Sample Dilution Techniques & Volumetric Measurements - LaMotte smart spectro 2 Operator's Manual

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 off ers 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 Spectro 2 gives an OUT OF RANGE message then the
sample concentration could be over range or under range. If it is over range, the sample
must be diluted. Then the test should be repeated on the diluted sample 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 fi lled 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
10 mL
5 mL
2.5 mL
1 mL
0.5 mL
If the above glassware is not available, dilutions can be made with the spectrophotometer
tube. Fill the tube to the 10 mL line with the sample then transfer it to another container.
Add 10 mL volumes of demineralized water to the container and mix. Transfer back 10
mL of the diluted sample to the tube and follow the test procedure. Continue diluting and
testing until a reading, which is in the concentration range for the test, is obtained. Be
sure to multiply the concentration found by the dilution factor (the number of total 10 mL
volumes used).
Example:
10 mL of sample is diluted with three 10 mL volumes of demineralized water; the dilution
factor is four.
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Deionized Water to Bring
Volume to 10 mL
0 mL
5 mL
7.5 mL
9 mL
0.5 mL
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Multiplication Factor
1
2
4
10
20
SMART Spectro 2 Operator's Manual 04.16
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