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Specific items related to the automotive industry/applications, such as VIAQ suited to key standard methods and/or sampling techniques. Or find out more about automotive applications.

Active sampling

Active sampling (pumped sampling) onto sorbent tubes is one of the most versatile TD sampling methods, used to target both known and unknown sample environments. This approach involves use of a pump to actively draw an air sample through the sorbent tube to trap the target analytes.

Active sampling is key to US EPA Method TO‑17, which involves pumping the

sample atmosphere onto the sorbent tubes, which are then capped and transported to the laboratory, for analysis by thermal desorption. It is also the recommended sampling approach in other standard methods, including ISO 16017-1, ASTM 6196, Chinese EPA HJ 644 & HJ 734, EN 14662-1, CEN/TS 13649, NIOSH 2549, UK Environment Agency LFTGN 04, and UK HSL MDHS 72.

Direct desorption/thermal extraction

Direct desorption is a variation on the principle of dynamic headspace that can be used to rapidly screen small quantities of solid or semi-solid materials. Small samples are placed directly into empty TD tubes or via tube liners. These are then heated in a stream of inert gas to sweep volatiles directly from the sample matrix onto the focusing trap of the thermal desorption instrument, for subsequent analysis by GC.

Direct desorption is typically applied to homogeneous waxes, powders or

pastes. Analytes monitored are generally in the range C3 to C30. Applications of direct desorption include the odour profiling and quality control of a range of materials:

  • Residual volatiles in ointments, packaging films, pharmaceuticals/drug powders and polymer beads.
  • Emissions from consumer goods, such as paints, car trim components, moulded PVC and adhesives.
  • Characteristic vapour profiles from foodstuffs and fragrant products, including soap powder and shampoo.

Microchamber sampling

Microchambers are compact, stand-alone test chamber units that allow rapid sampling of vapour-phase organic compounds from a product or material, complementing small-scale chamber testing by third-party laboratories. Microchamber sampling is a type of dynamic headspace sampling and a powerful tool for increasing laboratory productivity. The technique is usually used in combination with sorbent tubes and off-line thermal desorption–GC–MS.

Applications

for microchamber sampling include:

  • Quality-control of chemical emissions from products and materials, such as construction materials
  • Screening of products prior to long-term certification tests e.g. consumer products
  • Checking raw materials.
  • Comparing products to those of competitors.
  • Monitoring odour and emission profiles e.g. car trim.
  • Kinetic studies such as shelf-life tests or monitoring aroma or fragrance profiles as they change over time for the food and consumer industries.

Online air or gas sampling

‘Whole air’ sampling refers to collection of samples in the field using canisters or bags, or their direct introduction to the focusing trap of the thermal desorption instrument without the use of sorbent tubes (online sampling). The compounds remain in the gas phase throughout.

Air sampling bags are commonly used to collect whole air samples for landfill gas and soil

gas. A sample can be collected in the container using either pumped or passive sampling, and subsequently sealed and transported to the laboratory for analysis.

Where the compounds of interest are too volatile to be retained by sorbent tubes at ambient temperature (such as hydrogen sulfide), either on-line or canister analysis is required (as opposed to tube sampling).

On-line air monitoring is the method of choice for real-time monitoring of changes in vapour concentrations and for continuous remote monitoring.

Applications include:

  • Ozone precursor monitoring
  • Odours in urban air
  • Fenceline monitoring of petrochemical plants and other industrial installations
  • Odour from sewage treatment works

Supplies for standard methods

Markes’ application specialists are active on committees working on standard methods, and also in the development of products to support method compliance. A variety of standard methods are available for monitoring specific VOCs often in prescribed sample types. For example, an automobile industry standard method might focus on materials such as plastic, leather or foam.

Organisations developing standard methods can

be grouped into government agencies such as US EPA and UK HSE, international standards agencies such as ISO and CEN, and consensus-based standards organisations such as ASTM. When selecting an appropriate method to adopt, the following issues should be considered:

  • Any specific regulatory requirements/guidance.
  • Method scope e.g. ambient, indoor, workplace, material emissions test chambers.
  • Sampling and analytical requirements.
  • General guidance (e.g. choice of sorbents, selection of GC column).
  • Validation protocol.
  • Method limits – list of target analytes (if applicable), concentration range, detection limits, analyte volatility range, etc.

See our Standard Methods page listing all relevant methods.

Standards & calibration

Calibration of the complete analytical process is of paramount importance when conducting quantitative studies. For TD analysis, additional considerations should be made regarding the loading of standards to be representative of samples, with a variety of tools available to support this.

In addition to gas standards for both canister and tube-based methods, a number of products have been developed to

support laboratories with their calibration and validation:

  • The Calibration Solution Loading Rig (CSLR) was developed to optimise the introduction of liquid standards onto sorbent tubes, by transferring the standard in a flow of gas.
  • Check-standards are sorbent tubes pre-loaded with a suite of analytes that can be used to check instrument performance during set-up or troubleshooting.
  • CRS tubes are loaded with a certified level of analytes and are designed to validate calibration for QA, as described in international standards. They are supplied with a shipping blank, and example chromatograms of the sample and shipping blank.
  • Tubes for liquid calibration contain a short bed of sorbent for analysts wishing to inject a liquid standard directly onto the sorbent tube, rather than loading the tube using a flow of gas (e.g. with the CSLR).

Starter kits

Markes’ starter kits are designed to provide the essentials needed to get a thermal desorption system up and running quickly, by providing a single package with items such as tubes, traps, tools and other accessories.

Markes offers a selection of starter kits for a range of standard methods such as US EPA Method TO-17 and US EPA 325, as

well as application-specific starter kits such as the Material emissions starter kit and the Direct desorption starter kit.

Laboratory managers and technicians using the UNITY–ULTRA-xr or TD100-xr systems may also find the popular essential automated TD starter kit and the automated TD booster pack useful.

Other starter kits have been designed to help customers get up and running with tube tracking technology (TubeTAG) or adopting a new approach to sampling, such as HiSorb sorptive extraction.

Whole air canister sampling

Canisters for air sampling (often referred to as SUMMA® canisters) have long been used to monitor volatile organic ‘air toxics’. Whole air canister sampling is a simple form of ‘grab’ sampling and is useful for sampling very volatile, non-polar compounds such as C2 to C12 hydrocarbons and the most volatile freons, which can be difficult to retain quantitatively on sorbent tubes at ambient temperature.

For many analysts, the most familiar canister method is US EPA Method TO-15. This method involves

sampling of ambient air using evacuated canisters followed by thermal desorption preconcentration, and GC–MS or GC–FID analysis. It is widely used by commercial laboratories for analysis of VOCs in urban and industrial settings, especially in the USA and Asia.

Preconcentration/trapping is still required before analysis to allow injection of the sample in a small volume of carrier gas, and to eliminate the bulk constituents of air (especially oxygen) and water, which would otherwise adversely affect the performance of the GC column and detector.