The YSI 2300 Analyzer Replacement Meeting Report.

This is a summary report of the most important aspects discussed during the YSI 2300 Analyzer Replacement Meeting. The aim is to provide the interested reader with an overview of the complex topic and propose solutions for the current issue. This solution should not only be adequate for the United States or Europe markets but also for all other countries. The meeting addendum presents three outcomes of the meeting.

Simplified nitrate-reductase-based nitrate detection by a hybrid thin-layer controlled potential coulometry/spectroscopy technique.

A novel method for the detection of nitrate was developed using simplified nitrate reductase (SNaR) that was produced by genetic recombination techniques. The SNaR consists of the fragments of the Mo-molybdopterin (MO-MPT) binding site and nitrate reduction active site and has high activity for nitrate reduction. The method is based on a unique combination of the enzyme-catalyzed reduction of nitrate to nitrite by thin-layer coulometry followed by spectroscopic measurement of the colored product generated from the reaction of nitrite with Griess reagents. Coulometric reduction of nitrate to nitrite used methyl viologen (MV(2+)) as the electron transfer mediator for SNaR and controlled potential coulometry in an indium tin oxide (ITO) thin-layer electrochemical cell. Absorbance at 540 nm was proportional to the concentration of nitrate in the sample with a linear range of 1-160 µM and a sensitivity of 8000 AU M(-1). The method required less than 60 µL of sample. Detection of nitrate could also be performed by measuring the charge associated with coulometry. However, the spectroscopic procedure gave superior performance because of interference from the large background charge associated with coulometry. Results for the determination of nitrate concentration in several natural water samples using this device with spectroscopic detection are in good agreement with analysis done with a standard method.

Development and characterization of simulant pancreatic islets.

Insulin is stored in pancreatic islets as a zinc-insulin complex, and stimulating the islets results in the release of insulin and zinc. Simulant pancreatic islet beads have been developed using agarose beads (50-250 micro m diameter) derivatized with iminodiacetic acid that have been loaded with zinc. A qualitative comparison of the simulant beads with pancreatic islets has been made by staining with dithizone and a zinc-binding fluorescent dye, TSQ. The binding capacity of simulant beads was determined to be 34 micro mol Zn(2+)/g of dried beads using anodic stripping voltammetry. Hydrochloric acid was used to release zinc from beads to mimic the secretion of insulin from pancreatic islets and a release profile was established. The simulant beads can be used to optimize the islet isolation process and reduce the use of real islets in method development.