Chemistry: analytical and immunological testing – Oxygen containing – Inorganic carbon compounds
Reexamination Certificate
1998-11-12
2001-11-20
Snay, Jeffrey (Department: 1743)
Chemistry: analytical and immunological testing
Oxygen containing
Inorganic carbon compounds
C436S146000, C436S178000, C422S082020, C422S090000
Reexamination Certificate
active
06319723
ABSTRACT:
BACKGROUND
An apparatus is provided which is capable of detecting a selected gas in a sample with a sensitivity of less than one part per billion (10
9
) parts; that is, with a sensitivity in the range of parts per trillion (10
12
). Methods for detecting a selected gas in a sample with a sensitivity in the range of parts per trillion are also disclosed. The apparatus and methods provide for detection of a selected gas in amounts as low as 10 parts per trillion (10
12
).
The apparatus and methods disclosed herein provide means whereby a selected gas in a relatively large sample volume is concentrated into a relatively small volume. Substantially all the gas is recovered from the sample and is concentrated in a small volume of water.
Ordinarily, concentration of a sample also results in concentration of salts and other contaminants in the sample. The presence of such salts and contaminants, that is, any component that is not the sample carrier, such as water, or the gas of interest, in the sample creates ionic interferences in the detection of a selected gas of interest in the sample, thereby reducing the sensitivity with which the selected gas can be detected.
The present apparatus and methods, however, concentrate the selected gas of interest but substantially eliminate the ionic interference one would otherwise expect from concentration of the sample. By obviating ionic interference, the present apparatus and methods permit one to use conductivity to measure only the component of the sample that is of interest. Further, the sensitivity with which the component of interest is able to be detected is vastly enhanced. Typically, the sensitivity of detection is enhanced by about at least twenty (20) fold over that of an unconcentrated control. The high sensitivity of the present apparatus and methods provides detection of the component in amounts as small as 10 parts per trillion.
SUMMARY
For purposes of illustrative example only and not intended as a limitation of the present apparatus, the apparatus is described herein using an aqueous sample. The apparatus may be adapted for the detection of a selected gas in any vaporizable sample with the proper selection of materials, operating temperatures, and detection means. Also for purposes of illustrative example only and not intended as a limitation of the present apparatus, the apparatus is described herein using carbon dioxide (CO2) as the selected gas to be detected. The apparatus and methods may be adapted for the detection of any selected gas which is soluble and ionizes in a vaporizable sample.
Among the advantages of the apparatus and methods are (1) expendable gases are not required; and (2) reagents are not required either to react or to detect the selected gas.
A liquid sample, such as a relatively large volume of water, is heated to release the dissolved gas in the sample. These gases typically include CO2, oxygen and nitrogen. A portion of the water is evaporated to form a vapor. Sources of ionic interference, such as dissolved salts and metals in the water, remain in the water and do not enter the gas phase along with the vapor. The vapor is, therefore, free of sources of ionic interference.
The vapor is condensed to form a liquid condensate in the presence of the released gases. Equilibrium solubility favors the reabsorption of substantially all of the CO2 released from the heated water into the liquid condensate. Gases, such as oxygen and nitrogen, are not reabsorbed by the condensate due to limited solubility and remain free gases. The free gases may be removed by, for example, a gas permeable, liquid impermeable membrane.
The volume of the liquid condensate is very small compared to the beginning volume of the water sample. The CO2 is, therefore, greatly concentrated in the small volume of the condensate. The condensate is also free of sources of ionic interference.
Detecting the presence and quantifying the amount of CO2 in the condensate may be accomplished by a variety of methods or devices known to those skilled in the art, such as conductivity measurement, optical measurement such as ultraviolet absorption, pH measurement, colorimetric measurement, and others. The preferred mode of detection, however, is direct conductivity measurement.
An apparatus to detect a selected gas in a sample comprising a concentrator that concentrates the selected gas without concentrating sources of ionic interference and a detector in fluid communication with the concentrator is provided. The concentrator comprises a vaporizer to evaporate at least a portion of the liquid sample to form a carrier vapor, a mist trap to remove mist resulting from incomplete vaporization, and a condenser to condense the vapor in the presence of the free selected gas, whereby the selected gas is concentrated in the condensate volume which is free of sources of ionic interference.
To detect a gas in a sample with a sensitivity in the range of parts per trillion, it is important to prevent the carry over of mist when the vapor is condensed. Mist is the result of incomplete vaporization. Mist dropplets, therefore, may contain amounts of dissolved salts or metals that would interfere with the conductivity of the condensate if the mist were carried over to the condenser and contaminated the condensate. That is, mist is undesirable because salts are carried over by the liquid droplets of the mist. Vapor, on the other hand, is desirable because in a vapor all of the liquid is converted to its gas phase and is incapable of carrying over any salts, metals, or other sources of ionic interference. The present apparatus provides a mist trap which corrects for non-ideal operation of the vaporizer and minimizes contamination of the condensate with sources of ionic interference.
Mist may be trapped, for example, by borosilicate glass beads, which provide sufficient surface area and flow characteristics, such as turbulence, so that mist droplets accumulate on the beads and run off as liquid. Liquid from the concentrator may be utilized as a blank control to calibrate the apparatus. For example, a sample flow rate of 5 ml/min may be concentrated to a concentrated analyte flow rate of 0.25 ml/min. 4.75 ml/min of the original sample water volume (from which the dissolved gases have already been released by heat) remains as effluent or run off liquid. A portion of this effluent may be concentrated identically to the analyte sample to serve as a blank. 0.25 ml/min of the effluent liquid may be utilized as a blank, and the remaining 4.5 ml/min of effluent liquid is simply drained from the apparatus.
The amount of the selected gas in the condensed blank is very low, if not virtually undetectable, because the gas was released from the liquid by heating prior to concentration of the blank sample. Such a blank control is very reliable because it is provided from the same sample liquid as the analytical sample.
The apparatus may be adapted to provide such a blank control in parallel with the analytical sample by providing a concentrator comprising a u-tube whereby the analytical sample and the blank control sample are segregated and then concentrated and detected in parallel.
The apparatus performs optimally when the concentrator is tilted from the horizontal so that liquid runs off and is separated from vapor.
METHODS OF CO
2
DETECTION
A sample that has been concentrated and vaporized as described herein is now in condition for measurement of the selected component of interest, such as carbon dioxide. The method of measuring or detecting the component of interest may be any suitable method desired.
For example, CO
2
may be detected and measured by observing changes in conductivity of a conductive material brought about by the presence of carbon dioxide. Many such methods are possible, and the most prominent of these methods known are summarized below, merely for the purpose of illustrative example and not to limit the scope of the present disclosure and claims.
U.S. Pat. No. 4,666,860, “Instrument for Measurement of the Organic Carbon Content of Water” (reference 1); and U.S
Ejzak Edward M.
Jeffers Eldon L.
Remey, III William P.
Snay Jeffrey
The Matthews Firm
LandOfFree
Parts per trillion detector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Parts per trillion detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Parts per trillion detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599619