Sample Preparation in Global Metabolomics of Biological Fluids and Tissues - Proteomic and Metabolomic Approaches to Biomarker Discovery - page 64

(C)

1000

800

600

400

200

0

0 5 10 15 20 25 30 35

Retention time (min)

Probe
preconditioning

(A)

In vivo sampling Wash Desorption

￿ 30 min ￿1-5 min ￿ 30 sec

￿ 30-60 min

LC-MS

Evaporation
reconstitution
(optional)

(B)

Plasma or serum
separation

Solvent
precipitation

Blood collection

￿5 min ￿15-90 min ￿ 30-90 min ￿ 18 hr

(D)

1000

800

600

400

200

0

0 5 10 15 20 25 30 35

Retention time (min)

FIGURE 5 Schematic comparison of the main workflows for in vivo SPME (A) versus ex vivo solvent precipitation (B) with
estimated time requirements per step. Panels C ( in vivo SPME of circulating mouse blood) and D (methanol/ethanol
precipitation of mouse plasma) show example ion maps obtained using the two methods and illustrate that good metabolite
coverage of both polar and nonpolar species can be obtained with SPME. (Figure adapted from refs. 10 and 27 with permission of
Springer Science

þ Business Media and Wiley. Copyright 2012 and 2011.)

adverse reactions, protein adsorption, and/or
clotting. Furthermore, the proteins and other
macromolecules cannot diffuse into the coating;
thus, both metabolism quenching and extraction
processes are simultaneous and performed
directly in vivo . The comparison of in vivo
SPME (1,868 features) with solvent-precipitated
plasma

coverage is achievable even with a single SPME
coating, although the overall number of features
detected was lower than in plasma samples
due to the nonexhaustive nature (lower sensi-
tivity) of the microextraction technique and the
fact that the amount of metabolite extracted is
proportional to its free concentration in blood. 27
Figure 5 shows example ion maps obtained
from in vivo SPME versus solvent precipitation

ltration
(2,262 features) shows that good metabolite

(3,969 features) and ultra