consumables

Sorbents

In the context of thermal desorption, a sorbent (or adsorbent) is a material used to capture volatile compounds. Sorbents are fundamental to the process of TD and are used in both sorbent tubes and focusing traps. Many types of sorbents are available, with some of the most popular being porous polymers such as Tenax® TA, graphitised carbon blacks such as Carbograph and carbonised molecular sieves such as Carboxen 1000.

It is generally advised to match the sorbents in the sorbent tube and focusing trap, because analytes that can be trapped at ambient temperature on a tube can then be trapped at ambient temperature on a focusing trap. Being able to use near-ambient conditions helps reduce the impact of interferences due to water/moisture.

Read more: Sorbents - Quick reference guide

Starter kits

Markes offers a comprehensive range of starter kits – handy packages of tubes, traps, tools and accessories to get you up and running quickly. The range includes general-purpose kits for all UNITY-xr/TD100-xr models, specialist kits for environmental and material emissions applications, and convenient kits for specific instruments and accessories.

- Optimised for system and/or method setup: Providing the right tools for the job and saving time in the laboratory

- The most cost-effective approach to purchasing essential bundles of items

- Complement instrument shipping kits, to prevent duplication of parts

Application bundles - tubes and trap

Markes PFAS bundles contain two packs of tubes and a focusing trap, optimised for PFAS detection and analysis.

Tubes - sorbent tubes for TD

Pre-packed thermal desorption tubes are used to monitor VOCs, VVOCs and SVOCs. Compounds of interest are adsorbed onto the sorbents in the tube during active or passive sample collection, and subsequently desorbed by a thermal desorption system for analysis by GC–MS. Choose industry-standard tubes with our tube selector.

Industry-standard tubes (3½″ × ¼″ o.d.) are compatible with Markes TD systems as well as those of PerkinElmer, Shimadzu, Dani, CDS and Gerstel. All Markes’ sorbent tubes are permanently labelled with a unique serial number, barcode and sampling flow arrow for easier use and tracking.

Our range also includes 4.5-inch sorbent tubes in stainless steel or glass, for use in compatible thermal desorption systems. These include Markes’ specialist DAAMS TD Instruments, widely used in defence-related applications.

Tubes can be packed with a single sorbent bed for active or passive sampling, and multiple sorbent beds for active sampling of an extended hydrocarbon range. Tubes are sold conditioned and capped (with brass long term storage caps) or can be supplied unconditioned for analysts with their own means of conditioning.

Empty sorbent tubes

Empty industry-standard thermal desorption tubes are available in stainless steel, inert-coated stainless steel and glass. They are typically used as carrier tubes: stainless steel and inert-coated tubes are primarily used to hold HiSorb probes or radial sorbent cartridges in a thermal desorption instrument, and glass tubes are primarily used for direct desorption.

- Suitable for use with any industry-standard thermal desorption instrument

- Unique ID number in clear numerical and barcode format

- Sampling arrow to indicate the direction of flow though the tube

- For custom etching see tube customisation options

Focusing traps

Focusing traps (also known as cold traps) are at the heart of all Markes’ thermal desorption instruments and perform a preconcentration function by focusing analytes to achieve maximum sensitivity. They are constructed of quartz for optimum inertness and packed with a sorbent bed up to 60 mm long and a series of sorbents of increasing strength.

Markes also offer a custom-packing focusing trap service. Contact  to discuss your application.

The thermal desorption instrument transfers compounds from a sorbent tube, canister or via on-line sampling to the focusing trap, which is subsequently heated to rapidly transfer compounds to the GC column in a narrow band of carrier gas. Markes instrument's focusing trap module offers super-fast desorption in a reverse (‘backflush’) flow of carrier gas. This optimises transfer/injection of the widest range of analytes, enabling simultaneous analysis of VOCs and SVOCs with market-leading sensitivity.

Certified Reference Standard tubes

Certified reference standard (CRS) tubes are packed sorbent tubes loaded with certified levels of relevant analytes. Prepared by an expert national standard laboratory to ensure high accuracy in loading levels, they are a convenient tool for in-house quality assurance and auditing of the complete TD–GC(–MS) analytical process, including calibration protocols.

- Supplied with a shipping blank, and example chromatograms of the loaded tubes/shipping blank

- Designed to validate the instrument and analytical process for quality assurance.

- Recommended for routine use at a defined frequency, in line with good laboratory practice

Read more: Calibration and validation tools Infographic

Diffusion-locking caps (DiffLok)

DiffLok™ caps sit on both ends of a sorbent tube throughout the entire analytical sequence, in all Markes’ automated thermal desorption instruments. Their patented design prevents loss of sample and ingress of contaminants onto the tube, and avoids the need for complex robotics to cap and uncap tubes. DiffLok caps are available in stainless and inert-coated stainless steel.

Read the full story behind Diffusion-locking technology in our blog.

- Preserve sample integrity by preventing analyte loss and contamination

- Ensure reproducible results during analysis

- Push-fit for ease of use

Storage caps

For storage and transport of conditioned or sampled tubes, long-term storage caps fitted with PTFE ferrules must be used to ensure an effective seal is achieved and minimise loss of sample/ingress onto the tube. Typically, brass Swagelok style caps are used but aluminium caps are available as an alternative.

- Recommended by international standard methods such as US EPA Method TO-17, ASTM D6196 and EN ISO 16017

- Independently validated for up to 27 months

- Caps meet a stringent cleanliness specification and tight manufacturing tolerances

Diffusion caps

Diffusion caps are used to define the air gap between the sampling environment and sorbent surface during diffusive sampling (also known as axial or passive sampling). Used in combination with a single-bed sorbent tube, penclip and aluminium long-term storage cap (at the other end of the tube), diffusion caps offer a simple to use, lightweight approach to personal monitoring.

- Defines the air gap for diffusive sampling at 15 mm, allowing use of published uptake rates

- Prevents small insects/particulates from entering the tube

- Complies with standard methods such as US EPA Method 325

RFID tags for sorbent tubes (TubeTAG)

Markes’ patented TubeTAG technology is a unique RFID tagging and labelling system for thermal desorption tubes. TubeTAG allows automatic tracking of sample information from sampling through to analysis, and/or tube specific information (such as sorbent type or number of thermal cycles) to be associated with a tube for its lifetime.

- Sophisticated and fail-safe solution for recording tube history and tracking tubes in transit

- Can be written to/read online (on a Markes instrument), and offline using a TAGSCRIBE

- Relevant sample information is recorded in the sequence history when using TubeTAG on an automated Markes instrument

Read more: TubeTAG Instruction for use

4.5 inch DAAMS tubes

Depot Area Air Monitoring Systems (DAAMS) tubes are sorbent tubes used for air sampling in chemical defence and counter-terrorism applications and subsequent analysis by TD–GC–MS.

- Packed to ensure optimum recovery of challenging and toxic analytes such as chemical agents

- Tubes are permanently labelled with a unique serial number, barcode and sampling flow arrow

- Available in inert-coated stainless steel or glass