GB2120784A

GB2120784A - Chemical analysis

Info

Publication number: GB2120784A
Application number: GB08314617A
Authority: GB
Inventors: Reijo Antero Voutilainen
Original assignee: Orion Yhtyma Oy
Current assignee: Orion Oyj
Priority date: 1982-05-26
Filing date: 1983-05-26
Publication date: 1983-12-07
Also published as: DE3318574A1; FI64464B; GB8314617D0; FR2527773A1; FI821867A0; FI64464C; JPS5967447A

Abstract

In a method and apparatus for carrying out a chemical analysis by a measuring principle based on light on a sample placed in a cuvette (1), the measuring is carried out using at least one detector (4, 5) both along the direction of the incident light (6) and at an angle thereto. In order to reduce or eliminate the disadvantages of several different measuring principles, the cuvette (1) is placed in an opaque sleeve (2) having openings (3) for light, and the basic idea is to bring the sleeve (2) with its cuvette (1) into rotary motion in relation to a source (11) of light and the detector/ detectors (4, 5), in which case the light arrives at the detector(s) intermittently. In order to eliminate errors, the signal of one detector is preferably divided by the signal of the other detector. Alternatively, the sleeve and cuvette may be maintained stationary, the light source and detector(s) rotating therearound. <IMAGE>

Description

SPECIFICATION A method and apparatus for carrying out a chemical analysis The present invention relates to a method and apparatus for carrying out chemical analyses by using, when necessary, several different measuring principles. The invention is highly suitable for performing analyses used in medicine.

Various measuring principles suitable for use in the method and apparatus according to the present invention have various disadvantages, which will be described below.

One problem involved in nephelometry, i.e.

in measuring based on the scatter of light, consists of dust particles and other particles possibly affecting the travel of light, which move slowly in the solution to be analysed and are substantially larger than antigen-antibody complexes. A known method for reducing the errors caused by particles is to observe the intensity of scattered light over some period of time and then to select as the measurement the smallest signal which has appeared during this time. The principle is based on the observation that particles can hardly decrease the scatter of light but, instead, in a suitable position the particles may cause a considerable amount of extra scatter.

The true minimum is found with greater certainty the longer the follow-up is continued, but in practice the length of the follow-up time must be limited in order not to slow down the measuring process.

Another problem is connected with the positioning of the cuvette in relation to the optical axes of the measuring system. If the cuvettes are not reproducibly located always in the same place, the curved surface of the cuvette will cause differences in the refraction of the light and thereby in the final result. Furthermore, the distance travelled by a ray of light inside the cuvette and as a consequence, the absorption of light in the cuvette, may change. In an automatic analyser using separate cuvettes, it is therefore necessary to pay special attention to the precision of the cuvette transfer system.

A third problem is that of impurities are scratches in the surface of the cuvette and any deviations from symmetry of its shape.

These cause differences between cuvettes and lead to the requirement that the position of the cuvette must not change between the taking of the initial and the final readings.

The most precise positioning is achieved by placing the cuvette in a measuring site, for example a bore which has been drilled for it so that it fits tightly and which is firmly fixed in relation to the optical axes of the measuring system. Such a transfer has been difficult to automate, it may cause scratching, and it is not easy to ensure that the orientation of the cuvette remains unchanged. In general, the cuvettes have been placed in holders machined from metal and provided with openings for the travel of light, in such a way that the cuvettes can be kept in the holder throughout the time taken by the analysis, also during the times of measuring. The making of such a holder requires great precision and is therefore expensive.

The object of the present invention is to reduce and eliminate the above disadvantages in an effective and simple manner and by using an apparatus which is also of simple construction, inexpensive, and highly reliable in use. According to the invention it is also possible to use several different measuring principles in one and the same analyser. Thus, the method and apparatus according to the invention can be used for carrying out turbidimetric and fluorometric determinations, and determinations based on absorption and luminescence, with the exception of certain changes such as different light filters and different treatment of the signal. It is possible to select the measuring principle according to the requirements of the sample to be examined, in addition to which it is easy to automate the changing of the measuring principle.

Since, when the method according to the invention is used, the position of the cuvette no longer has any significance as a cause of errors, the cuvette transfer system of the analyser can be designed to be simpler than previous systems.

The above-mentioned advantages of the system are achieved by means of a method and apparatus the characteristics of which are given in the accompanying patent claims.

The invention is described below in greater detail with reference to the accompanying drawings, in which Figure 1 depicts a simplified side elevation of the apparatus intended for use in the method according to the invention, and Figure 2 depicts the same apparatus as seen from above, along section ll-ll.

In the schematic representation of the apparatus, Fig. 1, a conventional cuvette 1 made from an opaque material has been placed inside a sleeve-like part 2 provided with openings 3. When the sleeve is in the position shown in the figure, a source of light 11 emits light 6, possibly filtered using a filter 1 2, the light traveling via one of the openings 3 in such a way that the light travels through the cuvette and through the substance to be measured contained in the cuvette, leaving 7 the sleeve via another opening 3 and finally hitting a detector 4. Fig. 2 shows a top view of the same parts, and it also shows another detector 5 and a secondary filter 13, both of which have been depicted in this example at an angle of 90 in relation to the beam 6 of light.The figure shows that while the beam of light 6 travels to the detector 4, the light 8 scattered or produced through fluorescence in the cuvette can travel via one of the openings 3 through a possible filter 1 3 to the detector 5.

The cuvette and its sleeve 2 are rotated about their vertical central axis. At this time the openings 3 in the sleeve wall, as well as the opaque sleeve walls between the open ings, alternately open and close the paths of light from the source of light to the cuvette, from the cuvette to the detector 4, and from the cuvette to the detector 5 in such a way that ail of the paths of light are simultane ously open and all of them are simultaneously closed. From this it follows that the light received by the detectors is intermittent light, in which case the detectors produce an alter nating-current or alternating-voltage signal.

The rotary motion is produced by means of, for example, an electric motor 16, and the motion may, but it need not be, even. The signal is treated in, for example, the manner described below.

Electronics conventional in the art can be used for amplifying the detector signals, in which case, after the amplification, the signal is rectified, preferably synchronically with the rotary motion. After rectification and possible filtration, the signal obtained from the detector 5 is divided by the signal from the detector 4 in a manner known per se, either in an analog or a digital form. The division of one signal by the other eliminates the errors caused by variations in the intensity of the source of light, since such variation causes an equally great change in the signal of each detector. Furthermore, if there are on the cuvette surface any scratches or dirt hampering the travel of the light, their effect can be observed on the average to the same extent on each detector, owing to the rotary motion of the cuvette.In addition, the rotation has an advantageous effect on nephelometric mea surements in such a way that any dust particles in the cuvette cause only rapid momentary peaks of scatter, and the significance of such peaks in the mean signal remains insig nificant.

Conventional photometric measurements can also be carried out using the apparatus according to the invention in such a manner that, when the cuvette is in the sleeve, the dividend is formed from the signal of the detector 4 and the divisor is formed from the signal obtained by means of the same detector but without the cuvette. Thus, variations of the intensity of the source of light are taken into account, with the exception of the change which occurs during the time when absorption is measured and the cuvette is in the sleeve.

Even in luminometric methods, intermittent blocking of the path of light is useful, since in this manner the effect of diffuse light can be eliminated, the amplifiers can be simplified, and the measuring can be carried out within a frequency range more advantageous in terms of the detector 1 /f noise, and the zero creep of the amplifiers can be eliminated.

The advantages listed above are achieved in accordance with this invention in a simple manner by rotating the cuvette 1 in its sleeve 2. While several different measuring principles have been combined in the same apparatus to form a simple integral unit, it has been possible simultaneously to improve by means of the invention the precision of all the measu'- ing methods.

The apparatus according to the invention can be made simpler than the example described above by using, instead of detectors 4 and 5, only one detector which can be moved along for example an arc-shaped path alternately to the place of the detector 4 and that of detector 5. In this case only one signaltreatment chain is required, and the measuring electronics will be more economical than previously. The stability of the measuring system will in principle be improved, since, owing to the division of the signals, the changes in the amplifications of the detector and the amplifier will also be completely cancelled out.

Of it is not desired to carry out flurometric or nephelometric measuring by means of the apparatus, the detector 5 can, of course, be totally eliminated.

It should also be pointed out that in the description above the cuvette is described only as being round in shape, but some other symmetrical shape, for example, a regular polygon, is also possible. Furthermore, the number of the openings 3 may be four, as above, or any even number greater than four.

When more openings are used, the detector 5 can be placed even at some other angle than 90 . In laser nephelometry, a 12-opening sleeve enables the detector to be positioned at an angle of 150 , which is very close to the angles most commonly used in this connection. Also, for the sake of simplicity any optics necessary for the forming and orienting of the beams of light have also been left out of the description; such optics are generally known and are connected with most apparatus of this type.

It should, furthermore, be noted that only the rotation of the sleeve and the cuvette has been described above as the method for producing intermittent light, but, for example, keeping the said combination stationary and rotating the surrounding devices, such as the source of light and the detectors, yields the same result. Since, for example, the construction of the electrical connections is in such a case difficult, the said structure is probably limited to a very smell number of special applications, if applicable even to them.

Claims

1. A method for carrying out chemical analysis by a measuring principle based on light, comprising placing a sample in a cuvette; producing the light by means of a source of light; blocking the produced light intermittently by placing the cuvette containing the sample in a sleeve-like part which has openings in an opaque wall and rotating the sleeve about its central axis throughout the time of the measuring to achieve the blocking; and measuring the light by means of at least one detector, both at an angle of 180 and at an angle deviating from 180 in relation to the direction of the produced light.

2. A method according to claim 1, wherein the measuring is carried out using either one detector moving from one measuring point to another, or two detectors which are situated one at each measuring point.

3. A method according to claim 1 or 2, wherein two detectors are used, and the signal of one is divided by the signal of the other in order to obtain the measurement.

4. A method according to claim 3, wherein the measurement is obtained by dividing the detector signal. which is obtained by measuring at an angle deviating from 180 by the detector signal which is obtained by measuring at an angle of 180 .

5. A method for carrying out chemical analysis, substantially as hereinbefore described with reference to the accompanying drawings.

6. Apparatus for carrying out the method of claim 1, comprising a cuvette for containing a sample; a rotatable sleeve around the cuvette having an opague wall with at least one opening therein; a light source arranged to direct light towards a sample in the cuvette by way of said at least one opening whereby the light reaches the sample intermittently as the sleeve rotates; and a detector mounted for movement around the sleeve and cuvette for measuring the light from the sample both along the extension of the light path from the source to produce a first signal and at an angle in relation to said extension to produce a second signal.

7. Apparatus for carrying out the method of claim 1, comprising a cuvette for containing a sample; a rotatable sleeve around the cuvette having an opaque wall with at least one opening therein; a light source arranged to direct light towards a sample in the cuvette by way of said at least one opening whereby the light reaches the sample intermittently as the sleeve rotates; and at least two detectors, one of which measures light from the sample along the extension of the light path from the source to the sample to produce a first signal and the other of which measures the light from the sample along a direction at an angle to said extension to produce a second signal.

8. Apparatus according to claim 1, com prising means for dividing said second signal by said first signal.

9. Apparatus for carrying out a chemical analysis, constructed and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.