On-line titration using colorimetric end point detection

• US 5,181,082 A
• Filed: 04/24/1990
• Issued: 01/19/1993
• Est. Priority Date: 03/30/1989
• Status: Expired due to Fees

• Current Assignee: The Foxboro Company (Schneider Electric SE)
• Original Assignee: The Foxboro Company (Schneider Electric SE)
• Inventors: Gilby, Anthony C., Meneghelli, Barry J., Cheney, M. Charles, Jeannotte, Anthony C.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Pham, Hoa Q.
• Application Number:
  US07/514,061
• Time in Patent Office: 1,001 Days
• Field of Search: 356/432-437, 356/441, 356/442, 356/338, 356/41, 250/576
• US Class Current: 356/436
• CPC Class Codes: G01N 2021/054 Bubble trap; Debubbling
• CPC Class Codes: G01N 2021/1744 either absorption or scatter
• CPC Class Codes: G01N 21/83 Turbidimetric titration
• CPC Class Codes: G01N 21/8507 Probe photometers, i.e. with optical measuring part dipped into fluid sample
• CPC Class Codes: G01N 2201/064 Stray light conditioning
• CPC Class Codes: G01N 2201/0642 Light traps; baffles
• CPC Class Codes: G01N 2201/08 Optical fibres; light guides
• CPC Class Codes: G01N 2201/084 Fibres for remote transmission

Abstract

Radiant energy is transmitted to a probe element including an interior conical reflecting surface and a fluid sample chamber. Portions of the light which have been transmitted, partially attenuated, or scattered by a fluid sample in the sample chamber are directed by at least a portion of the interior conical reflecting surface to means for collecting the transmitted, partially attenuated, or scattered light. A stilling valve incorporated into the probe element enables elimination of entrained gas bubbles from the chamber. A specific application of the probe is disclosed in which a titration analyzer is combined with electro-optic signal conversion and processing circuits and a probe according to the invention to provide titration colorimetric endpoint determination in measuring the free fatty acid content of a fluid such as a edible oil or fat.

Claims

1. In apparatus for titration of a fluid, colorimetric endpoint detection apparatus comprising:

a) means for directing radiant energy from a source into and through a chamber to an exit;

b) first pathway means for conveying radiant energy to said means for directing radiant energy through said chamber;

c) means for collecting said radiant energy exiting from said chamber;

d) second pathway means for conveying radiant energy away from said chamber exit to a detector;

e) means for generating a modulated first optical signal on said first pathway means;

f) means for generating a modulated second optical signal on said first pathway means;

g) means for detecting a colorimetric optical signal on said second pathway means;

h) means for demodulating said first optical signal;

i) means for demodulating said second optical signal; and

j) means for relating the first and second demodulated optical signals to a colorimetric endpoint,

wherein said means for directing radiant energy into and through said chamber to said exit and said means for collecting radiant energy comprise partial surfaces of at least one interior conical reflecting surface.

2. The apparatus of claim 1, wherein the means for relating includes means for determining the logarithm of the ratio of said first and second optical signals.

3. The apparatus of claim 1, wherein said chamber contains a liquid, and said radiant energy is directed through said liquid.

4. The apparatus of claim 1, further including means for moving successive fluid samples through said chamber.

5. The apparatus of claim 1, further including an optical lens element between said first pathway and said means for directing.

6. The apparatus of claim 1, further including an optical lens element between said second pathway and said means for collecting.

7. The apparatus of claim 1, wherein said radiant energy wavelength is between 3×

10^-7 and 10^-5 meters.

8. The apparatus of claim 1, wherein said chamber includes a fluid flow path and an optical path and said optical path is perpendicular to the fluid flow path.

9. The apparatus of claim 1, wherein the modulated first optical signal is modulated at a frequency of between 1.0 and 10⁶ Hertz.

10. The apparatus of claim 1, wherein the modulated first optical signal is modulated at a frequency of about 500 Hertz.

11. The apparatus of claim 1, wherein the modulated second optical signal is modulated at a frequency of between 1.0 and 10⁶ Hertz.

12. The apparatus of claim 1, wherein the modulated second optical signal is modulated at a frequency of about 1000 Hertz.

13. The apparatus of claim 1, wherein the means for generating the modulated first optical signal is a red LED.

14. The apparatus of claim 1, wherein the means for generating the modulated first optical signal is a green LED.

15. The apparatus of claim 1, wherein said sample chamber forms a sample path having a sample path length about 6 millimeters.

16. The apparatus of claim 1, wherein the fluid is an edible oil.

17. The apparatus of claim 1, wherein the fluid is an edible fat.

18. The apparatus of claim 1, wherein the detector output is nearly constant until the endpoint is reached.

19. The apparatus of claim 1, further including an automatic on-line titration endpoint analyzer.

20. The apparatus of claim 1, further including a titration vessel adapted to receive a fluid and a probe and having means for directing a sample fluid through the probe.

21. An on-line colorimetric titration endpoint detection apparatus, comprising:

a) means for directing radiant energy from a source into and through a chamber to an exit;

b) first pathway means for conveying radiant energy to said means for directing radiant energy through said chamber;

c) means for collecting said radiant energy exiting from said chamber;

d) second pathway means for conveying radiant energy away from said chamber exit to a detector;

e) means for generating a modulated first optical signal on said first pathway means;

f) means for generating a modulated second optical signal on said first pathway means;

g) means for detecting a colorimetric optical signal on said second pathway means;

h) means for demodulating said first optical signal;

i) means for demodulating said second optical signal;

j) means for relating the first and second demodulated optical signals to a colorimetric endpoint,

wherein said chamber is located in a titration vessel, and wherein said means for directing radiant energy into and through said chamber to said exit and said means for collecting radiant energy comprise partial surfaces of at least one interior conical reflecting surface.

22. The apparatus of claim 21, wherein the means for relating includes means for determining the logarithm of the ratio of said first and second optical signals.

23. The apparatus of claim 21, wherein said chamber contains a liquid, and said radiant energy is directed through said liquid.

24. The apparatus of claim 21, further including an optical lens element between said first pathway and said means for directing.

25. The apparatus of claim 21, further including an optical lens element between said second pathway and said means for collecting.

26. The apparatus of claim 21, wherein said radiant energy wavelength is between 3×

10^-7 and 10^-5 meters.

27. The apparatus of claim 21, wherein said chamber includes a fluid flow path and an optical path and said optical path is perpendicular to the fluid flow path.

28. The apparatus of claim 21, wherein the modulated first optical signal is modulated at a frequency of between 1.0 and 10⁶ Hertz.

29. The apparatus of claim 21, wherein the modulated first optical signal is modulated at a frequency of about 500 Hertz.

30. The apparatus of claim 21, wherein the modulated second optical signal is modulated at a frequency of between 1.0 and 10⁶ Hertz.

31. The apparatus of claim 21, wherein the modulated second optical signal is modulated at a frequency of about 1000 Hertz.

32. The apparatus of claim 21, wherein the means for generating the modulated first optical signal is a red LED.

33. The apparatus of claim 21, wherein the means for generating the modulated first optical signal is a green LED.

34. The apparatus of claim 21, wherein said sample chamber forms a sample path having a sample path length about 6 millimeters.

35. The apparatus of claim 21, wherein the fluid is an edible oil.

36. The apparatus of claim 21, wherein the fluid is an edible fat.

37. The apparatus of claim 21, wherein said titration vessel is adapted to receive a fluid and further including means for directing a sample fluid through the probe.

38. The apparatus of claim 37, further including means for moving successive fluid samples through said chamber.

39. In apparatus for on-line colorimetric titration endpoint detection of a fluid with a probe, including a titration vessel enclosing a chamber having an optical entry and an optical exit, the method comprising:

a) providing radiant energy from a source of radiant energy;

b) conveying said radiant energy via a first pathway means to means for directing radiant energy through the chamber;

c) directing the radiant energy into and through said chamber to an exit using partial surfaces of an interior conical reflector;

d) collecting said radiant energy exiting from said chamber; and

e) conveying said collected radiant energy via second pathway means away from said chamber exit;

f) generating a modulated first optical signal on said first pathway means;

g) generating a modulated second optical signal on said first pathway means;

h) detecting a colorimetric optical signal on said second pathway means;

i) demodulating said first optical signal;

j) demodulating said second optical signal; and

k) relating the first and second demodulated optical signals to a colorimetric endpoint;

wherein said means for directing radiant energy into and through said chamber to said exit and said means for collecting radiant energy comprises partial surfaces of at least one interior conical reflecting surface.

40. The method of claim 39, wherein the step of relating includes determining the logarithm of the ratio of said first and second demodulated optical signals.

41. The method of claim 39, wherein said apparatus further includes a titration vessel adapted to receive a fluid and the probe and having means for directing a sample fluid through the probe, the steps of directing a plurality of successive fluid samples through the probe and detecting a succession of endpoints.