Thermal desorption tubes ....

Thermal desorption tubes ... to consider when selecting them!

For chemical analysts who are considering sampling VOCs and SVOCs, the selection of thermal desorption tubes with sorbents is usually one of the main elements to consider. In some cases it is mandatory to work with specifications that are already predetermined in the standards, in other cases some bibliographic help will be needed to find the most suitable tubes for our matrices and analytes. Markes tubes are manufactured following high quality controls, with high reproducibility, being compatible with various thermal desorption systems.

Let's take a look at what is meant by "industry standard" tubes and caps and those that are commercially available.

What criteria do sorbent thermal desorption tubes and stoppers have to follow?

The criteria for adsorbent tubes and plugs have been described in standard international thermal desorption methods for decades. In 1979, the UK Occupational Safety and Health Executive working group specified diffusive catchment tubes as 3.5-inch × 0.25-inch (outside diameter) systems, compatible with thermal desorption systems, which from then it has become the "industry standard". See the theory and practice of diffusive monitoring in the( Application note 08)

Other reference methods that define tubes are:

- ISO16000-6:

Indoor air - Part 6: Determination of volatile organic compounds in indoor and test chamber air by active sampling on Tenax TA sorbent, thermal desorption and gas chromatography using MS or MS-FID

specifies tubes with metal screw caps and ferrules PTFE length 89 mm (3.5 inches).

- EPA TO-17, Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling onto Sorbent Tubes indicates that the most commonly used desorption tubes are 3 1/2 inches (89 mm) long x 1/4 inches (6.35 mm) external diameter, in stainless steel or glass tubes with a bed of up to 6 cm. In addition, it indicates that conditioned or sampled adsorbent tubes should always be kept capped with 0.25-inch brass Swagelok screw plugs with PTFE ferrules

- ISO 16017, Indoor, ambient and workplace air - Sampling and analysis of volatile organic compounds by sorbent tube / thermal desorption / capillary gas chromatography - Part 1: Pumped sampling, Part 2: Diffusive sampling refers to the determination of the minimum air flow rate for thermal desorption using a standard 4mm to 5mm orifice, 6.4mm diameter sorbent filled tubes with sorbent fill in the range 12mm to 18mm from the sampling end of tube

For more details on the tubes recommended in our application see Application note 03: National and international standard methods relating to speciated monitoring of vapor-phase organic chemicals in air.

Markes International plays an active role in the continuous development of tubes for the analysis of VOCs and SVOCs, its experts serve on various international committees. This helps to ensure that Markes provides thermal desorption users with practical information and advice on consumables compatible with all commercial systems.

TUBOS DE DESORCIÓN TÉRMICA

Los tubos estándar de TD se pueden utilizar de tres maneras diferentes: empaquetados con un solo lecho sorbente para muestreo difusivo o activo, lleno de múltiples camas de sorbentes para muestreo activos o tubos vacíos para desorción directa de muestra. Los clientes de Markes pueden elegir entre:

- Tubos Universales: Diseñados para captar el máximo de compuestos volátiles posible en muestras dónde no se conoce la identidad de los compuestos.

- Tubo de un único sorbente: Empaquetados con Tenax, Carbograph 1TD y otros sorbentes

- Tubos Multi-Capas: Combinaciones más comunes: Tenax/Carbograph 5TD, Carbopack Y/Carbopack B/Carboxen 1003

- Tubos específicos según la aplicación: Se incluyen tubos empaquetados y acondicionados según lo establecido en métodos como: EPA TO-17, US EPHA 325

- Tubos vacíos: recomendados para usuarios aventajados que se preparan los tubos con sus propios sorbentes, o para usuarios que quieren realizar desorción directa de líquidos y sólidos

TAPONES DISPONIBLES PARA LOS TUBOS(0.25 inch/6.35 mm diámetro externo) hay diferentes diseños según el uso

Tapones de almacenamiento a largo plazo:Tapones tipos Swagelok Cobre o Aluminio

-Tapones de almacenamiento a corto plazo:También conocidos como tapones a presión (no están pensados para utilizarse con los equipos)

-Tapones difusivos:para captaciones pasivas

Con las especificaciones para tubos y tapones bien establecidos, ¿qué más debe buscar un comprador? Descargue nuestra infografía sobre algunos de los principales factores a tener en cuenta al elegir los consumibles para dar cumplimiento a las necesidades del mercado.