CN103698288A - Method for performing complexometric titration on magnesium ions - Google Patents
Method for performing complexometric titration on magnesium ions Download PDFInfo
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- CN103698288A CN103698288A CN201310739531.8A CN201310739531A CN103698288A CN 103698288 A CN103698288 A CN 103698288A CN 201310739531 A CN201310739531 A CN 201310739531A CN 103698288 A CN103698288 A CN 103698288A
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Abstract
The invention relates to the technical field of analytical chemistry and in particular discloses a method for performing complexometric titration on magnesium ions. Chrome black T serves as an indicator, and magnesium of a solution is titrated by using ethylene diamine tetraacetic acid (EDTA). The method is characterized in that the solution comprises magnesium ions and sodium ions; an ammonia buffer solution with the pH value being 10 and a masking agent are added into the solution before titration; the masking agent is mixed alcohol, hydroxylamine hydrochloride or a mixture of triethanolamine and mixed alcohol; the mixed alcohol is a normal butanol/ethanol mixture with the volume ratio of 1:(1-4); the maximal absorption wavelength of the titration end-point solution is close to blank reference wavelength. According to the method provided by the invention, interference of the sodium ions of the mixed solution can be effectively eliminated, accurate titration of the magnesium ions is realized and the average relative error can maintain below 1%. In the method provided by the invention, the titration end point is easy to judge.
Description
Technical field
The present invention relates to technical field of analytical chemistry, be specifically related to a kind ofly in complexometry magnesium ion process, eliminate the method for sodion impact.
Background technology
China's salt lake resources is abundant, the most representative with the salt lake resources in Qinghai, contains the elements such as a large amount of K, Mg, Na, Li, B in salt lake.Qinghai Salt Lake magnesium resource mainly comprises magnesium chloride and magnesium sulfate, and 4.18 * 1016 tons of available reservess (magnesium chloride and magnesium sulfate add up to), are the valuable sources of preparing chemical industry of inorganic salt product.
Take in the chemical products production run that salt lake bittern is raw material, Mg
2+, Ca
2+content analysis is an important step.The general method adopting is compleximetry at present, also has in addition spectrophotometric method, the chromatography of ions, atomic absorption method, ICP-OES method and spectrum of laser plasma method etc.ICP-OES method and the chromatography of ions are all applicable to the mensuration of trace, constant calcium, magnesium ion in water sample, but the chromatography of ions exists longer problem of analytical test cycle, simultaneously having relatively high expectations to solution purity.Atomic absorption method once can only measure an element and the range of linearity narrow, it is comparatively serious that matrix disturbs.In laboratory, for the magnesium in salt lake bittern, the mensuration of the magnesium in ore, calcium etc. adopts the method for complexometry more.In GB/T6730.13-2007, be also to adopt the method for EDTA complexometry to measure calcium and the magnesium in native iron ore, iron ore concentrate, sintering deposit and pellet.
Under physical condition, many and other metallic ion of magnesium ion coexists, and the metallic ion coexisting often can be to a certain extent and EDTA complexing.In the system coexisting at sodion and magnesium ion, particularly sodion is a large amount of exist in the situation that, sodion and EDTA complexing agent touch opportunity in solution are many, also can produce unsettled complexing, can have influence on to a certain extent the complexing of magnesium ion and EDTA.Therefore when sodium chloride exists, in the situation that particularly Na ion concentration is higher, during complexometry magnesium ion, sodium chloride needs to eliminate to the interference of titration.
Summary of the invention
The present invention is intended to eliminate the impact of sodion in complexometry magnesium ion process, and a kind of complex titration analysis method of magnesium ion more is accurately provided.
Technical scheme of the present invention comprises a kind of method of complexometry magnesium ion, take eriochrome black T as indicator, uses EDTA titration to comprise the magnesium in solution, and wherein said solution comprises magnesium ion and sodion; At solution described in titration forward direction, adding pH is 10 ammonia buffer and screening agent, described screening agent is mixed alcohol, oxammonium hydrochloride, triethanolamine, or their potpourri, described mixed alcohol is that volume ratio is 1:(1-4) normal butyl alcohol/alcohol mixture, and the maximum absorption wavelength of titration end-point solution is near blank reference wavelength.
Preferably, the maximum absorption wavelength of titration end-point solution is 627 ± 4nm.
In some embodiment, the sodium in described solution: magnesium mass ratio is less than or equal to 200:1.
In some embodiment, use mixed alcohol as screening agent, and described in every 10mL, solution is used the mixed alcohol below 20mL.
For example, the sodium in described solution: magnesium mass ratio is (0-50): in the time of 1, solution is used mixed alcohol below 5mL as screening agent described in every 10mL; Sodium in described solution: magnesium mass ratio is (50-100): in the time of 1, solution is used 5 to 10mL mixed alcohol as screening agent described in every 10mL; Sodium in described solution: magnesium mass ratio is (100-150): in the time of 1, solution is used 10 to 15mL mixed alcohol as screening agent described in every 10mL; Sodium in described solution: magnesium mass ratio is (150-200): in the time of 1, solution is used 15 to 20mL mixed alcohol as screening agent described in every 10mL.
In some embodiment, the sodium in described solution: magnesium mass ratio is (0-100): in the time of 1, use oxammonium hydrochloride as screening agent, and described in every 10mL, solution is used the oxammonium hydrochloride below 0.2g.
For example, the sodium in described solution: magnesium mass ratio is (0-50): in the time of 1, solution is used oxammonium hydrochloride below 0.1g as screening agent described in every 10mL; Sodium in described solution: magnesium mass ratio is (50-100): in the time of 1, solution is used 0.1 to 0.2g oxammonium hydrochloride as screening agent described in every 10mL.
In some embodiment, use the potpourri of triethanolamine and mixed alcohol as screening agent, in described potpourri, the volume ratio of mixed alcohol and triethanolamine is (3-1): 1.
For example, the sodium in described solution: magnesium mass ratio is (50-200): in the time of 1, solution is used potpourri below 5mL as screening agent described in every 10mL.
The average relative error of method of the present invention is below 1%.
Method of the present invention combines complexometry technology with spectral analysis technique, by selecting suitable screening agent according to the relative content of sodium ion in liquor, effectively got rid of the interference of the sodion that coexists, and has reduced analytical error.And compared with prior art, titration end-point more easily judges.
Accompanying drawing explanation
Fig. 1 is the volume diagram of the required EDTA of complexometry magnesium ion under the condition that exists of sodion.
Fig. 2 is the spectral scan curve of embodiment 1.
Fig. 3 is the spectral scan curve of embodiment 2.
Fig. 4 is the spectral scan curve of embodiment 3.
Embodiment
In the solution that magnesium ion and finite concentration sodion coexist, during with EDTA complexometry magnesium ion, the existence meeting of sodion produces certain impact to analyzing.Usually, Na ion concentration is higher, affects larger.And when Na ion concentration is higher, if do not add screening agent, directly do not carry out titrimetry, and the titration end-point of magnesium ion obviously lags behind, and the difficult judgement of terminal, and there is obvious positive error in titration results.Therefore, on magnesium ion, complexometry has larger impact in the existence of sodion.
With reference to figure 1, be illustrated in while there is sodion the volume of the required EDTA of complexometry magnesium ion.As seen from the figure, do not add the magnesium in screening agent titration magnesium sodion mixed solution, have larger analytical error in the process of titration, this is also the basic reason that the inventive method is set up.
Method of the present invention combines complexometry and UV-VIS spectrophotometry, in the process of complexometry magnesium ion, add appropriate screening agent, then carry out the analysis of titration results, when sodium magnesium mass ratio is within the specific limits time, the masking effect of screening agent is better, can eliminate the impact of sodion on titration process.
In the method for complexometry magnesium ion, conventionally use eriochrome black T as indicator, using EDTA as complexing agent, carry out titration, and generally also can to add pH be 10 ammonia buffer.
Method of the present invention comprises magnesium ion, both situations of sodion mainly for solution simultaneously.In order to reduce the interference of sodion, before titration, also to solution, add suitable screening agent, and the maximum absorption wavelength of controlling titration end-point solution is near blank reference wavelength.And the maximum absorption wavelength of titration end-point solution is near blank reference wavelength.
Blank reference wavelength refers to: when not having sodion to disturb, adopt the magnesium ion in same procedure volumetric soiutions, the titration end-point solution maximum absorption wavelength λ measuring
0.Its measuring method can be as follows: accurately pipette the magnesium chloride solution of certain volume and concentration in conical flask, the ammonia buffer that adds pH=10, take eriochrome black T as indicator, with EDTA, carry out titration, the winestone redness of solution before titration becomes the Celeste of titration end-point; Titration end-point solution is carried out to spectral scan in visible region, the maximum absorption wavelength λ of solution while determining titration end-point
0.
In method of the present invention, measuring blank reference wavelength is 627nm, and the maximum absorption wavelength of preferably controlling titration end-point solution is 627 ± 4nm.
Screening agent can be mixed alcohol, oxammonium hydrochloride, triethanolamine, or their potpourri.Here, mixed alcohol is that volume ratio is 1:(1-4) normal butyl alcohol/alcohol mixture.
Below with the standard solution configuration sodium magnesium ion mixed solution of concentration known, and carry out titration according to method of the present invention, so that feature of the present invention, advantage are more clear.
Concrete operations are: accurately pipette the magnesium chloride of certain volume and concentration and the mixed solution of different Na ion concentrations in conical flask, the ammonia buffer that adds 10mL pH=10, take eriochrome black T as indicator, and add respectively different volumes, different types of screening agent, with EDTA, carry out respectively titration; Titration end-point solution is carried out respectively to spectral scan, the absorbing wavelength λ of solution while determining titration end-point in visible region
1, and and λ
0compare, with both degrees of closeness of degree of closeness judgement titration end-point, control λ
1at λ
0near.(preferably control λ
1=627 ± 4nm).
Through experiment, find, when in 10mL solution, sodium magnesium mass ratio is less than or equal to 200:1, the mixed alcohol below available 20mL is made screening agent; When in solution, sodium magnesium mass ratio is less than or equal to 100:1, the oxammonium hydrochloride below available 0.2g is made screening agent; In solution, sodium magnesium mass ratio is when the scope of 50-200:1, and the mixed alcohol below available 5mL and triethanolamine potpourri are as screening agent, and wherein the volume ratio of mixed alcohol and triethanolamine is (3-1): 1.Particularly,
Use
mixed alcoholmake screening agent, obtain following result:
When mass ratio 0≤Na:Mg≤50:1, add mixed alcohol 0-5mL can reach good masking effect, average relative error≤0.02% of result;
When mass ratio 50:1≤Na:Mg≤100:1, add mixed alcohol 5-10mL can reach good masking effect, average relative error≤0.10% of result;
When mass ratio 100:1≤Na:Mg≤150:1, add mixed alcohol 10-15mL can reach masking effect, average relative error≤0.15%;
When mass ratio 150:1≤Na:Mg≤200:1, add mixed alcohol 15-20mL can reach masking effect, average relative error≤0.85%;
When mass ratio 200:1≤Na:Mg≤250:1, add mixed alcohol 20mL can reach masking effect above, average relative error is between 1.1-2%.
All in all, complexometry magnesium ion when there is sodion, when mass ratio Na:Mg≤150:1, makees screening agent with mixed alcohol, well titrimetry magnesium ion; When sodium magnesium mass ratio is at (150-250): in the time of between 1, mixed alcohol also can play masking action, but analytical error obviously increases.
Visible, when sodium magnesium mass ratio≤200:1, use 0-20mL mixed alcohol to make screening agent, can guarantee that the average relative error of titration is below 1%.
When sodium magnesium mass ratio≤200:1, all can guarantee that the average relative error of titration is below 1%.
Use
oxammonium hydrochlorideas screening agent, obtain following result:
When mass ratio 0≤Na:Mg≤50:1, with 0-0.1g oxammonium hydrochloride, make screening agent, just can play good masking effect, average relative error≤0.02%;
When mass ratio 50:1≤Na:Mg≤100:1, with the oxammonium hydrochloride of 0.1-0.2g, make screening agent, also can play masking effect relatively preferably.But with respect to the solution of low sodium magnesium ratio, average relative error increases, between 0.46%-1%, and along with the increase of sodium magnesium ratio, average relative error obviously increases.
When mass ratio Na:Mg >=150:1, with oxammonium hydrochloride, make screening agent, under the condition existing at sodion, complexometry magnesium ion, there is serious conditions of streaking in the terminal of titration, and this phenomenon becomes further obvious along with the increase of sodium magnesium mass ratio, to analysis, bring obvious positive error.
Visible, when sodium magnesium mass ratio≤200:1, use the oxammonium hydrochloride of 0-0.2g to make screening agent, can guarantee that the average relative error of titration is below 1%
Use separately
triethanolamineas screening agent, obtain following result:
When mass ratio Na:Mg >=50:1, with triethanolamine, make screening agent, complexometry magnesium ion under the condition existing at sodion, titration end-point is difficult for judgement, to analysis, brings obvious positive error, and average relative error surpasses 1%.
Use
the potpourri of mixed alcohol and triethanolamineas screening agent, obtain following result:
When mass ratio is 200:1 >=Na:Mg >=50:1, by mixed alcohol/triethanolamine volume ratio, be (3-1): 1 makees screening agent, can play good masking effect, average error 0.04%.
As fully visible, the sodium of method of the present invention in solution: when magnesium mass ratio is less than or equal to 200:1, can, by selecting suitable screening agent, effectively get rid of the interference of sodion in mixed solution, the accurate titration of realization to magnesium ion, average relative error can remain on below 1%.And in the method for the invention, the judgement of titration end-point is also more easy.
The method of complexometry magnesium ion provided by the invention, mainly utilize complexometry associating UV-VIS spectrophotometry, in the process of titration magnesium ion, add appropriate screening agent, then carry out the analysis of complexometry result, when sodium magnesium mass ratio is within the specific limits time, the masking effect of screening agent is better, can eliminate the impact of sodion on titration process.
Embodiment
Further set forth by the following examples the present invention, these embodiment are only presented for purposes of illustration, do not limit the scope of the invention.Except dated actual conditions, the test method in embodiment is all carried out according to normal condition.
determining of blank wavelength:
Accurately pipette 0.02mol/L magnesium chloride solution 10mL in conical flask, add 10mL ammonia buffer, take eriochrome black T as indicator, with EDTA, carry out titration, the winestone redness of solution before titration becomes the Celeste of titration end-point, this is blank contrast experiment, the solution of titration end-point is carried out to spectral scan in visible region, obtains λ
0(627nm).
embodiment:
Accurately pipette 10mL mixed solution (sodium chloride that comprises 0.02mol/L magnesium chloride and different amounts) in 200mL conical flask.Add 10mL ammonia buffer, take eriochrome black T as indicator, and add suitable screening agent, with EDTA, carry out respectively titration.The solution of titration end-point is carried out spectral scan simultaneously in visible region, obtain maximum absorption wavelength λ
1.Each embodiment all repeats 4 to 5 times, experimental result and blank assay is compared to the average relative error of experiment with computing.
Following table is listed the design parameter of embodiment 1 to 7.
Fig. 2, Fig. 3 and Fig. 4 illustrate respectively the spectral scan curve of embodiment 1, embodiment 2 and embodiment 3.As seen from the figure, use mixed alcohol, oxammonium hydrochloride as screening agent, all obtain good titration results, average error is little, has effectively got rid of the interference of sodion.But use separately triethanolamine, the absorption spectrum of titration end-point solution differs larger with blank to looking for, and titration error is also larger.
The above the specific embodiment of the present invention, does not form limiting the scope of the present invention.Various other corresponding changes and distortion that any technical conceive according to the present invention has been done, all should be included in the protection domain of the claims in the present invention.
Claims (10)
1. a method for complexometry magnesium ion, take eriochrome black T as indicator, uses EDTA titration to comprise the magnesium in solution, it is characterized in that:
Described solution comprises magnesium ion and sodion;
At solution described in titration forward direction, adding pH is 10 ammonia buffer and screening agent, described screening agent is the potpourri of mixed alcohol, oxammonium hydrochloride or triethanolamine and mixed alcohol, described mixed alcohol is that volume ratio is 1:(1-4) normal butyl alcohol/alcohol mixture, and
The maximum absorption wavelength of titration end-point solution is near blank reference wavelength.
2. the method for claim 1, wherein the maximum absorption wavelength of titration end-point solution is 627 ± 4nm.
3. method as claimed in claim 2, wherein, the sodium in described solution: magnesium mass ratio is less than or equal to 200:1.
4. method as claimed in claim 3, wherein, use mixed alcohol as screening agent, and described in every 10mL, solution is used the mixed alcohol below 20mL.
5. method as claimed in claim 4, wherein,
Sodium in described solution: magnesium mass ratio is (0-50): in the time of 1, solution is used mixed alcohol below 5mL as screening agent described in every 10mL;
Sodium in described solution: magnesium mass ratio is (50-100): in the time of 1, solution is used 5 to 10mL mixed alcohol as screening agent described in every 10mL;
Sodium in described solution: magnesium mass ratio is (100-150): in the time of 1, solution is used 10 to 15mL mixed alcohol as screening agent described in every 10mL;
Sodium in described solution: magnesium mass ratio is (150-200): in the time of 1, solution is used 15 to 20mL mixed alcohol as screening agent described in every 10mL.
6. method as claimed in claim 3, wherein, the sodium in described solution: magnesium mass ratio is (0-100): in the time of 1, use oxammonium hydrochloride as screening agent, and described in every 10mL, solution is used the oxammonium hydrochloride below 0.2g.
7. method as claimed in claim 6, wherein,
Sodium in described solution: magnesium mass ratio is (0-50): in the time of 1, solution is used oxammonium hydrochloride below 0.1g as screening agent described in every 10mL;
Sodium in described solution: magnesium mass ratio is (50-100): in the time of 1, solution is used 0.1 to 0.2g oxammonium hydrochloride as screening agent described in every 10mL.
8. the method for claim 1, wherein use the potpourri of triethanolamine and mixed alcohol as screening agent, in described potpourri, the volume ratio of mixed alcohol and triethanolamine is (3-1): 1.
9. method as claimed in claim 8, wherein,
Sodium in described solution: magnesium mass ratio is (50-200): in the time of 1, solution is used potpourri below 5mL as screening agent described in every 10mL.
10. the method as described in claim 1 to 9, wherein, the average relative error of described method is below 1%.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105092572A (en) * | 2015-08-27 | 2015-11-25 | 上海市农业科学院 | Method for detecting magnesium chloride in edible mushrooms |
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Application publication date: 20140402 |