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This query is concerned with the adduct formation of Itraconazole
during LC-MS bio-analyses of its plasma samples (processed by L-L
The adduct formation is direct fuction of the chemical structure and
the driven affinity of the compound towards the particular alkali
metal (Na, K Li)/alkaline earth metal (Ca, Mg) in positive mode and
with halides, formate, acetate in -ve mode, more pronounced with the
large molecules. Accordingly, for some drug molecules also, such
pheomenon are reported during LC-MS bioanalysis (like Paclitaxel,
itraconazole). Moreover, if adduct ions are more stable than the
parent ion and is quite reproducible in the given condition, it is
quite logical to monitor the adduct ion, [M+Na]+ for the quantitative
bioanalysis (Adduct formation in quantitative bioanalysis: effect of
ionization conditions on paclitaxel, Journal of the American Society
for Mass Spectrometry, Volume 15, Issue 4, 585-592). Also, there are
ample lit on the use of the adduct in bio-analytical quantitation in
the similar way. Also, sometimes, alkali salts are deliberately added
for the adduct formation of the poorly ionizable compounds and hence
to enhance the sensitivity via adduct formation
We have a different story. We could use successfully the [M+Na]+ peak
of itraconazole (and its metabolite) in presence of IS (all ionized
with similar peak profile/ratio; [M+H]+:[M+Na]+:[M+K]+) some months
back for the LC-MS bioanalytical quantitation. We are well aware of
the fact that the adduct ratio/profiles changes with the change in
mobile phase (different with ACN, MEOH, buffer, ion pairing agent,
organic modifiers and the concentration/composition thereof),
ionization parameters, sample preparation method and else. Now with
exactly similar medium, sample preparation techniques (reagents,
buffer, even we checked the quality of water), mobile phase, MS-
ionization parameters [M+K]+ peak is unexpectingly intense, in expense
of the [M+Na]+ that we used to observe earlier. We tried to track the
source of the K during analysis. The instrument was tuned and checked
with the standard with which, provided the perfect adduct formation
profile. Overall, the hurdle now is the abrupt loss of the sensitivity
([M+Na]+), that quantitation is not at all possible for the earlier
We would appreciate for your thoughtful inputs in this issue.
Thanking you in advance!!
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What are the possible sources of K+?
1) Biological-hemolysis of red cells?
2) Collection Na/K or K2EDTA/KHeparin?
3) Mislabeling or mis prep of buffer LLE or mobile phase K instead of
Edward F. O'Connor
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