FLUORIDE 31(2)
1998, pp 74 - 80		International Society for Fluoride ResearchTable of Contents
Home

DEVELOPMENTS IN THE ANALYSIS OF FLUORIDE 1995-1997

M L Wen, N H Shi, Y Qin* and C Y Wang Kunming, China

This biennial review is a continuation of the previous survey1 and covers the literature of the analysis of fluoride from July 1995 to June 1997.

Electroanalysis

Several different lanthanide fluoride (LnF3, Ln = Ce, Nd, Sm) crystals were grown and used for construction of fluoride ion-selective electrodes. Aspects of crystal growing, particularly the high-temperature dimorphism of SmF3 were addressed, and the effects on the electrode resistance and response characteristics of crystal quality, doping, and membrane geometric dimensions were studied.2 Hydroxide ion interference with three lanthanide fluoride single crystal membranes (LnF3, Ln = La, Ce, Nd) has been examined and shown to be due to the formation of hydroxo-complexes formed within a gel layer at the membrane surface. A mechanism has been proposed for the response of the electrodes to hydroxide ion.3

Based on integration of a pervaporation process and potentiometric detection in a laboratory-made module, methods were developed for the determination of F– in liquid and solid samples by formation of a volatile product with hexamethyldisiloxane. These methods were successfully applied to the determination of F– in orange tree leaves, tap water, well water, fertilizers, and ceramic industry waste water.4,5 Procedures for the determination of F– in plant material employing acid digestion and solution analysis by F-ISE (fluoride-ion selective electrode) were compared to alkali fusion using various plant materials. Owing to failure of the acids to liberate F– bound strongly within silicate minerals in plant materials, acid digestion could be only used to determine labile F– instead of total F in plant materials. With acid digestion procedures, F– concentrations determined in solution using the F-ISE were sensitive to solution pH, even at solution pH values where complexation of F– with H+ could be discounted. Therefore, both the ionic strength and the pH of sample and standard solutions should be matched when determining F– concentration using F-ISE.6

TISAB IV [disodium tartrate-tris(hydroxymethyl)methylamine-HCl] buffer was used to complex the Al ions, and NaOH was added to standard solutions to keep both the ionic strength and the Na+ concentration constant as well as the pH. No hydroxide ion interference was detected even though the pH of the solution was 8.57. The total fluoride in aluminum fluoride and cryolite samples was determined by direct potentiometry under these conditions.7 In order to analyze rain water continuously with a F-ISE, various buffer systems were examined for sensitivity enhancement. The sensitivity could be maximized at around pH 2.8 using the conventional acetate buffer. Sorensen's buffer (a mixture of glycine and hydrochloric acid, pH 2.8) was the most suitable for rain water analysis. The limit of linear response was 1 x 10-7 mol dm-3 and the detection limit was 1 x 18-8 mol dm-3 when the sample-to-buffer dilution ratio was 10:1.8

Both fluoride and molybdenum have been determined in the same serum sample. Fluoride was analyzed by direct potentiometry in a solution containing (CH2)6N4 and HNO3 at pH = 5.4 whereas molybdenum was determined by adsorptive voltammetry after the above mentioned solution had been nitrified with mixed acid containing HNO3 and HClO4.9 In another clinical setting, the degree of fluorosis in people working in a fluoride-polluted environment has been ascertained by analysis of fluoride in human hair. The method involves the oxygen flash method for decomposing the hair sample and the addition of auxiliary combustible adhesive paper to the sample wrapped in filter paper before ignition, combined with the use of Gran's multiple fluoride-electrode-coupled minicomputer.10

Based on the principle that enzymatic catalytic decomposition of hydrogen peroxide is inhibited by fluoride, a catalase biosensor has been developed to detect the substrate hydrogen peroxide and the inhibitors fluoride and cyanide in a phosphate buffer. The enzyme which catalyzes the decomposition of hydrogen peroxide to oxygen and water, was immobilized in a membrane by entrapment in polyacrylamide in contact with a Clark-type oxygen electrode. The F- detection limit was 1 mg/L.11 A simple, accurate and selective method has been described for determining morphine in illicit powders, based on monitoring the initial rate of fluoride ion liberated from the reaction of morphine with 1-fluoro-2,4-dinitrobenzene at pH 9 and 35°C with a solid-state fluoride ion-selective electrode.12 Using affinity binding of the glucoenzymes peroxidase and glucose oxidase on pF-sensitive field-effect transistors (Si/SiO2/Si3N4/LaF3 layers), Koeneke et al have developed new reloadable biosensors. The basic measuring principle of these ISFETs is the change in current in response to the concentration of F– ions. The immobilized glucoenzyme could be removed from the enzymatically inactive C or A basic membrane, and fresh enzymes could be bound again.13Electroanalysis methods for fluoride are shown in Table 1.

Spectral Analysis

Fluoride as an inhibitor of the immobilized liver esterase (EC3.1.1.1), which catalyzes the hydrolysis of ethyl butyrate to ethanol and butyric acid, was determined spectrophotometrically in a flow injection system. To monitor the reaction a second enzymatic reaction was employed, in which alcohol dehydrogenase (EC1.1.1.1) immobilized on controlled pore glass catalyzed the oxidation of ethanol and reduction of the coenzyme NAD+ to NADH, the latter being determined at 340 nm. There was a linear relationship between percent inhibition and fluoride concentration over the range 8x10-7 ~ 8x10-6 M (15-150 µgL-1) fluoride. The relative standard deviation at mid-calibration range was below 4% (n = 5). The more common inorganic compounds present in water samples did not interfere in the fluoride determination.14 Based on F– inhibitory effect on the photo-oxidation of acridine catalyzed by iron(III), F– has been determined by a flow injection spectrofluorometric method. A linear calibration curve was obtained over the range 0.76-9.5 µg/mL for F–15.

Determination of fluoride by spectral analysis is summarized in Table 2.


TABLE 1. Determination of fluoride by electroanalysis
Method Application Reference
F-ISE with an extrapolation method Continuous flow analysis of F– in city tap water Electroanalysis 7 (3) 221-224 1995
F-ISE F– in dentifrices Anal. Lab. 4 (1) 47-50 1995
Electrochemical recognition Selective recognition of F– in the presence of other halides and common anions J. Chem.Soc.Chem Commun. (3) 333-334 1995
F-ISE F– in diluted chromating solution Diandu Yu Tushi 14 (1) 11-12 1995
F-ISE F– in solutions at low temperature Zavod Lab. 61 (6) 1-4 1995
F-ISE with improved standard addition method F– in aqueous solution Nippon Kagaku Kaishi (9) 743-745 1995
F-ISE F– in lanthanide matrix Anal. Lab. 4 (2) 75-81 1995
F-ISE F– in alcoholic beverages and sugary solutions Ind. Bevande 24 (138) 357-364 1995
F-ISE F– in drinking water Analyst 120 (11) 2763-2767 1995
F-ISE F– in hexafluorosilicic acid Dopov. Nats. Akad Nauk Ukr. (2) 97-100 1995
F/pH-ISE automatic analysis system F– in serum J. Autom. Chem. 17 (6) 219-223 1995
F-ISE with ion exchange preconcentration-flow injection analysis F– in water Fenxi Huaxue 23 (6) 671-673 1995
F-ISE F– in fluoridated milk Weisheng Yanjiu 24 (6) 371-372 1995
F-ISE F– in natural water Guandong Weiliang Yuansu Kexue 2 (8) 32-34 1995
Solid pH electrode combined with F-ISE F– in aqueous solution J Anal. Chem. 51 (9) 892-895 1996
F-ISE F– in electroplating baths Rev. Acad. Cienc. Exactas, Fis., Quim. Nat. Zaragoza 50 85-91 1995
F-ISE with sequential injection analysis F– in drinking water Electroanalysis 8 (11) 1051-1054 1996
F-ISE with improved standard addition potentiometry F– in water/organic solvent mixtures Nippon Kagaku Kaishi(2) 112-118 1997
ISE-FIA (flow injection analysis) F– in serum Biomed. Res. Trace Elem. 7 (3) 125-126 1996
F-ISE F– In water Shuichuli Jishu 22 (6) 342-344 1996
ISE F– in water Fushun Shiyou Xueyuan Xuebao 16 (4) 21-25 1996


TABLE 2. Determination of fluoride by spectral analysis
Method Application Reference
Fluorescence quenching F– in hot spring water Fenxi Shiyanshi 14 (3) 30-32 1995
Graphite furnace molecular absorption spectrometry F– in oyster tissue and dental rinse Anal. Chim. Acta 315 (1,2) 167-176 1995
Spectrophotometric method F– in water Gaz. Woda Tech. Sanit 69 (8) 284-285 1995
Spectrophotometric or fluorometric method F– in aqueous solution Anal. Sci. 11 (2) 221-226 1995
Kinetic spectrophoto metric method F– in soil, vegetables and water Huanjing Kexue 17 (4) 65-66 1996
FIA-Spectrophotometric method F– in water J. Flow Injection Anal.13 (1) 35-43 1996
Alizarin complexone spectrometry F– in tea Iran Agric. Res. 14 (1) 111-117 1995
Spectrophotometry and dental preparations F– in dosage forms J. Pharm. Biomed. Anal 14 (8-10) 951-958 1996
Spectrophotometry F– in potable water Egypt. J. Anal. Chem. 5 (1) 31-39 1997
Spectrophotometry with Eriochrome Cyanine R indicator F– in water J. Chem. Educ. Software Ser. D 4D (2) 60-63 82-84 1997
Extraction/spectrophotometry by a long capillary cell F– in natural water Fenxi Huaxue 25 (2) 201-204 1997

Chromatography

A carbon IC BI-02 column (4.6 mm id x 50 mm, Bio Tech Research) was installed in an ion chromatography unit (Dionex 4500i) equipped with an anion micromembrane suppressor (AMMS-MPIC) for simultaneous determination of a mixture of 8 anions (F–, Cl–, NO2–, Br–, NO3–, SO4–, HPO42– and I–). Calibration curves obtained from the peak areas of the 8 anions were linear with a high correlation coefficient (> 0.999) and a good relative standard deviation of 0.2-0.9% (n=10).16 Methanol and dimethylformamide have been used as nonaqueous media for the separation of inorganic anions including fluoride. There were significant differences in separation selectivity with many anions showing reversed separation order compared to aqueous systems. Calibration of 11 inorganic anions separated in a phthalate electrolyte gave linear curves at 5x10-5 ~ 8x10-4 mol/L; detection limits were at 2.0 × 10-5 - 3.4 × 10-5 mol/L.17 A pellicular anion-exchange column has been developed for determining inorganic anions including fluoride and oxyhalides such as chlorite, chlorate, and bromate. In contrast to conventional latex-agglomerated resins, this new anion exchanger allows the retention of fluoride well out of the water dip with elution of sulfate in <15 min using a carbonate-hydrogen carbonate eluent under isocratic conditions.18

Fluoride analysis by chromatography is summarised in Table 3.

TABLE 3. Analysis of fluoride by chromatography
Method Application Reference
Capillary ion analysis (CIA) Deionized water used in nuclear power industry LC-GC 13 (2) 144-148 1995
Capillary electrophoresis (CE) Drinking water Fenxi Huaxue 23 (3) 365 1995
Single column high pressure anion chromatography Drinking water J. Liq. Chromatogr. 18 (7)1383-1403 1995
Ion chromatography (IC) Organic rich anaerobic waters from peatlands J. Chromatogr. A 706 (1,2) 281-286 1995
CE Rain water, river water and pond water Kankyo Kagaku 5 (2) 530-531 1995
Capillary zone electrophoresis (CZE) Drinking and waste water Biomed Chromatogr.9 (6) 281-282 1995
IC Water Anal. Sci 11 (6) 995-997 1995
IC Drinking water Kogyo Yosui 445 28-33 1995
IC Slag of electric furnace Yejin Fenxi 15 (4) 36-37 1995
CZE F– in boric acid J. Chromatogr. A 716 (1,2) 311-317 1995
CE River, rain, tap, and waste water Kankyo Seigyo 17 49-55 1995
Non-suppressor type F– in aqueous solutions Int. J. Environ. Anal. Chem. 62 (3) 191-205 1996
Low-pressure IC Acid rain Fenxi Shiyanshi 15 (1) 43-45 1996
IC Drinking water Am. Environ. Lab. 8 (4) 30 32-37 1996
Low-pressure IC Water and acid rain Huanjin Huaxue 15 (3) 273-277 1996
CZE Toothpaste J. Chromatogr. A 734 (2) 416-421 1996
CE Separation of F–, Cl–, Br–, I–,
S042–, N03–, HPO 42– and HCO3–		 Zheijiang Daxue Xuebao Ziran Kexueban 30 (2) 134-138 1996
IC F– in acids and concentrated inorganic salts Analusis 24 (2) 43-48 1996
Ion-exclusion-cation-exchange chromatography Acid rain Trends Anal. Chem. 15 (7) 266-273 1996
HPLC F– in bricks after de composition by melting GIT Fachz. Lab. 40 (8) 767-770 1996
Capillary GLC F– in dental creams Pharm. Acta Helv. 71 (4) 273-277 1996
IC with a novel stationary phase Separation of F– and other inorganic ions GIT Spez. Chromatogr. 16 (2)115-116 118-119 1996
CZE Separation of F– in toothpaste Anal. Commun. 34 (2) 67-68 1997
CE F– in rain water J. Chromatogr.A 734 (2) 416-421 1996

Miscellaneous methods for fluoride analysis are summarized in Table 4.



TABLE 4. Analysis of fluoride by miscellaneous methods
Method Application Reference
Microdiffusion Ionizable F– in cow's milk Analyst 120 (8) 2245-2247 1995
Shimadzu Ion Analyzer PIA-1000 F– in rain water and river water Kankyo Kagaku 5 (2) 528-529 1995.
Proton microprobe F– distributions in mollusk shells Nucl. Instrum. Methods Phys. Res. Sect. B 104 (1-4) 333-338 1995
Continuous fluoride analyzer HF emissions from ceramic ind. processes Tijdschr. Klei, Glas Keram.16 (8) 6-9 1995
Visual sensing utilizing a coupled redox reaction of ferrocenylboronic acids and dye molecules F– and saccharides Chem. Commun.(3) 407-408 1996
Energy-dispersive X-ray analysis Determination of fluorine- to-oxygen ratio Fresenius J. Anal. Chem. 356 (1) 37-40 1996
FIA F– in wastewater of aluminum plant An. Assoc. Bras. Quim. 45 (3) 106-110 1996


ACKNOWLEDGEMENT: We are grateful for support for this work from the Science Fund of Application and Foundation of Yunnan Province (Grant 96B008M) and the Science Fund of the Yunnan Education Committee (Grant 9512062).

REFERENCES

  1. Wen MI., Li QC, Wang CY. Developments in the analysis of fluoride 1993-1995. Fluoride 29 (2) 82-88 1996.
  2. Shen W, Wang XD, Catrall RW et al. Factors affecting the resistance and performance of fluoride ion-selective electrodes. Electroanalysis 7 (10) 930-934 1995.
  3. Wang XD, Shen W, Catrall RW et al. A study of the hydroxide ion interference on several fluoride ion-selective electrode membranes. Electroanalysis 7 (11) 1048-1053 1995.
  4. Papaefstathiou I, Luque de Castro MD. Integrated pervaporation/detection: continu-ous and discontinuous approaches for treatment/determination of fluoride in liquid and solid samples. Anal. Chem. 67 (21) 3916-3921 1995.
  5. Papaefstathiou I, Tema MT, Luque de Castro MD. On-line pervaporation separation process for the potentiometric determination of fluoride in "dirty" samples. Anal. Chim. Acta 308 (1-3) 246-252 1995.
  6. Stevens DP, McLaughlin MJ, Alston AM. Limitation of acid digestion techniques for the determination of fluoride in plant material. Commun. Soil Sci. Plant Anal. 26 (1,2) 1823-1842 1995.
  7. Corbilon MS, Carril MP, Madariaga JM et al. Fast Determination of total fluoride by direct potentiometry in samples of aluminum fluoride and cryolite. Analyst 120 (8) 2227-2231 1995.
  8. Hara H, Huang CC. Buffer composition suitable for determining very low fluoride using a fluoride ion-selective electrode and its application to the continuous analysis of rain water. Anal. Chim. Acta 338 (1-2) 141-147 1997.
  9. Wang LZ, Zhang XL., Yu Y et al. Determination of trace fluoride and molybdenum in serum sample by electrochemical analysis. Chin. Chem. Lett. 7 (2) 161-164 1996.
  10. Wang CY, Zhou YM, Yang WZ. Fluoride electrode-coupled minicomputer for determination of fluoride in human hair. Microchem. J. 51 (3) 373-378 1995.
  11. Stein K, Hain JU. Catalase biosensor for the determination of hydrogen peroxide, fluoride and cyanide. Mikrochim. Acta 118 (1-2) 93-101 1995.
  12. Hassan SS, El-Naby EH, Elnemma EM. Kinetic determination of morphine in illicit powders using a fluoride-selective electrode based on the reaction with 1-fluoro-2,4-dinitrobenzene. Mikrochim. Act 124 (1-2) 33-62 1996.
  13. Koeneke R, Menzel C, Ulber R et al. Reversible coupling of glucoenzymes on fluoride-sensitive FET biosensors on lectin-glucoprotein binding. Biosens. Bioelectron. 11 (12) 1229-1236 1996.
  14. Marcos J, Townshend A. Fluoride Determination by its inhibitory effect on immobilized liver esterase. Anal. Chim. Acta 310 (1) 173-180 1995.
  15. Perez-Ruiz T, Martinez-Lozano C, Tomas V et al. Flow injection spectrofluorometric determination of fluoride or phosphate based on their inhibitory effect on the photo-oxidation of acridine catalyzed by iron (III).
  16. Analyst 121 (4) 477-481 1996.
  17. Nagashima H, Okamoto T. Simultaneous determination of several inorganic anions by ion chromatography using a ceramic carbon column. Bunseki Kagaku 44 (2) 105-110 1995.
  18. Salimi-Moosavi H, Cassidy RM. Capillary electrophoresis of inorganic anions in nonaqueous media with electrochemical and indirect UV detection. Anal. Chem. 67 (6) 1067-1073 1995.
  19. Weiss J, Reinhard S, Pohl C et al. Stationary phase for the determination of fluoride and other inorganic anions. J Chromatogr. A 706 (1+2) 81-92 1995.

Department of Chemistry, Yunnan University, Kunming,Yunnan 650091, China.
Correspondence to Professor C Y Wang.
*Department of Chemistry, Baoshan Normal College, Baoshan, Yunnan 678000, China.

FLUORIDE 31(2)
1998, pp 74 - 80		 International Society for Fluoride Research
Home | Table of Contents | ISFR Board | Subscription
Submissions | Announcements | Authors | Subject Index