UNITY 2™: A universal thermal desorption platform for tagged and untagged tubes


UNITY 2™, Markes’ next generation thermal desorption platform, harnesses  technical advances. It incorporates every feature required for TD method compliance, every system innovation of the last ten years and the field-demonstrated reliability characteristic of all Markes instrumentation. It provides the platform for a state-of-the-art yet robust range of thermal desorbers with systems available at prices to suit every budget.


Building on the field-proven strengths of UNITY, UNITY 2 combines tube desorption with cryogen-free analyte re-focusing and efficient back-flush desorption of the focusing trap. Trap desorption injects analytes (split or splitless) into the GC capillary column in a narrow, focused band of vapour and triggers the GC(MS) run.


The patented, inert heated valve integrated into UNITY 2 facilitates the ambient temperature, zero flow leak testing specified by standard methods, and allows simultaneous analysis of volatile and semi-volatile compounds. The short, narrow-bore sample flow path is uniformly heated and optimises analyte recovery.


SecureTD-Q (re-collection of tube and/or trap desorption split flow) offers quantitative repeat analysis and is available as standard on every UNITY 2. SecureTD-Q overcomes the one-shot limitation of older thermal desorbers.


UNITY 2 provides a method-compliant TD platform that is ideally suited to meet the ever-more stringent demands of laboratory accreditation, data/method validation and good laboratory practice. It is operated using intuitive software loaded onto the same PC as that providing GC(MS) control/data handling.

(re-collection of tube and/or trap desorption split flow)


Key features include:

  • Compatible 3.5-inch (standard) or 4.5-inch (DAAMS*) length tubes, electronically-tagged or untagged. Unity 2 allows an individual TubeTAG™ to remain with a specifc sample tube throughout its life, recording tube history and facilitating sample tracking between field and lab.
  • Provides a single platform for all TD applications - labile species, semi-volatiles (up to n-C40), ultra- volatiles (including C2H2 and freons), trace levels (ppt) and high concentrations (ppm/%).
  • Repeat analysis via SecureTD-Q™: Overcomes the one shot limitation of conventional TD systems.
  • Cryogen-free operation: Electrically-cooled, sorbent trapping to -30°C eliminates ice plug formation and reduces running costs.
  • Fully method-compliant including stringent leak testing without heat or gas flow applied.
  • Fully upgradeable to multi-tube, multi-canister and/or online automation. Can also be coupled with headspace for even greater sample flexibility.
  • Time saving overlap mode allows desorption of a subsequent sample to begin while GC analysis of a previous sample continues.
  • Plug-and-play TD: UNITY 2 adds to any commercial GC(MS) and is designed for easy maintenance.

* DAAMS: Depot Area Air Monitoring System as used in some chemical agent destruction facilities

Universal TD platform for all applications

UNITY is renowned for its application flexibility and versatility. UNITY 2 takes this to the next level. With extended electrical cooling of the entire 60 mm sorbent bed, the UNITY 2 focusing trap offers quantitative, cryogen-free retention of ultra volatiles such as freons and acetylene from larger volumes of air/gas. Markes offers a range of off-the-shelf, pre-packed UNITY 2 traps, each containing up to four sorbents. Some of these are almost universally applicable, others are optimised for the retention of ultra-volatiles/volatiles (e.g. C2 hydrocarbons/freons to n-C12) and others offer quantitative retention of target analytes with selective purging of water or solvents prior to analysis.


Tube desorption and conditioning is now possible at temperatures above 400ºC. Critical sections of the internal flow path have also been optimised, both for enhanced recovery of higher boiling ‘sticky’ compounds and quantitative analysis of reactive components. Example analytes include: 5/6-ring PAHs, phthalates, PCBs, hydrocarbons to n-C40, mercaptans, explosives and chemical warfare agents.


The patented heated valve built into UNITY 2 is specifically designed for analytical TD. It can be operated at the low temperatures that are required for enhanced recovery of labile components and also allows quantitative recovery of high boilers such as n-C40.

Enhanced user accessibility

Simplifying routine maintenance operations has been a key focus during UNITY 2 development. Changing the focusing trap, for example, is a simple, user-enabled process. No tightening or loosening of fittings is required and a new easy-grip collar at the non-sampling end of each trap makes it very easy to withdraw and replace. Other relevant features include simple user access to split filters and transfer line connections. Sealing o-rings have also been selected both for long life (typically at least 12 months) and negligible artefact formation.

Error-free tube and sample tracking

Electronic tube tagging and tracking allows individual TD sample tubes to be tracked from laboratory to field and within a laboratory. RFID tags can be programmed with tube- and sample-specific data such as tube ID, type and date of packing, number of thermal cycles, sampling times/flows and customer reference number. (More information is given in the TubeTAG brochure).


TubeTAG is being heralded as a future standard requirement for large-scale environmental monitoring projects, industrial hygiene applications, civil defence,

etc. and is particularly important whenever monitoring data is being linked to human health/comfort or public safety. UNITY 2 can be used to analyse tagged tubes (tags do not have to be removed), thus simplifying the process of tracking tube history and performance. With TubeTAG compatibility as standard, UNITY 2 ensures a future-proof analytical platform.

Multiple tube sizes providing enhanced versatility

UNITY 2 is available in standard (3.5-inch long x ¼-inch O.D.) or DAAMS tube (4.5-inch long x 6 mm O.D.) configurations for both tagged and untagged tubes. Users can reconfigure UNITY 2 for 3.5- or 4.5-inch tubes by interchanging the desorption oven whenever required.

Unattended operation for extended periods

Featuring cryogen-free operation and lower consumption of supply gases than other brands of TD, UNITY 2 offers long-term unattended operation. It needs only 40 mL/min dry gas flow, which equates to >4 months continuous operation on a standard cylinder, making it ideal for continuous field monitoring and operation in mobile laboratories.

Fully upgradeable: Tubes, canisters & online gas streams

UNITY 2 is compatible with any transportable or bench-top GC(MS) and offers state-of-the-art two-stage TD performance for individual sorbent tubes in a small, affordable package. To complement UNITY 2, Markes International offers a wide range of configurable system upgrades which will allow your analytical capacity to expand as demand for TD increases.


UNITY 2 upgrade options include:


• The Universal Direct Heated Inlet for interfacing vapours from custom sample vessels UNITY 2 focusing trap.


• Online/canister sequencing.  Including 3- or 8-channel options for compliance with key methods such as continuous monitoring of trace-level ozone precursors (C2-C10 hydrocarbons) and US EPA Method TO-14/15 "Air Toxics".


• Series 2 UltrA 100-tube automation. Now available for standard 3.5-inch tubes or for 4.5-inch DAAMS tubes. The UltrA is available with built-in options for everything from internal standard addition to automated sample re-collection.


• Headspace (HS): The cost effective HS5-TD™ module adds to UNITY 2 to provide sensitive HS-TD analysis for volatiles in liquids or solids. The HS5-TD accommodates up to 5 samples in standard 20 mL headspace vials and offers 10-100 times improvement in detection limits relative to conventional static HS methods. UNITY 2 can also be interfaced to several leading brands of HS autosampler for high capacity HS-TD operation.

Enhanced electronic control of gas flows (ECC)

UNITY 2 offers compatibility with the back pressure-regulated electronic carrier gas control (ECC)  provides precise control of carrier gas flow/pressure through the entire TD-GC(MS) system as an integral part of the GC(MS) programme. This stabilises retention times, independent of TD analytical conditions (split flows, sorbents, desorption temperatures, of leading brands of GC. ECCetc.), ultimately aiding analyte identification. ECC also allows accurate monitoring and closed-loop control of the column head pressure whatever the stage of thermal desorption operation and whatever the required flow.


Multiple splitting options


Building on UNITY’s compatibility with analyte levels from sub-ppt to percent, every UNITY 2 offers unsurpassed split versatility. Users can select from splitless operation, single-split (split open during either tube or trap desorption) or double-split (split open during both tube and trap desorption).


Every UNITY 2 features SecureTD-Q quantitative re-collection of all split flow, for repeat analysis and method/data validation.


Automatic control over split flows


Standard UNITY 2 systems feature the full range of split options (splitless, single-split and double-split), but with manually controlled flow rates. Electronic control of split and desorb flows is offered by one or two optional mass flow controllers (MFC) integrated into UNITY 2. These provide versatile electronic control of both split and desorption flows, featuring flexible split flow rate selection combined with precise control at low flows. The UNITY 2 MFC modules also facilitate flow rate recall during an automated sequence with multiple TD methods.


Negligible Carryover

With significantly less than 0.1% carryover, UNITY 2 facilitates automated multi-method analysis when coupled with the ULTRA 2 autosampler. High level samples, such as stack gases or residual solvents, can be included in the same automated sequence as sub-ppb environmental air monitoring samples if required.

Building on the strengths of UNITY

In addition to the enhancements described above, UNITY 2 has drawn key strengths from its eminent predecessor. Key features pioneered on UNITY and now available on UNITY 2 include:




Repeat analysis: Secure TD-Q (i.e. quantitative re-collection of any or all split flow during both tube and trap desorption) was pioneered by Markes in 1998. Each sample is recollected on a conditioned tube (tagged or untagged) and may be used for repeat analysis, method/data validation or archiving of critical samples. Secure TD-Q is available as standard on every UNITY 2 and overcomes the one-shot limitation of traditional TD systems and methods. No other single tube desorber offers quantitative recovery of all split flow for repeat analysis

Method compliance and system validation

• Full compliance with key international standard methods such as EN ISO 16017, ISO 16000-6, ASTM D6196, US EPA Method TO-17, NIOSH 2549 and others.


• Stringent no-flow, ambient temperature leak test to ensure data integrity. Failed tubes are preserved intact for operator intervention. Fully interlinked ready/start signals ensure that trap desorption only occurs when the rest of the analytical system is ready for analysis.


• Validation of desorption efficiency/analyte recovery is simplified using SecureTD-Q (see above). Use of repeat analysis for TD method/data validation is described in standard TD methods such as ASTM D6196.


• Continuous monitoring of carrier gas pressure downstream of the sorbent tube and focusing trap. This pressure reading may be logged for every sample and for all stages of TD operation allowing tubes with anomalously high back pressure to be identified. Moreover, if a tube is completely blocked this is detected by the UNITY 2 leak test and logged as a sample failure. In the case of tagged tubes, backpressure can be recorded on the tag and stored as part of tube history if required.


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