LITERATURE CITED A. Curry, "Poison Detection in Human Organs", 2nd ed., Charles C Thomas, Springfield. Ill., 1969, p 117. E. G. C. Clarke, "isolation and Identification of Drugs", The Pharmaceutical Press, London, 1969, p 84. W. B.Furman, J. Assoc. Off. Agric. Chem., 5 1 , 1111 (1968). The Sadtler Standard Spectra-Pharmaceutical, Sadtler Research Laboratories, Philadelphia, Pa. "CRC Handbook of Analytical Toxicology", I. Sunshine, Ed., The Chemical Rubber Co., Cleveland, Ohio, 1969, p 212.
(6) "CRC Atlas of Spectral Data and Physical Constants for Organic Compounds", J. G. Grasselti, Ed., The Chemical Rubber Co., Cleveland, Ohio, 1973. (7) A. L. Hayden, 0. R. Sammul, G. R. Selzer, and J. Carol, J. Assoc. Off. Agric. Chem., 45, 797 (1962). (8) J. E. Wallace, J. D. Diggs, and S. L. Ladd, Anal. Chem., 40, 823 (1968). (9) F. A . Rotondaro, J. Assoc. Off. Agric. Chem., 40, 823 (1957).
RECEIVEDfor review August 18, 1975. Accepted October 27,1975.
Beryllium as a Masking Agent for Fluoride in the Spectrophotometric Determination of Iron and Titanium Allan F. M. Barton' and Stephen R. McConnel School of Mathematical and Physical Sciences, Murdoch University, Perth. Western Australia 6 153
The use of beryllium as an inhibitor for fluoride interference in the spectrophotometric determlnation of iron and lltanium using disodium-1,2-dihydroxybenzene-3,5-disulfonate is described. The method depends upon the formation of a beryllium fluoride complex.
During a study of the dissolution kinetics of natural ilmenite in acid solutions, it was necessary to analyze the solutions for iron and titanium in the presence of fluoride. In the absence of fluoride, the colorimetric reagent, disodium1,2-dihydroxybenzene-3,5-disulfonate (Tiron), first used by Yoe and Jones ( I ) for iron, and Yoe and Armstrong ( 2 ) for titanium, was satisfactory. However, in the presence of fluoride a t pH 4.7,both the yellow titanium-Tiron and violet iron-Tiron complexes are destroyed. The usual time-consuming practice of driving off the fluoride by evaporating to fumes of sulfur trioxide was unsatisfactory because of the large number of analyses required. Fujimoto ( 3 ) had used beryllium to eliminate fluoride interference in the analysis of titanium solutions by the common hydrogen peroxide colorimetric method. Since fluoride forms a more stable complex with beryllium than with either titanium or iron, the interference is removed. I t was then necessary to determine if the use of beryllium to complex fluoride could be extended to the Tiron determination of titanium and iron.
EXPERIMENTAL Instruments. Spectrophotometric measurements were made with a Varian Techtron 635 double-beam spectrophotometer, a t a slit width corresponding to 0.5-nm spectral bandpass. Reagent Solution. A solution containing 4 g of Tiron, C,,jH2(OH)2(S03Na)2. H20, in 100 cm3 of water was prepared giving a concentration of 0.12 M . Standard Titanium and Iron Solution. Exactly 0.1598 g of titanium dioxide was dissolved in a mixture of 20 cm3 of concentrated sulfuric acid and 8 g of ammonium sulfate under reflux. The resulting solution was transferred t o a 1-liter volumetric flask. Exactly 0.9644 g of ferric ammonium sulfate dodecahydrate was dissolved in 20 cm3 dilute sulfuric acid and transferred to the flask containing the titanium. When diluted to the mark, this stock solution was 2 X low3M in both titanium and iron. Procedure. The basic procedure used for the determination of iron and titanium was similar to that reported by Potter and Armstrong ( 4 ) .
The absorbance of standard solutions of Fe(II1)-Tiron complex buffered a t pH 4.7 was measured in the spectrophotometer a t a wavelength of 560 nm since the titanium complex has negligible absorbance a t this wavelength. The color due to the iron complex was then destroyed by reducing the ferric ion to the ferrous form with a little solid sodium dithionite, Na2S204. The absorbance of the Ti(1V)-Tiron complex solution was then measured at 410 nm. Since the titanium complex has a higher molar absorptivity, 1.000-cm glass cells for titanium and 4.000-cm glass cells for iron were employed. Beer's law was obeyed by both titanium and iron for concentrations up to a t least 8 X 10-5 M . To measure the effectiveness of beryllium as a reagent for removing fluoride interference, known quantities of fluoride, as 50% hydrofluoric acid, and beryllium, as a 2.4 M beryllium sulfate solution, were added to samples of stock solution containing known quantities of titanium and iron. The absorbance of the resulting solutions was measured, vs. blanks containing none of the Tiron reagent, a t 560 and 410 nm as described. The measured absorbance was then compared with that given by the calibration plot. A small polypropylene beaker was used to mix the solutions; but once the solution was neutralized with concentrated ammonium hydroxide and buffered a t pH 4.7, it was possible to transfer the solution to a glass 50-ml volumetric flask without danger of the glass being attacked.
RESULTS AND DISCUSSION Although experiments were carried out using solutions containing both titanium and iron in concentrations rangM, the results reing from 1 X 10-5 M through to 8 X ported in Table I and in Figure 1 are for solutions of 4 x M concentration only, Le., the middle of the working range, since all the solutions studied showed similar behavior. The standard deviation in absorbance calculated using the results of experiments 1 to 5 was 0.004 for Fe3+ and 0.001 for Ti4+. By comparing the absorbance values of solutions containing fluoride and beryllium with those obtained for solutions containing no fluoride or beryllium, it can be seen that the interference has been totally removed when [Be2+]/ [F-] 1 0.6. The scatter in data in Figure 1 for [Be*+]/[F-] < 0.5 is the result of variation in the volume of beryllium solution added; while, for higher ratios, the absorbance becomes independent of the exact Be2+concentration. Since the addition of beryllium above the ratio of 0.6 causes no additional increase in the absorbance, it suffices to ensure that an excess of beryllium is added. A ratio of [Be*+]/[F-] = 1 would be a suitable convenient condition.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 2, FEBRUARY 1976
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Table I. Experimental Data for Solutions Containing M Ti4+and Fe3+ 4x
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
[F-]/M
[Be*+]/M
... ... ... ... ...
...
[BeZ+]/ [F-]
... ...
... ... ... ... ...
0.096 0.096 0.0108 0.0144 0.018 0.0216 0.144 0.192 0.192 0.223 0.384 0.480 0.432 0.576
7.69 3.85 0.29 0.39 0.48 0.58 0.58 0.77 0.77 0.58 0.77 0.96 0.58 0.58
... ...
Absorbance 560nm
41Onm
0.752 0.760 0.752 0.757 0.760 0.762 0.757 0.736 0.746 0.757 0.753 0.760 0.752 0.759 0.760 0.754 0.759 0.758 0.760
0.507 0.507 0.506 0.507 0.508 0.508 0.507 0.420 0.500 0.507 0.507 0.507 0.506 0.508 0.507 0.508 0.508 0.507 0.510
;i-2 30 12
C 2
03
OL
05
06
07
28
09
1:
[Bez'l/ IF 1
Figure 1. Absorbance vs. [Be2+]/[F-] ratio for solutions of 0.5 M
F-I The fluoride ion concentration was varied from 0.0125 to
0.0125 0.025 0.0375 0.0375 0.0375 0.0375 0.25 0.25 0.25 0.3875 0.5 0.5 0.75 1.0
1.0 M and, at all concentrations, the interference could be
removed by addition of beryllium. The upper limit of 1.0 M fluoride concentration was set only by the use of a 50-ml volumetric flask, higher concentrations of fluoride not being possible within a total volume of 50 ml, because of the need to include beryllium solution, buffer solution, Tiron solution, etc. However in practice when analyzing a solution, obtained for example by dissolving a mineral or ore containing iron andlor titanium in a mixture of hydrofluoric and sulfuric acids, the fluoride ion concentration would rarely approach 1.0 M . Whenever the beryllium concentration of the solutions exceeded approximately 0.15 M , a transient, colorless, gelatinous precipitate was formed during the final stages of neutralization with concentrated ammonium hydroxide. This precipitate, presumably of beryllium hydroxide, completely redissolved on standing for 5 to 10 minutes. Stirring the solution during the addition of the ammonium hydroxide kept the quantity of precipitate to a minimum.
The violet iron-Tiron and yellow titanium-Tiron complexes were stable for long periods as reported by Yoe and Jones ( I ) and Yoe and Armstrong (2). The presence of the beryllium-fluoride complex appeared to have no affect upon this property. Solutions containing excess beryllium ( [Be2+]/[F-] 2 0.6) gave the same absorbance values for a t least 24 hours. This work confirms that the determination of titanium and iron using Tiron can be carried out, in the presence of up to 1 M fluoride, simply and quickly by the addition of beryllium.
LITERATURE CITED (1) J. H. Yoe and A. L. Jones, lnd. Eng. Chem.. Anal. Ed., 18, 111 (1944). (2) J. H. Yoe and A. R. Armstrong, Anal. Chem., 19, 100 (1947). (3) M. Fujimoto, Bull. Chem. SOC.Jpn, 29, 783 (1956). (4) G. V. Potter and C. E. Armstrong, Anal. Chem., 20, 1208 (1948).
RECEIVEDfor review July 17, 1975. Accepted October 6, 1975.
Determination of Ascorbic Acid in Foodstuffs, Pharmaceuticals, and Body Fluids by Liquid Chromatography with Electrochemical Detection Lawrence A. Pachla and Peter 1.Kissinger' Department of Chemistry, Purdue University, West Lafayette, Ind. 47907
A chromatographic method for the analysis of ascorbic acid utilizing a thin layer amperometric detector with a carbon paste electrode is described. Application of the new method is evaluated for multivitamin preparations, fruits, juice concentrates, milk products, urine, and serum. When possible, standard redox tltration procedures were used to corrobo384
rate the chromatographic method. When compared to ciassicai titrations or colorimetric redox procedures, the new assay features straightforward sample preparation and improved sensitivity and seiectivlty. A sample rate as high as 20/hr is possible, depending on the particular sample under study.
ANALYTICAL CHEMISTRY, VOL. 48, NO. 2, FEBRUARY 1976
