Accuracy is the degree of difference between the measured or calculated value and the true value. Data accuracy and analytical bias are often evaluated by the analysis of LCS and MS samples, with results expressed as a percentage recovery measured relative to the true (known) concentration.

The percentage recovery for LCS samples is given by:

where: A = measured concentration of the surrogate or LCS; and
T = known concentration.

The percentage recovery for MS samples is given by:

where: A = measured concentration of the spiked sample;

B = concentration of unspiked sample; and
T = amount of spike added