GB2480596A

GB2480596A - Disposable light scattering cuvette for liquid sample held by surface tension

Info

Publication number: GB2480596A
Application number: GB1001487A
Authority: GB
Inventors: Kenneth John Cunningham
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-01-29
Filing date: 2010-01-29
Publication date: 2011-11-30
Also published as: GB201001487D0; WO2011092510A1

Abstract

The invention utilises liquid surface tension to provide a disposable sample cuvette 42 which includes the combination of low cost and low sample volume together with high quality measurement capabilities. Light scattering equipment 40, 41 can allow users to identify certain properties of solutions and suspensions including the hydrodynamic size of particles and molecules by either static or dynamic light scattering without altering the sample in an invasive way. The cuvette 42 utilizes a small hole of precise dimensions to retain a liquid sample such that a light scattering measurement can take place. By correcting for the effects of refraction and from the meniscus at the surface of the liquid sample, an accurate measurement can be obtained from as little as a 5 microlitre sample volume. The path length may be about 1mm and the cuvette body may partly consist of an opaque material allowing light to be shielded or screened to reduce reflections.

Description

DISPOSABLE CUVETTE

Field of the Invention

This invention relates to the methods and apparatus for determining characteristics of solutions, such as the hydrodynamic size, concentration and molecular weight of macromolecules in solutions by static and/or dynamic light scattering.

Background of the Invention

Optical techniques known as static or dynamic light scattering are often deployed as a means to characterize particles and molecules in solution or suspension. Liquid samples must be held in a container (cuvette) with optically transparent windows to allow the measurement to take place. To produce the highest quality measurements, traditional cuvettes may be made from silica glass or quartz glass to reduce the background optical noise' to a minimum. Such cuvettes also offer very low sample volumes however, they are too expensive to dispose of after a single use and must therefore be cleaned prior to re-use. Transparent plastic disposable cuvettes are available and are both cheap and convenient, but suffer from poor optical transmission through the viewing windows or are of a much larger minimum sample volume than the quartz glass varieties.

Summary of the Invention

The invention provides the valuable combination of low cost, low sample volume together with high quality measurement capabilities. Several aspects of the invention are presented in this application. Systems according to the invention, can allow users to identify certain properties of solutions and suspensions including the hydrodynamic size of particles and molecules. This can allow characteristics of unknown materials to be discovered quickly and inexpensively without altering the sample in an invasive way.

Brief Description of the Drawings

Fig 1. Is an illustrative embodiment of a particle or moleculer characterization instrument Fig 2. Is an illustrative embodiment of the light path of a particle or molecular characterization instrument in the traditional (or classical) setup Fig 3. Is an illustrative embodiment of the light path of a particle or molecular characterization instrument according to the invention Fig 4. Is a further illustrative embodiment of the light path of a particle or molecular characterization instrument according to the invention Fig 5. Is a further illustrative embodiment of the light path of a particle or molecular characterization instrument according to the invention Fig 6. Is a diagram of the light paths within the sample retainment volume Fig.7 Is a diagram illustrating the use and control of surface tension within the sample volume Fig. 8 Is an illustration of the invention in elevation and isometric views

Detailed Description of an Illustrative Embodiment

Referring to Fig.1, a typical illustrative solution characterization instrument can include a light source 10, that shines into a sample cuvette 11. The sample cuvette may be a stand-alone batch type or flow though type. A scattered light detector 12, is positioned to collect light from the sample cuvette and deliver the light signal to a signal processing electronic circuit 13, such as an autocorrelator. The conditioned signal is then passed to a computer 14, for further analysis and characterization.

The solution characterization instrument described above may have an optical path according to the illustration in Fig. 2. The light source 20, shines light along a path 21 into a sample cuvette 23. Light scattered from the sample is collected along a second light path 22 into a scattered light detector 24 and onwards to the signal processing electronics as described iii Fig. 1. The angle 01 between the source 20 and detector 24 may be known and can typically, although not necessarily, be 90°. This is the traditional (or classical) optical setup.

Fig. 3 is an illustrative embodiment according to the invention. The disposable cuvette 31, replaces the sample cuvette 23 in the same optical configuration described in Fig.2. In this case the disposable cuvette 31 is presented at an angle 03 to the path of the light source 30. The angle 02 between the light paths remains as in Fig. 2.

Fig. 4 is a further illustrative embodiment according to the invention. In this arrangement, the disposable cuvette 42, replaces a sample cuvette 23. The disposable cuvette 42, is presented at an angle 04 to the path of the light source 40 & 44. The angle 05 between the light paths is now more than 90° and may be 173°, 165° or any angle between to 90° and 180°. This optical arrangement is known as backscattering'.

Fig. 5 is a further illustrative embodiment according to the invention. In this arrangement, the disposable cuvette 52, replaces a sample cuvette 23. The disposable cuvette 52, is presented at an angle 06 to the path of the light source 50 & 53. The angle 07 between the light paths is now less than 90° and may be 7°, 15° or any angle between 0° and 90°. This optical arrangement is known as forward scattering'.

In order to calculate the hydrodynamic size of a particle, the angle of scattered light collection must be known.

Fig. 6 illustrates the light path within the disposable cuvette sample retention volume. The liquid is retained within the volume by surface tension. Light 60, enters the sample volume 64, at a known angle 01 from the normal and refracts according to Snell's law [1].

sin O 712 [1] s'inO2 Due to the geometry of the optical paths, the collected light signal 61, leaves the sample volume at a known angle. The refracted light beams intersect at a point given by the refractive index of the medium, examples of which are indicated at positions 62 and 63 having refracted at angles 02 or 02'. By rearranging the formula, the corrected angle 02 can be used in the analysis of the scattered light signal 61.

The phenomenon of liquid surface tension modifies the corrected angle of refraction due to refraction occurring normal to the liquid surface. Fig. 7 illustrates a section through the sample volume of the invention where the material retaining the liquid is given by 71. In Fig. 7a, an overfilled sample volume causes a bulging meniscus to distort the corrected angle of refraction. Similarly, an under filled sample volume, Fig. 7b has a similar effect.

If the sample volume is filled precisely. Fig. 7c with a known volume, which exactly fills the void, the corrected angle of refraction is known.

Claims

Claims What is claimed is: 1. A cuvette for characterizing liquid samples by static and/or dynamic light scattering comprising: a substantially flat body containing an inner space designed to retain a liquid sample by surface tension alone, and a geometric shape allowing it to be used in a classical DLS optical setup, backscatter and forward scatter optical arrangments 2. A cuvette according to claim 1 wherein the sample retention volume is about 5il (microlitres) 3. A cuvette according to claim I wherein the path length is about 1mm 4. A cuvette according to claim I wherein the centre height of the retention volume is suitable for use with instrumentation using other cuvettes of 8.5mm centre height 5. A cuvette according to claim I wherein the centre height of the retention volume is suitable for use with instrumentation using other cuvettes of 15mm centre height 6. A cuvette according to claim 1 wherein the retention volume has defined edges designed to retain liquids by surface tension alone 7. A cuvette according to claim 1 wherein the body partly consists of an opaque material allowing light to be shielded or screened to reduce reflections 8. A cuvette according to claim 1 comprising an embosed finger grip and name and logo on the upper region 9. A cuvette according to claim I comprising a field which can be inscribed 10. A cuvette according to claim I comprising a symmetrical design which can be placed in a sample holder in either of two orientations 11. A cuvette according to claim I comprising a field to contain a bar code or serial number Amendment to the claims have been filed as followsCLAIMS1. A cuvette substantially as described herein by reference to the examples.
2. Use of a cuvette for characterising liquid samples by static andlor dynamic light scattering as substantially described herein by reference to the examples.
3. A cuvette substantially as described herein by reference to FIG. 8. C)