TEMPERATURE STABILIZED FLUID CALIBRATION SYSTEM

Abstract: A method and system for controlling the concentration of one or more gaseous species of interest in a sample medium throughout a range of temperatures in which a temperature related, time variable dominant independent source of the gaseous species of interest is used to control the partial pressure of one or more gaseous species of interest contained in the sample medium in a manner such that the concentration of the gaseous species of interest in the sample medium remains essentially the same over the temperature range. The source of the gaseous species of interest comprises a reservoir containing an amount of a temperature sensitive source of the gaseous species of interest. The sample and the reservoir are contained in separate fluid-tight, gas-permeable enclosures further confined by a common substantially gas-tight enclosure.

Description: TEMPERATURE STABILIZED FLUID CALIBRATION SYSTEM BACKGROUND OF THE INVENTION I. Field of the Invention The present invention is directed generally to a packaged, temperature stabilized reference or calibration system and, more particularly, to a method and system for stabilizing the concentration of a dissolved gaseous species of interest in a calibration sample medium by the provision of a reversible compensating reservoir or independent temperature dependent source of the dissolved species of interest which compensates the temperature dependency in the sample medium over the useful temperature range of the system. II. Description of the Related Art The field of diagnostic medicine is fast becoming more sophisticated and complex. The ability to make rapid or immediate diagnostic determinations characteristic of the current condition of a patient so that the proper emergency steps may be taken in a timely manner to improve or stabilize the condition of the patient, for example, during surgery or during the treatment of traumatic injury has become very important. The partial pressures of oxygen (P0 2 ) and carbon dioxide (PC0 2 ) in the blood are examples of extremely important instantaneous indications of respiratory deficiency, efficiency of inhalation therapy, renal function and other vital bodily processes. These measurements are made utilizing stationary clinical laboratory instruments which measure the parameters at a specific temperature and which are periodically calibrated to operate by a calibration system which is accurate only at a specific temperature. Calibration and use of the instruments are thus keyed to opening the calibration fluid, calibrating the instrument, and operating the instrument at a specific known temperature, e.g., 37°C. The specific composition of typical control or calibration fluid systems is such that the reference or known equilibrium partial pressures of oxygen and carbon dioxide are temperature dependent and so occur only at the specific calibration temperature, and opening or using the calibration system at a temperature other than the designed temperature may introduce a decided amount of error into the readings. Alternatively, gaseous C0 2 and 0 2 can be used to calibrate the instrument, but that requires the need for compressed gas cylinders for storage of the gases. A definite need exists for a calibration system which is small, easily portable and less temperature dependent to thereby enable the calibration of such devices as diagnostic systems of the class described to be accurately accomplished over a reasonable range of ambient temperatures. This, of course, applies to the temperature stabilization of the amount of contained dissolved or dissociated gaseous species of interest in a variety of media for a variety of applications. In this regard, particularly with respect to oxygen, one approach that has been used involves the use of relatively inert fluids which have the ability to dissolve rather large amounts of oxygen and which are stable with respect to biological media. One class of such compounds consists of fluorinated organic compounds known as perfluorocarbons. Certain other systems or approaches have been proposed to stabilize and buffer the partial pressure of species such as carbon dioxide, normally in an aqueous phase, which, when combined, may be emulsified with the perfluorocarbon phase. In a co-pending application Serial No. 07/604,666, filed October 26, 1990 and assigned to the same assignee as the present invention, one approach is disclosed in which a perfluorocarbon-based system is used which contains sufficient perfluorocarbon to give it ability to remain stable with respect to the relative concentration of dissolved oxygen over a range of ambient temperatures for example, between about 20°C and 30°C. An aqueous solution phase, which contains a specific amount of one or more C0 2 complexing agents, such as ethylene diamine, HC0 3 " , Ca++ and OH " , or the like, as agents to buffer the partial pressure of carbon dioxide in the aqueous phase is used to reduce sensitivity to changes in temperature with respect to complexed C0 2 . To the extent any information is deemed necessary to the proper completion or explanation with regard to material contained in the present application, such may be deemed incorporated by reference herein. The present invention involves a simple and accurate method for reversibly controlling the partial pressure of a contained dissolved or dissociated gaseous species of interest in a medium which exhibits time/temperature stability that would be applicable to a species such as carbon dioxide. Thus, for example, the design of a pre¬ packaged calibration system which is usable to quickly and accurately calibrate an instrument over a range of ambient temperatures is now possible. SUMMARY OF THE INVENTION In accordance with the present invention, it has been found possible to create a packaged system that can be used to provide a stable concentration of a gas in a sample medium despite changes in the temperature of the sample within a reasonable range of ambient temperature. The system involves the use of an additional separate reversible equilibrium compensating source containing an amount of the gas or gases of interest. The additional source or "reservoir" provides the ability to control changes in the partial pressure of the gas or gases of interest in the atmosphere of the package including the atmosphere contacting the sample liquid. The changes in partial pressure can be tailored to exactly compensate for changes in the solubility of the gas or gases of interest in the calibration sample over a designed range. The system can also be used to control change in the partial pressure of a species of interest as a function of temperature change. Both the sample medium enclosure and the reservoir are contained in liquid-tight, gas-permeable enclosures within an outer, common enclosure such that gaseous species may be exchanged with respect to the common atmosphere of the sealed outer enclosure. The reservoir equilibrium is designed to be more temperature dependent and its enclosure more permeable for the gas(es) of interest than the sample and, therefore, to react more quickly to temperature changes and thus to dominate changes produced in the sample container. Temperature changes which produce an increase or decrease in the partial pressure of a species of interest in the reservoir medium will cause a corresponding increase or decrease in the partial pressure of that species in the common atmosphere. This, in turn, anticipates and compensates changes that otherwise would occur thereafter in the sample. In operation, using the general case as an example, as the temperature of the environment and thus of the entire package including the sample and reservoir rises, the solubility of the gaseous species of interest in the sample decreases. This also occurs in the reservoir. To keep the concentration of the gas or gases of interest from changing in the sample, the reservoir expels amounts of the gas or gases into the package atmosphere anticipating the reaction of the sample by raising the partial pressures of these gases in the common atmosphere and thereby preempting the thermodynamic driving force for the gases to leave through the permeable shell of the sample container. In other words, the gas or gases of interest are preferably released and permeate the shell of the reservoir and increase the partial pressure of these species in the package atmosphere at a somewhat faster rate than they are lost from the sample medium such that the thermodynamic driving force for the gases to leave the sample and diffuse through the wall of the sample enclosure is eliminated. Conversely, if the system cools and the solubility of the gases of interest in the sample medium increases, the reservoir acts to reverse the phenomena of the heating mode and be reabsorbed into the reservoir medium from the package atmosphere at a somewhat faster rate than the reabsorption in the sample medium thereby lowering the partial pressure of the gas or gases of interest in the common atmosphere to eliminate any driving force for the gas or gases of interest in the common atmosphere to permeate the sample enclosure and dissolve in the sample medium. This preserves the resulting concentration of each such species of interest in the sample medium regardless of the direction of temperature change within a designed limited ambient temperature range. Typically, the sample medium and/or the reservoir medium are solutions of selective solvents with or without complexing agents or buffers. In the case where C0 2 is the species of interest, both the reservoir and the sample media may be aqueous solutions of C0 2 . A system where the sample pH is 7.4 and the reservoir is buffered to a pH of 8.6, for example, exhibits good temperature/concentration or (pC0 2 ) stability in the 20°C to 30°C range; but (pCO.,) is quite temperature dependent for a reservoir pH above 9.0. The invention, however, is not limited to the use of solutions as media. Gels or even solids exhibiting the properties required with respect to taking on and giving up the gaseous species can be employed. Gels may be based on natural materials such as collagen or agarose or based on synthetic materials such as polymers of a desired average molecular weight. Solids may include higher average molecular weight polymers or other materials which reversibly accept the species of interest. Of course, the sample medium may differ from or be the same type of medium as that of the reservoir. The material may undergo a phase change such as liquification at a temperature just above ambient. In a preferred embodiment, the typical environment of the invention is a sealed package, which might be a flexible poly-foil pouch, gas-filled, but not pressurized above atmospheric pressure, provided in which the sample or calibration medium is contained in a separate enclosure within the pouch such as a sealed, gas-permeable polymeric container. An additional liquid-tight, gas-permeable enclosure is provided in the form of the reservoir containing the reversibly available additional amount or amounts of the gas or gases of interest. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like numerals are utilized to designate like partes throughout the same: FIGURE 1 is a graphical representation of the partial pressure of carbon dioxide (pC0 2 ) of the sample medium, measured at 37°C vs. the temperature of the sample when it was removed from the package, for a system with and without a compensating reservoir; FIGURE 2 is a graphical representation of the pH of the sample medium measured at 37°C vs. the temperature of the sample when it was removed from the package, for a similar system to that of Figure 1 with and without a compensating reservoir; FIGURE 3 represents a theoretical response surface based on thermodynamic properties of the species of interest C0 2 in which the pC0 2 of the sample medium analyzed at 37°C is plotted with respect to the temperature of the sample at which it was removed from the package and one of the variables associated with the reservoir in the package, namely, the reservoir pH; and FIGURE 4 is a schematic representation of a possible system construction. DETAILED DESCRIPTION It will be appreciated that the concepts of the present invention can be modeled from thermodynamic principles for gaseous species and solutions of known reversible solubilities and permeabilities. As an example, the preferred or illustrative embodiment of this detailed description contemplates a system in which the gas carbon dioxide (C0 2 ) is the dissolved or complexed calibration species of interest, the concentration of which is sought to be controlled. The C0 2 is normally contained in a buffered aqueous solution which, for blood gas calibration or control, is used together with an amount of a perfluorocarbon-based medium containing oxygen, sealed in a rather slender sample tube in which the two phases are in intimate contact but do not mix. The sample tube, which may be Tygon ® (trademark of United States Stoneware Company) is further contained in a poly-foil substantially gas-tight, flexible pouch. The pouch is one which describes a flexible package which may be layered polyethylene with an aluminum foil layer or layers to provide a substantially gas-tight system with an internal pressure about equal to the external atmospheric pressure but not inflated above it, as is the case with a balloon. Of course, the system could also be designed using a rigid wall container such as a glass ampule as the package. The aqueous sample is typically 500 micro-liters of an aqueous phosphate buffer at pH 7.4. A larger, possibly 5 ml, bicarbonate and carbonate containing aqueous solution in the pH range of 8.0 to 9.0 is also in the package in a separate liquid-tight gas-permeable sealed bag made of polyethylene or other gas-permeable material to serve as the reservoir. The reservoir solution may also contain a buffer salt to give it a more temperature dependent pH. As the temperature of the system of this embodiment increases, the pH of the reservoir decreases, and this, in combination with the decrease in the solubility of C0 2 in the warmer medium, shifts the equilibrium of the C0 2 system consisting of the reservoir and the common or package environment toward a higher partial pressure of C0 2 in the package atmosphere. The increase in package partial pressure prevents the sample from losing C0 2 to the gas phase of the package environment through the Tygon tube. Conversely, if the temperature of the package is decreased, the pH of the reservoir and the solubility of C0 2 in the reservoir will increase at a greater rate than that in the sample. This will lead to a lower partial pressure of C0 2 in the common atmosphere or gas phase of package in relation to that of equilibrium in the sample such that C0 2 will not have a tendency to migrate from the package into the sample. Thus regardless of the direction of the temperature change, the resulting concentration of C0 2 in the sample will not change with changing temperature over the selected range. In an alternate embodiment, the temperature dependence of the solubility of C0 2 in the reservoir medium can be utilized without the additional effect of the temperature dependence of the pH of the reservoir solution. It is necessary, however, that the capacity of the reservoir for the gas be greater than that of the sample to insure that the reservoir will lead and dominate the gas phase of the package throughout the temperature range of interest. Whatever the thermodynamic temperature dependent property or properties selected as the criteria for the reservoir is, the basic kinetic requirement for the system remains that the reservoir needs to respond somewhat faster to the changes in temperature than the sample environment. This can be based on relative volumes, composition, relatively solubilities of the gas or gases of interest in the reservoir and in the sample, pH control, or even the utilization of different permeabilities with respect to the sample and reservoir enclosures such that the gas or gases of interest diffuse in and out of the reservoir enclosure at a higher rate than they do with respect to the sample container. It will further be appreciated that separate internal containers may be provided for each calibration species if desired or that all of them may be contained in a single solution or emulsion to address a particular application of the concept. Systems formulated in accordance with the teachings of the present invention can be formulated to exhibit stable overall concentrations with respect to the gases of interest within a range of ambient temperatures, such as between about 20°C and 30°C. In practical terms, this means, for example, that a sample calibration system can be opened and exposed to the ambient environment at any temperature within that range and used within a reasonable time without fear of calibration inaccuracy. Thus, in accordance with the present invention, the equilibrium solubility of any volatile constituent of a solution at a given temperature can be artificially controlled by compensating for anticipated changes in the partial pressure of that constituent in the vapor phase above the solvent medium in relation to the effects of temperature. The invention provides a means of offsetting the extreme temperature sensitivity of critical concentrations of dissolved gaseous species in liquids, gels or solids. In accordance with the illustrative embodiment, the dissolved species of interest is exemplified by carbon dioxide (C0 2 ) and its relation to temperature and pH in an aqueous solution. It is contemplated, however, that such principles can be extended by those skilled in the art to produce similar results with respect to many other gaseous species of interest in the same and other types of solutions. One environment of the system is shown generally in Figure 4 and includes an outer enclosure or package designated by 10 which may be a flexible pouch-type package of poly-foil which has an internal pressure about equal to atmospheric pressure and which is generally impervious to the passage of gases, especially atmospheric molecules including nitrogen, oxygen and carbon dioxide. The package 10 contains a further enclosed sample reservoir, shown generally at 11, which, in turn, contains separate liquid calibration solutions or phases 12 and 13 in intimate contact but not emulsified or mixed. In this respect, phase 12 may contain oxygen reversibly dissolved in a perfluorocarbon substance operating as a source of 0 2 in the calibration system. Typically, for blood gas analysis, for example, the p0 2 is in the range of 10 to approximately 200 mm Hg. The phase 12, then, is an amount of C0 2 in reversible equilibrium with water which may contain certain additives, and typically contains a phosphate buffer which establishes the solution at about pH 7.4. The preferred rang'., of partial pressures for C0 2 (pC0 2 ) is from about 5 to about 100 mm Hg. The volumes for the calibration solutions are typically 500 micro-liters (μl) . The envelope or ampule 10 further contains an additional separate enclosure in the form of a polyethylene reservoir, or the like, 14. The reservoir is typically much larger volume, e.g., 5 milliliters (ml) v. 500 μl of a bicarbonate and carbonate containing aqueous solution buffered in the pH range of about 8.0 to 9.0. It serves as a comparatively large reservoir of carbon dioxide. The reservoir solution may also contain a buffer salt which produces a temperature dependent pH in the reservoir. The reservoir container enclosure 14 should have a higher permeability for the C0 2 or other gaseous species of interest than the sample envelope 11 so that the relative partial pressure of the species of interest in the envelope 10 outside of both internal containers is dominated both in terms of size and time by the reaction of the material in the reservoir 14 rather than that in the sample tube 11. As recited above, the general thermodynamic design of the compensating system is such that as the temperature of the package and the aqueous sample solution 13 increases and the solubility of the C0 2 in the sample decreases; the reservoir 14 expels C0 2 gas into the package atmosphere raising the partial pressure of the C0 2 in the package atmosphere and thereby eliminating the compositional thermodynamic driving force for C0 2 to leave the sample enclosure 13. Conversely, when the system is cooled, the reservoir reverses its action and receives C0 2 gas from the package atmosphere thereby lowering the partial pressure of the C0 2 in the package and eliminating any driving force for C0 2 in the package atmosphere to dissolve in the sample. So long as the operation of the reservoir system dominates the atmosphere of the package, both in terms of size and time, the system functions very well. This is depicted in Figure 1 where it shows an almost constant pC0 2 for data points in the range of about 15°C to 30°C utilizing the reservoir and illustrates the sharp contrast or radical change in pC0 2 without the reservoir. Likewise, Figure 2 illustrates the same principle with respect to pH over the same temperature range. Without the reservoir, the pH is seen to increase with the loss of C0 2 from the solution as the temperature is raised from 15°C to 30°C. Concepts of the present invention further represented as a mathematical model for a CO., system from known thermodynamic data are shown in the form of the complex surface generated in Figure 3. That Figure represents a system with 500 micro-liters of buffered aqueous as the calibration sample and 5 ml of reservoir at a higher pH (approximately 8.5 vs. 7.4). The other two axes represent the temperature at which the package was theoretically opened and the pC0 2 of the sample when analyzed at 37°C. The plot suggests that the pH of the reservoir significantly affects the pC0 2 of the sample at the analysis temperature. A pH in the 8.5 range in the reservoir appears to eliminate the temperature dependence of the pC0 2 in the sample, while it is clear that systems with reservoir pHs of 7 or 10, for example, obviously show temperature dependent pC0 2 values. It is now possible to design a system, for example, that as the temperature of the system increases, the pH of the reservoir decreases and this, in combination with a decrease in the solubility of C0 2 in the reservoir shifts the equilibrium of the C0 2 system consisting of the reservoir and the package environment toward a much higher partial pressure C0 2 in the package. This increase in partial pressure prevents the sample from losing C0 2 to the gas phase. If the temperature of the package is thereafter decreased, the pH of the reservoir and the solubility of C0 2 in the reservoir increase, lowering the partial pressure of C0 2 in the common gas phase. Regardless of the direction of temperature change, then, the resulting concentration of C0 2 in the sample does not change with changing temperature. If the reservoir does not dominate the sample in terms of time rate of change, the concentration of C0 2 in the sample may not be at its equilibrium value shortly after a temperature change. It will return to the desired level only after the entire system including the gas phase, the sample and the reservoir have reestablished equilibrium at the new temperature. A successful system can also be designed which makes use of the temperature dependence on the solubility of C0 2 in the reservoir only and in which the pH of the reservoir need not be temperature dependent. The principles can also be adapted for use in systems having a plurality of dissolved gases, the partial pressure of one or more of which are sought to be controlled. This may include a plurality of samples and a plurality of compensating reservoirs in a single envelope. Of course, concentration, additives and buffers can be designed and tailored specifically to one's needs in such a situation. Additional parameters which may be varied in accordance with the principles of the invention include the volume of the gas phase in the envelope, the relative volume and composition of the reservoir, solubility of gas in the reservoir, composition of the sample, and the solubility of gas in the sample. This invention has been described in this application in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be further understood that the invention can be carried out by specifically different equipment and devices and that various modifications can be accomplished without departing from the scope of the invention itself.

Claims: A ENDED CLAIMS [received by the International Bureau on 27 May 1993 (27.05.93); original claims 1-20 replaced by amended claims 1-20 (6 pages)] 1. A method of controlling the concentration of a gaseous species of interest in a reference medium as a predetermined function of temperature throughout a selected temperature range comprising steps of: separating the reference medium containing the gaseous species of interest in a gas-permeable reference enclosure; providing a separate temperature dependent source of the gaseous species of interest comprisng a reservoir containing the gaseous species of interest outside but in communication with the gas permeable reference enclosure, the reservoir comprising a reservoir medium containing the gaseous species of interest maintained in a manner that provides a temperature sensitive source of amounts of the gaseous species of interest; enclosing the reference medium and the source in a substantially gas-tight hollow structure in the orm of a common enclosure for both the reference enclosure and the reservoir surrounded by a gas phase that forms a common atmosphere; and formulating a temperature dependence in the reservoir in which the partial pressure of the gaseous species of interest contacting an outer surface of the gas-permeable reference enclosure varies as a function of temperature such that the concentration of the gaseous species of interest in the reference medium varies according to the desired function of temperature over a selected temperature range. 2. The method of claim l wherein the reservoir is formulated such that the partial pressure of the gaseous species of interest varies in a manner which preempts changes in partial pressure of the gaseous species of interest within the reference enclosure to sufficiently Keep the concentration of the species of interest in the reference medium within the reference enclosure substantially constant over the selected temperature range. 3, The method of claim 1 wherein at least one of the reservoir and the gas-permeable reference enclosure includes a gas phase. 4. A method of controlling the concentration of a gaseous species of interest in a reference medium essentially as a predetermined function of time variable temperature or substantially constant throughout a range of time variable temperatures comprising steps of: separating the reference medium containing an amount of the gaseous species of interest by a gas- permeable reference enclosure means; providing a separate temperature dependent source of the gaseous species of interest comprising a gaβ permeable reservoir enclosure having a reservoir medium containing an amount of the gaseous species of interest; providing a substantially gas-tight hollow structure in the form of a common enclosure for containing both the reference enclosure and the reservoir enclosure surrounded by a gas phase that forms a common atmosphere; formulating the reservoir and the contents thereof in a manner such that changes in temperature related equilibrium solubility of the species of interest in the reservoir medium produce an exchange of amounts of the species of interest to and from the common atmosphere thereby changing the concentration of the species of interest in the common atmosphere contacting the gas-permeable reference enclosure means in a manner that controls changes in equilibrium concentration of the gaseous species of interest within the reference medium and such that the partial pressure of the gaseous species of interest in the common atmosphere contacting the gas- per eable reference enclosure means dominates, as a function of temperature, the concentration of the gaseous species of interest in the reference medium remaining essentially controlled according to the desired function of temperature over the selected temperature range. 5. The method of claim 4 wherein the gas-permeable reference enclosure means comprises, at least in part, a gelled solvent for the gaseous species of interest. 6. The method of claim 4 wherein control by the reservoir is based on the existence of one or more conditions selected from the group consisting of a higher permeability of the reservoir enclosure to the gaseous species of interest, more rapid changes in the solubility of the species of interest in the reservoir enclosure with respect to given changes in temperature, higher rate of change in the solubility of the species of interest in the reservoir enclosure in relation to given changes in temperature, and a reservoir volume larger than that of the reference medium. 7. The method of claim 4 wherein at least one of the reservoir and the gas-permeable reference enclosure includes a gas phase. 8. The method of claim 4 wherein the concentration of the gaseous species in the reference medium is held essentially constant over the selected temperature range. 9. The method of claim 4 wherein the reference medium and the reservoir medium are selected f om the group consisting of liquids, gels and solids, with or without buffers or complexing agents. 10. The method of claim 4 wherein the reference medium and the reservoir medium contain liquid solvents for the species of interest. 11. The method of claim 4 further comprising the step of controlling the concentration of a plurality of gaseous species of interest. 12. The method of claim 4 wherein the solubility of the species of interest changes more rapidly in the reservoir enclosure than in the reference enclosure in response to a temperature change in the selected temperature range. 13. The method of claim 4 wherein the solubility of the species of interest in the reservoir enclosure exhibits a greater change in relation to given changes in temperature than that in the reference medium in the selected temperature range. 14. The method of claim 4 wherein the reservoir volume exceeds the sample volume. 15. The method of claim 4 wherein the species of interest is carbon dioxide (C0 2 ) . 16. The method of claim 15 wherein the reservoir medium is an aqueous medium having a pH ≥ 8.0 and the sample medium is an aqueous medium with a pH < 7.7. 17. The method of claim 8 wherein the species of interest is carbon dioxide (C0 2 ) . 18. The method of claim 17 wherein the reservoir medium is an aqueous medium having a pH ≥ Θ.O and the sample medium is an aqueous medium with a pH ≤ 7.7. 19. A method of maintaining the concentration of a gaseous species of interest in a reference medium con ined in a gas-permeable reference enclosure substantially constant in a selected time variable temperature range comprising steps of: con ning the reference medium containing the gaseous species of interest in a gas-permeable reference enclosure including a gas phase; providing a separate source of the gaseous species of interest comprising a reservoir having a reservoir medium containing a temperature dependent amount of the gaseous species of interest confined in a gas-permeable reservoir enclosure including a gas phase; enclosing the reference medium and the source in a substantially gas-tight hollow structure in the form of a common enclosure for containing both the reference enclosure and the reservoir enclosure surrounded by a common atmosphere; constructing the reservoir and formulating contents thereof in a manner such that changes in temperature related equilibrium partial pressure of the gaseous species of interest in the reservoir enclosure cause exchange of amounts of the gaseous species of interest across the gas- permeable reservoir enclosure with the common atmosphere thereby changing the concentration of the species of interest in the common atmosphere contacting the outer surface of the gas-permeable reference enclosure such that the partial pressure of the gaseous species of interest in the common atmosphere contacting the outer surface of the gas-permeable reference enclosure dominates as a function of temperature in a manner such that the concentration of the gaseous species of interest in the reference medium remains essentially constant over the selected temperature range. 20. A packaged multi-phase reference system containing controlled amounts of at least one gaseous species of interest comprising: a reference medium containing known reference concentrations of each gaseous species of interest; a gas-permeable reference enclosure retaining the reference medium containing the gaseous species of interest; a separate temperature dependent source of the gaseous species of interest comprising a reservoir having a reservoir medium containing an amount of the gaseous species of interest in gas-permeable relation to the reference medium; a substantially gas-tight hollow structure in the orm of a common enclosure for containing both the reference enclosure and the reservoir surrounded by a gas phase that forms a common atmosphere; the reservoir functioning via the common atmosphere to vary a partial pressure of the gaseous species of interest contacting the gas-permeable reference enclosure as a function of temperature such that the reference concentration of the gaseous species of interest in the reference medium varies according to a desired function of temperature over a selected temperature range. STATEMENT UNDER ARTICLE19 The amended claims 1-20 are submitted to replace the originally submitted claims 1-20. The modifications attempt to clarify and more appropriately describe the invention. The International Search Report cites two documents as category "Y" as follows: USA 4 960 708 (Zowtiak et al, issued 02 October 1990, particularly with reference to column 2, lines 25-50), and USA 4 851 195 (Matthews et al, 25 July 1989, with particular reference to column 3, lines 23-25). It is the applicant's position that the substance of the present invention differs fundamentally from the cited references. Zowtiak et al utilize a single sealed, flexible, gas and liquid-impermeable container enclosing but a single phase (liquid) of an aqueous solution containing known concentrations of oxygen (0 2 ) or carbon dioxide (C0 2 ) or both, maintained at a pressure above the total of the partial pressures of the 0 2 and co 2 . There is no gas phase at all and the system contains no separate source of either species of interest to maintain equilibrium. Equilibrium against barometric pressure change is maintained only by over-pressure and the absence of a gas phase. No separate temperature dependent source of the gases is provided to compensate for fluctuations in temperature. T h e preβent invention, in contrast, optionally includes a gas phase in exchange relation to both a reference system containing the gaseous species of interest to be controlled and a separate temperature dependent controlling source of the gaseous species of interest (reservoir) . A gas-permeable reference enclosure contains the reference system and it and the reservoir are contained in common enclosure that defines a common gas phase or atmosphere which allows a free gas exchange between the common atmosphere and both the reference enclosure and the reservoir, Only the common enclosure is essentially gas- impermeable. It is the temperature-responsive exchange back and forth between the reservoir, the common atmosphere and the reference media enclosure that provides the controlled stability for the reference system of the present invention. The present invention is decidedly dependent on the functioning of an equilibrium gas phase in which the partial pressure of each gas of interest in the common atmosphere is controlled by the reservoir or separate source and it, in turn, controls the temperature/concentration relation of the dissolved species of the gas of interest in the reference media. This depends on a continual exchange between the common atmosphere and the reservoir in order to control the exchange between the common atmosphere and the reference system. Matthews et al show that an integral component of a co 2 sensor can include a gel. The present invention, however, is not directed to sensing C0 2 or any sensor function per se but rather to controlling a medium which might be used to calibrate a sensor. This is considered to be substantially different from the use of a gel in the formulation of optical gas sensors as in Matthews et al. Where the location of the gel in the Matthews et al reference is between an optical fiber and a containment membrane. Its function is to stabilize fluorescing entities to improve the quality of the sensor. The development of gas or other sensors appears quite different and involves art diverse from that involved in the development of calibration systems. The problems faced, approaches and uses of components are quite different. With respect to the "Y" combination, it is believed that neither of the references contains any information or disclosure which would lead one to stabilize a reference or calibration system in accordance with the present invention. The present invention emphasizes the use of rather than the elimination of the gas phase, and the use of a gel merely may be preferred aε a medium for dissolving the gaseous species of interest or even providing the gas-permeable separation barrier. The additional references cited under category A are not considered to be particularly relevant. They involve the use of natural substances, such as blood cells or hemoglobin as part of specially formulated reference fluids (Sim onds et al, USA Patent 4 469 792) and a control for standard for quality control (Louderback Patent USA 4 126 575) . These involve entirely different types of solutions with dissimilar concerns. It is believed that the present statement presents an explanation which will be helpful in future examination of the claims during the continued prosecution of this PCT application.

Inventors: DEETZ DAVID W, MORRIS RUSSELL L, DEETZ, DAVID, W., MORRIS, RUSSELL, L.
Applicants: DIAMETRICS MEDICAL INC, DIAMETRICS MEDICAL, INC.
Application year: 1993
Main classification: G01N31
IPC codes: A61B5, G01N33