LaMotte SMART Colorimeter, Operator'S Manual

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sample is then tested. The determined concentration of the spiked
sample should equal the concentration of the first 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.
SAMPLE DILUTION TECHNIQUES
& VOLUMETRIC MEASUREMENTS
If a test result using the SMART Colorimeter gives an
OVER-RANGE!
message, the sample must be diluted.. Then the test should be repeated to
obtain a reading which is in the concentration range for the test. (Note:
This is not true for colorimetric determination of pH.)
Example:
Measure 5 mL of the water sample into a graduated cylinder. Add
demineralized water until the cylinder is filled to the 10 mL line. The
sample has been diluted by one-half, and the dilution factor is therefore 2.
Perform the test procedure, then multiply the resulting concentration by
2 to obtain the test result.
The following table gives quick reference guidelines on dilutions of
various proportions. All dilutions are based on a 10 mL volume, so several
dilutions will require small volumes of the water sample. Graduated pipets
should be used for all dilutions.
Size of Sample
Deionized Water to Bring
Volume to 10 mL Multiplication Factor
10 mL 0 mL 1
5 mL 5 mL 2
2.5 mL 7.5 mL 4
1 mL 9 mL 10
0.5 mL 9.5 mL 20
14 SMART COLORIMETER