[1] Univ London, Birkbeck Coll, Dept Chem, London WC1H 0PP, England
[2] Gen Hosp Kettering, Dept Urol, Kettering NN16 8UZ, Northants, England
[3] Bruker Analyt Messtech GmbH, D-76287 Rheinstetten, Silberstreifen, Germany
[4] Pfizer Ltd, Cent Res, Sandwich CT13 9NJ, Kent, England