New product qualification frequently requires that a manufacturer provide customers with several independent samples for evaluation. For continous manufacturing processes, equipment residence time distributions (RTDs) introduce serial dependence among the samples. Determining RTD by pulse or step modulation of a tracer or process variable can produce off-spec material and add costs by limiting the opportunity to conduct other product or process development experiments. A novel method of determining a continuous process' RTD does not risk production of off-spec material. Through analysis of serial component analytical data, the process' washout curve can be inferred. The theoretical basis for the method is presented and experimental requirements enumerated. Applicability to well-mixed, laminar flow and convective-dispersive processes is demonstrated. Experimental validation in a specialty polymer pilot plant resulted in an error of about 5% in mean residence time, when compared to estimates from pulse tests and calibrated level measurements.