Evaluation of a discrete samples/stopped-flow mixer system for equilibrium and kinetic analyses

This paper describes the evaluation of a system for computer-controlled discrete sampling and stopped-flow mixing for equilibrium and kinetic determinations of several sorts of analytes in human serum. The instrumental system features a wash-out sampling system that permits rapid change-over from one sample and (or) reagent type to another, and a mixing-measurement system that can provide reliable data as soon as 10 ms after reagent and sample are mixed. Examples discussed include equilibrium procedures for glucose and cholesterol, slow kinetic procedures for glucose and lactate dehydrogenase, and a fast kinetic method for thiocyanate. The regression equation for all stopped-flow results (n = 114) vs. results by conventional methods is y = (103 +/- 0.01)x - (0.016 +/- 0.019) for numerical values of y between 0.3 and 3.0. The correlation coefficient for these data was 0.991. These results demonstrate that the stopped-flow method is a viable analytical approach for equilibrium, slow kinetic, and fast kinetic determinations that require measurement times shorter than 0.1 s.