Apparatus and method for measuring a gas

Abstract

In a measuring method for measuring an atmospheric concentration of a compound, such as a volatile organic compound (VOC), an adsorptive element is provided within a target atmosphere for a period of time to allow adsorption of a compound of interest, and then removed from the target atmosphere, and placed within a closed measuring space. The adsorptive element is heated within the measuring space to cause de-adsorption of the compound into the closed measuring space, and a concentration of the de-adsorbed compound is measured. A concentration of the compound in the target atmosphere is determined based on the concentration of the compound within the closed measuring space. The adsorptive element may be formed of an adsorptive material such as carbon fibers, cellulose or other adsorptive materials, and a binder. The adsorptive element may be optimized for adsorption of a specific compound.

Claims

1. A method for measuring an atmospheric concentration of a compound, comprising steps of: providing an adsorptive tag within a target atmosphere for a period of time to allow adsorption of a compound of interest for measurement, wherein the adsorptive tag comprises a porous substrate, a heating element disposed on or embedded within said porous substrate and an adsorptive element disposed on the porous substrate over said heating element; removing the adsorptive tag from the target atmosphere after said period of time, and placing the adsorptive tag within a closed measuring space; activating said heating element to heat the adsorptive element to cause de-adsorption of the compound of interest into the closed measuring space; measuring a concentration of the de-adsorbed compound of interest within the closed measuring space; and determining a concentration of the compound of interest in the target atmosphere based on the concentration of the compound of interest within the closed measuring space.

2. The method of claim 1, wherein said adsorptive element is a carbon based adsorptive element.

3. The method of claim 1, wherein said adsorptive element comprises a plurality of carbon particles.

4. The method of claim 3, wherein said plurality of carbon particles comprises carbon nano particles.

5. The method of claim 4, wherein said carbon nano particles are carbon nano tubes.

6. The method of claim 1, wherein said adsorptive element is a cellulose based adsorptive element.

7. The method of claim 6, wherein said cellulose based adsorptive element is coated with a polypyrrole/silver nitrate preparation.

8. The method of claim 1, wherein said porous substrate comprises a circuit board, the circuit board having a plurality of through-holes formed therein.

9. The method of claim 1, wherein said porous substrate comprises a fabric substrate.

10. An adsorptive tag for collecting and releasing a measurement sample, comprising: a porous substrate; and an adsorptive element disposed on said substrate; wherein adsorptive element is adapted to adsorb at least one volatile organic compound, and to release said least one volatile organic compound upon heating; wherein said porous substrate comprises a circuit board, the circuit board having a plurality of through-holes formed therein.

11. The adsorptive tag of claim 10, further comprising a heating element disposed on said circuit board substrate, the heating element being adapted to heat said adsorptive element.

12. The adsorptive tag of claim 11, wherein said heating element comprises a printed circuit formed on said circuit board substrate.

13. The adsorptive tag of claim 10, wherein said plurality of through-holes are arranged to facilitate dispersion of said at least one volatile organic compound from said adsorptive element.

14. The adsorptive tag of claim 10, wherein said adsorptive element is a porous mass comprising adsorptive particles and a binder.

15. The adsorptive tag of claim 14, wherein said adsorptive particles comprise carbon particles.

16. The adsorptive tag of claim 14, wherein said adsorptive particles comprise cellulose.

17. An adsorptive tag for collecting and releasing a measurement sample, comprising: a fabric substrate; and a heating element disposed on or within said fabric substrate; an adsorptive element disposed on said fabric substrate; wherein adsorptive element is adapted to adsorb at least one volatile organic compound, and to release said least one volatile organic compound upon heating.

18. The adsorptive tag of claim 17, wherein said heating element comprises a wire heating element woven into said fabric substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a flowchart showing a method for measuring an atmospheric concentration of a volatile organic compound using an adsorptive element.

(2) FIG. 2 illustrates an embodiment of an adsorptive element of the present invention.

(3) FIG. 3 is a diagrammatic depiction of an adsorptive tag including a substrate, heating element and adsorptive element.

(4) FIGS. 4a-4d illustrate certain possible configurations of an adsorptive tag.

(5) FIG. 5 is a diagrammatic view of a measuring device adapted to receive an adsorptive tag in a closed measuring space.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

(6) Referring to FIG. 1, a measuring method for measuring an atmospheric concentration of a compound, such as a volatile organic compound (VOC), can be broadly described as comprising steps of: providing an adsorptive element within a target atmosphere for a period of time to allow adsorption of a compound of interest for measurement; removing the adsorptive element from the target atmosphere, and placing the adsorptive element within a closed measuring space; heating the adsorptive element to cause de-adsorption of the compound of interest into the closed measuring space; measuring a concentration of the de-adsorbed compound of interest within the within the closed measuring space; and determining a concentration of the compound of interest in the target atmosphere based on the concentration of the compound of interest within the closed measuring space.

(7) An adsorptive element 201 of the invention is, in one embodiment, a carbon mass, which may be formed of carbon particles 203 such as carbon fibers, carbon nanofibers, carbon nanotubes and the like. The carbon particles 203 may be formed into a disk or pill in certain embodiments. The disk or pill may be cast from a wet slurry comprising the carbon particles 203 and a binder 205. Suitable binders 205 include, but are not limited to, water soluble phase change polymers, such as poly vinyl acetate, or wood glue. In certain embodiments, a wet slurry includes carbon particles with poly vinyl acetate at about 2-8% of the weight of the particles.

(8) Polysiloxanes as well as polyvinylalcohol are also suitable binders. Copper oxide (CuO) may be included, such as for example a mixture of carbon nanofibers, CuO and polyvinylalcohol. In a mixture of carbon nanofibers, together with CuO (at about 6-18% of the weight of the nanofibers) and polyvinylalcohol (at about 15% of the weight of the nanofibers), a resulting adsorber has been found effective to detect ethylene in less-than 100 ppb concentrations.

(9) It is advantageous that a ratio of the carbon particles 203 to the binder 205 is such as to maximize porosity of the disk (hence maximizing an exposed surface area of the carbon particles 203), while at the same time minimizing shedding of the carbon particles 203. It can be recognized that if too much of the binder is used, the disk becomes insufficiently porous for good adsorption, while if too little of the binder is used, the disk may be prone to spalling, releasing loose carbon particles into the environment. Prevention of spalling becomes especially desirable if the adsorptive element is used in proximity to food items.

(10) In addition to a carbon based adsorber, other adsorbing materials may be used. For example, in certain embodiments an adsorber may be formed of cellulose, cellulose coated with silver particles, silver nitrate, a mixture of polypyrrole and silver nitrate, silver nanoparticles or the like. For example, cellulose may be coated with mixture of polypyrrole and silver nitrate at about 0.1M concentration. Cellulose based adsorbers have been found effective to detect ethylene at as low as 10 ppb concentrations, when the sample is heated at 100-125 C.

(11) Similarly, an adsorber may be formed of alumide, alumide coated with silver particles, silver nitrate, a mixture of polypyrrole and silver nitrate, silver nanoparticles or the like. Further, mesoporous silica is another suitable adsorbant.

(12) An ionic liquid may be incorporated to further enhance adsorption. For example, in the case of ethylene, an ionic liquid used as an ethylene trapping agent aides in ionization of silver nanoparticles (to Ag+), which binds to electron donor groups in ethylene, helping to remove ethylene from the surrounding atmosphere.

(13) As described above and with reference to FIG. 1, the adsorptive element 201 in use is placed in a target atmosphere for a time period during which the VOC will be adsorbed. Subsequently, the adsorptive element 201 is removed from the target atmosphere, placed within an enclosed, sealed measuring space, and heated to cause de-adsorption of the collected VOC. In certain embodiments, a heater may be incorporated within a sealed measuring space of a measuring device, while in other embodiments a heater may be formed together with the adsorptive element 201 such as in an adsorptive tag 300.

(14) A general arrangement for an adsorptive tag 300 is shown in FIG. 3, wherein a substrate 301 is provided with an electrical heating element 303 formed on or embedded in the substrate 301, electrical contact elements 305 are disposed on the substrate 301 and in electrical connection to the heating element such that an electrical current may be supplied to the electrical heating element 303 from a sampling or measurement device, and an adsorptive element 201 is disposed on the substrate 301 over the heating element 303.

(15) Referring to FIGS. 4a-4d, embodiments of a substrate 301 having an integral heating element are shown. Broadly speaking, the heating element 303 comprises one or more heating wires formed on, or embedded in, a substrate 301, and arranged such that an adsorptive element 201 may be disposed on the substrate 301, over the heating wires. In FIGS. 4a and 4b, a plurality of parallel heating wires of the heating element 303 are provided and arrayed such that positive and negative electrical contacts 305 may be provided at opposite ends of the wire array of the heating element, to provide an electric current for heating the heating wires of the heating element 303. In FIG. 4c, the heating element 303 comprises a single heating wire, arranged in a meander pattern.

(16) In certain embodiments, the substrate 303 may be a woven or embroidered fabric, with the heating wires woven into the fabric such that at least end portions of the heating wires are exposed for electrical contact, defining electrical contact regions 305. The electrical contact regions 305 are arranged to make electrical contact with electrical terminals provided in a measuring device.

(17) Alternatively, shown in FIG. 4d, a substrate 301 may be provided in the form of a circuit board substrate 401 with an etched foil heating element matrix 403. It can be recognized that porosity of the substrate, inherent to a fabric substrate, may facilitate dispersion of the de-adsorbed compound from the adsorbing element into the measuring space. Accordingly, apertures 405 may be formed through the circuit board substrate 401 to similarly facilitate dispersion such dispersion.

(18) In certain embodiments, the adsorptive element may be optimized for adsorption of a particular compound, such as by addition of electroactive dopants.

(19) Referring to FIG. 5, a measuring device 500 is adapted to receive an adsorptive tag 300 in a closed measuring space 505. Within a body of the measuring device 500, a receiving space, or measuring space 505 is defined, where in the measuring space 505 is closed or closable such as by a cover 509. Within the measuring space 505 is disposed a sensor 503 which is adapted for measurement of a substance of interest, such as a volatile organic compound (VOC). In an illustrated embodiment, proximate to or within the measuring space 505, electrical terminals 507 are arranged to correspond with electrical contact elements 305 of the adsorptive tag 300 for supplying an electrical current to the heating element of the adsorptive tag 300. In alternative embodiments, a heating element may be disposed within the body of the measuring device such that the measuring device may be used with an adsorptive element or adsorptive tag lacking an integrated heating element.

(20) A control circuit is provided to activate the heating element and the sensor 503, to obtain and display or report a measurement of the substance of interest within the measuring space 505. Referring again to FIG. 1, an adsorptive element such as the adsorptive tag 300 is placed within the measuring space 505, and the measuring space 505 is then closed. Following closure of the measuring space 505, the adsorptive element is heated, such as by applying an electrical current to the heating element, to cause de-adsorption of the compound of interest into the closed measuring space. A measurement of a concentration of the de-adsorbed compound of interest within the within the measuring space is taken by the sensor 503, from which can be determined a concentration of the compound of interest in the target atmosphere.

(21) In view of the concentration, or amplification, of the compound of interest in the target atmosphere achieved by the adsorber, the concentration in the target atmosphere is determined as a function of the measured concentration, and the expected amplification. For example, considering an adsorber that achieves a 1000 times amplification, a measured value of 50 ppm would correspond to a 50 ppm concentration in the target atmosphere. Approximate amplifications resulting from this process are of the order of 300 to over 1000 times, and may be as high as 10,000 times.

(22) It will be understood that the above-described embodiments of the invention are illustrative in nature, and that modifications thereof may occur to those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited only as defined in the appended claims.