CyberTech (United States)

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Biomedical diagnostic systems perform as combinations of multiple components, each introducing an experimental uncertainty. The present study examines the uncertainty in spectrophotometric measurements of absorbance A for different models of detector response. Modeling this response provides both a quantitative estimate of the minimum relative concentration error (RCE) and limits on the operating range for which the RCE falls within specified limits. For the constant uncertainty model the operating range corresponding to RCE no greater than twice the minimum value ranges from A approximately 0.07 to A approximately 0.79. A photomultiplier-like response results in the limits 0.2 < A < 2.3. A Beer's Law model predicts that RCE contributions from sample concentration uncertainty decrease monotonically with increasing absorbance. Assay chemistry factors dominate at low A values making high precision difficult at low A.