Question

What is the reason behind developing a standard curve to determine concentration in an unknown solution?

What is the reason behind developing a standard curve to determine concentration in an unknown solution? 5.

Answer 1

Standard curves are used to determine the concentration of substances. They are obtained by relating a measured quantity to the concentration of the substance of interest in "known" samples, i.e. Standards of known concentration. These standards provide a reference to determine unknown concentrations. Thus amounts chosen of standards need to span the range of concentrations expected to be found in the "unknown" sample concentration.

The quantity (assay measurements as i.e. luminescence, radioactivity, fluorescence, and optical density of various known concentrations of a substance) graphed on y-axis and standard concentrations on x-axis. Data analyzed by fitting a line on curve

To determine the unknown concentration of a substance in a sample (with same assay as for standards used), intersect across the assay measurement on y with standard concentration, and down to x. The concentration of substance in unknown sample is the value on x.

Most analytical techniques use a standard curve. There are a number of advantages to this approach. First, the standard curve provides a reliable way to calculate the uncertainty of the concentration calculated from the standard curve

Second, the standard curve provides data on an empirical relationship. The mechanism for the instrument's response to the analyte may be predicted or understood according to some theoretical model, but most such models have limited value for real samples. (Instrumental response is usually highly dependent on the condition of the analyte, solvents used and impurities it may contain; it could also be affected by external factors such as pressure and temperature.)

Many theoretical relationships, such as fluorescence, require the determination of an instrumental constant anyway, by analysis of one or more reference standards; a standard curve is a convenient extension of this approach. The standard curve for a particular analyte in a particular sample provides the empirical relationship needed for those particular measurements.