Stopped-Flow Time Difference Analysis A Review

A novel analytical method which includes absorbance measurements by using stopped-flow apparatuses was developed, which can be applied to determine absorbance changes as low as 0.002 O.D, with good precision in a time range of less than seconds, even for background absorbances of 1.5 to 2.0 O.D. This method, termed "stopped -flow time difference analysis" (abbreviated to SFTDA), utilizes the progress curve of a reaction for both quantitative and qualitative analyses, based on the absorbance change and the rate of reaction, respectively. A differential kinetic analysis of mixed components is possible, due to the different reaction rates of the components, which can also be effective to exclude interference by coexisting materials. Several examples of the applications of the SFTDA method with macro-apparatuses are described, which include a determination of ascorbic acid down to 10-' M, a highly sensitive determination of inorganic phosphate of ppb and sup-ppb level in environmental water, and an improvement in several characteristics of the methods for protein determination. Two types of microstopped-flow apparatuses were built, which need only 1/10 of the sample amount necessary for conventional macro-apparatuses, and still have a comparable performance. Their utility in clinical chemistry is demonstrated.