Detection of Picogram or Sub-picogram Semi-volatile Compounds by Full Scan GCMS in Using a High-efficiency Source A Game Changer?

Oral Presentation

Prepared by D. Walker, H. Prest, M. Churley
Agilent Technologies, Inc., 5301 Stevens Creek Blvd, Santa Clara, CA, 95051, United States


Contact Information: dale.walker@agilent.com; 916-458-2940


ABSTRACT

Introduction

Semi-volatile organic compounds (SVOCs) are a broad class of environmentally significant contaminants of global interest. These compounds are found on a variety of target analyte lists in GCMS methods such as the USEPA 8270 and 525 methods and comparable methods elsewhere. Although listed as targets that are appropriate for selected ion monitoring (SIM) mode in GCMS analysis, scan mode would provide the advantage of full scan spectra for compound confirmation. In the past, however, method detection limits could not be reached using scan mode. We report that a high efficiency source represents a revolution in ion source design with greatly enhanced sensitivity that can be exploited to produce scan detection limits for SVOCs that were formerly only approached by SIM.

Methods

A 7890GC coupled to a 5977B GCMS with a high efficiency source was operated in scan mode from 50 to 550 u (sampling = 4). Detector gain was set to 0.1. A 5% phenyl phase GC column (DB-8270D column, 30 m x 0.25 mm i.d. x 0.5 m) was used, as is common in this analysis. Standards were made in dichloromethane and 0.5 L was injected, via 5 L syringe, in pressure-pulsed splitless mode into a double-taper liner. Replicate injections of a 5 ng/mL standard were used to determine an instrument detection limit (IDL) for each compound, where IDL = t99% (RSD/100 %) amount measured.

Preliminary Data or Plenary Speakers Abstract *

A total of 53 compounds were surveyed. Estimated IDLs for the scan data were calculated using the external standard method and were based on eight consecutive injections. The average of five individual IDL determinations was reported as the final IDL. Sub-picogram scan detection is common with a few compounds showing picogram levels due primarily to lowered compound target ion response. Example IDLs determined are (in pg): Dimethylphthalate, 0.4; phthalate, 0.5; 1,3-dichlorobenzene, 0.3; hexachlorobenzene, 2.1; 4-nitroaniline, 3.8; and benzo[b]fluoranthene, 0.7. Less than optimal compound chromatography was a factor in some cases (e.g., benzo[b]- and [k]fluoranthene). One approach to leverage these significantly lower IDLs and improve workflow efficiency would use split injections with accelerated run times if high sample concentration is to be maintained. Additionally, injecting less sample would introduce less matrix in the liner, column, etc. and improve robustness. Finally, processing less sample would save time and costs in transportation as well as solvent use and disposal. These dramatically lowered scan IDLs also suggest that SIM IDLs will be enhanced and so a combination of both strategies is possible, resulting in the most time and cost effective analysis. Ongoing experiments utilize smaller i.d. and thinner film approaches.

Novel Aspect * Detection in scan mode is now approaching that previously attained only in SIM, allowing several analytical strategies to be explored.