LaMotte SMART3 Colorimeter - Manual (Page 18)

 STANDARD ADDITIONS
A common method to check the accuracy and precision of a test is by standard
additions. In this method a sample is tested to determine the concentration
of the test substance. A second sample is then “spiked” by the addition of a
known quantity of the test substance. The second sample is then tested. The
determined concentration of the spiked sample should equal the concentration
of the fi rst plus the amount added with the spike. The procedure can be
repeated with larger and larger “spikes.” If the determined concentrations do not
equal the concentration of the sample plus that added with the “spike”, then an
interference may exist.
For example, a 10.0 mL water sample was determined to contain 0.3 ppm iron.
To a second 10.0 mL sample, 0.1 mL of 50 ppm iron standard was added. The
concentration of iron due to the “spike” was (0.10 mL x 50 ppm)/10.0 mL = 0.50
ppm. The concentration of iron determined in the spiked sample should be 0.3
+ 0.5 = 0.8 ppm iron. (Note: any error due to the increased volume from the
“spike” is negligible).
LaMotte offers a line of calibration standards which can be used to generate
calibration curves and perform standard additions.
16 SMART3 Colorimeter 11.10