Abstract:
The present invention relates to a dry control cartridge for providing a plurality of voltage and impedance inputs to an electrochemical analysis instrument for verification of its proper functioning. The dry control cartridge includes a battery and a plurality of electrical circuits for providing a plurality of predetermined voltage and impedance outputs. The dry control cartridge is adapted for insertion into an electrochemical analysis device using probe electrodes to measure microvolt-range potential differences, appropriate to the input ranges inherent in the instrument. By comparing the measured voltage and impedance inputs to the predetermined outputs of the cartridge, verification of the instrument&#39;s proper functioning and accuracy may be made.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to electrochemistry and, more particularly, to an apparatus for automatically providing a plurality of standard reference impedance and voltage values to an electrochemistry analysis device. 
     BACKGROUND OF THE INVENTION 
     Electrochemical analysis techniques are commonly used to generate medical data about biological fluids, such as blood and urine. Most electrochemical analyses of biological fluids are currently performed away from the patient care site at specialized analytical laboratories. The analytical process usually consists of the physician drawing one biological fluid sample from the patient for each test desired, sending the samples away to a centralized location for analysis, and waiting for the results to come back. The process is expensive, time consuming, and prone to communications error since both the sample and the results have to pass through several different people. Moreover, many samples have short shelf lives necessitating a rushed turnaround time that can foster mistakes. A delay in processing the sample might mean having to draw yet another sample from the patient. Further, it is advantageous to the patient that the test results are obtained as quickly as possible, since the patient can begin receiving treatment only after his condition has been properly diagnosed. 
     One alternative to sending fluid samples away for electrochemical analysis has been developed in the form of the automatic field analysis unit. A number of miniature field analysis units for automatically conducting electrochemical tests on biological fluids are known, such as those described in the claims and specifications of U.S. patent application Ser. No. 09/248,607 for a “Cartridge-Based Analytical Instrument with Optical Detector”, U.S. patent application Ser. No. 09/248,614 for a “Cartridge-Based Analytical Instrument with Rotor Balance and Cartridge Lock/Ejection System”, and U.S. patent application Ser. No. 09/248,737 for a “Cartridge-Based Analytical Instrument Using Centrifugal Force/Pressure for Mechanical Transport of Fluids”. Typically, such miniature electrochemical testing units include disposable electrochemical test cells or cartridges in which two electrolytic solutions are connected by a salt bridge. One electrolytic solution is a reference solution while the other is the fluid sample to be analyzed. Probe electrodes connected to an electronic controller are introduced into the solutions and the electrical potential therebetween is measured. 
     It is important that the electrochemical data so generated by the analysis unit be accurate, since it will be used as the basis of a medical diagnosis. To this end, the analysis unit requires regular verification of its testing functions. The electrochemical testing function of the instrument may be checked by inserting a control cartridge containing standardized analytes having a known potential difference. This type of verification of function is known as testing with wet controls or wet testing. While wet controls offer an accurate measure of proper systems operation, they are inconvenient, expensive, and have limited reuse potential. 
     Another known way of verifying electrochemical function of the instrument is by inserting a control cartridge containing a battery and an electrical circuit to offer a predetermined voltage to the test probe electrodes of the analysis device. This type of verification of function is known as testing with dry controls or dry testing. While dry testing constitutes a quick and convenient one-point test, it is less effective than a test that exercises the instrument across a wide range of input conditions. There is therefore a need for a fast, convenient, inexpensive, and reusable test cartridge capable of providing a range of input voltage conditions to an automated electrochemical analysis instrument for verification of electrochemical testing functions. A means for satisfying this need has so far eluded those skilled in the art. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a dry control cartridge for providing a plurality of voltage and impedance inputs to an electrochemical analysis instrument. The cartridge includes a battery and a plurality of electrical circuits for providing a plurality of predetermined voltage and impedance outputs. The cartridge is adapted for insertion into an electrochemical analysis device using probe electrodes to measure electrochemical potential differences. The cartridge is further adapted to provide voltage and impedance outputs appropriate to the input ranges inherent in the instrument. By comparing the measured voltage and impedance inputs to the predetermined outputs of the cartridge, verification of the instrument&#39;s accuracy may be made. 
     One form of the present invention relates to an electrochemical dry control cartridge including a battery, a plurality of circuits, and a connector. The cartridge is adapted to be operationally connected to the probe electrodes of an electrochemical analysis instrument, such that the connector is in electrical communication with the probe electrodes. The cartridge may provide a plurality of predetermined voltage and impedance outputs to the instrument to verify its analytical accuracy. 
     One object of the present invention is to provide an dry control cartridge for verification of the accurate functioning of an electrochemical analysis instrument. Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a first embodiment dry control cartridge of the present invention. 
     FIG. 2 is a schematic illustration of an electrical circuit contained in the dry control cartridge embodiment of FIG.  1 . 
     FIG. 3 is a partial view of the probe electrode assembly of a typical electrochemical analysis instrument. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Background of Electrochemical Measurement 
     A typical portable electrochemistry analysis instrument is an automated diagnostic tool adapted for use at a patient treatment site, such as a doctor&#39;s office or clinic. The typical portable electrochemistry analysis instrument includes a power source (such as a battery), a carousel for holding a plurality of disposable test cartridges, an electrode assembly for measuring electrical potentials within the test cartridges, a rotor for turning the carousel to sequentially introduce the test cartridges to the electrode assembly, and a controller for tracking the test cartridges, collecting the raw data, and generating, coordinating, and storing data points. The instrument can perform electrochemical analyses on stationary test cartridges by introducing the electrode assembly into the test cartridge and measuring the electric potentials and impedances of the cartridge containing an electrolytic test fluid and a reference standard electrolytic solution housed therein in electric communication. The test cartridges are typically disposable and pre-loaded with everything required for the test except the fluid sample upon which the desired tests are to be performed. 
     As multiple tests are performed, the electrodes may become contaminated by electrolytes or dirt adhering to the surface. Such contaminants can contribute to erroneous electric potential and/or impedance measurements. Also, in the case of battery operated instruments, as the battery is drained the current and voltage outputs may change, also contributing to measurement errors. Therefore, it is important to periodically check the accuracy of the instrument. 
     The present invention relates to a dry control cartridge for providing a plurality of discrete voltage and impedance values for use in the verification of the proper functioning of an electrochemical analysis instrument. FIG. 1 illustrates one embodiment of the present invention, a dry control cartridge  5  containing electric circuit  10  adapted to provide a plurality of predetermined voltage and impedance outputs. 
     Circuit Overview 
     Circuit  10  is illustrated schematically in FIG.  2 . In a preferred embodiment, circuit  10  includes a power source assembly  12  connected in series to a resistor set  14 , each resistor having a predetermined resistance value. Power source assembly  12  preferably includes a battery  20  as a DC power supply, a switch  22 , and a resistor  24  connected in series, although in other contemplated embodiments DC power may be supplied by a rectified AC source. As most electrochemical measurements are made in the millivolt range, the voltage supplied by power source assembly  12  may be dropped into the millivolt range by resistor  24  electrically connected in series to battery  20 . A diode  26  may also be electrically connected in parallel with power source assembly  12  to insure the provision of a stable reference voltage from which tap voltages may be derived. 
     In the present embodiment, power source assembly  12  is connected in series to resistor set  14 , which includes resistors  28 ,  30 ,  32 , and  34 . As current flows from battery  20  through each resistor  28 ,  30 ,  32 ,  34  there is a corresponding voltage drop across each resistor (according to V=IR). The voltage drop across each resistor  28 ,  30 ,  32 ,  34  may therefor be predetermined by the voltage output of power source assembly  12  and the resistances chosen for each resistor  24 ,  28 ,  30 ,  32 ,  34  electrically connected in series thereto. 
     Circuit  10  also includes a connector  40  adapted to receive probe electrodes  80  from an electrochemical analysis device (see FIG. 3) and electrically connect them to circuit  10 . Connector  40  includes a plurality of pins for the reception of probe electrodes  80 . In this embodiment, connector  40  includes six pins that can be grouped for convenience into three pairs,  42  and  44 ,  46  and  48 , and  50  and  52 . Pins  42 ,  46 , and  50  are each electrically connected to a tap point  54  defined as the junction between resistors  30  and  32 . Pin  44  is electrically connected through a resistor  60  to a point between resistors  28  and  30 . Pin  48  is electrically connected through resistor  64  between resistors  32  and  34 . Pin  52  is electrically connected through resistor  62  to a point between battery  20  and resistor  34 . The values of resistors  24 ,  28 ,  30 ,  32 ,  34 ,  60 ,  62 , and  64  are chosen such that the voltage drops across each pair of pins  42  and  44 ,  46  and  48 , and  50  and  52  are predetermined to be within the measurement range desired to be verified. 
     A capacitor  70  may also be included in circuit  10 , bridging resistors  30 ,  32  and  34  to further stabilize current flow through circuit  10 . 
     Detailed Circuit Description 
     The preferred embodiment circuit  10  is described in detail hereinbelow. A battery  20  is provided as a voltage source and includes battery terminals  20 A and  20 B. Battery  20  is electrically connected to switch  22 . Switch  22  has an open position in which current is prevented from flowing therethrough, and a closed position allowing current to flow therethrough. Switch  22  includes two switch terminals,  22 A and  22 B, with switch terminal  22 B electrically connected to battery terminal  20 A. Switch terminal  22 A is electrically connected to resistor  24  at resistor terminal  24 A. Resistor  24  also includes resistor terminal  24 B. Diode  26  is connected in parallel with battery  20 , switch  22  and resistor  24 . Diode terminal  26 A is electrically connected to resistor terminal  24 B while diode terminal  26 B is electrically connected to battery terminal  20 B. 
     Resistors  28 ,  30 ,  32 , and  34  are electrically connected to receive current from battery  20  when switch  22  is closed. Each resistor  28 ,  30 ,  32 , and  34  has two resistor terminals,  28 A and  28   b,    30 A and  30 B,  32 A and  32 B, and  34 A and  34 B, respectively. In particular, resistor terminal  28 A is electrically connected to resistor terminal  24 B. Resistor terminal  28 B is electrically connected to resistor terminal  30 A. Resistor terminal  30 B is electrically connected to resistor terminal  32 A. Resistor terminal  32 B is electrically connected to resistor terminal  34 A. Resistor terminal  34 B is electrically connected to battery terminal  20 B. Tap point  54  is defined as the electric connection between resistor terminals  30 B and  32 A. 
     Connector  40  includes a plurality of pins for the reception of probe electrodes. Connector  40  includes six pogo pins  42 ,  44 ,  46 ,  48 ,  50 , and  52 . Pins  42 ,  46 , and  50  are each electrically connected to tap point  54 . Pin  44  is electrically connected to resistor  60  at second resistor terminal  60 B. Resistor terminal  60 A is electrically connected to resistor terminals  28 B and  30 A. Pin  48  is electrically connected to resistor terminal  64 B. Resistor terminal  64 A is electrically connected to resistor terminal  34 B. Pin  52  is electrically connected to resistor terminal  62 B. Resistor terminal  62 A is electrically connected to resistor terminals  32 B and  34 A. In this embodiment, the resistor values are chosen as follows: resistor  24  has a resistance of 82.5K Ohms, resistor  28  has a resistance of 392K Ohms, resistor  30  has a resistance of 10.5K Ohms, resistor  32  has a resistance of 845 Ohms, resistor  34  has a resistance of 11.3K Ohms, resistor  60  has a resistance of 100K Ohms,  62  resistor  62  has a resistance of 20M Ohms, and resistor  64  has a resistance of 20M Ohms. 
     Capacitor  70  is connected at capacitor terminal  70 A to resistor terminal  28 B and at capacitor terminal  70 B to diode  26  terminal  26 B. Capacitor  70  has a capacitance of 0.022 Farads. 
     METHOD OF VERIFYING INSTRUMENT FUNCTION 
     Referring back to FIG. 1, to verify the proper functioning of an electrochemical analysis instrument, dry control cartridge  5  containing test circuit  10  is loaded into the instrument such that electrodes  80  (see FIG. 3) operationally engage connector pins  42 ,  44 ,  46 ,  48 ,  50  and  52 . Dry control cartridge  5  supplies several test voltages and impedances to the instrument, preferably by providing a different voltage and impedance to each pair of connector pins  42 - 44 ,  46 - 48 , and  50 - 52 . Test voltages and impedances are supplied to the instrument when switch  22  is closed. Switch  22  must be closed before cartridge  5  may supply voltages to the instrument, so as to conserve power (and operational lifetime) of battery  20 . In the preferred embodiment, pogo pins  42 - 52  yield under pressure from electrodes  80 , thereby maintaining even pressure contact on all pins, regardless of alignment differences. The analysis instrument then measures the potentials and impedances between each pair of connector pins  42 ,  44 ,  46 ,  48 ,  50  and  52 . The measured values are compared to the expected or known voltages and impedances supplied by dry test cartridge  5 . In the event that the expected and measured values do not substantially match, the instrument can be troubleshot and repaired. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are to be desired to be protected.