Permeation and Diffusion Tubes

Why use Permeation Tubes?

The purpose of a calibration gas standard is to establish accurate reference points for the verification of an analysis. Static mixtures in gas cylinders are unreliable and inaccurate at the levels (ppm-ppb) that analytical technology now demands. In gas cylinders containing low level mixtures, the trace components adsorb onto the cylinder walls causing the standard to be inaccurate and unreliable. Also, if the analyte is polar or reactive, establishing a reliable reference point using gas cylinder mixture is impossible. The Permeation Tube Method solves these problems.

We can also supply a wide range of Refillable Diffusion Tubes and these can be used for compounds with low vapour pressure and for custom applications.

Accuracy

Permeation Tubes are reliable and accurate. They are certified gravimetrically and are traceable to N.I.S.T. or other national standard. Because the calibration standard delivered by the permeation tube method is used fresh, eliminating the adsorption problems and the problems caused by polar and highly reactive compounds that are inherent in gas systems.

Compliance

Many of our customers are increasingly concerned about compliance issues, OSHA, ISO 9000, GMP, and other industry requirements. Addressing all of these concern, calibrated permeation tubes can overcome many issues connected with calibration.


Safety

Permeation Tubes are very small compared to high-pressure gas cylinders. Because they are so small (only about the size of a pencil), they contain only a fraction of the volume of toxic chemical contained in a gas cylinder. They are constructed of unbreakable material thus limiting the possibility of exposure. They eliminate the danger of handling high pressure cylinders, again because they are so small, are not breakable, have no valves and are not under very high pressure. Permeation tubes do not require special equipment to handle them or transport them.

Savings

Permeation Tube can replace as many as 10 gas cylinders. One Permeation Tube can deliver 10 or more different calibration concentrations. Plus, this can be done with accuracy traceable to N.I.S.T. or other national standard.

Permeation Tubes are small devices that have a permeable membrane and are filled with a pure chemical analyte. When held at a constant temperature, these devices emit a small stable flow of chemical vapor that is measured in nanograms or nanoliters per minute. Permeation Tubes are used in our range of Gas Standards Generators to create traceable calibration standards. Each certified permeation tube is serial numbered and the certification data is kept on file for 5 years.