Nitrate nitrogen test cadmium reduction method – LaMotte DCL-20 Colorimeter User Manual
Page 19
NITRATE NITROGEN TEST
CADMIUM REDUCTION METHOD
QUANTITY
CONTENTS
CODE
2 x 60 mL
*Mixed Acid Reagent
*V-6278-H
5 g
*Nitrate Reducing Reagent
*V-6279-C
1
Spoon, 0.1g
0699
*WARNING: Reagents marked with a * are considered hazardous substances. Material Safety Data Sheets (MSDS) are
supplied for these reagents. For your safety, read label and accompanying MSDS before using.
Nitrogen is a component of the chlorophyll (green color) in plants, thus giving plants the rich green color characteristic of
a healthy plant. Nitrogen promotes succulence in forage crops and leafy vegetables. When used at the recommended rates,
nitrogen improves the quality of leaf crops. It also simulates the utilization of phosphorus, potassium and other essential
nutrient elements. The above-ground growth of plants is enhanced with nitrogen. Nitrogen hastens crop maturity
(assuming all other nutrients are adequately supplied and excessive nitrogen rates are not applied). Nitrogen is very
influential in fruit sizing.
RANGE:
0-150 lbs/A
METHOD:
Pow dered cad mium is used to re duce ni trate to ni trite. The ni trite that is orig i nally pres ent plus re -
duced ni trate is de ter mined by diazotizing sul fa nil amide and cou pling with
N-(1 naphthyl)-ethylenediamine dihydrochloride to form a highly col ored azo dye which is
mea sured colorimetrically.
IN TER FER ENCES:
Strong oxiding and re duc ing sub stances in ter fere. Low re sults might be ob tained for sam ples that
con tain high con cen tra tions of iron and cop per.
PROCEDURE
1. Select setting 4 on the “Select Wavelength” knob.
2. Use the 1 mL pipet (0354) to add 1 mL of soil filtrate to a clean colorimeter tube (0967) and dilute to the line with
deionized water. Cap tube and mix.
3. Measure 5 mL of the diluted soil filtrate to another colorimeter tube (0967), then add 5 mL of *Mixed Acid Reagent
(6278). Use the 10 mL graduated cylinder (0416) for these measurements. Cap the tube and mix, then insert tube into
colorimeter chamber and press the “30 Second Read” button. Adjust “100"%T with the ”Set Blank" knob.
4. Remove the tube from the chamber. Use the 0.1 g spoon (0699) to add two level measures of *Nitrate Reducing
Reagent (6279) to the contents of tube and cap.
5. Hold tube by index finger and thumb and mix by inverting approximately 50-60 times in a minute, then let stand 10
minutes for maximum color development. (
NOTE: At the end of the waiting period an undissolved portion of the
*Nitrate Reducing Reagent may remain in the bottom of the tube without affecting the results.)
6. At the end of the 10 minute waiting period, insert tube into chamber of colorimeter, press the “30 Second Read”
button and measure %T as soon as reading stabilizes.
7. Consult chart to find the concentration of Nitrate Nitrogen, in the soil, in pounds per acre.
NITRATE NITROGEN CALIBRATION CHART (lbs/acre)
%T
9
8
7
6
5
4
3
2
1
0
90
2
3
5
6
7
8
10
11
12
14
80
15
16
18
19
20
22
23
25
26
27
70
29
30
32
34
35
37
38
40
42
43
60
45
47
48
50
52
54
56
58
60
62
50
64
66
68
70
72
74
76
78
81
83
40
86
88
90
93
96
98
101
104
107
110
30
113
116
119
122
125
129
132
136
140
144
20
148
152
19
1985-01 • 10/01