Question

Explain Calibration, Linear Range, LOL, LOQ, and LOD.

Answer 1

Calibration - Calibration is the process of comparing a reading on one piece of equipment or system, with another piece of equipment that has been calibrated and referenced to a known set of parameters. Basically, calibration is the act which determines the functional relationship between measured values and analytical quantities.

Linear range and LOL - A calibration curve can also help define the linear range, the range of concentrations that the instrument gives a linear response. Outside this range, the response may taper off due to instrumental considerations, and the equation from the calibration cannot be used. This is known as the limit of linearity (LOL).

LOQ and LOD - Limit of detection is the lowest amount that can be statistically determined from the noise. Generally this is defined as a signal that is 3 times the noise. The limit of detection can be calculated from the slope of the calibration curve and is generally defined as LOD=3*S.D./m, where S.D. is the standard deviation of the noise.  

The noise is measured by taking the standard deviation of multiple measurements. Alternatively, in one trace, noise can be estimated as the standard deviation of the baseline. The limit of quantitation (LOQ) is the amount that can be differentiated between samples and is usually defined as 10 times the noise.