Series 2 Air Server™ option: Automated canister and on-line air/gas analysis


Series 2 Air Server modules add to any series 2 (ULTRA-)UNITY system to allow a controlled flow of whole-air or gas to be introduced directly into the electrically-cooled focusing trap of the desorber. The combined systems operate cryogen-free (to minimise running costs/maintenance) and offer optimum analytical performance/sensitivity.


With 3- and 8-channel options available, method-compliant series 2 (ULTRA-)UNITY-Air Server systems are suitable for both automated analysis of canister/bag samples and round-the-clock unattended monitoring of on-line air/gas streams.


Key applications include:

  • Continuous monitoring of ozone precursors (C2 to C10 hydrocarbons) in ambient air and/or vehicle emissions
  • On- or off-line odour monitoringe.g. measuring reduced sulphur species such as H2S, mercaptans and sulphides in canisters, bags or on-line air streams at sub- to low-ppb levels
  • "Air Toxics" in ambient air e.g. US EPA Method TO-(14)15
  • Industrial process control of gas purity and odour
  • Atmospheric researche.g. global background pollution levels, pollution transport and kinetic studies, such as monitoring diurnal changes in urban air pollution or biogenic emission profiles.

Series 2 (ULTRA-)UNITY-Air Server systems connect to standard GC/GCMS technology and/or real-time process detectors.

Air Server 2 main features

  • Adds automated canister and on-line air/gas stream analytical capability to any series 2 (ULTRA-)UNITY thermal desorption (TD) system.
  • Cryogen-free operation and low consumption of gas supplies for lower running costs and higher uptime.
  • Minimum 3 channels for sequencing between sample, zero and standard air/gas streams during unattended on-line monitoring.
  • Up to 8 channel operation available for high throughput analysis of whole-air/gas samples – canisters, bags, etc.
  • Quantitative retention of ultra-volatiles such as acetylene from increased sample volumes (up to 1.5 L) combined with peerless high-resolution capillary chromatographic performance (even under splitless conditions)ensure optimum sensitivity. Parts per trillion (ppt) levels are readily detected.
  • Method compliant tube desorption capability included with every system. Can be automated.
  • Thermostatted flow path and internal standard addition options for compliance with standard canister methods.
  • Negligible sample carryover plus versatile sampling flows & flexible splitting options allow analysis of both high and low concentration samples.
  • Small footprint: Especially useful for installation in mobile labs.
  • Versatile water management options for analysis of both dry and humid air/gas samples.
  • Connects to any commercial GC/GCMS and offers enhanced selective purging for compatibility with real-time detectors such as process MS and sensor-arrays.

Overview of Air Server operation

Series 2 Air Servers connect to any series 2 UNITY or Ultra-UNITY TD system. They contain 3- or 8- inert sample/stream selection valves uniquely configured to eliminate dead volumes and prevent carryover. Each whole air/gas sample (pressurised or at (sub-)atmospheric pressure) is introduced directly into the electrically-cooled, sorbent-packed, focusing trap of the UNITY 2 thermal desorber for a user-specified sampling time. Conventional sorbent sampling tubes are not used in this process.


The sampling flow is regulated by an electronic mass flow controller (MFC) and optional pump located downstream of the trap to eliminate risk of contamination. Focusing trap sorbent and trapping temperatures are selected for quantitative retention of the compounds of interest and for selective purging of potential interferences such as CO2 and water. No liquid cryogen is required and only inert, non-emitting components come into contact with the sample. All sampling parameters are monitored by system software as an integral part of the analytical method.


At the end of sample introduction, the flow path is purged with carrier gas to prevent carryover and eliminate oxygen from the focusing trap. The trap then heats rapidly in a reverse stream of carrier gas to inject/transfer retained compounds into the measurement system and trigger the analysis. This transfer/injection may be performed splitless for maximum sensitivity.


Once the focusing trap has desorbed, it cools and reequilibrates at the trapping temperature. Focusing of the next air/gas sample in the sequence may begin while analysis of the previous sample is ongoing to optimise throughput.

Intuitive user interface

Series 2 (Ultra-)UNITY-Air Server control is intuitive and integrated with the UNITY 2 TD software to provide one comprehensive and easy to understand user interface (UI).


The UI offers a specific mode for on-line/canister operation and, once selected, users are prompted to enter the relevant sampling parameters such as sampling time, flow rate and purge times.


Sequence building


Automated sequences for on-line monitoring and/or automated canister/bag analysis are easily constructed via the sequence builder. Samples may be assigned individual desorption methods. Each sample is classified as sample, calibrant or blank and all sequences may be stored and recalled for future reference or repeat use.


Graphical sequence viewer


The sequence viewer presents a clear graphical display of current sequence status.


Sequence reporting


Information associated with each analysis, such as the time, date and any deviations, are all recorded in the sequence reporter. Any sample sequence failure triggers the GC(MS) system to start a blank run to keep the analyser in step with the autosampler.

Air Server versatility

Unattended operation for extended periods


Cryogen-free operation and low consumption of gases simplify installation in mobile labs and offer extended periods of unattended operation in remote field monitoring stations. Markes’ cryogen-free series 2 UNITY–Air Server systems consume only 40 mL/min dry gas/air when configured without a Nafion dryer and less than 200 mL/min when a dryer is configured. This means the duty cycle of every dry gas cylinder is 3–10 times longer with series 2 UNITY-Air Server than it is with any other cryogen-free online air monitoring system.




Quantitative retention of ultra-volatiles such as acetylene from up to 1.5 L air sample volumes combined with efficient splitless desorption at low (<2 mL/min) flows ensures best possible detection limits (typically 1-50 ppt levels).


Reliably excellent chromatographic performance


Great resolution, stable retention times and repeatable concentration data minimise measurement uncertainty and simplify data interpretation/validation.


Small footprint


The Series 2 UNITY with integrated 3- or 8-channel Air Server is only 22 cm (9-inches) wide making it suitable for installation in mobile laboratories.


Timed start


Series 2 UNITY–Air Server systems allow the start of a monitoring sequence to be programmed for a specific date and time, and for the period between each sampling cycle to be fixed. The sampling cycle used for ozone precursor monitoring for example, is typically 1 hour. In this case air is usually sampled into the UNITY 2 focusing trap for 40 minutes of every hour starting on the hour.


No sample carryover


The inert stream selection valves and and narrow-bore flow path minimise sample carryover even when monitoring over a wide concentration range. This allows ambient air samples to be calibrated with small volumes of relatively concentrated standard gas. It also allows automated sequencing of samples varying widely in concentration over 2–3 orders of magnitude without fear of contamination.


Compatibility with samples over a wide concentration range is further enhanced by sophisticated, electronically-controlled sample splitting during trap desorption (and during tube desorption, if applicable)


Online monitoring and tube desorption


All Markes systems incorporating series 2 Air Server technology offer complementary tube desorption. This can be further automated for high-throughput laboratories by the addition of an UltrA autosampler


Measurement system


The majority of TD systems incorporating Markes series 2 Air Server technology are connected to standard or portable GC(MS) systems. However, it is also possible to configure the system with real-time detector technology, either in parallel with the GC(MS) or as an alternative to GC(MS).


Most environmental monitoring applications require the resolution of capillary GC(MS) because of the diversity and variability of organic vapour profiles which can occur in most atmospheres. However, for some industrial process applications or for monitoring well characterized atmospheres (where the various failure modes are known), it can be advantageous to combine the online TD system with simpler real-time detection technologies; process MS, sensor arrays, infra-red, etc.