Liquid separation

Abstract: A liquid is separated into its constituent species by electrophoresis along a capillary channel (4). A plurality of the channels (4) is provided in the thickness of an injection moulded plastics disc (2). The disc is rotatably mounted such that samples are dispensed into successive channels. When all twelve channels have been used, the disc is replaced with a fresh one.

Description: Field of the Invention This invention relates to the separation of liquid into its constituents by the application thereto of an electric field. Background of the Invention It may be desired to analyse a liquid not, or not only, for its bulk properties, but for the properties of its constituents, for example properties of its ionic species. Therefore, the constituents have to be separated. It is known to do this by electrophoresis, including isotachophoresis, in which a sample of liquid is introduced into one end of a capillary tube and is subjected to an electric field. The sample, or constituents thereof, moves along the tube under the influence of the field, separating, for example into its various species, depending on their mobilities. Analysis can then be carried out on the individual species. US 3,956,099, US 4,715,943, WO 94/03631 and US 4,375,401 all disclose apparatus for separation of constituents of a sample by electrophoresis. Thus, apparatus and methods for separating at least two liquids into their constituents by the application thereto of an electric field, comprising a disc that is rotatably mounted about an axis substantially perpendicular to the plane thereof, the disc having at least two discrete channels for liquid samples, wherein each channel has an inlet at one end for receiving a liquid sample, the apparatus having at least one electrode at each end of a channel for applying an electric field to the sample thereby to cause the sample, or constituents thereof, to be driven towards the other end and to be longitudinally separated into its constituents, are known. Problem to be Solved by the Invention It is one object of the present invention to provide apparatus for and a method of separating liquid into its constituents in a quick and convenient manner. Summary of the Invention In accordance with one aspect of the present invention, there is provided apparatus for separating at least two liquids into their constituents by the application thereto of an electric field, comprising a disc that is rotatably mounted about an axis substantially perpendicular to the plane thereof, the disc having at least two discrete capillary channels for liquid samples, wherein the ratio of the length to the maximum transverse dimension of each channel is at least 100:1, and wherein each channel (a) has an inlet at one end for receiving a liquid sample, (b) has at least one electrode at each end for applying an electric field to the sample thereby to cause the sample, or constituents thereof, to be driven towards the other end and to be longitudinally separated into its constituents, and (c) has means at said other end for detecting the separated constituents of the liquid sample. It is to be understood that reference to a component of the apparatus being "at" an end of a channel includes the component being adjacent thereto. Preferably, the channels are formed in the thickness of the disc. The disc may be formed from two plates secured together, and the channels may then extend across the interface, or alternatively may be formed in one of the plates, the other plate forming a lid. The disc, of electrically-insulating material, may be formed from a plastics material, or from glass. The disc may be injection moulded, and the channels may be formed therein during this process. At least one, and preferably each, of the channels may extend between the periphery and a central region of the disc. At least one, and preferably each, of the channels may extend substantially linearly, or in a serpentine path, in the plane of the disc. The liquid inlets may be at the inner or at the outer end of the channels. The channel dimension ratio is preferably between 200:1 and 500:1. Each channel may be of rectilinear, circular, V-or U- configuration. The detection means may detect the separated components electrochemically, electrically or optically. For example, the detection means may comprise a set of electrodes for detecting the different electrical conductivity of the separated constituents. Alternatively, the refractive index or the colour of the constituents may be used to differentiate them. In another embodiment, the differentiation may be carried out electrochemically, for example using a silver electrode. Although in general the same means of detection would be used for each of the channels of a single disc, it is envisaged that different means may be employed from one channel to another. The apparatus may comprise means for effecting the rotation of the disc so as to dispose the inlets of successive channels adjacent a liquid dispenser. The disc may be mounted on a support arrangement of the apparatus so that it is interchangeable with a fresh disc. The apparatus may comprise means at said other end of each channel for analysing the separated constituents of the sample, for example electrochemically, electrically or chemically using voltammetry, potentiometry, titration, conductivity, colourmetric or optical analysis. In accordance with another aspect of the present invention, there is provided a method of separating a plurality of liquid samples into their constituents, wherein a sample is dispensed into an inlet at one end of a channel of a disc, the disc is rotated and another sample is dispensed into an adjacent channel, applying a voltage between electrodes at each end of each channel so as to drive the samples, or constituents thereof, along their respective channels to the other ends thereof, and detecting the separated constituents at said other ends of each of the channels, and wherein the ratio of the length to the maximum transverse dimension of each channel is at least 100:1. The disc may have at least three of said channels and may be rotated so that successive liquid samples are dispensed into adjacent channels. The separation of the constituents of each sample detection may be carried out electrically or optically. The separated constituents may be analysed. Advantageous Effect of the Invention The liquid separating apparatus of the present invention is particularly suited for operation with a plurality of samples in a quick and convenient manner. When the disc is interchangeable, the apparatus is particularly suited for inexpensive, single-use operation. Brief Description of the Drawings Apparatus for and a method of separating liquid into its constituents, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic plan view of one embodiment of the disc of the apparatus; and Figure 2 is a simplified schematic plan view of a modified disc. Detailed Description of the Invention Referring to Figure 1, a disc 2 of diameter 15 cm and thickness 0.5 cm is injection moulded from a plastics material. The disc 2 contains twelve equispaced capillary channels 4 extending radially through the body thereof. Each channel 4 is 10cm long, 300µm wide and 60µm deep. A first set of electrodes 6 and a second set of electrodes 8 are moulded into the disc 2 at the outer and inner ends respectively of the channels 4. A respective sample well 10 in the upper surface of the disc 2 communicates with each channel 4 adjacent its outer end electrode 6. In operation, a sample of the liquid whose chemical species are to be separated for analysis is introduced from a dispenser (not shown) into the well 10 at the outer end of one of the channels 4, and a high voltage, of 1500V, is applied between the electrodes 6 and 8 of that channel 4. The electric field causes the sample, or constituents thereof, to move towards the inner end of the channel 4, and in so doing the species separate along the channel 4 in accordance with their different mobilities. The strength of the electric field for a given length of channel 4 is chosen with respect to the liquid being sampled so that complete separation takes place before the sample reaches the inner end of the channel 4. The separated species of the liquid sample are detected at the inner end of the channel 4 by a pair of electrodes 12, which respond to the different electrical conductivities thereof. The species may then be treated separately, for example by electrical, electrochemical or optical analysis. The disc 2 is then rotated about its vertical axial shaft 14 so as to dispose the well 10 of the next channel 4 beneath the dispenser. The next sample is then dealt with as above. The second sample may be of the same liquid as, or different from, the first. The detector at the inner end of the second channel 4 may be the same as, or different from, that of the first. The analysis carried out on the second sample may be the same as, or different from, that carried out on the first. The disc 2 is successively rotated until a sample has been dealt with in each of the twelve channels 4. Owing to the comparatively high electric field that extends along the channels 4, it is important that they be sufficiently separated from each other to avoid any interference therebetween. The arrangement of channels in the disc need not be radial as shown in Figure 1. A modification is shown in Figure 2, in which the detector electrodes have been omitted for clarity. Referring to Figure 2, a disc 20 has twelve channels 22 that extend in curves between respective inner and outer electrodes 24 and 26, with respective sample inlets 28 located at the inner ends thereof. Such a path allows the channels 22 to have an increased length with respect to the linear paths of the channels 4 whilst maintaining the same disc diameter. It will be appreciated that the channels may follow paths different from those exemplified in the Figures.

Claims: Apparatus for separating at least two liquids into their constituents by the application thereto of an electric field, comprising a disc (2) that is rotatably mounted about an axis substantially perpendicular to the plane thereof, the disc having at least two discrete channels (4) for liquid samples, wherein the ratio of the length to the maximum transverse dimension of each channel is at least 100:1, and wherein each channel (a) has an inlet (10) at one end for receiving a liquid sample, (b) has at least one electrode (6, 8) at each end for applying an electric field to the sample thereby to cause the sample, or constituents thereof, to be driven towards the other end and to be longitudinally separated into its constituents, and (c) has means (12) at said other end for detecting the separated constituents of the liquid sample. Apparatus according to claim 1, wherein the channels (4) are formed in the thickness of the disc. Apparatus according to claim 1 or claim 2, wherein the disc (2) is formed from two plates secured together. Apparatus according to any one of the preceding claims, wherein at least one, and preferably each, of the channels (4) extends between the periphery and a central region of the disc (2). Apparatus according to any one of the preceding claims, wherein at least one, and preferably each, of the channels (4) extends substantially linearly in the plane of the disc (2). Apparatus according to any one of the preceding claims, wherein at least one, and preferably each, of the channels (4) extends in a serpentine path in the plane of the disc (2). Apparatus according to any one of the preceding claims, wherein the channel (4) dimension ratio is between 200:1 and about 500:1. Apparatus according to any one of the preceding claims, wherein each channel is of rectilinear configuration. Apparatus according to any one of the preceding claims, wherein the detection means detects the separated components electrochemically, electrically or optically. Apparatus according to any one of the preceding claims, comprising means at said other end of each channel for analysing the separated constituents of the sample. Apparatus according to any one of the preceding claims, comprising means for effecting the rotation of the disc so as to dispose the inlets of successive channels adjacent a liquid dispenser. A method of separating a plurality of liquid samples into their constituents, wherein a sample is dispensed into an inlet at one end of a channel of a disc, the disc is rotated and another sample is dispensed into an adjacent channel, applying a voltage between electrodes at each end of each channel so as to drive the samples, or constituents thereof, along their respective channels to the other ends thereof, and detecting the separated constituents at said other ends of each of the channels, and wherein the ratio of the length to the maximum transverse dimension of each channel is at least 100:1. A method according to claim 12, wherein the disc has at least three of said channels and is rotated so that successive liquid samples are dispensed into adjacent channels. A method according to claim 12 or claim 13, wherein the detection of the constituents of each sample is carried out electrochemically, electrically or optically. A method according to any one of claims 12 to 14, wherein the separated constituents are analysed.

Inventors: EDWARDS STEPHEN, MCINTYRE STEPHANIE, EDWARDS, STEPHEN, MCINTYRE, STEPHANIE
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1999
Main classification: B01D57
IPC codes: B01D57, G01N27