Check matrix effects by obtaining mass spectra of known
amounts of
13 C-labeled and nonlabeled carotenoids added to
a blank (blank spike) and to a plant sample during extraction
(matrix spike).
13 C-labeled standards of lutein and β-carotene
are commercially available.
12. To find out the mass range of isotopologs, you can analyze two
contrasting samples with the lowest and the highest degree of
13
C labeling when these are known. In the case of
13 C pulsechase labeling experiment, for instance, you can use the samples taken at the beginning and at the end of
13 C labeling or
subsequent chase.
13. Equations for calculation of BPI and DoL:
BPI i ¼
I i
I i max
ð
Þ
∙100
BPI i : Base peak intensity of an isotopolog with i
13
C
atoms.
i: Number of
13
C atoms.
I i : Intensity of an isotopolog with i
13
C atoms.
I i(max) : Highest intensity of all isotopologs
Fig. 4 Correlation between BPI i(norm) of lutein isotopologs obtained by FTICR-MS
and LC-MS. The values were taken from Table 4 to Table 5 for FTICR-MS and
LC-MS, respectively
Carotenoid Isotopologue Profiling
275