JPS6243134B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the concentration of a component to be measured contained in a gas phase, and more specifically to a method for measuring the concentration of a component to be measured contained in a gas phase. Concerning gas analysis methods.

Conventionally, the following method has been used to detect and quantify components contained in gas by electrochemical means.

(a) Constant potential electrolysis method. This is a method in which gas is electrolyzed directly or after being dissolved in a liquid on an electrode held at a constant potential.

In this method, the selectivity of gas detection is provided by the catalytic action of the electrodes, the activation overpotential of the contained components with respect to the electrodes, and the permselectivity of the gas components with respect to certain porous membranes; This is only a slight improvement in the sensitivity of the detector, and does not, in principle, impart selectivity to the detector.

Therefore, even if the electrode potential is set to a certain value, components that interfere with the analysis must be removed before the sample gas is introduced to the detector.

(b) Solution conductivity method. In this method, the target component to be analyzed is dissolved in a solution, and the concentration is determined from changes in the conductivity of the solution using the AC bridge method or the like.

However, in principle, all gas components that dissolve and become ionized are detected, so the selectivity is poor and its applications are limited.

(c) Iodometry etc. This is a method in which a sample gas and a redox substance are brought into contact, and the generated oxidized or reduced redox substance is quantified using a galvanic cell or the like to measure the gas concentration.

Therefore, the presence of more powerful oxidizing or reducing substances becomes a direct interfering component.

(d) A method using semiconductor sensors, etc. This is a method of determining gas concentration by detecting changes in conductivity caused by gas adsorption on a semiconductor sensor.
Gas adsorption is physical adsorption and has poor selectivity, making it difficult to create a detector with chemical selectivity.

As mentioned above, all of the conventional methods (a) to (d) have problems with selectivity, and the number of detectors increases as the types of components to be analyzed increase.

This is due to the fact that the conventional methods are a so-called static constant potential electrolysis method and a gas analysis method using a specific redox substance.

The present invention aims to eliminate these drawbacks, and provides a so-called dynamic gas analysis method that significantly improves detection selectivity and at the same time allows measurement of multiple components with one detector. We aim to provide the following.

In order to achieve such an object, the present invention uses a stationary system with a liquid phase and an electrode, applies a voltage to the stationary electrode by a potential sweep method, and processes the electrolytic current value from the electrode at this time. Wave height based on the measured component in the obtained voltamgram,
Alternatively, the concentration of the component to be measured in the gas phase is measured by measuring the Peter area.

Embodiments of the present invention will be described below based on the drawings.

The analyzer used in the present invention is shown, for example, in the system diagram shown in FIG. 1, and its main parts are an absorption liquid 2,
a detection unit consisting of a detection electrode 1, a counter electrode 4, etc.; a constant potential electrolysis device 9 that applies and sweeps a DC voltage and an AC wave superimposed thereon, a pulse, etc., detects a current flowing through the electrode, and outputs it; polarograph 8
It is composed of a voltam graph section consisting of a voltamic graph section, etc., and a data processing section consisting of a voltamic graph control and data processing device 10, a printer 11, etc. that further processes the output data, displays the concentration of the component to be analyzed, and controls the voltamgraph section. has been done.

To measure the concentration of a component to be measured in the gas phase using such an analyzer, a sample gas is supplied to the absorption liquid 2, and the component to be measured in the sample gas is dissolved, emulsified, or After phase shifting by suspension or the like, a voltage is repeatedly applied to the detection electrode 1, which is considered to be a stationary system, by a potential sweep method.

That is, the voltage applied to the electrodes, that is, the electrode potential, is repeatedly swept within a certain range.

Simultaneously with this potential sweep, the value of the electrolytic current in the detection electrode 1 is data-processed by the voltamgraph control and data processing device 10 to obtain the wave height or peak area corresponding to the component to be analyzed.

On the other hand, using a standard gas with a known concentration of the component to be measured, a voltamgram is obtained in advance by the same method as above, and the relationship between the concentration of the component to be measured and the wave height of the voltamgram, or the concentration of the component to be measured is known. The relationship between
Store it in memory.

Next, by comparing the wave height or area of the voltamgram of the component to be measured with unknown concentration with the value determined from the standard gas, the concentration of the component to be measured in the sample gas can be determined.

Here, the application of voltage by the potential sweep method, which is one of the characteristics of the method of the present invention, is performed by moving the detection electrode 1 to a differential pulse polarograph 8 as shown in FIG.
A pulse is applied to the detection electrode 1 under external control by the voltamgraph control and data processing device 10, and the differential pulse method is used to calculate the difference between the electrolytic current immediately before the pulse is applied and the electrolytic current after the pulse is applied. However, the method is not limited to this method, and the method is not limited to this method. Depending on the type of component to be measured, a DC method in which only a DC triangular wave is applied as the applied waveform when applying a voltage, and an AC method in which AC is superimposed on a DC triangular wave. An alternating current method in which a rectangular wave is superimposed on a direct current triangular wave, or a rectangular wave method in which a rectangular wave is superimposed on a direct current triangular wave, etc. can be used as appropriate.

The range of the voltage applied by the potential sweep method can be selected depending on the type of voltage application method described above and the type of component to be measured. The applied voltage range when measuring the component is the reference electrode (saturated Amane electrode).
The potential is usually in the range of -0.3V to -1.1V.

Furthermore, in general, in the case of voltammetry, in order to obtain stationary or quasi-stationary data, a so-called hydraulic electrode system such as a rotating electrode or a dropping mercury electrode is used to create a diffusion layer of the electrolyte at the electrode-solution interface. The conventional method is to stabilize the thickness of the material.

However, in the method of the present invention, like the conventional constant potential electrolysis method, a static system is used without taking any measures to stabilize the thickness of the diffusion layer of the substance to be electrolyzed.

For this reason, on the one hand, the detection section is easily affected by external vibrations, etc., but by using the voltamgraph control and data processing device 10, the electrolytic current value is data processed as described below to adjust the data variation. There is.

That is, data processing in the method of the present invention is normally performed by three methods: (a) removal of abnormal data, (b) smoothing processing, and (c) cumulative averaging processing.

(a) is to remove values that have an abnormally large difference from the previous data when potential sweeps are repeated;
Normally, this process eliminates data with a difference of 50% or more.

(B) is a smoothing process using a weighted moving average that takes 11 points, for example, and can also be performed in combination with (B).

(C) is a process of integrating and averaging every four sweeps, and can also be performed in combination with (B).

All types of data processing (a) to (c) may be used in response to noise generation in the voltamgram caused by the environment at the time of measurement.If the measurement environment is good and there is little noise generation, (a) and (b) are omitted and (c)
It is also possible to perform only a single process.

Furthermore, if there is almost no noise, (c)
In the integrated averaging process, it is possible to obtain a sufficiently satisfactory measured value by just averaging two potential sweeps before and after.

The absorption liquid 2 can be selected as appropriate depending on the type of the component to be measured in the sample gas, and either dissolves the component to be measured or creates a chemical bond between the component to be measured and the component of the absorption liquid 2. For example, the component to be measured can be phase-shifted into the absorption liquid 2 by forming a complex, or the component to be measured can be emulsified or suspended.

Furthermore, the component to be measured can be anything contained in the gas phase, but it is usually sulfur oxides, nitrogen oxides, or hydrogen sulfide, and the measurable lower limit is the gas phase. The content of the component to be measured in the phase is usually at the level of several ppm.

As mentioned above, the method of the present invention is a dynamic method in which a potential is applied to a stationary electrode using a potential sweep method, so it has various advantages that are different from static measurement methods such as potentiostatic electrolysis. The effect is produced.

First, the accuracy of analysis can be improved by repeatedly performing potential sweeps to obtain a plurality of data, and subjecting this data to smoothing processing and/or cumulative averaging processing, for example.

In particular, if microcomputers, which have been significantly developed in recent years, are used, digital processing of data is easy, and the improvement of analysis accuracy is further promoted.

Further, the method of the present invention is a gas analysis method that incorporates a voltammetric technique. In addition, it is possible to improve the detection sensitivity of signals caused by the target component of analysis in data obtained using DC voltammetry, alternating current, square wave, differential pulse voltammetry, etc. It is possible to improve the mutual separability of signals corresponding to .

Furthermore, in the conventional constant potential electrolysis method, strongly oxidizing or strongly reducing coexisting substances, which cannot be separated in principle and are interfering components, can be separated from the analyte by considering the composition of the absorption liquid. It is possible to separate these components, and also to measure the concentration of such coexisting interfering components.

Furthermore, although the electrochemical gas analysis method is generally inferior in selectivity and stability to other methods, such as optical methods, it has been considered advantageous that the equipment cost is low.

In the method of the present invention, the power supply, current detection, and data processing section are more complicated than in the conventional electrochemical analysis method, and the price inevitably increases accordingly.
Recent developments in electronic equipment have more than compensated for the rise in equipment prices, and it remains advantageous over other analytical methods both overall and in terms of price.

Moreover, the selectivity and stability were also significantly improved as mentioned above.

Additionally, the method of the present invention is no different from the conventional constant potential electrolysis method in that it uses a stationary liquid and a stationary electrode.

Therefore, even though analytical accuracy and separation performance have improved, the operation is hardly complicated.

Next, examples of the present invention will be described.

Example 1 Nitrogen oxides and sulfur dioxide in a sample gas were detected using the system diagram shown in FIG.

For the absorption liquid 2, a phosphoric acid/sodium phosphate buffer solution with a pH of 2 containing a 0.01 moldm ^-3 iron ethylenediaminetetraacetic acid complex was used, and for the detection electrode 1, mercury was used.

On the counter electrode side, a platinum wire was used as the counter electrode 4, a phosphoric acid/sodium phosphate buffer solution with a pH of 2 was used as the counter electrode solution 5, and the counter electrode solution and the absorption solution were separated by a diaphragm 6 made of a cation exchange membrane.

By the way, the iron ethylenediaminetetraacetic acid complex absorbs nitrogen monoxide well in the ferrous state to form a nitrosyl complex.

This nitrosyl complex is decomposed at the detection electrode 1, and a signal based on nitrogen oxides in the sample gas is obtained in the voltamgram.

However, the ferrous ethylenediaminetetraacetic acid complex is oxidized by oxidizing substances such as oxygen and nitrogen dioxide coexisting in the sample gas, and a ferric ethylenediaminetetraacetic acid complex that does not absorb nitrogen monoxide is generated.

Therefore, the ferric complex was reduced to a ferrous complex using the mercury pool electrode 12.

The potential of the detection electrode 1 and the mercury pool electrode 12 was regulated by the reference electrode 7, which was a saturated mercury electrode.

Further, the mercury pool electrode 12 was set to -0.9V saturation electrode reference by the constant potential electrolyzer 9.

The detection electrode 1 was connected to a differential pulse polarograph 8, and a potential sweep was repeated from −0.3 V to −1.1 V versus the saturated Gampa electrode reference.

The measurement conditions of the differential pulse polarograph 8 are as follows.

Measurement conditions: 3-electrode differential pulse voltammetry Potential sweep: -0.3V held for 5 seconds, then 20mVsec ^-1
It was swept to the cathode at -1.1V and returned to -0.3V.

Pulse width 100 msec, pulse height 5 mV Current measurement time 20 msec (current measurement time before and after pulse application) Current measurement interval 40 msec (current measurement interval before and after pulse application) Pulse interval 0.5 sec (from pulse application to next pulse application) The potential sweep of the differential pulse voltamgraph 8 was controlled by the microcomputer of the voltamgraph control and data processing device 10.

First of all, standard gas cylinder 1 is used as standard gas.
3 to 446ppm nitrogen monoxide, sulfur dioxide
Using 662ppm nitrogen balance gas, each
The gas was introduced into the absorption liquid 2 through the gas flow line 14 and the three-way valve 15 at a flow rate of 50 ml min ^-1 , and the constant potential electrolyzer 9 and voltamgraph 8 were operated to perform measurements. This operation is a calibration of the device with standard gases.

This operation was continued for about 10 minutes, and after digitizing the voltamgrams obtained for each sweep, the following data processing was performed.

(b) Data processing in one potential sweep.

(A-1) Compare the data sampled before and the data sampled at the current time during one sweep, and if the values differ by 50% or more, the current data is rejected and the data sampled at that point is I took steps to input the previous data as is.

(A-2) After the processing in (A-1), a smoothing process using a weighted moving average taking 11 points was performed.

(b) Data processing in repeated potential sweeps.

(Ro-1) Compare the data of the same electrode potential among the data of the previous potential sweep, and
Data with a difference of more than % was removed, and the data of the same potential from the previous sweep was inserted as is.

(Ro-2) After performing the processing in (a), then (b) after performing the processing in (ro-1), an integrated averaging process is performed every four sweeps to create a smooth image with noise removed. Obtained the voltamgram.

These four types of data processing from (A-1) to (RO-2) remove abnormal data caused by noise, etc., and eliminate measurement variations.
When the environment at the time of measurement is good and there is almost no large noise, satisfactory results were obtained by performing only the cumulative averaging process (Rho-2) for the two previous and subsequent potential sweeps.

The wave height based on sulfur dioxide and nitrogen oxide was measured from this voltamgram, and the relationship between the gas concentration and the wave height was stored in the data processing device 10.

Next, the delivery of the standard gas was stopped, and 100ml of a separately prepared mixed sample gas of air, sulfur dioxide, and nitrogen oxide was delivered to the detection unit using the air pump 16.
It was introduced at a flow rate of min ^-1 . Electrolytic detection and data processing were performed in the same manner as in the standard gas calibration.

The peak heights based on the obtained sulfur dioxide and nitrogen oxide were measured, and the concentrations of sulfur dioxide and nitrogen monoxide were determined from the relationship between the wave height and the concentration measured during the calibration.

As a result, the obtained value matched the concentration determined from the dilution ratio during sample gas preparation.

Furthermore, in the above experiment, the concentrations of sulfur dioxide and nitrogen monoxide in the sample gas were determined by measuring the area of the peak instead of measuring the height of the peak.

The results were as good as the wave height measurements.

Note that FIG. 3 shows an example of the voltamgram of the sample gas when no data processing is performed.

In this figure, the peak seen from −0.5V to −0.6V is sulfite, the peak around −0.9V is the nitrosyl complex, and the rise around −1.0V is due to hydrogen generation. Noise can be seen in between.

However, this noise could also be removed by the data processing described above.

Example 2 The same apparatus as in Example 1 was used, except that the detection electrode 1 was lead and the absorption liquid 2 was a phosphoric acid-sodium phosphate buffer solution with a pH of 2 that did not contain iron ethylenediaminetetraacetic acid. Detection of sulfur dioxide in sulfur mixed gas (sulfur dioxide concentration known),
Quantification was performed.

A nitrogen balun gas containing 662 ppm sulfur dioxide was used as the standard gas.

The data processing method is the same as in Example 1, by removing abnormal data that has a large value with the previous data, smoothing processing, and integrating averaging processing, and determining the sulfur dioxide concentration in the mixed gas from the peak ratio of the voltamogram. Ta.

As a result, the obtained sulfur dioxide concentration is
The concentration agreed with the concentration calculated from the sulfur dioxide mixing ratio.

Example 3 Using the detector shown in FIG. 2, a potential sweep was performed using the same mixed gas of air, sulfur dioxide, and nitrogen monoxide as in Example 1, and the state of the voltamgram obtained was observed.

In this detector, as in Example 1, the detection electrode 1
Mercury was used as the material, and a phosphoric acid-sodium phosphate buffer solution of pH 2 containing iron ethylenediaminetetraacetic acid was used as the absorption liquid 2.

However, for the counter electrode side, potassium iodide was dissolved in a phosphoric acid-sodium phosphate buffer solution to prepare the counter electrode solution 5.
A silver-silver iodide electrode was made by inserting silver nets 4 and 7 into this, and the counter electrode 4 and the reference electrode 7 functioned simultaneously.

A cation exchange membrane was used as a diaphragm 6 between the detection electrode 1 and the detection electrode 1 .

Further, the gas phase containing the sample gas and the liquid phase of the absorption liquid were separated by a gas permeable porous membrane 17.

FIG. 4A shows an example of a voltamgram before data processing obtained by just one sweep.

The sulfite peak seen from 0.0V to -0.2V and the nitrosyl complex peak seen from -0.3V to -0.6V both have their apexes split into two, making it difficult to measure the wave height as is. By carrying out an integrated averaging process in which sweeps are repeated 10 times, the voltamgram in FIG. 4A becomes a smooth curve as shown in FIG. 4B.

If the detector is kept stable, only 1
Since the noise is greatly reduced even in the voltamgram obtained by sweeping twice,
Alternatively, a smooth voltamgram could be obtained by simply performing smoothing processing using a simple moving average with only one sweep.

In addition, when data processing was performed, there were variations in the data before and after.

Next, we considered the case of using only a standard gas that does not contain any oxygen, but it was relatively easy to maintain the detector in a stable state.

Figure 5 shows the results when the standard gases of sulfur dioxide and nitrogen monoxide were mixed.

The dot-dash line in Figure 5 indicates the first 10 minutes after standard gas ventilation.
The solid line is the voltamgram of the second to fifth sweeps.

From this, it can be understood that a sufficiently steady voltamgram can be obtained after the second sweep.

Example 4 Using the same detector and mixed gas as in Example 3, voltage was applied using the direct current method, alternating current method, square wave method, and differential pulse method, and the voltamgram was observed using the potential sweep method. .

Good signals for sulfite and nitrosyl complexes were obtained using both methods, except that the direct current method had difficulty in separating the waves related to nitrosyl complexes and hydrogen generation.

[Brief explanation of the drawing]

Figure 1 is a system diagram of the measuring device used in the present invention, Figure 2 is a schematic diagram of its detector, and Figures 3, 4, and 5 are all images observed using the method of the present invention. It is a figure showing an example of a voltamgram. DESCRIPTION OF SYMBOLS 1...Detection electrode, 2...Absorption liquid, 3...Sample gas, 4...Counter electrode, 7...Reference electrode, 8...Differential pulse polarograph, 10...Voltangram control and data processing device.

Claims (1)

[Claims] 1. A gas analysis method in which a gas phase containing a component to be measured is brought into contact with a liquid phase, and the component to be measured whose phase has shifted into the liquid phase is electrolytically detected and quantified by an electrode in direct contact with the liquid phase, The liquid phase and the electrodes are set as a static system, and a voltage within the applied voltage range is repeatedly applied to the electrodes, and the electrolytic current value from the electrodes is smoothed and/or integrated and averaged. Measuring the concentration of a component to be measured contained in a gas phase, characterized in that the concentration of the component to be measured in the gas phase is measured by measuring a wave height or a peak area based on the component to be measured in a voltamgram. Method.