Standard Addition Calibration Curve

Shown at the top is a set of six standard additions for the determination of Mn²⁺. The flask on the left is a 25.00-mL sample diluted to 50.00 mL. The remaining flasks contain 25.00 mL of sample and, from left to right, 1.00, 2.00, 3.00, 4.00, and 5.00 mL of an external standard of 100.6 mg/L Mn²⁺. Shown below are two ways to plot a standard additions calibration curve. The absorbance for each standard addition, S_spike, is shown by the filled circles.