Nitrite nitrogen test diazotization method – LaMotte DCL-20 Colorimeter User Manual
Page 21
NITRITE NITROGEN TEST
DIAZOTIZATION METHOD
QUANTITY
CONTENTS
CODE
2 x 60 mL
*Mixed Acid Reagent
*V-6278-H
5 g
*Color Developing Reagent
*V-6281-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.
Nitrites are formed as an intermediate step in the production of nitrate. Soils that are well drained and aerated contain only
small amounts of nitrite nitrogen. Excessive nitrites, which are toxic to plants, may result from soil conditions unfavorable
to the formation of nitrate, such as inadequate aeration. High nitrite readings may also be encountered in soils with large
amounts of nitrates, where a portion of the nitrate nitrogen decomposes to form nitrites.
RANGE:
0-53 lbs/A
METHOD:
The diazonium com pound formed by diazotization of sul fa nil amide by ni trite in wa ter un der acid
con di tions is cou pled with N-(1-naphthyl)-ethylenediamine to pro duce a red dish-pur ple color
which is read colorimetrically.
IN TER FER ENCES:
There are few known in ter fer ences of sub stances at con cen tra tions less than 1000 times that of ni -
trite; how ever, the pres ence of strong ox i dants or reductants may readily af fect the ni trite
con cen tra tions. High al ka lin ity (above 600 mg/L) will give low re sults due to a shift in pH.
PROCEDURE
1. Use the 1 mL pipet (0354) to add 2 mL of soil filtrate to a clean colorimeter tube (0967) and dilute to the line with
deionized water. Cap tube and mix.
2. Select setting 4 on the “Select Wavelength” knob.
3. Measure 5 mL of diluted soil filtrate into another colorimeter tube, then add 5 mL of *Mixed Acid Reagent (6278).
Use the small graduated cylinder (0416) for these measurements. Cap the tube and mix, then insert the 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. Using the 0.1 g spoon (0699), add two level measures of *Color Developing
Reagent (6281) to the contents of tube and cap.
5. Shake tube for approximately one minute to dissolve the powder, then let stand for 5 minutes for maximum color
development.
6. At the end of the 5 minute waiting period, insert tube into chamber, press the “30 Second Read” button and measure
%T as soon as reading stabilizes.
7. Consult chart to find the nitrite nitrogen concentration in pounds per acre.
NITRITE NITROGEN CALIBRATION CHART (LBS/A)
%T
9
8
7
6
5
4
3
2
1
0
100
0.0
0.1
0.2
90
0.3
0.5
0.6
0.7
0.8
1.0
1.1
1.2
1.3
1.5
80
1.6
1.7
1.9
2.0
2.1
2.3
2.4
2.6
2.7
2.8
70
3.0
3.1
3.3
3.4
3.6
3.7
3.9
4.1
4.2
4.4
60
4.5
4.7
4.9
5.0
5.2
5.4
5.6
5.8
5.9
6.1
50
6.3
6.5
6.7
6.9
7.1
7.3
7.5
7.7
7.9
8.2
40
8.4
8.6
8.8
9.1
9.3
9.6
9.8
10.1
10.3
10.6
30
10.9
11.2
11.4
11.7
12.0
12.4
12.7
13.0
13.4
13.7
20
14.1
14.4
14.8
15.2
15.6
16.1
16.5
17.0
17.5
18.0
10
18.5
19.1
19.7
20.4
21.0
21.8
22.6
23.4
24.3
25.3
0
26.5
27.7
29.2
30.9
32.9
35.5
38.8
43.8
53.0
21
1985-01 • 10/01