4 Notes
- If you cannot prepare the fecal samples immediately after col-
lection, store them at 80 C. - For each experiment, the magnetic field homogeneity must be
optimized through an accurate shimming. To check if a sample
is properly shimmed, you can observe the full-width at half-
maximum of lactate peak that should be less than 1.7 Hz,
before applying apodization and symmetric shape. TSP peak
is not a reliable signal to check the quality of shimming due to
the huge amount of proteins present in the sample, which
influence its line-width because TSP binds to proteins. - Samples must be acquired in randomized order.
- It is useful to run a standard solution to identify potential
impurities arising from reagents and preparation procedures. - The most common method of spectral binning is the so-called
equidistant binning, i.e., each spectrum is divided into bins
with fixed width, typically 0.04 ppm. The weakness of this
method is that, under certain experimental conditions, single
peaks can be divided into two neighboring bins, generating
artifacts. To avoid this problem, several mathematical algo-
rithms [14–17] have been developed to vary the individual
size bin. For example, ACD intelligent bucketing method
(ACD/NMR processor, Advanced Chemistry Development
Inc. (ACD/Labs), Toronto, ON, Canada), a combination of
equidistant binning and non-equidistant binning, sets the
bucket divisions at local minima (within the spectra) to ensure
that each resonance is in the same bin throughout all spectra.
Table 4
Pearson’s correlation analysis among PC1, PC4, clinical status (healthy or sick), and pancreatic
insufficiency factor (PI)
PC1 PC4
Pancreatic
insufficiency factor
Clinical status (healthy
or sick)
PC1 1.000 0.012
(0.334)
0.388 0.382 (0.120)
PC4 0.012
(0.334)
1.000 0.604 0.592 (0.210)
Pancreatic
insufficiency factor
0.388 0.603 1.000 0.822
Clinical status (healthy
or sick)
0.382
(0.120)
0.592
(0.210)
0.822 1.000
In parenthesis, partial correlation coefficients among PC1, PC4, and clinical status adjusted for the PI effect are reported
Metabolomics and Clinical Needs 335