JPS5979151A - Determination of nitrate ion - Google Patents

Abstract

PURPOSE:To enable simply and efficiently measurement by an inexpensive electrode by using an amalgamated copper electrode as a working electrode in the presence of hydrochloric acid in a prescribed concentration and uranyl ions and measuring a polarogram. CONSTITUTION:After an enameled copper wire 1 polished at a top end is inserted into a tapered glass tube at a top end and fixed with epoxy resin 3, the top end 4 of the copper wire 1 is immersed in mercury 5 under hydrochloric acid 6 to form an amalgamated layer 7. By using this body, a saturated calomel electrode and a platinum coil as a working electrode, a reference electrode 10 and a counter electrode 9 respectively, nitrate ions are measured by a direct current polarograph and a differential pulse polarograph 13 in the presence of an electrolyte 12 incorporating 10<-4>-0.1M hydrochloric acid and 0.02-1.0mM UO2<2+>. The measured results are recorded and indicated on a recorder 14. By this method, a trace quantity of nitrate ions are measured rapidly, efficiently and sensitively over the wide range of potential, and without effect of coexistent substances.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for quantifying nitrate ions in a sample solution. Quantification of this type of substance is extremely important in environmental measurement, soil analysis 9 food additive analysis, etc., and a highly accurate and simple method for quantifying it is strongly required.

Conventionally, in polarographic analysis of nitrate ions,
Reduction waves of nitrate ions were observed using a dropping mercury electrode in the presence of 0.01 MHCl and 0.2 mM uranyl ions. However, this method produces a large amount of waste mercury and has a limited electrode surface area that regulates current sensitivity, making it difficult to quantify trace amounts of nitrate ions. Another potential difference measurement method is to quantify nitrate ions using a nitrate ion-selective electrode, but it has been pointed out that the influence of coexisting substances is very large and that there are problems with the lifespan of the electrode. In addition, as a measurement method using an enzymatic reaction,
A method has been reported in which ammonium ions are generated from nitrate ions using nitrate reductase and nitrite reductase and quantitatively determined using an ammonium ion electrode or an ammonia gas electrode, but this method is difficult to obtain because nitrate reductase is generally expensive and difficult to obtain. Not practical.

The main object of the present invention is to more easily and accurately quantify nitrate ions in a sample by the polarographic method. The specific objective is to create an electrode that has similar characteristics and is easy to handle in place of the dropping mercury electrode used to quantify nitrate ions in the conventional polarographic method, and to find measurement conditions suitable for quantifying nitrate ions. That's true.

For the above-mentioned purpose, the present inventors created a copper amalgam electrode and invented a method for quantifying nitrate ions by amperometric measurement using a copper amalgam electrode as the working electrode.

It has been reported that the electrode reduction reaction of nitrate ions using uranyl ions (UO?) as a catalyst is a five-electron reduction, as shown by equation (1).

No, + 6H+ 5e -) 172 N, +,
3H20(i)0, OIMHct, 0.2mMUO,
c7. The reduction wave of nitrate ions measured using a dropping mercury electrode in the presence of -1,0 V vs. SCE appears,
The wave height increases in proportion to the nitrate ion concentration.

The measurement principle of the present invention is as described above, but in the present invention,
The feature is that a copper amalgam electrode is used instead of a dropping mercury electrode. In general, the hydrogen overvoltage and pressure of metal solid electrodes is low, and especially in acidic solutions, the hydrogen overvoltage is extremely low. <, Therefore, it is not suitable for analysis of nitrate ions.

On the other hand, mercury has a high hydrogen overvoltage, and the reduction waves of nitric acid can be fully observed. Therefore, in the present invention, solid lightning is used.

In order to take advantage of the advantages of the electrode and the mercury electrode, we used an amalgam layer of mercury on the copper surface and used it as an electrode, and we obtained good results as shown in the following examples.

FIG. 1 shows a method for manufacturing a copper amalgam electrode.

First, as shown in FIG. 1 (5), a copper enamelled wire 1 whose tip has been polished in advance is inserted into a glass tube with a thin tip and fixed with an epoxy resin 3. After the resin has hardened, as shown in FIG. 1(B), the @ wire 4 portion at the tip is immersed in mercury 5 in dilute hydrochloric acid 6 to fully coat the surface with mercury. Finally, thoroughly wash the electrode tip shown in Figure 1 (C) with water. Note that 7 is an amalgam layer.

Figure 2 shows a system diagram of the polarographic measurement used in this experiment. Measurements were performed using a three-electrode blade method to improve accuracy. A saturated calomel electrode (scE) and a platinum coil were used as the reference electrode 10 and the counter electrode 9, respectively, and a copper amalgam electrode prepared as shown in FIG. 1 was used as the working electrode 8. A commercially available device can be used as the polarographic analyzer 13. In addition, in the box 2 diagram, 11 is a nitrogen gas blowing pipe, 12 is an electrolytic solution, and 14 is a recorder.

The present inventors investigated the measurement conditions shown in equation (1) above, and found that the concentration of hydrochloric acid was in the range of 10-4 to 0.1M, and UO, was in the range of 0.02 to 0.1mM. Although we have determined that it is possible to measure within the range, the optimal condition is (1) above.
As reported for the formula, hydrochloric acid was 0.01 M1F 00 and 0.2 mM. Therefore, all measurement solutions were 0.01 M Oct, 0.2 mM UO2
It is an aqueous solution containing.

Measurements were performed at room temperature (25-26'O), and dissolved oxygen was removed with nitrogen gas as necessary.

Example 1 Figure 3 shows the reduction wave of nitrate ions measured by DC polarography under the above conditions. Characteristic line 15 is the current-lightning 1st curve when nitrate ions are not present, and UO2 (71
) R liquid emitting car 1. OVvs, SCE lc current t1. Tiru. Characteristic line 16 is a d current-potential curve when nitrate ion is adjusted to 0.1 mM. These curves are exactly the same as when using a dropping mercury electrode.

FIG. 4 is a graph in which the diffusion current value obtained from the reduction wave is plotted against the concentration while changing the nitrate ion concentration.

Nitrate ion concentration 0.05mM (0.31mgNO,/
dL ) to 0.8 mM (5 mg NO,/dt
), a good linear relationship is obtained. Furthermore, in a low concentration region, sensitivity can be improved by increasing the potential sweep speed. UO to use
:”The ion can be prepared from uranyl acetate and uranyl chloride.

Example 2 The results of measuring a differential pulse polarogram using the DC polarography method and the same solution conditions are shown in FIG. In FIG. 5, a characteristic line 17 is a current-potential curve in the absence of nitrate ions, and a characteristic line 18 is a current-potential curve when nitrate ions are present at 0.2mM.
This is a current-potential curve when adjusted to . The reduction peak of nitrate ions appears at -1,03 Vvs, almost overlapping with the reduction peak of uranyl ions in SCE. This peak current value depends on the concentration of nitrate ions QjmM~1. A good relationship is shown in QmM. The feature of this method is that (]) the current value is peak-shaped and the power gills are 9. -1,2Vv, S It is easy to distinguish from hydrogen waves rising from around CE, (2
) Because the peak potential that gives the peak 1F current takes a value close to the half-wave potential of the DC polarogram or pulsed polarogram, it is important to understand the shift of the reduction wave.

In the above two examples, measurements were performed by replacing and removing dissolved oxygen in the solution with nitrogen gas, but good results were obtained even in the state where oxygen was dissolved. That is, the diffusion W of the DC polarogram, the current value, and the peak of the differential pulse polarogram +1? Similarly to the de-dredging state, it was found that in the stream f1, there was a lot of waste that had a relationship between the nitrate ion concentration and the straight culm'-1.

According to the invention, the working electrode is preferably a drop of mercury.

Instead of poles, copper amalgam progressive poles are used to define the polarogram of nitrate ions, resulting in the following effects.

(1) Electrode reactions, aerial and polar jumps can be handled in the same way as on a dropping mercury electrode.

(2) Unlike general metal electrodes (for example, platinum), hydrogen overpressure is large even in acidic solutions. Therefore, j′T! over a wide potential range! Can emit original waves.

(3) Unlike a dropping mercury electrode, since it is a static IF lightning electrode, the sensitivity of the flow value can be improved by increasing the potential sweep speed.

(4) The amount of mercury used is very small compared to the dripping mercury 1h electrode, making it easier to handle.

(5) Since copper enamel 8Jp is used in the present invention, the N electrode can be manufactured easily and at low cost.

(6) Since the reduction 1 position of coexisting ions is generally different from that of nitrate ions, the reduction current of only nitrate ions can be measured.

The present invention can also be applied to quantifying nitrite ions, iodate ions, etc. in addition to nitrate ions. In addition to uranyl ions, La and Ce can also be used widely as working electrodes for portammetry.

[Brief explanation of the drawing]

FIG. 1 shows the structure 1 used in the embodiment of the present invention. FIG. 2 is a schematic diagram of polarographic measurement, FIG. 3 is a portammogram of nitrate ions using the copper amalgam electrode of the embodiment of the present invention, and FIG. A diffusion current-nitrate ion concentration characteristic diagram showing the effect of the implementation, and FIG. 5 is a differential pulse polarogram of nitrate ions showing an example of the present invention. 1... Copper enamelled wire, 5... Mercury, 7... Amalgam layer, 8... Copper amulgam electrode, ]2...'r4
i solution, 13...polarographic analyzer. (A
(B)
(C gloss 1 flash/, d'f2(3) E/v vs3cE age 30 0 0, f θ, 2 θ, 3 0.4
υ, 50 stones 0.8CtJINOs3 / 777
M age 4 (3) 9QA E/V vs, 5CE 'f', ff diagram

Claims (1)

[Scope of Claims] 1) A method for quantifying nitrate ions, which comprises quantifying nitrate ions in a sample by amperometric method using a copper amalgam electrode as a working electrode in the presence of a predetermined concentration of hydrochloric acid and uranyl ions. 2. In the method for determining nitrate ions as set forth in claim 1, the hydrochloric acid concentration of the electrolyte is 10-4 to 0.1M. The concentration of uranyl ions is between 0.02 and 1. QrrillJ
A method for quantifying nitrate ions characterized by a concentration range of . 3) A method for quantifying nitrate ions according to claim 1 or 2, characterized in that uranyl ions are prepared from uranyl chloride or uranyl acetate. 4) A method for determining nitrate ions according to any one of claims 1 to 3, characterized in that the amperometric method is carried out by direct current polarography or differential pulse polarography. 5) Claims 1 to 4) I'L,
2. The method for quantifying nitrate ions described in claim 1, wherein the copper amalgam electrode is prepared using mercury.