Samples for Metabolomics Analysis

The biological sample to be used in a metabolomics study will de- 

With regards to urine samples, both 24 hour urine samples and spot urine samples have been used successfully in nutritional metabolomics. In both cases, careful collection procedures must be followed to ensure the molecular integrity of the sample addition of a preservative or chilling of the sample is an absolute necessity. Diurnal variation has been well documented in urine samples taken from healthy volunteers (Walsh et al. 2006 Maher et al. 2007) and is essential to consider for collection of spot urine samples. Indeed it is recommended that a very specific description of the sample to be collected is given such as, first void midstream urine samples, (Scalbert et al. 2009). 

For metabolomic analysis of blood, both serum and plasma samples are used. With respect to serum samples, details such as clotting time, clotting temperature, and treatment conditions prior to centrifugation need to be considered (Teahan et al. 2006). For collection of plasma samples it is important to consider the anticoagulant to be used and the possibility of unwanted peaks (Scalbert et al. 2009). It should be noted that the choice of anticoagulant will depend on the method employed downstream and the metabolites to be analysed. For NMR-based metabolomics, lithium heparin plasma is most suitable whereas for studying lysophospholipids EDTA plasma is recommended (Seppanen-Laak-so and Oresic 2009). 

More recently, the application of metabolomics to study the metabolite composition of fecal samples has appeared in the literature (Vitali et al., Jacobs et al. 2007). This method has proven to be a useful mode of assessing gut microbiota activity. Collection of fecal samples should be performed in a controlled fashion to minimize unwanted variation. 

For animal studies, tissue samples are readily available for analysis and extraction of metabolites can be performed in a number of ways depending on the metabolites of interest. Metabolomic analysis of cultured cells is emerging as a useful technique to study effects of certain 

---