SENSITIVITY AND NOISE IN GC-MS: ACHIEVING LOW LIMITS OF DETECTION FOR DIFFICULT ANALYTES

Authors: FIALKOV, ALEXANDER - TEL AVIV UNIVERSITY; STEINER, URS - VARIAN, INC; Lehotay, Steven; AMIRAV, AVIV - TEL AVIV UNIVERSITY

Submitted to: International Journal of Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2006
Publication Date: 8/4/2006
Citation: Fialkov, A.B., Steiner, U., Lehotay, S.J., Amirav, A. 2006. Sensitivity and noise in gc-ms: achieving low limits of detection for difficult analytes. International Journal of Mass Spectrometry. 260:31-48

Interpretive Summary: Gas chromatography-mass spectrometry (GC-MS) is the most effective analytical tool for scientists to detect, quantify, and identify volatile and semi-volatile organic chemicals in samples (gas, liquid, or solid). Any improvement in the performance of GC-MS has wide impact on the ability for scientists to make analytical measurements in their applications. The use of supersonic molecular beams (SMBs) in GC-MS provides a host of benefits over traditional GC-MS for the analytical chemist. One major benefit is the lower chemical detection limits made possible by GC-SMB-MS, and this manuscript describes the concepts and experimental evidence to show how GC-SMB-MS achieves the lowest detection limits reported thus far among GC-MS techniques, and more importantly, how this improves real-world applications. If GC-SMB-MS becomes a commercial instrument, the impact of the technique on scientists using GC-MS will be tremendous improvements in their analytical capabilities.

Technical Abstract: GC-MS instrument limit of detection (LOD) is typically listed by major vendors as that of octafluoronaphthalene (OFN). Most current GC-MS instruments can achieve LODs in the low fg range. However, GC-MS LODs for realistic analytes in actual samples are often a few orders of magnitude higher than OFN's. Users seldom encounter 1 pg LOD in the single ion monitoring mode in their applications. We define this detectability difference as the "OFN gap". In this paper we demonstrate and discuss how the OFN gap can be significantly reduced by the use of GC-MS with supersonic molecular beams (SMB). Experimental results were obtained with a recently developed GC-MS with SMB named 1200-SMB, that is based on the conversion of the Varian 1200 system into a GC-MS-MS with SMB. With this 1200-SMB system, the LOD of all types of analytes, including OFN, in real samples is significantly improved. The 1200-SMB LODs of common and/or difficult compounds are much closer to its OFN LOD, even in complex matrices. We crossed the <1 fg OFN LOD milestone to achieve the lowest LOD to date using GC-MS, but more importantly, we attained LOD of 2 fg for diazinon, a common pesticide analyte. In another example, we achieved an LOD of 10 fg for underivatized testosterone, which is not amenable in traditional GC-MS analysis, and conducted many analyses of naturally incurred testosterone in alligator blood extracts. In general, the harder the compound analysis, the greater is the gain in sample detectability using the 1200-SMB versus traditional GC-MS.