1. Merck Research Laboratories, Rahway, New Jersey, United States
2. Division of Analytical Biosciences, LACDR, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
3. Sirna Therapeutics Inc., San Francisco, California, United States
4. Netherlands Metabolomics Centre, LACDR, Leiden University, P.O. Box 9502, 2300RA Leiden, The Netherlands