pH adjustment prior to extraction
is an important step in water
sample pretreatment processes for exploration of new/unknown disinfection
byproducts (DBPs) in drinking water. To achieve a better extraction
efficiency, the pH of a water sample is usually adjusted to a low
level (e.g., < 0.5) to ensure that target DBPs are in their neutral
forms. However, such a practice may elude some amphoteric DBPs (especially
those nitrogenous DBPs with multiple functional groups), which can
accept protons at a low pH and lose protons at a high pH. In this
study, with careful extraction pH selection and optimization, we first
report the detection and identification of a new group of heterocyclic
nitrogenous DBPs, halogenated pyridinols, in simulated drinking water
using ultra performance liquid chromatography/electrospray ionization-triple
quadrupole mass spectrometry and time-of-flight mass spectrometry,
including 5-chloro-3-pyridinol, 2-bromo-3-pyridinol, 2,6-dichloro-4-pyridinol,
2,6-dibromo-3-pyridinol, 3-bromo-2-chloro-5-pyridinol, 5-bromo-2-chloro-3-pyridinol,
3,5,6-trichloro-2-pyridinol, and 2,4,6-tribromo-3-pyridinol. On the
basis of the speciation of dissociated chemical species and recovery
tests at different extraction pH values, it was found that, only at
a pH of 3.0, all the eight new DBPs could achieve recoveries of >50%.
With subsequent instrumental parameter optimization, the method detection
and quantitation limits of the eight new DBPs were determined to be
0.04–1.58 and 0.15–4.11 ng/L, respectively. The optimized
method enabled an accurate detection of the eight new DBPs in two
real drinking water samples. Further aided with in vivo developmental and acute toxicity assays using zebrafish embryos,
the developmental and acute toxicity of the new DBPs were found to
be slightly lower than those of halogenated benzoquinones but dozens
of times higher than those of commonly known DBPs such as tribromomethane
and iodoacetic acid.
