LaMotte DCL-20 Colorimeter User Manual
Page 30
PROCEDURE
A. PREPARATION OF DILUTED ZINC INDICATOR SOLUTION
1. Use one pipet (0352) to measure exactly 5.0 mL of Zinc Indicator Solution into the 10 mL graduate cylinder. The
bottom of the curved surface (the meniscus) of the liquid should be at the 5.0 mL mark. Pour this into the bottle
labeled “Diluted Zinc Indicator Solution”.
2. Use the unrinsed graduated cylinder first to add 10.0 mL and then 7.8 mL (total of 17.8 mL) of methyl alcohol, 6319,
to the bottle labeled “Diluted Zinc Indicator Solution”. Cap and mix the ingredients in this bottle. Do not leave this
bottle uncapped.
B. DETERMINATION OF ZINC
1. Fill a clean colorimeter tube (0967) to the 10 mL line with the soil filtrate then neutralize according to the procedure
on page 10.
2. Select setting 6 on the “Select Wavelength” knob and press the “30 Second Read” button.
3. Insert the tube into the colorimeter chamber and adjust to “100”%T with the “Set Blank” knob. This is the 100%T
blank.
4. Remove the tube, add 0.1 g of Sodium Ascorbate (6316) with the 0.1 g spoon (0699) and 0.5 g of *Zinc Buffer
Reagent (6315) with 0.5 g spoon (0698), cap and shake vigorously for 1 minute.
5. Add 3 drops of *Sodium Cyanide Solution (6565), cap and mix contents of tube.
6. Use the 1 mL pipet assembly to add 1 mL of *“Diluted Zinc Indicator Solution”. Cap and mix contents.
7. Use a second plain pipet (0352) to add 4 drops of *Formaldehyde Solution, 37% (5128). Cap and mix by inverting 15
times.
8. Press the “30 Second Read” button and insert the tube into colorimeter chamber. Measure the test result as soon as the
reading stabilizes.
9. Consult the calibration chart to find the concentration of zinc in parts per million (ppm).
ZINC CALIBRATION CHART
%T
9
8
7
6
5
4
3
2
1
0
90
80
0.0
0.1
0.1
0.2
0.2
0.3
0.3
70
0.4
0.4
0.5
0.5
0.6
0.6
0.7
0.7
0.8
0.9
60
0.9
1.0
1.0
1.1
1.2
1.2
1.3
1.4
1.4
1.5
50
1.6
1.7
1.7
1.8
1.9
2.0
2.0
2.1
2.2
2.3
40
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
30
3.4
3.5
3.6
3.8
3.9
4.0
4.2
4.3
4.4
4.6
20
4.8
4.9
5.1
5.3
5.5
5.6
5.9
6.1
6.3
6.5
10
6.8
7.0
7.3
7.6
8.0
8.3
8.7
9.1
9.5
10.0
0
10.6
11.2
11.9
12.8
13.8
15.1
16.8
19.2
23.6
ZINC CONCENTRATION CHART
%T
RANGE
PARTS PER MILLION
82-100%
Low
0-0.5 ppm
77-81%
Marginal
0.6-1.0 ppm
69-76%
Adequate
1.1-2 ppm
30
1985-01 • 10/01