METHOD AND APPARATUS FOR OPTICAL ANALYSIS OF THE CONTENTS OF A SHEATHED STREAM

• US 3,661,460 A
• Filed: 08/28/1970
• Issued: 05/09/1972
• Est. Priority Date: 08/28/1970
• Status: Expired due to Term

• Current Assignee: Technicon Instruments Corporation
• Original Assignee: Alan H. Elking, Alex M. Saunders, Warren Groner
• Inventors: Elking, Alan H., Saunders, Alex M., Groner, Warren
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Sklar, Warren A.
• Application Number:
  US05/067,819
• Time in Patent Office: 620 Days
• Field of Search: 356/36,39-40,102-104,134,201,207-208,246 250/218,222PC
• US Class Current: 356/36
• CPC Class Codes: G01N 15/1404 Handling flow, e.g. hydrodynamic focusing
• CPC Class Codes: G01N 2021/0346 Capillary cells; Microcells
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10

Abstract

There is provided a method and apparatus for optical analysis by photometry of a substance flowing in a liquid stream within a coaxial sheath stream of a transparent liquid. The sheath stream, flowing in the same direction, entrains the inner stream so as to confine it concentrically. A photometer is used which includes a light source on one side of the sheathed stream in a position to direct light onto the inner stream which is cylindrical, the outer or sheath stream also being cylindrical. The photometer also includes a light detector externally of the sheathed stream in an angular position to detect the photometric results of impingement of light on the contents of the inner stream. Refraction of light at the interfaces of the sheath stream is compensated by varying the radius of the inner stream through the control of the flow of one stream with reference to the other. The concept also includes the narrowing of the sheathed stream to a very small diameter in which it is confined by a wall structure in the area of examination.

Claims

1. Apparatus for optical analysis of a sample stream including a liquid in a coaxial sheath stream liquid comprising:

means defining a flow chamber having an elongated passageway portion having a forward outlet end and at a rear end of said portion a tube inlet of substantially smaller diameter than said passageway portion extending concentrically a distance forwardly into said passageway portion and terminating forwardly in a free tube end, the last-named means defining a second inlet in said passageway portion at a location a distance rearwardly from said free tube end, and the last-named means also defining a restriction with a narrow sloping approach in said passageway portion intermediate said outlet end thereof and said free tube end, the internal and external surfaces of said free tube end and the internal surface of said passageway portion being circular in cross section, means for flowing a sample stream through said tube inlet into said passageway portion, means for flowing a sheath stream into said second passageway inlet at a greater flow rate than the sample stream to entrain the latter so as to increase the velocity of the sample stream and narrow it as the streams flow toward said restriction of the passageway portion, photometric means downstream from the upstream extremity of said restriction of the passageway portion in proximity to the sheathed stream and including a light source on one side of the sheathed stream in a position to direct light onto the contents of the sample stream and a light detector externally of the sheathed stream in angular position to detect the photometric results of impingement of light on the sample stream, and means controlling the relative flow rates of said streams into said flow chamber, which controls the radius of the sample stream, so that in the area where said light is directed on the sample stream the last-named radius may be varied proportionately to the radius of the inner surface of the sheath stream for equal and opposite refraction of light at the interfaces of said sheath stream.

2. Apparatus as defined in claim 1, wherein:

said means controlling the relative flow rates of Said streams comprises a device operative to restrict the flow of the sheath stream into the flow chamber.

3. Apparatus as defined in claim 1, wherein:

said means for flowing the sheath stream into said flow chamber comprises a constant-level reservoir establishing a head of sheath stream liquid.

4. Apparatus as defined in claim 1, wherein:

said means for flowing the sample stream into said tube inlet of the flow chamber comprises a pump upstream of the tube inlet.

5. Apparatus as defined in claim 1, wherein:

said outlet end of the flow chamber is connected to a pump.

6. Apparatus as defined in claim 1, wherein:

said means controlling the relative flow rates of the streams comprises a valve operative to vary the flow of the sheath stream into the flow chamber.

7. Apparatus as defined in claim 1, wherein:

said means for flowing the sample stream into said sample tube inlet of the flow chamber comprises a pump upstream of the tube inlet, said outlet end of the flow chamber being connected to a liquid trap through an outlet conduit, and further comprising a vacuum pump operatively connected to the last-named outlet conduit.

8. Apparatus as defined in claim 1, wherein:

the flow chamber is vertically arranged.

9. Apparatus as defined in claim 1, wherein:

the sheathed stream is directed from said outlet end of the flow chamber into a gas, and said photometric means examines the sheathed sample stream in said gas.

10. Apparatus as defined in claim 1, wherein:

the sheathed stream is directed into ambient air from said outlet end of the flow chamber, and said photometric means examines the sheathed sample stream in said ambient air.

11. Apparatus as defined in claim 1, wherein:

the flow chamber is horizontally arranged.

12. Apparatus as defined in claim 1, wherein:

said means defining a flow chamber comprises a tubular body having said restriction of the passageway portion therein.

13. Apparatus as defined in claim 1, wherein:

said means defining a flow chamber comprises a tubular body having said restriction of the passageway portion therein, said restriction enclosing the sheathed stream where light from said source is impinged on the sample stream.

14. A method for optical analysis of a sample stream including a liquid in a coaxial sheath stream liquid comprising:

providing means defining an elongated passageway portion of circular cross section in a flow chamber which portion has at one end thereof a circular restriction;

flowing a first laminar liquid stream into said passageway portion in a direction toward said restriction;

concurrently flowing in the same direction a slower moving liquid stream of cylindrical cross section and of a substantially smaller diameter than said first stream, containing a sample, into the first stream concentrically so that the latter sheaths and entrains the second stream, accelerating and narrowing it as the streams approach said restriction in a concentric relation to one another;

directing an impinging light beam of a photometer, in a direction transversely of the aforementioned direction of flow, onto the sample-containing stream for photometric analysis of the sample by a light detector of the photometer, downstream from the upstream extremity of said restriction; and

controlling the relative flow rates of the streams into said passageway portion, which controls the radius of the second or sample stream, so that in the area where said light beam impinges said sample stream the last-named radius may be varied proportionately to the radius of the inner surface of the sheath stream for equal and opposite refraction of light at the interfaces of the sheath stream.

15. The method as defined in claim 14, wherein:

the step of controlling the relative flow of the streams into said flow chamber comprises controlling said sheath stream.

16. The method as defined in claim 14, wherein:

the step of flowing the sheath stream into the flow chamber comprises flowing the sheath stream from a constant-pressure soUrce.

17. The method as defined in claim 14, further comprising introducing the sheath and sample streams into the flow chamber under positive pressure, and withstanding the sheath stream from the flow chamber under negative pressure through an outlet of the flow chamber downstream from said restriction.

18. The method as defined in claim 14, further comprising narrowly confining the sheath stream where said light beam is impinged on the sample stream.

19. The method as defined in claim 14, further comprising directing the sheathed stream into a gas from the flow chamber in a downward direction and examining the sheathed stream by the photometer in said gas.