4 Notes
1. The strength of the NaOH solution should ensure that excess
OH
À ions are present after the decomposition of the oxidant.
The amount of NaOH in the solution should be adequate
for neutralization of the 2 mol of H
+ formed per mol of
persulfate.
2. For complete oxidization of organic material, oxygen available
from the persulfate oxidation should be at ten times greater
level than that of organic material in the sample.
3. Total nitrogen and total phosphorus can be analyzed after
simultaneous oxidation with persulfate using more concentrated oxidizing reagent.
4. Use five different dilution steps for calibration, and determine
the blank with ultrapure water since ultrapure water may contain nitrogen traces.
5. It is critical to have proper training before running the analyzer. This will depend on the system that you are using, and
it is beyond the scope of this chapter to go into the details of
the operation of the instrument. We have used a Hitachi 1100
UV spectrophotometer for TN analysis.
6. Calibration curve is prepared by plotting measured absorbance
or area of standards versus standard concentrations (linear
regression). Reduce the absorbance of the blank from the
absorbance of the standards.
7. If the total nitrogen content is higher than 600 μg/l, the
sample should first be diluted with ultrapure water. The total
carbon content of the sample should not exceed 20 mg/l when
using 5 ml of the oxidizing solution for 5 ml of sample.
8. Determine the blank caused by the oxidant since persulfate
contains traces of nitrogen.
9. Start each sample run with ultrapure water blank(s) and reference material to verify proper operation of the instrument.
Analyze samples in sequences of max 20 samples followed by
a blank and reference material. Insert also standards in the
sequence to test accuracy and drift during the analytical runs.
10. Determine concentration in the sample by the slope of the
calibration curve. Reduce the absorbance of the measured
reagent blank and the reagent blank value taken from the
intercept of the calibration line with the ordinate from the
absorbance of the sample.
Determining Total Nitrogen
85
1. The strength of the NaOH solution should ensure that excess
OH
À ions are present after the decomposition of the oxidant.
The amount of NaOH in the solution should be adequate
for neutralization of the 2 mol of H
+ formed per mol of
persulfate.
2. For complete oxidization of organic material, oxygen available
from the persulfate oxidation should be at ten times greater
level than that of organic material in the sample.
3. Total nitrogen and total phosphorus can be analyzed after
simultaneous oxidation with persulfate using more concentrated oxidizing reagent.
4. Use five different dilution steps for calibration, and determine
the blank with ultrapure water since ultrapure water may contain nitrogen traces.
5. It is critical to have proper training before running the analyzer. This will depend on the system that you are using, and
it is beyond the scope of this chapter to go into the details of
the operation of the instrument. We have used a Hitachi 1100
UV spectrophotometer for TN analysis.
6. Calibration curve is prepared by plotting measured absorbance
or area of standards versus standard concentrations (linear
regression). Reduce the absorbance of the blank from the
absorbance of the standards.
7. If the total nitrogen content is higher than 600 μg/l, the
sample should first be diluted with ultrapure water. The total
carbon content of the sample should not exceed 20 mg/l when
using 5 ml of the oxidizing solution for 5 ml of sample.
8. Determine the blank caused by the oxidant since persulfate
contains traces of nitrogen.
9. Start each sample run with ultrapure water blank(s) and reference material to verify proper operation of the instrument.
Analyze samples in sequences of max 20 samples followed by
a blank and reference material. Insert also standards in the
sequence to test accuracy and drift during the analytical runs.
10. Determine concentration in the sample by the slope of the
calibration curve. Reduce the absorbance of the measured
reagent blank and the reagent blank value taken from the
intercept of the calibration line with the ordinate from the
absorbance of the sample.
Determining Total Nitrogen
85