A direct, ambient ionization method
has been developed using atmospheric
pressure thermal desorption–extractive electrospray–mass
spectrometry (AP/TD-EESI-MS) for the detection of the genotoxic impurity
(GTI) methyl p-toluenesulfonate (MTS) in a surrogate
pharmaceutical matrix. A custom-made thermal desorption probe was
used to the desorb and vaporize MTS from the solid state, by rapid
heating to 200 °C then cooling to ambient temperature, with a
cycle time of 6 min. The detection of MTS using EESI with a sodium
acetate doped solvent to generate the [MTS+Na]+ adduct
ion provided a significant sensitivity enhancement relative to the
[M+H]+ ion generated using a 0.1% formic acid solvent modifier.
The MTS detection limit is over an order of magnitude below the long-term
daily threshold of toxicological concern (TTC) of 1.5 μg/g and
the potential for quantitative analysis has been determined using
starch as a surrogate active pharmaceutical ingredient (API).
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