LaMotte smart spectro 2, Operator'S Manual

Page: 15 / 304

SMART Spectro 2 Operator’s Manual 04.16 15

PREPARING DILUTE STANDARD SOLUTIONS
Standard solutions should be prepared to create a calibration curve. Standard solutions
can be prepared by diluting a known concentrated standard by specifi ed amounts. A
chart or computer spreadsheet can be created to determine the proper dilutions. Use
volumetric fl asks and volumetric pipets for all dilutions.
1. In Column A – Record the maximum concentration of test as determined by the range
and path length.
2. In Column B – Record the percent of the maximum concentration the standard
solution will be.
3. In Column C – Calculate the fi nal concentration of the diluted standard solutions
by multiplying the maximum concentration (In Column A) by the % of maximum
concentration divided by 100. (C = A x ).
4. In Column D – Record the fi nal volume of the diluted sample (i.e. volume of volumetric
fl ask).
5. In Column E – Record the concentration of the original standard.
6. In Column F – Calculate the milliliters of original standard required (C x D/E = F).
A sample chart appears below:
A B C=A x B/100 D E F=C x D/E
Maximum
concentration
of test
% of Maximum
concentration
Final concentration of
Diluted Standard
Volume of
Standard
Concentration of
Original Standard
mL of
Original Standard
Required
10.0 ppm 90 9.0 ppm 100 mL 1000 ppm 0.90 mL
10.0 ppm 70 7.0 ppm 100 mL 1000 ppm 0.70 mL
10.0 ppm 50 5.0 ppm 100 mL 1000 ppm 0.50 mL
10.0 ppm 30 3.0 ppm 100 mL 1000 ppm 0.30 mL
10.0 ppm 10 1.0 ppm 100 mL 1000 ppm 0.10 mL
10.0 ppm 0 0 ppm 100 mL 1000 ppm 0 mL

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.
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