Sample Collection: 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 Mi 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
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.
Typical requirements may include:
- Data every 10 minutes or less
- High sampling rate (>500 ml/min) for optimum sensitivity
- 100% data capture - i.e. truly continuous sampling
- Reliability
TT24-7
Markes have developed an innovative continuous monitoring system to meet these needs. The model TT24-7 is a robust, transportable unit convenient for installation on-site or in mobile response vehicles as well as conventional laboratories. It interfaces to GC(-MS) or process MS technology and incorporates two electrically-cooled traps which operate in tandem to ensure 100% sampling efficiency (- no dead times).
Operation
Air / gas is first sampled onto the channel A focusing trap at electronically controlled flow rates up to 1 L/min. At the end of the sampling time, channel B is switched in-line while channel A is pre-purged, desorbed and analysed. Trap heating rates approaching 100°C/sec combined with a reverse flow of carrier gas ensure efficient backflush desorption of analytes over a wide boiling range - giving narrow peak widths and optimum sensitivity. When sampling switches back to channel A, channel B is desorbed and analysed.
Patented inert valves inside the TT24-7 isolate the sampling process from the analytical system allowing the analysis to overlap with collection of a subsequent sample. Sampling can proceed on the desorption system while GC or MS analysis of the previous sample continues.
Continuous monitoring with multistream selection.
Trace heated and ambient temperature options are available on a custom basis for multi-stream selection. Systems can be configured to suit your network monitoring requirements.
Tube desorption for calibration and verification
The TT24-7 can be pre-configured with a tube desorption accessory to allow desorption of tube-based calibration standards and samples. This facilitates routine calibration and allows certified reference standard tubes to be introduced for auditing analytical quality assurance.
Parallel sampling onto a sorbent tube at the inlet of a TT24-7 on-line sampling line also allows comparison of on- and off-line monitoring data for system verification. The sampled sorbent tubes are analysed on the TT24-7 system via the tube desorption accessory. Since the quantitative recovery of GC compatible organics from sorbent tubes is well documented, satisfactory correlation of the tube results with those for the same sample analysed on-line verifies analyte recovery through the on-line sample interface.
