METHOD OF MEASUREMENT AND A CUVETTE

Abstract: Method and apparatus for the measurement of the properties of a liquid (14) placed in a cuvette (2) by means of radiation (22) and of a detector (12) that receives radiation. The beam of measurement (22) passes substantially in the direction of the vertical axis of the cuvette through a measurement window (16) that is located in the bottom of the cuvette and that has a horizontal inside face. Moreover, a cuvette (2) is used whose walls and/ or bottom is, at the inside face, outside the path of passage of the beam of measurement (22), provided with one or several parts (17) projecting from the substantially vertical walls and/or horizontal bottom of the cuvette and being either separate from the cuvette or made of one piece with the cuvette. According to the invention, the shortening of the path of measurement of the beam of measurement (22) passing through the liquid column, resulting from the rising of the surface of the liquid towards the walls of the cuvette, is compensated for by means of the total volume of the projecting part (17) or parts so that the total volume of the projecting part (17) or parts is substantially equal to the volume of the liquid portion that rises from the horizontal level of the middle portion of the liquid surface towards the walls of the cuvette as a result of the adhesion force between the liquid and the inside face of the cuvette wall and as a result of the reduction in the capillary action of the liquid (14).

Description: Method of measurement and a cuvette The present invention is concerned with a method for the measurement of the properties of a liquid placed in a cuvette by means of radiation and of a detector that receives radiation, whereat the beam of measurement passes substantially in the direction of the vertical axis of the cuvette through a measurement window that is located in the bottom of the cuvette and that has a horizontal inside face., whereat a cuvette is used whose walls and/or bottom is, at the inside face, outside the path of passage of the beam of measurement, provided with one or several parts projecting from the substantially vertical walls and/or horizontal bottom of the cuvette and being either separate from the cuvette or made of one .piece with the cuvette. The invention is also concerned with a cuvette or with a cuvette set consisting of several cuvettes, for the implementation of the method, in which case the said one or several projecting part(s) in the cuvette is made of one piece with the cuvette. When the measurement is performed by means of the principle of vertical measurement, in which case, e.g., the absorbance is obtained from the following P? equation ( 1 ) - A = ε. -2- (i) wherein A = absorbance, ζ, = molar absorptivity, m = mass of the substance to be measured, and a = bottom area of the cuvette, the circumstance is ascertained that the more the beams of measurement meet the mass to be measured, the higher is the absorbance value obtained. It follows from this, e.g., that the higher the absorbance value obtained for a certain quantity of mass, the better are the ability of distinguishing and the precision obtained. When, in a cylindrical cuvette, the free liquid surface adopts a concave form owing to the samples or reagents reducing the caoillary action and contained in the liquid, the distance passed by the beams of measurement through the liquid in the cuvette becomes shorter, whereby a correspondingly lower value of absorbance is obtained. In view of the precision of the measurement results it is important that the distance passed by the beams of measurement should be a precisely known, predetermined distance. The objective of the present invention is to provide a cuvette in which the rise of the liquid surface at the sides of the vessel, caused by the capillary action, and the resulting lowering of the liquid level in the middle part of the vessel are compensated for. The method and the cuvette or cuvette set in accordance with the invention are mainly characterized in that the shortening of the path of measurement of the beam of measurement (22) passing through the liquid column, resulting from the rising of the surface of the liquid towards the walls of the cuvette, is compensated for by means of the total volume of the projecting part (17) or parts so that the total volume of the projecting part (17) or parts is substantially equal to the volume of the liquid portion that rises from the horizontal level of the middle portion of the liquid surface towards the walls of the cuvette as a result of the adhesion force between the liquid and the inside face of the cuvette wall and as a result of the reduction in the capillary action of the liquid (14). In each cuverte the upper face of the optical window corresponds the curve form of the liquid surface in the cuvette so that the path of light in the liquid is the same as if the upper face of the optical window in each cuvette and the free surface of the liquid in the cuvette were horizontal. According to a preferred embodiment of the invention, in the cuvette-set matrix (cuvette set) the optical window of each cuvette is placed above the level of the bottom face of the cuvette-set matrix, being thereby protected, e.g., from dirt and scratches. O PI Moreover, at some edge of the cuvette-set matrix there may be an optically readable code in which one part informs the measurement apparatus as to what method is concerned and another part states what number or letter constitutes the code of the cuvette-set matrix concerned. The cuvette-set matrix in accordance with the invention is suitable for use in analyzer apparatuses operating by means of the principle of vertical measure¬ ment (Suovaniemi, Os o ' : ''Performance and Properties of the Pinnpipette Analyzer System", ' Proceedings of the Second National Meeting on Biophysics and Biotechnology in Finland, 183, 1976, and "Method for the improvement of the dosage and ' 'Measurement results of chemical analyses", U.S. Patent 4,144,030) such as PP-9 and PP-901 Analyzer Systems (Labsystems Oy, Finland) as well as Titertek Multiscan (Eflab Oy, Finland). In a cuvette-set matrix the reaction results and codes can be measured in one wide matrix so that the measurement radiation or any other measurable signal, produced for each sample and code, is passed to each cuvette and code of the matrix and further to the corresponding detector in the vertical direction. The cuvette-set matrix to be described now is suitable for methods in which measurements based, e.g., on photometry, spectrophotometry, fluorometry, turbido- metry, or on the use of laser beam are 'used. The cuvette-set matrix is highly suitable, e.g., in EIA (enzyme immune assay) reactions, blood-group serology (e.g. ABO and Rh) , in HLA (human leucocyte anti- gen) serology, in MIC (minimum inhibitory concentration) determinations, like also in other types of ascertaining of the growth or inhibition of growth of micro-organisms, and further in all methods based on the CF (complement fixation) phenomenon. The following list includes some of the advantages of the cuvette-set matrix in accordance with the present invention: OMPI 1. Since, in the present invention, the form of the cuvette bottom is such that it compensates for the shortening of the distance passed by the beams of measurement in the liquid to be measured, resulting from the concavity of the liquid surface, in this case very high values of absorbance are obtained. . 2. In the cuvette-set matrix in accordance with a preferred embodiment of the present invention the lower face of the optical window (cuvette bottom) of each cuvette is placed higher than the bottom face of the cuvette-set matrix, on -which the cuvette-set matrix rests on a plane surface. It follows from this that the lower face of the optical window of the cuvette is protected, e.g., from scratches, finger prints, or from any other contamination. 3. The entire cuvette-set matrix can be made of various types of plastic materials or of mixtures of same, also as of the colour in each particular case most appropriate. In such a case, if the measurement is to be performed, e.g., photometrically, the optical window of each cuvette in the cuvette-set matrix functions as a filter of a certain colour, whereby no filter devices are needed in the apparatus of measurement itself in order to obtain the desired wave length for the beams of measurement. 4. Each cuvette in the cuvette-set matrix in accordance with the invention can be protected from one another so that the beams of measurement of adjoining cuvettes, diffused light, external light, or equivalent do not disturb the measurement, by placing a protection around the cuvettes in the cuvette-set matrix or by using a protection inhibiting disturbing beams either in connection with the detector matrix or in connection with the matrix of measurement beams. 5. The cuvette-set matrix may be coded, e.g., so that from the code it is possible to read either* the number of the cuvette-set matrix or the desired method _O PI or both, by for code .reading using the same sort of radiation as is used for the measurement at each parti¬ cular time. In such a case separate code-reading systems are avoided. Moreover, the cuvette-set matrixes may already be coded in a certain way in connection with the manufacture, or the operator may code them in any desired way by placing the code in the place provided for it on the cuvette-set matrix. In the attached Figures 1 to 3 an exemplifying embodiment of the present invention will be described, together with some of the advantages obtainable by means of the invention. Figure 1 is a perspective view of a cuvette-set matrix in accordance with the invention, Figure 2 shows a vertical section of a part of the cuvette-set matrix, and Figure 3 shows a vertical section of one cuvette of the cuvette-set matrix. In Figure 1 the cuvette-set matrix 1 includes cuvettes 2, a matrix base Λ a code position 4, and therein a number code 5 and a method code 6, both of which can be read by using the same .type of a beam of measurement for each element 7 of the code as is used for each cuvette 2. The method code 6 can be used in the apparatus of measurement for the introduction of a desired pre¬ programmed mode of measurement and output for each cuvette-set matrix. The method code β calls, e.g., the program for the method MIC (minimum inhibitory concsn- tration) in determinations of the sensitivity of bacteria to antibiotics, which program selects the number of times of measurement required and processes the results of measurement in the predetermined, way. Both the number code 5 and the method code β consist of a line made of elements 7, in which line the position of each element corresponds the position of a cuvette in one line of cuvettes or vertical row in the O PI • set of cuvettes. The elements 7 are penetrable to light in different ways, some of them being, e.g., completely transparent and some others completely non-transparent. By combining the elements in the line in different ways, a desired code is obtained, which can be read by means of the same apparatus of measurement as is used for reading the absorbances of the reaction mixtures con¬ tained in the cuvettes. Such a code system is described in the Finnish Patent Application No. 80,1356. In Figure 1 each cuvette in the cuvette-set matrix is coded by means of number 1 to 10 (vertical line) and. by means of letter A to F (horizontal line). Thereby the apparatus of measurement indicates the results in the order, e.g., as follows: MIC 8 A 1 0.050 8 A 2 0.125 which means that in the MIC method, in the 8th cuvette-set matrix, e.g., the absorbance value of cuvette A 2 is 0.125 The results may of course also be indicated as values other than absorbance values, and, moreover, they may be classified and/or combined in the way most appropriate in each particular case, e.g. by making use of the electronics of the apparatus of measurement in consider¬ ation of the requirements of the method at each parti- cular time concerned, or of any other requirements. Figure 2 shows two cuvettes 2 of the cuvette- set matrix as a sectional view and as placed in the measurement head of the measurement apparatus. In Fig. 2 the matrix 9 of measurement beams and therein the sources 10 of measurement beams are seen below each cuvette 2. Above the cuvettes there are the detector matrix 11 and therein the detectors 12. For each cuvette 2 there are the corresponding sources 10 of measurement beams and detectors 12. In Fig. 2 each cuvette 2 is pro- tected from measurement beams of the adjoining cuvettes, from diffused beams, external beams, and from any other radiation disturbing the measurement by means of a O PI_ VIPO limi er 13 placed around the cuvettes. In Fig.-2, the cuvette 2 is illustrated as containing liquid 14, whose free liquid surface 15 is concave. In order to compensate for this concavity, the inside face of the window lβ of each cuvette 2 is provided with an additional rim or equivalent appendix 17, by means of which, despite the curved form of the liquid surface 15, the path a. of light in the liquid is maintained as long as possible. The length of the path a. of light and the height of the liquid column are substantially equal at every point of the cuvette, also at the sides. In Figure 2-, the lower face 18 of the optical window 16 is placed higher than the bottom face 19 of the cuvette-set matrix. In Figure 3 a cuvette 2 of the cuvette-set matrix and the corresponding source 10 of measurement beams together with the measurement beams 22 emitted from same are seen. The measurement beams 22 pass via the liquid 14 in the cuvette 2 through the optical window Iβ of the cuvette to the corresponding detector 12 in the detector matrix 11. The matrix 9 of measurement beams is provided with limiters 13 for the protection of each cuvette from radiation disturbing the measurement. The sources of measurement beams are fitted above the cu- vettes and the detectors below the cuvettes. The invention is not confined to the above embodiments only, but it may show even considerable vari¬ ation within the scope of the patent claims. The part projecting from the bottom or from the walls may also be a separate piece, e.g. a ring fitted onto the bottom, whose volume corresponds the volume of the liquid rising onto the sides of the vessel. It is also possible to use one or several ver¬ tical projections on the inside walls of the cuvette, whose volume corresponds the volume of the liquid rising onto the sides of the vessel and which promote mixing of the cuvette contents when the cuvette is shaken. O PI

Claims: _ WHAT IS CLAIMED IS: 1. A method for the measurement of the pro¬ perties of a liquid (14) placed in a cuvette (2) by means of radiation (22) and of a detector (12) that receives radiation, whereat the beam of measurement (22) passes substantially in the direction of the vertical axis of the cuvette through a measurement window (Iβ) that is located in the bottom of the cuvette and that has a hori¬ zontal inside face, whereat a cuvette (2) is used whose walls and/or bottom is, at the inside face, outside the path of passage of the beam of measurement (22), pro¬ vided with one or several parts (17) projecting from the substantially vertical walls and/or horizontal bottom of the cuvette and being either separate from the cuvette or made of one piece with the cuvette, c h a r a c t e r ¬ i z e d in that the shortening of the path of measure¬ ment of the beam of measurement (22) passing through the liquid column, resulting from the rising of the surface of the liquid towards the walls of the cuvette, is com- pensated for by means of the total volume of the pro¬ jecting part (17) or parts so that the total volume of the projecting part (17) or parts is substantially equal to the volume of the liquid portion that rises from the horizontal level of the middle portion of the liquid sur- face towards the wails of the cuvette as a result of the adhesion force between the liquid and the inside face cf the cuvette wall and as a result of the reduction in the capillary action of " the liquid (14). 2. A cuvette or a set of cuvettes consisting of several cuvettes (2) for the implementation of the method as claimed in claim 1, the one or several pro¬ jecting part(s) (17) placed in the cuvette being of one piece with the cuvette, c h a r a c t e r i z e d in that the total volume of the projecting part (17) or parts is substantially equal to the volume of the liquid portion that rises from the horizontal level of the middle portion of the liquid surface towards the walls of the OMPI cuvette as a result of the adhesion force between the liquid and the inside face of the cuvette wall and as a result of the reduction in the capillary action of the liquid (14). 3. A cuvette or set of cuvettes as claimed in claim 2, c h a r a c t e r i z e d in that the inside face of the projecting part (17) becomes narrower towards the bottom and has the shape of a frustrum of a body of revolution, e.g., a cone, ring sector, or ball segment, the shape and volume of the said frustrum being substantially the same as the shape and volume of the part of the surface of the liquid (14) that rises towards the walls of the cuvette (2). 4. A cuvette or set of cuvettes as claimed in ' claim 2 or 3 . c h a r a c t e r i z e d in that the bottom (3) of the cuvette set consists * of a plate 'to which the measurement windows. (lβ) have been fitted, whose lower face (18) is placed higher than the lower face (19) of the bottom plate (3). 5- A cuvette or set of cuvettes as claimed in any of the claims 2 to 4, c h a r a c t e r i z e d in that it is provided -with a code (6) that determines the desired mode of measurement and processing of the measurement results and which can be read by means of the beam (22) that measures the properties of the reaction mixtures.

Inventors: SUOVANIEMI O
Applicants: LABSYSTEMS OY
Application year: 1981
Main classification: G01N21
IPC codes: G01N21