1. Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
2. SIMS Laboratory, Shared Equipment Authority, Rice University, MS 126, 6100 Main Street, Houston, Texas 77005, United States
3. Department of Chemical and Biomolecular Engineering, Rice University, MS 362, 6100 Main Street, Houston, Texas 77005, United States