The quality of analytical data is fundamentally dependent on effective validation of the method used and is especially critical whenever potentially toxic organic emissions are being measured from complex, real-world samples.

Thermal desorption has historically been a single shot process and this presents a unique challenge for validation.  For this reason, many international thermal desorption methods specify key sample and data protection features, particularly for automated instrumentation.  These include:

• Stringent leak testing of each sample tube prior to desorption (without flow or heat applied)
• Effective sealing of sample tubes, both before and after analysis, to prevent loss of analytes and/or ingress of contaminants from lab air
• Pre-purge of air to vent before desorption to eliminate oxidation
• Internal standard addition capabilities
• Inert flow path

As well as all these standard method/data validation tools, Markes TD systems uniquely feature:


SecureTD-Q - Quantitative re-collection of the split flow for repeat analysis and method or data validation

Markes systems are explicitly designed for SecureTD-Q.  Any aliquot of sample which is directed to split may be quantitatively re-collected onto a clean sorbent tube for repeat analysis and method/data validation.

If the chromatographic profile obtained from the SecureTD-Q tube matches that of the original sample, taking into account the split ratio, quantitative recovery is confirmed.

SecureTD-Q - validation of routine method performance
Desorption of a re-collected sample should produce an exact match to the original chromatogram, but at a lower peak area - proportional to the split ratio used.  By producing a replicate chromatogram or series of chromatograms from re-collected samples, SecureTD-Q can be used to demonstrate lack of bias & quantitative performance.  It is thus a convenient tool for validation of routine methods. 

SecureTD-Q - validation of challenging methods
SecureTD-Q is also an ideal tool for the validation of challenging applications such as:

• Thermally labile compounds - for example phosphorous pesticides and odorous sulphur compounds.
• Chemical agents such as VX are particularly challenging samples due to their low volatility, extreme reactivity and ultra-low concentration in the environment.  SecureTD-Q was used to validate the quantitative analysis of sub-ng masses of free-VX and to demonstrate >90% recovery through the system.

SecureTD-Q - for repeat analysis and third party confirmation
As well as method validation, quantitative repeat analysis gives numerous other benefits to the TD user:

• Back-up for situations when the primary analysis fails, for example due to the GC run finishing prematurely or the GC detector failing
• Sample archiving for future analysis or for third party confirmation - particularly useful for forensic applications such as monitoring drugs of abuse and arson debris analysis
• Data confirmation - because SecureTD-Q overcomes the one shot limitation of TD it allows critical samples (which may be hard to collect in duplicate) to be re-analysed if necessary
• Repeat analysis by alternative technology e.g. selective detection such as FPD, process mass spec etc.

ULTRA 50:50 - Low cost, single ULTRA automation of quantitative re-collection for repeat analysis

The ULTRA 50:50 offers automated thermal desorption for up to 100 tubes plus re-collection of up to 50 samples into a corresponding number of re-collection tubes. Alternatively, up to 100 TD samples can be automatically re-collected back into the original sorbent tube if required. The ULTRA 50:50 system comprises an ULTRA-UNITY configured with a 50:50 module accessory.


AutoSecureTD-Q™ - Automated re-collection 

An ULTRA 50:50 system can be further enhanced by the addition of a second ULTRA configured for SecureTD-Q re-collection of both inlet and outlet split for every sample in a sequence.  The second ULTRA may be easily reconfigured to sampling mode for maximum operational flexibility.  DiffLok caps are fitted to both desorption and re-collection tubes ensuring the integrity of primary and re-collected samples.  Trays on the autosampler are colour coded for clear identification of sample and re-collection tubes.


For part numbers and pricing please contact your local Markes distributor or visit our on-line shop.

Relevant technical support publications from Markes International can be automatically downloaded from this web site (registration required). Examples include:

• Brochure - Validation of Thermal Desorption featuring SecureTD-Q
• Brochure - UNITY, ULTRA, Air Server thermal desorption systems
• Brochure - Thermal Desorption and Air Monitoring Products
• TDTS 24 - Using UNITY to re-collect desorbed samples for repeat analysis
• TDTS 35 - Thermal desorption of dioctyl-phthalate and other plasticizers
• TDTS 39 - Analysis of semi-volatile phosphorus pesticides using Mi thermal desorption systems - demonstration of method validation using SecureTD-Q

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