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QUI-1057
Page 50
Markes International Ltd
T:
+44 (0)1443 230935
F:
+44 (0)1443 231531
E:
www.markes.com
Ensure that empty tubes are fitted with a sorbent retaining gauze in the correct position at the front of the
tube - the position of this gauze is critical for diffusive sampling. (Factory supplied empty tubes arrive with
the gauze pre-fitted). Insert a quantity of quartz wool after the gauss to prevent migration of fine sorbent
particles out of the tube.
Tubes should be gravity filled with sorbent (not filled under pressure). For compliance with International
Standards and accreditation schemes the mass of sorbent packed into the tube should be measured and
recorded.
Once the appropriate mass of sorbent has been poured into the tube a few taps on a hard surface will be
sufficient to settle the packing.
A small amount of quartz wool should be inserted followed by a second sorbent retaining gauze, inserted
using a TubeMate (C-TBMTE) or other suitable tool, until the gauze sits firmly on top of the sorbent
(without compressing the packing).
A gauze retaining spring is then inserted using the TubeMate to hold the gauze in place.
Tubes should be impedence tested prior to use
A range of pre-packed sorbent tubes is available from Markes International (see relevant Accessories for
Thermal Desorption catalogue or contact Markes on
)
5.2.2
Lifespan of tubes
The lifespan of a freshly packed tube will depend upon the following:
The sorbent type
The maximum temperature the tube has been desorbed at
The temperature the tube has routinely been desorbed at
The number of desorption cycles (analytical and tube conditioning) it has undertaken
Assuming the sorbents have not been taken over their maximum temperatures, Tenax TA tubes and tubes
packed with carbon based sorbents are good for 100 - 200 cycles, other porous polymers such as
Chromosorb, Porapak and HayeSep tubes should be re-packed once they have undergone 100 thermal
cycles.