Figure 2. The slopes of the standard-addition curves (A) used for quantification of ATP vary by a factor of 2.5 due to matrix effects. Single-point measurements of luminescence may be used to determine the content of ATP (B) with an average standard deviation of 8.6%, but due to matrix effects the results obtained may differ from the results obtained with the standard-addition method by 50% for samples containing less than 2 pg ATP.