Five trends to watch in sample extraction
14 January 2022
Modern laboratories are under increasing pressure to balance management of new analytical challenges with increasing workloads. They must also accommodate the demands of improving quality and quantity of information from each sample while reducing cost per sample. The sample preparation and extraction process has been identified as one of the biggest process bottlenecks in the lab.
Sorptive extraction – a technique to extract volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) from a sample and transfer them into a gas chromatograph–mass spectrometer for analysis – is commonly used as an alternative to liquid–liquid extraction and solid-phase extraction. The technique can be used to take VOCs from solids (extracting from the sample’s headspace) and liquids (by headspace sampling and by immersing a probe into the sample). Sorptive extraction is ideal for complex samples, in which target analytes can be selectively absorbed by choosing a suitable phase type.
Sorptive extraction can be used to monitor organic pollutants in environmental waters and soil to ensure public safety, and to profile aromas, flavours and taints in foods, beverages and other products derived from natural sources for quality and authenticity. Recently, it has been applied to biomarker discovery applications to determine unique markers of different diseases to further research into early diagnosis and relieve pressures on healthcare systems.
Here, we highlight five trends that anyone working with sorptive extraction should be aware of, using the following techniques: high-capacity sorptive extraction (HiSorb™), solid-phase microextraction (SPME), thin-film SPME and Twister®/stir-bar sorptive extraction (SBSE).
Green sample extraction
Emphasis is being placed on environmentally friendly and sustainable sample extraction, which was an important theme in the 1st European Sample Preparation e-Conference held in March 2021. Sorptive extraction is a step towards a more environmentally friendly technique because it is solvent-free, so unlike liquid–liquid extraction, it does not produce large amounts of solvent waste. Also, the extraction probes are re-usable, making them more environmentally friendly than the single-use cartridges used for solid-phase extraction, for example.
Using new techniques to discover more
The range of compounds that can be extracted during sorptive extraction is governed by phase type mainly but is also affected by phase length, thickness, surface area and sampling parameters. Sampling parameters such as sample volume and incubation temperature must be considered during initial method development and optimised for the sample type under investigation. The phases used in SBSE and thin-film SPME have a higher capacity than that of traditional SPME, resulting in detection limits up to 1000 times lower. High-capacity sorptive extraction (HiSorb) also has a phase with a much higher capacity than that of SPME. This results in more of each analyte being extracted for detection, leading to improved identification of trace-level compounds and providing more confidence in results.
Simplified sample preparation
We have seen a drive towards simplicity in the sample preparation process. However, the techniques vary in the levels of simplicity they offer. SPME and SPME Arrow provide higher throughput and minimal manual handling errors because both can be automated. However, because samples can only be handled one at a time, long overall run times are common with large sample batches. High-capacity techniques, such as HiSorb and SBSE, enable simultaneous sample extractions. SBSE is a manual process, but HiSorb is fully automatable, so reduces the manual handling steps. In addition, smarter sample management via a ‘prep-ahead’ function with HiSorb allows simultaneous sample extraction, which reduces the overall analysis time considerably.
Combining sampling techniques
To overcome limitations, such as sensitivity, techniques can be combined to enable a better understanding of samples. Tandem extraction, whereby two (or more) extraction techniques are combined for a single analysis (e.g., immersive and headspace HiSorb extractions of the same sample), not only reduces analysis time but enables a more comprehensive view of samples. Multi-step enrichment (MSE®) is another form of tandem extraction that enriches multiple extractions from the same sample vial (or an extraction from multiple replicate vials) using the same technique, e.g., SPME, followed by a single analytical run. MSE provides an enhancement in sensitivity whilst extending the range of analytes extracted in some cases, improving analysts’ understanding of their samples. To do this, a focusing trap within the sampling instrument retains analytes from each previous extraction during subsequent ones. This part of the flow path is isolated from the analytical system, enabling the enrichment to take place prior to analysis. It is worth noting that by using a focusing trap, analytes are injected to the GC in a much narrower band of vapour, providing sharp chromatographic peaks, significantly improving the sensitivity.
Automation to deliver more
Automation increases sample throughput and produces results quickly by drastically reducing the number of manual handling steps, which also reduces the chances of human errors. Not all sample extraction techniques lend themselves to automation, however. Techniques where manual user intervention is required (such as SBSE) cannot easily be automated. Nevertheless, the use of HiSorb probes is now automated by the Centri extraction and enrichment platform, allowing unattended sampling, washing and drying of the phase (to remove residual matrix), analyte desorption and injection to the analytical system for separation and detection. This automated workflow maximises productivity, while saving analysts valuable time.
When you combine the power of automation with the ability to use techniques in tandem, the benefits become clear. That’s why sample extraction platforms such as Centri are being adopted. Markes continues to invest in sample supplies, such as multi-phase HiSorb probes, now available to extend the range of analytes extracted to gain a deeper insight into sample composition compared to polydimethylsiloxane alone.
Find out more about HiSorb here.