ml. portions of chloroform and dilute to 50 ml. Evaporate 2 ml. of this solution (2.0 y of ll-desmethoxyreserpine) to dryness under nitrogen. Take the residue up in 5147 acetic acid and carry out the fluorescent procedure as described. Parenterals and Elixirs. Pipet a volume of sample t o contain 0.25 mg. of 1I-desmethoxyreserpine into a centrifuge tube containing 10 ml. of 1% sodium bicarbonate. Extract with three 10-ml. portions of chloroform and proceed as above. The chloroform extraction is carried out of 1% sodium bicarbonate to remove any 3,4,5-trimethoxybenzoic acid or 11-desmethoxyreserpic acid formed from possible breakdown of ll-desmethoxyreserpine. Although other substances present are also extracted into chloroform, the large dilutions allowed by the enhanced fluorescence brought on by the cerate reagent apparently dilute out interfering fluorophors to a level where they are not measured. This became evident when dosage forms were
extracted such th:it the final solution contained more than 5 y of 11-desmethoxyreserpine per 10 ml. I n these cases spurious fl iorescence was encountered, giving high figures for the drug content. g e a r the COmpletiOll of this work, the procedure wae applied to mixtures of 11-desmethoxyreserpine and reserpine. It was founll that with reserpine the cerate reagent produces a fluorescence of about one third the intensity as that of 11-desmi:thoxyreserpine on an equal weight basis. Using the AmincoB o ~ m a n sPectroPhotofluorometer it was found that with samples of 1 to 5 y, mixtures of the two alkaloids treated with cel-ate gave a linear fluorescence respcnse. Thus, used in conjunction with another method for reserpine that giv2s a fluorescent peak in a region remoyied from the cerateinduced ll-desmet]loxyreserpine peak, both components may be determined using simple algelxaic equations. Details of this procedure and a comparison
with other possible procedures for mixtures of these alkaloids will be published
(I), LITERATURE CITED
(1) Gordon,
J. A., Campbell, D. J., unpublished work. (2) Harrisson, J. W. E., Packrnan, E. W., Smith, E., Hosansky, N., Salkin, R., J . Am. Pharnt. Assoc. 44, No. 11,688 (1955). (3) MacPhillamy, H. B., Dorfman, L., Huebner, C. F., Schlittler, E., St. And&, A. F., J . Am. Chein. SOC. 77,1071 (1955). (4)Schlittler, E., Ulshafer, P. R., Pandow, M. L., Hunt, R. M., Dorfrnan, L., Experientia 11, 64 (1955). (5) Slater, 1. H., Rathbun~ Henderson, G., Neuss, N., Proc. SOC. Exptl. Biol. Med. 88, 293 (1955). (6) Stoll, A., Hofmann, A., J . Am. Chern. SOC.77,820 (1955).
RECEIVED for review September 6, 1956. Accepted December 8, 1956. Division of Analytical Chemistry, 130th Meeting, ACS, Atlantic City, r\~. J., september 1956.
Spect rophoto met ric Determination of Te IIuriu m M. W. HANSONI, W. C. BRADBURY2, and J. K. CARLTOId3 Universify o f Arkansas, Department of Chemistry, Fayefteville, Ark.
,Tellurium(lV) can be determined rapidly and accurately by a simple spectrophotometric method which overcomes the difficulties involved in the usual gravimetric procedures. The absorbance a t 376 mp i s measured in a concentrated hydrochloric acid solution. The method i s applicable to lower concentrations of teIIurium(IV) than the gravimetric procedures. Ions which interfere in the determination are discussed.
T
ELLuRIubf has been determinecl by numerous methods (1-7, 9, 11, 15, I C ) . The best gravimetric procedures described are the precipitation of tellurium metal by sulfur dioxide or stannous chloride. Precipitation with sulfur dioxide requires rather careful control of experimental conditions. The method is unsatisfactory for low
1 Present address, Chemical Warfare Laboratory, Army Chemical Center, hld. 2 Present address, Celanese Corp., Corpus Christi, Tex. 3 Present address, Dept. of Chemistry, Georgia Institute of Technology, Atlanta, Ga.
490
ANALYTICAL CHEMISTRY
concentrations of tellurium as i t produces very finely divided tellurium metal. Although stannous chloride can be used successfully for lower concentrations of telluriim, its application a t very low concentrations is also hindered for the same reason. Two spectrophotometric methods for determining telhriuni have been reported. The mei,hod of Wiberley and coworkers (15) ulilizes the red color of the addition compound of tellurium and sulfuric acid, and is applicable only in a concen;ration range up t o 6 p.p.m. of tellurium. Scott and Leonard ( I d ) have reported a spectrophotometric method for the determination of telluric acid which covers a concentration range of 65 to 210 mg. of telluric acid per 100 ml. of soh tion. Although sligh,ly less sensitive than the method of Wiberley, the present method offers a simple, direct, and accurate means of determining tellurium and extends the range over which it may be determined. Because tellurium(1V) in concentrated hydrochloric acid produces a yellow color, the possibility of using this reaction for spec;rophotometric determination was invc stigated. It was found
that tellurium could be determined with a high degree of accuracy and that the method was applicable to solutions containing tellurium(1V) in concentrations from 0.8 to 9.6 mg. per 100 ml. of solution. REAGENTS AND EQUIPMENT
Tellurium(1V) dioxide, prepared according to Marshall (8). Hydrochloric acid, Baker and Adamson, C.P. grade. Reagents for interference study, analytical reagent grade. Beckman Nodel DU spectrophotometer. Xatched set of 1-em. silica absorption cells. PROCEDURE
Weigh out a sample containing 1 t o 120 mg. of tellurium(1V) dioxide, transfer to a 100-ml. flask, and dilute to the mark with concentrated hydrochloric acid. Transfer a 10-ml. aliquot to a second 100-ml. flask and dilute to the mark with concentrated hydrochloric acid. Measure the absorbance a t 376 mp. Use concentrated hydrochloric acid as the blank.
which form colored solutions with concentrated hydrochloric acid (Table I). Only those ions which form yellow solutions interfere in the telluriuni determination. These ions were found to interfere when present in quantities less than 10 mg. per 100 ml. Although cobalt and nickel form colored solutions with concentrated hydrochloric acid, they do not interfere in the determination. The iron interference could not be removed by complexing with phosphate. Of the three metals frequently found in tellurium samples-lead, bismuth, and selenium-only lead gave no interference. Selenium interfered in the determination when present in amounts greater than 4.9 mg. per 100 ml. and bismuth interfered when present in amounts greater than 88 mg. per 100 ml. of solution.
DiSCUSSlON
Table 1.
Interference Study
(Solutions contain 10 mg. of tellurium(1V) dioxide per 100 ml.) Concn. of Interfering Ion, Mg./lOO Ion Test hll. Fe++ Pellow 10 Fe+++ Yellow 10 c u+ Yellow 10 Cu++ Yellow 10 sn++ Black ppt. 10 Ce +4 Yellow 10 Bi+++ Colorless 300 VOa--CmO,-Se03-I-
(?)
Yellow Yellow Yellow Black ppt.
10 10
8 10
If telluriuni(V1) is present, it can be reduced to tellurium(1V) by boiling with hydrobromic acid, adding concentrated hydrochloric acid, and boiling to displace the bromine. Tellurium(V1) is also reduced by concentrated hydrochloric acid, but the reduction with hydrobromic acid is faster. Tellurium metal may be dissolved in n minimum aniount of hot concentrated nitric acid. T o displace the oxides of nitrogen, concentrated hydrochloric acid is added and the solution evaporated to dryness a t a temperature below
I
d calibration curve is prepared by varying the concentration of tellurium(117) . dioxide in concentrated hydrochloric acid. The curve conforms to Beer's lam up to a concentration of 12 mg. of tellurium(1V) dioxide per 100 ml. At 13 mg. per 100 nil. of solution, the absorbance m s too high to permit measurement in a 1-em. cell. Analysis of 10 separately prepared samples which contained 5.00 mg. of tellurium(1V) dioxide per 100 nil. of solution gave an average value of 4.99 mg. per 100 ml., a n average deviation of 0.014 mg., a range of 0.04 mg., and a standard deviation of 0.01 mg. INTERFERENCES
There are several other metal ions
WAVE
LENGTH
I m F 1
Figure 2. Absorptivity vs. wave length in visible region A.
6F hydrochloric acid B. 9F hydrochloric acid C. 12F hydrochloric acid
100" C. The tellurium is then taken up in concentrated hydrochloric acid and the absorbance of the solution is determined on the spectrophotometer. Investigations of tellurium(1V) in hydrochloric acid solutioiis (IO)indicate that there is more than one species of ion present. These ion species apparently are dependent upon the fornial concentration of the hydrochloric acid. Prom 12- to 9F hydrochloric acid, the absorptivity of the species is independent of the h i drochloric acid concentration, There are two absorption maxima, one occurring a t 269 mp and the other a t 376 mp (Figures 1 and 2). I n 6F hydro1:hloric acid, the solution no longer shows an absorption maximum in the ultraviolet region; the absorbance has drcipped appreciably in the visible region, although the maximum still occurs a t the mine wave length. Therefore, when the absorption a t 376 mp is used, the optimum acid conccntration a t which the experiment can be run is from 9- to 12F hydrochloric acid. The absorption maximum a t 269 mp was not thoroughly investigated, but it mas found that it could not be used a t concentrations belorr 0.1 mg. or above 0.5 mg. of telluriuni(1V) dioxide per 100 ml. of solution.
LITERATURE CITED
(1) Bflek, P., Collection Czechoslov. C h e w Conzinzins. 10,430 (1938). (2) Clauder, 0. E., 2. anal. Cheni. 89,
270 (1932). (3) Hecht, I?., John, L., 2. anorg. u. dlgem. Chein. 251, 14 (1943). (4) Johnson, R. A., IZwan, F. P., ANAL. CHERI. 23, 651 (1951). (5) Khaled, B., Khaled, V., J . pharm. chim. 27,443 (1938). (6) Lingane, J. J., Niedrach, L., J . Ani. Chem. Soc. 70,1997 (1948). (7) ?tIcKenn,%, F. E., Templeton, D. H., National Piuclear Energy Series, Div. 17111, "Analytical Chemistry of the .\lanhattan Project," p. 303, RIcGraw-Hill, Sew York, 1950. (8) Marshall, H., Inorg. Syntheses 3, 143 (1951). (9) Norwitz, G., Anal. chinz. acta 5 , 106 (1951). (10) Plank, P[. F., Ph.D. thesis, Massachusetw Institute of Technology, 1951. (11) Schoeller, W. R., Analyst 64, 318 (1934) (12) Scott, L. W., Leonard, G. W.,Jr., ANAL.CHEM.26,445 (1954). (13) Shakhov. A. S., Zavodskaya Lab. 11,893 (1945). (14) TomiEek, O., FilipoviE, P.,'Collection Czechodov. C h e w Conzmuns. 10, 415 (1!)38). (15) Wiberley, S. E., Bassett, L. G., Burrill, A. hl., Lyng, Helen, ANAL. CIIEJI. 25, 1586 (1953). RECEIVED for review September 12, 195G. Accepted November 27, 1956. VOL. 29, NO. 4, APRIL 1957
491
