Table 1 – Instrument conditions for ESI-HPIMS analysis of food contaminants and additives


ESI-HPIMS instrument conditions


90:10 methanol:water ESI solvent (HPLC grade, Alfa Aesar [Ward Hill, MA])


0.5% (v/v) acetic acid in positive ion mode Liquid sample injection rate for ESI Drift tube voltage


ESI source voltage (negative mode) ESI source voltage (positive mode)


Drift tube temperature (food dyes, drug residues) Drift tube temperature (phthalate) Gas preheater temperature Mobility spectrum width


Bradbury-Nielsen gate pulse width Bradbury-Nielsen gate voltage


Data acquisition sampling rate Number of spectra summed per cycle Drift gas flow rate Curtain gas pumping rate


1.5 µL min–1 8000 V 2200 V 2400 V 170 °C 180 °C 180 °C


25 msec 150 µsec 45–55 V


200,000 s-1 10


1.5 lpm 0.3–0.6 lpm Directspray ESI


Table 2 – Comparison of figures of merit for HPIMS separations vs other separation methods using the method of Asbury and Hill14


Resolving power (R)


HPLC-UV UHPLC-UV IMS 65


65


Number of theoretical plates (N) 25,000 Separation time


Throughput (N/sec)


30 min 14


another sample, eliminating the long capillary tubing of traditional infusion-type ESI sources and minimizing carryover.


The instrument in Figure 1 (left) operates at atmospheric pressure, eliminating vacuum


25,000 3 min 140


30 5000


10 sec 50


HPIMS 70


27,000 10 sec 2700


pumps needed for low pressures, and uses air as the mobility drift medium. The ions from the ESI source (1) have remaining ESI solvent removed in the desolvation region (2) prior to injection into the drift region using a Bradbury-Nielsen


AMERICAN LABORATORY • 11 • JUNE/JULY 2013


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