CN109406612B - Electrolyte solution for detecting hexavalent chromium by using mercury membrane electrode and hexavalent chromium detection method thereof - Google Patents
Electrolyte solution for detecting hexavalent chromium by using mercury membrane electrode and hexavalent chromium detection method thereof Download PDFInfo
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- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 title claims abstract description 80
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 title claims abstract description 53
- 229910052753 mercury Inorganic materials 0.000 title claims abstract description 53
- 239000008151 electrolyte solution Substances 0.000 title claims abstract description 45
- 239000012528 membrane Substances 0.000 title claims abstract description 21
- 238000001514 detection method Methods 0.000 title abstract description 15
- 239000000243 solution Substances 0.000 claims abstract description 79
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims abstract description 28
- 238000000034 method Methods 0.000 claims abstract description 27
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims abstract description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 22
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims abstract description 20
- 229910001385 heavy metal Inorganic materials 0.000 claims abstract description 17
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims abstract description 16
- 238000002156 mixing Methods 0.000 claims abstract description 15
- 239000007974 sodium acetate buffer Substances 0.000 claims abstract description 15
- BHZOKUMUHVTPBX-UHFFFAOYSA-M sodium acetic acid acetate Chemical compound [Na+].CC(O)=O.CC([O-])=O BHZOKUMUHVTPBX-UHFFFAOYSA-M 0.000 claims abstract description 15
- 239000004317 sodium nitrate Substances 0.000 claims abstract description 14
- 235000010344 sodium nitrate Nutrition 0.000 claims abstract description 14
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 12
- 239000011780 sodium chloride Substances 0.000 claims abstract description 12
- 239000004323 potassium nitrate Substances 0.000 claims abstract description 10
- 235000010333 potassium nitrate Nutrition 0.000 claims abstract description 10
- 229910021397 glassy carbon Inorganic materials 0.000 claims abstract description 9
- 238000007747 plating Methods 0.000 claims abstract description 9
- 238000004140 cleaning Methods 0.000 claims abstract description 8
- 235000011164 potassium chloride Nutrition 0.000 claims abstract description 8
- 239000001103 potassium chloride Substances 0.000 claims abstract description 8
- 229910052697 platinum Inorganic materials 0.000 claims abstract description 6
- 239000011259 mixed solution Substances 0.000 claims description 27
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 claims description 25
- 239000008139 complexing agent Substances 0.000 claims description 11
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 3
- 229910052709 silver Inorganic materials 0.000 claims description 3
- 239000004332 silver Substances 0.000 claims description 3
- 239000003792 electrolyte Substances 0.000 abstract 3
- 239000000203 mixture Substances 0.000 abstract 2
- 239000011651 chromium Substances 0.000 description 56
- 239000012086 standard solution Substances 0.000 description 25
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 22
- 229910052804 chromium Inorganic materials 0.000 description 22
- 238000012360 testing method Methods 0.000 description 10
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 9
- 238000004090 dissolution Methods 0.000 description 9
- 230000009467 reduction Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 150000002500 ions Chemical class 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 229910002651 NO3 Inorganic materials 0.000 description 5
- 239000003153 chemical reaction reagent Substances 0.000 description 5
- -1 colorimetry Chemical compound 0.000 description 5
- 238000005303 weighing Methods 0.000 description 5
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 4
- 229910001430 chromium ion Inorganic materials 0.000 description 4
- 238000002474 experimental method Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 238000007254 oxidation reaction Methods 0.000 description 4
- 238000004832 voltammetry Methods 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 238000007865 diluting Methods 0.000 description 3
- 238000012544 monitoring process Methods 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- VMHLLURERBWHNL-UHFFFAOYSA-M Sodium acetate Chemical compound [Na+].CC([O-])=O VMHLLURERBWHNL-UHFFFAOYSA-M 0.000 description 2
- 229960000583 acetic acid Drugs 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229940075397 calomel Drugs 0.000 description 2
- 238000004752 cathodic stripping voltammetry Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical compound Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 239000012362 glacial acetic acid Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 239000001632 sodium acetate Substances 0.000 description 2
- 235000017281 sodium acetate Nutrition 0.000 description 2
- PCTMTFRHKVHKIS-BMFZQQSSSA-N (1s,3r,4e,6e,8e,10e,12e,14e,16e,18s,19r,20r,21s,25r,27r,30r,31r,33s,35r,37s,38r)-3-[(2r,3s,4s,5s,6r)-4-amino-3,5-dihydroxy-6-methyloxan-2-yl]oxy-19,25,27,30,31,33,35,37-octahydroxy-18,20,21-trimethyl-23-oxo-22,39-dioxabicyclo[33.3.1]nonatriaconta-4,6,8,10 Chemical compound C1C=C2C[C@@H](OS(O)(=O)=O)CC[C@]2(C)[C@@H]2[C@@H]1[C@@H]1CC[C@H]([C@H](C)CCCC(C)C)[C@@]1(C)CC2.O[C@H]1[C@@H](N)[C@H](O)[C@@H](C)O[C@H]1O[C@H]1/C=C/C=C/C=C/C=C/C=C/C=C/C=C/[C@H](C)[C@@H](O)[C@@H](C)[C@H](C)OC(=O)C[C@H](O)C[C@H](O)CC[C@@H](O)[C@H](O)C[C@H](O)C[C@](O)(C[C@H](O)[C@H]2C(O)=O)O[C@H]2C1 PCTMTFRHKVHKIS-BMFZQQSSSA-N 0.000 description 1
- 241001465754 Metazoa Species 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 238000001479 atomic absorption spectroscopy Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000007853 buffer solution Substances 0.000 description 1
- 238000004587 chromatography analysis Methods 0.000 description 1
- PHFQLYPOURZARY-UHFFFAOYSA-N chromium trinitrate Chemical compound [Cr+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O PHFQLYPOURZARY-UHFFFAOYSA-N 0.000 description 1
- 238000004737 colorimetric analysis Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000000536 complexating effect Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000008034 disappearance Effects 0.000 description 1
- 238000000840 electrochemical analysis Methods 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000002372 labelling Methods 0.000 description 1
- 238000004949 mass spectrometry Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- YPJKMVATUPSWOH-UHFFFAOYSA-N nitrooxidanyl Chemical compound [O][N+]([O-])=O YPJKMVATUPSWOH-UHFFFAOYSA-N 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 230000001988 toxicity Effects 0.000 description 1
- 231100000419 toxicity Toxicity 0.000 description 1
- 239000011573 trace mineral Substances 0.000 description 1
- 235000013619 trace mineral Nutrition 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Molecular Biology (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
The invention provides a novel electrolyte solution for detecting hexavalent chromium by using a mercury membrane electrode and a hexavalent chromium detection method thereof, wherein the electrolyte comprises the following components in concentration: 0.2-2mol/L acetic acid-sodium acetate buffer solution, 10-60g/LDTPA, 1-4mol/L sodium nitrate, potassium nitrate or their mixture, and 0.1-1mol/L sodium chloride, potassium chloride or their mixture. The method comprises the following steps: 1. uniformly mixing the electrolyte and a water sample containing hexavalent chromium to be detected according to a volume ratio of 1:10 to 1: 1; 2. connecting a glassy carbon electrode, a reference electrode and a platinum electrode three-electrode system pre-plated with a mercury film with a heavy metal detector, and inserting the system into the detector2+In the mercury plating solution, the treatment is carried out until a mercury film appears on the surface of the plated glassy carbon electrode; 3. and cleaning a three-electrode system, inserting electrolyte, connecting the three-electrode system with a heavy metal detector, continuously applying different enrichment potentials for 10-120 s twice, and scanning within the range of-0.9 v to-1.5 v.
Description
Technical Field
The invention belongs to the technical field of analysis and determination of hexavalent chromium in water, and relates to a method for continuously and accurately detecting hexavalent chromium ions by a cathodic stripping voltammetry method; in particular to a novel electrolyte solution for detecting hexavalent chromium by using a mercury membrane electrode and a hexavalent chromium detection method thereof.
Background
In the environment, chromium mainly exists in the form of inorganic chromium, two common stable oxidation states of chromium are trivalent chromium Cr (III) and hexavalent chromium Cr (VI), the trivalent chromium Cr (III) is a trace element necessary for human bodies, animals and plants to maintain life, but the trivalent chromium Cr (III) is harmful to the human bodies when the concentration is too high; hexavalent chromium Cr (VI) is mainly CrO in the environment4 2-And HCrO4 -The hexavalent chromium has high activity and strong toxicity, and the hexavalent chromium Cr (VI) is easy to be absorbed and stored in the human body and has potential harm to organisms. Therefore, hexavalent chromium Cr (VI) is listed as a pollutant which is preferentially controlled in the water body of China. Therefore, it is very important to accurately measure the content of hexavalent chromium ions in the water body.
There are many methods for detecting chromium, including colorimetry, fluorescence, mass spectrometry, atomic absorption spectrometry, chromatography, electrochemical analysis, and the like. These methods each have advantages and disadvantages and have different fields of application in the analytical determination of chromium.
A great deal of reports are made in domestic and foreign documents on the detection of hexavalent chromium by a voltammetry method, but compared with other heavy metal ions, the measurement condition is complex, the detection range is narrow, and the method is difficult to be applied to the rapid monitoring of a portable heavy metal instrument. The main problems are that:
1. chromium is a multi-valence metal, and mutual conversion between ions with different valence states is easy to occur in the reaction process;
2. the mercury film is easy to fall off in the measuring process of hexavalent chromium measured by the pre-plated mercury film, so that the mercury film needs to be pre-plated frequently in the measuring process, and the workload of a tester is increased;
3. if the content of the complexing agent DTPA is less than a certain concentration, no characteristic peak of hexavalent chromium appears. While the complexing agent DTPA was slightly soluble in water (about 5g/L) and only soluble in hot water and alkaline solution. This is why many domestic and foreign documents react in a thermostatic water bath at 40 ℃ for about 30min, so that complicated, tedious and time-consuming reaction conditions cannot be practically applied to portable heavy metal instruments.
Aiming at the problems, the key for solving the detection of hexavalent chromium is to develop a proper detection reagent.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects in the prior art, and provides a novel detection reagent for detecting hexavalent chromium by using a mercury membrane electrode, the reagent is used without a constant-temperature water bath device, after a mercury membrane is pre-plated, 2ml of novel electrolyte solution for detecting hexavalent chromium is added into 20ml of water sample to be detected, and the total time of two times of different potential enrichment, scanning, dissolution and cleaning is less than 2min, so that the test of a sample can be completed. And the detection signal is stable, and the phenomena of multiple peaks, disappearance of chromium peaks or shedding of mercury films do not appear any more.
The technical problem to be solved can be implemented by the following technical scheme.
The electrolyte solution for detecting hexavalent chromium by using the mercury membrane electrode is used for rapid detection of a portable heavy metal instrument, and compared with a final mixed solution, the electrolyte solution comprises the following components in concentration:
(1) 0.2-2mol/L acetic acid-sodium acetate buffer solution;
(2) 10-60g/L DTPA;
(3) 1-4mol/L sodium nitrate solution, potassium nitrate solution or mixed solution of the sodium nitrate solution and the potassium nitrate solution;
(4) 0.1-1mol/L sodium chloride, potassium chloride solution or the mixed solution of the two.
As a further improvement of the technical scheme, the pH value of the acetic acid-sodium acetate buffer solution is 5-7.
As a preferred embodiment of the invention, the concentration of the acetic acid-sodium acetate buffer solution relative to the final mixed solution is 2 mol/L.
The concentration of the DTPA solution relative to the final mixed solution was 60 g/L.
The concentration of the sodium nitrate solution, the potassium nitrate solution or the mixed solution of the sodium nitrate solution and the potassium nitrate solution relative to the final mixed solution is 2 mol/L.
The concentration of the sodium chloride solution, the potassium chloride solution or the mixed solution of the sodium chloride solution and the potassium chloride solution relative to the final mixed solution is 1 mol/L.
Another technical problem to be solved by the present invention is to provide a method for detecting hexavalent chromium using the above electrolyte solution.
The technical scheme is as follows.
The method for detecting hexavalent chromium by adopting the electrolyte solution is characterized by comprising the following steps of:
(1) uniformly mixing the electrolyte solution and a water sample containing hexavalent chromium to be detected according to a volume ratio of 1:10 to 1:1 for later use;
(2) connecting a glassy carbon electrode, a reference electrode and a platinum electrode three-electrode system pre-plated with a mercury film in advance with a heavy metal detector, and inserting the system into the detector2+In the ionic mercury plating solution, the surface of the plated glassy carbon electrode is treated to be covered with a layer of uniform silver gray mercury film;
(3) and (3) cleaning the three-electrode system treated in the step (2), inserting the three-electrode system into the mixed solution obtained in the step (1), connecting the three-electrode system with a heavy metal detector, and continuously applying voltage for two times: applying (-1.2 to-1.5) v enrichment potential 1(30 to 60) s; applying an enrichment potential of (-0.1 to-0.8) v for 2(10 to 120) s.
As a further improvement of the process, in step (2), Hg2+The ionic mercury plating solution is 0.1mol/L HCl mercury plating solution, and the treatment step comprises applying a potential of-1.0V for 120s and repeating the operation three times.
As a preferred embodiment of the method, the specific parameters in step (3) are:
enrichment potential 1: -1.5 v;
enriching time: 30 s;
enrichment potential 2: -0.1 v;
enriching time: 10 s;
rest time: 20 s;
scanning potential: -0.9v to-1.5 v;
cleaning potential: -1.5 v;
cleaning time: and 20 s.
In addition, in the step (1), the preferred mixing volume ratio of the electrolyte solution to the water sample containing hexavalent chromium to be detected is 1: 10.
According to the novel electrolyte solution for detecting hexavalent chromium by using the mercury membrane electrode, the chloride ions contained in the solution overcome the defects that the mercury membrane electrode cannot exist stably and is easy to fall off in the range that the pH value is close to neutral; nitrate ions contained in the chromium nitrate salt solution play a role in catalytic oxidation in the scanning process of the cathodic stripping voltammetry, and trivalent chromium Cr (III) generated by the reduction of hexavalent chromium Cr (VI) is inhibited from being continuously reduced into divalent chromium Cr (II); the solubility of the DTPA complexing agent is increased, so that a constant-temperature water bath is not needed for detecting hexavalent chromium by a voltammetry, and the operation is simplified; meanwhile, the concentration ratios of various ions contained in the electrolyte solution are optimized, so that the sensitivity of the electrolyte solution to the detection of hexavalent chromium is greatly improved, the enrichment time is only 10s, the time for continuously reducing trivalent chromium Cr (III) into divalent chromium Cr (II) is reduced, and the problem that the current value of a dissolution peak is reduced in the detection process is successfully solved.
Drawings
FIG. 1 is a graph of a series of standard solution tests of example 1; in the figure: 1 is a curve chart of 20 mu g/L hexavalent chromium standard solution, 2 is a curve chart of 40 mu g/L hexavalent chromium standard solution, 3 is a curve chart of 60 mu g/L hexavalent chromium standard solution, 4 is a curve chart of 80 mu g/L hexavalent chromium standard solution, and 5 is a curve chart of 100 mu g/L hexavalent chromium standard solution.
FIG. 2 is a graph of example 3 with 2 consecutive tests marked; in the figure: 1 is a curve chart of a prepared 2 mu g/L hexavalent chromium standard solution, 2 is a hexavalent chromium standard solution added with 60 mu L and 1mg/L for the first time, and 3 is a hexavalent chromium standard solution added with 60 mu L and 1mg/L for the second time.
Detailed Description
The invention aims to overcome the problems in the prior art and provide an electrolyte solution for measuring hexavalent chromium by using a mercury membrane electrode, and by adding various ions with special functions into the solution, the mercury membrane electrode can be ensured to stably exist within the pH value range of 5-7 without shedding, the solubility of DTPA is increased, the added special ions play a role in catalytic oxidation in the scanning process, the continuous reduction of Cr (III) into bivalent Cr (II) is inhibited, the enrichment time is shortened under the condition of high detection sensitivity so as to inhibit the reduction of trivalent Cr (III) into bivalent Cr (II), the reduction of the dissolution peak current value is prevented, and the continuous and accurate detection of hexavalent chromium ions in water can be ensured.
The electrolyte solution for measuring hexavalent chromium by using the mercury membrane electrode provided by the invention comprises the following components in concentration:
(1) acetic acid-sodium acetate buffer solution with pH value of 5-7;
(2) (10-60) g/L of DTPA;
(3) (1-4) at least one of sodium nitrate and potassium nitrate solutions in mol/L;
(4) (0.1-1) at least one of sodium chloride and potassium chloride solution.
Mixing the above solutions according to a certain proportion to obtain an electrolyte solution for detecting hexavalent chromium by using a mercury membrane electrode, namely, uniformly mixing the electrolyte solution and a water sample to be detected containing hexavalent chromium according to the proportion of 1:10 to 1:1, inserting a glassy carbon electrode, a reference electrode and a platinum electrode three-electrode system which are pre-plated with a mercury membrane into the electrolyte solution, applying a voltage in the range of-0.1 v to-0.8 v in a very short time, reducing hexavalent chromium Cr (VI) to trivalent chromium Cr (III) on the surface of a working electrode which is pre-plated with the mercury membrane, adsorbing DTPA existing in the solution on the surface of the mercury membrane to form a complex Cr (III) -DTPA with the trivalent chromium Cr (III), when the voltage is scanned towards a negative electrode, continuously reducing part or all of Cr (III) -DTPA to Cr (II) -DTPA, and oxidizing the Cr (II) -DTPA to Cr (III) -DTPA by the strong oxidizing property of nitrate radicals, thereby solving the problem that the current value of the dissolution peak becomes small; because the chloride ions are added into the mixed solution, the dropping of the mercury film caused by the generation of calomel on the surface of the electrode is inhibited, and the reduction of the surface activity of the mercury film is prevented.
In the specific implementation, the following steps are adopted:
1) weighing sodium acetate and transferring glacial acetic acid to prepare (0.2-2) mol/L acetic acid-sodium acetate buffer solution;
2) weighing DTPA to prepare (10-60) g/L complexing agent solution;
3) weighing sodium nitrate to prepare a sodium nitrate solution with the mol/L of (1-4);
4) weighing sodium chloride to prepare a (0.1-1) mol/L sodium chloride solution;
5) connecting the treated three-electrode system with a portable heavy metal detector, and inserting the three-electrode system containing Hg2+And (3) applying a potential of-1.0V for 120s in 0.1mol/L of HCl mercury plating solution of ions, repeating the steps for three times, and covering a layer of uniform silver gray mercury film on the surface of the plated glassy carbon electrode.
6) Transferring 2mL of (0.2-2.0) mol/L acetic acid-sodium acetate buffer solution into a measuring cup, adding the solution obtained in the step 2)3)4) into 20mL of 50 mu g/L hexavalent chromium standard solution by the following method of A, B, C, D, and uniformly mixing for later use;
of these, four ABCD experiments were conducted by adding different ratios of comparative experiments to verify the role of DTPA, nitrate ions and chloride ions for the purpose of illustrating the rationality of the concentration ratios obtained in steps 1), 2), 3) and 4).
Then, the determined optimum ratio of the electrolyte solution is followed, and the effects of the electrolyte solution of the invention are verified by using the following examples 1 to 3 (indicating error experiments, repeatability experiments and accuracy).
Test A:
moving (0.2-2.0) mol/L acetic acid-sodium acetate buffer solution 2mL into an electrolytic cup according to the step 6), adding (10-60) g/L DTPA complexing agent solution in the order of (0.1-2) mL gradual increase, adding into 20mL of 50 mu g/L hexavalent chromium standard solution, uniformly mixing, and then executing the step 7), wherein a tiny peak current value appears at about-1.164V, the dissolution peak current value is slightly increased along with the increase of the content of DTPA, and no hexavalent chromium characteristic peak exists due to the dropping of a mercury film.
Test B:
moving 2mL of acetic acid-sodium acetate buffer solution of the step 1) (0.2-2.0) mol/L into an electrolytic cup according to the step 6), adding 1mL (0.1-1) mol/L of sodium chloride solution, adding the DTPA complexing agent solution of the step 2) according to the increasing sequence of (0.1-2) mL, adding into 20mL of 50 mu g/L hexavalent chromium standard solution, uniformly mixing, executing the step 7), slightly increasing the current value of a dissolution peak at about-1.172 v, fixing the dissolution peak at a certain value along with the increase of the content of DTPA, and determining to add 0.3mL of DTPA complexing agent solution. With the addition of chloride ions, the pre-plated mercury film does not fall off any more, but only the chloride ions and the DTPA complexing agent exist in the acetic acid-sodium acetate buffer solution, and compared with a hexavalent chromium standard solution of 50 mu g/L, the hexavalent chromium buffer solution does not have an obvious characteristic peak of hexavalent chromium. The concentration time was increased and the dissolution peak current values were almost unchanged.
Test C:
moving 2mL of acetic acid-sodium acetate buffer solution of the step 1) (0.2-2.0) mol/L into an electrolytic cup according to the step 6), adding 0.3mL (10-60) g/L of DTPA complexing agent solution of the step 2), then adding the solutions of the steps 3) and 4) according to a certain proportion, adding the solutions into 20mL of 50 mu g/L hexavalent chromium standard solution, uniformly mixing, and then executing the step 7), wherein a larger dissolution peak current value appears at a position of about-1.2V. The elution peak current value gradually increased as the nitrate ion content increased in step 3).
Test D:
pre-plating a mercury film again according to the step 5), moving 2mL of the acetic acid-sodium acetate buffer solution of the step 1) (0.2-2.0) mol/L into an electrolytic cup according to the step 6), adding 0.3mL (10-60) g/L DTPA complexing agent solution of the step 2) and 0.6mL (1-4) mol/L sodium nitrate solution of the step 3) into 20mL of 50 mu g/L hexavalent chromium standard solution respectively by adding the solution of the step 4) and not adding the solution of the step 4), uniformly mixing, and then executing the step 7). Through experimental analysis, the pre-plated mercury film can stably exist in an acid solution, and the stability and the activity of the pre-plated mercury film can be improved by adding a large amount of chloride ions in a nearly neutral environment.
Tests A-D show that the addition of chloride ions prevents the mercury membrane from falling off; the nitrate ions are added to play a role in catalytic oxidation; in the electrolyte solution, the solubility of DTPA is greatly increased, and hexavalent chromium ions can be detected without complex devices such as constant-temperature heating. Compared with the similar products, the reagent is more suitable for the application in the aspect of rapid monitoring.
7) And after the three-electrode system processed in the step 5) is washed clean by deionized water, the three-electrode system is inserted into the solution in the step 6) (remark: through the verification of the step 6), the mixed solution of the four reagents obtained by 1), 2), 3) and 4) is used in the actual operation, and is connected with a heavy metal detector (portable heavy metal detector), and different voltages are continuously applied for two times: applying (-1.2 to-1.5) v enrichment potential 1(30 to 60) s; applying an enrichment potential of (-0.1 to-0.8) v for 2(10 to 120) s, and scanning in a range of-0.9 to-1.5 v.
Among them, it is preferable to set the following preferred parameters in table 1:
table 1:
the present invention will be described below with reference to more specific examples.
The preparation method of the electrolyte solution comprises the following steps:
respectively weighing 109.2g of sodium acetate, (10-30) g of DTPA, (42.5-170) g of sodium nitrate, and (2.93-29.3) g of sodium chloride, transferring 2.4mL of glacial acetic acid, adding water to dilute to 500mL, and uniformly mixing for later use. The solution can be stored for at least more than half a year in a sealed state.
The sampling method for detecting hexavalent chromium in the water sample by using the solution comprises the following steps:
and (3) transferring 20mL of water sample into a measuring cup, adding 2mL of the electrolyte solution, uniformly mixing, inserting a glassy carbon electrode, reference electrode and platinum electrode three-electrode system pre-plated with a mercury film, and connecting a heavy metal detector to analyze and test the water sample.
Example 1:
1) and taking 5 clean 100mL volumetric flasks, adding 10mL of the electrolyte solution into each volumetric flask, transferring 20 mu L, 40 mu L, 60 mu L, 80 mu L and 100 mu L of 100mg/L hexavalent chromium standard solution into the 5 volumetric flasks, diluting to a scale, preparing into 20 mu g/L, 40 mu g/L, 60 mu g/L, 80 mu g/L and 100 mu g/L series standard solutions, and transferring 20mL of the standard solutions into measuring cups.
2) And connecting a three-electrode system consisting of a mercury membrane electrode, a reference electrode and a platinum electrode to the portable heavy metal instrument.
3) And sequentially putting the three-electrode system into an electrolytic cup containing series of standard solutions of 20 mug/L, 40 mug/L, 60 mug/L, 80 mug/L and 100 mug/L. And selecting a calibration key, sequentially calibrating each point, and storing calibration data after 5-point calibration is finished.
FIG. 1 is a superposition of the peak profiles of the series of standard solutions of example 1, in which the curves of different concentrations show that the hexavalent chromium tested using the electrolyte solution has a good linearity in the range from (0 to 100) μ g/L.
Example 2:
1) and taking 1 clean 200mL volumetric flask, adding 20mL of the electrolyte solution, transferring 100 mu L of 100mg/L hexavalent chromium standard solution into the volumetric flask, diluting to a scale, preparing 50 mu g/L hexavalent chromium standard solution, and transferring 20mL into a measuring cup.
2) The three-electrode system of example 1 was placed in a hexavalent chromium standard solution of 50. mu.g/L, and the "measurement" key was selected, and the solution was measured 6 times in succession. The results of 6 measurements are: 48.5. mu.g/L, 50.4. mu.g/L, 49.0. mu.g/L, 50.9. mu.g/L, 49.3. mu.g/L, with a relative standard deviation of 1.87%.
Example 3:
1) and taking 1 clean 100mL volumetric flask, adding 10mL of the electrolyte solution, diluting to a scale, mixing uniformly, transferring 20mL, and adding into a measuring cup for later use.
2) And accurately transferring 40 mu L of 1mg/L hexavalent chromium standard solution into a measuring cup of 1), wherein the theoretical value is 2 mu g/L.
3) And putting the three-electrode system into the measuring cup, starting to perform a labeling test, continuously adding 60 mu L of 1mg/L hexavalent chromium standard solution into the solution in the same cup twice respectively, and directly reading the result by an instrument after the measurement to be 2.58 mu g/L which is close to the theoretical value of 2 mu g/L.
It can be known from the above embodiments that hexavalent chromium Cr (vi) is reduced to trivalent chromium Cr (iii) on the surface of the working electrode pre-plated with mercury film, while DTPA present in the solution is adsorbed on the surface of the mercury film to form a complex Cr (iii) -DTPA with the trivalent chromium Cr (iii), when the voltage is scanned toward the negative electrode, part or all of the Cr (iii) -DTPA is continuously reduced to Cr (ii) -DTPA, and at this time, the strong oxidizing property of nitrate radical oxidizes Cr (ii) -DTPA to Cr (iii) -DTPA, thereby solving the problem of decreasing the peak current value of elution; because the chloride ions are added into the mixed solution, the dropping of the mercury film caused by the generation of calomel on the surface of the electrode is inhibited, and the reduction of the surface activity of the mercury film is prevented.
The electrolyte solution for detecting hexavalent chromium by using the pre-plated mercury film has the following beneficial effects:
(1) the added chloride ions prevent the mercury membrane from falling off and prevent the surface activity of the mercury membrane from being reduced;
(2) the added nitrate ions prevent the trivalent chromium generated by reduction from being reduced into the divalent chromium;
(3) the solubility of DTPA is at least 60g/L from 5g/L of DTPA dissolved in water to the electrolyte solution, so that the complexing effect is improved, a constant temperature device is not required to be used, and the operation of detecting hexavalent chromium by a voltammetry method is simplified;
(4) the different proportions of the components in the electrolyte solution greatly improve the sensitivity of the voltammetry for measuring hexavalent chromium, the enrichment time is only 10s, and the time for continuously reducing trivalent chromium Cr (III) into divalent chromium Cr (II) is reduced.
Compared with the similar products, the functions and the adaptability of the device are more suitable for the application of the portable heavy metal instrument in the aspect of rapid monitoring.
Claims (9)
1. A method for detecting hexavalent chromium by adopting an electrolyte solution is used for quickly detecting a portable heavy metal instrument when a constant-temperature water bath device is not equipped, and is characterized by comprising the following steps:
(1) uniformly mixing the electrolyte solution and a water sample containing hexavalent chromium to be detected according to a volume ratio of 1:10 to 1:1 for later use;
(2) connecting a glassy carbon electrode, a reference electrode and a platinum electrode three-electrode system pre-plated with a mercury film in advance with a heavy metal detector, and inserting the system into the detector2+In the ionic mercury plating solution, the surface of the plated glassy carbon electrode is treated to be covered with a layer of uniform silver gray mercury film;
(3) and (3) cleaning the three-electrode system treated in the step (2), inserting the three-electrode system into the mixed solution obtained in the step (1), connecting the three-electrode system with a heavy metal detector, and continuously applying voltage for two times: applying an enrichment potential of (-1.2 to-1.5) v for 1(30 to 60) s; applying an enrichment potential of (-0.1 to-0.8) v for 2(10 to 120) s;
wherein,
the electrolyte solution is an electrolyte solution for detecting hexavalent chromium by using a mercury membrane electrode, and compared with a final mixed solution, the concentration of each component constituting the electrolyte solution is as follows:
(1) 0.2-2mol/L acetic acid-sodium acetate buffer solution;
(2) 10-60g/L DTPA;
(3) 1-4mol/L sodium nitrate solution, potassium nitrate solution or mixed solution of the sodium nitrate solution and the potassium nitrate solution;
(4) 0.1-1mol/L sodium chloride, potassium chloride solution or the mixed solution of the two.
2. The method for detecting hexavalent chromium in the electrolyte solution according to claim 1, wherein the pH of the acetic acid-sodium acetate buffer solution is 5 to 7.
3. The electrolyte solution for detecting hexavalent chromium according to claim 1, wherein a concentration of the acetic acid-sodium acetate buffer solution in the final mixed solution is 2mol/L with respect to the final mixed solution.
4. The method for detecting hexavalent chromium in accordance with the electrolyte solution of claim 1, wherein a concentration of the DTPA complexing agent solution in the final mixed solution is 60g/L with respect to the final mixed solution.
5. The method for detecting hexavalent chromium in accordance with the electrolyte solution of claim 1, wherein a concentration of the sodium nitrate solution, the potassium nitrate solution, or the mixed solution of the sodium nitrate solution and the potassium nitrate solution in the final mixed solution is 2mol/L with respect to the final mixed solution.
6. The method for detecting hexavalent chromium using the electrolyte solution according to claim 1, wherein a concentration of the sodium chloride solution, the potassium chloride solution, or a mixed solution of the sodium chloride solution and the potassium chloride solution in the final mixed solution is 1mol/L with respect to the final mixed solution.
7. The method for detecting hexavalent chromium using the electrolyte solution according to claim 1, wherein in the step (2), Hg is added2+The ionic mercury plating solution is 0.1mol/L HCl mercury plating solution, and the treatment step comprises applying a potential of-1.0V for 120s and repeating the operation three times.
8. The method for detecting hexavalent chromium using the electrolyte solution according to claim 1, wherein the specific parameters in the step (3) are:
enrichment potential 1: -1.5 v;
enriching time: 30 s;
enrichment potential 2: -0.1 v;
enriching time: 10 s;
rest time: 20 s;
scanning potential: -0.9v to-1.5 v;
cleaning potential: -1.5 v;
cleaning time: and 20 s.
9. The method for detecting hexavalent chromium using the electrolyte solution according to claim 8, wherein the mixing volume ratio of the electrolyte solution to the sample containing hexavalent chromium to be tested in step (1) is 1: 10.
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