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IUPAC Prize for Young Chemists - 2000
Honorable Mention

 

 

Olivier P. Haefliger receives one of five Honorable Mention awards associated with the IUPAC Prize for Young Chemists, for his Ph.D. thesis work entitled "Development of two-step laser mass spectrometry as a competitive analytical-chemical method"

Current address (at the time of application)

FIRMENICH SA
Analysis & Perception
Corporate R&D Division
1, Route des Jeunes
CH-1211 Geneve 8, Switzerland

Tel.: +41 22 780 3239
Fax: +41 22 780 3334
E-mail: OLIVIER.HAEFLIGER@firmenich.com

Academic degrees

  • Ph.D., Swiss Federal Institute of Technology (ETH), Zurich
  • Diploma in Chemistry, Swiss Federal Institute of Technology (ETH), Zurich

Ph.D. Thesis

Title Development of two-step laser mass spectrometry as a competitive analytical-chemical method
Advisers Prof. Renato Zenobi
Thesis Committee Prof. Renato Zenobi (ETH, Zurich), prof. Walter Giger (EAWAG, Dubendorf), PD Dr. Urs Baltensperger (PSI, Villigen)

Essay

Two-step laser mass spectrometry (L2MS) is an innovative technique for the direct analysis of selected compounds in complex mixtures such as environmental samples. In the first step, an infrared laser pulse desorbs intact neutral molecules from the sample surface, or ablates them from a solid matrix. In the second step, a pulse from a tunable ultraviolet laser is used for resonance-enhanced multiphoton ionization (1+1 REMPI) of the desorbed species; this soft ionization scheme prevents fragmentation of the analytes. Mass analysis is then performed in a reflectron time-of-flight mass spectrometer. The mass spectra are dominated by intact parent ions of those mixture components that strongly absorb the selected ultraviolet laser wavelength. Major advantages are the detection limit in the low attomole range and minimal need for sample preparation, therefore giving the possibility to measure large numbers of samples within short periods of time.

In an initial characterization stage, the potential capabilities offered by L2MS for both quantitative and qualitative measurements were assessed in this thesis. A new, fast, and convenient sample preparation procedure was developed that allows accurate and reproducible control over the amount of analytes desorbed by each laser pulse. Quantitative L2MS measurements were demonstrated for polycyclic aromatic hydrocarbons (PAHs) over three orders of magnitude using this sample preparation method. The wavelength (238 - 310 nm) dependence and the laser pulse energy dependence of the 1+1 REMPI ion yield was then studied for 17 PAHs. This data allows one to determine which wavelengths are optimal to measure with high sensitivity and selectivity the analytes of interest using L2MS or related methods.

Chemical analyses of atmospheric aerosol particles were performed during extended field measurement campaigns. First, the aerosols emitted by all major emission sources including Diesel vehicles, gasoline vehicles, residential heating, wood fires, and cigarettes were characterized. For each emission source, tracer mass spectral patterns were identified, notably based on specific PAHs and other polycyclic aromatic compounds (PACs). Only small sample quantities were necessary and the measurements were performed within minutes. L2MS was found to be a valuable alternative to more laborious chemical analysis techniques that often require extensive sample preparation.

These results were then applied to the study of the dynamic behavior of aerosol-bound PACs in urban air over the course of several whole days, both next to a street with heavy traffic and in a city park. L2MS allowed measurements with 15 minute time resolution. Large variations in particle concentration and chemical composition were observed, reflecting the contributions from Diesel trucks and gasoline-powered cars to urban aerosols. The photochemically induced decay of oxygenated polycyclic aromatic hydrocarbons (OPAHs) was observed in real time. In a similar way, the dynamic behavior of aerosol-bound PACs in air was studied over the course of a whole year at four sites representative of the different types of aerosol exposure in Switzerland. This project was completed in the framework of a collaboration between several research institutes in order to achieve a chemical characterization of the aerosol samples that would be as thorough as possible. L2MS allowed the measurement of about 1000 samples, which would not have been possible within a reasonable amount of time using chromatographic techniques. A strong seasonal dependence of the amount of aerosol-bound PACs was observed.

Finally, to exemplify the versatility of L2MS, studies were undertaken to demonstrate the applicability of L2MS to the chemical analysis of contaminants in environmental water. This thesis establishes L2MS as a competitive analytical-chemical method that can provide innovative contributions to unanswered analytical problems due to its-specific advantages.


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