Non-seizing tapers for use in purged connections of capillary tubing used in gas chromatography

Abstract

A non-seizing taper used for purged capillary tubing connections in gas chromatography that stops capillary tubing at a predictable position within the taper during installation and maintains space for gas to flow past the capillary tubing. The disclosed taper is an improved component of commonly used purged devices such as inlet liners and purged unions. The arresting aspect of the taper simplifies the process of capillary tubing installation while ensuring that the tubing will reproducibly be positioned in the taper. One or more features of the taper prevent tubing from seizing within the taper so that the devices can be reused and ensure that there is open space for a portion of gas to flow around and past the tubing. The angle of the taper, the dimensions of the taper, and the nature of the features within the taper can be adjusted to meet specific performance, usability and / or manufacturability requirements.

Description

TECHNICAL FIELD[0001]This invention relates generally to the field of instrumentation for chemical analysis but has specific application to purged connections of capillary tubing used in conjunction with gas chromatographs.[0002]CLASS 96 / 106; 96 / 101[0003]Note: This is a continuation of prior-filed pending non-provisional application Ser. No. 14 / 106755 filed Dec. 15, 2013.BACKGROUND OF THE INVENTION[0004]Gas chromatographs are used for chemical analysis. Chromatographic techniques in general are used and for chemical analysis of mixtures because they can partially or completely separate mixtures into individual components, thereby providing unique information about sample composition. Gas chromatography is often chosen over other potential chromatographic techniques because of its speed of analysis, unique detectors, lower cost per sample and simplicity of use.[0005]Determining what is in a sample is called “qualitative analysis”. Determining how much of given substance is in a sampl...

AI Technical Summary

Benefits of technology

[0061]The embodiments of the invention comprise means to reduce or eliminate variability in column positioning, to provide features that prevent column seizing, to provide purged paths in tapered connectors that scale or track with the outer dimension of capillary columns inserted therein, and / or to simplify the process of connecting capillary columns to inlets or other purged capillary tubing connectors. The invention improves overall instrument performance and quality of analytical results by improving the reproducibility of sample transfer from the inlet to the capillary tubing connected thereto or between capillary tubes in the case of a purged connector. In addition, the current invention can improve laboratory productivity by simplifying the process of capillary tubing installation—a task that is performed daily in some analytical laboratories.

[0062]The arresting nature of the taper stops capillary tubing when it is inserted therein at a specific position where the narrowest radial axis of the taper equals the outer diameter of the capillary. This embodiment of the invention simplifies the process of capillary tubing installation and / or reduces variability in tubing positioning. When installing capillary tubing into a non-seizing purged taper, for example, one would first place the nut and ferrule on the tubing end and then trim a short section off the end. One would then simply insert the tubing into to the base of the inlet and within the taper in the base of the liner until it stops. Then one would tighten the nut to create a pneumatic seal. The requirement for instrument operators to measure and mark the tubing at a prescribed position is eliminated while the position of the column is reproducibly arrested in the correct position each time. By incorporating a non-seizing taper into purged capillary tubing connections, most of the variables associated with the current art are reduced or eliminated.

[0063]The arresting characteristic of the taper also provides a means of designing and producing purged connections for inlet liners or capillary tubing connectors that are optimal for a wide range of tubing dimensions. Whether optimal performance for a category of applications requires a constant open space for gas to flow around and by the column independent of column diameter or a space that scales with column diameter, the design of the taper shape and features can be adjusted to provide a very predictable column positioning and aspect ratio of tubing radial cross-sectional area to extra-tubing radial cross-sectional area. In this manner, a small number of taper designs will be applicable to a wide range of capillary tubing dimensions while still providing improved performance related to current commercial purged connections that have generic straight channel designs.

Problems solved by technology

It is very difficult to achieve truly representative sampling in gas chromatography because the sample must change from a condensed state to a gaseous state and then must undergo the physical process of transferring down and out of the inlet into the column.

The changes in sample composition caused by non-ideal sample introduction and transfer processes in gas chromatography can manifest as an increase or decrease in the relative amounts of components as a function of their volatilities, resulting in non-representative sampling.

Partial or complete losses of specific components can also occur due to degradation (decomposition or other chemical or physical changes in the sample component) or adsorption on active inlet surfaces.

The current art includes many different styles of liners, each with design attributes that are favorable for some analyses but unfavorable for others.

It is well known in the art that liners with straight internal diameters can suffer from issues of sample discrimination, decomposition, and peak broadening.

An additional deficiency of straight liners is that the concentric positioning of the column tip within its base is irreproducible, even with the same person doing the installation.

Capillary tubing inserted too far up protrudes into the larger internal diameter of the liner and does not benefit from the tapered internal diameter.

Reproducibly positioning of the end of the column inside the narrowed bore of the liner is somewhat difficult in the current art, especially with different operators, instrument models and locations.

Such a restriction could exaggerate the negative consequences of several variables involved with sample evaporation and transfer to the column as well as complicate pneumatic control.

Two significant deficiencies of this style liner are that (1) they are designed for only splitless injections, and (2) typically can only be used for a single column installation.

Each operator adopts his own technique to accomplish this task but each has limitations.

Capillary column installation is time consuming, often cumbersome to perform and is prone to variability among and between operators.

All current art for installing capillary columns into gas chromatograph inlets suffer from the stack up of variability in design choices and operator use.

Column positioning errors can degrade method performance in several ways including but not limited to increased discrimination, increased loss of labile components, decreased chromatographic efficiency due to broadening or tailing of initial peak widths, leaks, and / or infiltration of air.

Following insertion through the ferrule, the operator cleaves a small length of tubing from the end of the column to be sure the operative column end is open and free of small particles or ferrule shavings which would obstruct the flow of mobile phase during chromatographic separation and cause additional deleterious effects.

There are alternative column installation and affixing approaches in the current art that aim to simplify the process of column installation and increase repeatability of installing columns; however these approaches have a combination of deficiencies that limit their adoption and those skilled in the art have generally not found them to be improvements over the previously stated process.

The limitations include prohibitive cost, complexity, necessity for stocking of non-standard parts, and inability to achieve the intended performance or benefits.

Having the liner tight against the baseplate can lead to excessive resistance to flow of gas around the base to the split / purge vent, causing pressure control issues and decreasing sample introduction and transport performance.

Connections of capillary columns to purged unions suffer from some of the same usability and repeatability issues as those found with connecting capillary columns to inlets.

In addition, insertion of column ends too far into the union can break the column ends, potentially leading to failed pneumatic seals or degraded performance.

Not positioning columns in far enough creates peak tailing due to increased volume of the inter-column space and / or increased exposure of solutes to the sealing ferrule.