Radiant energy – Ionic separation or analysis
Reexamination Certificate
2000-08-07
2002-10-08
Berman, Jack (Department: 2881)
Radiant energy
Ionic separation or analysis
C250S282000, C250S288000, C073S864810
Reexamination Certificate
active
06462334
ABSTRACT:
The invention relates to a method of and apparatus for analysing a sample, and particularly to those comprising the use of conveying means to convey a sample to an analyser.
For many years it has been known to provide a chromatography column for separating liquid mixtures containing various components dissolved or dispersed therein. During the chromatographic process, the individual components are separated by a known process using apparatus comprising a mobile phase supply, a sampling device, a column and a detector, such as HPLC, gel permeation chromatography, or ion exchange chromatography enabling the quantity and nature of each component to be determined. Hitherto, different methods of detection have been proposed.
In one method, UV detection has been found to be highly sensitive, accurate and simple to use. However, one major limitation is that for UV detection to be effective, the compound to be analysed must absorb UV. This means that the technique cannot be used for several major classes of compounds, including carbohydrates, alcohols, detergents and aliphatic hydrocarbons. Also solvent choice is limited to U.V. transparent solvents.
In another method, refractive index detection is used. Whilst it is a widely used method, it is less sensitive than the UV method described above and tends to be subject to considerable instability arising from eluent changes. It cannot be used with what is known in the art as Gradient Elution techniques.
In a further method, the components separated by chromatography are transported on a wire to a furnace where they are heated and pyrolysed. The pyrolysis products then pass by means of a complex set of conduits into an argon detector and are detected. In another embodiment the solute on the wire is burnt to carbon dioxide which is sucked into a hydrogen stream that passes over a nickel catalyst. The nickel catalyst converts the carbon dioxide quantitatively to methane which is detected by a flame ionisation detector (FID). The disadvantage of these processes is the need for a complex set of conduits and the dilution of the pyrolysis or oxidation product during the process. As the argon detector is concentration sensitive the dilution of pyrolysis produced in the carrier argon stream reduces the sensitivity. As the FID is mass sensitive and not concentration sensitive dilution is not important but the dispersion of the peak in the conduit (peak broadening) and the high noise generated by the catalytic conversion significantly reduces the sensitivity.
An object of the present invention is to provide improved methods and apparatus for detecting components of a mixture which may have been separated by chromatography.
According to a first aspect of the invention there is provided an analytical apparatus comprising:
(i) supply means for supplying a sample to be analysed;
(ii) analysing means for analysing at least one property of the sample to be analysed; and
(iii) conveying means operable to convey the sample between the supply means and the analysing means, wherein the conveying means comprises an oxidised surface layer which receives the sample.
The property may be a physical property, such as viscosity or melting temperature, of the sample or a chemical property, such as the chemical composition of the sample.
The sample may be components of a mixture which has been previously separated by chromatography.
The anlaysing means may be an analysing chamber, preferably without the need for conversion steps known hitherto.
Preferably the oxidised surface layer is in the form of a continuous surface film. The oxidised surface layer may be porous. The oxidised surface layer is preferably readily wettable by solvents, especially aqueous and non-aqueous solvents such as water and polar solvents. Examples of polar solvents include alcohols, such as ethanol and propanol, and DMSO. Preferably the oxidised surface layer is readily wettable by hydrocarbons including aromatic and non-aromatic, substituted and non-substituted alkyls.
Preferably the sample is applied to the conveying means without substantial diffusion along the conveying means.
The conveying means may comprise a metal, the metal having an oxidised surface layer.
Preferably, the conveying means is a wire which has an oxidised surface layer.
Alternatively a tape of material or a disk of material may be used instead of the wire. The latter two forms of conveyor have an oxidised surface layer, and are less likely to break than wire. Tape is especially preferred. A typical width of tape is 1.5 mm, with a thickness of 0.1 mm.
In that respect, and according to a second aspect of the invention, there is provided a method of detecting components of a mixture which have been separated by chromatography comprising the steps of providing a conveyor, such as a metal wire or tape, which has an oxidised surface layer, depositing sequentially on the oxidised surface layer the separated components of the mixture, and moving the wire and each component thereon to detection apparatus where analysis of each sample takes place.
Preferably, the conveying means, such as wire or tape, is made of titanium and the layer is oxidised titanium. The oxidised titanium forms a continuous porous surface film on the titanium metal and greatly enhances the carrying capabilities of the wire or tape. The oxidised wire wets very easily and will carry without difficulty both aqueous and non-aqueous liquids. Preoxidised titanium wire comprising an oxidised surface coating is commercially available, for example from Alloy Wire International, Cradley Heath, West Midlands, United Kingdom.
Other suitable metals comprising an oxidised surface layer include molybdenum, aluminium, iron, palladium and platinum.
The conveying means such as wire or tape is preferably carried on a supply spool and the invention may include drawing off the wire from the supply spool by means of a take up spool. A motor, such as a stepper motor, may be computer controlled to draw the wire or tape at a desired rate from the supply spool. The invention preferably includes controlling the tension of the wire between the spools to maintain a substantially constant tension in the wire particularly when the wire is heated as set out below.
A traverse mechanism may be provided to ensure that, for example, the tape/wire is regularly wound across the take up spool.
Alternatively the conveying means may be moved by means of one or more rollers in contact with the conveying means. This has the advantage that the speed of the conveying means does not vary according to the amount of e.g. tape/wire on the take up spool.
Preferably, the apparatus of the invention comprises an analyser chamber.
In a preferred embodiment the inventors have found that where a conveying means, such as tape or wire, is used according to the first or second aspect of the invention, wetting of the tape or wire with the separated components of the mixture can be improved by providing a polar cone opposite an aperture supplying the separated components of the mixture.
The separated components of the mixture may be supplied to the surface of the tape or wire from an aperture in, for example, the end of a supply tube the end of which may be cone-shaped. The cone, such as a titanium cone, comprising an oxidised surface coating, may be provided on the opposite side of the tape or wire with the tip of the cone directed towards the aperture. The cone draws off surplus mixture by directing the surplus mixture away from the tip of the cone, down the sides of the cone, to collection means. The oxidised layer on the surface of the cone improves the wettability of the cone and improves the ability of the cone to direct surplus mixture away from the wire or tape, thus preventing diffusion of the separated components along the wire or tape. Titanium is especially preferred as the material for the cone.
The aperture and cone may be positioned so that a continuous stream of separated components joins the aperture to the cone, with the wire or tape passing through the stream.
A strongly dispersive coating may be
De La Pena John Michael Devereux
Little Christopher John
Scott Raymond Peter William
Berman Jack
Fernandez Kalimah
Kilpatrick & Stockton LLP
Scientific Detectors Limited
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