METHOD AND APPARATUS FOR VOLUMETRIC DETERMINATION, DILUTION AND TRANSFER OF LIQUID SPECIMENS

Abstract: The present invention relates to a method for volumetric determination, dilution and transfer of liquid specimens, especially blood samples for counting corpuscles. The method comprises the steps of sucking up a relatively large amount of specimen, and of pres­ sing, by means of a fixed volume of a reagent, a fixed volume of the sucked-up specimen into a mixing beaker, so as to obtain a mixture in a first dilution. According to the invention, the method comprises the steps of transferring, via a volume buffer, the mixture to a counting beaker by means of excess pressure in the mixing beaker. Before the entire mixture has been transferred from the mixing beaker, but after the mixture has entirely filled the volume buffer, the transfer from the mixing beaker is terminated. Any excess in the counting beaker is sucked off, and then the mixture in the volume buffer is flushed out into the counting beaker by means of a fixed volume of a hemolysing agent exceeding the volume of the buffer, so as to obtain a mixture in a second delution. After the flushing of the mixture has been terminated, the volume buffer is entirely filled with the hemolysing agent. The invention also relates to an apparatus for carrying out the method.

Description: The present invention relates to a method and an apparatus for volumetric determination, dilution and transfer of liquid specimens, especially blood samples for blood-count. A blood-count is normally carried out in two different dilutions, a less diluted solution, for example 1:400, and a more diluted solution, for example 1:40,000. The reagent used for diluting is a physiological saline solution. White corpuscles are counted in the less diluted solution after addition of a so-called hemolysing agent which destroys the red corpuscles. The hemolysing agent can be supplied in concentrated form or strongly diluted, but then the dilution previously made must be adjusted such that the final dilution ratio becomes correct, in our example 1:400. When the red corpuscles are destroyed by the hemolysing agent, hemoglobin is released, and after a chemical conversion together with the hemolysing agent, the hemoglobin content or the so-called blood value is measured photometrically (degree of red colouring). The red corpuscles are counted in the more diluted solution (in our example 1:40,000). The two dilutions mentioned above are normally effected in two steps. For example, 20 µl blood sample in 8 ml reagent yields a dilution of 1:400, and then 100 µl of the first dilution in 10 ml reagent yields a dilution of 1:40,000. In known methods and apparatus for volumetric determination, dilution and transfer of blood samples, the first dilution is made in a mixing beaker, and part of the mixture is transferred to a counting beaker and is further diluted with a reagent for counting the red corpuscles. The remainder of the mixture in the mixing beaker is transferred to another counting beaker, and a hemolysing agent is added for destroying the red corpuscles. When the last portion of the contents of the mixing beaker is transferred, air will also flow into the mixing beaker. Since the hemolysing agent is strongly frothing, large amounts of microscopic bubbles of air are formed. These bubbles remain for a long time and then make cell counting impossible since the bubbles themselves will be counted or interpreted as cells (white corpuscles). However, cell counting should start promptly, thereby to reduce the total time of a diluting/counting cycle. The object of the present invention is to obviate the above-mentioned disadvantages of microscopic bubbles of air by simply eliminating them. This is achieved in that only a fixed portion of the contents of the mixing beaker is transferred to the counting beaker, and in that the transfer will thus not be concluded by a supply of air. An embodiment of the invention will now be described with reference to the accompanying drawing in which Fig. 1 illustrates schematically a prior art method and apparatus for the transfer of liquid specimens, and Fig. 2 shows schematically a method and an apparatus for the transfer of liquid specimens according to the present invention. Fig. 1 shows schematically a prior art method and apparatus for volumetric determination, dilution and transfer of liquid specimens. From a blood sample 1, a relatively large amount of blood is sucked up through a spout 2 and through a first turning valve 3 in the direction of arrow A. The suction is terminated, and the turning valve 3 is turned through 90° to a horizontal position. The volume of the turning valve 3 is for example 20 µl. In the direction of arrow B, a fixed volume of reagent, for example 8 ml, is now added and presses the smaller amount of blood down into the mixing beaker 4, which yields a dilution ratio of 1:400 in the beaker. From the beaker 4, a small portion of the mixture is sucked up through a second turning valve 5 in the direction of arrow C. The suction is terminated, and the turning valve 5 is turned to a vertical position. The volume of the turning valve 5 is for example 100 µl. A fixed volume of reagent, for example 10 ml, is now added in the direction of arrow D and presses the mixture in the turning valve 5 into a counting beaker 6 for counting red corpuscles. A dilution ratio of 1:40,000 is now obtained in the counting beaker 6. Since the dilution ratio in the mixing beaker was 1:400, this means that a dilution of 1:100 (100 µl in 10 ml) has now been achieved. The contents of the mixing beaker 4 are transferred, for example by pressure, to a counting beaker 7 for white corpuscles, at the same time as a hemolysing agent in concentrated or diluted form is supplied in the direction of arrow E. As mentioned above, the hemolysing agent is strongly frothing so that, when the mixing beaker has been drained of its contents, the counting beaker 7 will also contain air which together with the hemolysing agent forms large amounts of microscopic bubbles. As explained above, the counting of white corpuscles therefore cannot start before the bubbles have disappeared. Fig. 2 shows schematically a method and an apparatus according to the present invention, in which the problem of the above-mentioned bubble formation has been eliminated. The first step in the dilution and transfer of liquid specimens to the mixing beaker 4 can be effected according to the method described above, but with the difference that the dilution in the mixing beaker is adjusted to have a higher concentration than that finally desired in the counting beaker. When the transfer from the mixing beaker 4 to a counting beaker 10 is to be effected, a positive pressure is applied to the mixing beaker 4 through a valve 8. The mixture is pressed down through a tube 9, a valve 11 and a volume buffer 12 into the counting beaker 10. The volume buffer 12 consists of, for example, a hose coil or a tube. The mixture fills the entire volume buffer 12 whose volume from a point 13 to a point 14 at the mouth of the volume buffer in the counting beaker 10 is known and fixed. The excess which flows into the counting beaker 10, is sucked off through a valve 17. The essential thing is that the volume buffer 12 between the points 13 and 14 is entirely filled with the sample, and that there are no air bubbles. One way of ensuring this is to measure the level in the mixing beaker 4. When this has reached the level 15, which can be indicated by e.g. a detector consisting of an electrode 16, the second electrode being the tube 9, the valve 11 is closed. A valve 19 is opened, and the remainder of the contents of the mixing beaker 4 is pressed out through the valve 19, and at the same time any excess in the counting beaker 10 is sucked off in a few seconds, whereupon the valve 17 is closed. Now a valve 18 is opened, and a fixed amount of hemolysing agent, for example twice the amount of the volume of the volume buffer 12 between the points 13 and 14, is supplied in the direction of arrow F and flushes the mixture into the counting beaker 10. If the dilution ratio in the mixing beaker has, for example, been fixed at 1:200, and if the volume of the hose between points 13 and 14 is 2.6 ml, and the volume of hemolysing agent flushing the contents of the hose into the counting beaker is 5.2 ml, the total volume in the counting beaker will be 5.2 ml, and the dilution ratio 1:400, i.e. 2.6 ml of the mixture from the hose and 2.6 ml of the hemolysing agent. The last 2.6 ml hemolysing agent fills the hose. In this manner, no microbubbles can form, since no air will enter the counting beaker 10. Therefore, the counting of white blood corpuscles can start promptly. The technique described above further brings the advantage that for manually prediluted samples, for example when a limited amount of whole blood from children or animals is available, one need merely dilute the sample to the correct mixing ratio and see to it that the total volume exceeds a given minimum volume. The prediluted sample can be supplied to the mixing beaker 4 by a special supply duct, and only part of the sample is removed from the mixing beaker in the manner described above, in our example down to level 15. The invention is, of course, not restricted to the embodiment described above and shown in the drawing, but may be modified within the scope of the appended claims.

Claims: A method for volumetric determination, dilution and transfer of liquid specimens, especially blood samples for counting corpuscles, comprising the steps of sucking up a relatively large amount of specimen, and of pressing, by means of a fixed volume of a reagent, a fixed volume of the sucked-up specimen into a mixing beaker, so as to obtain a mixture in a first dilution, characterised by the steps of transferring, via a volume buffer, the mixture to a counting beaker by means of excess pressure in the mixing beaker, of terminating the transfer from the mixing beaker before the entire mixture has been transferred from the mixing beaker, but after the mixture has entirely filled the volume buffer, of sucking off any excess in the counting beaker, and of flushing, by means of a fixed volume of a hemolysing agent, which exceeds the volume of the buffer, the mixture in the volume buffer into the counting beaker, so as to obtain a mixture in a second dilution, the volume buffer being entirely filled with the hemolysing agent after the flushing has been terminated. The method as claimed in claim 1, characterised in that the volume of hemolysing agent is twice the buffer volume. The method as claimed in claim 1 or 2, characterised in that the dilution ratio of specimen to reagent in the mixing beaker is in the order of magnitude of 1:200, and in the counting beaker in the order of magnitude of 1:400. An apparatus for volumetric determination, dilution and transfer of liquid specimens, especially blood samples for counting corpuscles, for carrying out the method as claimed in claim 1, comprising a means for sucking up an amount of specimen through a turning valve in a first position, and a means for pressing out, by a fixed volume of the reagent, the amount of specimen included in the turning valve turned to a second position, into a mixing beaker, whereby a mixture in a first dilution is obtained, characterised by a means for applying excess pressure to said mixing beaker (4), a tube (9) between the mixing beaker (4) and a counting beaker (10) for transferring the mixture to the counting beaker, a valve (11) in said tube (9) for terminating the transfer, a detector (16) in the mixing beaker (4) for sensing when the level in the mixing beaker (4) falls below a fixed level (15), a means for sucking off any excess in the counting beaker (10), and a means for supplying a fixed volume of a hemolysing agent to the tube (9), the tube (9) downstream of the valve (11), from a point (13) at which the hemolysing agent is supplied and up to the mouth (14) of the tube in the counting beaker (10), having such length and cross-sectional area that a volume buffer (12) having a fixed volume is formed.

Inventors: BERNDTSSON, INGEMAR
Applicants: MEDONIC INGEMAR BERNTSSON AB
Application year: 1988
Main classification: G01N15
IPC codes: G01N1, G01N33, G01N15