Sample tube holder

Description

REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 60/692,166 that was filed Jun. 20, 2005.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to an improvement in devices for monitoring air and other gases.

More particularly, this invention relates to an improvement to the mounting means for a sampling tube used in an air or industrial gas monitoring system.

2. Description of Related Art

A common method for monitoring air and other gas streams to detect the presence of chemical agents, toxic industrial chemicals, and other compounds that might be of interest employs sorbent-packed tubes for sample collection. Those sample tubes, commonly referred to as DMMS tubes (an acronym for depot area air monitoring system) comprise a glass or stainless steel tube that is filled with a solid adsorbent such as activated carbon or a molecular sieve. The adsorbent filling is selected according to the chemicals that are being monitored.

A sample is collected by aspirating air or other sample gas through the tube for a predetermined period of time at a controlled gas flow rate. Vapors of the compounds of interest are adsorbed on the solid sorbent, and the sample tube is then removed from its sampling site for its analysis in a laboratory. The laboratory procedure commonly employed thermally desorbs the sample and passes it into an analytical system which may be, for example, gas chromatography, or gas chromatography in combination with mass spectrometry.

In field use, one end of a sample tube is connected to a vacuum manifold that maintains a known negative pressure relative to the atmosphere being sampled. If the seal between the sample tube and the manifold is not secure and leakage occurs, then the sample results are compromised and cannot be trusted. Forming a secure seal on the end of a sample tube is difficult because an end seal requires that the tube end meet strict requirements for flatness and squareness. A chip or other imperfection on the tube end creates a potential leakage site causing an end seal to fail. It is also possible to use an O-ring to form a seal on the outside diameter of the tube, but that type of seal often makes it difficult to insert the tube end into and to remove it from a mating fitting on the vacuum manifold. That is particularly true if the tube is enclosed in some manner in order to protect it from physical damage. Another complication arises from the fact that variation in the length of sample tubes is common.

The device disclosed and claimed in this application overcomes all of those problems, and does so in a simple, dependable, and cost effective manner.

SUMMARY OF THE INVENTION

This sample tube mounting means of this invention comprises a compression fitting having an elastomeric ferrule into which a sorbent-filled sample tube is inserted. The cap member of the compression fitting is extended as a torque tube that fits over and protects the sample tube. The free end of the torque tube extension is preferably formed as a thumb wheel for ease in removal and replacement of the sample tube without the use of tools

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE is a partial sectional view of the sample tube holder according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention will be described with reference to the drawing FIGURE where the sample tube holder is shown in a partial cross-sectional view at 10. The tube holder includes a compression fitting body 12 having an end 14 that is adapted for connection to a source of vacuum such as a vacuum manifold (not shown.) End 14 may be threaded as shown in the drawing or may comprise any other gas tight connection means such as a snap coupling or the like. The other end of the compression fitting body 12 is adapted to accept and seat an end of a sample tube and to provide communication between the vacuum source and the seated tube end. Fitting body 12 is threaded for connection to a compression fitting cap 16 that is extended as a torque tube 18. The free end of torque tube 18 opposite fitting cap 16 preferably terminates as a thumb wheel 20. Wheel 20 may be provided with a knurled or otherwise patterned surface for ease in gripping and turning without use of a wrench or other tool.

The inside diameter of torque tube 18 is sized somewhat larger than the exterior diameter of a sorbent-filled sample tube, such as a DAAMS tube 22, to allow for easy insertion and removal of the tube. An elastomeric ferrule 24, sized to make a sliding fit with the exterior of tube 22, is seated within compression fitting cap 16 adjacent the tube end that extends into the body 12 of the compression fitting. It is preferred that the ferrule be fabricated from a chemically inert material such as Vespel® or Teflon®. As the torque tube is tightened, the ferrule is compressed about the exterior of the sample tube to thereby provide a gas-tight seal between the tube end and the vacuum source. It is preferred that the length of torque tube 18 be approximately the same as that of the sample tube to thereby provide maximum physical protection for the sample tube while not interfering with its insertion into or removal from the fitting site.

In use, a fresh sample tube is connected to a vacuum source using the sample tube holder of this invention. A stream of gas from the atmosphere being sampled is drawn through the tube by the pressure differential between the vacuum source and the atmosphere being sampled for a predetermined time period to adsorb upon the tube packing those atmospheric components that are being monitored. The loaded sorbent tube is then removed from the sample tube holder, is replaced with a fresh tube, and the loaded tube is transported to a laboratory or other analysis site. The cycle then is repeated.

As may now be appreciated, the sample tube holder of this invention provides a convenient and practical means for connecting a sorbent-filled sample tube to a vacuum source and to facilitate its exchange with a fresh tube while also protecting it from physical damage during the sampling procedure.

It will be understood that the specific embodiments described herein are exemplary and that persons skilled in the art may make variations and modifications that have not been specifically described without departing from the spirit and scope of the invention as is defined by the following claims.