of traces of beryllium and silica from the borosilicate glass beaker. The reaction between acetylacetone and nitric acid is very vigorous. If unmoderated, it will throw the reactants out of the beaker and very serious burns may result. Oxidation of the extracts should be started on a hot plate just hot enough to boil chloroform. After the chloroform has been removed and the main oxidation reaction completed, the beaker can be placed on a hotter plate and evaporated to fumes of perchloric acid. Particular caution should be exercised when oxidizing larger quantities of acetylacetone and chloroform should be added to moderate the reaction. All personnel should be kept a t a safe distance routinely, while the reactions are taking place. If necessary to approach the hot plate, face shields and other protective devices should be worn. APPLICATION TO ANALYSIS
OF ORE A N D STEEL
Although the present method was developed for use on air dusts, urine, and other materials of biological importance, it has valuable applications to ore and steel. Because of its high sensitivity, beryllium can be determined in ores in concentrations of practical significance without a single separation in most cases by using samples so small that potentially interfering elements cannot acquire the concentrations necessary to interfere. A 0.100-gram sample of ore is fused with sodium pyrosulfate and boiled with dilute hydrochloric acid to hydrolyze pyrophosphates. The solution is diluted to volume in a 1-liter volumetric flask and appropriate aliquots are measured directly. A 1-ml. aliquot (100 y of sample) will permit determination of 0.01 to 1%. The most likely source of interference will be from moderate concentrations of those elements forming fluorescent complexes.
For higher concentrations of beryllium, even smaller sarriples will have to be used, which reduces the possibility of interference alm:ist to the vanishing point. To deteirnine smaller concentrations, a 100-nil. aliquot can be extracted with acetylacetone to concentrate the berylliitm and remove interferences accordin!: to the regular procedure. With stainless steel, 0.5 gram of the steel is dissolved by boiling with 10 ml. of 72% perch101.i~acid in a 250-ml. Erlenmeyer flask. When the sample had dissolved a1 (1 the solution has a bright red color, indicating complete oxidation of chroinium to the sexivalent state, chromium isj volatilized as chromyl chloride by addit on of two or three 0.5gram portions of solid sodium chloride with short periods of fuming between additions to reoxidize any chromium that gets reduced by chloride. The last portion should bv added after the solution has fumed bo the point a t which salts begin to scprate. The sodium chloride is not ti*ansposed rapidly and continuous volatilization and reoxidation are effected. The salts are dissolved in 25 ml. cf mater, and boiled for a few minutes, arid the small quantity of silica that may be present is filtered off, The solution is cooled thoroughly, and 40 nil. of 107; disodium EDTA and 10 drops of ace ,ylacetone are added, followed by concentrated ammonium hydroxide until the yellow color of the ferric-EDTA com1)lex changes to red. Solid sodium tlithionite is added in small portions until the solution is decolorized, the e>cess dithionite being kept relatively s n d l to minimize reduction of acetyl acetone. If the red color returns, more di;hionite is added immediately. A precipitate of metallic copper will freq iently collect in the chloroform layer. but does not affect recovery of beryllium. Both copper and traces of iro 1 are then eliminated by shaking the c,.rtract with 2 ml. of 1 to 1 sulfuric aci.1 containing a drop of 30% hydrogen pcbioside, adding 50 ml.
of xash solution and sufficient ammonium hydroxide to raise the p H to t,he phenol red end point. Beryllium can then be extracted back into the chloroform and the analysis finished as described. ACKNOWLEDGMENT
The author thanks his associates for assistance during many valuable discussions and in reviewing the manuscript. Special thanks are extended to J. Kenneth Plygare, Jr., for assistance in obtaining some of the data and to T. Y. Toribara for the very generous gift of pure, resublimed morin with which this work was begun. LITERATURE CITED
(1) Adam, J. A,, Booth, E , Strickland, J. D. H., Anal. Chim. Acta 6, 462 ( 1952). (2) Beeee, N. C., Riarden, J. W., J . Opt. Soc. Anz. 32,317 (1942). (3) Bird, L. H., New Zealand J . Sci. Technol. 30B,334 (1949). (4) Blaedel, W. J., Knight, 15.. T., ANAL. CHEJI.26, 741 (1951). (5) Bonner, J. F., Jr., U. S. Atomic
Energy .Comm. Rept. UR-111 (April
1950). (6) Eisenbrand, J., 2. physik. Chem. 144, 441 (1929).
(7) Feldman, I., Havill, J. R., J . Am. Cheni. Sac. 74, 2337 (1952). (8) Gilbert, R. A,, Garrett, A. B., Ibid., 78, 5501 (1956). (9) Laitinen, H. A,, Kivalo, P., ANAL. CHEW24,1467 (1952). (10) Linden, B. R.,Xucleonics 11, No. 9, 30 (1953). (11) hlnttock, G., J . Am. Che'hem. Soc. 76,4835 (1954). (12) Sandell, E. B., IND.ENO. CHEU., ANAL.ED. 12,762 (1940). (13) Schn-eitzer, G . IC.. Nehls, J. It7., J . Am. Chem. Sac. 75,4354 (1953). (14) Toribara, T. Y., Chen, P. S., Jr., h A L . CHEM. 24, 539 (1952). (15) Welford, G., Harley, J., Anz. Ind. Hyg. Assoc. Quart. 13,4 (1952).
RECEIVEDfor review July 17, 1958. Accepted October 20, 1958.
High Frequency Titrations of Silver and Thallium(1) with Sodium Tetraphenylborate ANlL K. MUKHERJI and BHARAT R. SANT Coates Chemical Laborafories, louisiana Sfafe Universify, Bafon Rouge 3, La.
The precipitation of tetraphenylborates of silver and thallium(l) has been studied with the aid of a high frequency instrument (oscillometer). These compounds are formed in a 1 to 1 ratio. It is possible to titrate 100 ml. of to 10-4M aqueous solutions of either metal ion or the negative tetraphenylborate ion with an error of about 1%. 608
ANALYTICAL CHEMISTRY
FREQCRNCY (oscillometric) titrations cf silver and mercury(11) with thiocjxnate are especially suited for the estimation of very small quantities of metal ions or thiocyanate in high dilutions (9, 11). Chemical oscillometry has found useful applications for end point detection in titrations of inorganic ions or organic functional groups, direct determination
IGH
of percentage composition of twocomponent single phase mixtures, dipole measurement studies, and determination of reaction rates (18). Hara and West (6) adapted it for the investigation of EDTA complexes of several metal ions in high dilutions. The peculiar advantage of the oscillometric technique-isolation of the sample from the electrodes-eliminates the
undesirable influences of electrode potentials and other electrolytic alteration. The instrument characteristics are then a result of changes in the dielectric, the conductivity, or both. The discovery in 1949 of sodium tetraphenylborate (TPB) as a suitable precipitating reagent for potassium ion (15) has evoked much interest in this field (1). Lane (8) has suggested the possibility of determining potassium as tetraphenylborate using a 250-mc., high frequency titrator. The reagent is also useful for rubidium, cesium, silver, thallium(I), and ammonium ions and for several organic nitrogen compounds. The quantitative precipitation of thallium(1) as tetmphenylborate was first noted by Wittig and Raff (16). Wendlandt ( I S ) adapted this reaction for the gravimetric analysis of thallium and also studied it conductometrically (14) for the estimation of 10.5 to 21 mg. of thallium in a total volume of 15 to 20 ml. The reaction between silver nitrate and negative tetraphenylborate ion has been a subject of considerable interest, especially for determining organic basic compounds by potentiometric titrations. Findeis and De Vries (4) developed a method for potassium which is based upon its precipitation as tetraphenylborate, dissolution in acetonitrile-water mixture, and aniperometric titration of the tetraphenylborate component with standard silver nitrate. No attempt seems t o have been made to study the precipitation of silver or thallium(1) as tetraphenylborate by direct titration employing the high frequency end point. The studies reported here have utilized this technique, especially t o examine the stoichiometric formation of Ag(C&)rB and TI(C6HJ4B. The results conform reasonably to this stoichiometry. The method is suitable for determining milligram quantities of either of the metal ions or the negative tetraphenylborate ion in comparatively high dilutions.
adjustment was made. An aliquot of silver or thallium(1) nitrate solution was transferred into the cell and diluted t o 100 ml. with water. This brings the solution level about 1 cm. above the upper edge of the electrode areas, minimizing the effect of further changes in the level by the addition of titrant. The initial measurement reading (capacitance) was recorded and small increments of tetraphenylborate solution were added from a microburet. After each addition the system mas well stirred with a thin glass rod and
RESULTS
VOL OF TITRANT
Figure 1 . Typical curve for titration of silver or thallium(l) nitrate with sodium tetraphenylborate
Reagents. An aqueous solution of sodium tetraphenylborate (0.lN) was prepared by accurately weighing the reagent grade sample (assay, 99.8%) supplied b y J. T. Baker Chemical Co. Aqueous thallium(1) and silver nitrate solutions were standardized by the iodate and Mohr methods, respectively. For the Mohr titration, a dry sample of analytically pure potassium chloride was used. Apparatus. A Sargent Model V oscillometer, operating a t 110 t o 120 volts and 60 cycles, was used. Titrations were carried out in a 100-ml. cell. Procedure. After the instrument was preconditioned for 30 to 60 minutes, the cell, clean and dry, was placed in position and the zero
A N D DISCUSSION
In the direct titration of silver or thallium(1) nitrate with sodium tetraphenylborate, thc instrument reading (capacitance) first decreases and then increases after the equivalence point (Figure 1). The intersection of the two straight 1ine:i denotes the precise end point. I n the reverse titration, however, there is an over-all increase in the readings, the magnitude of which is smaller before and larger after the end point (Figure 2). Because instrument charact:ristics are a result of conductance a id/or capacitance of
Table 1.
Determination of Silver and Thallium with Sodium Tetraphenylborate
Final Molarity of
Nitrate
Solution, AP X l o 4
Cation, N g . Found Calcd. Diff. S her
8.258 6.193 5.161 4.129 3.097
8.953 6.720 5.595 4.472 3.363
9.915 7.892 5.949 4.957 3.946
20.40 16.32 12.12 10.20 8.161
8.888 6.683 5.569 4.444 3.342
0.065 0.037 0.026 0.028 0.021
Thrtllium V O L O F TITRANT
EXPERIMENTAL
about 30 seconds allowed before recording the readings. Final adjustment was made a t the high sensitivity position. The strength of the reagent was adjusted so that i,he total change in the volume did not exceed 3%. Under these circumsLances, volume correction was considered ncgljgible. The reverse titrations were crzried out in a similar manner. The experimental value of the elid point was obtained from a plot of the reagent volume :idded versus the difference in the instrument readings. Typical curves ale shown in Figures 1 and 2 and rep-esentatire data are given in Tables I md 11.
Figure 2. Typical curve for titration of sodium tetraphenylborate with silver
20.26 16.21 12.16 10.13 8.104
0.14 0.11 0.04 0.07 0.057
or thallium(1) nitrate
Table II.
Determination of Sodium Tetraphenylborate with Silver or Thallium(1) Nitrate NaTPB, Mg. Final Molarity Found - Diff., Mg. TlN03, Calcd., of NaTPB, AgN03, 11.1 x 104 a b X a -x b - x ~
15.01 10.0 9.984 4.801 5.264 5.003 4.992 4.001
50.79 33.78 20:32 17.94 17.27 13:86
51.03 34.04 34.04 17:02 17.02 13.55
51.36 34.24 34.18 20.54 18.01 17.12 17.09 13.69
VOL. 31,
0.57 0.46
...
0.22 0.07 0.15
...
0.17
NO. 4, APRIL 1959
0.33 0.20 0.14
... ...
0.10 0.07 0.14
609
the sample, these behaviors are expected. Table I shows that the values are in reasonable agreement with those calculated by the standard procedures. Table I1 shows that the method can also be used for the estimation of tetraphenylborate with standard silver or thallium(1) nitrate. Crane (2, S), in a study of the potentiometric titration of negative tetraphenylborate ion with silver nitrate, found that the results obtained using sodium chloride instead of potassium tetraphenylborate as a primary standard deviate by 5.4%. Kirsten et al. (7) attributed this discrepancy to the tendency of silver ion to precipitate more tetraphenylborate than that required for one valence. The standardization of silver nitrate against potassium tetraphenylborate under the conditions used in the determination was therefore recommended. However, Findeis and De Vries (4) performed experiments using the amperometric end point for the titration of the tetraphenylborate part of the potassium compound with silver nitrate and noticed no discrep-
ancy. They wported accurate results for potassium on the basis of silver nitrate as a ftandard. Similarly, the argentometric titration of tetraphenylborate part using eosin (10) or chromate (6) indicator p v e good results. The results reportad here show that the precipitation of silver or thallium tetraphenylboixte takes place stoichiometrically untler the conditions described in a l to l ratio. Although t t c high frequency method is not very awurate, its ability to accommodate s n d 1 concentrations of materials in comparatively high dilutions is a distinct advantage. ACk:I4O WLEDGMENT
The authors are indebted to Philip
W. West for wearch facilities and his keen interest i n the work. LI’TRATURE CITED
(1) Barnard, .I, J., Chemist Analyst 44, 104 (1955); 45, 110 (1956); 46, 16 (1957). (2) Crane, I?. ‘I
