II. Measurement operation
1. Preheat spectrophotometer/microplate reader for 30 minutes, adjust wavelength to 630 nm, set zero
with distilled water.
2. Dilute 100 μg/mL nitrogen standard solution with distilled water to 2.5 μg/mL for standby.
3. Sampling table
Reagent name (μL)
Sample
Blank tube (B)
Standard tube (S)
Test tube (T)
-
400
-
-
-
400
-
Distilled water
Standard
400
80
60
-
Reagent I
80
60
80
60
Reagent II
Mix well and place at room temperature of 25℃ for 30 minutes.
460 460
Distilled water
460
After fully mixing, measure the absorption value at 630 nm, and record it as AB, AS and AT. Calculate
ΔAS=AS-AB, ΔAT=AT-AB.
III. Calculation:
+
NH4 -N (μg/g Soil)= ΔAT÷ΔAS×CS×VE÷W=2.5×ΔAT÷ΔAS÷W
CS: Concentration of standard solution, 2.5 μg/mL;
VE: Volume of extract solution, 1 mL;
W: Sample mass, g.
Note:
+
1. Soil after Air-drying or drying can easily cause changes in NH4 -N content, so it is recommended to use
fresh soil for determination. The samples should be sealed, transported and stored at 4°C after collection,
and the analysis should be completed within 3 days. Otherwise, it should be stored in small pieces at -20°C
+
(deep freezing) and can be stored for several weeks. When determining the NH4 -N content of deep
freezing, the temperature and time of thawing should be controlled. When thawing at room temperature,
the sample must be thawed, homogenized and extracted within 4 hours; if it is thawed at 4°C, the thawing
time should not exceed 48 hours.