LaMotte SMART Spectro Spectrophotometer User Manual
Page 15
SMART Spectro Operator’s Manual 2.11
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