GB2273780A - Electrochemical determination of fluoride in acid solution of pH <2.0. - Google Patents
Electrochemical determination of fluoride in acid solution of pH <2.0. Download PDFInfo
- Publication number
- GB2273780A GB2273780A GB9226740A GB9226740A GB2273780A GB 2273780 A GB2273780 A GB 2273780A GB 9226740 A GB9226740 A GB 9226740A GB 9226740 A GB9226740 A GB 9226740A GB 2273780 A GB2273780 A GB 2273780A
- Authority
- GB
- United Kingdom
- Prior art keywords
- fluoride
- sensor
- voltage
- sample
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 title claims abstract description 43
- 239000002253 acid Substances 0.000 title claims abstract description 18
- -1 fluoride ions Chemical class 0.000 claims abstract description 5
- 239000000243 solution Substances 0.000 claims description 23
- 238000000034 method Methods 0.000 claims description 20
- 238000007792 addition Methods 0.000 claims description 17
- 150000002500 ions Chemical class 0.000 claims description 16
- 239000003929 acidic solution Substances 0.000 claims description 5
- 238000005259 measurement Methods 0.000 claims description 4
- 239000007864 aqueous solution Substances 0.000 claims description 2
- 229910010272 inorganic material Inorganic materials 0.000 claims description 2
- 239000011147 inorganic material Substances 0.000 claims description 2
- 239000000463 material Substances 0.000 claims description 2
- 230000007935 neutral effect Effects 0.000 claims description 2
- 239000007787 solid Substances 0.000 claims description 2
- 239000000523 sample Substances 0.000 description 14
- 150000007513 acids Chemical class 0.000 description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 3
- 229910017604 nitric acid Inorganic materials 0.000 description 3
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 235000010755 mineral Nutrition 0.000 description 2
- 239000003758 nuclear fuel Substances 0.000 description 2
- 238000012958 reprocessing Methods 0.000 description 2
- 239000012488 sample solution Substances 0.000 description 2
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 2
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 229910001515 alkali metal fluoride Inorganic materials 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 239000007853 buffer solution Substances 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 239000011775 sodium fluoride Substances 0.000 description 1
- 235000013024 sodium fluoride Nutrition 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- 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
- G01N27/4166—Systems measuring a particular property of an electrolyte
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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
Total fluoride concentration in acid solution 3 of pH <2.0 is determined from the voltage generated by a fluoride ion selective electrode 9 responsive to free fluoride ions. The voltage is measured relative to a reference electrode 11 and temperature of the solution may also be measured at 13. The output voltage is converted to a readout of total fluoride present. <IMAGE>
Description
The determination of fluoride concentration in solutions
The present invention relates to the determination of fluoride concentration in solutions especially acidic solutions in which the fluoride is present as a trace impurity.
In certain applications it is desirable to measure the concentration of fluoride present as a trace impurity in strong mineral acids. For example, concentrated nitric acid used in the dissolution of irradiated nuclear fuel for reprocessing may be contained in vessels made from zirconium and such vessels are prone to corrosion if the nitric acid contain F ions in excess of a few parts per million. Another application is the determination of fluoride in reagent grade mineral acids - for specification purposes. However, no suitable methods has been known hitherto for measurement in strong acids of F concentrations less than about 10 parts per million.
Fluoride ion selective sensors have been used in the prior art for the determination of the concentration of F ions in acidic solutions. They respond to the concentration of free F ions. However, the pH of the solutions tested has required adjustment to the range pH 4.0 to 6.0 to ensure that all of the fluoride present in the solution exists as F ions. In acidic solutions having a pH less than 4.0 the fluoride ions become complexed with hydrogen ions to form HF:
H+ + F ++ HF
In dilute and strong acids the concentration of H+ is very high causing the residual concentration of F ions to be very low.It is widely believed that the concentration of F ions, especially in strong acids, is too low to measure by an ion selective sensor. Furthermore, attempts to neutralise the acid by adding buffer solutions have not been generally successful because of the large volumes of solution required and the large quantities of heat evolved.
According to the present invention there is provided a process for the determination of the fluoride concentration of an aqueous solution which comprises immersing in the solution a fluoride ion selective sensor which generates an electrochemical voltage whose magnitude depends upon the number of free fluoride ions in the solution and measuring the voltage generated by the sensor, characterised in that the said solution comprises an acid solution of pH less than 2.0 and the said voltage is converted into a readout proportional to the said voltage representing the total fluoride content of the said solution.
The said ion selective sensor may be used in conjunction with a reference sensor which generates a constant electrochemical voltage providing a reference for the voltage generated by the said ion selective sensor.
Surprisingly, we have found that the extremely small concentration of F ions may be measured by an ion selective sensor immersed in a strong acid. We have found that if the concentration of H+ is both high and constant the concentration of F is not only constant and measurable but also proportional to the total concentration of fluoride present in the solution. The electrochemical voltage developed by the said sensor therefore represents a measure of the total fluoride content.
Measurement of the concentration of fluoride in strong acids is carried out in the prior art by converting the fluoride present into HF gas and measuring the quantity of
HF evolved. This indirect method is costly and time consuming to operate.
In contrast, determining the fluoride concentration directly in the solution under investigation by the process of the present invention, the only practical direct process, has the following advantages:
(i) minimum sample preparation is required; (ii) the risk of contamination is reduced and there are no 'blank' problems; (iii) the process may be operated quickly and cheaply with minimum operator involvement.
In the process according to the present invention the voltage generated by the ion selective sensor may be converted into a readout representative of the total fluoride content present by use of a calibration process which involves applying one or more so-called standard additions to the solutions being investigated. Standard additions are solutions of known volume and different known fluoride concentrations, eg various dilute solutions of an alkali metal fluoride, eg sodium fluoride. The standard additions may be made manually or by a known automatic dispensing apparatus.
Desirably, each readout value is monitored until it becomes stable indicating, eg after the making of standard additions, that the concentration being measured has stabilised.
The measurement of the fluoride content of a given sample may be converted into digital form and recorded, eg in the memory of a computer, together with an identifier reference code for the sample.
A computer employed for this purpose may also be used to calculate the sample fluoride concentration from the sensor output voltages (with reference to the output voltage from a reference sensor). The computer may also control the making of the standard additions by automatic dispensing apparatus. -In fact, a sample may be investigated by carrying out an automatic analysis programme under the control of a computer in which automatic standard additions are made, output sensor voltage readings are taken and fluoride concentration determinations are made all under the control of the computer. The computer may store and/or display the results obtained. This procedure can also confirm that the ion selective sensor response expected from theory, viz about 58 mV change per decade change in F concentration.
The present invention may be employed to determine the trace fluoride concentration of batches of concentrated acid, eg to be used as a dissolver medium for nuclear fuel reprocessing, and more generally in reagent grade acids.
Alternatively, the fluoride content of solid inorganic materials which cannot be easily be dissolved in neutral or mildly acidic solutions can be determined by dissolving a known quantity of the material in question in a strong acid, eg concentrated nitric acid, and then measuring the fluoride content in the manner described above. For example the fluoride content in UO2; and other oxides and carbonates may be measured in this way.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
Figure 1 is a part schematic cross-sectional side elevation of an autoanalyser for carrying out a process embodying the present invention.
As shown in Figure 1, the autoanalyser comprises a beaker 1 containing a sample 3 of the acid whose fluoride content is to be determined. The beaker 1 is stirred by a magnetic stirrer 5, an insulating base 7 being provided between the beaker 1 and stirrer 5. A fluoride ion selective electrode 9 and a reference electrode 11 are suspended in the sample 3. The electrode 9 may be an ORION (TM) Model 94-09 Fluoride Electrode and the electrode 11 may be an ORION (TM) Model 90-01 Single Junction Reference
Electrode both supplied by Orion Research Inc of Boston,
Massachusetts, USA. A temperature probe 13 is also suspended in the sample 3. An injector 15 permits various solutions which are so-called standard additions to be added to the sample 3. The injector 15 may be a 0.5 ml syringe fitted via a delivery tube 16 to an automatic solution dispenser 17, eg a Hamilton Microlab M dispenser.
The voltages detected respectively by the electrodes 9, 11 are applied via conducting leads 18, 20 to an interface 19 which converts the readings into digital inputs to a digital computer 21, eg IBM PS2 Model. The computer 21 also controls (directly via a serial interface not shown) the making of the standard additions by the dispenser 17.
If the dispenser 17 is malfunctioning the computer 21 indicates this giving the user the opportunity to make standard additions manually to the sample 3.
An identifier code input by the operator for the sample 3 is recorded by the computer 21. According to a set programme the computer 21 issues a sequence of control signals to the dispenser 17 to make a number, eg five, discrete standard additions to the sample 3. The additions made may be such as to attempt to double the fluoride concentration from that present before the addition was made. After each addition the output voltage from the electrode 9 is monitored until it is stable indicating that the added solution has fully mixed with the sample 3. At this point in time the voltages detected by the electrodes 9, 11 are recorded by the computer 21. The next control signal for the dispenser 17 is then given.After all of the standard additions have been made and the results recorded the computer 21 carries out a calculation according to a form of the well known Nernst Equation, viz:
E = Eg + S log (A + B) where E is the varying potential measured by the electrode 9, Eg is a standard potential, A is the cumulative fluoride ion concentration added to the sample solution, S is a constant, the so-called electrode slope having a typical value of 58 mV per decade, and B is the fluoride concentration in the original sample solution. From this equation using the results obtained from the series of known standard additions the computer is able to calculate both the electrode slope S and the parameter B.
The value of Parameter B may be displayed in a known way, eg as a digital value on the computer monitor and/or as a recording on a paper print-out.
Claims (10)
1. A process for the determination of the fluoride concentration of an aqueous solution which comprises immersing in the solution a fluoride ion selective sensor which generates an electrochemical voltage whose magnitude depends upon the number of free fluoride ions in the solution and measuring the voltage generated by the sensor, characterised in that the said solution comprises an acid solution of pH less than 2.0 and the said voltage is converted into a readout proportional to the said voltage representing the total fluoride content of the said solution.
2. A process as in Claim 1 and wherein the said ion selective sensor may be used in conjunction with a reference sensor which generates a constant electrochemical voltage providing a reference for the voltage generated by the said ion selective sensor.
3. A process as in Claim 1 or Claim 2 and wherein the voltage generated by the ion selective sensor is converted into a readout representative of the total fluoride content present.
4. A process as in Claim 3 and wherein each readout value is monitored until it becomes stable indicating that the concentration being measured has stabilised.
5. A process as in any one of the preceding Claims and wherein the measurement of the fluoride content of a given sample is converted into digital form and recorded in the memory of a computer, together with an identifier reference code for the sample.
6. A process as in Claim 5 and wherein the computer is also used to calculate the sample fluoride concentration from the sensor output voltages with reference to the output voltage from a reference sensor and to control the making of standard additions to the sample being analysed by automatic dispensing apparatus.
7. A process as in Claim 6 and wherein a sample is investigated by carrying out an automatic analysis programme under the control of the computer in which automatic standard additions are made to the investigated sample, output sensor voltage readings are taken and fluoride concentration determinations are made all under the control of the computer, the computer storing and/or displaying the results obtained.
8. A process as in any one of the preceding Claims and which is employed to determine the trace fluoride concentration of batches of concentrated acid.
9. A process wherein the fluoride content of solid inorganic materials which cannot be easily be dissolved in neutral or mildly acidic solutions is determined by dissolving a known quantity of the material in question in a strong acid and then measuring the fluoridevcontent in the manner described in any one of the preceding Claims.
10. A process as in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9226740A GB2273780B (en) | 1992-12-22 | 1992-12-22 | The determination of fluoride concentration in solutions |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9226740A GB2273780B (en) | 1992-12-22 | 1992-12-22 | The determination of fluoride concentration in solutions |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9226740D0 GB9226740D0 (en) | 1993-02-17 |
| GB2273780A true GB2273780A (en) | 1994-06-29 |
| GB2273780B GB2273780B (en) | 1996-07-17 |
Family
ID=10727046
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9226740A Expired - Fee Related GB2273780B (en) | 1992-12-22 | 1992-12-22 | The determination of fluoride concentration in solutions |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2273780B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7033483B2 (en) * | 2002-04-27 | 2006-04-25 | Prominent Dosiertechnik Gmbh | Fluoride-sensitive electrode |
| WO2009113994A1 (en) * | 2008-03-14 | 2009-09-17 | Eugene Shalyt | Analysis of fluoride at low concentrations in acidic processing solutions |
| WO2010027273A1 (en) * | 2008-09-08 | 2010-03-11 | Sinvent As | Method for potentiometric analysis of fluoride in biological material |
| CN103792269A (en) * | 2014-01-23 | 2014-05-14 | 包头华美稀土高科有限公司 | Analytical method for directly measuring fluorine ion content in carbonic acid rare earth by using fluorine ion electrode method |
| CN109374695A (en) * | 2018-10-26 | 2019-02-22 | 西北民族大学 | A kind of measuring method of calcium ion concentration to fluorine influence of extraction in Pu'er tea |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2208532A5 (en) * | 1972-11-16 | 1974-06-21 | Avesta Jernverks Ab | Potentiometric determination of acid bath strength - using selective elec-trodes for F and H ions calibrated against KCL control electrode for pickling baths |
| JPS5033682A (en) * | 1973-07-23 | 1975-03-31 |
-
1992
- 1992-12-22 GB GB9226740A patent/GB2273780B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2208532A5 (en) * | 1972-11-16 | 1974-06-21 | Avesta Jernverks Ab | Potentiometric determination of acid bath strength - using selective elec-trodes for F and H ions calibrated against KCL control electrode for pickling baths |
| JPS5033682A (en) * | 1973-07-23 | 1975-03-31 |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7033483B2 (en) * | 2002-04-27 | 2006-04-25 | Prominent Dosiertechnik Gmbh | Fluoride-sensitive electrode |
| WO2009113994A1 (en) * | 2008-03-14 | 2009-09-17 | Eugene Shalyt | Analysis of fluoride at low concentrations in acidic processing solutions |
| WO2010027273A1 (en) * | 2008-09-08 | 2010-03-11 | Sinvent As | Method for potentiometric analysis of fluoride in biological material |
| CN103792269A (en) * | 2014-01-23 | 2014-05-14 | 包头华美稀土高科有限公司 | Analytical method for directly measuring fluorine ion content in carbonic acid rare earth by using fluorine ion electrode method |
| CN103792269B (en) * | 2014-01-23 | 2016-04-20 | 包头华美稀土高科有限公司 | Fluoride ion electrode method directly measures the analytical approach of content of fluoride ion in carbonated rare earth |
| CN109374695A (en) * | 2018-10-26 | 2019-02-22 | 西北民族大学 | A kind of measuring method of calcium ion concentration to fluorine influence of extraction in Pu'er tea |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2273780B (en) | 1996-07-17 |
| GB9226740D0 (en) | 1993-02-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20071222 |