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Rapid identification, confirmation, and quantitation using an open-air ion source coupled to a time-of-flight mass spectrometer

Author

Teresa M. Vail, University of the Pacific

Date of Award

2007

Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)

Department

Chemistry

First Advisor

Patrick R. Jones

First Committee Member

Jianhua Ren

Second Committee Member

James W. Blankenship

Third Committee Member

O. David Sparkman

Abstract

The ability to identify and confirm a compound using mass spectrometry usually involves time consuming sample preparation and method development. The open-air ion source DART (Direct Analysis in Real Time) can ionize compounds in the gas, solid, or liquid phase without chromatography or sample preparation due to the interactions of helium metastable atoms with gas molecules commonly found in air. The coupling of the DART to a time-of-flight (TOF) mass spectrometer allows the rapid determination of an analyte's elemental composition based on accurate mass measurement and isotope peak intensities. Mass spectrometric fragmentation data can aid in the structural identification of an analyte as compounds produce characteristic fragment-ions based on their structure. The TOP's ability to produce fragmentation spectra was compared to the more traditional tandem mass spectral method (MS/MS) considering the TOF lacks the ability to select pre-cursor ions. The TOF produced in-source CAD (collisionally activated dissociation) spectra comparable to MS/MS spectra for three well known pharmaceuticals acetaminophen, phenylbutazone and clenbuterol. Further structural confirmation was explored through a determination of the number of active hydrogen atoms in an analyte molecule achieved by hydrogen/deuterium (H/D) exchange by treatment with deuterium oxide (D₂0) in the DART sample gap. Mass spectra acquired in the presence of D₂0 of analytes containing active hydrogen atoms associated with hydroxyl, amino and carboxylic acid groups showed that H/D exchange was predictable and reproducible.

Using accurate mass measurement and isotope peak intensities, the elemental composition of an unknown captured on filter paper was identified as dipropylene glycol (DPG) analyzed directly from the surface of the filter paper. Data from in-source CAD and H/D exchange of both the unknown and authentic standards confirmed that the unknown was DPG. The cross-correlation of accurate mass measurement and isotope peak intensities, in-source CAD and HID exchange data provided an unambiguous identification of the contaminant melamine in dog food without the need for any sample preparation.

Once analytes are identified and confirmed, quantitation of the analyte is desirable. The calibration curves here are constructed using the net extracted ion-current associated with the analyte relative to the internal standard. In cough syrup, a complicated matrix, the linearity, R², is shown to be 0.992.

Pages

139

Recommended Citation

Vail, Teresa M.. (2007). Rapid identification, confirmation, and quantitation using an open-air ion source coupled to a time-of-flight mass spectrometer. University of the Pacific, Thesis - Pacific Access Restricted. https://scholarlycommons.pacific.edu/uop_etds/666