Abstract:
A disposable sensor card ( 74 ) includes a polymeric substrate ( 80 ), such as polyester, printed with a plurality of electrodes ( 78 ), and a reuse-prevention system ( 150 ) which includes a fuse link ( 152 ) and a cut link ( 154 ). A controller ( 70 ) tests the fuse link and cut link to see if they have been destroyed. If the controller determines that the two links are good, a sensor card support system ( 72 ), which includes a ram ( 130 ), clamps the sensor card over an opening in a manifold ( 138 ) so that the electrodes are in contact with a decontaminant solution, such as peracetic acid solution, passing through the manifold. The controller detects an electrical property of the electrodes and determines a concentration of the decontaminant therefrom. During the clamping process, a cutter ( 170 ) severs the cut link. A memory of the cut link is retained by the controller. If power to the controller is interrupted, the memory is lost and the controller detects that the cut link is broken when power is regained. At the end of a decontamination process, the controller switches to a “power off” mode and detects that the cut link is severed. When the controller detects that the cut link is severed, the controller blows the fuse link and the sensor card support system unclamps the sensor card. The severed cut link provides a visual indication that the card is spent.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the sterilization and disinfection arts. It finds particular application in conjunction with the detection of peracetic acid concentrations in decontamination systems used for the sterilization or disinfection of medical and pharmaceutical equipment, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to the detection of other oxidizable and reducible species in fluid flow systems. 
     Endoscopes and similar medical devices having tubes or lumens formed therethrough are being used on an ever increasing basis in the performance of medical procedures. The popularity of these devices has lead to the development of improved decontamination systems, both in terms of the speed of the decontamination process and in the effectiveness of the decontamination. High temperature steam sterilization tends to be destructive towards some of the components of the endoscopes. As a result, liquid sterilization processes have been investigated. Glutaraldehyde, a common liquid disinfectant, is generally effective for disinfection of medical instruments. However, the sterilization process generally takes from 10 to 12 hours, which is frequently too long in today&#39;s health care facilities. Another drawback with glutaraldehyde systems is that they sterilize without cleaning. That is, they leave non-living biological contaminants on the medical instruments. The contaminants, although sterile, can break down and liberate harmful toxins when the instruments are subsequently reused. 
     Recently, peracetic acid sterilization systems have proven effective for the sterilization of medical instruments. Due to its limited shelf life and shipping restrictions, the peracetic acid is often prepared as needed from a mixture of precursors. The peracetic acid precursors are typically mixed with water and other chemicals in the bath. U.S. Pat. No. 5,116,575 to Badertscher, et al. discloses a powdered antimicrobial composition comprising acetylsalicylic acid and sodium perborate. Inhibitors and surfactants are also included in the composition, to aid in cleaning and preventing corrosion of the metal parts of the instruments. The composition is mixed with water in a bath. Items to be sterilized or disinfected are immersed in the bath for a period sufficient to effect sterilization or disinfection. Decontaminated items are rinsed before use to remove traces of the acid and other cleaning chemicals. 
     To insure effective sterilization or disinfection within a preselected period of time, the concentration of peracetic acid is maintained above a selective minimum effective level, typically around 2300-2500 ppm for sterilization of medical instruments. 
     The bath sterilization procedures does however have disadvantages. Operator errors can contribute to unsatisfactory sterilization. Specifically, inaccuracy in mixing the components may result in levels of peracetic acid below the minimum level required for sterilization. Thorough cleaning of the instruments is not insured if the instruments are removed from the bath before a minimum exposure period is completed. Handling of the instruments between sterilization and rising stages may lead to recontamination of the instruments. 
     Recently, dedicated decontamination systems have been developed which sterilize and rinse the medical instruments in an enclosed, automated system. Peracetic acid, either generated in situ or diluted from a concentrate, is delivered to a sterilization vessel and circulated over the instruments to be sterilized. U.S. Pat. No. 5,217,698 to Siegel, et al. discloses an office size instrument sterilization system of this type. Instruments to be sterilized are inserted in a cassette and the sterilant fluid circulated through the cassette. After sterilization, the instruments remain in the cassette in a sterile condition until needed in the hospital. For decontamination of larger instruments, U.S. Pat. No. 5,225,160 to Sanford, et al. discloses a wheeled decontamination apparatus. 
     To insure that an accurate dose of the powdered sterilants is provided, it is preferable to contain the components in a cup which is opened within the sterilization system when needed. U.S. Pat. No. 5,439,654 discloses a cutter for opening a sterilant-containing cup. 
     The use of a measured dose of sterilants or precursors does not always guarantee adequate levels of peracetic acid. Peracetic acid precursors and concentrates can decompose over time. Thus, even when the dosage is accurately measured, the concentration for peracetic acid in the solution is not always assured. Further, the peracetic acid concentration may be reduced when the medical instruments are heavily contaminated with biological materials. 
     Methods have been developed for detection of peracetic acid, and other oxidizable and reducible species, in solution. Dippable papers, for example, are easy to use, but lack accuracy, particularly at concentrations suitable for sterilization or disinfection. Chemical titration methods provide a more accurate measure of peracetic acid in solution, but are time consuming to perform and are prone to operator errors. They do not provide the rapid detection needed for automated sterilization and disinfection systems. 
     Recently, a number of electrochemical techniques have been developed for detection of oxidizable or reducible chemical species, such as mixtures of peracetic acid and hydrogen peroxide. U.S. Pat. No. 5,400,818 to Consentino, et al. discloses such a sensor. The sensor measures the resistivity of the solution, which is dependent on both the peracetic acid and the hydrogen peroxide concentrations. European patent application EP 0333246 A to Unilever PLC, discloses an electrochemical sensor using an amperometric method, in which a fixed potential is maintained between the reference and the working electrode. The current at the working electrode is used to determine the concentration of peracetic acid. Other species present, however, influence the current flowing, and hence the accuracy of the results. 
     U.S. Pat. No. 5,503,720 to Teske discloses a process for the determination of reducible or oxidizable species, such as peracetic acid, in sewage waste. The process uses potentiostatic amperometry to detect peracetic acid concentrations. The technique, however, depends on the achievement of a steady state, which frequently takes several hours. Such a detection system is unsuited to a fairly short term sterilization process. 
     The electrode systems used in such detection systems are generally bulky devices which are both costly to manufacture and require careful preparation of the electrode surfaces prior to use. Prolonged exposure to the test solution tends to degrade the electrodes and thus recalibration is generally employed before each use. Inaccurate measurements result when recalibration is not carried out or the electrodes are not thoroughly cleaned. 
     Recently disposable electrodes have been developed for analytical assays in medical and biochemical samples. The electrodes are laid down as an ink onto a plastic card. Leads connect the electrodes to electrochemical monitoring equipment. Typically, a few drops of the solution placed on the electrode. However, there is generally no method of determining when the electrode has reached the end of its useful life and for preventing reuse of an electrode intended for a single use. 
     The present invention provides for a new disposable plastic sensor card for peracetic acid and associated reader and sterilization equipment which overcomes the above-referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a decontamination system for sterilizing or disinfecting instruments with a decontaminant solution is provided. The system includes a decontamination cabinet which defines a chamber for receiving the instruments to be decontaminated, a source of the decontaminant solution, and a fluid line fluidly connecting the source of the decontaminant solution with the chamber. A sensor card support system supports a disposable sensor card in fluid communication with the fluid line. The sensor card includes a plurality of electrodes and a reuse-prevention system. Further, the system includes a controller for detecting an electrical property of the electrodes and determining a concentration of a decontaminant in the decontaminant solution from the detected electrical property and for detecting whether the reuse-prevention system has been activated. 
     In accordance with another aspect of the present invention, a sensor system for detecting a concentration of a component of a liquid disposed in a liquid treatment system is provided. The system includes a sensor card support system for supporting a disposable sensor card in fluid communication with the liquid in the liquid treatment system. The sensor card includes a plurality of electrodes and a reuse-prevention system. A controller for establishing electrical contact with the electrodes electrically measures an electrical property of the electrodes which is dependent on the concentration of the component in the liquid. A reuse-prevention activation system activates the reuse-prevention system. A detector detects an activation of the reuse-prevention system. 
     In accordance with yet another aspect of the present invention, a method for preventing reuse of a disposal sensor card for detecting the concentration of a decontaminant in a decontaminant solution is provided. The sensor card includes a plurality of electrodes and a reuse-prevention system. The method includes determining whether the reuse-prevention system on the sensor card has been activated, and, if the reuse-prevention system has not been activated, clamping the sensor card such that the electrodes are in contact with the decontaminant solution. The method further includes sensing an electrical property of the electrodes which is dependent on the concentration of the decontaminant in the decontaminant solution and activating the reuse-prevention system. 
     One advantage of the present invention is that an effective concentration of decontaminant. 
     Another advantage of the present invention is that a peracetic acid decontamination cycle is halted or extended if an insufficient concentration of peracetic acid is detected. 
     Another advantage of the present invention is that a fresh sensor card is dictated for each decontamination cycle, ensuring accurate operation of the decontaminant detection system. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment, and are not to be construed as limiting the invention. 
     FIG. 1 is a schematic view of a decontamination system according to the present invention; 
     FIG. 2 is an enlarged perspective view of the sensor system of FIG. 1; 
     FIG. 3 is an enlarged front view of the sensor card of FIG. 2; 
     FIG. 4 is a schematic view of the controller of FIG. 1; 
     FIG. 5 is a front elevational view of the exterior of the decontamination system of FIG. 1; 
     FIG. 6 is an enlarged perspective view of the rear face of sensor card and cut-link cutter according to the present invention; 
     FIG. 7 is an enlarged perspective view of the sensor card, cutter and ram of the present invention; and, 
     FIG. 8 is a flow diagram indicating the steps taken by the controller during a decontamination cycle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A sensor system A is used to detect the concentration of a component of a liquid in a fluid flow path. In a preferred embodiment, the sensor system is used for detecting the concentration of a sterilant or disinfectant in an aqueous solution flowing through an automated peracetic acid sterilization or disinfection system for decontamination of medical instruments, such as endoscopes, and the like. It should be understood, however, that the sensor system is not limited to the detection of sterilants and disinfectants and that the detection of other oxidizable and reducible species in a variety of fluid systems is also contemplated. 
     With reference to FIG. 1, an automated liquid decontamination system  1  for sterilization or disinfection of medical and pharmaceutical instruments, and the like, is shown. The system includes a decontamination cabinet  10  which defines a chamber  12 . Items to be cleaned and sterilized or disinfected are loaded into the chamber through a door  14  in a wall of the decontamination cabinet. Nozzles  16 , within the chamber, spray a liquid sterilant or disinfectant and other cleaning and rinsing liquids (herein jointly referred to as decontaminants) over the items. A collection tank or sump  18 , at the base of the cabinet receives the sprayed decontaminant as it drips off the items. 
     A first pump  20  delivers the decontaminant under pressure to the nozzles  16  through fluid lines  22 . Preferably, quick connect couplings  24  connect the fluid lines adjacent an exterior wall of the cabinet to interior fluid lines  26 , within the chamber, so that the fluid lines can be uncoupled for removal of the cabinet from the rest of the system  1 . 
     A second pump  28  withdraws the sprayed decontaminant from the tank  18  for reuse or disposal. Valves  30  and  32  control the flow of decontaminant into and out of the cabinet, respectively. 
     A supply cabinet  40 , located adjacent the decontamination cabinet  10 , houses a source  42  of the decontaminant and the sensor system A. The source  42  of the decontaminant preferably includes a disposable cup or other container  44  which holds a measured dose of concentrated decontaminant, in either liquid or solid form. A fresh cup is used for each decontamination cycle. 
     A well  46  receives the cup  44 . The well is connected by a fluid line  48  to the pump  20 . A cutter  50  cuts a wall of the cup to release the decontaminant when required. A water inlet line  54  delivers water to the well for mixing with the concentrated decontaminant to provide a dilute solution of the decontaminant. The water used may be tap water or treated water, such as distilled water. The quantity of water entering the system  1  is regulated to provide a decontaminant solution of a desired nominal concentration flowing through the chamber  12 . The water is first passed through a microporous filter  56  which filters out particles of dirt and microorganisms. 
     Alternatively, the decontaminant is delivered in liquid form and metered from a bulk supply source (not shown). The liquid may be a concentrate, or diluted with water, ready for use. 
     A heater  58 , disposed in fluid line  48  heats the decontaminant to a desired temperature for effective decontamination. The second pump  28  returns the sprayed decontaminant solution to chamber  12  via a return fluid line  60 . The return fluid line preferably directs the returned decontaminant solution through the well  46  to insure thorough mixing and dissolution of the concentrated decontaminant. 
     The sensor system A measures the concentration of the decontaminant in the decontaminant solution flowing through the chamber  10 . As shown in FIG. 1, the sensor system is disposed in the return fluid line  60 , so that the concentration of the decontaminant solution is measured after contact with the instruments being decontaminated. It should be appreciated, however, that the sensor system is also conveniently disposed in any of the fluid flow lines  22 ,  26 ,  60  of the decontamination system, although greater initial fluctuations in concentration measurements are to be expected if the sensor is located between the well  46  and the chamber nozzles  16 . These fluctuations are reduced, however, by allowing the decontaminant solution to circulate through the chamber one or more times before initiating sensing. 
     With reference also to FIGS. 2 and 3, the sensor system A includes a controller  70 , and a sensor card support system  72 . The sensor card support system receives a disposable sensor card  74  and holds the sensor card in contact with the circulating decontaminant solution. 
     The sensor card includes a substrate  76  formed from a sheet of a polymeric or ceramic support material, such as polyester, plastic, or other relatively inert material. A particularly preferred substrate material is polyester. Electrodes  78  are supported on a front face  80  of the substrate for electrochemical detection of the concentration of the decontaminant. 
     For detection of peracetic acid, in particular, the sensor card  74  preferably includes three electrodes  78 , namely a working electrode  82 , a reference electrode  84 , and a counter electrode  86 . A suitable reference electrode is a silver/silver chloride electrode. The working electrode is preferably a catalyst for peracetic acid. A particularly preferred working electrode includes gold, either alone, or doped with an inert material. Gold is an effective catalyst for peracetic acid and is selective for peracetic acid in the presence of hydrogen peroxide. The counter electrode is preferably formed from an inert conductive material, such as carbon, which readily accepts electrons. Alternatively, suitable counter electrodes are formed from silver, gold, or titanium. 
     Electric leads  88  electrically connect the electrodes and the controller  70  through connecting points  90 . An insulation layer (not shown) partially covers the substrate and portions of the leads that would otherwise be exposed to the circulating decontaminant solution. The insulation layer exposes only a preselected area of each electrode to the solution and inhibits current from leaking into the solution from the leads. A thermistor  92  detects the temperature of the decontaminant solution in a region adjacent the sensor card. 
     Electrical components of the sensor card, including electrodes, electrical connection points, and electrical leads are all laid down on the front face of the substrate. This may be done by thin or thick film printing technology, or other conventional techniques. In one preferred method, materials for the electrodes and connection points are separately dispersed in inks and printed onto the substrate. The substrate is heated to evaporate solvents and set the inks. The sensor cards produced in this way are inexpensive and thus are suited to the intended single use. 
     The ink is selected so as to bond the electrode or lead to the substrate in such a way that it will not be disbanded when immersed in a peracetic acid solution at temperatures between around 25° C. and 75° C. The choice of ink also affects the conductivity to some degree. 
     With reference also to FIG. 4, the controller  70  electrochemically monitors the peracetic acid concentration. Amperometric techniques are suited to the detection of peracetic acid. One suitable amperometric controller  70  is disclosed in PCT application WO 97/08544 and is incorporated herein by reference, although other conventional electrochemical monitoring systems may be used. In its simplest form, the controller includes a voltage regulator, such as a potentiostat  94  which maintains a constant voltage between the reference electrode  84  and the working electrode  82  and a current monitor  96  which detects the current flowing between the working electrode and the counter electrode  86 . A temperature detector  98  receives temperature correction signals from the thermistor  92 . 
     The voltage regulator, current monitor, and temperature detector are all controlled by a main processor  100 . The main processor controls the voltage output of the voltage regulator  94  and receives current signals from the current monitor  96  and temperature signals from the temperature detector  98 . The main processor accesses a look up table  102  to determine the concentration of peracetic acid. To load the look up table, samples of known concentration at known temperatures are measured and the monitored current noted. Due to the discrete intervals, an interpolator is optionally employed. 
     By repeating the measurements of current output and temperature over a period of time, at intervals of about 30 seconds, an accurate average measurement of the peracetic acid concentration in the flowing decontaminant solution is obtained. Preferably, the main processor  100  also controls the operation of the sensor card support system  72  and deactivation of the sensor card  74  to prevent reuse, as will be described in greater detail later. 
     With reference once more to FIG.  2  and reference also to FIGS. 5 and 6, the sensor card support system  72  positions the sensor card  74  so that the portion of the sensor card where the electrodes and thermistor are situated is disposed in fluid communication with the flowing decontaminant solution. The substrate is shaped like a credit card for insertion into a slot  110  in a front cover  112  of the supply cabinet  40 . The sensor card is inserted into the slot in the direction of arrow A, as shown in FIG.  5 . 
     Inside the supply cabinet  40 , the sensor card  74  is received by upper and lower support channels  114  and  116  of the support system  72 . The support channels loosely support upper and lower ends  118 , 120  of the sensor card  74  while permitting some movement of the sensor card in a direction perpendicular to the front face  80  of the sensor card. 
     Once inserted, the sensor card  74  is clamped in position in the slot, so that it cannot be removed during a decontamination cycle. Specifically, the sensor card support system  72  includes a ram, such as a pneumatic piston  130  which is attached to a clamping plate  132  by a piston rod  134 . The support channels  114 ,  116  position the sensor card between the clamping plate and an opening  136  in a manifold  138  in the fluid line  60 . The ram  130  is actuated by the controller  70  to apply a clamping force in the direction of arrow B. The force is delivered by the piston rod to the clamping plate and thence to a rear face  140  of the sensor card  74 , as best shown in FIG.  6 . The sensor card is pressed by the clamping plate  132  against the manifold  138 . An O-ring  144 , positioned around the opening  136  in the manifold, creates a seal between the front face  80  of the sensor card  74  and the manifold around the manifold opening when pressure is applied to the clamping plate  132 . 
     A portion  146  of the sensor card where the electrodes  82 ,  84 ,  86  and thermistor  90  are located is thus positioned for contact with decontaminant solution that circulates through the manifold. Some of the decontaminant solution circulating through the fluid line  60  enters the manifold and contacts the electrodes. 
     Concentration measurements are made at intervals throughout the decontamination portion of a cycle and compared with preselected low concentration set points. The controller  70  signals the measured concentration to a display panel  148  on the front  112  of the supply cabinet  40 . If the concentration of the decontaminant drops slightly below a preselected first operating concentration set point, the controller automatically extends the preprogrammed cycle by a corresponding time to compensate for the lower decontaminant concentration. If the concentration of the decontaminant falls below a second, lower minimum operating concentration set point the controller automatically ends the cycle and signals the display panel  148  to indicate a stoppage by visual or audible means, such as a flashing warning light or an alarm sound. 
     It should be appreciated that FIG. 2 exaggerates the distance between the manifold opening  136  and the clamping plate  132  for purposes of describing the features of the sensor card support system. In practice, the clamping plate and manifold opening are preferably separated by a relatively short distance, only slightly wider than the width of the sensor card. 
     The ram  130  maintains the pressure on the clamping plate  132  throughout the decontamination cycle. At the end of the cycle, the controller  70  signals the ram to release the pressure, allowing the sensor card  74  to be removed from the slot  110 . Before releasing the sensor card, however, the sensor card is mutilated in a manner which is recognizable by the controller, to prevent reuse. 
     With reference once again to FIGS. 2 and 3, a preferred reuse-prevention system  150  is incorporated into the sensor card  74 . The reuse prevention system includes two separate components, a fuse link  152  and a cut link or electrical line  154  which are separately deactivated by the sensor system to prevent reuse of the sensor card. The sensor system A includes a two-part reuse-prevention activation system  156  which selectively deactivates the fuse link and the cut link. The activation system  156  includes a fuse link deactivator  158 , in the controller  70 , and a cut link deactivator  160 , within the sensor card support system  72 . 
     The fuse link  152  is laid down on the sensor card  74  in a similar manner to the electrodes. The fuse link deactivator  158  is preferably operated by the main processor  100 . At the end of a decontamination cycle, or if the power is switched off, the main processor  100  signals the fuse link deactivator  158  to send a brief burst or pulse of current through the fuse link, blowing the fuse. If the sensor card is subsequently reinserted into the slot  110  a fuse link detector  162  within the controller  70  recognizes the lack of electric continuity indicating that the link has been blown and prevents initiation of a new decontamination cycle until a fresh sensor card has been inserted. 
     The cut link  154  is laid down on the sensor card  74  adjacent one or other of the ends  118 ,  120  of the sensor card. The cut link completes a circuit with the controller  70 . When the cut link is severed, the circuit is broken. Before initiating a sterilization cycle a cut link detector  166  within the controller tests the circuit through the cut link. The cut link also serves as a visual indication of whether the sensor card has been used. 
     With reference also to FIGS. 6 and 7, the cut link deactivator  160  includes a cutter  170  which severs the cut link  154 . The cutter is preferably connected to the ram  130 , such that when the ram is actuated by the controller  70 , the cutter moves towards the rear face  140  of the sensor card in tandem with the clamping plate  132 . As shown in FIG. 6 the cutter is optionally connected by a second rod  172  to the piston rod  134 , although other methods of connecting the cutter to the ram are also contemplated, such as dual piston rods. 
     Although FIG. 7 shows the cut link  154  printed on the rear face  140  of the sensor card  74 , it should be appreciated that the cut link may be laid down on either the front face or the rear face of the sensor card. For convenience, the cut link is preferably laid down on the front face of the sensor card at the same time as the electrodes, thermistor and fuse link, in a similar manner. 
     An anvil plate  176  firmly holds the end of the sensor card  74  adjacent the cut link  154 . An opening  178  in the anvil plate provides access to the cut link and receives a cutting edge  180  of the cutter therethrough. The ram  130  forces the cutting edge through the opening and the sensor card, severing the cut link in the process. The cut link detector  166  within the controller recognizes that the link has been broken. The cutter  170  remains inserted through the sensor card until the pressure from the ram  130  is released. This inhibits removal of the sensor card during the sterilization cycle. 
     Accordingly, the cut link  154  is severed before the decontamination cycle commences. Although the cut link has been broken, the controller does not halt the decontamination cycle before it is completed unless power to the controller is prematurely switched off. Rather, the controller creates a “memory” of the previously detected validity of the cut link which is only destroyed at the end of a cycle or when the power is switched off. The memory overrides detection of the severing of the cut link. If the cycle is temporarily halted during the decontamination cycle, the memory is not lost and the controller allows the cycle to recontinue when the cycle is restarted. When the cycle is halted, the controller signals the display panel  148  to show a “ready” light, indicating that the cycle may be recommenced without inserting a fresh sensor card. If the memory is lost, the controller detects that the cut link has been severed, blows the fuse link  152 , and signals the display panel  148  to switch the “ready” light off. 
     Alternately, the cutter  170  can cut other leads such as leads  82 , at the end of the cycle. The cut link detector can be embodied in a logic circuit that detects then non-responsiveness of the sensor electrodes or the thermistor. 
     FIG. 8 summarizes a preferred sequence of steps taken by the controller during a typical decontamination cycle. The controller  70  detects that the sensor card  74  has been inserted into the slot and checks the fuse link  152  and cut link  154 . If both of these are unbroken, the controller signals the display panel  148  to indicate a satisfactory test of the sensor card and actuates the ram  130 . The controller recognizes that the cutter  170  has severed the cut link and creates a memory. If either of the cut link or the fuse link have been deactivated, however, the controller signals the display panel  148  to indicate that the sensor card should be replaced and halts the decontamination cycle until a fresh sensor card is inserted. 
     Once the memory has been created, the controller allows the decontamination cycle to commence and monitors the peracetic acid concentration periodically. If the cycle is halted temporarily, the controller  70  retains the memory, and switches the ready light on. If the cycle is recommenced, the controller continues peracetic acid detection. If the cycle is aborted, the controller switches to a “power off” mode. The memory is lost and the controller goes through the steps of blowing the fuse link  152  and disengaging the ram  130 . If the cycle continues to completion, the controller switches to the power off mode and repeats the same sequence. 
     When the sensor card  74  is released by the ram  130 , it is removed from the slot and may be stored together with a printout of the cycle to confirm that peracetic acid monitoring was carried out. 
     While the decontamination system has been described with particular reference to detection of peracetic acid, it should be appreciated that the system is also applicable to detection of hydrogen peroxide and other oxidizing and reducing species. By choosing counter and working electrodes which are particularly suited to the species to be detected, and appropriate electrochemical monitoring techniques, the system may be tailored to the specific detection of a variety of species. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.