Interface instrumentation between computer and spectrophotometer for reaction rate measurements.

An instrument interface which generates an output voltage level proportional to rate of change of an input voltage is described. The interface permits direct connection of routine spectrophotometric rate measurements to a real-time laboratory computer system. The form of the voltage level output enables the computer to read rates in the same manner as peaks are read for AutoAnalyzers, permitting the clinical laboratory LABCOM system to compute and report results for rate methods with no software changes. Spectrophotometric rates from about 10 to 0.025 absorbance units per mm can be measured with an accuracy and precision of less than 1% relative in measurement times of about 10 to 30 s, respectively. The interface is readily constructed from commercially available components. Test results are presented for simulated rates, lactic dehydrogenase, and alkaline phosphatase.