Method and apparatus for precise control of vapor phase concentrations of volatile organics

• US 4,388,272 A
• Filed: 04/08/1981
• Issued: 06/14/1983
• Est. Priority Date: 04/08/1981
• Status: Expired due to Fees

• Current Assignee: Northwestern University
• Original Assignee: Northwestern University
• Inventors: Gesteland, Robert C.
• Primary Examiner(s): Gron, Teddy S.
• Application Number:
  US06/252,039
• Time in Patent Office: 797 Days
• Field of Search: 252/408, 252/372, 252/408.1, 23/230 R, 23/230 B, 23/232 R, 23/907, 73/19, 73/23, 73/1 G, 422/5, 422/123, 422/88, 422/99, 422/102, 422/103, 424/76, 424/2, 436/9, 53/97, 53/79
• US Class Current: 422/501
• CPC Class Codes: G01N 30/00 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 G01N3/00, G01N5/00, G01N7/00, G01N9/00, G01N11/00, G01N13/00, G01N15/00, G01N17/00, G01N19/00, G01N21/00, G01N22/00, G01N23/00, G01N24/00, G01N25/00, G01N27/00, G01N29/00 take precedence
• CPC Class Codes: G01N 33/0006 Calibrating gas analysers
• CPC Class Codes: G01N 33/4972 Determining alcohol content for vehicle safety devices B60K28/06
• CPC Class Codes: Y10T 436/100833 Simulative of a gaseous composition

Abstract

A method and apparatus for precise control of vapor phase concentrations of volatile organic compounds is provided which utilize desorption of monolayers of the organic compound from a solid adsorbent. The method and apparatus can be used for measuring human olfactory system performance, for calibration of analytical chemical instruments, and in other applications.

Claims

1. The method of providing a predetermined concentration of a volatile organic compound in a gas carrier sample, comprising:

(a) applying the volatile organic compound free of any other volatile compound to a solid granular adsorbent to partially coat its adsorptive surfaces, the amount of said compound on said adsorbent being less the minimum amount capable of saturating a gas in contact therewith at an ambient temperature, said compound and said adsorbent being chemically non-reactive;

(b) introducing said organic compound-containing adsorbent into an enclosed space from which gas samples can be selectively removed, said enclosed space containing a carrier gas in contact with said adsorbent at said ambient temperature;

(c) maintaining said adsorbent in contact with said gas until an adsorption-desorption equilibrium is reached so that said gas at said ambient temperature contains a predetermined concentration of said organic compound; and

(d) removing a gas sample from said enclosed space containing said predetermined concentration of said organic compound.

2. The method of claim 1 in which the amount of said organic compound on said adsorbent is less than 10% of the minimum amount capable of saturating a gas in contact therewith at said ambient temperature.

3. The method of claim 1 in which a plurality of identical gas samples are removed from said enclosed space, the amount of said organic compound removed in each gas sample being less than 0.01% of the amount adsorbed on said adsorbent.

4. The method of claim 1 in which said adsorbent is silica gel.

5. The method of claim 1, or claim 2, or claim 3 in which said organic compound is an odor substance and said carrier gas is odorless, whereby said method can be used for dispensing odor samples.

6. The method of providing a predetermined concentration of a volatile organic compound in a gas carrier sample, comprising:

(a) applying the volatile organic compound free of any other volatile compound to a solid granular adsorbent to partially coat its adsorptive surfaces, the amount of said organic compound on said adsorbent being limited to less than 10% of the minimum amount capable of saturating a gas in contact therewith at an ambient temperature, said compound and said absorbent being chemically non-reactive;

(b) introducing said organic compound-containing adsorbent into an enclosed space from which gas samples can be selectively removed, said enclosed space containing a carrier gas in contact with said adsorbent at said ambient temperature;

(c) maintaining said adsorbent in contact with said gas until an adsorption-desorption equilibrium is reached so that said gas at said ambient temperature contains a predetermined concentration of said odor substance; and

(d) removing a plurality of gas samples from said enclosed space with said organic compound therein, each of said gas samples containing an amount of said organic compound less than 0.01% of the amount initially adsorbed on said adsorbent, whereby a large number of samples of the same concentration can be removed from said enclosed space.

7. The method of claim 6 in which the amount of said organic compound on said adsorbent is less than 1.0% of the minimum amount capable of saturating said gas in contact therewith at said ambient temperature.

8. The method of claim 6 or claim 7 in which the adsorbent is silica gel.

9. The method of claim 6 or claim 7 in which said organic compound is an odor substance and said carrier gas is odorless, whereby said method can be used for dispensing odor samples.

10. An assembly for dispensing gas samples containing a reproducible predetermined concentration of a volatile organic compound, comprising a container with at least one opening to the space enclosed thereby, openable means for closing said opening to seal said container, said space containing a carrier gas in contact with a solid granular adsorbent having a volatile organic compound adsorbed thereon, said organic compound on said adsorbent being free of any other volatile compound and said organic compound and said adsorbent being chemically non-reactive, the amount of said organic compound on said adsorbent being less than 10% of the minimum amount capable of saturating said carrier gas at 25°

C., said gas containing a substantially equilibrium concentration of said organic compound.

11. The assembly of claim 10 in which the said gas in said container contains less than 0.01% of the amount of said odor substance on said adsorbent.

12. The assembly of claim 10 or claim 11 in which said container is in the form of a tube having an inlet at one end for admission of said odorless gas and an outlet at the other end for discharge of gas containing said odor substance, said inlet opening being provided with inlet check valve means, and said outlet opening being provided with outlet check valve means, and said adsorbent being disposed within said tube so that said gas in flowing through said tube passes through said adsorbent.

13. The assembly of claim 12 in which said outlet opening for said gas sample is connected to a nose adapter to facilitate sniffing of said gas samples, where said assembly can be used with odorous organic compounds as an olfactometer.

14. The assembly of claim 12 in which said outlet opening for said gas sample is connected to an injector for introducing said sample into a gas analyzer instrument, whereby said assembly can be used to calibrate said instrument for response to said organic compound.