 # Standard Curve Calculator

### Introduction

The measurements made using many analytical instruments, like plate readers, require the conversion from a raw signal to a concentration or other known readout. For example, a ubiquitous Organ-Chip readout is the concentration of a given substance (either biological or pharmaceutical), in the Chip effluent. Typical assays on a plate reader, however, yield a raw signal, like optical density or fluorescence intensity. The conversion from signal intensity to the readout of interest is performed using a standard curve.

The standard curve process requires: first, the preparation of solutions of known concentrations; second, the quantification of the signal intensity of those solutions on an analytical instrument like a plate reader; and third, the establishment of a relationship between the measured signal and known concentrations through some curve fitting method. This relationship can then be used to convert the measured signal intensity from experimental samples to the particular readout, like concentration.

Like other standard curve calculators, the calculator within this excel can be used to establish the relationship between the measured signal from an analytical instrument to known concentrations. After entering the measured signal and the corresponding known concentrations in the “Standard Curve” tab, a curve is fit to the data using a log-log linear regression, which minimizes the percent error between the data and the fitted curve. This ensures a “best-fit” for both relatively low and high concentrations. The equation corresponding to this curve is displayed on a plot of the data/best-fit curve and additionally saved in the calculator’s memory to convert the signal from experimental samples of unknown concentrations.

To analyze the results from an entire plate, simply copy and paste plate reader results/signal into the tab marked “Measurement”; the calculator will take the equation found in the “Standard Curve” tab and apply it to the signal in order to automatically calculate and display the corresponding readout. While this readout will usually be concentration, this calculator applies broadly to any readout and any signal. The results can be copied and pasted for further processing and analysis (e.g. using an output like “effluent concentrations” of a tracer molecule to then calculate apparent permeability).