PROCEDURE FOR ACCOMPLISHING LIQUID CONTACT AT SLOW LIQUID FLOW

Abstract: A procedure for establishing liquid contact at slow liquid flow for a measurement in which is measured the potential difference between two liquids, and a measuring pick-up manufactured by an according procedure, one of these liquids (the known liquid) being located in a reference channel (2) and the other (the liquid to be measured) being located in a sample liquid channel (10). With a view to producing such flow, the invention is mainly characterized in that in between the reference channel (2) and the sample liquid channel (10) is pressed a substance transforming to be fibrous on compression, such as Teflon (17).

Description: Procedure for accomplishing liquid contact at slow liquid flow The present invention concerns a procedure fo accomplishing liquid contact at slow liquid flow for such measurement wherein is meas¬ ured the potential difference between two liquids, one of these (the known liquid) being located in a reference channel and the other (the liquid to be measured) being located in the sample fluid channel. An ion-selective analyser is used to measure from liquids, for instance from blood, various matter contents such as potassium, sodium or calcium. The measurement is based on the potential dif¬ ference between a so-called reference electrode and an electrode sensitive to the substance to be determined, potassium for in¬ stance. The electrode in the reference channel has been inserted in a solution with known composition and of which solution part is conducted to join the liquid under measurement in order to obtain ~ a closed electrical circuit (= liquid contact). The problem connected with the conduction of reference solution into the liquid under measurement has commonly been that the flow rate of the reference solution has been difficult to adjust. Using an excessive solution quantity is expensive and causes inconvenience, and if too little of the solution is used, the result may be that the continuity between the reference solution and the liquid under measurement is lost. It is furthermore necessary to prevent the liquid under measurement from entering the reference channel. If any of the liquid under measurement gains access to the reference channel, the composition of the solution in this channel will change and at the same time the potential difference between the reference electrode and the other electrodes changes, thus causing an erroneous result of measurement. In analysers of prior art," the reference channel of the measuring pick-up has been manufactured e.g. by grinding two pieces conically together and leaving the ground surfaces just sufficiently rough to OMPI allow reference solution to seep through between the surfaces to become admixed with the liquid under measurement. The drawback of such a procedure is that it is expensive, and the drawback of the measuring pick-up is its large size. This makes for a large dis¬ tance between the reference channel and the measuring channels with the result that the quantity of liquid under measurement must also be large. If one aims to minimize the quantity of the liquid under measurement, or of the sample, the sample channel has to be made to have a small diameter. This, again, results in numerous drawbacks, among them the risk of obstruction and the air bubble risk. An air bubble in a small channel may interrupt the electrical continuity, whereby of course an incorrect result of measurement is incurred. In another procedure of prior art, the junction between the refer¬ ence channel and the sample liquid channel is prepared of sintered glass powder. The drawback of this procedure and pick-up is still its large size with the attendant detriments already reported above. It has been exceedingly difficult to affix a small piece of glass sinter in the reference channel. Furthermore, glass has the*-*, property that it is slowly soiled down for instance by the sample, which is blood in most instances. The object of the present invention is to eliminate the drawbacks mentioned and to provide a procedure by which it is possible to manufacture economical, reliable and small reference electrodes for the measuring pick-ups of ion-selective analysers. The procedure of the invention is characterized in that between the reference channel and the sample liquid channel is pressed material, such as Teflon for instance, which acquires fibrous consistency on being so pressed. The advantage of the procedure is its ease and speed of application. Moreover, plastic granulate is inexpensive and only a minimal quantity of it is needed for each reference channel. Teflon is inherently liquid-repellent and therefore the risks of contami¬ nation, and obstruction are low. Furthermore, Teflon structures assume fibrous shape on being ' pressed, and hereby gaps are pro¬ duced through which the reference solution runs into the sample fluid. The procedure according to an advantageous embodiment of the in¬ vention is characterized in that the granulate is kept moistened during the pressingstep. The invention also relates to a measuring pick-up manufactured in accordance with the procedure mentioned, comprising a sample liquid channel, measuring channels therewith connected for each substance to be measured, and a reference channel. The measuring pick-up of the invention, is characterized in that between the reference channel and the sample liquid channel there is a fibrous, liquid- repellent substance, such as Teflon for instance. The invention is described in the following with the aid of an example, with reference made to the attached drawings, wherein:- Fig. 1 illustrates the pressing of Teflon sinter into the reference channel, the measuring pick-up being longitudinally sectioned, and Fig. 2 presents the longitudinal section of a finished measuring pick-up. The measuring pick-up may be manufactured e.g. of acrylic plastic. In the body component 1 is provided a channel for the reference solution and for the reference electrode 6. This channel is called the reference channel 2. Likewise, in the body component are pro¬ vided measuring channels 3, 4 and 5 for electrodes 7, 8 and 9, by the aid of which different matter contents are measured, for in¬ stance sodium, potassium and calcium. The channels 2 through 5 are most simply produced by drilling. Furthermore, in the pick-up are drilled ' the sample liquid channel 10 and the reference solution entrance channel 11. The sample liquid channel 10 communicates with the channels 2-5 through a funnel-shaped reducing portion 23- Similarly, the reference solution entrance channel i1 communicates with the reference channel 2. In the reducing portions of the measuring channels 3-5 is established, by pouring, an ion-selective membrane 18, 19 and 20 known in itself in the art, which is sensi- tive to a given substance, for instance specifically to sodium, potassium and calcium, separately to each of them. Furthermore, the measuring channels are fitted with electrodes 7 through 9« The Teflon granulate standing by in the reducing portion 23 of the reference channel 2 is placed in a tool 21 by means of which the granulate 17 is pressed into the reducing portion 23 of the refer¬ ence channel 2. In the sample liquid channel 10 has been inserted a counterpiece 22 against which the Teflon granulate is pressed. On pressing e.g. by means of a hydraulic press, the granulate is "sintered", in which connection the Teflon granules are transformed to be brous. The reference liquid may flow in the interstices between the fibres thus formed. The pressing force may be used to¬ wards adjusting the granulate plug to permit a given flow rate. The flow rate may also be adjusted by varying the thickness of the Teflon layer. The pressing is done in moistened condition, whereby liquid remains between the Teflon fibres. Hereby the capillary force acting between the fibres will maintain a slight leakage in the pressed Teflon mass. It is obvious to a person skilled in the art that the invention is not confined solely to the example above presented and that on the contrary dif erent embodiments of the invention may vary within the scope of the claims stated below.

Claims: Claims 1. Procedure for establishing liquid contact at slow liquid flow for a measurement in which the potential difference between two liquids is measured, one of these, the known liquid, being located in a reference channel (2) and the other, the liquid under meas¬ urement, being located in a sample liquid channel (10), character¬ ized in that between the reference channel (2) and the sample liquid channel (10) is pressed a substance assuming fibrous shape on pressing, such as Teflon (17). 2. Procedure according to claim 1 , characterized in that the granulate is kept moistened during the pressing step. 3. Measuring pick-up manufactured by a procedure according to claim 1, comprising a sample liquid channel (10), measuring chan¬ nels (3-5) thereto connected for each substance to be measured, and a reference channel (2), characterized in that between the refer¬ ence channel (2)- and the sample liquid channel (10) there is -= ' fibrous, liquid-repellent substance such as Teflon (17).

Inventors: JOHANSSON HENRIK, JOHANSSON, HENRIK
Applicants: KONE OY
Application year: 1983
Main classification: G01N27
IPC codes: G01N27