Micro-device for detecting volatile organic compounds, and method for detecting at least one volatile organic compound contained in a gas sample

Abstract

This invention relates to a micro-device for detecting volatile compounds comprising: an input (E) and an output (S); collection means (2) for taking a gas sample containing at least one compound to be detected; sampling means enabling a gas volume of 100 mL or less to be sampled, arranged after the collection means; injection means (3) of said gas sample; separation means (5) of the compound to be detected in the gas sample; compound detection means (6); and a gas circulation circuit (1) located downstream of the collection means and passing through the sampling means, injection means (3), separation means (5) and detection means (6);
characterized in that the gas circulation circuit (1) has a volume of between 0.2 cm.sup.3 and 2.0 cm.sup.3.

Claims

1. Micro-device for detecting volatile compounds comprising: an input and an output; a collection means for taking a gas sample containing at least one compound to be detected, arranged at the input of the micro-device; a sampler enabling a gas volume of between 10 pL and 500 pL to be sampled, arranged after the collection means; an injection means for injecting said gas sample, arranged after the sampling loop; a separation means for separating the compound to be detected in the gas sample, arranged after the injection means; a compound detection means, arranged between the separation means and the output of the micro-device, where the compound detection means is a photoionization micro-detector; and a gas circulation circuit located downstream of the collection means and passing through the sampling loop, injection means, separation means and detection means, wherein the gas circulation circuit has a volume of between 0.2 cm.sup.3 and 2.0 cm.sup.3.

2. Detection micro-device according to claim 1, wherein the separation means of the compound to be detected are a gas-phase microchromatography device comprising a micro-column.

3. Method of detecting at least one volatile compound in a gas sample comprising: (i) collecting a gas sample containing the compound to be detected; (ii) sampling the gas sample having a volume of 100 mL or less, said sampling being performed in a sampling loop; (iii) injecting the sample taken in step (i) and sampled in step (ii) into means enabling the separation of the compound to be detected; (iv) separating the compound to be detected, and (v) detecting the compound, said method optionally also including a step of injecting a vector gas at step (i) and/or (ii) and/or (iii) and/or (iv) and/or (v), wherein the total vector gas consumption is between 0.1 mL/min and 5 mL/min.

4. Method according to claim 3, wherein the sampling step (ii) is performed using sampling loop having a volume of between 10 L and 500 L.

5. Method according to claim 3, wherein the method includes a step of pre-concentration after step (ii).

6. Method according to claim 5, wherein the sampling step (ii) is achieved using a sampling loop having a volume of between 0.5 mL and 100 mL.

7. Method according to claim 5, wherein the transfer of the sampled volume to the concentration means is achieved using a transfer gas at a flow rate of between 0.1 mL/min and 100 mL/min.

8. Method according to claim 3, wherein the separation of the compound to be detected in step (iii) is achieved using a gas-phase micro-chromatography device comprising a micro-column.

9. Method according to claim 8, wherein the vector gas used during separation by gas-phase micro-chromatography is selected from the group consisting of hydrogen, nitrogen, helium, argon and their mixtures.

10. Method according to claim 8, wherein the gas-phase micro-chromatography is performed with an elution flow rate of between 0.1 mL/min and 5 mL/min.

11. Method according to claim 3, wherein compound detection is achieved using a detector selected from the group consisting of a photoionization micro-detector (PID), a spectrometer for colorimetric detection, a katharometer, a flame ionization detector (FID), a mini- or micro-mass spectrometer, an acoustic detector and an infrared detector based on tunable laser diodes.

12. Method according to claim 3, wherein the volatile compound to be detected is selected from the group consisting of benzene, toluene, ethylbenzene, paraxylene, orthoxylene and metaxylene.

13. Use of the micro-device as defined in claim 1 or of the method as defined in claim 3 to detect compounds selected from the group consisting of benzene, toluene, ethylbenzene, paraxylene, orthoxylene and metaxylene.

Description

(1) A clearer understanding of the invention will emerge from the accompanying drawings, in which

(2) FIG. 1 is a descriptive diagram of a micro-device according to an embodiment of the invention;

(3) FIGS. 2a and 2b represent the different steps of the detection method according to an embodiment without the pre-concentration step;

(4) FIGS. 3a to 3c represent the different steps of the detection method according to another embodiment with a pre-concentration step; and

(5) FIG. 4 is a chromatogram showing the separation of 100 ppb of BTEX compounds.

(6) The micro-device shown in FIG. 1 comprises an input E and an output S and a gas-circulation circuit beginning after the collection means and passing through the sampling means ME (for example a sampling loop), concentration means, if applicable, (for example a pre-concentrator), injection means (for example a 6-way valve V1 without a pre-concentrator or V2 with a pre-concentrator), separation means MS for the compound to be detected (for example a micro-chromatography device comprising a micro-column arranged in an oven) and compound detection means (for example a photoionization micro-detector). The gas circulation circuit is in particular characterized by its small volume of between 0.2 cm.sup.3 and 2 cm.sup.3, preferably between 0.5 cm.sup.3 and 1.5 cm.sup.3. Upstream of the gas circulation circuit are the collection means MP for collecting a gas sample (in this case, ambient air) containing at least one compound to be detected, which are arranged at the input of the micro-device. According to an embodiment, the collection means MP are a collection line on which is installed a pump connected to an airflow regulator.

(7) The sampling means ME located after the collection means MP are connected to a six-way valve V1.

(8) The 6-way valve V1 is used in order to inject the gas sample from the collection means towards the separation means or to transfer the gas sample from the collection means towards the concentration means (depending on whether the micro-device has concentration means) but also to inject other fluids necessary for separation and detection such as a vector gas.

(9) The sampling loop allows a volume of gas of 100 mL or less, preferably between 10 L and 100 mL, to be sampled.

(10) When the micro-device has no pre-concentration means MC, the 6-way valve V1 allows the sample to be injected directly into the separation means MS. The valve V1 in this case fulfills the role of injection means.

(11) When the micro-device has pre-concentration means MC, the valve V1 allows the sampled gas volume to be transferred to the pre-concentration means MC.

(12) In this case, the injection means are represented by a second valve V2 allowing the pre-concentrated sample to be injected towards the separation means MS. The separated gas sample is then detected by the detection means MD.

(13) FIG. 2 shows the different steps of the method according to an embodiment in which the method does not include a pre-concentration step.

(14) The first step consists in taking and sampling the gas sample (FIG. 2a).

(15) The valve V1 is in position 1 in order to sample the gas sample in a sampling loop having a volume of between 10 L and 500 L, preferably between 50 L and 300 L and particularly preferably between 100 and 200 L.

(16) For this, the sample to be analyzed is introduced into way 1 of the valve V1 and exits through way 6 in order to pass through the sampling loop connected to ways 6 to 3.

(17) Valve V1 also allows a vector gas (entering through way 4 and exiting through way 5) into the separation (MS) and detection (MD) means but also allows the undesirable compounds to be rejected (way 2).

(18) The second step involves injecting the gas sample towards the separation means, then detecting the separated sample by the detection means (FIG. 2b where the valve V1 is in injection position 2).

(19) For this, the sample sampled in the sampling loop emerges through way 6 and is injected into the separation means through way 5 where the vector gas required for the separation and detection of the gas sample is also introduced.

(20) FIG. 3 represents the different steps of the method according to an embodiment where the method comprises a pre-concentration step.

(21) The first step involves taking and sampling the gas sample (FIG. 3a).

(22) Valve V1 is in position 1 in order to sample the gas sample in the sampling loop having a volume of between 0.5 mL and 100 mL, preferably between 1 mL and 40 mL, and even more preferably between 5 mL and 20 mL.

(23) For this, the sample to be analyzed is introduced into way 1 of valve V1 and exits via way 6 in order to pass through the sampling loop connected to ways 6 to 3.

(24) Valve V2 is in position 2 and allows the separation means (MS) and detection means (MD) to be supplied with vector gas. Vector gas is introduced into V2 through way 4 and exits through way 5 in order to supply the separation and detection means.

(25) The second step (FIG. 3b) involves transferring the sampled gas volume to the pre-concentration means. Valve 1 is therefore in position 2 during this step and thus allows the gas volume to be transferred by means of said gas which itself is used as vector gas and is necessary for this transfer. The flow rate used during this transfer can be substantially different from that of the vector gas passing into the separation means (a micro-column for example).

(26) During this step, the sample sampled in the sampling loop connected to ways 3 to 6 is transferred to the concentration means via the same gas as that used as a vector gas entering through way 4 of V1. The sampled sample then exits through way 5 of V1 and is introduced into valve V2 through way 1 in order to be introduced into the concentration means via way 6 of V2.

(27) The transfer of the sampled volume towards the concentration means is achieved at a flow rate of between 0.1 mL/min and 100 mL/min, preferably between 0.2 mL/min and 40 mL/min and even more preferably between 1 mL/min and 20 mL/min.

(28) Valve V2 is still in position 2 and can supply the separation (MS) and detection (MD) means with vector gas (the vector gas enters through way 4 of V2 and exits towards the separation means through way 5 of V2).

(29) Lastly, the third step (FIG. 3c) involves injecting the pre-concentrated gas sample towards the separation means MS then detecting the separated sample by the detection means MD.

(30) Valve then passes back to position 1 and valve 2 is in position 2.

(31) During this step, the vector gas enters through way 4 of valve V2, exits through way 5 in order to pass through the pre-concentrator conveying with it the pre-concentrated gas sample, which enters through way 6 of V2 and exits through way 5 of V2 towards the separation means.

EXAMPLE: SEPARATION AND DETECTION OF DIFFERENT BTEX COMPOUNDS

(32) In this example, the following compounds have been separated and detected according to the method of the present invention: 1: Benzene 2: Toluene 3: Ethylbenzene 4: Meta- and para-xylenes 5: Orthoxylene

(33) Detection of the compounds contained in the generated synthetic air has been achieved with the aid of the device as described in FIG. 1, according to the following steps: (i) the generated synthetic air comprising all of compounds (1)-(5) is taken with the aid of a pump at a flow rate of 10 to 50 mL/min, then injected into a sampling loop for a period ranging from 5 seconds to 10 min so as totally to renew the air contained in the sampling loop; (ii) the sample exiting the sampling loop is then injected into a gas-phase micro-chromatography micro-column arranged in an oven, with the aid of a 6-way valve that simultaneously also injects hydrogen as the vector gas into the micro-column so that the sample is conveyed into the column by the vector gas.

(34) Technical Characteristics of the Separation Step: micro-column: RTX-624 elution flow rate: 2.5 mL/min of hydrogen column temperature: 70 C. (iii) the sample is then detected with a photoionization micro-detector (PID).

(35) FIG. 4 represents the chromatogram obtained on implementing the method previously described.

(36) It reveals that the most volatile compounds (benzene 1, toluene 2) exit first and the heaviest last (ethylbenzene 3 and the xylenes: meta- and para-xylenes being co-eluted 4 and orthoxylene 5).

(37) This detection method thus enables a rapid quantitative analysis (in less than 10 minutes) of the BTEXs and requires only a small quantity of vector gas (2.5 mL/min in the example shown in FIG. 4).