LaMotte DC1600 Colorimeter - Manual (Page 28)

PROCEDURE
HEXAVALENT CHROMIUM
1. Rinse a clean colorimeter tube (0967) with sample water. Fill to 10 mL line with sample water.
2. Select setting 4 on “Select Wavelength” knob and press “30 Second Read” button.
3. Insert colorimeter tube into colorimeter chamber and adjust to 100% T with “Set Blank” knob. This is the 100% T
blank.
4. Remove tube from colorimeter. Use 0.1 g spoon (0699) to add one level measure of *Chromium Reagent Powder
(V-6276). Cap and shake for one minute. Wait 2 to 3 minutes.
5. During the waiting period, fold a piece of filter paper in half, then in half again to form a cone. Push corners together
to open end, and insert into funnel (0459).
6. Filter sample into a clean colorimeter tube (0967). Insert tube into colorimeter chamber and press “30 Second Read”
button. Record %T as soon as reading stabilizes.
7. Consult calibration chart (page 26) to determine hexavalent chromium concentration in parts per million (ppm).
TOTAL CHROMIUM WITH ACID DIGESTION
1. Fill graduated cylinder (0418) to 50 mL line with sample water. Transfer to Erlenmeyer flask (0431).
2. Use the 1 mL pipet (0354) to add 5 mL (five measures) of *Sulfuric Acid, 5N (7681). Swirl to mix.
NOTE: Highly buffered waters may require pH adjustment. Order the Chromium pH Adjustment
Package, Code 2087.
3. Place flask on burner or hot plate. Bring solution to a gentle boil.
4. Fill pipet (0341) with Potassium Permanganate, 0.5% (7682). While gently swirling flask, add Potassium
Permanganate, 0.5% (7682), 2 drops at a time to boiling solution, until solution turns a dark pink color which persists
for 10 minutes. Continue boiling.
5. Add one drop of *Sodium Azide, 5% (7683) to boiling solution. Boil for approximately 30 seconds. If pink color does
not fade, add another drop of *Sodium Azide, 5%. Continue adding *Sodium Azide, 5% one drop at a time until pink
color disappears.
6. Remove flask from heat. Cool sample under running water. This is the digested sample.
7. Pour digested sample into clean graduated cylinder (0418). Dilute to the 50 mL line with Deionized Water (5115).
8. Rinse a clean colorimeter tube (0967) with sample water. Fill to 10 mL line with sample water.
9. Select setting 4 on “Select Wavelength” knob and press “30 Second Read” button.
10. Insert colorimeter tube into colorimeter chamber and adjust to 100% T with “Set Blank” knob. This is the 100% T
blank.
11. Remove tube from colorimeter. Use 0.1 g spoon (0699) to add one level measure of *Chromium Reagent Powder
(V-6276). Cap and shake for one minute. Wait 2 to 3 minutes.
12. During the waiting period, fold a piece of filter paper in half, then in half again to form a cone. Push corners together
to open end, and insert into funnel (0459).
13. Filter sample into a clean colorimeter tube (0967). Insert tube of filtered sample into colorimeter chamber and press
“30 Second Read” button. Record %T as soon as reading stabilizes.
14. Consult calibration chart (page 26) to determine total chromium concentration in parts per million (ppm).
TRIVALENT CHROMIUM
Subtract hexavalent chromium from total chromium. Record as ppm trivalent chromium.
Trivalent Chromium = Total Chromium − Hexavalent Chromium
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