14 February / March 2016
Sample Preparation Options for Aroma Analysis by Kathy Ridgway, Anatune Ltd
Unit 4, Wellbrook Court, Girton Road, Cambridge, CB3 ONA
kathy.ridgway@anatune.co.uk
Following developments in Gas Chromatography (GC) instrumentation and data analysis software, the need for good reproducible sample preparation is often underestimated. The choice of sample preparation procedure can be critical in obtaining key information about a sample, or reaching required limits of detection. A number of sample preparation techniques are available that provide extraction and enrichment in one step, and can be easily automated.
This article will discuss some of the options that are particularly suited to Aroma analysis. Aroma compounds can have a range of chemical and physical properties and it is not always safe to assume that all compounds can be extracted using one analytical approach. The choice of technique will depend on the information required. Methods may involve the use of sophisticated GC systems (such as the Agilent GC-Quadrupole-Time of Flight (QTOF), or for real time aroma release measurement Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS).
Some established and more recently developed techniques will be presented and discussed.
As instrumentation and software tools have improved and the trend for multi-analyte methods has increased, the importance of effective, reproducible, sample preparation can sometimes be forgotten. The requirement to see everything in a sample means that often, very specifi c targeted sample preparation methods, with one or only a small number of target analytes are becoming less common. Increasingly a 2-step approach is taken, employing both a non-target screen method, followed with a more robust targeted analysis for known analytes. For both these approaches, the choice of sample preparation procedure can be critical in obtaining the key information about a sample. The choice will depend on the requirements, and the reasons for sample preparation, whether for clean-up, enrichment, or both. Objectives for the method in terms of selectivity and sensitivity need to be defi ned.
The ideal sample preparation will contain the minimum number of steps in order to achieve these objectives. In terms of cost – both monetary and environmental, it is also preferable to avoid the use of large volume of solvents.
Miniaturisation and automation of sample preparation is not new, but an increasing number of steps that form part of standard preparation protocols can now be automated. These include liquid extraction,
solid phase extraction, centrifugation and evaporation/reconstitution. Other automated sample preparation techniques are available that provide extraction, clean up and enrichment in one step.
Aroma analysis is one area where the choice of sample preparation can be key to obtaining the desired information about a sample. Analysis of Aroma compounds presents several challenges and the purpose of the analysis needs to be well defi ned to develop a method that is fi t for purpose. Extremely low levels can be relevant, which can present a challenge in some complex matrices, particularly for a non-target approach where selective clean up cannot
be used. In profi ling work, it is also critical to understand what differences are within the normal variation for your sample and the impact of each of the components from a sensory perspective.
A direct ‘dilute and shoot’ approach may be suffi cient for a simple Quality Control (QC) analysis, but for a complete Aroma profi le, or identifi cation of a taint or ‘off’ odour, it is likely that alternatives will need to be considered. In the case of taints or ‘off’ odours, the wrong approach may result in the compounds responsible not being detected at all and if you have limited sample size, repeat analysis may not be an option.
Figure 1: Comparison of Gerstel Multi-Purpose Sampler (MPS) for liquid-liquid extraction and a more complex dual rail system (a:CF200 centrifuge, b:mVap, c:Mvorx, d:sample tray, e:solvent fi ling station, f:cooled sample tray, g: wash station, h: agitator)
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