A novel hyphenated technique namely the combination of HPLC with
direct analysis in real time (DART®) mass spectrometry (MS) is
presented. The coupling of HPLC to DART®-MS was achieved by a simple
interface design with a capillary end piece transferring the HPLC
effluent to the ionization region of the DART®. Flow rates (0.3-1.6 mL
min-1) and inner diameters of the capillary (50-150 ìm) were
harmonized to provide a stable liquid jet. Ionization-related
parameters optimized included positioning of the capillary end piece
with respect to He outlet of the ionization source and the MS inlet,
He heater temperature and He flow rate. Among DART®-MS voltages, the
grid electrode voltage proved to have the most pronounced effect on
signal intensities. A major benefit of this setup is the possibility
to employ (commonly not MS-compatible) HPLC eluents such as phosphate
buffers up to a phosphate concentration of 120 mM even at typical HPLC
flow rates such as 1 mL min-1 and above without negative side effects
like contamination of the ion source or ion suppression. Experiments
evaluating the correlation of signal intensity to mass-flow and
concentration revealed that DART®-MS can be seen as a mass flow
sensitive detector. The usability of this hyphenated technique has
been tested on the example of four parabenes (measured in the negative
ion mode) as well as a set of pyrazine derivatives (measured in the
positive ion mode). For the parabenes limits of detection (LOD) in the
range of 20-55 ìg L-1 and linear ranges from at least 200-10000 ìg L-1
with correlation coefficients better than 0.997 were obtained.
direct analysis in real time (DART®) mass spectrometry (MS) is
presented. The coupling of HPLC to DART®-MS was achieved by a simple
interface design with a capillary end piece transferring the HPLC
effluent to the ionization region of the DART®. Flow rates (0.3-1.6 mL
min-1) and inner diameters of the capillary (50-150 ìm) were
harmonized to provide a stable liquid jet. Ionization-related
parameters optimized included positioning of the capillary end piece
with respect to He outlet of the ionization source and the MS inlet,
He heater temperature and He flow rate. Among DART®-MS voltages, the
grid electrode voltage proved to have the most pronounced effect on
signal intensities. A major benefit of this setup is the possibility
to employ (commonly not MS-compatible) HPLC eluents such as phosphate
buffers up to a phosphate concentration of 120 mM even at typical HPLC
flow rates such as 1 mL min-1 and above without negative side effects
like contamination of the ion source or ion suppression. Experiments
evaluating the correlation of signal intensity to mass-flow and
concentration revealed that DART®-MS can be seen as a mass flow
sensitive detector. The usability of this hyphenated technique has
been tested on the example of four parabenes (measured in the negative
ion mode) as well as a set of pyrazine derivatives (measured in the
positive ion mode). For the parabenes limits of detection (LOD) in the
range of 20-55 ìg L-1 and linear ranges from at least 200-10000 ìg L-1
with correlation coefficients better than 0.997 were obtained.
