Topics - Linearity
In chromatography, linearity usually refers to the response of the detector. A detector is linear if the output of a detector is given by the product of a constant and the solute concentration (or, for a mass sensitive detector, the mass of solute passing though it per unit time). If a detector is declared to be linear, the linearity is usually limited to a specific concentration range (or range of mass of solute passing though it per unit time). No practical detector is perfectly linear, but its response can approach linearity and therefore, linearity needs to be measured. Linearity is a difficult property to define and measure. One method is to assume that the output of a detector is proportional to a power function of the concentration (or mass of solute passing though it per unit time) and, thus, for a perfectly linear detector the exponent would be unity. The value of this exponent for a given detector has been termed the response index of the detector and has been used to define the detector linearity. If the detector is to be considered sufficiently linear for accurate quantitative analysis it should have a response index that lies between 0.97 and 1.03 over the concentration range stated.