A REAGENTLESS AMPEROMETRIC ELECTRODE BASED ON CARBON-PASTE, CHEMICALLY-MODIFIED WITH D-LACTATE DEHYDROGENASE, NAD(-LACTIC ACID ANALYSIS .1.CONSTRUCTION, COMPOSITION, AND CHARACTERIZATION(), AND MEDIATOR CONTAINING POLYMER FOR D)

A reagentless carbon paste electrode was designed for D-lactic acid an alysis in a flow injection system for the monitoring of the production of D-lactate in a batch fermentation. D-lactate dehydrogenase, nicoti namide adenine dinucleotide (NAD(+)), a synthetic redox polymer contai ning covalently attached toluidine blue O as mediator, graphite powder , and paraffin oil were used for the construction of the modified carb on paste electrode. D-Lactate selectivity was indicated by insignifica nt responses from a variety of possible interferences including L-lact ate. The electrodes gave a linear response in the range between 0.05 a nd 5 mM D-lactate, with a detecting limit of 30 mu M, allowing a sampl e throughput of 20 h(-1). Preliminary investigations were made by cove ring the electrode surface with electropolymerized membranes. Satisfac tory stability was observed, indicated by a reproducibility of 3.3% re lative standard deviation (RSD, n = 31), with a non-membrane-covered e lectrode for the analysis of D-lactate in fermentation broth. A long-t erm stability (230 broth samples) was proven, suggesting the electrode s to have a good potential for use in on-line monitoring of fermentati on processes. (C) 1995 John Wiley & Sons, Inc.