We recently developed a pseudo-enantiomeric reaction which was monitored on-line via 2D-fluorescence spectroscopy in different reaction media. During enzymatic reactions, conclusions about the converted substrates and the enantioselectivity could be drawn immediately, using two different fluorescence spectroscopic detectable substrates, L-phenylalanine-7-amido-4-methylcoumarine and D-phenylalanine-7-amido-4-trifluoromethylcoumarine. Now, due to the enlargement of one of the coumarin substrates via salt formation, it was possible to influence the enzymatyic enantioselectivity in toluene and to monitor the impact of the bulky counterion on-line. (c) 2005 Elsevier Inc. All rights reserved.