1. Department of Analytical and Pharmaceutical Chemistry, The Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen, Denmark, Bruker Analytische Messtechnik GmbH, Silberstreifen, D-76287 Rheinstetten, Germany, and Department of Chemistry, Birkbeck College, University of London, Gordon House, 29 Gordon Square, London WC1H 0PP, U.K.