Abstract:
A basic unit for a mobile water analyzing system includes a photometer, a test element receptacle, a photometric measuring track, and a pump actuator. The photometer comprises a light source configured to generate a measurement beam and a light detector configured to receive the measurement beam. The test element receptacle is configured so as to allow a separate test element comprising a measuring section and a pump port to be inserted into the test element receptacle. The photometric measuring track is defined by the measuring section when the separate test element is inserted into the test element receptacle. The measurement beam and the photometric measuring track are aligned during a photometric measurement so that a photometric measurement occurs along a longitudinal length of each of the photometric measuring track and the measuring section. The pump actuator is cooperatively connected with the pump port.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/122,560, filed on May 10, 2011, which is a U.S National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2009/062521, filed on Sep. 28, 2009 and which claims benefit to German Patent Application No. 10 2008 050 092.5, filed on Oct. 6, 2008. The International Application was published in German on Apr. 15, 2010 as WO 2010/040655 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The present invention provides a basic unit and a test element for a mobile water-analyzing system for determining an analyte in a water-sample. “Mobile” means that the water-analyzing system of the present invention is not stationary as a continuously working process analyzing-device. 
     BACKGROUND 
     The prior art in the field of mobile water-analysis is currently represented by so-called photometric cuvette tests as described in DE 41 09 118 A1. The use of these tests is performed manually. First, a water-sample is taken by a pipette and given into the cuvette which contains a key-reagent. The cuvette is closed and shaken to mix the water-sample with the key-reagent. It can then be inserted into a photometer and measured. 
     The handling of such a cuvette test is inconvenient and extremely susceptible to errors. The key-reagent used can be dangerous for health and the environment, so that the used cuvette tests must be disposed in an appropriate way. The inconvenient handling makes the cuvette tests practical only for use in a laboratory. 
     SUMMARY 
     An aspect of the present invention is to provide a basic unit and a test element for a mobile water-analyzing system for determining an analyte in a water-sample with an improved handling. 
     In an embodiment, the present invention provides a basic unit for a mobile water analyzing system which includes a photometer, a test element receptacle, a photometric measuring track, and a pump actuator. The photometer comprises a light source configured to generate a measurement beam and a light detector configured to receive the measurement beam. The test element receptacle is configured so as to allow a separate test element comprising a measuring section and a pump port to be inserted into the test element receptacle. The photometric measuring track is defined by the measuring section when the separate test element is inserted into the test element receptacle. The measurement beam and the photometric measuring track are aligned during a photometric measurement so that a photometric measurement occurs along a longitudinal length of each of the photometric measuring track and the measuring section. The pump actuator is cooperatively connected with the pump port. 
     In an embodiment, the present invention also provides a test element for a mobile water analyzing system which includes a sample line comprising an inlet opening, a pump port, an inlet section, a measuring section, and a key reagent. The inlet opening is disposed at a first end. The inlet opening is configured to receive a water sample. The pump port is disposed at a second end of the sample line. The inlet section is disposed between the inlet opening and the pump port. The measuring section comprises at least one window arranged at an end of the measuring section. The measuring section is arranged between the inlet section and the pump port and is coincident with a sample pathway. The key reagent is disposed in the sample line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below on the basis of embodiments and of the drawings in which: 
         FIG. 1  shows a schematic drawing of a mobile water-analyzing system comprising a basic unit and a test-element; 
         FIG. 2  shows the test-element of the water-analyzing system of  FIG. 1 ; 
         FIG. 3  shows an embodiment of a mobile water-analyzing system including a removable cartridge with several test-elements; 
         FIG. 4  shows the removable cartridge of  FIG. 3 ; 
         FIG. 5  shows a front view of an embodiment of an electrochemical test-element; 
         FIG. 6  shows a rear view of the test-element of  FIG. 5 ; 
         FIG. 7  shows a side view of an embodiment of a test-element with a pump membrane, which is controlled via a pump actuator from the basic unit; 
         FIG. 8  shows an embodiment of a test-element with a key-reagent and an auxiliary-reagent, whereby both reagents are arranged between an inlet opening and a measuring section; 
         FIG. 9  shows an embodiment of a test-element with a key-reagent and a auxiliary-reagent, whereby both reagents are arranged between a measuring section and a pump opening; and 
         FIG. 10  shows the test-element of  FIG. 9  in a cross-sectional view in the X-X direction. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment of the present invention, the mobile water-analyzing system is provided with a mobile basic unit and a removable disposable test-element which is insertable into the basic unit. The test-element is a complex prefabricated part, whereby the test-element is provided with a sample-line with an inlet opening which is positioned at the distal end of the test-element. A measuring section is provided in line of the sample-line, the sample-line being provided with a measuring track for an analyzer. A pump opening at the other end of the sample-line can furthermore be connected with a pump mimic of a different nature, the pump mimic of the basic unit comprising the pump actuator. The water-sample can be transported in the sample-line in both directions and can be exactly positioned by using the pump actuator or the pump mimic, respectively. All other parts of the analyzer can, for example, be in the basic unit but outside of the test-element. 
     The test-element is furthermore provided with a key-reagent positioned inside the sample-line, the key-reagent being, for example, in a dry state. The key-reagent can be positioned between the inlet opening and the measuring section or between the measuring section and the pump opening. 
     The basic unit is provided with a test-element slot for holding the inserted test-element. The basic unit is provided with an analyzer to measure the water-sample inside the measuring section photometrically or electrochemically. The basic unit is also provided with a pump actuator which is connected cooperatively with the pump opening of the inserted test-element. The pump actuator sucks the water-sample into the sample-line and transports the sucked water-sample inside the sample-line. 
     The determination of an analyte of a water-sample is performed by first inserting a test-element manually or automatically into the basic unit. The inlet opening is then immersed manually into the water to be analyzed and the pump actuator is activated. The activation can be performed manually or automatically. By activation of the pump actuator, a water-sample is pumped through the inlet opening toward the measuring section. 
     A defined volume of the water-sample is sucked and is segregated as a sample-column whereby the sample column at both ends is terminated by air. By limiting the sample-column with a defined volume, a defined ratio between the water-sample and the key-reagent is provided. In addition, by pumping the segregated water-sample column repeatedly back and forth, the water-sample is mixed with the key-reagent in the sample-line, whereby the contact of the water-sample column with the sample-line wall causes a turbulence flow, so as to provide a homogeneous mixing of the water-sample with the key-reagent. 
     The limitation of the water-sample portion to a defined portion can be realized by giving the customer a signal after the pump actuator has stopped after sucking a defined volume of the water-sample so that the customer obtains the information that the sampling is finished and that the inlet opening can be taken out of the water to be analyzed. Alternatively, the segregation of the water-sample can also be made automatically by using an appropriate valve which conducts air into the sample-line after the defined water-sample volume is sucked. 
     If the key-reagent is, seen from the inlet opening, positioned before the measuring section, the water-sample is mixed with the key-reagent by flowing from the inlet opening toward the measuring section. 
     If the key-reagent is positioned between the measuring section and the pump opening, the water-sample can be first pumped to the measuring section to determine in a first step a background value with the analyzer. The water-sample can thereafter be pumped to the section between the measuring section and the pump opening to react with the key-reagent, and subsequently pumped backwards to the measuring section to quantitatively determine the analyte in the water-sample. 
     On the way from the inlet opening towards the measuring section, the water-sample is mixed with the key-reagent in the sample-line. This can be provided, for example, by a relatively long mixing section between the key-reagent position and the measuring section. The homogenous mixing can also be intensified by pumping the mixture repeatedly back and forth through the sample-line. 
     The key-reagent reacts with the analyte in the water-sample so that the optical and electrochemical properties of the water-sample change. Referring to the example of a photometrical analyzer, the absorption spectra of the water-sample changes particularly at defined spectra lines or defined spectra areas, respectively. The treated and mixed water-sample is measured in the measuring section by the analyzer in the basic unit electrically or optically. 
     The result of the measurement is evaluated and, when necessary, displayed and/or saved. As soon as the result is obtained, the test-element can be removed manually or automatically. 
     The test-element can have a size of a flat match stick so that the sample-line can have a corresponding small cross-section, which is in a range between 0.01 mm 2  and some square millimeters. The photometrical section or the measuring track, respectively, should be as long as possible, for example, in the range of some millimeters to some centimeters. Therefore, the volume of the water-sample in the photometrical section is in the range of one to circa fifty cubic millimeters. According to the dimensions, the amount of the key-reagent is small so that the potential danger for health and environment is also small. As a consequence, the need for an appropriate disposure can be avoided so that a considerable effort for appropriate disposure or recycling to the distributor or producer, respectively, is avoided. 
     All steps which are relevant for the quality of the measurement results of the water analysis, such as the dosage of the key-reagent, the mixing of the key-reagent with the water-sample and the waiting for the reaction time etc., are performed semi- or full-automatically, respectively, and air-tight. Errors and hazards resulting from inaccurate handling can therefore be almost completely excluded. 
     In an embodiment of the present invention, the disposable test-element can be provided with a bottom part and a separate cover part, whereby both parts form the sample-line therebetween. For instance, the bottom part is made out of plastic via injection die-casting whereby the bottom part is provided with an open U-shaped groove. The cover part can, for example, be a clear-transparent plastic film which is adhered or welded to the bottom part after all the reagents and substances have been inserted into the sample-line. The two-part embodiment of the test-element allows for a precise placement of the reagents and substances into the sample-line. This is especially so because the cross-section of the sample-line are a maximum of several square millimeters. 
     In an embodiment of the present invention, the analyzer can, for example, be a photometer with a light source for generating a measurement beam and a light detector for receiving the measurement beam, whereby the measuring section which is passed through by the beam is formed by a photometer section. The photometer can, for example, be provided as a transmission-photometer. A transmission-photometer has, compared with a reflection-photometer, a better information signal. The transmission-photometer allows a more precise quantitative determination of an analyte at a relative short measuring track. The measuring section is provided with at least one photometrical-window for the inlet and the outlet of the measuring beam. With the photometrical method, different ions, for example, chlorine, phosphate and ammonium, can be measured. 
     The analyzer can alternatively be an electrochemical analyzer which determines an electrical parameter in the measuring section. The measuring section is provided with at least one electrode or sensor area, respectively, which is connected through electric lines with contacts or contact areas of the test-element, respectively. The contacts of the test-element are connected with the basic unit through contacts or through contact areas, respectively, and therefore with the analyzer of the basic unit. The electrode or sensor area, respectively, has an area of some square micrometers to some millimeters. Different parameters, such as conductivity, redox potential, pH-value and oxygen content, can be measured with the electrochemical method. 
     The analyzer is alternatively able to measure turbidity or scattering, respectively. 
     The basic unit can be provided with a photometrical, an optical or an electrochemical analyzer, respectively, so that photometrical, optical and also electrochemical test-elements can be used alternatively via the basic unit. 
     In an embodiment of the present invention, the measuring track of the measuring section can, for example, be formed by a longitudinal section of the sample-line. The measuring track is thereby arranged in longitudinal direction, not in a cross direction. In this way, the measuring track is much longer as it would be the case if the measuring track would be in cross direction. The longer the measuring section, the more precise the measurement. 
     The test-element can be provided with a positioning element, which provides an exact positioning of the test-element in the basic unit. The measuring section of the test-element should be exactly in line with the photometer of the basic unit to provide a photometrical measurement without errors. The test-element can therefore be provided with at least one separate positioning element, which provides the positioning in addition to the lateral surface of the test-element in the basic unit. The test-element can, for example, comprise a groove, a cavity or an opening in which a respective snap element of the basic unit snaps in, to position and fix the test-element into the basic unit. 
     The key-reagent can, for example, be provided in a dry state in the sample-line. 
     In an embodiment of the present invention, the sample-line can be provided with an auxiliary-reagent in addition to the key-reagent. The auxiliary-reagent can be arranged between the inlet opening and the measuring section or between measuring section and pump opening, depending on the function. 
     The auxiliary-reagent can, for example be an activator which activates the key-reagent once the auxiliary-reagent is mixed with the water-sample. This can improve the durability, the non-hazardous and/or the insensibility abilities of the key-reagent. 
     The auxiliary-reagent can be a separate reagent which serves to analyze a second analyte in the water-sample. The auxiliary-reagent can cause a multi-stage reaction based on or after the key-reagent has reacted with the water-sample. The support-reagent can also be an analyte-standard, which, for example, can be used to perform a standard addition. 
     The auxiliary-reagent can also be a neutralization-reagent which can be arranged between the measuring section and the pump opening. After the water-sample has been analyzed in the measuring section, the water-sample can be pumped to the auxiliary-reagent which reacts with the key-reagent so that the key-reagent is neutralized. 
     The auxiliary-reagent can also gelatinize and/or color the water-sample after the water-sample has been analyzed. Changing the color of the water-sample shows the customer that the test-element is used. Gelatinizing caused a fixation of the water-sample in the sample-line so that leakage is avoided. 
     It is also possible to arrange numerous of different reagents in series in the sample-line to analyze different analysts of the same water-sample. Once the water-sample arrives at the respective reagent, the reagent can be dissolved in the water-sample so as to react with the analyte, for example, by changing the color. The analyte can be determined in the measuring section and subsequently, the water-sample can be mixed with the second reagent to determine a second analyte in the water-sample. 
     In an embodiment of the present invention, the test-element can be provided with a pump-membrane which seals the pump opening fluid-tight and gas-tight, whereby the pump-membrane encloses a pump volume which can be higher than the total pump-channel volume. This allows a precise transport and placement of the water-sample with only one stroke of the pump-membrane at the complete length of the sample-line. The pump-membrane can be controlled via the pump actuator of the basic unit, whereby the pump actuator can be provided with a rod which pushes the pump-membrane. For example, by pushing the rod, the water-sample can be pumped backwards in direction to the inlet opening and by pulling the rod, the water-sample can be pumped forward in direction to the pump opening. 
     In an embodiment of the present invention, the pump actuator can, for example, be a part of the sample-pump whereby the sample-pump is connected with the pump opening of the inserted test-element. All movable parts of the sample-pump can be arranged at the basic unit. The basic unit and/or the test-element can provide an elastic seal in the pump opening section which provides a sealed connection between the pump opening and the sample-pump. A gas-tight and fluid-tight connection between the pump opening and the sample-pump allows for an accurate and fail-safe operation. An elastic seal provides a sealed fluidic connection between the sample-pump and the sample-line of every test-element. This embodiment provides an accurate and fail-safe analyzing operation even after a long life time and after many measurements. 
     The test-element can be provided as a multi-analyte-test-element with two separate sample-lines with different key-reagents so that the test-element is able to analyze two or more different analysts. The test-element comprises, for each analyte, a complete analyzing-mimic which comprises a sample-line with an inlet opening, a measuring section and a respective key-reagent. This allows the determination of numerous analysts with only one measurement. 
     The test-element can be provided as a stripe. The stripe shaped test-element can, for example, be made out of an elongated and flat casting-component in which the sample-line and the measuring section is formed as a groove. The groove which forms the sample-line can be filled with the key-reagent before the stripe is closed by a clear-transparent plastic film. 
     The photometer window(s) of the photometrical section can be made out of a separate transparent window. The elongated and flat casting-component can alternatively be completely made out of a transparent plastic. 
     It is also possible to arrange numerous of the test-elements in a removable cartridge which can be inserted into the basic unit. The cartridge can, for example, have the shape of a drum with numerous drum chambers, whereby each drum chamber houses a test-element which is inserted air-tight. The removable cartridge allows the use of numerous test-elements in line by using an appropriate manual, semiautomatic or fulllyautomatic load and unload mechanism. 
     In an embodiment of the present invention, an absorption body can, for example, be arranged between the measuring section and the pump opening. The absorption body serves to absorb the water-sample after the measurement has been finished and the sample has been pumped to the absorption body. The water-sample is thereby immobilized and a leakage of the water-sample is avoided. The absorption body can, for example, be a fleece body, a clay body like bentonite or can be a so called super-absorber. The body can additionally comprise a neutralizing reagent. 
     In an embodiment of the present invention, the sample-line can, for example, be provided with a sample filter which filters the water-sample which is sucked through the inlet opening of the test-element. The filtration can be performed before the water-sample is transported to the measuring section to be measured. The sample filter can be made of mineral wool. 
     According to an embodiment of the present invention, the basic unit can be provided with a heating and/or cooling element to heat or to cool the test-element. The heating or cooling can be controlled so that an adjustment of the temperature of the test-element is possible. A temperature of, for example, 40° C. can significantly accelerate the reaction of the key-reagent with the analyte in the water-sample or can stabilize the reaction, respectively. A cooling of the test-element or the water-sample in the sample-line of the test-element, respectively, reduces the outgassing or the formation of disturbing gas bubbles which can cause errors during photometrical measurements. 
     In an embodiment of the present invention, the sample-line can be provided with a hydrophobic stopper capillary. The stopper capillary can be arranged close to the pump opening so that the stopper prevents the transportation of the water-sample through the pump opening into the basic unit. 
     According to an embodiment of the present invention, the sample-line can be provided with a dose capillary arranged between the inlet opening and the measuring section. The dose capillary can, for example, be arranged adjacent to the inlet opening. By using a dose capillary, the water-sample can be sucked, basically by the capillary force, into the test element so that a defined water-sample volume can be segregated. The water-sample can thereafter be pumped repeatedly forth and back inside the sample-channel by using the pump actuator. 
     The reagent can be arranged adjacent to the inlet opening to prevent an interaction of unreacted analyte with the sample-line wall. This is reasonable for the determination of chlorine, if the test-element or the sample-line wall is made of plastic. 
     The test-element can be provided with a drying agent to protect the key-reagent against humidity. For example, the drying agent can be separated in the sample-line by using a hydrophobic stopper capillary, whereby the humidity can flow through the stopper capillary to the drying agent. 
     The inlet opening and/or the pump opening can be sealed with a humidity-tight transport-seal, which can be opened manually or automatically by inserting the test-element into the basic unit, for example, by piercing. Alternatively or additionally, the single test-element can be sealed in a humidity-tight package. 
       FIG. 1  and  FIG. 3  schematically show a mobile water-analyzing system  10 ,  10 ′ for a quantitative determination of an analyte in a water-sample. With the described embodiment of a photometrical analyzing system  10 ,  10 ′ chlorine, phosphate or ammonium can be determined. Alternatively or additionally, the analyzing system can be provided as an electrochemical analyzing system. 
     The analyzing system of  FIG. 1  comprises a basic unit  14  and a removable disposable test-element  16 , which is presently inserted into the basic unit  14 . 
     The test-element  16  is provided with a test-element body  18  made out of plastic. The test-element body  18  has a sample-line  20  which is formed as a groove. The side with the groove opening of the test-element body  18  is closed with a transparent plastic film or aluminum cover, respectively (not shown). 
     The sample-line  20  is provided with an inlet opening  22  which is positioned at the distal referring to the basic unit  14  and through which a water-sample is sucked from a water-reservoir  12 . The distal area of the sample-line  20  is provided with a dry key-reagent  24  arranged in the sample-line  20 . Adjacent to and, in the flow direction, behind the key-reagent  24  is a meander like mix section  26  of the sample-line  20  in which the key-reagent  24  and the sucked water-sample are mixed homogeneously. 
     Adjacent to the mix section  26  is a measuring section  28  in which the analyte is determined quantitatively. The present measuring section  28  is a photometrical section, whereby the measuring section  28  forms a measuring track for the respective photometrical analyzer  30  of the basic unit  14 . Both sides of the measuring section  28  comprise a clear-transparent photometrical window  44 ,  46  as shown in  FIG. 2 . The test-element body  18  can be completely made out of a clear transparent plastic which allows the measuring beam  35  to pass the measuring section  28 . The measuring track of the measuring section  28  is formed by a linear longitudinal section of the sample-line  20 , i.e., the measuring track is running along an imaginary longitudinal axis of the sample-line  20  in the measuring section  28 . This provides substantially much longer measuring track as it would be the case, if the track would run in cross-direction through the sample-line  20 . 
     At the sample-line end opposite to the inlet opening  22 , a pump opening is provided  40  which is connected with a pump actuator of the sample pump of the basic unit when the test-element is inserted. 
     The basic unit  14  is provided with an analyzer  30  which is a transmission photometer with two light sources  32 ,  33  and a light detector  34 . The light-sources  32 ,  33  emit light of different wavelengths. 
     The basic unit  14 ; 114  is furthermore provided with a heat and cooling element  140  which is a peltier-element and is used to heat or to cool the test-element ( FIG. 7 ). The heating or cooling is controlled, so that a constant temperature of the test-element  16 ; 116  is adjusted. A temperature of, for example, 40° C. can significantly accelerate the reaction between an analyte in the water-sample and a key-reagent  24 , or can stabilize the reaction, respectively. A cooling of the test-element  16  or the water-sample in the sample-line  20  of the test-element, respectively, reduces the outgassing or the formation of disturbing gas bubbles which cause errors during photometrical measurement. 
     The test-element  16  is provided with two positioning elements  48 ,  48 ′ which are realized as openings. The positioning element  48 ,  48 ′ cooperates with a respective snap element of the basic unit  14  so that the test-element  16  is fixed reproducibly and exactly. This provides that the measuring beam  35  generated by the light source  32 ,  33  is exactly in line with the photometrical measuring section  28 . The test-element receptacle of the basic unit  14  is formed as a slot  15  in which the test-element  16  fits without any clearance. 
       FIG. 3  shows an embodiment of a mobile water-analyzing system  10 ′ including a removable cartridge  60  which is formed as a drum with 15 drum chambers  62 , whereby each drum chamber  62  carries a test-element  16 . The plastic drum body  64  is sealed axially with a circular sealing foil  66  so that the chambers  62  are sealed gas-tight and fluid-tight. 
     As showed in  FIG. 3 , the removable cartridge  60  is inserted into a respective cartridge slot of the basic unit  14 ′. The basic unit  14 ′ is provided with a cartridge rotary actuator  67  and a test-element shifter  70 . The shifter  70  can shift a test-element  16  automatically from a chamber  62  into the measuring position as shown in  FIG. 3 . 
     As soon as the measurement is finished, the shifter  70  moves the test-element  16  out of the measuring position and ejects it out of the basic unit  14 ′. In a next step, the shifter  70  is completely removed from the cartridge  60 . The rotary actuator  67  then turns the cartridge  60  by one chamber angle so that the next chamber  62  with the test-element  16  is in line with the shifter  70 . As soon as a measurement request is signalized by the customer, the shifter  70  moves the test-element  16  from the chamber  62  into the measuring position so that the measurement can start. 
       FIG. 5  and  FIG. 6  show the respective front view and the rear view of two embodiments of a test-element  80 . The test-element  80  is an electrochemical test-element which is provided with an electrochemical measuring section  82  in the sample-line  84 . The measuring section  82  is provided with two electrodes  86 ,  88  in positioned opposed to each other, the electrodes being connected through electric lines  90 ,  92  with contacts  94 ,  96 . The contacts  94 ,  96  are arranged in line to respective contacts of the basic unit whereby the contacts are connected with the electrochemical analyzer of the basic unit. 
     The rear view of the test-element in  FIG. 6  shows the pump opening  40 . A circular seal element  41  is provided surrounding the pump opening  40  to provide a vacuum-tight connection between the sample-line  84  and a sample-pump realized as a pump actuator  42 . 
       FIG. 7  schematically shows a side view of a part of an embodiment of a mobile water-analyzing system  10 ″. The water-analyzing system  10 ″ is provided with a disposable test-element  116  which is provided with a convex and vesicular pump membrane  118  above the pump opening  40 . The pump element which is formed as a pump membrane  118  has a pump volume which is higher as the total volume of the sample-line  84 . 
     The basic unit  114  is provided with a pump actuator  120  with a motor  122  whereby the pump actuator  120  controls a rod  124 . The rod  124  pushes against the pump membrane  118  of the inserted disposable test-element  116 . The water-sample can be moved over the complete length of the sample-line forward and backward by the rod  124  deforming the pump membrane  118 . 
     To determine an analyte in a water-sample, first a test-element  16  is inserted into the test-element receptacle  15  of the basic unit  14 . This can, if given, activate the basic unit  14 . In a next step, the inlet opening  22  of the test-element is immersed manually into the analyzing water-reservoir  12  so that the sample-pump  42  sucks a water-sample into the measuring section  28  of the sample-line  20 . The analyzer  30  determines the background signal of the water-sample in the measuring section. 
     As soon as the background signal determination is finished, the water-sample is pumped forward from the measuring section  28  into the reagent section  23 . The water-sample meets with the key-reagent  24  in the reagent section  23  so that the key-reagent  24  is mixed with the water-sample. The key-reagent  24  reacts with the analyte in the water-sample so that the optical properties of the water-sample change. 
     By pumping backwards, the water-sample flows back from reagent section  23  to the measuring section  28 . The water-sample is analyzed photometrically by the analyzer  30 . The result of the measurement is a gross-value. Subtracting the background from the gross-value leads to a net concentration of the analyte in the water-sample. 
     With the test-element  80  of  FIG. 5  and  FIG. 6 , an even more precise determination of the analyte in a water-sample can be realized by using standard addition. After the determination of the analyte in the measuring section  82 , the water-sample is pumped again forward to the section with the support-reagent  25 , whereby the water-sample is mixed with the first auxiliary-reagent  27  which forms a first analyte standard. 
     The water-sample is then pumped backwards from the section with the auxiliary-reagent  25  into the measuring section  82 , whereby the water-sample is analyzed again photometrically. The water-sample is transported again forward to the section with the second auxiliary-reagent  29 , whereby the water-sample is mixed with the second auxiliary-reagent  31  which forms a second analyte standard. Finally, the water-sample is transported again backwards from the section with the second auxiliary-reagent to the measuring section, whereby the water-sample is measured by the photometer. 
     Both photometrical analyte standard measurements lead to a concentration-absorption characteristic line which allows an exact determination of the analyte concentration of the water-sample by using the net concentration value. 
       FIG. 8  shows an embodiment of a test-element  130  in which the key-reagent  132  is arranged close to the inlet opening  22 . This positioning of the key-reagent  132  is particularly useful for a chlorine reagent to prevent a reaction of the analyte chlorine with the plastic wall of the sample-line  20 . The sample-line  20  or the complete body of the test-element  130 , respectively, is made out of a material inert for chlorine, such as polystyrene. 
     Between the measuring section  28  and the pump opening  40 , an auxiliary reagent  134  is provided. The auxiliary reagent  134  can be a separate reagent for analyzing a second analyte in the water-sample. The auxiliary reagent  134  can cause a multi-stage reaction with the water-sample, based on or after the key-reagent  132  has reacted with the water-sample. The auxiliary-reagent  134  can also be an analyte-standard which, for example, can be used to provide a standard addition. 
     The auxiliary-reagent  134  can also be a neutralization-reagent. After the water-sample has been analyzed in the measuring section  28 , the water-sample is transported to the auxiliary-reagent  134 , which reacts with the key-reagent  132 . The key-reagent  132  is neutralized so that the test-element can be disposed in the community waste. 
     The auxiliary-reagent  134  can also gelatinize and/or color the water-sample after the water-sample has been analyzed. Changing the color of the water-sample shows the customer that the test-element  130  has been used. By gelatinizing, the water-sample is fixed in the sample-line  20  so that the water-sample cannot leak. 
       FIG. 9  shows an embodiment of the test-element  140 . The key-reagent  142  and the auxiliary-reagent  144  are positioned relatively close to each other between the inlet opening  22  and the measuring section  28 . For instance, the auxiliary-reagent  144  is an activator which activates the key-reagent  142  once the auxiliary-reagent  144  is mixed with the water-sample. Both reagents  142 ,  144  can alternatively be arranged between the measuring section  28  and the pump opening  40 . 
     The sample-line  20  is provided with an absorption body  146  which is a fleece body and is arranged between the measuring section  28  and the pump opening  40 . The sample-line  20  is provided with a dose capillary  148  adjacent to the inlet opening  22 . Adjacent to the pump opening  40 , the sample-line  20  can be provided with a stopper capillary  150  which prevents any leakage out of the sample-line  20 . The sample-line  20  is also provided with a sample filter  152  between the inlet opening  23  and the measuring section  28 , and in particular close to the inlet opening  23 , to filter the sucked water-sample. 
       FIG. 10  shows, as an example, a cross section of the test-element  140  of  FIG. 9 . The test-element  140  comprises basically two parts: a plastic bottom part  150  which is made by injection die-casting and a separate cover part  152  which is a clear-transparent plastic film adhered or welded to the bottom part. The bottom part  150  is, in the cross section, provided with a U-shaped sample-line groove  21  which is closed by the cover part  152 . In this way, the bottom part  150  and the cover part  152  form the sample-line  20 . 
     The present invention is not limited to embodiments described herein; reference should be had to the appended claims.