Sorbent Tube Accessories
Sorbent retaining gauzes, gauze retaining springs, penclips and push-on aluminium caps
Sorbent retaining gauzes are manufactured to critical tolerences to ensure that they will correctly fit into the front groove of a stainless steel tube. The placement of this front gauze is critical for diffusive sampling as it defines the diffusive gap. All Markes stainless steel and inert coated stainless steel tubes are supplied with this front gauze correctly and firmly fitted.
Gauze retaining springs are used to ensure the rear sorbent retaining gauze remains in the correct position. They should be inserted and removed from the tubes using the TubeMate™ tool.
Removable clips attach to the groove on stainless steel tubes so that they may be easily fastened to a lapel or pocket when being worn as personal monitors.
Push-on aluminium caps may be used for convenience for short term storage of cleaned or sampled tubes, e.g. when tubes are being analysed almost immediately after sampling. They should not be used for long-term storage except for SafeLok tubes.
Ready assembled long-term storage caps and one-piece PTFE ferrules
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¼-inch brass caps fitted with one-piece (combined) PTFE ferrules are recommended for long-term storage by international standard methods such as US EPA Method TO-17, ASTM D6196 and ISO 16017. They have been evaluated for up to 27 months storage of sampled tubes and are also suitable for storing and transporting blank tubes.
Ready assembled long-term storage caps incorporating combined PTFE ferrules are available in both brass and aluminium. The caps meet a stringent cleanliness specification and tight manufacturing tolerances. PTFE ferrules should be replaced after approximately 20 uses. |
CapLok™ tool
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In order to achieve a leak tight seal, long term storage caps should be tightened with a wrench/spanner. However this can be time consuming and awkward in field situations – especially if the operator is not used to handling tubes. “Over-enthusiastic” tightening of the caps can also lead to distortion of the PTFE ferrules and hence to a leaking seal.
The CapLok™ tool has been designed by scientists at INERIS – the French National Institute for the Industrial Environment – to simplify tube capping and uncapping procedures. It helps prevent over tightening and distortion of the PTFE seals inside the caps thus extending their life.
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TubeMate™ tool
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TubeMate™ has been designed to help with packing and unpacking thermal desorption tubes. Once the chosen sorbent is packed into a tube, one end of the TubeMate can be used to push the second sorbent retaining gauze gently down the tube to the sorbent surface. Using TubeMate ensures the gauze stays flat, and comes to rest evenly on top of the sorbent bed.
The other end of TubeMate is designed for inserting and removing the gauze retaining spring. Once partially inserted into the end of the tube, TubeMate grips the spring and enables you to twist it into place with very little effort. This end of the tool is also used for easy removal of sorbent retaining springs when unpacking sorbent tubes. |
DiffLok™ caps
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Markes International automated thermal desorber - ULTRA, uses unique, patented* DiffLok caps to ensure the integrity of both sampled and cleaned tubes via a unique diffusion limiting design.
DiffLok caps remain on the sample tubes throughout the entire automated thermal desorption process. They are designed to provide an effective tube seal until pressure is applied, causing gas to flow.
All tubes on the ULTRA autosampler require 2 DiffLok caps (one on either end). DiffLok caps are available in stainless steel or inert coated stainless steel.
DiffLok caps protect sample tubes for up to 8 days, but should not be used for long term storage
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PTFE inserts for direct desorption of materials
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Thermal desorption is often used for the direct desorption of VOCs in solids, liquids or pastes. Examples include coffee, polymers, fibres, pharmaceuticals, cough mixture, paints, petroleum jelly products, resins and foodstuffs such as mustard or syrup and textiles.
Products compatible with direct desorption may be weighed straight into an empty thermal desorption tube. This works well for many materials but can result in irreversible contamination with samples such as adhesives or paint. Using PTFE inserts (liners), protects the inner walls of the tubes and can simplify sample weighing. Two types of PTFE inserts are available from Markes - the original “snug-fit” liners which should be used for most powdered / granular samples (e.g. dry spice, powdered drug) and the newer “loose-fit” liners which are suitable for “semi-solid” samples such as resins and viscous liquids which should be smeared around the inside of the liner. "Loose-fit” liners may be inserted into tubes packed with a small bed (ca. 1 cm) of Tenax TA. The Tenax prevents any high boiling debris from the sample migrating into the flow path of the thermal desorber. “Loose fit” PTFE liners must be used in this case so that they can be tipped back out of the tube easily after use. |
¼-¼-inch stainless steel unions
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Multi sorbent tubes are commonly used for pumped sampling of atmospheres containing VOCs with a wide range of volatilities. However, there are times, for example when large sampling volumes are required or when sampled tubes must be stored for several weeks prior to analysis, when single sorbent tubes connected in series provide a better option.
Up to 3 tubes may be connected in series using ¼-¼-inch stainless steel unions which have been fitted with one-piece (combined) PTFE ferrules.
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TubeTAG™: RFID sorbent tube tagging
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Further information on TubeTAG |
For part numbers and pricing please contact your local Markes distributor or visit the Markes eShop.
Relevant technical support publications from Markes International can be automatically downloaded from this web site (registration required). Examples include:
* GB 2337513, US 6,564656 B1