This invention relates to cuvettes, for removably retaining a liquid sample in position in analytical apparatus, and to such apparatus when fitted with such a cuvette.

Background to the Invention

A conventional cuvette is a small tube of circular or square cross-section which is sealed at one end, and which removably holds samples in analytical apparatus such as apparatus for performing photometric or spectrophotometric analysis of the liquid sample. Sometimes, this type of apparatus is used in the analysis of low volume liquid samples, for example volumes of 5μ1 or less, such as would be used in the quantative analysis of aqueous samples of DNA created in the laboratory. Such DNA is a valuable resource, and only a very small sample is usually available for assessment.

Typically, a beam of electromagnetic radiation, such as ultraviolet light would be incident on a transparent wall of the cuvette, so as to pass through the sample in the cuvette and then exit the cuvette through an opposed transparent wall for subsequent analysis, in particular to determine the amount of light/radiation absorbed at different wavelengths.

Introducing a relatively small sample into conventional cuvettes so that, during the analysis, the sample is properly positioned in the path of the beam, can be difficult, as can removing a sample after a measurement has taken place. The sample is introduced or removed through the open end of the cuvette which can be some distance away from the measuring position (i.e. the portion of the cuvette to which the beam passes in use).

US7688492 describes a device for adapting a standard spectrophotometer so that it can more readily handle small samples. To that end, the device has a housing which is inserted into the cuvette holder of the spectrophotometer and which contains a reflector for reflecting light from the cuvette holder to a sample stage at the top of the device. The device is capped with a reflector so that light passing through a sample at the sample stage is then reflected back down and onto another reflector which re-directs the light, again, to the instrument's spectrometer.

Although the sample is at an elevated, relatively accessible, position, the device is also complicated, and uses optical elements to deviate the path of light generated by the spectrophotometer, which elements can introduce inaccuracies to measurements taken by a spectrophotometer fitted with the device. The device is also top heavy and relatively fragile

Summary of the Invention

According to the invention, there is a provided a cuvette for removably retaining a liquid sample in position in analytical apparatus to enable the sample to be analysed by a method involving irradiating the sample with electromagnetic radiation, the cuvette comprising an elongate body that, in use, contains a chamber for holding the sample, the body having first and second body portions, each of which carries a respective part of the inner surface of the chamber, wherein either portion is moveable away from the other portion to open the chamber so as to allow access to the latter.

Preferably, the cuvette body is so shaped as to be able to fit into the cuvette holder of a conventional spectrophotometer and to that end is of a square section.

For example, the body may be cubic, and be inserted into or removed from the cuvette holder by an elongate handle, such as a rod, permanently or removably mounted on the body.

Preferably, however, the body is elongate, the chamber, when opened, being accessible at a position spaced from either end of the body.

Thus a sample can be introduced to or removed from the chamber without the user having to access the chamber through an end of the cuvette, which may be remote from the chamber. The cuvette thus facilitates the analysis of small volume samples. Preferably, therefore, the cuvette is a micro-volume cuvette.

The chamber of such a cuvette may have a volume of less than ΙΟμΙ, but preferably has a volume in the range of 1-2μ1. Preferably, the body is a cuboid (i.e. is parallelepipedal in shape), preferably being of a square cross-section.

Such a shape of body corresponds to the shape of conventional cuvettes for use in spectrophotometers, and can thus be received in the cuvette holder of such apparatus, without the need to modify the latter. Typically, the outer dimension of a conventional cuvette are 12.5 x 12.5 x 45mm.

Preferably, the chamber is defined by a window, mounted on one body portion, a surface opposed to said window, and mounted on the other body portion, and at least one rigid spacer member that defines the thickness of the chamber, and hence the path length of electromagnetic radiation through the sample, either the window or the opposed surface being resiliently mounted on its respective body portion.

Preferably the opposed surface is another window or a reflector, and the spacer member comprises a ring.

Preferably, the cuvette includes a pair of opposed windows which define part of the chamber and which allow a beam of electromagnetic radiation, with which the windows are, in use, aligned, in the analytical apparatus to pass into the chamber to interact with a sample in the chamber and then to exit the chamber for analysis by the apparatus.

Thus the beam can interact with the sample in the same way as it would if the sample were contained in a conventional cuvette, and the direction of the beam does not need to be altered in order for the sample to be irradiated and for the beam that exits the sample to reach the relevant part of the analytical apparatus (for example the spectrometer of the spectrophotometer) .

In that connection, the windows may to an advantage be situated such that the distance from the bottom of the device to the centre line of the windows is either 15mm or 8.5mm. These distances correspond to the two standards used in spectrophotometry, so that the windows of the cuvette will, in use, automatically be aligned with the beam of electromagnetic radiation generated by apparatus which conforms to either standards, when the cuvette is placed in the cuvette holder of the apparatus.

Preferably, each window is mounted on a respective body portion and each body portion has at least one surface, which faces away from the chamber, and on which that body portion may stand on an underlying planar supporting surface, the windows being so positioned that they are spaced from the surface when the body portions are so supported.

To that end, the windows are preferably recessed within the body.

Consequently, the body or a portion thereof may be placed on a support surface, to expose the respective part of the inner surface of the chamber, without a window coming into contact with the support surface. This facilitates, for example, the emptying or refilling of the chamber without scratching or dirtying either window.

Preferably, each body portion extends along the length of the cuvette and the portions meet at a longitudinal interface.

The area of the interface can thus be large in relation to the size of the chamber, which assists in the correct positioning of the portions relative to each other and the maintaining of the portions in the correct relative position.

Preferably, the body portions are separate components.

Thus the body portions are not joined together by, for example, a hinge or other link. This simplifies construction of the cuvette, helps to ensure an even force of contact across the interface and enables the portions to be handled individually (when separated from each other). The body portions may to an advantage be so shaped that they matingly engage each other.

This facilitates location of the body portions in register with each other and hence the correct positioning of the portions on the inner surface of the chamber. At least one of the body portions may with advantage have one or more protuberances each of which matingly engages, in use, with a respective recess in the other body portion.

Preferably, the cuvette includes at least one magnet for releasably holding the two body portions together.

The chamber may with advantage be defined by the two windows and a spacer ring that is mounted on one window. In this case, one of the windows is preferably resiliently mounted on a respective body portion to exert, in the assembled cuvette, a compressive biassing force urging the windows towards each other. This enables the cuvette to absorb the shock of excess sample, which can be ejected into a suitable receptacle (such as a containment ring) in the cuvette body.

In addition, the path length of light through the sample will be defined by the spacer ring, and can be accurately predetermined by using a spacer ring made to a high dimensional accuracy. This enables the body portions to have a higher dimensional tolerance (i.e. to have greater inaccuracies/variations to their dimensions) without adversely affecting the accuracy to which said path length has been determined.

The invention also lies in a spectrophotometer, fluorometer or spectrofluorometer, having a cuvette holder, and a cuvette as aforesaid, wherein the cuvette is so dimensioned as to be a releasable fit in the cuvette holder.

Brief Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is an isometric view of a first embodiment of cuvette in accordance with the present invention;

Figure 2 is a sectional side view of the cuvette;

Figure 3 is an exploded sectional side view showing the cuvette when its two body portions are separated;

Figure 4 is an isometric view of one of the body portions;

Figure 5 is a sectional side view of the same body portion, when a droplet of liquid sample has been deposited on that portion;

Figure 6 is a corresponding view showing the two body portions mounted on each other after sample has been deposited as shown in Figure 5;

Figure 7 shows the cuvette, with sample, when mounted in a cuvette holder of a spectrophotometer;

Figure 8 is a side elevation of a second embodiment of cuvette in accordance with the invention;

Figure 9 is an elevational view of the underside of the cuvette of Figure 8;

Figure 10 is a sectional side view, corresponding to Figure 2, of the second embodiment of cuvette;

Figure 11 is an exploded sectional side view of the second embodiment of cuvette, showing the two body portions of the cuvette when separated;

Figure 12 is a front elevation of one of the body portions of the second embodiment of cuvette; Figure 13 is a corresponding view of the second body portion of that embodiment;

Figures 14 and 15 are respectively views of the opposite sides of the body portions of Figures 12 and 13, i.e. the sides that are on the exterior of the assembled cuvette;

Figure 16 is an isometric view of the body portion shown in Figures 12 and 14;

Figure 17 is a corresponding view of the other body portion; and

Figure 18 is an exploded isometric view of the two body portions of the embodiment.

Detailed Description

With reference to Figure 1 , a cuvette in accordance with the invention comprises a body generally referenced 1 which is of a parallelepipedal shape, having a square horizontal section and oblong rectangular longitudinal section. The width and depth of the body, i.e. the length of the sides 2 and 4 are 12.5mm whilst height of body, i.e. the length of side 6, is 50mm.

The body 1 is formed from two body portions, a first body portion 8 and a second body portion 10, which may be separated to split the body 1 longitudinally, and which meet along a substantially rectangular longitudinal interface 12. With reference to Figures 2 and 3, each body portion is of the same width and height as the body 1 and is of a thickness which is half that of the body 1. The body portions 8 and 10 are formed from PEEK thermoplastic resin.

The body portion 8 includes two protuberances 14 and 16 in the form of cylindrical bosses which project perpendicularly from the upper and lower regions of the portion 8. As can be appreciated from Figure 1, the protuberances 14 and 16 are each equidistant from the longer sides of the body portion 8. Each protuberance is situated at the end of a respective blind bore 18 and 20 in the portion 8. The blind bores allow magnets 22 and 24 to be inserted into the portion 8 to sit against the reverse sides of the protuberances 14 and 16, i.e. the sides opposite the sides that form part of the interface 12. The body portion 10 is provided with a pair of recesses in the form of cylindrical blind bores 26 and 28 in the surface of the portion forming part of the interface 12. The recesses 26 and 28 are of a complementary shape to the bosses 14 and 16 and are in corresponding positions to those bosses so that when the two body portions 8 and 10 are brought together the bosses 14 and 16 extend into the recesses 26 and 28 to help to locate the body portions 8 and 10 in register with each other. Behind each of the recesses 26 and 28 there is a respective blind bore 30 and 32 which houses a respective magnet 34 and 36 at its inboard end.

The pole of the magnet 34 that sits against the inboard end of the bore 30 is the opposite of the pole of the magnet 22 seated against end of the bore 18 and the magnets 24 and 26 are similarly orientated relative to each other so that the magnets exert an attractive force on each other as the two body portions 8 and 10 are brought together (with the protuberance 16 extending into the recess 28 and the protuberance 14 into the recess 26).

As can be seen from Figure 4, the portion 10 includes a pair of opposed, concave recesses, referenced 29,31 in its sides and the surface to form the interface 12. The portion 8 has a corresponding pair of recesses, one of which is visible at 33 in Figure 1. Each of these recesses in the portion 8 is, in the assembled cuvette, aligned with a respective one of the recesses 29 and 31, so that the four recesses define two opposed thumb holds for facilitating the separation of the portions 8 and 10, against the action of the magnets, by a user.

The body portion 8 also has a tapered through bore 38 the inboard end of which includes an annular shoulder on which a circular window 40 is mounted and held in position by means of a suitable adhesive. The material constituting the window 40 is chosen in accordance with the need for the window to be able to transmit light of the wavelength used in the spectrophotometer in which the cuvette is to be used. In the present example, the wavelength of that light can be as low as 200nm, and the window 40 is formed from fused silica. The window 40 is surrounded by an annular ridge 42. The ridge 42, is in turn, surrounded by an overflow capture ring shaped channel 44 and is very slightly sub flush with the main face 43 of the position 8 to provide an opening through which excess sample can escape into the ring 44 until the windows settle into their rest position. The portion 10 has a cylindrical bore 46 which has been machined into the portion 10 to a sufficient depth to leave a thin PEEK membrane 48 at its inboard end. A circular aperture is formed in the centre of the membrane 48 which is therefore annular, and a second fused silica circular window 50 is attached by an adhesive to the inside edge of the membrane 48. A stainless steel spacer ring 52 is bonded to the inboard side of the window 50 and in the assembled cuvette bears against the window 40, to define the thickness of the chamber that contains the sample, and hence the path length of light through the sample.

As can be seen from Figure 4, the ring 52 carries three equiangularly (i.e. with 120° spacing) spaced hemispherical protuberances 54. In use, these are the portions of the ring that engage the window 40, and therefore also define a small gap between the ring and the window. In use, a droplet of sample (of 1-2μ1) 56 is deposited on the upper surface of the window 50 as shown in Figure 5. The two portions 8 and 10 are then brought together as shown in Figure 6. As this happens, the sample 56 will be spread to fill the space between the windows 40 and 50. The shock of compressing any excess sample (i.e. where the volume of the sample is larger than that of the chamber) is absorbed by the membrane 48, and the excess sample can flow through the spaces between the protuberances 54 and into the overflow capture ring 44.

The cuvette can then be inserted into a cuvette holder 57 of the spectrophotometer, as shown in Figure 7, in which a beam 58 of ultraviolet (or other) light is directed onto the window 40 through which it passes into the sample chamber, to interact with the sample 56 and exit the chamber through window 50 to travel in the path indicated by arrows 60 to the spectrometer of the spectrophotometer. The input beam 58 (is generally focussed on the centre of the cuvette (i.e. the sample chamber) and is therefore of a convergent conical shape. The tapered design of the bore 38 helps to ensure that the beam 58 is not unnecessarily clipped by the body of the cuvette. It will be appreciated that the chamber that contains the sample is defined by the windows 40 and 50 and the spacer ring 52, the interior surface of the chamber being constituted by the opposed faces of the windows, the inner periphery of the ring 52 and the inner portions of the hemispherical protuberances 54. The thickness of the chamber is determined by the axial extent of the ring 52 (and protuberances 54) and will typically be 0.2 or 0.5mm, to an accuracy of more than 99% (less than 1% error).

If the path length is known to be within 1% of its stated value (as governed by the spacer ring), then the user will not need to perform any time consuming calibrations in order to be able to apply the Beer's law equation to the measurements obtained using the spectrophotometer. In the present design, only the ring 52 (with protuberances 54) needs to be made to a high dimensional accuracy to achieve the accuracy of path length.

As can be seen from Figure 5, if the portion 10 is laid on an underlying supporting surface (which would bear against the face of the portion 10 opposite that which forms part of the interface) the window 50 would be readily accessible for application (or removal) of the drop whilst being kept out of contact with the underlying surface by virtue of being recessed into the body 10.

The second embodiment of cuvette in accordance with the invention, as shown in Figures 9-18 is substantially identical to the first embodiment, and the parts of the second embodiment that correspond to those of the first embodiment have been denoted by the reference numbers used in Figures 1-7 raised by 100.

As can be seen from Figures 10 and 11, for example, the bore 146 in the body portion 110 is not a straight cylinder, but instead has a smaller diameter portion 147 at the entrance to the bore, which leads to a larger diameter portion 149 that is terminated by the membrane 148 and window 150. The other principal difference is that the body portion 108 carries a handle 200 to facilitate the insertion of the cuvette into and its subsequent removal from a spectrophotometer. However, the two body portions 108 and 110 fit together in exactly the same way as the body portions 8 and 10 of the first embodiment. As can be seen from Figures 14 and 15 the orientation of the magnets 122, 124, 134 and 136 is such that, when the body portions are together, the north pole of the magnet 134 will be adjacent to the south pole of the magnet 122, whilst the south pole of the magnet 136 will be adjacent to the north pole of the magnet 124, so that the body portions are releasably held together by the force of attraction between those two pairs of magnets.

Because of the handle 200, the second embodiment of cuvette is longer than the first embodiment, and has outer dimensions of 12.5mm x 12.5mm x 60mm. In the second embodiment, it is more convenient for the drop initially to be placed on the body portion 108 when the latter is laid horizontally on the supporting surface, in the orientation shown in, for example, Figure 11.

The handle has a recess 202 (Figure 18) in its top that will carry a label to denote the path length of the cuvette. Alternatively or additionally, the handle and affixed to the portion 108 by a screw retainer (not shown), may be coloured by anodising to indicate the path length variant (using a colour coding system) in the specification.