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Sample extraction, solids & liquids

Products shown here are concerned with sample extraction from solids and liquids.

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.

Soil gas sampling

Quantitative purge-and-trap with GC(–MS) is a common approach for the analysis of VOCs and SVOCs in soil, but it involves labour-intensive sample preparation and pre-screening analysis. Soil probes are a complementary approach to purge-and-trap for analysis of VOCs in soil vapour that overcomes many of these issues. Their use supports compliance with ASTM D7758.

Stainless-steel assemblies are inserted into the

ground, allowing soil gas to be sampled in-situ onto a sorbent tube, either pumped or passively.

Established VOC air monitoring technology has also been applied to the monitoring of contaminated land, but the frequently-used approach of canister sampling excludes many heavier organic pollutants. Sampling onto sorbent tubes, followed by thermal desorption analysis, allows a much wider volatility range to be addressed. Soil probe technology therefore has the potential to significantly speed up and reduce the cost of surveys of contaminated land.

Sorptive extraction

Featured product: HiSorb Starter kit

  • A flexible alternative to methods such as stir-bar sorptive extraction (SBSE)
  • Detection limits are lower than for SPME
  • Easier and quicker to use than solvent extraction
  • Re-usable probes and tubes minimise cost per sample
  • Robust and easy to use with multiple phases available
  • Exclusive to Markes International
  • Automated by the Centri sample extraction and enrichment platform

SPME

Solid-phase microextraction (SPME) uses a small fiber coated with absorptive phase(s), to extract volatiles in either headspace or immersive modes. SPME extraction is an equilibrium process dependent on the partitioning of analytes between the sample matrix (either liquid, solid or headspace) and the absorptive phase. Analytes that become absorbed into the SPME phase are subsequently desorbed using a heated injector, before transfer to the GC column.

The simple, solvent-free nature of SPME has led to its increased popularity across a

range of application areas, particularly in food and beverage analysis, clinical studies and environmental analysis. Compared with static headspace, SPME can offer improved selectivity and concentration capability, resulting from the sampling capacity of the sorptive phase. A variety of sampling phases are available to extend the applicability of SPME over a range of target analytes.

Headspace sampling

Headspace (HS) has been widely used for quantitative evaluation of VOCs in solid and liquid samples for many years. Samples are placed into vials, sealed and incubated. Once equilibrium is reached VOCs partition into the headspace at levels that are proportional to their concentration in the original liquid or solid sample. A precise aliquot of headspace vapour is then transferred/injected directly into the GC (traditional methods) or via an electrically-cooled focusing trap for enhanced performance.

Headspace sampling can be enhanced

in combination with a preconcentration focusing trap step. Headspace–trap results in enhanced sensitivity by allowing larger injection volumes to be used, as well as multiple extractions from a single sample to be ‘concentrated’ in one GC–MS run. It also offers improved peak shape, optional sample splitting, and re-collection for repeat analysis without the need to repeat extraction steps.

Common application areas of headspace sampling include environmental monitoring, and analysis of foods, beverages and fragranced products.

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.