CN103852500A

CN103852500A - Method for measuring pH value of gas in real time by pH electrode

Info

Publication number: CN103852500A
Application number: CN201410023799.6A
Authority: CN
Inventors: 肖丹; 杨钦兰; 郭勇; 朱晓琼
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2014-01-20
Filing date: 2014-01-20
Publication date: 2014-06-11
Anticipated expiration: 2034-01-20
Also published as: CN103852500B

Abstract

The invention discloses a method for measuring the pH value of gas in real time by a pH electrode; the method is suitable for the field of researching the product quality by measuring the pH value of gas. The method comprises the steps of putting the pH electrode into water solution of macromolecule materials such as polyethylene glycol-20000, polyvinyl alcohol and starch as micromolecule materials such as polyethylene glycol-200 and glycerine, and forming a liquid absorption film on the surface of a glass film of the pH electrode; quickly putting the electrode into a circulation tank, feeding the gas to be tested after a system is stable; detecting the change of the pH electrode caused by the gas to measure the pH value of the gas. The method has the advantages that the liquid absorption film arranged on the surface of the glass film of the pH electrode is small in buffer capacity and hardly has interference for the small change of the pH value of the gas, and the water in the liquid absorption film is not easily volatilized, so that the method is beneficial to the stability of the system; due to the structure of the circulation tank, the gas to be tested is fully contacted with the liquid absorption film, so that the pH electrode can make rapid response to the gas; the method is simple, convenient and rapid, and can be used for continuously measuring the pH value of the gas in real time.

Description

A kind of method by pH electrode the real time measure gas pH value

Technical field

The present invention relates to a kind of method by pH electrode the real time measure gas pH value, be applicable to the field of product quality being studied by mensurated gas composition pH value.

Background technology

Research shows, non-neutral gaseous matter is (as SO ₂, CO ₂, HCl, H ₂s, NH ₃deng) existence very large on the potential of hydrogen impact of surrounding environment, the Acidity of Aikalinity of gas has great impact for the quality that is in the product in this environment; Especially HF, SO ₂etc. toxicity and the extremely strong material of corrosivity, very big to harm.In recent decades, the pH of gas as in commercial production for one of important parameter of the control of product and quality evaluation, all obtained paying close attention to widely in a lot of fields.Such as, in the SCR of ammonia/urea process, gas is carried out to pH and measure the concentration that can control ammonia; At tobacco business, the pH of flue gas is measured and can the quality of cigarette be assessed, also can be used for instructing the production of cigarette; Even, in some industry, can judgment device whether break down by detecting acidic and alkaline gas product.

Along with the development of modern science and technology, although various pH sensor new or specific use has obtained research widely, traditional glass electrode is still widely used due to the impact of not oxidated dose, reductive agent and other impurity.At present, with the method for glass electrode mensurated gas composition pH value be mainly first to absorb gas to be measured with solution, the pH value of this solution is measured in vibration after mixing again, the pH value using the pH value of the solution measured as gas.Although this method accuracy and reappearance are all better, pH value that can not the real time measure gas.Aspect the pH of the real time measure gas value, forefathers have also done some related works.1967, Sensarbaugh and Cundiff etc. propose method (the Tob. Sci. 1967 (10): 25-30) of a kind of mensurated gas composition pH, the method is the buffer solution liquid film that is first coated with the uniform pH=7.0 of last layer at pH electrode surface, then by the pH value of this determination of electrode gas.The weak point of the method is that the buffer solution that is coated in pH electrode surface can not extract gas completely, and the subtle change of gas pH is had a certain impact, and electrode has certain equilibration time in addition, so measured pH can not reflect real gas pH value.The defect existing in order to overcome this method, the people such as KLUS have proposed a kind of new method in the flue gas research meeting of CORESTA in 1981, and the method is directly used the pH of pH determination of electrode gas.The method is convenient and swift, is not suitable for the direct mensuration of gaseous substance but weak point is pH meter.1999, Canadian tobacco worker proposed a kind of new method (Health Canada, 1999 of measuring smoke pH, T-113,1-11), the method is wrapped in electrode node with linen thread is with repacking pH electrode, after the pH electrode after repacking soaks in buffer solution for mensurated gas composition pH.The method that the method proposes with Sensarbaugh etc. is very similar, although the buffer solution that has solved to a certain extent pH electrode surface can not extract the problem of gas completely, but operation is comparatively complicated, and still exists damping fluid to have this problem of certain influence to the subtle change of gas pH.Therefore, further set up simple and fast and can be exactly the method for mensurated gas composition pH value in real time, be that we need the further problems of solution, be also a very important problem.

Summary of the invention

Technical matters to be solved by this invention is by a kind of simple, fast method the real time measure gas pH value.

The provided method by pH electrode the real time measure gas pH value is provided in the present invention: first pH electrode is put into the aqueous solution of the small-molecule substances such as macromolecular substances and polyglycol-200, glycerine such as PEG-400, polyvinyl alcohol (PVA), starch, formed one deck absorb liquid film on the glass-film surface of pH electrode; PH electrode put into rapidly to flow cell again and started record data, passing into gas to be measured after stable system, the variation that detects the pH electrode that gas to be measured causes can record the pH value of gas.

The invention has the advantages that: adopt the aqueous solution of the small-molecule substances such as macromolecular substances and polyglycol-200, glycerine such as PEG-400, polyvinyl alcohol (PVA), starch to form and absorb liquid film on the glass-film surface of pH electrode, the buffer capacity of these liquid films is little, the subtle change of interference gas pH hardly, and the moisture in liquid film is not volatile in mensuration process, contribute to the stable of system; The structure of flow cell make the to circulate gas to be measured in pond can fully contact with the absorption liquid film on pH electrode glass film surface, and pH electrode pair gas can be made response fast; Assay method is easy, quick, can be in real time the pH value of mensurated gas composition continuously.

Brief description of the drawings

This instructions comprises following four width accompanying drawings:

Fig. 1 is the schematic diagram of pH electrode mensurated gas composition pH value in flow cell, and in figure, 1 absorbs the pH combination electrode of liquid film for there is one deck on glass-film surface, and 2 is flow cell;

Fig. 2 forms and absorbs liquid film, the signal response schematic diagram while measuring the sample gas that contains carbon dioxide on the glass-film surface of pH electrode with 50% glycerine water solution;

Fig. 3 is that PEG-20000 content is the stability comparison diagram of the absorption liquid film that forms of 0% and 10% aqueous solution;

Fig. 4 is that PEG-20000 content is the response comparison diagram of the absorption liquid film that forms of 0% and 10% aqueous solution to gas;

Fig. 5 forms and absorbs liquid film on the glass-film surface of pH electrode with 10% PEG-20000 aqueous solution, the signal response schematic diagram while measuring the sample gas of a series of different carbon dioxide contents.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in detail.

The present invention by the method for pH electrode the real time measure gas pH value is: first pH electrode is put into 50% glycerine water solution or 10% PEG-20000 aqueous solution, formed one deck absorb liquid film on the glass-film surface of pH electrode; PH electrode put into rapidly to flow cell again and started record data (see figure 1), passing into gas to be measured after stable system, the variation that detects the pH electrode that gas to be measured causes can record the pH value of gas.

Embodiment 1, we form and absorb liquid film on the glass-film surface of pH electrode with 50% glycerine water solution, have measured the pH value of the sample gas that contains carbon dioxide, have obtained the signal response figure of the sample gas of measuring by the method, see Fig. 2.As can be seen from the figure: gas circulates behind pond, electromotive force increases gradually and tends towards stability.Due to the pK of glycerine in water _abe 14.15, in glycerine water solution, glycerine can be counted as buffer components, and glycerine water solution can be regarded HB-B as ^-the buffer system of type, the computing formula of buffer capacity is

, wherein [H ⁺] and [OH ^-] be respectively H in solution ⁺and OH ^-concentration, the total concentration that c is glycerine.The buffer capacity that can calculate 50% glycerine water solution by formula is 1.07 × 10 ^-6molL ^-1pH ^-1, as can be seen here, the buffer capacity of this solution is minimum, hardly the subtle change of interference gas pH.Therefore, can directly judge the variation of gas pH from the variation of electromotive force of measuring, the pH value that can obtain sample gas by calculating is 5.63.

Embodiment 2, in order to describe better the present invention, we form the sample gas that absorbs liquid film, different carbon dioxide contents as gas to be measured as example taking 10% PEG-20000 aqueous solution on the glass-film surface of pH electrode, the present invention will be described in detail, and the content of carbon dioxide obtains by the volume ratio of regulation of carbon dioxide and nitrogen.

In order to set up the method for simple, stable energy the real time measure gas pH value, the present invention has investigated the impact on test system stability and response of absorption liquid film that aqueous solution that intermediate water that PEG-20000 content is 0% and PEG-20000 content are 10% forms on the glass-film surface of pH electrode.In order further to investigate the stability of detection system, the stability of the absorption liquid film that the present invention forms 10% PEG-20000 aqueous solution in flow cell has been carried out statistical study.

In order to keep in each test system the consistance of other location parameters except variable, in described method, the degree of depth that pH electrode is put into flow cell will be consistent.

With reference to Fig. 3, in the situation that other conditions are certain, the intermediate water that we are 0% with PEG-20000 content and 10% PEG-20000 aqueous solution form and absorb liquid film on the glass-film surface of pH electrode respectively, and have tested two kinds and absorb the stability of liquid film in flow cell.As can be seen from the results, the absorption liquid film that 10% PEG-20000 aqueous solution forms is more stable than the absorption liquid film that intermediate water containing PEG-20000 does not form.

With reference to Fig. 4, in the situation that other conditions are certain, the intermediate water that we are 0% with PEG-20000 content and 10% PEG-20000 aqueous solution form and absorb liquid film on the glass-film surface of pH electrode respectively, and have tested two kinds of absorption liquid films response to same sample gas in flow cell.As can be seen from the results, in mensuration process, the absorption liquid film that 10% PEG-20000 aqueous solution forms is more stable than the absorption liquid film that intermediate water containing PEG-20000 does not form, and response is better.

We repeatedly form and absorb liquid film on the glass-film surface of pH electrode by 10% PEG-20000 aqueous solution, have done statistical study to absorbing the stability of liquid film in flow cell.Concrete operations are: pH electrode has formed respectively 10 times and absorbed liquid film in two part of 10% PEG-20000 aqueous solution, and statistics absorbs the initial pH value of liquid film, and statistics is with reference to table 1.As can be seen from the results, the stability that absorbs liquid film is fine, and the initial pH value that absorbs liquid film can be regarded a definite value as.

Table 1 absorbs the statistical study of the initial pH value of liquid film

* u _i=pH _i– pH ₀, pH ₀be the mean value of 20 measured values; PH ₀=7.17, s=0.028,3s=0.084, | u _i| < 3s, s is the standard deviation of 20 determination datas.

Under selected condition, we form and absorb liquid film on the glass-film surface of pH electrode with 10% PEG-20000 aqueous solution, measure the pH value of the sample gas of a series of different carbon dioxide contents, obtained the signal response figure of the sample gas of measuring by the method, seen Fig. 5.As can be seen from the figure: gas circulates behind pond, and electromotive force increases sharply, about two minutes after-potentials are stable gradually.Can be judged the variation of gas pH by the variation of electromotive force, the pH value of gas can be passed through formula

calculate, wherein pH ₀for absorbing the initial pH value of liquid film, Δ E is potential change value.The results are shown in Table 2.

The pH value of the sample gas that table 2 the inventive method records

。

Claims

1. by the method for pH electrode the real time measure gas pH value, it is characterized in that: aqueous solution little, not volatile by buffer capacity, stable chemical nature forms and absorbs liquid film on the glass-film surface of pH electrode.

2. use the method for pH electrode the real time measure gas pH value, it is characterized in that: the absorption liquid film on pH electrode glass film surface is formed by the aqueous solution of the small-molecule substances such as macromolecular substances and polyglycol-200, glycerine such as PEG-400, polyvinyl alcohol (PVA), starch, the buffer capacity of these liquid films is little, the subtle change of interference gas pH hardly, and the moisture in liquid film is not volatile in mensuration process, contribute to the stable of system.

3. the method by pH electrode the real time measure gas pH value as claimed in claim 1 or 2, it is characterized in that: first pH electrode is put into the aqueous solution of the small-molecule substances such as macromolecular substances and polyglycol-200, glycerine such as PEG-400, polyvinyl alcohol (PVA), starch, formed one deck on the glass-film surface of pH electrode and absorb liquid film; PH electrode put into rapidly to flow cell again and started record data, passing into gas to be measured after stable system, the variation that detects the pH electrode that gas to be measured causes can record the pH value of gas.

4. the method by pH electrode the real time measure gas pH value as claimed in claim 3, it is characterized in that: the structure of described flow cell make the to circulate gas to be measured in pond can fully contact with the absorption liquid film on pH electrode glass film surface, and pH electrode pair gas can be made response fast.