Analysis of liquid-carried impurities by means of sparging

• US 5,218,856 A
• Filed: 07/30/1992
• Issued: 06/15/1993
• Est. Priority Date: 03/06/1992
• Status: Expired due to Fees

• Current Assignee: Axiom Analytical, Inc. (Hellma Holding Gmbh)
• Original Assignee: Axiom Analytical, Inc. (Hellma Holding Gmbh)
• Inventors: Doyle, Walter M.
• Primary Examiner(s): Noland, Tom
• Assistant Examiner(s): ROSKOS, JOSEPH
• Application Number:
  US07/922,754
• Time in Patent Office: 320 Days
• Field of Search: 73/19.1, 73/19.01, 73/64.45, 73/61.41
• US Class Current: 73/19.1
• CPC Class Codes: G01N 1/22 in the gaseous state specially adapted for biological material G01N33/497; measuring breath flow A61B5/087
• CPC Class Codes: G01N 2001/4066 using difference of solubility between liquid and gas, e.g. bubbling, scrubbing or sparging
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 33/1826 organic contamination in water

Abstract

A method for determining the concentration of individual solutes in a body of liquid, e.g., measuring contaminants in waste water. A sparging IR process is used, in which gas in the form of minute bubbles moves upwardly in a non-flowing body of liquid. The gas remove vaporized samples of the subject solutes and flows to a gas cell, where it is subjected to infrared spectrometer analysis. The true concentration of each subject solute is measured by plotting its concentration values against elapsed time, and then extrapolating back to time zero to determine the initial concentration of the solute. In addition, the rate of depletion is used to determine the ratio of vapor pressure to solubility of the solute. Replotting the original data using logarithm values can simplify the extrapolation.

Claims

1. A method for determining the concentration of a subject solute in a volume of liquid, which comprises:

providing in a container a volume of liquid including a subject solute whose concentration is to be measured;

flowing a gas through the liquid for the purpose of removing a vaporized sample containing the subject solute;

directing the vaporized sample to an analytical instrument capable of measuring gas concentration as a function of time;

measuring the flow rate of the gas;

obtaining data proportional to the concentration of the gas as a function of time, such data being measured by means of the analytical instrument;

recording said data at a plurality of spaced points in time, some of which points are sufficiently spaced from the starting time to occur when the concentration of the subject solute is not rising; and

extrapolating, from the concentration data at said plurality of spaced points in time, the value of the vapor concentration of the subject solute which would have existed at point zero except for the initial rising period of concentration.

2. The method of claim 1 in which the measurement is accomplished by an infrared spectrometer, used in conjunction with a gas cell.

3. The method of claim 2 which also comprises:

causing the vapor phase of the subject solute to be substantially in equilibrium with its liquid phase.

4. The method of claim 2 which also comprises:

converting the time-spaced recorded gas cell data into a logarithmic slope preparatory to extrapolating back to time zero to determine the initial vapor concentration of the subject solute.

5. The method of claim 4 in which the steps of the method are performed to determine the time zero vapor concentrations of a plurality of subject solutes.

6. The method of claim 2 in which the steps of the method are performed to determine the time zero vapor pressures of a plurality of subject solutes.

7. The method of claim 2 which also comprises:

fitting the depletion curve to an exponential form so as to determine a depletion rate constant.

8. The method of claim 7 which also comprises:

using the depletion rate constant, in conjunction with the measured flow rate and water volume, to determine the ratio of inherent vapor pressure to solubility for solute.

9. The method of claim 7 which also comprises:

determining the concentration of the solute in solution directly from the measured initial vapor concentration and the vapor pressure to solubility ratio.

10. The method of claim 9 in which the steps of the method are performed to determine the concentrations of a plurality of subject solutes.

11. The method of claim 8 in which the steps of the method are performed to determine the vapor pressure to solubility ratios of a plurality of subject solutes.

12. The method of claim 1 which also comprises:

causing the vapor phase of the subject solute to be substantially in equilibrium with its liquid phase.

13. The method of claim 1 which also comprises:

converting the time-spaced recorded gas cell data into a logarithmic slope preparatory to extrapolating back to time zero to determine the initial concentration of the subject solute.

14. The method of claim 13 in which the steps of the method are performed to determine the time zero vapor concentrations of a plurality of subject solutes.

15. The method of claim 1 in which the steps of the method are performed to determine the time zero vapor concentrations of a plurality of subject solutes.

16. The method of claim 1 in which also comprises:

fitting the depletion curve to an exponential form so as to determine a depletion rate constant.

17. The method of claim 16 which also comprises:

using the depletion rate constant, in conjunction with the measured flow rate and water volume, to determine the ratio of inherent vapor pressure to solubility for the solute.

18. The method of claim 16 which also comprises:

determining the concentration of the solute in solution directly from the measured initial vapor concentration and the vapor pressure to solubility ratio.

19. The method of claim 18 in which the steps of the method are performed to determined the concentrations of a plurality of subject solutes.

20. The method of claim 17 in which the steps of the method are performed to determine the vapor pressure to solubility ratios of a plurality of subject solutes.

21. A method of determining the concentration of a subject solute in a volume of liquid, which comprises:

providing in a container a volume of liquid including a subject solute whose concentration is to be measured;

flowing a gas through the liquid for the purpose of removing a vaporized sample containing the subject solute, thereby causing controlled depletion of the solute;

directing the vaporized sample to an analytical instrument capable of measuring gas concentration as a function of time;

measuring the flow rate of the gas;

obtaining data proportional to the concentration of the gas as a function of time, such data being measured by means of the analytical instrument;

recording said data at a plurality of spaced points in time, some of which points are sufficiently spaced from the starting time to occur when the concentration of the subject solute is not rising; and

using the recorded time dependent concentration data to determine the initial concentration of solute in the liquid volume.

22. The method of claim 21 in which the concentration of solute is assumed to follow an exponential time dependence.

23. The method of claim 21 in which the initial liquid solute concentration is assumed to be proportional to the area under the depletion curve.

24. The method of claim 23 in which the area under the depletion curve is determined by first fitting an exponential function to the recorded date.

25. The method of claim 23 in which the measurement is accomplished by an infrared spectrometer, used in conjunction with a gas cell.

26. The method of claim 23 which also comprises:

causing the vapor phase of the subject solute to be substantially in equilibrium with its liquid phase.

27. The method of claim 23 in which the steps of the method are performed to determine the time zero vapor concentrations of a plurality of subject solutes.