60.0
10.0
d
g
1.0
E n 0
.IO
I
1
.03
I
60 20 40 MOLE PER CENT COPPER
I 80
Figure 3. Copper to nickel peak ratio vs. mole % of copper for lower concentration analysis
respective peaks appeared the strongest of the four metal ions on the x-ray patterns. The procedure was the same as before eucept t h a t the precipitate3 were still in their filter papers when placed in the cellophane envelopes. Results for copper(I1) in the range of 0 to 1.2 mg. and nickel(T1) in the range of 0 to 1.3 mg. are shown in Figure 3. The ratios agree well
with those obtained earlier for copper(I1) and nickel(I1) in Figure 1, although the calibration line is more curved. The results indicate a relative error of *3y0. It seems probable that the analysis may be taken to still lower concentrations for these as well as for other binary combinations. The limitations in analyzing solutions of lower concentrations are with the solubilities of the chelates, the decrea,se in the peak to background ratio, and the differences in the emission energies of the metal ions under consideration. Analysis of Quaternary Mixtures. A series of samples was run with all four metal ions preqent in the mixtures. Each analysis was conducted by taking the iron to nickel ratio for the iron(II1) concentration, the copper t o cobalt ratio for the copper(I1) concentration, the nickel to cobalt ratio for the nickel(I1) concentration, and the copper t o cobalt ratio for the cobalt(I1) concentration. With two metals present, secondary fluorescence (enhancement) is compensated in the binary metal curveq for each of the binary metal syqtems. For precise results, when more than two metals are preqent, a correction must be made for secondary fluorescence. For the four metals studied, these corrections are extremely difficult. However, reasonable results are obtained (without correcting for secondarv fluorescence) by selecting the specified metal pairs in the above ratios for analysis of the six samples investigated. The results of this analysis are found in Table 11.
Table II. Analysis of Fe(lll), Co(ll), Ni(ll), and Cu(ll) Quinolate Mixture Milligrams of metal
Present Found Present Found Present Found Present Found Present Found Present Found
ion in each sample Fe(II1) Co(I1) Si(I1) Cu(I1) 2 8 3 0 3 0 3 3 3 4 2 8 3 3 3 6 2 8 3 0 3 0 3 3 2 7 2 9 2 9 3 6 11 1 6 0 2 9 3 3 9 7 2 8 4 9 11 1 9.6 1.4 3.1
5 5 3 0 3 8 6.0 7.6 1.5
2.3
3 4 5 9 7 4 1.5 1.3 5.9 7.4
4 6 13 1 9 2 1.6 1.7 13.1 9.0
LITERATURE CITED
(1) Daugherty, K. E., Robinson, R. J., Slueller, J. I., -4ii.4~.CHEM.36, 1098 (1964).
KENNETH E. DSUGHERTY REXJ. ROBINSON Department of Chemistry University of Washington Seattle, Wash. 98105 J A M E S I. ~ I U E L L E R Ceramic Engineering Division University of Washington Seattle, Wash. 98108 Presented at 147th RIeeting, ACS, Philadelphia, Pa., April 5-10, 1964. Work supported in part bv fellowships from the Sational Science Foundation and the Standard Oil Co. of California to Kenneth E. Daugherty.
Spectrophotometric Determination of Rhenium with A Ipha -Pyrid iIdioxime SIR: Three a-dioximes, dimethyla-benaildioxime ( 5 ) , and glyoxime (4, a-furildioxime ( I ) , have been proposed as colorimetric reagents for rhenium. a-Prridildioxime has now been investigated and has been found to provide a simple, rapid, sensitire method for the colorimetric determination of rhenium. T h k compound reacts with the perrhenate ion in the presence of tin(I1) chloride in dilute hydrochloric acid to produce a yellow, water-soluble compound with an absorption maximum at 440 mp, and which conforms to Tker'q lan- to 4 x 10+Ji with a molar absorptivity of 31,500. EXPERIMENTAL
Reagents
and
Apparatus.
a-
Pyridildioxinie XI as prepared by the method of Trask ( 3 ) . 3lelting point: found, 215' C. ( d , ) ; literature, 215" C. (d.) ( 3 ) . For the determination of rhenium bv the method described below the m a l l amounts of impuritieq found in the crude product from the oximation reaction do not interfere, and recrystallization 17 not necessary. h 1870
ANALYTICAL CHEMISTRY
0.01.11 stock solution was prepared by dissolving 1.213 grams of the crude dioxime in 500 ml. of water. Potassium hydroxide pellets were added as needed to effect solution of the dioxime. A 0.01.11 solution of potassium perrhenate was prepared and diluted as needed. The potassium perrhenate was analyzed bv the tetraphenylarsonium chloride method. Results of 99.9, 99.9, and 100.O~opotassium perrhenate were obtained. The tin(I1)-hydrochloric acid reducing solution was prepared by diqsolving 100 grams of reagent grade tin(I1) chloride dihydrate in 1 : 1 of 6 M hvdrochloric acid." A411 other chemicals were reagent grade. Spectrophotometric measurements were made with a Hitachi PerkinElmer Model 139 spectrophotometer using matched 1-em. silica cells. Procedure. ;idd a n aliquot containing less than 375 ~ g of. rhenium to a 50-ml. volumetric flask. If the rhenium is in the form of the hexachloro- or hexabromorhenate(IV), add one pellet of potassium hydroxide and heat in a boiling water bath for 10
minutes, then cool. If the rhenium is present as perrhenate, no treatment with base is necessary. A4ddone drop of phepolphthalein and treat with potassium hydroxide or hydrochloric acid until the indicator is just changed to its colorless form. Add 5 ml. of 0.01M a-pyridildioxime and 10 ml. of tin(I1) chloride solution and dilute to the mark with distilled mater. After 20 minutes read the absorbance of the solution against a distilled water blank at 440 mp. The colored compound is stable for about 1 hour. Molybdenum interferes with the above procedure. Rhenium can be conveniently separated from molybdenum by extracting the perrhenate into pyridine from an aqueous solution which is 5 M in sodium hydroxide ( d ) . RESULTS
The results of analyses using this procedure are given in Table I. The purity of the compounds used had been previously established by analysis for rhenium with tetraphenylarsonium chloride.
Table
I.
Determination of Rhenium with a-Pyridildioxime
Rhenium Rhenium Rel. Comtaken, found, error, rg. 9% pound KReO4 37.2 37.2 0.0 KReOl 74.4 74.2 -0.3 KReO4 112 112 0.0 KReO4" 112 113 +0.9 KReO4 149 150 +0.7 K2ReC16 171 171 0.0 KzReBrs 179 179 0,0 KRe04 186 186 0.0 a 100 mg. of Mo added as XaaMo04. Perrhenate separated by extraction from 531' NaOH into pyridine.
Effect of Reagent Concentrations. T h e maximum color intensity and the time required t o reach it were studied as a function of t h e acid concentration, and the optimum concentration was found t o be 1.2M in hydrochloric acid. At lower and higher concentrations the color intensity was lower and the time required to reach t h e maximum was longer. Color intensity increased with increasing ligand concentration until a ligand to metal ratio of 7 : l was reached.
Beyond this point the ligand concentration had no effect on color intensity. Experiments in which all concentrations except that of the tin(II) chloride were held constant indicated that the optimum concentration of this reagent is 1 gram per 50 ml. of final iolution. Cse of more or less of this reagent lowers the absorbance by a significant amount. Order of Addition of Reagents. T h e order of addition of reagents was unimportant when the rhenium was in the form of the perrhenate ion. K i t h the hexachloro- and heuabromorhenate(IV) ions, more reproducible results \+ere obtained when the ligand was added before the tin(I1) chloride. Effect of Foreign Ions. To determine the effect of foreign ions, 112 p g . of rhenium as the perrhenate were treated with 100 mg. of the foreign ion and the recommended procedure b a s followed. Those ions causing less than 2y0 relative error were Pb(II), Al(Ill), Ri(III), K(I), Mg(II), Cd(II), Mn(II), Zn(II), Sr(II), and acetate. Those ions causing more than 27, but less than 5% relative error were Cu(II), Sb(III), sulfate, phosphate, and citrate. X relative error of less than 557, resulted from Ni(I1) if twice the
recommended amount of ligand was used. I relative error of leqt than 2% resulted with Cu(I1) under the .ame conditions. While 100 mg. of Fe(II1) and Co(II) caused relative error5 of lo%, 50 mg. of Fe(II1) or 25 mg. of Co(I1) caused relative errors of less than 27,. Complete interference resulted from the presence of Cr(III), molybdate, oxalate, and thiocyanate. LITERATURE CITED
( 1 ) ;Ileloche, V. l f . , llartin, R. I,., Webb, W. H., .%NAI,. CHEM 29, 52i
( 1957). (2)-Meshri, D. T., Haldar, R . C., J . S e i . Ind. Res. Indza 20B, 551 (1961). ( 3 ) Trask, W. T., Jr., Ph.D. thesis, Iowa State University, '1957. (4) Tougarinoff, M. B., Rvll. Soc. Chim. Relges 43, 111 (1934). ( 5 ) Tribalat, S.,Compt. Rend. 224, 469 (1947). FREDTRCSELL~ RICHARD J. THOMPSOX
Department of Chemistry Texas Technological College Lubbock, Texas
WORK carried out under Grants D-094 and D-097 from The Robert A. Welch Foundation, Houston, Texas. Present address, Marathon Oil Co., Denver Research Center, Littleton, Colo.
Spectrophotometric Determination of Glycyrrhizic Acid in Licorice Extract Sir: I n the L-nited States the tobacco industry is the largest user of licorice extract, Succus liphii!iae, which serves as a characteristic :flavorant and a moisture-controlling agent in tobacco casing solutions. The active principle of licorice is a sweet-tasting material rrhizin, a glycoside in the otassium ;and calcium salt form of glycyrrhizic acid. Proper evaluation of licorice estract is dependent in part on accurate determination of the glycyrrhizic acid content. Xieman ( 3 ) , in his excellent study, gives not only the means of assay and chemical structure for glycyrrhizin, but other details on the licorice root and estract including its pharmacology. Thp most widely used technique for rrhizin determination is the acid precipitation proce Houseman ( 2 ) . T h painstaking, and larks both accuracy and specificity. The most promising; method for specific determination of glycyrrhizic acid is to hydrolyze it to its aglycon, glycyrrhetinic acid, and after extraction determine the aglycon eit,her by colorimetric, ultraviolet, or polarographic means. W e a t (5) and Brieskorn and blahran ( 1 ) describe colorimet,ric meth-
ods, whereas Onrust, Jansen, and Wostmann (4) describe a polarographic method. These methods were investigated a t considerable length, and the procedure finally evolved was a modification of the colorimetric procedure described by Wiest (6),using a modification of Onrust, Jansen, and Wostmann (4) to hydrolyze glycyrrhizic acid to glycyrrhetinic acid. EXPERIMENTAL
Reagents. Vanillin, 1% in absolute ethanol. Store in an amber bottle. Glycyrrhetinic acid, st,andard. No commercially available material was of sufficient purity for use as a standard. Prepare by dissolving 5 grams of ammonium glycyrrhizinate in 500 ml. of 50y0 dioxane (v./v.) and reflux with 100 ml. of 5 N sulfuric acid for 3 hours. Extract with chloroform and evaporate the chloroform solution to dryness under reduced pressure. Dissolve the residue in ethanol, char-treat, and filter. Heat the filtrate to boiling point, add water until slightly turbid, remove from heat, and allow to crystallize. Recrystallize two additional times in similar manner and drv at 110" C. Melting point (uncorr.), "294-297' C. Purity by nonaqueous titration, 100.28'%.
M o n o a m m o n i u m glycyrrhizinate MacXndrews and Forbes Co. Purified by two recrystallizations from dilute ethanol. Purity by nonaqueous titration, 99.82%. Hydrolysis Procedure. A4ccurately weigh 0.1 gram of licorice into a 250ml. T Erlenmeyer flask, add 20 ml. of 50% dioxane, and connect to a reflux condenser. Apply heat and when the licorice is dissolved, add 20 ml. of 12N sulfuric acid through the top of the condenser. Reflux vigorously for 1 hour, add 70 ml. of water, then 100 ml. of chloroform t,hrough the top of the condenser. Reflux an additional 15 minutes, cool, then transfer the contents of the flask t'o a 250-ml. separatory funnel. Shake vigorously, allow the phases to separate, and draw the chloroform layer into a second funnel containing 100 ml. of 2% sodium bicarbonate. Shake vigorously, and after phase separation drain the chloroform layer into a chromatographic tube containing 25 grams of sodium sulfate, collecting the filtrate in a 200-ml. volumetric flask. Repeat the extractions with 75, then 25 ml. of chloroform, finally adjusting the volume of the filtrate to 200 ml. Analysis for Glycyrrhetinic Acid, Pipet 4.0 ml. of the chloroform dilution into a 20- X 200-mm. test tube, and 4.0 ml. of chloroform into a second tube to serve as a blank. VOL. 36, NO. 9, A U G U S T 1964
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