Application
News
No. O77
Total Nitrogen/Total Phosphorus Analysis
Measurement of Total Nitrogen/Total Phosphorus in
Wastewater by TNPC-4110 Plus
As a measure to improve eutrophication of closed bodies of
water, total pollutant load control regulations were
implemented in Japan from 1979 to reduce the total load of
organic contaminants discharged into such waters to a
standard value or less. Beginning with the 5
th
Total Pollutant
Load Control regulations, total nitrogen and total phosphorus
were added and designated to the object items. Many places
of business which are subject to those regulations measure
these substances with automatic measuring devices. In a
recent model change, Shimadzu improved the performance
and functions of its TNPC-4110 series online total
nitrogen/phosphorus analyzer, which had been used since the
5
th
Total Pollutant Load Control regulations were implemented,
and now offers the new model as the TNPC-4110 Plus series.
In the improved model, the thermal decomposition/
chemiluminescence method was adopted for measurement of
total nitrogen. This method provides the same high oxidative
decomposition capacity and enables detection with minimal
interference as the previous model, and samples containing
contaminants or sea water can be measured with virtually no
interference effects. The reagent and measurement sequence
were also improved in this series, and in total phosphorus
measurement, the influence of contaminants was minimized
as far as possible, enabling highly accurate measurement.
This article introduces an example of measurement of samples
containing seawater and minerals with the TNPC-4110 Plus.
M. Tanaka
Total Nitrogen (TN) Analysis Method
The thermal decomposition/chemiluminescence method is
used in measurement of total nitrogen (TN) in the TNPC-4110
Plus. This method enables measurement unaffected by metal
ions and bromide ions, which are interference components in
ultraviolet (UV) spectrophotometry. Therefore, measurement
unaffected by coexistent substances is possible, even when
the sample is contaminated with seawater.
The sample used in this experiment was prepared by adding
a nitrogen compound to a solution of diluted seawater
(dilution rate: 2×) to obtain a concentration of 0.5 mgN/L (i.e.,
nitrogen concentration: 0.5 mg/L), and measurements were
carried out by the summation method (manual analysis),
ultraviolet spectrophotometry (manual analysis), and
thermal decomposition/chemiluminescence method.
Table 1 Total Nitrogen Measurement Conditions
with TNPC-4110 Plus
Analyzer : TNPC-4110 Plus total nitrogen/phosphorous
analyzer
Measured item : Total nitrogen (TN)
Measurement method : Thermal decomposition/chemiluminescence
Calibration : 2-point calibration using 0-2 mgN/L potassium
nitrate aqueous solution
(full scale (FS): 2 mgN/L)
Sample : Liquid prepared by adding potassium nitrate
to natural diluted seawater (dilution rate 2×) to
a concentration of 0.5 mgN/L
Total Nitrogen (TN) Analysis Results
Table 2 shows the measurement results for each method. The
column on the right shows the difference between the UV
spectrophotometry/TNPC-4110 Plus results and the value
measured by the summation method as a standard,
calculated as the full scale ratio (%FS). UV spectrophotometry
gave a large value, showing the interference effect of
components contained in the seawater. On the other hand,
the result by the TNPC-4110 Plus measurement was
approximately the same as that by the summation method,
demonstrating that measurement unaffected by seawater
components is possible.
Table 2 Total Nitrogen Measurement Results
Analysis
method
Measurement
principle
Measurement
results
(mgN/L)
Difference from
summation
method (%FS)
Manual
analysis
Summation 0.59 —
Manual
analysis
UV
spectrophotometry
0.84 +12.5%
TNPC-4110
Plus
Thermal
decomposition/
chemiluminescence
0.54 -2.5%
