unit (14 Da) going from one congener to the next. The most
abundant HAQs, contrary to AHLs, contain an odd number of
carbons on their side chain. Going from the most abundant conge-
ner to the next most abundant ones generally entails successive
addition (or subtraction) of 28 Da. These methods can also be
used to quantify the open form of the AHLs (o-AHLs) (Fig.1),
in which the lactone ring is hydrolyzed, which corresponds to the
addition of one molecule of water (18 Da) to the unmodified
AHLs. Depending on the growth conditions and age of the cul-
tures, these o-AHLs can be found in abundance. The methods
presented can be adapted to perform the desired analysis. For
instance, someBurkholderiaspecies produce modified HAQs car-
rying an additional methyl substitution [6]; detection and quantifi-
cation of these 4-hydroxy-3-methyl-2-alkylquinolines (HMAQs)
are possible by taking into account the additional mass of 14 Da
resulting from the replacement of a proton by a methyl group on
the quinoline ring (Fig.1).
Various scanning modes can be used with a triple quadrupole to
acquire quantitative data, each mode having its advantages and
limitations. Hence, in full-scan mode, a wide range of masses can
be acquired, allowing for subsequent analysis of other compounds
of interest aside from the intended HAQs and AHLs. In this
scanning mode, the sensitivity is not maximal if only quantification
of a few molecules is needed. On the other hand, it is very useful for
detecting other members of the various families of HAQs or AHLs,Fig. 1Chemical structure of HAQs and AHLs
HAQ and AHL Analysis Using LC/MS 51