Patent Document

FIELD OF THE INVENTION 
     This application relates generally to the detection of a chemical agent in a solution and more particularly to a system and method for controlling the levels of a biocide in process water. 
     BACKGROUND OF THE INVENTION 
     Chemical agents are used as detergents, disinfectants, food additives, medicinal agents, etc. Use of these agents is often tied to the concentration of the chemical agent in a solution, i.e., the required concentration of the agent needed to accomplish the target use. It is therefore important to both measure and control the concentration of an agent in a solution during its use. For example, biocides are used to disinfect surfaces in the food and beverage industry, i.e., used in the cleaning and disinfecting of food surfaces, such as fruits and vegetables, food contact surfaces, such as counter tops and dishware, and in the cleaning and disinfecting of the inside surfaces of polyethylene telephthalate (PET) bottles. It is critical that a biocide be delivered to the target at a proper use concentration. Delivery of an insufficient amount of biocide may result in the target being tainted with possible hazardous levels of microbes and/or may result in the user violating certain predetermined regulatory requirements, causing the user to be fined or suspended by the relevant regulatory agency. Alternatively, delivery of an excessive amount of a biocide to a target may have a toxic effect on the field worker and/or consumer of the treated product, i.e., from fumes, skin contact or consumption. Further, excessive levels of biocide add unnecessary cost to the disinfection process, i.e., the biocide costs money, and a higher than necessary concentration of biocide may result in increased corrosion to delivery equipment thereby reducing the equipment&#39;s life expediency and potentially increasing maintenance costs. Therefore, it is of great importance to accurately monitor and determine the concentration of a chemical agent being delivered to a target over the time period of its target use, and to have the ability to modify the agent&#39;s concentration during that same time period. 
     One common technique for determining the concentration of a chemical agent in a solution is through the use of a manual titration kit. Here, a field worker manually takes a sampling of the solution having the target chemical agent that is being tested, adds an indicator agent to the sample and then adds titrant in a drop wise fashion until the approximate endpoint of the chemical reaction has been reached (the endpoint being a detectable point at which the concentration of the chemical agent is determined from the amount of titrant added, as discussed in greater detail below). The manual titration process tends to be fairly inaccurate because the amounts of sample solution, indicator agent and titrant can vary significantly with manual delivery, and the detection of the endpoint can vary significantly with manual detection. As a result, manual titration of a chemical agent&#39;s concentration of any two identical solution samples may vary as much as 20 to 50% by a typical worker in the plant. This variation in results is often unacceptable, as it continues to leave a large amount of uncertainty with regard to the target chemical agent&#39;s true concentration. 
     Furthermore, manual detection is labor intensive and time consuming. On average, a field worker may test a solution every hour or two, requiring the field worker to travel to and perform the titration. In addition, it is difficult to ensure a constant concentration or control of chemical if it is being measured and tracked only every 1 to 2 hours. 
     A recent attempt has been made to automate the processes used to detect chemical agents in a solution. A syringe mixing device draws a sample from the solution into a syringe and then draws titrant into the syringe until the endpoint of the reaction is reached. However, the equipment required in this approach is expensive, and the added accuracy and precision unnecessary. 
     Against this backdrop the present invention has been developed. 
     SUMMARY OF THE INVENTION 
     Above problems are solved by a method for determining the concentration of a chemical agent in a source. The method includes receiving a sample from the source that contains the chemical agent, triggering the release of a number of drops of titrant into the sample, detecting the number of drops of titrant released into the sample and computing the concentration of the chemical agent in the sample source based on a change in a characteristic of the sample, for example, optical characteristics, oxidation-reduction potential, tracer element concentration, and pH, where the characteristic is dependent on the number of drops of titrant released into the sample. The above problems are further solved by a system for determining the concentration of a chemical agent in a sample, of tracking the concentration of the chemical agent in the sample, and of taking corrective action. 
     The system includes a reaction cell for receiving a sample from a source, a titrant dropper for releasing one or more drops of titrant into the sample in the reaction cell, a first photosensor for receiving light from a light source where the photosensor senses a disruption in the light for every drop of titrant released by the titrant dropper into the reaction cell, an instrument for detecting or sensing a change in the sample, for example a second photosensor, and a controller for communicating with the detection instrument where the controller determines the concentration of the chemical agent in the sample from the data it receives from the detection instrument and the number of light disruptions detected by the first photosensor. Further, the system can include a dosing pump for controlling the concentration of the chemical agent and a user interface for alerting a user of the determined concentration of the chemical agent. 
     These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an embodiment of the system for controlling the concentration of a target chemical agent in a solution in accordance with the present invention. 
         FIG. 2  illustrates an exemplary titration reaction in accordance with the present invention. 
         FIG. 3  illustrates a representative titration curve showing the endpoint of one potential chemical reaction in accordance with the present invention. 
         FIG. 4  illustrates a representative curve used to determine the final concentration of a target chemical agent in a sample in accordance with the present invention. 
         FIG. 5  illustrates operations taken to control the chemical agent concentration in a sample source in an embodiment of the present invention. 
         FIG. 6  illustrates detailed operations taken to control the chemical agent concentration in a sample source in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention control the concentration of a chemical agent in a source. For example, embodiments of the present invention may be used to control the concentration of a biocide in process water at a fruit and vegetable processing plant, where a biocide is used to reduce or eliminate any microbes resident on the fruits and vegetables before sale and consumption by the public. As such, an embodiment of the present invention detects and modifies, i.e., controls, the biocide concentration in the process water so that a proper concentration of biocide is maintained in the process water and, therefore, is applied to the fruits and vegetables. A further example of an embodiment of the present invention may be used to control the biocide concentration in solutions used to disinfect the internal surfaces of polyethylene telephthalate bottles. Other uses for the methods and systems for controlling a concentration of a chemical agent in a source are envisioned, and are within the scope of the present invention. 
     Aspects of the invention are based on detecting a target chemical agent&#39;s concentration in a solution by using volumetric titration. As known in the art, volumetric titration is based on analyzing a composition, i.e., a chemical agent, of a solution by adding known amounts of a standardized solution until a given reaction (for example, change in an optical characteristic, precipitation, change in conductivity, change in pH, and the like) is produced. For purposes of illustration, the present invention will be described using a change in an optical characteristic, for example a color change, to signal the given reaction. However, other titration reactions are envisioned to be within the scope of the present invention, for example, using a pH meter to follow a change in pH based on the concentration of the target agent in the solution. 
     A titrant is mixed in known increments with a sample from the solution, the sample having an unknown concentration of a target chemical agent, and an “indicator,” until a given reaction point, for example color change, is produced. The reaction point is typically termed the “endpoint,” and is directly indicative of the concentration of the target chemical agent in the solution, as is discussed in greater detail below. The analysis of the chemical agent is automated so that numerous concentration readings may be performed and analyzed over the course of a source run (the period during which the solution containing the unknown concentration of chemical agent is being used to accomplish its predetermined goal). A corrective action may be taken when the titration provides results showing that the target chemical agent concentration is outside a series of predetermined parameters. 
     A chemical analysis is used to elicit the chemical agent&#39;s concentration in the solution. As is known in the art, a typical chemical analysis involves adding a known concentration of an s oxidizing agent, i.e., an agent that oxidizes, to an unknown concentration of a reducing agent, i.e., an agent that reduces, (or vice versa). Typically, an indicator having a distinctive colored reaction product serves to show the endpoint of the chemical reaction, i.e., the point at which the electrons lost by the oxidized species equals the number of electrons gained by the reduced species. The “indicator” in the chemical reaction typically has a distinctive color in one oxidative state as compared to other oxidative states. By knowing the concentration and volume of the known chemical agents, as well as the balanced equation for the chemical reaction, one can determine the concentration of the unknown or target chemical agents by following the distinctive color change of the indicator. Alternatively, as discussed in greater detail below, a standard curve using similar experimental conditions with known amounts of both titrant and target chemical agent may be plotted, to provide a relationship between the amount of titrant required to reach the endpoint of a known amount of target chemical agent (see below). 
     An appropriate enzyme or catalytic device can be added to the solution being tested so as to reduce the background levels of species that interfere with the chemical agent being tested. For example, catalase enzyme or platinum can be added to a solution being tested for peracid levels (biocide levels) so as to reduce the background levels of hydrogen peroxide but not substantially effect the peracid levels. The reduction in hydrogen peroxide levels helps minimize its effects on the chemical analysis, thereby providing a more distinct endpoint of the chemical reaction. 
     This system could also be used to measure more than one species in a solution. For example, hydrogen peroxide could be determined in the first step of the titration and peracid could be determined in the second step of the titration. 
       FIG. 1  illustrates a system  106  for controlling the concentration of a chemical agent in a source according to an embodiment of the present invention. A sample pump  108  receives a signal from a controller  110  to initiate the determination of the chemical agents concentration in the sample source  112 . The sample pump  108  may flush out a reaction cell  114  with a volume of solution from the sample source  112 . The flush of the reaction cell  114  may be accomplished by flushing from 20 to 50 volumes of solution through the reaction cell  114 . The flush should be adequate to remove residual reactants, i.e., indicator, residual solution sample, in the reaction cell  114  from any previous use. Solution from the sample source  112  is flushed through the reaction cell  114  through the combined effort of the sample pump  108 , which continually fills the reaction cell with solution and either a self primed drain pump  118 , aspirator or simple gravity overflow for removal of the solution. 
     After the reaction cell  114  has been flushed, the reaction cell  114  is filled with solution to a predetermined level, termed the “flushing level”  120 . The flushing level  120  is typically near the top of the reaction cell  114  but may be modified dependent on the available sample source sizes and reaction volumes. A drain pump  118  is either self-activated or activated by the controller to remove solution from the reaction cell  114  until the solution volume corresponds to a predetermined level in the reaction cell  114 , termed the “monitoring level”  122 . Note that the removal of solution from the reaction cell may also be accomplished by gravity overflow, for example by actuating a relief valve located at the monitoring level  122  or other like means. The monitoring level  122  represents a predetermined amount of solution to be tested on that particular run, i.e., one determination/modification of the target chemical agent&#39;s concentration, of the system  106 . The solution that fills the reaction cell to the monitoring level  122  is referred to as the solution sample  116 . As with the flushing level  120 , the monitoring level  122  can be altered between determinations of chemical agent concentration dependent on, for example, available sample volume, reaction parameters, etc. The monitoring level  122  in the reaction cell  114  provides a precisely regulated reaction volume for the volumetric titration that is not dependent upon adding predetermined volumes of solution to the reaction cell  114 , where residual solution may add up in the reaction cell  114  and change the reaction volume of the volumetric titration. Typical sample sizes, as determined by the monitoring level  122 , are from 2 to 100 mls, and preferably from 10 to 20 mls. 
     The reaction cell  114  is preferably, i.e., where an optical characteristic is being followed, a light permeable reaction vessel having the capacity to hold a liquid. In one embodiment of the present invention, the reaction cell is a flow cell or cuvet. Other types of reaction cells are within the scope of the invention as long as the cell is complementary with the system  106 . 
     A reaction stirrer  124  is activated by the controller  110  during or soon after the sample  116  is delivered to the reaction cell  114 . The reaction stirrer  124  is typically a magnetic stirring device located below the reaction cell, having a Teflon™ coated stir bar within the reaction cell. The speed and timing of a reaction&#39;s stirring is controlled by the controller and may be manipulated dependent upon reaction volume and speed with which the reagents  126  must be combined during a chemical agent detection run. Alternatively, the reaction stirrer  124  may be a stand alone device that is manually turned on and left on during the entire course of a run or runs, thereby not receiving or dependent upon a signal from the controller  110 . Note that the reaction stirrer  124  may also be or include a shaft stirrer, recirculation pump or other like devices. 
     In one embodiment, a light-emitting diode (LED)  128 /photosensor  130  (termed the second photosensor) assembly measures the initial light intensity of the sample. (see also  FIG. 3 ) The LED  128  emits light at a wavelength of from 380 nm to 800 nm through the reaction cell  114 . The second photosensor  130  receives the light and measures the received lights intensity and transmits this information to the controller  110 . This initial reading of the sample in the reaction cell  114  is the baseline (comparison point) mV response or I(hi) (see below). 
     A reagent pump  132  receives a signal from the controller  110  to add a set of reagents  126  to the sample  116  in the reaction cell  114 . Reagents  126  are typically used in a titration in order to optimize the sensitivity and precision of the detection of the target chemical agent in the sample source  112 , and so numerous different reagent combinations may be used dependent on the target chemical agent, sample source and indicator chemistries. Titrations are based on a chemical reaction whereby the concentration of the chemical agent may be determined by adding a solution of known volume and strength until a reaction point is reached, usually indicated by a color change (see below). One example of a titration chemistry for use with the present invention is shown in  FIG. 2  where the concentration of a biocide, e.g., peracid, may be detected in process water. An unknown concentration of peracid (CH 3 COOOH) from a sample source is reacted with I −  to form an unknown amount of I 3   − , which is further reacted with starch to form a dark blue I 3   − /starch complex. This portion of the reaction takes place when the reagents are added to the reaction cell. As discussed more fully below, a known amount of titrant (2S 2 O 3   2− ) (reducing agent) is then added to the reaction cell where it reacts with the colored I 3   − /starch complex to dissociated I 3   − /starch complex to a colorless 3I −  and starch mixture. The reaction produces a color change from dark blue (I 3   − /starch complex) to colorless (3I −  plus starch) which is followed by the LED ( 128 ) and the second photosensor ( 130 ) until the endpoint of the reaction is reached. Other titration chemistries can be used in conjunction with the present invention. Titrations depend on the mode of detection, i.e., optical characteristic, pH, conductivity, etc, so that a method of the present invention may also utilize NaOH as the titrant and detect a change in the sample with a pH meter as well as other known means within the art. 
     Still referring to  FIG. 2 , the reagents  126 , for the presently illustrated embodiment, can include an acid (H + ) to modify the reaction pH to between 1 and 4, and an indicator (3I −  and starch) to sharply define the endpoint. Acids for use with the reaction illustrated in  FIG. 2  include, but are not limited to, phosphoric acid, hydrochloric acid, sulfuric acid, etc. The preferable acid is phosphoric acid (H 3 PO 4 ). One preferable combination of reagents for detecting peracids using the chemical reaction illustrated in  FIG. 2  is to have a sample that contains 53% phosphoric acid, 10% potassium iodide and 2% starch solution. Further, a catalyst may be added to facilitate one or more aspects of the target chemical reaction, for example, ammonium molybdate may be used to facilitate the redox reaction or catalase enzyme can be used to reduce the background of hydrogen peroxide. 
     Preferably, the combined reagents  126  are mixed together into one solution for addition to the reaction cell  114 , and hence the solution sample  116 . Surprisingly, sequential addition of each reagent to the reaction cell has proven to be less accurate, yielding larger data standard deviations. 
     Referring again to  FIG. 1 , the reagents  126  are mixed with the solution sample  116  for a predetermined amount of time by the action of the reaction stirrer  124 . If the sample contained peracid, the potassium iodide reacts with the peracid to form a carboxylic acid, water and iodine (I 3   − ). (see  FIG. 2 ). The iodine further reacts with the starch to form a complex having a dark blue color. It is important that the peracid is the limiting reagent so that all the peracid has reacted to form a quantitative amount of iodine/starch complex. After the reagents  126  react with any peracid in the sample, a second reading is taken through the reaction cell  114  by the LED  128 /photosensor  130  assembly to measure the light intensity in mV, this is often termed the I(lo) point (see below). 
     After the I(lo) reading has been communicated to the controller  110 , a signal is sent by the controller  110  to trigger a titrant pump  134  to add titrant to a titrant dropper  138 . The titrant pump  134  is activated and removes a predetermined amount of titrant from the titrant reservoir  140  and fills the titrant dropper  138 . A preferable amount of titrant for addition to the titrant dropper  138  is between 1 and 2 milliliters (mls). The titrant used to illustrate the embodiment of the present invention in  FIG. 2  is sodium thiosulfate (Na 2 S 2 O 3 ). Note that as the sodium thiosulfate is added to the reaction cell it reacts with the dark blue iodine/starch complex to form colorless reaction products, I 3   −  and S 4 O 6   2− . The addition of titrant continues until the endpoint, or other such target point, of the reaction is reached. The endpoint of the reaction indicates the point where a known concentration of titrant causes a determinable number of electrons to be gained or lost from the target species, associated with a distinctive color change (dark blue to colorless in the example discussed in  FIG. 2 ). 
     Again referring to  FIG. 1 , addition of titrant  136  to the reaction cell occurs when individual drops of titrant  136  are released from the titrant dropper  138  into the reaction cell  114 , and hence solution sample  116 /reagent mixture. A LED  142 /photosensor  144  (termed the first photosensor) assembly detects the number of drops  136  released from the titrant dropper  138  by detecting each drop as an interruption of light—causing a substantial pulse of light for each drop that falls from the titrant dropper  138  into the reaction cell  114 . A pulse counter  143  relays the information to the controller  110  and counter  147 . In preferable embodiments, the release of each drop  136  of titrant is timed so that the drop is fully mixed into the solution sample  116 /reagent  126  mixture and a reading made by the LED  128 /photosensor  130  before the next drop of titrant is released. One embodiment for facilitating the delay is to have a valve  146  in the titrant dropper  138  that is responsive to a signal from the controller  110 . As titrant is added to the reaction cell, the LED  128 / 130  is continually transmitting the light intensity of the solution sample within the reaction cell to the controller  110 . 
       FIG. 3  illustrates a graphical representation of a titration using an optical characteristic, i.e., light intensity, to follow the reaction. Using the chemical reaction discussed in  FIG. 2 , in the absence of reagents, the solution sample allows the majority of light to pass through to the second photosensor  130 , as indicated by arrow  100  (I(hi)). Addition of reagents  126  causes the peracid in the sample to induce the formation of a dark blue complex, e.g., I 3 /starch complex, as indicated by arrow  102  (I(lo)). The dark blue complex causes a drastic reduction in the light intensity detected at the second photosensor  130 . Addition of titrant to the sample causes the dark blue complex to react and form a colorless solution. As the colorless reaction species are formed, more light is detected by the second photosensor until the endpoint is reached, as indicated by arrow  104 . 
     Again referring to  FIG. 1 , once the endpoint is reached the controller  110  signals the titrant pump  134  to turn off. Note that the endpoint is any reproducible point that avoids noise at the transition region, for example, at ½[I(hi)+I(lo)], ⅓[I(hi)+I(lo)], highest point of the 1 st  derivative of the curve, and the like, and can be in a linear or log scale. 
     Once the controller  110  has determined the amount of titrant required to reach the endpoint of the reaction, it may send a signal to the reaction stirrer  124  to turn off. A second drain pump (not shown) or waste valve may be activated to remove the test sample. In preferred embodiments, a post flush of sample or water may be used to minimize any lingering starch or other contaminant in the reaction cell. The number of drops of titrant required to reach the endpoint of the reaction may then be compared to “standard curve” data stored in the memory of the controller  110 . Note, the standard curve data stored in the controller  110  is determined by having previously taken a series of samples, each sample having a sequentially larger concentration of the target chemical agent, and testing each sample on the system  106 . The number of drops of titrant required to reach the endpoint (as determined by light intensity) or any standardized points of light intensity, for each sample is plotted to provide a relationship between chemical agent concentration and drops of titrant required to reach the endpoint. As shown in  FIG. 4 , parts per million of a chemical agent  149  in a sample are plotted against the number of titrant drops  151  required to reach the endpoint  153  for that chemical agent under the reaction conditions, and repeated for accuracy  155 . The data plot is referred to as a standard curve and is stored in a table in memory in the controller  110 . The controller  110  takes the data in memory and determines the unknown concentration of the target chemical agent from the number of drops of titrant required to reach the endpoint of the reaction. In preferred embodiments, a parametric fit, e.g., linear least square, is performed and a conversion performed by equation with the parameters determined from the fit. Note, as discussed previously, other standard curve data can be stored in the controller  110 , for example, the number of drops of titrant in relation to a target pH, etc. 
     A user interface  148  is alerted at the completion of a sample run and the concentration results of the chemical agent are displayed. Results can be transmitted to a field operator, to an operation facility, or to a central data base for future use, etc. For example, a central data base  157  can be created having data from previous sample runs. The stored data can be generated from the same or other like sources and can be used as a comparison point for tracking the performance of the system  106  at controlling the chemical agent&#39;s levels in the source, for tracking the efficiency of how much chemical agent is added to the source as compared to how well the source&#39;s chemical agent levels have been controlled, i.e., the efficiency of sample run. The generated results from the sample run can be compared to the data in the central data base to determine if additional supplies need to be obtained for future runs/treatments, as well as like circumstances. 
     When the concentration of the chemical agent is below or above certain predetermined critical parameters an alarm can be triggered, for example, if the chemical agent is at a toxic concentration in the sample source  112 , an alarm is set off, and optionally the sample source  112  drained. In a preferred embodiment, the user interface  148  can transmit manual instructions from the user to the controller  110 . For example, the user may request that the sample run be repeated, concentration parameters altered, sample size adjusted, etc. 
     When the analyte concentration in the sample  116 , and hence the sample source  112 , is below a predetermined parameter, the controller  110  determines a corrective amount of agent to be added to the sample source  112 . Controller  110  signals a dosing pump  150  to pull the corrective amount of agent from a supply  152  and release it into the sample source  112 . Release of the agent is controlled into the sample source  112  to quickly and safely change the agent&#39;s concentration. When the chemical agent concentration in the solution sample  116 , and hence the sample source  112 , is above a predetermined parameter, the controller  110  determines the corrective dilution required to bring the existing agent&#39;s concentration within the predetermined parameters. Controller  110  signals the dosing pump  150  to pull the corrective amount of water or other non-agent containing solution  154  from a supply and release it into the sample source  112 . 
     One method in accordance with a preferred embodiment of the present invention is shown in  FIG. 5 . In operation  500 , the parameters for the target chemical agent are set and input into the controller. Parameters include, for example, the sample size, reaction chemistry, the concentration of each reagent and volume of reagent required for each sample run, titrant concentration and volume of titrant to be loaded into the titrant dropper, delay time between each drop of titrant release, standard curve conversion between the number of titrant drops and the target agent concentration, the range for acceptable sample chemical agent concentrations, dosing data for corrective action, etc. 
     Operation  502  assumes control from operation  500 . In operation  502 , solution of appropriate volume is removed from the sample source for analysis, and a sample added to the reaction cell. The sample is mixed with the appropriate reagents for analysis. Operation  502  surrenders control to operation  504 . In operation  504 , release of a titrant is triggered. The titrant is released one drop at a time so that the titrant drop falls into the sample. In one embodiment of the present method there is a sufficient delay between the release of each drop of titrant to allow the titrant to be mixed into the sample and a reading made of the sample. One embodiment for this delay is a valve in the titrant dropper that is triggered at appropriate preset intervals. Operation  506  assumes control from operation  504 . In operations  506  and then operation  508 , the release of a drop of titrant is detected and transmitted to the controller as a counted drop, while the response to the drop of titrant in the sample is monitored. A preset reaction point, for example the endpoint, is compared by the controller to the monitored data received from the sample. When the preset reaction point is the same or within a preset range of the reaction point, the concentration of target chemical agent is calculated from the number of drops of titrant released into the sample. Operation  510  assumes control from operation  508 . In operation  510 , a result from the run is displayed on a user interface. Operation  512  assumes control from operation  510 . In operation  512 , a determination is made as to whether corrective action is required to either dilute or concentrate the agent&#39;s concentration in the sample source. In one embodiment, the chemical agent is automatically released as a result of the determined concentration. 
     Another method in accordance with a preferred embodiment of the present invention is shown in  FIG. 6 . In operation  600 , the measurement range for the next sample run is entered from either a preset menu of existing standardized ranges or new ranges entered. The ranges may be automatically entered, i.e., use last data unless commanded otherwise, or may require a manual command for each sample run. Operation  602  assumes control from operation  600 . In operation  602 , the concentration of the titrant is entered. Preferably, the information obtained in operations  600  and  602  is sufficient to calculate a target chemical agent concentration from a number of titrant drops required to reach an endpoint for a particular titration run. 
     Operation  604  assumes control from operation  602 . In operation  604 , the reaction stirrer is turned on to a preset speed. Sample volume size, titrant concentration, length of delay between release of each titrant drop, viscosity of the sample, etc, are factors in determining the reaction stirrer&#39;s set speed. Alternatively, a default speed may be set and used to accommodate the most extreme reaction conditions. Operation  606  assumes control from operation  604 . In operation  606 , the sample pump is activated and solution is taken from the sample source and flushed through the reaction cell. The amount of solution flushed through the reaction cell is preset, and dependent on the size of the reaction cell, sample size, flow time, flow rate, sensitivity required for the chemical analysis, etc. The solution can be flushed through the reaction cell either passively, by allowing the solution to flow out of the reaction cell, or actively by siphoning or pumping the excess solution from the reaction cell as the reaction cell fills. Operation  608  assumes control from operation  606 . In operation  608 , the drain pump is activated and solution removed from the reaction cell until a preset volume of sample remains for testing. 
     After operation  608  is completed, operation  610  assumes control. In operation  610 , the light intensity through the sample is ascertained. The light intensity reading is the baseline (I(hi)) for further readings made on the sample during the course of the analysis. (see  FIG. 3 ) In an embodiment of the present method, a determination operation  612  ascertains whether the light intensity of the sample is within a preset range of light intensity. A lower than expected light intensity suggests either a damaged light source or reaction cell, i.e., scratched glass, smudged glass, etc, or possibly that contaminates from previous reactions remain in the reaction cell. Operation control branches YES if the light intensity of the sample is within the appropriate range and operation control is assumed by operation  614 . Operation control branches NO if the light intensity of the sample is not within the appropriate range and operation  606  assumes control. If operation control branches NO a second time in a row, operation control switches to operation  642 , and the system is switched off. 
     In operation  614 , the reagent pump is activated and a preset volume of reagent is added to the reaction cell. Operation  614  delays for a preset period of time to allow the added reagents to mix with the sample before surrendering control to operation  616 . In operation  616 , the light intensity is ascertained for the sample/reagent mixture (I(lo)). (see  FIG. 3 ) Operation  618  assumes control from operation  616 . In operation  618  the pulse counter is reset. 
     Operation  620  assumes control from operation  618 . Operation  620  triggers the titration pump to add titrant to the titrant dropper. Optionally, operation  620  may control a valve in the titrant dropper to regulate the release of each drop of titrant. Operation  622  assumes control from operation  618 , a drop of titrant is released from the titrant dropper into the sample. 
     Operation  624  assumes control from operation  622 . Operation  624  detects the drop of titrant released from the titrant dropper which is relayed to the pulse counter. The pulse counter counts the drop and relays the information to the controller/counter. Operation  626  assumes control from operation  624 . In operation  626 , the light intensity of the sample/reagent/titrant mix is determined. Operation  626  delays before ascertaining the light intensity so that the titrant is properly mixed into the reaction mixture, and the reaction allowed to come to an equilibrium. After operation  626  is completed, determination operation  628  ascertains whether the endpoint (or other reaction stop point) has been reached. Operation control branches YES if the light intensity is within a predetermined range from the light intensity endpoint (½(I(hi)+I(lo) or other endpoints that avoid noise at the transition point) and control is surrendered to operation  630 . Operation control branches NO if the light intensity is below the predetermined range from the light intensity endpoint and operation  622  assumes control. This cycle will continue until results allow operation control to branch YES. 
     Operation  630  assumes control from operation  628  to turn off the titrant pump and in embodiments with a titrant valve, to close the valve in the titrant dropper. Operation  632  assumes control from operation  630 . Operation  632  assimilates the number of drops of titrant required to reach the endpoint of the reaction with preset data from standard curves or other analyte conversions, to calculate the concentration of target analyte in the sample and hence the sample source. Operation  634  assumes control from operation  632  and displays the chemical agent concentration for viewing by a field worker, facility manager or other interested user. After operation  632  is complete, determination operation  636  ascertains whether the sample source agent concentration is within the preset ranges. Operation control branches YES if the agent concentration is within preset ranges and determination operation  638  assumes control. Operation control branches NO if the agent concentration is not within preset ranges and operation  640  assumes control. 
     Determination operation  638  ascertains whether multiple determinations for each sample are required. Operation control branches YES where a next reading is required at some future time. Variable delay periods may be present with operation control, so that a next sample is analyzed in 1 minute, 5 minutes, 15 minutes or any other desirable interval. When the delay period has expired operation control is surrendered to operation  606 . Operation control branches NO where a next reading is not required and operation  642  assumes control. Operation  642  turns off the reaction stirrer, sample pump, drain pump, light sources, pulse counter, and display. 
     When operation  640  has assumed control, operation control determines the amount of chemical agent required, or the dilution factor needed, to bring the agent&#39;s concentration within predetermined agent concentrations. Operation  644  assumes control from operation  640  once the appropriate corrective action has been determined. In operation  644 , the dosing pump is activated to release either chemical agent, to concentrate the chemical agent concentration, or water (or other sample compatible liquid), to dilute the chemical agent concentration, into the sample source. Once complete, operation  638  assumes control from operation  644 . 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.

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