US3765841A - Method and apparatus for chemical analysis - Google Patents

Method and apparatus for chemical analysis Download PDF

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US3765841A
US3765841A US00169687A US3765841DA US3765841A US 3765841 A US3765841 A US 3765841A US 00169687 A US00169687 A US 00169687A US 3765841D A US3765841D A US 3765841DA US 3765841 A US3765841 A US 3765841A
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sample
signal
time interval
fixed time
reagent
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G Paulson
R Ray
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Beckman Coulter Inc
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Beckman Instruments Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
    • G01N27/3271—Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/17—Nitrogen containing
    • Y10T436/171538—Urea or blood urea nitrogen

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  • Hinderstein [5 7] ABSTRACT A method and apparatus for determining the concentration of a component in a sample, i.e. the concentration of urea in biological fluids, such as blood serum, wherein the sample, upon being introduced into solution with a reagent, reacts therewith, causing a continuing change in a characteristic of the solution, and wherein the rate of the reaction is indicative of the concentration of the component in the sample.
  • a sensor is provided for monitoring the characteristic of the solution and for generating a first electrical output signal proportional thereto.
  • Differentiator circuit means are provided for producing a second electrical signal proportional to the time derivative of the first signal, the time derivative signal being indicative of the concentration of the component in the sample.
  • the present invention relates to a method and apparatus for chemical analysis and, more particularly, to a method and apparatus for the quantitative determination of the concentration of substances which are reactive with enzymes.
  • One general area within the field of this invention is the chemical analysis of biological substances to determine the chemical composition thereof. For example, a common procedure is to determine the concentration of glucosein blood or urine since the concentration of glucose in these body fluids is indicative of the operation of various fundamental body functions. Another common procedure is to determine the concentration of urea in blood serum since the concentration of urea in this body fluid is indicative of the operation of the kidneys.
  • colorimetric chemical analyzing systems are capable of producing accurate indications of the concentration of a component in a sample
  • problems associated therewith In the first instance, most colorimetric techniques are subject to large disturbances and interferences which may provide grossly inaccurate indications.
  • the strong oxidizing agent, hydrogen peroxide can react with other reducible substances and other impurities interfere with the peroxide-peroxidase reaction causing aloss in specificity and accuracy.
  • availabe colorimetric and analyzing systems require measurement of the intensity of the color of the product at the completion of the reaction. Accordingly, the analysis is time consuming.
  • the assay often cannot be conducted without deproteinization of the blood samples or prepurification of urine samples.
  • reaction that occurs when blood, containing urea, is mixed with the enzyme urease.
  • the non-ionic urea in the serum reacts with the enzyme urease to form ionic ammonium .carbonate.
  • the rate at which ammonium carbonate is formed is proportional to the quantity of urea in the serum .sample. Since ammonium carbonate is ionic, the AC conductivity of the solution will change at a rate proportional to the quantity of urea present.
  • the recorded rate signal results in a sharply defined peak corresponding to apparent maximum rate which is directly proportional to initial concentration.
  • the apparent maximum rate is obtained in a relatively short time interval, thus saving analysis time and permitting more samples to be run in the same time interval.
  • the invention does not require preliminary purification or deproteinization of blood or urine samples, gives highly accurate results on an absolute basis and is insensitive to many impurities known to interfere with many other analytical procedures.
  • the Sternberg analyzer determines the quantity of glucose in blood or urine by using an oxygen sensor to measure the rate of oxidation of glucose with glucose-oxidase to produce hydrogen peroxide and gluconic acid.
  • the reaction may be controlled so that there is no initial change in oxygen level when the sample is introduced into solution with the reagent.
  • an oxygen sensor cannot be utilized to monitor the reaction.
  • the present method and apparatus is capable of rapidly determining the concentration of a component in a sample, such as biological fluids.
  • the present apparatus is rapidly set up and put into operation, makes the determinations rapidly and accurately, uses a small sample size, and measures true concentration.
  • the present method and apparatus relies on the measurement of true instantaneous rate at a very early stage of a reaction before the reactant is consumed and, even with gaseous reactants, the reactions can be open to the atmosphere since the indicative data is collected before back diffusion of gas into the solution can influence the results.
  • the present method and. apparatus recognizes that introduction of the sample into solution with the reagent may cause an instantaneous change in the characteristic of the solution which is being measured. Accordingly, the present system inhibits measurement of the rate of change signal during a predetermined, fixed time interval starting with introduction of the sample into the reagent, which time interval is sufficient to eliminate the effect of the instantaneous change in the solution as well as to permit thorough mixing of the sample with the reagent. lmmediately after the termination of the fixed time interval, the present system measures the value of the rate of change of the reaction.
  • the present invention contemplates a method and apparatus for determining the concentration of a component in a sample, i.e. the concentration of urea in biological fluids, such as blood serum, wherein the sample, upon being introduced into solution with a reagent, reacts therewith, causing a continuing change in a characteristic of the solution, and wherein the rate of the reaction is indicative of the concentration of the component in the sample.
  • a sensor is provided for monitoring the characteristic of the solution and for generating a first electrical output signal proportional thereto.
  • Differentiator circuit means are provided for producing a second electrical signal proportional to the time derivative of the first signal, the time derivative signal being indicative of the concentration of the component in the sample.
  • a large, instantaneous change in the characteristic of the solution being measured also takes place when the sample is added. Therefore, means are provided for measuring the value of the time derivative signal after a predetermined, fixed time interval from introduction of the sample into the reagent so as to eliminate the effect of the instantaneous change in the characteristic of the solution and topermit thorough mixing of the sample with the reagent.
  • the present invention is capable of handling a large instantaneous change in the solution which is of little or no interest followed by a smaller and slower change which is indicative of the concentration of the component of interest.
  • Another object of the present invention is the provision of a novel electrode for measuring AC conductance.
  • FIG. 1 is a graph illustrating oxygen (0 concentration as a fimction of time (t) in a glucose oxidaseglucose reaction
  • FIG. 2 is a graph illustrating the time derivative of oxygen concentration (dO /dt) for reaction of FIG. 1;
  • FIG. 3 is a graph illustrating AC conductivity (C) as a function of time (t) for certain enzyme reactions, such as a urea-urease reaction;
  • FIGS. 4-6 are graphs illustrating the rate of change of AC conductivity (dC/dt) versus time (t) for the graph of FIG. 3 and showing three alternative methods for measuring the value of the rate of change signal after a predetermined, fixed time interval from introduction of the sample into the reagent;
  • FIG. 7 is a simplified block diagram showing a preferred embodiment of apparatus constructed in accordance with the teachings of the present invention.
  • FIG. 8 is a partial block diagram showing a possible modification to the apparatus of FIG. 7;
  • FIG. 9 is a view, partly in section, showing a preferred embodiment of sample cup for use in the apparatus of FIG. 7;
  • FIG. 10 is a side elevation view of a preferred embodiment of sensor for use in the apparatus of FIG. 7;
  • FIG. 11 is an end elevation view of the sensor of FIG. 10.
  • the level ofoxygen 0 may have a value 0
  • the level of oxygen follows a curve 10 which decreases asymptotically.
  • an electrical signal may be derived which is the time derivative of the oxygen concentration signal and thus proportional to the time rate of change of concentration of oxygen.
  • curves 11, I2 and 13 represent three possible outputs of such differentiating circuit.
  • the time derivative increases to a maximum value and then decreases as the rate of reaction decreases.
  • the maximum value of the output time rate of change signal is directly proportional to the 7 initial concentration of glucose and provides a convenient, rapid and accurate output signal.
  • curve 15 shows the change in AC conductance with time measured by a conductance sensor positioned within a sample cup.
  • the AC conductance has a value C O.
  • the AC conductivity jumps to a value C becuase of the conductivity of the reagent.
  • the conductivity continues to increase asymptotically to a maximum value C the change in conductivity from C to C being caused by the formation of ammonium carbonate.
  • Sample cup 21 in which the enzyme reaction occurs.
  • Sample cup 21 may have any one of many known configurations and includes means for permitting introduction of the reagent and the sample as well as means for insuring thorough mixing of the solution. A preferred embodiment of sample cup 21 will be described hereinafter with reference to FIG. 9.
  • sensor 22 Extending into sample cup 21 is a sensor 22 for monitoring a characteristic of the solution or a component or a product of the reaction and for producing a first electrical output signal on a line 23 proportional to such characteristic.
  • sensor 22 may be any type of known sensor such as the oxygen sensor of the before-mentioned copending application of Sternberg, such as a spectrophotometric sensor or the like.
  • sensor 22 is a conductivity sensor, of a type to be described more fully hereinafter with regard to FIGS. 10 and 11, including first and second spaced electrodes for sensing the AC conductance of the solution within sample cup 21.
  • a constant amplitude AC voltage is applied to one electrode of sensor 22 from an oscillator 24.
  • the output of oscillator 24 may be a symetrical wave of any shape, i.e. sinusoidal, square, triangular, etc., having any desired frequency, depending on circuit parameters, as will be explained more fully hereinafter.
  • the change in AC conductivity of the solution produces a change in the current on line 23 connected to the other electrode of sensor 22, which current is reflected as an amplitude modulation of the basic frequency signal from oscillator 24.
  • the amplitude modulated signal from sensor 22 is applied to a demodulator 25 which produces a DC voltage on a line 26 proportional to the AC conductivity of the solution in cup 21.
  • Line 26 is connected to one fixed terminal 27 of a switch 28 which includes a moveable arm 29.
  • Arm 29 is connected to a suitable display device 30 such as a digital voltmeter. Accordingly,,by positioning arm 29 of switch 28 in contact with terminal 27, the DC voltage proportional to the AC conductivity of the solution may be directly read out on display 30. This signal should appear as curve 15 in FIG. 3.
  • This feature permits monitoring of the actual AC conductance of the solution in sample cup 21 to determine the values of C C C and C
  • the DC voltage proportional to AC conductivity on line 26 is also applied to a differentiator circuit 31 which is operative to produce, on a line 32, a second electrical output signal proportional to the time derivative of the AC conductivity signal on line 26.
  • the electrical signal on line 32 is proportional to the time rate of change of AC conductance of the solution in sample cup 21 and is directly proportional to the concentration of the reactants in sample cup 21.
  • apparatus 20 is useful in monitoring a large class of enzymatic reactions, such as those where a change occurs from a non-ionic to an ionic species, or vice-versa, as described more fully in the before-mentioned copending application of Sternberg.
  • a reaction occurs when blood serum containing urea is reacted with the enzyme urea'se to form ammonium carbonate.
  • the urea is initially non-ionic and since ammonium carbonate is ionic, the AC conductivity of the solution will change, and at a rate proportional to the initial concentration of urea.
  • curve shows the output of demodulator 25 on line 26 as a function of time.
  • a measured volume of reagent, containing the enzyme urease is injected into sample cup 21 at time t,, completely immersing sensor 22. when this occurs, the AC conductivity'on line 26 jumps to a value C 1 because of the conductivity of the reagent.
  • a more elaborate discussion of the reagent will be provided hereinafter.
  • a very small volume of sample serum is then introduced into sample cup 21 at time and mixed with the reagent. Accordingly, and as shown in FIG. 3, at time there is an immediate jump in conductivity to a-value C because of the conductivity of the blood serum.
  • the non-ionic urea reacts with the urease to form ammonium carbonate at a rate which is proportional to the quantity of urea in the sample. Accordingly, the conductivity continues to increase until a maximum value C is reached.
  • Differentiator 31 provides an output voltage proportional to the rate of change of AC conductivity. Becuase of the instantaneous jump in solution conductivity at time the rate of change of conductivity initially jumps toward infinity (dotted curve 16), preventing the measurement of maximum value of time rate of change.
  • the output on line 26 from demodulator 25 is applied to a rate sensing circuit 35 which senses the jump in conductivity when the serum sample is injected and which generates an electrical signal on aline 36 indicative of such jump.
  • the output on line 26 from demodulator 25 may be applied to a conductivity level sensing circuit (not shown) which would sense the 5 jump in conductivity when the sample is injected and which would also generate an electrical signal indicative of such jump.
  • the signal on line 36 is applied to a time delay circuit 37 which generates, on a line 38, a suitable electrical control signal, a characteristic of which changes after a predetermined, fixed time interval.
  • the length of this fixed time interval is chosen based upon several considerations. In the first instance, the time interval is selected to be long enough to permit the transient from the jump in conductivity to disappear sufficiently to make an accurate measurement of rate of change of conductivity. The time interval is also selected to permit elimination of other transients, such as temperature upset and the like. Finally, the fixed time interval is selected to be long enough to permit thorough mixing of the sample serum with the reagent. In a preferred embodiment, as described hereinafter, the change in characteristic of the output of time delay 37 occurs approximately 12 seconds after sample introduction.
  • the output of time delay 37, on line 38 is applied to differentiator 31 for inhibiting the operation thereof until the end of the time interval, at time At time after the termination of the time interval, and as shown in FIG. 4, the output 41 of differentiator 31, on line 32, rises to the actual signal level (dotted curve 17) and then falls with the reaction rate.
  • a signal peak 42 is obtained which is proportional to the value of the rate of change signal after a predetermined, fixed time interval from introduction of the sample into the reagent and is, therefore, proportional to the urea concentration in the sample.
  • time delay 37, differentiator 31 and rate measuring circuit 40 just described is only one specific manner of affectuating the broader teaching of the present invention, namely measuring the value of the output of differentiator 31 after a predetermined, fixed time interval from introduction of sample into the reagent.
  • the control signal from time delay 37, on line 38 is used to inhibit the operation of differentiator circuit 31 until time 2;, whereupon rate measuring circuit 40 measures the maximum value of the signal on line 32 immediately thereafter.
  • Other techniques are obviously possible. For example, with reference to FIGS.
  • rate measuring circuit 40 may be in the nature of a sample and hold circuit and the control signal from time delay 37, on line 38, may be applied to rate measuring circuit 40 to select the time or times for sampling the output of differentiator 31. More specifically, time delay 37 may be operative to generate on a line 48, a second electrical control signal, a characteristic of which changes at a time t, occurring after time 1 but prior to time t;,. As shown in FIG.
  • this second control signal on line 48 inhibits differentiator 31 from time 1 to time t,, to prevent the disturbance of differentiator 31 in the presence of the large jump in conductivity at time t
  • the second control signal on line 48 permits differentiator circuit 31 to begin operation so that the output thereof rises along curve 49 until reaching the actual signal level (dotted curve 17) and then falls with the reaction rate.
  • differentiator 31 is permitted to start operation at time I it is still desirable to wait until time to measure the output of differentiator 31 so as to provide a sufficient amount of time to eliminate the effects discussed previously.
  • rate measuring circuit 40 which is activated at time Rate measuring circuit 40 measures the instantaneous value 50 of the output of differentiator circuit 31, at time 1 and applies such value as an output signal to display 30 via switch 28.
  • rate measuring circuit 40 samples the value 51 of the signal on line 32 at a time so as to derive the value of the signal on line 32 at a predetermined time which need not necessarily coincide with the apparent rate peak 50.
  • a preferred embodiment of sample cup includes a cylindrical, hollow body 60, forming a chamber 59, the bottom of which is tapered at 61.
  • the apex of tapered section 61 is-connected to a vertical passageway 62 which is connected to a horizontal passageway 63 extending entirely through body 60, adjacent the bottom thereof.
  • One end 64 of passageway 63 provides an inlet for conducting reagent from a suitable source through passageways 63 and 62 into chamber 59.
  • the other end 65 of passageway 63 provides a convenient location for emptying the solution in cup 21. It will be apparent that exit 65 is blocked during filling of cup 21 whereas inlet 64 is blocked during draining of cup 21.
  • Body 60 is open at the upper end thereof, at 66, and may include a suitable collar 67 if desired.
  • the tip 68 of a pipette 69 is adapted to be extended through the open upper end 66 of body 60 to introduce a very small volume of sample, such as serum, into the reagent in chamber 59.
  • sample cup 21 includes a stirrer 70.
  • Stirrer 70 should have a shape similar to that shown in FIG. 9.
  • stirrer 70 may be magnetized and may be driven by the rotating magnetic force generated by a rotating drive magnet 71 sample, such as serum, is introduced into sample cup 21 via pipette 69 where it is mixed with the reagent due to the action of stirrer 70.
  • sample such as serum
  • body 60 of sample cup 21 may include an opening 75 in the side thereof, which is partially threaded, at 76, for receipt of sensor 22.
  • Any suitable sensor having a pair of electrodes may be used for measuring AC conductivity.
  • the beforementioned U. S. Pat. No. 3,421,982 to Shultz et al teaches the use of a pair of parallel electrodes in a conductimetric system.
  • such electrodes should have a specific construction in order to eliminate many problems that occur in conductance measuring systems.
  • the preferred embodiment of electrode constructed in accordance with the present invention the following discussion of the problems involved is provided.
  • stirrer 70 may be tapered, as at 74, at approximately the same angle as tapered section 61 of I chamber 59.
  • stirrer 70 By making stirrer 70 of some suitable material, such as teflon, the tapered surfaces 74 and 61 provide adequate bearing surfaces for stirrer 70.
  • a drainage passage from cup 21 is provided by slots 74 in the bottom of stirrer 70.
  • a suitable type of stirrer is disclosed in U. s. Pat. No. 3,591,309 issued to Robert A. Ray et al and assigned to Beckman Instruments, Inc.
  • Sensor 22 includes an elongated cylindrical body 80 having a diameter equal to the diameter of the opening 75 in body 60 of sample cup 21. The forward end of body may be threaded at 81 to engage with threads 76 in opening 75. Body 80 may also include a retaining nut 82 which is adapted to be tightened against the outer surface of body 60 of cup 21.
  • first and second electrodes 84 and 85 Positioned on surface 83 are first and second electrodes 84 and 85 which are connected to leads 86 and 87, respectively, extending through body 80 of sensor 22. Leads 86 and 87 may be connected to oscillator 24 and demodulator 25, respectively.
  • the capacitive reactance term may be minimized and, in effect, eliminated, by making electrodes 84 and 85 planar and by positioning them coplanar. By so positioning electrodes 84 and 85, the DC resistance is uneffected but the capacitance is substantially minimized thereby permitting the capacitive reactance term X to become very small at a much lower frequency.
  • Electrodes 84 and 85 may be conductive areas deposited thereon.
  • surface 83 is not compatible with the cylindrical configuration of the wall of chamber 59 and would prevent rapid and thorough mixing of the solution therein and efficient drainage thereof. Accordingly, and as shown in FIGS. and 11, surface 83 is generally curved, having the shape of a segment of a sphere. With such a configuration, electrodes 84 and 85 may be in the shape of half circles positioned with the straight sides parallel and spaced apart. With such a configuration, it has been found that the capacitive reactance term X in the reciprocal impedence Z is effectively reduced to zero by increasing the frequency of oscillator 24 to 10 kHz.
  • the frequency at which the reciprocal impedence plateaus is quite dependent upon the electrode configuration and the 10 kHz value only corresponds to the electrode configuration shown in FIGS. 91 1.
  • the AC impedance becomes a very close approximation to the DC re-- sistance and no capacitance balancing circuit is required.
  • the output of oscillator 24 may be connected directly to one'of leads 86 or 37 whereupon the other lead provides the electrical signal on line 23 for direct connection to demodulator 25.
  • the reagent is usually buffered with salts which are highly conductive so that the pH of the solution remains relatively constant as the reaction continues. This technique permits the reaction rate to proceed at its maximum potential value. With the present invention, it is apparent that this would be objectionable since it is herein desired to allow the conductivity of the solution to change, which change and the rate thereof is measured to determine the concentration of one of the components of the reaction. Accordingly, the present invention contemplates starting with essentially pure urease, dissolved in water, a low salt preparation having a relatively low initial conductivity. Typically, before the sample is injected, the conductance C, as in FIG.
  • the concentration of enzyme reagent relative to the usual concentration of enzyme is relatively high.
  • the conductance jumps to C, which will have a value in the vicinity of 80 percent of the final conductance C
  • the initial conductance C, of the reagent may have a wide range of values since there still will be a change of conductance during formation of ammonium carbonate.
  • a method and apparatus for chemical anaylsis which not only solves the problems of the prior art solved by the beforementioned Rate Sensing Batch Analyzer, but is applicable to a wider variety of enzyme reactions.
  • the present method and apparatus is capable of rapidly determining the concentration of a component in a sample, such as the concentration of components in biological fluids.
  • the method and apparatus represented by block diagram 20 may be rapidly set up and put into operation to make quantitative determinations of true concentration rapidly and accurately, using small sample sizes.
  • the present method and apparatus relies on the measurement of true instantaneous rate at a very early stage of a reaction before the reactant is consumed and during a non-linear portion of the reaction.
  • the present invention reconizes that introduction of a sample into solution with a reagent may .cause an instantaneous change in the characteristic of the solution which is being measured.
  • the present system inhibits measurement of the rate of change signal during a predetermined, fixed time interval starting with introduction of the sample into the reagent, which time interval is sufficient to eliminate the effect of the instantaneous change in the solution as well as to permit thorough mixing of the sample with the reagent.
  • the present invention contemplates measuring a value of the rate of change of the reaction. Several specific embodiments have been described for accomplishing this result.
  • the present in vention contemplates a novel conductivity sensor for eliminating capacitive influences in a conductance measurement.
  • a method for determining the concentration of a component in a sample, wherein the sample, upon being introduced into solution with a reagent, reacts therewith, the rate of the reaction being indicative of said concentration, comprising:
  • said time interval being sufficient to permit thorough mixing of said sample with said reagent.
  • a chemical analyzing system for determining the concentration of a component in a sample, wherein said sample, upon being introduced into solution with a reagent, reacts therewith, the rate of the reaction being indicative of said concentration
  • a chemical analyzing system for determining the concentration of a component in a sample, wherein said sample, upon being introduced into solution with a reagent, reacts therewith, the rate of the reaction being indicative of said concentration
  • such system comprising sensor means for monitoring a characteristic of said solution or a component or a product of said reaction and for producing a first electrical output signal porportional thereto, and differentiator circuit means for producing a second electrical signal proportional to the time derivative of said first signal, said time derivative signal being indicative of said concentration of said component in said sample
  • the improvement comprising:
  • a chemical anaylzing system for determining the concentration of a component in a sample, wherein said sample, upon being introduced into solution with a reagent, reacts therewith, the rate of the reaction being indicative of said concentration
  • system comprising sensor means for monitoring a characteristic of said solution or a component or a product of said reaction and for producing a first electrical output signal proportional thereto, differentiator circuit means for producing a second electrical signal proportional to the time derivative of said first signal, said time derivative signal being indicative of said concentration of said component in said sample, and means responsive to said second signal for generating an output signal indicative of the value thereof, the improvement comprising:
  • said inhibiting means inhibits the operation of said generating means during 6 being indicative of said concentration, such system the time derivative of said first signal, said tirne deriva-' tive signal being indicative of said concentration of said component in said sample, and means for measuring the value of said time derivative signal, the improvement comprising:
  • a chemical anaylzer comprising:
  • sensor means operatively associated with said receiving means for monitoring the concentration of a component or product of the reaction between said sample and said reagent and for producing a first output signal proportional to said concentration; differentiator circuit means coupled to said sensor means and responsive to said first output signal for producing a second output signal proportional to the time derivative of said first output signal and thus proportional to the time rate of change of concentration of said conponent or product; means coupled to said differentiator circuit means for measuring the value of said second signal; and
  • a chemical analyzer according to claim 12 wherein said inhibiting means comprises:
  • timing means responsive to an abrupt change in said first output signal for producing a control signal, a characteristic of which changes after said predetermined, fixed time interval; and wherein said measuring means comprises:
  • a chemical anaylzer according to claim 13 wherein said control signal is applied to said differentiator circuit means for inhibiting the operation thereof during said fixed time interval and wherein said measuring means measures the maximum value of said second output signal.
  • a chemical anaylzer according to claim 13 wherein said timing means produces a second control signal, a characteristic of which changes before the termination of said fixed time interval, wherein said second control signal is applied to said differentiator circuit means for inhibiting the operation thereof during a first portion of said fixed time interval, and wherein said first-mentioned control signal is applied to said measuring means for inhibiting the operation thereof during said fixed time interval.
  • a chemical analyzer according to claim 12 wherein said sensor means comprises:
  • said second output signal is proportional to the rate of change of conductance of said solution, and wherein:
  • a chemical anaylzer according to claim 16 further comprising:
  • oscillator means operatively coupled to one of said electrodes of said sensor means, said oscillator means generating an AC output signal
  • demodulator means operatively coupled to the other of said electrodes of said sensor means, said demodulator means receiving an amplitude modulated signal and producing a DC signal which comprises said second output signal.
  • a chemical analyzer according to claim 16 wherein said sensor means includes a surface which is exposed to said solution, and wherein said electrodes comprise first and second conductive areas positioned on said surface, said conductive areas being spaced apart.
  • a chemical analyzer according to claim 16 wherein said sensor means includes a surface which is exposed to said solution, said surface conforming to a segment of a sphere, and wherein said electrodes comprise first and second conductive areas positioned on said surface.
  • timing means responsive to an abrupt change in said first signal for producing a control signal, a characteristic of which changes after a predetermined, fixed time interval after said abrupt change in said first signal;
  • control signal is applied to said differentiator circuit means for inhibiting the operation thereof during said fixed time interval and wherein said determining means measures the maximum value of said second signal.
  • timing means produces a second control signal, a characteristic of which changes before the termination of said predetermined fixed time interval, wherein said second control signal is applied to said differentiator circuit means for inhibiting the operation thereof during a first portion of said fixed time interval, and wherein said firstmentioned control signal is applied to said determining means for inhibiting the operation thereof during said fixed time interval.
  • said sensor means comprises first and second conductive elements for monitoring the conductance of said solution, wherein said second electrical signal is proportional to the rate of change of conductance of said solution, and wherein said determining means measures the value of said rate of change of conductance after said predetermined, fixed time interval from introduction of said sample into said reagent.
  • said sensor means includes a surface which is exposed to said solution, said surface conforming to a segment of a sphere, and wherein said conductive elements comprise first and second conductive areas positioned on said surface.
  • said conductive areas have the shape of half circles which are positioned with their straight sides parallel and spaced apart.

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Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4085009A (en) * 1976-07-28 1978-04-18 Technicon Instruments Corporation Methods for determination of enzyme reactions
US4095272A (en) * 1977-01-11 1978-06-13 Phillips Petroleum Company Automatic turbidimetric titration
WO1980002849A1 (en) * 1979-06-18 1980-12-24 Johnston Lab Inc Pulsed voltammetric detection of microorganisms
US4256832A (en) * 1978-12-12 1981-03-17 Bioresearch Inc. Carcinogen and mutagen screening method and apparatus
US4271001A (en) * 1978-03-23 1981-06-02 Asahi Kasei Kogyo Kabushiki Kaisha Apparatus for measuring membrane characteristics of vesicles
US4321322A (en) * 1979-06-18 1982-03-23 Ahnell Joseph E Pulsed voltammetric detection of microorganisms
US4376026A (en) * 1980-08-01 1983-03-08 The North American Manufacturing Company Oxygen concentration measurement and control
US4679426A (en) * 1985-09-09 1987-07-14 Fuller Milton E Wave shape chemical analysis apparatus and method
US4765179A (en) * 1985-09-09 1988-08-23 Solid State Farms, Inc. Radio frequency spectroscopy apparatus and method using multiple frequency waveforms
US4810650A (en) * 1986-09-22 1989-03-07 Kell Douglas B Determination of biomass
DK155765B (da) * 1975-06-12 1989-05-08 Beckman Instruments Inc Fremgangsmaade til bestemmelse af koncentrationen af et stof i en proeve og apparat til anvendelse ved udoevelse af fremgangsmaaden
US4863868A (en) * 1987-09-11 1989-09-05 Prolitec Aktiengesellschaft Apparatus for detecting the presence of micro organism in liquid
WO1989010556A1 (en) * 1988-04-26 1989-11-02 Universiteit Twente Detection method
WO1992001928A1 (en) * 1990-07-20 1992-02-06 I-Stat Corporation Method for analytically utilizing microfabricated sensors during wet-up
US5120648A (en) * 1988-05-26 1992-06-09 Lim Technology Laboratories, Inc. Chemical analyzer using rf radiation attenuation measurements
US5882937A (en) * 1997-07-09 1999-03-16 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Ammonia monitor
US6268162B1 (en) 1986-08-13 2001-07-31 Lifescan, Inc. Reflectance measurement of analyte concentration with automatic initiation of timing
US6458326B1 (en) 1999-11-24 2002-10-01 Home Diagnostics, Inc. Protective test strip platform
US6525330B2 (en) 2001-02-28 2003-02-25 Home Diagnostics, Inc. Method of strip insertion detection
US6541266B2 (en) 2001-02-28 2003-04-01 Home Diagnostics, Inc. Method for determining concentration of an analyte in a test strip
US6562625B2 (en) 2001-02-28 2003-05-13 Home Diagnostics, Inc. Distinguishing test types through spectral analysis
US20060205082A1 (en) * 2005-03-10 2006-09-14 Middleton John S Reaction rate determination
US20210077753A1 (en) * 2019-04-01 2021-03-18 Bn Intellectual Properties, Inc. Nebulizer delivery systems and methods

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GB8420116D0 (en) * 1984-08-08 1984-09-12 Elchemtec Ltd Apparatus for monitoring redox reactions
WO1996008714A1 (en) * 1994-09-13 1996-03-21 Toto Ltd. Material concentration measuring method and material concentration measuring apparatus
CN103760356B (zh) * 2007-12-10 2019-06-28 安晟信医疗科技控股公司 斜率式补偿
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Cited By (32)

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DK155765B (da) * 1975-06-12 1989-05-08 Beckman Instruments Inc Fremgangsmaade til bestemmelse af koncentrationen af et stof i en proeve og apparat til anvendelse ved udoevelse af fremgangsmaaden
US4085009A (en) * 1976-07-28 1978-04-18 Technicon Instruments Corporation Methods for determination of enzyme reactions
US4095272A (en) * 1977-01-11 1978-06-13 Phillips Petroleum Company Automatic turbidimetric titration
US4271001A (en) * 1978-03-23 1981-06-02 Asahi Kasei Kogyo Kabushiki Kaisha Apparatus for measuring membrane characteristics of vesicles
US4256832A (en) * 1978-12-12 1981-03-17 Bioresearch Inc. Carcinogen and mutagen screening method and apparatus
WO1980002849A1 (en) * 1979-06-18 1980-12-24 Johnston Lab Inc Pulsed voltammetric detection of microorganisms
US4321322A (en) * 1979-06-18 1982-03-23 Ahnell Joseph E Pulsed voltammetric detection of microorganisms
US4376026A (en) * 1980-08-01 1983-03-08 The North American Manufacturing Company Oxygen concentration measurement and control
AU604651B2 (en) * 1985-09-09 1991-01-03 Solid State Farms, Inc. Wave shape chemical analysis apparatus and method
US4679426A (en) * 1985-09-09 1987-07-14 Fuller Milton E Wave shape chemical analysis apparatus and method
US4765179A (en) * 1985-09-09 1988-08-23 Solid State Farms, Inc. Radio frequency spectroscopy apparatus and method using multiple frequency waveforms
EP0236434B1 (en) * 1985-09-09 1995-10-25 Solid State Farms, Inc. Wave shape chemical analysis apparatus and method
US6821483B2 (en) 1986-08-13 2004-11-23 Lifescan, Inc. Reagents test strip with alignment notch
US6268162B1 (en) 1986-08-13 2001-07-31 Lifescan, Inc. Reflectance measurement of analyte concentration with automatic initiation of timing
US6887426B2 (en) 1986-08-13 2005-05-03 Roger Phillips Reagents test strip adapted for receiving an unmeasured sample while in use in an apparatus
US6881550B2 (en) 1986-08-13 2005-04-19 Roger Phillips Method for the determination of glucose employing an apparatus emplaced matrix
US6858401B2 (en) 1986-08-13 2005-02-22 Lifescan, Inc. Minimum procedure system for the determination of analytes
US4810650A (en) * 1986-09-22 1989-03-07 Kell Douglas B Determination of biomass
US4863868A (en) * 1987-09-11 1989-09-05 Prolitec Aktiengesellschaft Apparatus for detecting the presence of micro organism in liquid
WO1989010556A1 (en) * 1988-04-26 1989-11-02 Universiteit Twente Detection method
US5120648A (en) * 1988-05-26 1992-06-09 Lim Technology Laboratories, Inc. Chemical analyzer using rf radiation attenuation measurements
WO1992001928A1 (en) * 1990-07-20 1992-02-06 I-Stat Corporation Method for analytically utilizing microfabricated sensors during wet-up
US5112455A (en) * 1990-07-20 1992-05-12 I Stat Corporation Method for analytically utilizing microfabricated sensors during wet-up
US5882937A (en) * 1997-07-09 1999-03-16 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Ammonia monitor
US6979571B2 (en) 1999-11-24 2005-12-27 Home Diagnostics, Inc. Method of using a protective test strip platform for optical meter apparatus
US6458326B1 (en) 1999-11-24 2002-10-01 Home Diagnostics, Inc. Protective test strip platform
US6562625B2 (en) 2001-02-28 2003-05-13 Home Diagnostics, Inc. Distinguishing test types through spectral analysis
US6541266B2 (en) 2001-02-28 2003-04-01 Home Diagnostics, Inc. Method for determining concentration of an analyte in a test strip
US6525330B2 (en) 2001-02-28 2003-02-25 Home Diagnostics, Inc. Method of strip insertion detection
US7390665B2 (en) 2001-02-28 2008-06-24 Gilmour Steven B Distinguishing test types through spectral analysis
US20060205082A1 (en) * 2005-03-10 2006-09-14 Middleton John S Reaction rate determination
US20210077753A1 (en) * 2019-04-01 2021-03-18 Bn Intellectual Properties, Inc. Nebulizer delivery systems and methods

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DE2238479B2 (de) 1977-08-18
DE2238479A1 (de) 1973-02-15
IT974628B (it) 1974-07-10
GB1395223A (en) 1975-05-21
DK150805C (da) 1988-01-25
SE389736B (sv) 1976-11-15
CH583904A5 (en:Method) 1977-01-14
DE2238479C3 (de) 1978-04-13
JPS5647497B2 (en:Method) 1981-11-10
JPS4829495A (en:Method) 1973-04-19
CA972810A (en) 1975-08-12
DK150805B (da) 1987-06-22

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