linear dynamic range
/ DY-nam-ik /
The linear dynamic range is the span of concentrations over which an instrument plays fair — where doubling the amount of analyte roughly doubles the signal, in a clean straight line. Picture a bathroom scale that reads honestly from a small child up to a heavy adult, but jams below and pegs out above: the honest middle stretch is its linear range.
Concretely, it runs from the lowest concentration the method can reliably measure up to the highest concentration where the calibration line is still straight. Below the bottom, signal disappears into noise; above the top, the line bends over as the instrument saturates and equal increases in concentration give smaller and smaller increases in signal.
It matters because measurements are only trustworthy inside this band. Outside it, the simple straight-line calibration no longer holds, and readings become unreliable. A wide linear range is convenient — it lets you measure dilute and concentrated samples without re-diluting — but you must still keep your unknowns inside it, diluting samples that read too high before trusting the number.
A spectrophotometric method is linear from 0.1 to 10 mg/L. A sample reading 18 mg/L is off-scale, so it is diluted twofold to about 9 mg/L — back inside the linear range — before the result is trusted.
Trust readings only inside the straight stretch; dilute samples that climb above it.
Linear dynamic range is not the same as working range. The working range can include curved portions handled by a non-linear fit, whereas the linear dynamic range is specifically the straight-line part. The lower end is set near the limit of quantitation.