In this application note, we demonstrate the benefit of a novel technique – large volume preconcentration (LVP) – for enhancing traditional headspace analysis of trace-level volatile organic compounds (VOCs) that contribute to aroma and flavour in a food product – tomato paste. Using the Centri® sample extraction and enrichment platform in headspace–trap mode, the extracted analytes are preconcentrated on an electricallycooled, cryogen-free focusing trap. This allows for large extraction volumes to be used (up to 5 mL) while maintaining optimum chromatographic performance. We also highlight the benefits of multi-step enrichment (MSE), whereby repeat extractions from a single vial or multiple vials are delivered to the trap prior to a single GC injection. This results in a further improvement in the discovery and confident identification of trace-level aroma and flavour compounds.
Aroma and flavour compounds have important roles in the consumer sensory experience, so their analysis is vital in the food and beverage industry for product development, determination of shelf-life and product quality, investigation of off-odours and analysis of competitor products. Whilst headspace sampling, in conjunction with GC–MS, is routinely used for the analysis of principal aroma compounds, the detection of trace-level active odour components (with low odour threshold values (OTVs)) is more challenging. Typically, headspace extraction volumes are limited to 1 mL due to the poor chromatographic performance, such as peak broadening, that occurs when using larger volumes, limiting the response achieved from lower-level analytes. Therefore, an enhancement in the sensitivity of the technique is required, making large volume preconcentration (LVP) and multi-step enrichment ideal for this scenario.
The Centri automated multi-mode platform allows the headspace injection and GC column flow to be separated (Figure 1). The extracted headspace volume is injected to an electrically-cooled, cryogen-free, multi-sorbent-bed focusing trap where the analytes are refocused and preconcentrated. Following this step, the carrier flow is reversed (‘backflushed’) and the trap is heated rapidly (up to 100°C/s heating rate), transferring the analytes to the capillary column in a concentrated band of vapour (~100 µL).
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