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On-line and near-real-time sampling for food analysis

On-line sampling, whether carried out continuously or discontinuously (stepwise), allows the monitoring of changes in odour profile with time (e.g. for accelerated shelf-life tests), as well as making it easier to focus on key aroma components, for meaningful quality control.

What Markes can offer

Markes’ systems allow both continuous and discontinuous on-line sampling, as described below.

Continuous on-line monitoring

Markes’ TT24-7 thermal desorber uses twin-trap technology to continuously sample odour compounds over a wide boiling range with 100% sample collection efficiency. When used in conjunction with rapid or real-time analytical methods (such as fast GC), near-real-time monitoring can be achieved, allowing the analyst to identify even relatively minor changes in odour profiles as they occur. This can be useful, for example, to monitor the decay in the odour profile of a fragrance released into a room.

Discontinuous on-line monitoring

A versatile option for on-line sampling is the Universal Direct Inlet Accessory (U-INLET), Markes’ direct inlet accessory, which pulls a fixed flow of air through a sample chamber and delivers the headspace directly into the focusing trap of the UNITY thermal desorber. It can also be used to provide a carrier gas purge of sealed sample vessels, and for pulling a fixed flow of air through open sample chambers – for example vessels containing living organisms.

Use of the U-INLET allows large volumes of vapour to be sampled, greatly enhancing sensitivity relative to conventional equilibrium (static) headspace. It also allows characterisation of analytes over a wider volatility range, because the dynamic extraction of vapours prevents the bias towards more volatile compounds. Selective elimination of unwanted, high-concentration interferents such as water or ethanol is also possible.

An alternative solution for discontinuous on-line sampling is the Air Server accessory for the UNITY thermal desorber, which provides automation for up to eight channels.

Further information

  • For examples of the use of TD-based methods for the analysis of the flavour and fragrance profiles of foodstuffs and consumer products, see Application Note 052, the literature compilation in Application Note 004, or contact us to obtain a copy of our TD Applications Guide on food, flavour, fragrance and odour profiling.
Markes International Ltd
Gwaun Elai Medi-Science Campus
Tel: +44 (0)1443 230935
Markes International GmbH
Bieberer Straße 1-7
63065 Offenbach am Main
Tel: +49 (0)69 6681089-10
USA (West)
Markes International, Inc.
2355 Gold Meadow Way
Gold River, Sacramento
California 95670
Tel: +1 866-483-5684 (toll-free)
Markes Instruments (Shanghai) Co., Ltd
Unit 1002, Building 1
No.418, Guilin Road
Shanghai 200233
P.R. China
Tel: +86 21 5465 1216
Part of Schauenburg International

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