inert) .
  • the gas, entering 173, is directed towards the injector, which sorts the flow by actuating the valves V1-V5.
  • the injector, the tubes and the valves are included in the term “flow control means", which may be constructed in various manners.
  • O-rings 180 in the construction of some pipes, other means with the same function may be used in the device according to the invention.
  • gaskets or connections with metal alloys may be used, for example, a soft metal- based fluidic junction (soft metallic seals) . More generally, reference is therefore made to fluidic junctions or sealing means for the O-rings or gaskets or other .
  • the gas-chromatographic column 150, the pre-concentrator 160 and the injection unit 140 are constructed as MEMS to provide a miniaturization to the device.
  • the injection unit 140 acts both as an injector and as a fluidic manifold (connection) to interconnect with the pre-concentrator and the gas-chromatographic column, so as to minimize the dead volumes while allowing to keep the entire analytical circuit crossed by the sample at high temperatures (since MEMS valves are resistant to high temperatures), and therefore to optimize analytical performance .
  • V1-V5 valves are preferably all in the injection unit 140.
  • the circuit in the state in Figure 8 has three open and two closed valves, so as to create, by virtue of the underpressure -dP, a flow in the pre-concentrator 160 so that precisely the analytes are concentrated there.
  • the gas-chromatographic column is however affected by a flow controlled by the overpressure +dP, otherwise it may be subject to contamination.
  • the closing/opening of the valves is reversed, so that, from the pre concentrator suitably heated for releasing the sample, the gas, pushed by the overpressure +dP, passes to the gas-chromatographic column 150 and then to the detector (not shown) .
  • the MEMS valves are controlled by the group of solenoid valves 110.
  • Figure 10 exemplifies the operation of the MEMS valves.
  • Such on/off valves are preferably polymeric micro-membranes obtained between two silicon wafers.
  • the two overpressure and underpressure pumps are preferably different.
  • the pre-concentrator 160 is in thermal connection or integrates (for example, constructing them as MEMS) one or more heaters and one or more temperature sensors (not shown) .
  • the same thing may be expected for the chromatographic column.
  • Thermal connection means any connection (contact, radiant, etc.; internal or external) capable of conveying heat from the heater to the heated element (pre-concentrator and chromatographic column) .
  • a heater may also be included for the fluidic head 170.
  • electric Kapton/Copper heaters may be used, although, even simple resistors or armored glow plugs may work.
  • the injector MEMS chip 140 will be heated by radiation from the fluidic head 170, which is very close thereto.
  • the system may comprise in the injector 140 a sampling loop, to allow the use, alternatively, of a thermal desorption trap or of a sampling loop.
  • a sampling loop to allow the use, alternatively, of a thermal desorption trap or of a sampling loop.
  • valves are not all inserted in a single component as in the present invention.
  • the circuit valves are decoupled from the solenoid valves allows to work at high temperature. It is thus possible to keep the MEMS injector at temperatures up to 250°C to avoid the condensation of high-boiling molecules, while implementing an almost-zero dead volume injection system.
  • the MEMS injector acts in all respects as a "microfluidic manifold” (which may also be referred to as a "pneumatic motherboard” or “microfluidic motherboard”) to interconnect the MEMS pre-concentrator to the MEMS GC column, thus creating a set of 3 interconnected MEMS, directly facing them (for example by means of micro-O-rings ) towards one another, without the aid of additional components such as tubes/capillaries/manifolds.
  • a microfluidic manifold which may also be referred to as a "pneumatic motherboard” or “microfluidic motherboard”
  • the detector is not specific to the present invention, as it may be any type of detector used in GC; by way of explanation, the following are cited: the Thermal Conductivity Detector (TCD) , the Photoionization Detector (PID) , the Flame Ionization Detector (FID) , the Electron Capture Detector (ECD) , the Pulsed Discharge Detector (PDD) , the Metal Oxide Detector (MOX) , the Ion Mobility Spectrometer Detector (IMS), the Mass Spectrometer Detector (MS) , the Infrared Absorption Detector (IRAS) , photoacoustic detectors, and electro chemical sensors .
  • TCD Thermal Conductivity Detector
  • PID Photoionization Detector
  • FID Flame Ionization Detector
  • ECD Electron Capture Detector
  • PPD Pulsed Discharge Detector
  • MOX Metal Oxide Detector
  • IMS Ion Mobility Spectrometer
  • the system according to the invention may be used, in accordance with the applications, with MEMS GC columns of different nature (capillary, packed) , which use inert carrier gases originating from cylinders (for example nitrogen, helium) or autonomously generated (for example hydrogen by electrolysis), or, in some cases, simple filtered air.
  • MEMS GC columns of different nature capillary, packed
  • inert carrier gases originating from cylinders for example nitrogen, helium
  • autonomously generated for example hydrogen by electrolysis
  • the system according to the invention comprising, for example, 3 MEMS (pre-concentrator, injector/microfluidic manifold, GC column) , the solenoid valves (which are used only for the injector pressure actuation), the mounting supports, the heaters etc., only measures a few cubic centimeters.
  • the system in accordance with the invention may be used according to the following steps :
  • the temperature of said pre-concentrator 160 is adjusted by means of said one or more pre concentrator heaters and said one or more pre concentrator temperature sensors;
  • an analysis system is provided with a first and second micro-fabricated gas-chromatographic column in the GCxGC configuration, as well as having a micro- fabricated modulator injector.
  • the modulator may implement two states of the fluidic system, in which:
  • the modulator implements a first fluidic circuit in which the separated sample eluted from the first GC column is accumulated inside a microfluidic circuit (microfluidic ring) while the second GC column elutes a sample using a carrier gas pressure difference;
  • the modulator injects the eluted sample of the microfluidic ring into the second GC column by means of a carrier gas pressure difference.
  • the two states are implemented by the modulator always by means of a series of micro-fabricated valves, in which, again, the injector chip also acts as a pneumatic manifold, directly connecting the two GC columns.
  • the system in accordance with the invention is used in an analysis method via gas-chromatographic separation and photoacoustic spectroscopy, comprising the following steps :
  • step B operating the aforesaid one or more solenoid valves 110 so as to open and close said one or more valves VI, V2, V3, V4, V5 for achieving said first state;
  • step C between step B and step D, a further step C is carried out, in which the temperature of said pre- concentrator 160 is adjusted by means of said one or more pre-concentrator heaters and said one or more pre-concentrator temperature sensors;
  • step D operating said one or more solenoid valves 110 so as to open and close said one or more valves VI, V2, V3, V4, V5 for achieving said second state;
  • step E between step D and step F, performing a further step E in which the temperature of said chromatographic separation column 150 is adjusted by means of said one or more separation column heaters and one or more separation column temperature sensors .
  • the GC-QEPAS system was tested according to such method, under laboratory conditions, on a series of nerve and blistering agent simulants, as shown in Table 1.
  • Table 1 simulants of nerve and blistering agents used for laboratory validation
  • test samples were prepared by evaporating some microliters of the target species inside a box of 60 liters of inner volume and then sampling the contents of the box for periods between 30 and 120 seconds. Ideally assuming the total vaporization of the injected liquid, it is possible to estimate the maximum concentrations in the range between a few ppm and a few tens of ppm. However, depending on the different volatility of the tested compounds and considering the partial condensation on the cold inner walls of the gas container, lower vapor concentrations are expected.
  • Figure 11 shows a typical acquisition, including the integral absorbance chromatogram in (a) and the IR spectra of nerve and blistering agent simulants in (b) , (c) .
  • Figure 12 shows the IR spectra of the other two nerve agent simulants. They were identified by the GC-QEPAS sensor even when sampled together with gasoline-saturated vapors, which were successfully separated from the GC column prior to detection .
  • the present invention which relates to a GC and photoacoustic analysis system, has, among others, the following advantages:
  • the photoacoustic spectra are very similar to the infrared absorption spectra and contain information on the functional groups of the molecules, such to be capable of distinguishing cis-trans isomers;
  • the invention further allows the extreme miniaturization of a system for purge&trap pre concentration and the subsequent (gas-) chromatographic separation of sample mixtures, thus allowing to obtain high sensitivity and high selectivity.
  • the "all-MEMS" construction of the system unlike the background art of miniaturized instruments, allows to work at higher temperatures, since all the components crossed by the sample are silicon-based and therefore resistant to high temperatures, allowing, the same time, to limit the times of a complete measurement cycle, from the initial sampling up to the result of the analysis, in an interval of a few minutes, typically between 5 and 10 minutes. This also allows to analyze high-boiling substances.
  • the invention may be used in the following fields, not listed by way of limitation: field analysis of complex samples; safety&security (explosives, CBRNe) , industrial monitoring, monitoring of environments hazardous for the health of the operators, biomedical analysis (e.g., breath analysis), environmental/air quality, indoor air quality, agro-food, industrial process monitoring, energy and natural gas (odorant quantification) .
  • field analysis of complex samples e.g., safety&security (explosives, CBRNe)
  • industrial monitoring e.g., monitoring of environments hazardous for the health of the operators
  • biomedical analysis e.g., breath analysis
  • environmental/air quality e.g., indoor air quality, agro-food
  • industrial process monitoring e.g., energy and natural gas (odorant quantification) .

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Abstract

La présente invention concerne un système d'analyse chimique portable permettant d'identifier des substances chimiques à l'état de trace (concentrations sous-ppm) également en présence d'autres substances interférentes, grâce à la sélectivité bidimensionnelle obtenue à partir de la combinaison entre la technique de séparation par chromatographie en phase gazeuse (GC) et la technique d'analyse infrarouge photoacoustique (PA), en particulier, mais pas exclusivement, dans sa mise en œuvre désignée par spectroscopie photoacoustique améliorée à quartz (QEPAS). Le module GC est de préférence mis en œuvre sous la forme d'un dispositif MEMS du type FAST, apte à séparer, avec des budgets thermiques réduits et des temps d'élution très courts (quelques minutes), des échantillons même complexes et peu volatils. Le module QEPAS est de préférence fabriqué autour d'une cellule d'analyse avec un volume interne microscopique, pouvant traiter, avec une sensibilité élevée et une excellente sélectivité, des débits de vapeur même très petits, tels que ceux fournis par une colonne FAST-GC.
PCT/IB2020/055226 2019-06-10 2020-06-03 Système d'analyse chimique au moyen d'une séparation par chromatographie en phase gazeuse et d'une spectroscopie photoacoustique de mélanges d'échantillons WO2020250086A1 (fr)

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