Gas Chromatography Atmospheric Pressure Chemical Ionization (GC-APCI) GC/MS/MS for the Determination of Semivolatiles

New Organic Monitoring Techniques (Session 2)
Oral Presentation

Prepared by D. Stevens, F. Dorman, K. Rosnack
Waters Corporation, 34 Maple Street, Milford, MA, 01757, United States


Contact Information: [email protected]; (508) 369 8311

ABSTRACT

In contrast to the high vacuum requirements of an electron ionization (EI) source for GC/MS, optimum CI requires conditions that bring the ionization region nearer to atmospheric pressure. Source design elements, such as a dual orthogonal ion introduction (Z-Spray TM), originally implemented to facilitate coupling LC to MS, have been incorporated into the design of GC-APCI systems. However, the CI mechanisms employed in GC-APCI are well understood because they are the same as those discovered during fundamental studies in the earliest days of CI development.

On a tandem quadrupole (TQ) mass spectrometer, GC-APCI has specificity and sensitivity similar to LC-APCI which result from high abundance of the molecular ion combined with analyte-specific MRM (multiple reaction monitoring) transitions. High molecular ion abundance is due to the soft ionization of CI. Specificity gains are due to creating fragments in a collision cell that is physically separate from ionization and the inclusion of two stages of MS (MS/MS). Therefore, MRM decouples ionization from product ion creation which results in significant performance advantages for GC-APCI MS/MS versus GC-EI MS.

To evaluate the potential for broader adoption of the technique it is necessary to test methods that included multiple chemical classes in a single analysis. A representative set of over 70 semivolatile compounds was chosen for this investigation. Samples were analyzed on a Waters XevoTM TQ-XS TQ fitted with the Atmospheric Pressure Gas Chromatography (APGC TM) source. The source was operated in positive ion mode using a configuration that provides efficient ionization of compounds amenable to both protonation and charge exchange ionization. A minimum 25% valley between benzo(b)fluoranthene and benzo(k)fluoranthene was achieved in a 20 minute analysis and the majority of analytes, 88%, achieved a detection limit of 1 pg on column while 45% reached as low as 10fg on column.