JPH0196533A - Method for measuring total nitrogen by eliminating influence of bromide - Google Patents

Abstract

PURPOSE:To obtain exactness by measuring absorbancy at arbitrary two wavelengths with a liquid prepd. by diluting a sample and a sample liquid prepd. without diluting the same, then by making calculation by using the absorbancy obtd. in such a manner. CONSTITUTION:The sample water is diluted twice by pure water to decrease the concn. of the sea water to <=1.5-2.0% in the case of, for example, the sea water sample. This sample water is then put into a high-pressure steam sterilizer, etc., where an oxidizing agent and an alkaline agent, etc., at need are added to the sample water. The vessel is hermetically closed and is heated. The decomposed liquid is taken out and an acid is added at need to the liquid to adjust the pH to 2-3. The measurement of the absorbancy of this soln. is executed by selecting the measuring wavelengths at two wavelengths, for example, 220nm and 210nm or 220nm and 215nm and calculating the content of nitrogen by calculation from the absorbancies at the two wavelengths. The correct content of the nitrogen is thereby determined.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring total nitrogen. For more details,
This invention relates to a method for accurately measuring the total amount of nitrogen in seawater while excluding the effects of bromide. It is also useful for measuring seawater pollution, especially eutrophication, predicting the occurrence of red tide, and managing aquaculture in marine areas.

In conventional technology, especially when measuring total nitrogen in seawater, the way to eliminate the influence of bromide and obtain correct total nitrogen measurements is to separate bromide and nitrogen by performing complex chemical operations. A method was used in which the amount of nitrogen was measured after separation. Therefore, measurement takes time, requires special techniques, and has the problem that automation is particularly difficult due to complicated operations. Automatic total nitrogen measuring devices have been developed in recent years, but these automatic total nitrogen measuring devices did not have a function to separate bromide. Therefore, although this automatic total nitrogen measuring device could be used for lake and river water samples that do not contain bromide, it had a major drawback in that it could not be used for seawater.

In this way, in the conventional technology, complicated chemical operations were performed to separate bromide and nitrogen, and then the amount of nitrogen was measured, which took time and required a lot of skill. Otherwise, there were problems in that it could not be operated or automated equipment could not be created.

The present invention is a novel method that is easy to operate, does not require any skill, and is capable of measuring total nitrogen without the influence of bromides, such that automated equipment can be easily created. This method provides a method.

In the conventional method for measuring total nitrogen, sample water is placed in a high-pressure steam sterilizer or a similar container made of pressure-resistant, heat-resistant, chemical-resistant material, and then treated with an oxidizing agent such as potassium belloxonisulfate and, if necessary, sodium hydroxide. Add the alkaline agent, seal the container, and heat. This operation oxidizes and decomposes all nitrogen compounds and converts them into nitrate nitrogen. After adjusting the pH of the decomposition solution obtained in this way, the amount of nitrogen is determined by measuring light absorption in the ultraviolet region, for example, absorbance at 220n+o.

In this case, if bromide coexists in the sample water, some of the bromide may become a bromate during the oxidative decomposition process. Both bromide and its oxidation product, bromate, absorb in the ultraviolet region, e.g. 22Or+a+, so when measuring nitrogen, either bromide or bromate will introduce a positive error. become. At this time, the rate at which bromate is generated from bromide is not constant and depends on the salt concentration in the sample water, and the absorption strength of bromide and bromate is 1
Another problem is that the molar extinction coefficients are different.

The present invention proposes the following method.

In the case of a seawater sample, first dilute the sample water with pure water. For example, dilute it twice with pure water to reduce the salt concentration to 1.5 to 2.0.
% or less. If the sample has a salinity of 1.5 to 2.0% or less, such as because it is a mixture of seawater and river water, this dilution operation is not necessary. Next, this sample water is placed in a high-pressure steam sterilizer or similar pressure-resistant, heat-resistant, and chemical-resistant container, and an oxidizing agent and, if necessary, an alkaline agent are added.
Seal the container and heat. The time for this thermal decomposition is usually 3
It is 0 minutes. Next, the decomposition liquid is taken out, and an acid is added as necessary to adjust the pH to, for example, 2 to 3. The absorbance of this solution is measured, and the measurement wavelength is, for example, 220 nm.
Two wavelengths are selected, such as and 210 nm, or 220 nm and 215 nm. Finally, the amount of nitrogen is calculated from the absorbance at these two wavelengths.

The principle of the present invention is as follows.

In other words, first, in the case of a seawater sample with a high salinity concentration, first dilute the sample water with pure water to bring the salinity concentration to 1.5 to 2.0% or less, or for a sample that is a mixture of seawater and river water. If the salt concentration is 1.5 to 2.0% or less, the undiluted sample water is decomposed at high temperature and pressure in the presence of an oxidizing agent or an alkaline agent to convert nitrogen compounds into nitrate nitrogen.

When operated in this manner, the coexisting bromide does not change to bromate because the salt concentration is relatively low, and remains as bromide.

The absorbance of the solution after the decomposition operation is measured at two wavelengths in the ultraviolet region, and in this case, both nitrate nitrogen and bromide exhibit absorption at two wavelengths.

However, since their respective molar extinction coefficients are different, for example, in the presence of lppm bromide, at 220 nm, 0.0074.210 at 0.0021.215 nm,
It shows an absorbance of 0.0225 in nm. On the other hand, nitrate nitrogen, which is a change from total nitrogen to be measured, also exhibits different absorbance at each wavelength. For example, lppm of nitrate nitrogen is 0.2134 at 220 nm and 0 at 215 nm.
．． It has an absorbance of 0.4166 at 3486.210 nm. Therefore, ippm of nitrate nitrogen and ippm of
When bromides coexist, they exhibit absorbance corresponding to the sum of their respective absorbances at each wavelength. In reality, this sum of absorbance is further supplemented by salt, other components in seawater, and the absorption of the absorption cell itself used for measurement. As mentioned above, both nitrate nitrogen and bromide exhibit different absorbances at each wavelength, so if the absorbance per unit concentration is determined in advance at any two wavelengths using seawater with a known concentration, it is possible to By measuring the absorbance at these two wavelengths and calculating the correct amount of nitrogen, it is possible to determine the correct amount of nitrogen.

Tsunen - Ikkou Niwa The present invention will be explained in more detail with reference to Examples.

Example-1 Artificial seawater was prepared, and nitrate nitrogen and bromide of known concentrations were added thereto. That is, nitrate nitrogen is O,0,50
, ■, 0.1.5 ppm each, bromide 10.20.40
．． 60 ppm of each were added.

Next, this artificial seawater was diluted twice with pure water to reduce the salinity to about 1.5 to 2.0% or less. Nitrate nitrogen in this diluted seawater is 0.0.25.0.50.0.75 ppm, and bromide is 5.10, 20.30 ppm.

This solution was placed in a high-pressure steam sterilizer, potassium belloxonisulfate and sodium hydroxide were added, and the solution was heated and decomposed for 30 minutes in a closed state. Take out the solution and add acid to adjust the pH to 2~
Adjusted to 3.

And 220nm, 215r+m, 21Or+II+
Absorbance was measured at three wavelengths. The dilution due to the addition of various reagents was calculated, and the average absorbance per 1 ppm of nitrogen and bromide was calculated using an absorption cell with an optical path length of 10 mm. The results are shown in Table 1.

Table 1 Average value of absorbance per ippm of nitrogen and bromide at each wavelength From these results, when nitrogen and bromide coexist, the absorbance at each wavelength is as follows when using an absorption cell with an optical path length of 10 mm:
It is expressed by the following formula. In these formulas, N, and Br
represents the content in ppm, and A represents the absorbance at each wavelength.

A220 = 0.2134N +〇, 0021Br+0
．． 0140-(1) A215=0.3486N +0.
0074Br+0.0260-(2)A210=0.
4166N +〇, 0225B r+0.0810-(
3) Next, by solving the simultaneous equations using any two of these equations, the following equations (6) and (9) are obtained.

For example, when using equations (1) and (3).

First, by multiplying both sides of equation (1) by 10.7, equation (4) is obtained.

10.7A220=2.283N +0.0225Br
+0.150...(4) By subtracting equation (3) from equation (4), equation (5) is obtained.

10.7A 220-A 210 = 1.866N
+0.0690...(5) Equation (6) is obtained by transforming equation (5).

7Q=10. "18""" -0,0370-,,-
, (G)1.866 Similarly, when using equations (1) and (2), first
Multiplying both sides of the equation by 3.52 yields equation (7).

3.52A220 =0.7512N +0.0074
B r+0.0493 (7) By subtracting equation (2) from equation (7), equation (8) is obtained.

3.52A220-A215=0.402(iN+
0.0233...(8) Transforming equation (8), (9
) to obtain the formula.

0.4026 That is, by this method, for example, 220 nm and 21
By measuring the absorbance at two wavelengths, 0 nm or 220 nm and 215 nm, entering the absorbance at each wavelength into equation (6) or equation (9), and solving each equation, the concentration of N can be determined in ppm value. After that, the nitrogen concentration in the original seawater sample can be determined correctly by diluting the sample with pure water and correcting the volume with various reagents in the first operation. Here, for convenience, 220nm, 210r+m, 220n
Although m and 215r+m were selected as two arbitrary wavelengths, the present invention is not limited to these wavelengths. Note that according to the present invention, the concentration of bromide ions can also be determined as necessary.

Example-2 Coastal seawater was collected using Amagasaki-type, Nishinomiya-fu, and Kobe-fu in front of Osaka.
This was designated as seawater 1.2.3.

The absorbance of these samples was measured in the same manner as in Example 1. In addition, samples in which a certain amount of nitrogen or bromide was added to these seawaters were similarly treated and measured. At the same time, the nitrogen concentration in these samples was measured using an autoanalyzer.
Quantification was done by spectrophotometry. The results are shown in Table 2.

The error in the measured value by the method of the present invention was calculated based on the measured value by the O-J-analyzer for the case where Equation (6) was used and the case where Equation (9) was used. The results showed that the results agreed with the autoanalyzer measurement results with an error of about 7% or less.

(Margin below)

Claims (1)

[Claims] When measuring total nitrogen in a sample containing bromide by optical absorption method, measure the absorbance at two arbitrary wavelengths for a diluted sample solution or an undiluted sample solution, and perform calculations using the obtained absorbance. How to accurately measure total nitrogen in a sample by eliminating the influence of bromide