Abstract: An apparatus 20 for the separation of a subpopulation of cells from an intact organ or other biological material is provided. The apparatus 20 includes: (1) a digestion chamber 24 that integrates the primary digestion process, (2) a measuring cylinder 26, (3) a cell collection chamber 28, (4) a heat exchanger 30 for raising and lowering temperatures in the digestion chamber 24 to activate or inactivate enzymes, (5) sensors 112, 114, 116, 118, 120, 122 to complete a closed feedback loop for allowing optimization of the digestion process, and (6) mock cells which mimic the cells to be harvested and which are used to fully optimize the process without unnecessary destruction of harvested cells. The manipulation of the digestion process may be manual or may be automated under computer control.

Abstract: The concentration of NADH or NADPH in a test solution is determined by adding a redox coupling agent, preferably 2,6 dichloroindophenol DCIP, to the test solution. The coupling agent reacts with the NADH or NADPH to form an electroactive coupling agent (DCIPH.sub.2) which is then detected electrochemically at a lower voltage than would be required to detect the NADH or NADPH. This can be used to detect NADH or NADPH formed by any well known enzymatic or immunoassay method which produces NADH as a detectable product. This has particular application to biological fluids such as whole blood which does not require any treatment of the test sample prior to electrochemical analysis. In particular, red blood cells do not have to be removed from whole blood samples to provide reliable data.