METHOD FOR DETERMINING A CUVETTE FORM CORRECTION VALUE

Abstract

The invention refers to a method for determining a cuvette form correction value (F) for a laboratory analysis cuvette (10) filled with a liquid reagent (60) and having a transparent cuvette body (12) comprising a vertical wall (14) and a bottom wall (13), comprising the method steps: Determining the liquid reagent volume (V) of the liquid reagent (60) filled into the laboratory analysis cuvette (10), optically determining the liquid reagent level (H) of the liquid reagent (60) in the laboratory analysis cuvette (10) by a level determination camera (24), calculating a horizontal inner width (D) of the laboratory analysis cuvette (10) from the determined liquid reagent volume (V) and the determined liquid reagent level (H) by an electronic control (26), and calculation of the form correction value (F) from the calculated horizontal inner width (D) and a reference inner width (D) of the laboratory analysis cuvette (10) by the electronic control (26).

Claims

1-8. (canceled)

9. A method for determining a cuvette form correction value for a laboratory analysis cuvette filled with a liquid reagent and having a transparent cuvette body comprising a vertical wall and a bottom wall, comprising the method steps: determining the liquid reagent volume of the liquid reagent filled into the laboratory analysis cuvette; optically determining the liquid reagent level of the liquid reagent in the laboratory analysis cuvette by a level determination camera; calculating a horizontal inner width of the laboratory analysis cuvette from the determined liquid reagent volume and the determined liquid reagent level by an electronic control; and calculating the form correction value from the calculated horizontal inner width and a reference inner width of the laboratory analysis cuvette by the electronic control.

10. The method for determining the cuvette form correction value according to claim 9, wherein the liquid reagent type is determined before the calculation of the horizontal inner width.

11. The method for determining the cuvette form correction value according to claim 10, wherein the determination of the liquid reagent volume is carried out by a cuvette scale which determines the mass of the filled liquid reagent and which is informationally connected to the electronic control.

12. The method for determining the cuvette form correction value according to claim 10, wherein the electronic control comprises a meniscus interpretation module and a meniscus library in which meniscus form values are respectively stored for different liquid reagent types, wherein the electronic control evaluates the camera signal on the basis of the meniscus form value assigned to the respective liquid reagent type.

13. The method of determining the cuvette form correction value according to claim 9, comprising the step of: after calculating the form correction value: storing the form correction value at the laboratory analysis cuvette.

14. The method for determining the cuvette form correction value according to claim 13, wherein the form correction value is stored as an optically readable marking at the laboratory analysis cuvette.

15. The method for determining the cuvette form correction value according to claim 9, wherein the cuvette vertical wall is configured to be circular-cylindrically and the horizontal inner width is the inner diameter of the vertical wall.

16. The method for determining a cuvette form correction value according to claim 9, wherein the liquid reagent reacts in a colour-changing manner with the analyte depending on the analyte concentration of a liquid sample filled into the cuvette.

Description

[0022] FIG. 1 a longitudinal section through a laboratory analysis cuvette,

[0023] FIG. 2 an arrangement for determining the horizontal inner width of the cuvette body of the cuvette of FIG. 1,

[0024] FIG. 3 an enlarged view of the level determination camera and the cuvette of the arrangement of FIG. 2, and

[0025] FIG. 4 an analyser unit with an inserted cuvette.

[0026] FIG. 1 shows a cuvette 10 containing a liquid reagent 60, which cuvette 10 is closed by a lid-like transport cap 18. The cuvette 10 is defined by a beaker-shaped cuvette body 12 of transparent glass defining a horizontal bottom wall 13 and a circular cylindrical vertical wall 14. A two-dimensional barcode 22 is applied to the outside of the cuvette body 12 as an optically readable marking 22.

[0027] The total internal volume of the cuvette 10 is approximately 10 ml and the horizontal reference inner width D, which corresponds to the inner diameter on the inner side 16 of the vertical wall 14, is in the single-digit millimetre range, and is for example 4.0 mm. The actual horizontal inner width D can differ from the reference inner width D due to the production process. The liquid reagent 60 may comprise a liquid reagent volume V of 200 l to 5 ml, depending on the type of liquid reagent. Typical water analysis liquid reagents for the determination of ammonium concentration, nitrate concentration or chemical oxygen demand are phosphorus-sulphuric acids, chromium-sulphuric acids, etc.

[0028] FIGS. 2 and 3 show an arrangement for the determination of a cuvette form correction value F. This arrangement comprises a level determination camera 24 which is directed laterally towards the cuvette 10 standing on a cuvette scale 50. The cuvette 10 is placed on a scale platform 52 of the cuvette scale 50. The arrangement comprises an electronic control 26 for determining the cuvette form correction value F. The controller 26 comprises a meniscus interpretation module 25 and a meniscus library 27 in which meniscus form values MF are stored for different liquid reagent types T, respectively. The meniscus form value MF comprises the extent to which the liquid reagent level H optically detected by the level determination camera 24 must be corrected in order to obtain a normalised level H of the liquid reagent 60 for the subsequent volume calculation.

[0029] Finally, the arrangement of FIG. 2 comprises a barcode printer 28 which prints an optically readable identification 22 in the form of a two-dimensional barcode 22 which is finally applied to the vertical wall 14 of the cuvette 10.

[0030] FIG. 4 shows a laboratory analyser unit 30 for the quantitative determination of an analyte or a parameter of a liquid sample using a so-called cuvette test.

[0031] The analyser unit 30 comprises a cuvette compartment 42 for positioning the cuvette 10. A turntable 36 is arranged at the bottom of the cuvette compartment 42, which can be rotated by an electric drive motor 38. Furthermore, the analyser unit 30 comprises a two-dimensional barcode reader 32 configured as a digital camera, which reads the barcode 22 as a photograph through a corresponding opening of the cuvette compartment wall. The analyser unit 30 comprises a photometer 34 defined by a photometer transmitter 341 and a photometer receiver 342. Finally, the analyser unit 30 comprises an electronic analyser unit controller 40.

[0032] After the laboratory analysis cuvette body 12 has been manufactured, it is filled in a filling unit with the predetermined target volume of a liquid reagent 60 of a specific liquid reagent type T, for example with a chromium-sulphuric acid for determining the chemical oxygen demand parameter. The reagent reacts with the analyte to be determined of the liquid sample filled later into the cuvette 10 to change its colour. During filling, the cuvette 10 may in general already be placed in the arrangement shown in FIGS. 2 and 3. The controller 26 receives the liquid reagent type T and the filled liquid reagent volume V from the filling system.

[0033] Alternatively, the controller 26 receives only the liquid reagent type T from the filling system, but not the filled liquid reagent volume V. Instead, the liquid reagent volume V is determined by means of the cuvette scale 50 by a differential measurement, i.e. a determination of the mass difference of an empty weighing and of a full weighing of the cuvette 60 without and with the liquid reagent 60. Since the liquid reagent type T and thus the specific weight of the liquid reagent 60 are known, the exact filled liquid reagent volume V can be calculated using the calculated mass M of the filled liquid reagent 60.

[0034] By means of the camera 24 and a corresponding image recognition, the control 26 determines the visible actual level H of the liquid reagent 60 in the laboratory analysis cuvette 10. The actual level H of the liquid reagent 60 visible through the camera 24 is defined by the cuvette central surface 63 of the liquid reagent 60. The controller 26 further determines from the meniscus library 27 the meniscus form value MF associated with the liquid reagent type T, with which the liquid reagent level H optically detected by the camera 24 is corrected accordingly, for example by addition. This is necessary because, depending on the surface tension of the liquid reagent 60 in question, the annular meniscus 62 may comprise a more or less relevant meniscus volume which, particularly in the case of a small total liquid reagent volume, may have a considerable influence on the accuracy of the following calculations.

[0035] In FIG. 3, a relatively small and less relevant possible meniscus 62 and a relatively large and, in the case of a relatively small liquid reagent volume, very relevant possible meniscus 62 are shown for supplementary and purely informative purposes. The meniscus volume may indeed amount to several percent of the liquid reagent volume V, and therefore could make a significant error in the following calculation of the form correction value F.

[0036] Based on the meniscus-corrected true liquid reagent level H and the filled liquid reagent volume V, the control 26 calculates the horizontal inner width D of the hollow cylindrical cuvette body 12. The horizontal inner width D corresponds exactly to the length of the measuring section 35 of the photometer 34 within the cuvette 10. The actual inner width D determined in this way is set in relation to a reference inner width D stored for the cuvette 10, and a form correction value F is calculated from this ratio.

[0037] A barcode 22 is virtually generated from the form correction value F, which contains further information about the liquid reagent 60. The barcode 22 is printed on a label representing the optically readable identification 22 and is adhered to the outside of the cuvette body 12. Together with the transport cap 18, the cuvette 10 is then ready for shipping or for the analysis process.

[0038] For quantitative determination of an analyte, the transport cap 18 is removed, a defined volume of the liquid sample to be analysed, for example a wastewater sample from a treatment process, is pipetted into the cuvette, and the cuvette 10 is closed again with the transport cap 18. Then the liquid reagent 60 is mixed with the filled liquid sample by shaking, and the cuvette 10 is inserted into the cuvette compartment 42 of the analyser unit 30. After the reagent has reacted with the analyte to be determined in the liquid sample, the analysis process is started.

[0039] A turntable 36 is arranged at the bottom of the cuvette compartment 42, which can be rotated by the electric drive motor 38. The cuvette 10 is first rotated until the barcode reader 32, which is configured as a digital camera, has found the barcode 22 on the outside of the cuvette body 12. The barcode reader 32 then reads the barcode 22 so that the analyser unit control 40 derives from this, among other things, the form correction value F.

[0040] The photometer 34 photometrically determines the absorption or transmission in the measuring section 35. This is done while rotating the cuvette 10, for example, at ten different rotational positions, so that artefacts are statistically compensated or averaged if necessary and a reliable measured photometric value is available. In the analyser unit control 40, a true and more accurate measured value for the specific parameter is calculated from the measured photometric value, i.e. the absorbance or the transmission, by using the form correction value F, and is finally output visually, acoustically and/or electronically.