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Sampling Technologies

Caps - end caps for tubes

Using appropriate end caps on your TD sorbent tubes is the best way of eliminating risks to sample integrity. As well as long-term brass storage caps, other types of cap include DiffLok™ caps, Diffusion caps and Aluminium push-on caps.

Sorbent tubes should be sealed at all times, except when samples are being collected or the tubes are being prepared for analysis. Once sampling or analysis is completed, tubes should be re-capped with long-term storage caps as soon as possible and returned to a clean environment for storage.

Long-term storage caps for industry-standard tubes are required when using Markes, PerkinElmer, Dani, CDS, Gerstel or Shimadzu instruments, and are recommended by international standard methods. Markes’ long-term storage caps are available in brass or aluminium and have been validated for periods of up to 27 months. To ensure caps are correctly tightened, use of the CapLok tool is recommended.


In addition to long-term storage caps, a range of other sorbent tube caps are available:

Aluminium push-on caps with O-ring seals are convenient for short-term storage of cleaned or sampled ¼-inch tubes – for example, when analysis is carried out very soon after sampling. They are an alternative to traditional brass caps in cases where long-term storage or transport is not required. Aluminium push-on caps can also be used in combination with SafeLok™ tubes. Note that push-on caps should not be used for long-term storage or transport of tubes.

Diffusion caps for passive monitoring using sorbent tubes replace the storage cap at the sampling end of the tube for the duration of the exposure period. The cap at the other end of the tube is left in place, and a penclip can be added for personal monitoring.

DiffLok™ caps for automation use a patented design to optimise productivity by avoiding the need to cap and uncap tubes when used on Markes’ TD autosamplers. Caps are used on both ends of every tube to preserve sample integrity throughout the analytical sequence by preventing both analyte loss and contamination. DiffLok caps do not use a valve or other moving part, and so are inherently simple and robust.