The limit of detection, expressed as the concentration, cL, or the quantity, q L, is derived from the smallest measure, x L, that can be detected with reasonable certainty for a given analytical procedure. The value of x L is given by the equation \[x_{\text{L}}=\overline{x}_{\text{bi}}+k\ s_{\text{bi}}\] where x ̄ bi is the mean of the blank measures, s bi is the standard deviation of the blank measures, and k is a numerical factor chosen according to the confidence level desired.