Injection liner

Details Injection liner Injection liner

2001-11-29

2003-05-20

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Chromatography type apparatus

Including injection system or inlet fluid distributor

C096S106000, C095S089000

Reexamination Certificate

active

06565634

ABSTRACT:

This invention is concerned with an injection liner, and relates in particular to a novel form of liner utilisable with a septum and cap and intended for use in the injector of a gas chromatograph.
Gas chromatography is a technique widely employed in industry. It finds particular application in the fields of medical care, pharmaceutical analysis, petroleum chemistry, petrochemicals and environmental analysis, and is especially valuable for the separation of complex mixtures into their components, typically such mixtures as contain organic chemicals, either as a simple mixture or in a solvent, such as water.
Basically, chromatography involves the transferring of a mixture of materials (the “sample mixture”) by means of a flowing medium (the “mobile phase”) along a passageway (the “column”) containing a substance (the “stationary phase”) to which the different components of the mixture are weakly, but differentially, attracted, so that gradually the less attracted components get ahead of the more attracted ones, and eventually, if the column is long enough, they are completely, separated. It is called “chromatography”—colour writing—after its original use, which was to separate mixtures of coloured dyes. In the case of gas chromatography, the mobile phase is a gas.
There are a number of different types of gas chromatography, but those in common use employ as the column a long tube containing the stationary phase. There are several designs of column, but typically it is long, narrow tube made from fused silica (like glass) coated on the outside with a polyimide or similar plastic layer to prevent corrosion and add strength. The silica tube may typically be from 5 to 50 meters (about 16 to 160 ft) long, and be of internal diameter 100 to 750 microns (0.0001-0.00075 m, or 0.01-0.075 cm, or about 0.004-0.03 in). The stationary phase chemical is either bonded on the inside of this tube or, in some cases, is deposited on solid, porous inert support materials which fill the tube.
When a small amount of the sample mixture is introduced to the inlet end of the column, with the mobile phase passing from the inlet end of the column to the outlet end, the mixture is blown slowly through the column. The stationary phase selectively slows down some of the compounds in the sample mixture, whereas other compounds are slowed much less or not at all. Compounds that are not slowed travel at the speed of the mobile phase, while compounds that are slowed down travel more slowly than the mobile phase. Because some compounds are slowed down and others are slowed less, those which are slowed less emerge from the far end of the column before those which are slowed more. Thus the mixture becomes separated into (some of) its components
In operation, a very small amount of the sample mixture—typically one milligram or less—is injected into the inlet end of the column which is sealed into ant elongate tubular device called an injector. The injector facilitates the introduction of this small amount of sample into the system, provides the required carrier gas flow for the column, and may also perform other functions, including the evaporation and concentration of the sample. Gas from the injector flows through the column from the inlet, injector end, and the individual components of the mixture emerge separately from the outlet end of the column at a time that depends on the velocity of the carrier gas and the extent to which the components are slowed by the stationary phase.
These separated compounds are then passed into a device called a detector, which can simultaneously detect the presence of the components and, in general, measure the amount of each one present. The detector produces an electrical signal that is amplified and passed to data-processing equipment which measures both the time after injection that the component emerged from the column and also the amount of signal produced; it can then produce a report on the composition of the original mixture, which can be utilised by the User to determine what actions, if any, should be taken.
There are several points in this analytical process at which errors can be introduced. Two of these are at and before the point of injection.
Sample mixtures may be derived from a number of sources, and may require a variety of preparations, including concentration, extraction and reaction. In order to maintain the integrity of the sample, these steps are kept to a minimum and, wherever possible, they are automated. It is also important that the skill level of those preparing the samples does not affect the integrity of the results.
Samples may also be dirty. That is, they may contain materials that remain in the injector, may not pass through the column at all, or may contaminate the detector. Such materials can cause the deterioration of the results of subsequent analyses.
To overcome some of these problems, injection liners are frequently used in the injector of the chromatography An injection liner is a narrow tube that fits inside the injector interior, literally providing a liner for the injector, and samples are injected into this liner tube rather than directly into the injector itself. Materials that would remain in the injector are thus deposited and remain in the liner instead, and when the liner becomes too contaminated with these materials it can be removed and replaced with a new liner.
Injection liners may also deliberately contain materials that selectively hold back compounds, by chemical or physical processes. These materials are called packing materials, and are able selectively to absorb specific components of the mixture.
In some instances the absorption of components in the liner packing material is reversible. That is, a material may be absorbed at a low temperature, and may thereafter be released by raising the temperature. One such packing material absorbs organic components at a low temperature, but allows water to pass freely through it at the same low temperature; the water can thus be diverted out of the system whilst the organic materials remain within the packing material. Subsequently, the gas flows within the system can be redirected, and the liner and its contents heated up so that the organic materials are then displaced into the column for analysis.
However, the liners themselves become contaminated, and need to be changed from time to time. This is frequently a difficult process, and one that is also very difficult to automate. It involves first cooling the injector, and then reducing the gas pressure in the chromatography system. When the pressure inside the injector is at atmospheric pressure, the top of the injector is opened. The top of the injector generally has a number of pipes attached to it. Getting the top off with the pipes attached is an operation requiring considerable operator skill and dexterity. Once the top is out of the way, the liner can be pulled out and removed. A new liner must then be placed in the injector, and the above process repeated in reverse before the next analysis can be started.
This replacement process involves significant skills and a number of steps at which leaks and other errors can be introduced. The process is also very difficult to automate. Even in an otherwise automatic system, the replacement of the liner tends to be a manual operation. This means, unfortunately, that very often the liner is left in place far longer than it should be, leading to deterioration of the performance of the injector, possible degradation of samples in the injector, and potential errors in the results presented to the analyst.
The present invention proposes a novel type of injection liner that can more easily be replaced either manually or automatically. More specifically, the invention suggests an injection liner the input end of which has a laterally-extending external flange against which in use there can be placed an injection septum for closing and sealing the input end, which septum is then sealed in place against the flange by a closure cap that fits tightly over and around the two. For use with an in

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