perature was too short, the blank value became higher, but the color yield was not so much influenced. Too high a concentration of ammonium thiocyanate caused a slight loss of the complexes of the acids to be determined. More polar soltents were more effective for extraction of thiocyanato complexes. However, too high polarity of solvent increased the loss of the arid complexes. When the ratio of 1-butanol to ethyl acetate was more than 2 to 1, the blank value decreased markedly, but the color yield was very low and fluctuated. Complexes of monobasic acids, especially those of fatty acids, were readily extractable by the abovementioned solvents. Therefore, these acids were not determined by this method. On the other hand, polybasic acids or other highly functional organic acids could be determined in the presence of monobasic acids. Color Development with EDTA. Cdlini and Valiente (2) reported that the color developed by the reaction of chromium with EDTA was constant a t pH 1.5 to 4.0. The author, however, found that in the reaction of chromiumorganic acid complex with EDTA, the color yield was markedly dependent on pH, and was optimum at p H 2.8.
I
Color Yield and Structure of Acids. Table I shows the absorbance per 10 pmoles of organic acid8, when the final volume was 10 ml. When an acid reacts in the molar ratio of 1 t o 1 with cis-dichlorobis(ethy1enediamine) c h r omium(111) ion, the absorbance per 1 pmole of the acid should be 0.0193. Most of the dibasic acids gave values very near to this, while the value for hydroxy acids was always abnormally high-for example, the value for tartaric acid was three times as high. Most of the monobasic acids gave no or very weak color in this method. However, spectrographic studies showed that reaction between these acids and the reagent was quantitative. In the case of lactic acid, for example, a molar reaction ratio of 1 to 1 was found by spectrophotometric experiments. The low color yield obtained in the rase of these acids may, therefore, be attributed to the high extractability of complexes of acid into an organic solvcnt used in the extraction. Application to Chromatography. Figure 2 shows a liquid chromatogram of organic acids. A sample solution containing pyruvate, oxalate, succinate, malate, tartrate, 2-oxoglutarate, maleate, and fumarate was applied
. -
tometric Determination ot
to the top of a 1 X 25 em. column of anion exchange resin. Dowex 1 X 8 bromide (200- to 40O-mesh), was eluted with piperazine-hydrobromic acid buffer solution (pH 5.0, bromide, ion concentration 0.05M) at a rate of 1 ml. per minute. The volume of each fraction was 5 ml. The acid content in each fraction was determined by the spectrophotometric method mentioned above. ACKNOWLEDGMENT
The author thanks Ryutaro Tsuchida of Osaka University and Shoao Tanaka of Kyoto Cniversity for thcir continuous guidance and encouragement throughout this work. LITERATURE CITED
(1) Bush, H., Hurlbert, R., van Potter, R. J. B i d . Chem. 196, 717 (1952). (2) kellini, R. F., Valiente, E. .4., Anales real 80:. fis. y qu?ni. (biadrid) 51B
,e%@.
RECEIVED for review January 30, 1061.
Accepted July 25, 1981.
.
JBMANN KORKISCH and G. E. JANAUER Analyfical Institute, University o f Vienna, I X . Wuhringerstrasse 38, Vienna, Austria
b A sensitive and accurate method is described for the spectrophotometric determination of microgram amounts of thorium using the azo dye Solochromate Fast Red. This dyestuff reacts with thorium in hydrochloric acid-methanol solutions to form an orange complex which shows maximum absorption at 490 mp. Beer's law is valid over a range from 0.1 to 20 pg. of thorium per mi. of measuring solution. The molar absorptivity of the thorium-dyestuff complex is 13,970. Only a very small number of foreign ions interfere; hence, this method can b e expected to find general application, as in the determination of thorium in minerals and rocks.
research work on the application of azo dyes for the spectrophotometric determination of thorium and uranium in mixed solvents has REVIOUS
1930
ANALYTICAL CHEMISTRY
proved a number of azo dyes of the Solochrome class to be suitable for the determination of uranium(1V) and (VI) (5, 6). Solochromate Fast Red is also a very sensitive and rather specific reagent for thorium. Because of its low solubility in water, a series of organic solvents was investigated for use in the spectrophotometric determination of thorium. The best results were obtained in a methanolic medium in which the solubility of inorganic salts is also sufficiently high. All the interfering ions can be separated from thorium by anion exchange methods (4, '7) developed in this laboratory, which ensure quantitative removal of practically all elements. In many cases separation will not be necessary, as the common interferences of small amounts of iron(I11) and copper(I1) are eliminated by addition of ascorbic acid, which does not interfere under the conditions applied here (Table 11).
The determination of thorium by Solochromate Fast Red is as seneitivc! and accurate as the extensively used Thorono1 method (@, yet Y, La, Pr, and Nd do not interfere, and this reagent is much less expensive than Thoronol. EXPERIMENTAL
Reagents. STANDARDTHORLUM SOLUTIONS. Thorium nitrate was transformed t o the chloride by repeated evaporation with 6N hydrochloric acid. The thorium chloride was dissolved in 1N hydrochloric acid. This solution, containing 3. mg. of thorium per ml., was used as a stack solution and standardized spectrophotometrically ( 2 ) . By dilution with 1N hydrochloric acid, standard solutions of lower thorium concentrations were prepared. DYESTUFF SOLUTIONS. Solochromate Fast Red 3 G 200 (C.T. Nordant Red 19) (250 mg.) of the formula 6-amino-4chloro-1-phenol-2-sulfonic acid -+ 3methyl-1-phenyl-5-pyrazolone
/
0.4
I\
c
P
< 2 0.3 .
si2 0.2 w--
0.1 *
'., 480
420
- -.*
-
_-
o--
540
--
600
---I
640
WAVE LENGTH, M r
Figure 1 .
Selection of suitable wave length
-e
-1 0 +I LOG [HCII OF MEASURING SOLUllON
Figure 2.
A+-
NaOSP \
/ CI
0
OH HO-C-iY-/
/
-
\[
drochloric acid were made up to 100 ml. with methanol. PROCEDURE
AH,
was dissolved in 100 ml. of methanol. Since the dyestuff contained small amounts of iiiorgnnic substances insoluble in nwthanol, it was filt,ered after 6 hours' digestion. This solution will be referred to as 0.25%. By dilution 1 to 1 with methnnol, a 0.125% dyestuff solution w m also prepared, These solutions ncw &able for more than 2 weeks. For drtcrniination of the mole ratio of the dye nnd thorium the dyestuff was specially purified by repeated recrystallisntion from methanol. A 2.16 X 10-5.11 solution of the purified dye was employed for this purpose only. STASDARUSOLUTIOKS OF DIVERSE IONS.A great number of 1N hydrochloric acid solutions containing all the common foreign cations and a number of anions (Table 11) were employed. Methnnolic solutions of sodium and magnesium chloride (0.1M) were used for studying the effect of ionic strength. ASCORBICACID SOLUTION. By dissolving of 0.3 gram of ascorbic acid in 20 ml. of methanol a n approximately 2.5% solution was prepared. This solution should not be stored for more than a few hours. METHANOL - HYDROCHLORIC ACID MIXTURE. Fifty milliliters of 1N hy-
The thorium-containing solution [if it is an eluate after a n anion exchange operation, the, solution must be processed as described earlier (4, 7 ) ] is evaporated to complete dryness on a water bath. Using 10 MI. of Measuring Solution. The residue is taken up in 1 ml. of l N hydrochloric acid and digested for about 15 minutes by shaking the beaker intermittently. Thereafter 0.2 ml. of the methanol-ascorbic acid solution is added and the contents of the beaker are transferred t o a 10-ml. measuring flnsk by rinsing the beaker with 7 ml. of methanol. After 1 ml. of the 0.25% dyestuff solution has been added, the flask is made up to volume with methanol. The absorbance of the thoroughly mixed solution is then measured against a reagent blank solution at 490 mp, using a Beckman Model 13 spectrophotometer. Using 5.2 M1. of Measuring Solution. The residue is taken up in 1 ml. of methanol-hydrochloric acid mixture and left standing for about 15 minutes with occasional shaking. After 0.2 ml. of the ascorbic acid solution and 1 ml. of the 0.125% dyestuff solution have been added, the solution is diluted with 3 ml. of methanol, which also mashes traces
Influence of acidity
of dyestuff from the walls of the beaker. The solution is homogenized by shaking the vessel carefully. The absorbance of this solution is then measured against a simultaneously prepared reagent blank solution a t 490 mp. In all cases when thorium is assayed in 5 2 ml. of measuring solution, the measurements must be carried out as soon as possible after preparation of the measuring solutions to avoid loss of methanol because of evaporation. Selection of Suitable Wave Length. A solution containing 100 p g . of thorium dissolved in 1 ml. of 1N hydrochloric acid and 1 nil. of 0.25% dyestuff solution was filled to the 10-ml. mark with methanol and measured against a reagent blank solution in the range from 420 to 650 mp.
The results of these measurements are ehomn in Figure 1, where the maximum absorbance of the thorium-dyestuff complex is shown to be a t 490 mp. Influence of Acidity and Ionic Strength. Solutions containing 100 pg. of thorium in 1 ml. of aqueous hydrochloric acid of varying normality and 1 ml. of 0.25% dyestuff solution were diluted to 10 mi. with methanol and measured against reagent blank solutions a t 490 mp.
As shown in Figure 2, the absorbance gradually decreases with increasing acidity of the solutions. Although tho
0.6
I
.-
P
4
6
8
10
IONIC STRENGTH X 10-2
Figure 3.
Effect of ionic strength on color development 0 E
0.1M NaCl added 0.1M MgCl added
12
Y.
A
0 0.5 1 1.5 ML. 0.25% DYESTUFF SOLN./IO ML. MEASURING SOLN.
Figure 4.
P
Influence of dyestuff concentration VOL. 33,
NO. 13,
DECEMBER 1961
1931
against reagent blank solutions a t 490 mp.
o.2 0.1
I
L
1
,
I
,
I
I
!
I
I
2 4 6 8101Q141618PO MOLES OF DYE PER MOLE OF Th
+'
Figure 5. Moie ratio method absorbance of solutions containing 1 ml. of less than 1N hydrochloric acid is higher, 1 ml. of IN acid was used to ensure complete dissolution of thorium chloride. To study the effect of ionic strength on color development, solutions containing 1 to 6 ml. of the 0.lM methanolic sodium chloride or magnesium chloride solution, respectively, per 10 ml. of measuring solution were prepared corresponding to over-all salt concentrations from 0.01 to 0.06M. These solutions, which also contained 100 pg. of thorium dissolved in 1 ml. of 1N hydrochloric acid, 1 mk of 0.25% dyestuff solution, and 7 to 2 ml. of methanol to fill up to volume, were measured against a reagent blank solution containing no salts. In Figure 3 the absorbances are plotted against the increase of ionic strength of the measuring solutions caused by the presence of sodium or magnesium chloride. From Figure 3 it is seen that the absorbance remains practically unaffected up to an ionic strength of 0.025, meaning that the measuring solutions may be 5 X 10-2iM in sodium chloride or 1.25 X 10+M in magnesium chloride. Further increase of ionic strength causes linear decrease of the absorbance. Influence of Dyestuff Concentration. Solutions containing 100 pg. of thorium in 1 ml. of 1N h drochloric acid and from 0.2 t o 2.0 mE of 0.25% dyestuff solution were diluted to 10 ml. with methanol and measured Table
I.
Influence of Solvents on Absorbance
Absorbance at 490 Solvents Methanol Ethyl alcohol llcPropyl alcohol Isopropyl alcohol n-Butyl alcohol Isobutyl alcohol Acetone Dioxane Ethylene glycol 1932
@
M/r 0.602 0.496 0.412 0.357 0.232 0.241 0.061 0.045 0.246
ANALYTICAL CHEMISTRY
The results in Figure 4 show that for 0.8 to 1.5 ml. of the dyestuff solution, the absorption remains constant. For all other experiments, therefore, 1 ml. of 0.25Y0 dyestuff solution was used. Nature of Colored Complex. Preliminary investigation of the mole ratio of the thorium-dyestuff complex did not give satisfactory results, because of the above-mentioned impurity of the dyestuff. After preparation of a specially purified portion of the dyestuff, it was possible to establish the empirical formula of the complex in solution applying the mole ratio method (9) and Job's method of continuous variations (3, 8). Both methods indicate that a 4 to 1 complex between the dye and thorium ion was formed under the condition studied (see Figures 5 and 6). Influence of Other Solvents. Solutions containing 100 pg, of thorium in 1 ml. of 1N hydrochloric acid and 1 ml. of the 0.25% dyestuff solution were filled to the 10-ml. mark with the solvents listed in Table I. They were measured at 490 mp against reagent blank solutions containing the corresponding solvents. The results are recorded in Table I, from yhich it is seen that maximum absorbance is reached in methanol. In a series of experiments methanol was stepwise replaced by increasing amounts of water, which effected a slow decrease of the absorbance. I n presence of more than 6 ml. of aqueous phase per 10 ml. of measuring solution the thorium-dyestuff complex waa precipitated, whereas no dyestuff precipitation occurred in the blank solutions. Influence of Time, Temperature, and Sequence of Reagent Addition. No change of absorbance within 24 hours could be observed, although the measuring solutions contained ascorbic acid. I n the range from 10' to 25' C. no effect of temperature on the absorbance could be noticed. The sequence of reagent additions is not critical except when measuring in 5.2 ml. of measuring solution. Influence of Foreign Ions. The cations and anions tested and the amounts of each are listed in Table 11. The ions were added to 1 ml. of 1N hydrochlorio acid containing 100 pg. of thorium and the solutions evaporated to dryness and treated as described in the procedure. The results of the measurements compared to the value for 100 p g . of thorium in a calibration curve obtained in 10 ml. of measuring solution showed (Table 11) that only iron (111), copper(II), titanium(IV) , zirconium(1V) , hafniunn(IV), cerium (1111, molybdenum(VI), vanadium(V), and tungsten(V1) among the cations, and
0.5 .
8 0.4 .
f
2 0.3
8 2 0.2 . 0.1 .
0 0.1 0.2 0.3 0.4 0.5 X ML. 2.16 X 10-8 7HORIUM SOLN. PER (1 ML. EQUIMOLAR DYE SOLN.
Figure method
6. Continuous
0.6
- X)
variations
fluoride, sulfate, oxalate, phosphate, and citrate among the anions interfered more or less seriously, whereas all the other foreign ions tested showed no interference. However, the interference of up t o 200 pg. of iron(II1) and/or 200 fig. of copper(I1) can be
Table !I. Influence of Foreign Ions on Thorium Determination
Ion
t2?iII:'
Sr(I1) Ba(I1)
Al(II1)
Y(II1) La(II1) Hf(1V) Zr(1V) Ti(IV)
Pr(II1) Nd( 111)
Ce(II1) Sn(I1)
Pb(1I)
Bi(II1) Fe( 111) Co(I1) Ni(I1) Cu(I1) Zn(1I) Cd(I1) HgW) :i:;,1,
Mo(V1) W(V1) U(V1) Mn(I1) Pd(I1) Pt(1V)
FBrINosPOP -a sod-2
SCN Citrate Oxalate Ascorbic acid
Error,
Present as % 1000-pg. Amounts Chloride -0.5 -0.4 Chloride $0.2 Chloride $0.7 Chloride +I .2 Chloride -0.6 Nitrate Nitrate -0.5 Nitrate $45.0 Chloride $45.6 Nitrate $55.6 Nitrate $0.8 Nitrate -0.5 Nitrate 4-38.2 -0.9 Chloride Chloride f0.6 Nitrate f0.4 Chloride +102.5 -0.7 Chloride Chloride f0.8 +140.2 Chloride Chloride +1.1 -1.3 Chloride -1.0 Chloride Vanadate +33.5 $1.5 Nitrate $29.2 Molybdate - 16 .O Tungstate -0.5 Chloride $0.8 Chloride f1.0 Chloride -1.4 Chloride 2000-pg. Amounts K salt -89.5 -1.1 K salt -0.6 K salt K salt KHaPOi Ka salt
+0.7 -98.8 -80.1 -1.5
salt K salt Na salt 50,OOO-pg. amount
-25.0 -97.0 -0.4
AmmoniUIll
eliminated r e d i l y by addition of mcorbic acid. Consequently, 0.2 ml. of a Table 111. Comparison of Two Dye 2.5% methanolic solution of ascorbic Methods for Determination of Thorium acid was invariably used for the preparain Manganese Nodules tion of the measuring solutions. Thorium, P.P.M. All the interfering and noninterferManganese Soloing ions (Table 11) can be quantitatively Nodule chromate separated by anion exchange (4, 7 ) , Fraction” Fast Thoronol Red SO that thorium can be determined in (2) samples of greatly varying composi17813 12.5 12.8 tion. 44.5 45.0 17823 17850 12.0 12.0 Calibration Curves. IN10 ML. of 17824 86.3 86.0 MEASURINQ SOLUTION. The solutions 63.9 64.2 17836 contained 0 to 250 yg. of thorium dis17821 73.5 74 .O solved in 1 ml. of IN hydrochloric acid, 0 The chemical and mineralogical com0.2 ml. of the methanol-ascorbic acid position of these samples has been desolution, and 1 ml. of 0.25% dyestuff scribed (1). The geochemical significance of the data will be discussed further elsesolution. These solutions were made where. up to volume with methanol and measured against a reagent blank solution at 490 mp. Beer’s law holds from 0 to 200 pg. of thorium. IN6.2 ML. OF MEASTJRING SOLUTION. above 10 pg. has a value of 5=1.5% for 10 ml. and 3% for 5.2 ml. of measurThe solutions contained 0 to 150 pg. ing solution, respectively. At lower of thorium dissolved in 1 ml. of the thorium concentrations the error may methanol-hydrochloric acid mixture, increase up to *5 to 10%. 0.2 ml. of the ascorbic acid solution, Application. To test the applic1 ml. of 0.125’% dyestuff solution, and ability of the method, six composite 3 ml. of methanol. These solutions mineral samples (ma’rine manganese were measured against a simultaneously nodules) were analyzed. Thorium prepared reagent blank solution at 490 was separated from accompanying my. Beer’s law applies from 0 to 120 elements by the anion exchange pg. of thorium. methods long used in our laboratory Sensitivity and Accuracy. Two for the assay of thorium in marine minmicrograms of thorium per 10 m1.1.0 pg. of thorium per 5.2 ml. of measur. erals (4, 5‘). In each sample the final ing solution-can still be determined. determination of thorium was performed The average deviation of absorbance spectrophotometrically with Thoronol and Solochromate Fast Red. The reover the whole concentration range
sults of these analyses are shown in Teble 111, which shows that Solochromate Fast Red can be applied tu successfully as Thoronol. ACKNOWLEDGMENT
The authors express appreciation to G. Arrhenius, University of California Scripps Institution of Oceanography, La Jolla, Calif., for furnishing the samples analyzed, and Imperial Chemical Industries, Ltd., Hexagon House, Blackley, Manchester, England, for supplying the Solochromate Fast Red. LITERATURE CITED
(1) Arrhenius, G., “Pelagic Sediments.
The Sea,” Interscience, New York, in press. (2) Banks, C. V., Byrd, C. H., ANAL. CHEM.25, 416 (1953). (3 Job, P., Ann. chim. 109,113 (1928). (41 Korkisch, J., Antal, P., 2. anal.
Chem. 171,22 (1959). (5) Korkisch, J., Janauer, G. E., Anal. Chim. Acta, in press. ( 6 ) Korkisch, J., Janauer, G. E., Mikrochim. Acta (Wien),1961, 537. (7) Korkisch, J., Tera, F., ANAL. CHEM. 33,1264 (1961). (8) Vosbukgh, W. C., Cooper, G. R., J . Am. Chem. SOC.63,437 (1941). (9) Yoe, J. H.,Jones, A. L., IND.ENQ. CHEW,ANAL. ED. 16, 111 (1944).
RECEIVED for review April 4 1961. Accepted July 28, 1961. Work sponsored by the International Atomic Energy Agency and the U. S. Atomic Energy Commission under Contract 67/US, and by the latter agency also under contract AT(l1-1)-34, Project 44.
Spectrophotometric Determination of Cobalt with Thioglycolic Acid V. D. ANAND,’ G. S. DESHMUKH, and C. M. PANDEY Chemical laboratories, Banaras Hindu University, Varanasi-5, India
b The yellow-red color of cobalt(l1) with thioglycolic acid (sodium salt) having maximum absorbance at 3 5 8 mp has been employed as the basis for a spectrophotometric method for the quantitative determination of cobalt. The system was found to obey Beer’s law between the concentration limits of 1.0 to 10.0 X 10-6 gram of cobalt(l1) and to remain stable for over 4 8 hours at room temperature. The effects of pH, reagent concentration, time of heating, and aging were studied. Interference by heavy metals such a5 copper, nickel, iron, chromium, molybdenum, uranium, vanadium, etc. was prevented by extracting cobalt from the solutions
as the dithizonate. Most of the common anions had no effect. The procedure has been applied to the determination of cobalt in steels and alloys and cobalt determined in National Bureau of Standards samples 153a, 167, 437, and 440 of cobalt alloys, and tool steels. The method is convenient, sensitive, reproducible, and accurate.
T
~n first use of thioglycolic acid, variously described in the literature as mercaptoacetic acid, thioethanolic acid, and thiolactic acid (WI), in quantitative analysis was reported by Mayr and Gebauer (IS).
A number of metals, including iron, cobalt, nickel, lead, bismuth, mercury(I), uranium (U02+2), silver, and gold produce more or less stable colors with thioglycolic acid. The deep blue to purple color due to iron in ammoniacal medium has found extensive application in iron determination (1, 4, 6, 9, 11). Those due to cobalt (yellowred) and uranyl (orange) ions are very deep and stable (18). Although the deep color, comparable in intensity to the color of iron or uranium, given by the cobalt reaction with 1 Present address, Indian Institute of Technology, Kanpur, India.
VOL. 33, NO. 13, DECEMBER 1961
* 1933
