unknown alkylpyridines (2-methyl-3isopropyl-, 2-methyl-5-tert-butyl-, and 2,6-dimethyl-3-isopropylpyridine) and of another alkylpyridine 2-methyl5-isopropylpyridine which m s described only once before but not fully characterized, were assigned on the basis of these correlations. It was later found that the chemical and physical properties, elemental analyses, and neutral equivalents were also in accord with these assignments. The infrared correlations have been used for determining the pyridine base impurities present in the alkylpyridines here studied and in following the course of their purification. Thus, by determining the pyridine base impurities present in commercial samples of 2methyl-:-ethyl- and 2,4,6-trimethylpyridine (S), it mas possible to choose methods for selectively separating these close-boiling pyridine base impurities. Finally, the infrared spectra ha\-e been used as a criteria of purity for some of these pyridine bases, and have agreed with the results obtained by other analytical methods, such as cryoscopic methods. ACKNOWLEDGMENT
The author wishes to thank Verne R a l s h and Heino Susi for the infrared measurements, Robert Curry for the ultraviolet measurements, Herbert C. Brown for suggesting the infrared correlation, and Charles Snioot for the discussions concerning these correlations. The author is also indebted to Xavier 3lihm and Bernard Kanner for use of their spectral data on the higher monoalkylpyridines and on the
Table VII.
Additivity of Ultraviolet Absorption Maxima of Alkylpyridines
In Acid Pyridine 2-3112 2-Et 2-iso-Pr 2-tert-Bu 3-?.le 3-Et 3-iso-Pr 3-tert-Bu 4-hIe
4-Et 4-iso-Pr 4-t~rt-Bii
2-iIe-3-lXe
2-Me-3-Et 2-Me-3-iso-Pr 2-RIe-5-hle 2- hIe-5-E t 2-Me-5-iso-Pr 2-lle-6-tert-Bu 2,4-di-Me 2,6-di-hIe 2-Me-6-tert-Bu 2-E t-6-tert-Bu 2-iso-Pr-6-tert-Bu 2,6-di-tert-Bu 2,4,6-tri-Me 2,6-di-lIe-3-iso-Pr
In Base
Xobsd.
Xoalcd.
Xobad.
285.5 262.5 263 263.3 263.3 262.5 262.3 262.3 261.2 252.5 252 251.7 252.5 267 ~. 267 267,5 269.5 269,5 269 269 259 270 271 271 27 1 271 267.5 275.5
255.5 262.5 262.5 262.5 262.5 262.5 262.5 262.5 262.5 252.5 252.5 252.5 252.5 269.6
257 262 262 261.5 261 263 262.3 262 261.3 255 255 255 255 265 265 265 268 268 267.5 267,O 259 268
2,&dialkylpyridines, respectively, and to Russel L. Hudson of the Ethyl Corp. for his helpful suggestions in the preparation of this manuscript. LITERATURE CITED
(1) Barnes, R. B., Gore, R. C., Stafford, R. Williams, V. Z., ASAL. CHEW20, 102 (1948). (2) Bellamy, L. J., “Infrared Spectra of Complex hlolecules,” p. 232, Wiley, NeTy Tork, 1954. (3) Brown, H. C., Johnson, S., Podall, H., J . Am. Chem. SOC.76, 5556 (1954). (4) Cannon, C. G., Sutherlanct, G. B.
269.5
269.5 269.5 269.5 269.5 269.5 259.5 269.5 269.5 269.5 269.5 269.5 266.5 276.5
Xcalcd.
257 262 262 262 262 263 263 263 263 255 255 285 255 268 268 268 268 268 268 268 260 267
...
...
264: 5 271.0
265 273
... ...
B. M., Spectrochim. Acta 4, 37395 (1951). (51 ColthruD. S . B.. J . Oat. Soc. Ant. 40, 397 (i&o). Cook. G. L.. Church. F. AI.. J . Phus. .. Ch&. 611 458 (1957). ’ Herz, E., Kahovec, L., Kohlrausch, K. W.F., 2. physzk. Chenk. (Leipzzg) B53, 124-46 (1943). hlanzoni-Xnsidei. R., Boll. sci. fucoltd chim. ind., Bologna 1940, 137-42. Thompson, H. W,,J . Chena. SOC. I
.
1048.328.
Y & ~ g , ’ C ~ kDuvall, ., R. B., Wright, N., h A L . CHEV. 23,709 (1951).
RECEIVED for review October 22, 1956. Accepted Rlay 11, 1957.
Color Reaction between Thorium and Quercetin and Separation Scheme for Interfering Ions OSCAR MENIS, D. L. MANNING, and GERALD GOLDSTEIN Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Jenn. The color reaction between thorium and quercetin i s the basis of a precise method for the spectrophotometric determination of thorium. The yellow complex exhibits maximum absorption from 420 to 425 mp when measured against a reagent blank. The absorbance of the complex at 422 mp i s constant in solutions ranging from a pH of 2.7 to 3.5, and adheres to Beer’s law over a range of 10 to 150 y of thorium in a 25-ml. volume. The ratio of quercetin to thorium in the
1426
ANALYTICAL CHEMISTRY
complex i s 2 to 1, while the dissociation constant i s calculated to be approximately 1.2 Major interferences are discussed. The separation of thorium from interfering substances i s effectively accomplished b y a combination of ion exchange separation and thenoyltrifluoroacetone extraction.
x
I
COKNECTION with a survey of organic compounds t o be used as colorimetric and fluorometric reagents pi
for thorium, the properties of the thorium-quercetin complex and its applicability to the colorimetric determination of thorium were studied. Of the previously described colorimetric methods for the determination of thorium, the thoron method is perhaps the most widely used. The method has been utilized extensively in the analysis of monazite sands (2, 7 , 8, 20, 21, 24) and thorium compounds (4, 15, 35, 36). Other reagents which have been utilized successfully
T h e following procedure is used for t h e formation a n d subsequent absorbance measurement of t h e thoriumquercetin complex in t h e absence of diverse ions. Prepare a solution t h a t contains 10 to 150 y of thorium in a volume of about 15 nil. Adjust the pH to 2.8 to 3.0 b y addition of a 10% solution of sodium carbonate. Transfer the test solution to a 25-ni1. volumetric flask. Add 4 ml. of ethyl alcohol and 2 ml. of the quercetin in that order. Dilute to 25 ml. with water. Prepare a blank t h a t contains all of the reagents. .411ow the prepared samples to stand for 15 minutes, then measure the absorbance against the reagent blank a t a wive length of 422 1nM in 1-em. cells. Phosphate Present. If phosphate is present, t h e separation of thorium from t h e solution is accomplished prior t o t h e formation of t h e complex. Prepare a Don-ex 50-A2 column that is 3 cm. in height and 1 em. in diameter. T a s h the column first with 100 ml. of 1 O M hytlrochloric acid, then with 100 ml. of 0.1M hydrochloric acid. Adjust the volume of the sample to 25 ml. and to p H 1; then pass the solution through the column a t a floiv rate of 0.5 to 1 ml. APPARATUS AND REAGENTS per minute. K a s h the column free Beckman Model DU spectrophotomof phosphate n i t h 50 nil. of 0 . l X hydroeter. chloric acid. Elute the thorium from Beckman Model H pH meter. the column n i t h 35 nil. of 10X hydroWarren Spectracord, a recording chloric acid. If interferences other spectrophotometer. than phosphate are present, continue Thorium perchlorate stock solution, with the procedure given below; otherapproximately 1 mg. per ml. Dissolve nise, add 3 ml. of perchloric acid and 2.5 grams of thorium nitrate [Th(SO& evaporate the solution to 0.5 ml. H20] in 25 ml. of water, and add 10 ml. Allow the sample to cool, add 15 ml. of of concentrated perchloric acid. Evapwater, then proceed a s with solutions orate the solution to fumes of perchloric of pure thoriim. acid, then fume the solution for 10 Other Interfering Materials Presminutes. Cool, then cautiously add ent. Prepare a D i w e x 2 X 10 colxater to dilute the solution to 1 liter. u m n t h a t is 10 cm. in height a n d Standardize by taking a 25-ml. portion 1 em. in diameter. Wash t h e column and precipitating the thorium as tlie thoroughly with n a t e r , then with 50 ovalate. Ignite the precipitate and nil. of 0 . l M hydrochloric acid followed w i p h as thorium oxide. b y 50 ml. of 10.V hydrochloric acid. Prepare less concentrated solutions Adjust t h e volume of t h e sample t o by the appropriate dilution of the 25 t o 35 nil. n i t h 10-11 hydrochloric standard thorium perchlorate. acid. Add 1 mg. of chromium(V1) Quercetin (3,3’,4’.5,7-pentahydro~yif vanadium is present. Pass the sample flavonc), 0.1%. Dissolve 1 gram of through the column a t a f l o ~rate of quercetin (d. 13. Penick and Co.) in 1 0.5 to 1 nil. per minute. K a s h the litcr of reagent grade ethyl alcohol. column n ith 35 ml. of 1 0 N hydrochloric Prcparc more dilute solutions of querceacid and conibine this solution with the tin by diluting the stock solution rvith initial effluent. ethanol. Add 3 nil. of perchloric acid, then Thenoyltrifluoroacetone, 0.5M (apevaporate the combined effluent soluproximately 10%). Dissolve 110 grams tions to fumes of perchloric acid. Heat of thenog-ltrifluoroacetone in 1 liter the solution until about 1 nil. remains. of reagent grade carbon tetrachloride. Dilute to 20 ml., then adjust to p H 2.0 Hydrochloric acid, 10.11. Dilute 840 with 10% sodium acetate. Add 5 mg. mi. of concentrated hydrochloric acid to of Tiron if titanium is present. Transfer I 1itc.r. Prepare less concentrated soluthe solution to a n extraction apparatus tions by making the proper dilution of and extract for 2 minutes n i t h 10 ml. the d o c k solution. of the 0 . 5 X thenoyltrifluoroacetone. Ethyl alcohol, reagent grade. Drain the organic phase into a second Doweu 2-Xl0 anion exchange resin, extraction apparatus. Repeat the ex50 to 100 mesh. traction of the aqueous phase n i t h a n Sodium carbonate, 10% aqueou.. additional 10-ml. portion of thenoylSodium acetate, 10% aqueous. trifluoroacetone. Combine the organic Don-ex 50-A2 cation exchange resin, phases and re-extract the thorium for 50 mesh. 2 minutes into 10 ml. of 6JI hydrochloric acid. Remol-e the hydrochloric acid PROCEDURE phase, then repeat tlie re-extraction with a n additional 10 nil. of 6IlP hyNo Interfering Materials Present.
are Alizarin Red S (28, 34, carminic acid ( l 7 ) , and p-arsonic acid (33). Several proposed reagents are Carmine Red (11), naphthazarin (27), quinalizarin (SO), and oxalohydroxamic acid (9). Morin is reported to be extremely sensitive to thorium (12). I n this laboratory a study was initiated of the applicability of the closely related quercetin as a possible colorimetric reagent. It was found that quercetin, in common v i t h the other reagents for thorium, is a sensitive but not a selective reagent. T o overcome this disadvantage, a separation scheme was developed which effectively eliminates all the iaterferpiices which were investigated. Quercetin is used to form colored compounds with a variety of metals. It has been utilized in the quantitative methods for the determination of uranium (22), germanium ($9) zirconium (1‘4, tin (W6),and in the gravimetric detcrniination of niobium and tantalum (37). Quercetin has also been tested as an indicator in the titration of fluoride with thorium (38).
drochloric acid. Combine the acid phases and wash this solution with 10 ml. of carbon tetrachloride. Discard the carbon tetrachloride. Evaporate the hydrochloric acid solution that contains the thorium to fumes after adding 3 ml. of perchloric acid. Fume the solution until about 0.5 ml. remains. Then cool the sample, add 15 ml. of water, and proceed a s with solutions of pure thorium.
It is necessary to perform a thenoyltrifluoroacetone extraction in conjunction with the anion exchange separation procedure; otherwise, the absorbances of the test solutions are abnormally high and erratic. This is believed t o be due in part to the dissolution of organic material from the resin. This impurity, d ~ i c his not completely destroyed by wet ovidation methods, exhibits appreciable absorption a t 422 mp, The impurity is also extracted into thenoyltrifluoroacetone; however, it is not back-extracted with 6111 hydrochloric acid. Consequently, this treatment effectively eliminates the interference. EXPERIMENTAL
Effect of pH on Absorption Spectra. T o determine t h e optimunl p H for color development, a series of solutions t h a t differed only in p H was prepaied, aftei which t h e absorption spectrum of each sample n a s measured against a reagent blank. T h e data are p i e s w t e d in Figure 1. T h e complex exhibits absorption between 400 and 500 mp. nith a maximum betn-een 420 and 425 nip when measured against a reagent blank. A wave length of 422 mp was chosen for all further absorbance measuremmts. The absorbance of the complev a t a nave length of 422 mp is essentially constmt over a pH range of 2.7 to 3.5; a t higher and loner pH values the absorbanw diminislic~rapidly. K i t h the evception of a broadcning of the absorption peak of tlie thorium-quercetin complex nith increasing pH, no shift in the nave length of maximum absorption n-aq noteJ. Additional tests of the effect of p H on the absorption of the reagent blank showed that, in the acid p H range. the abqorbance varied only slightly a t the wave length of 422 nip. Furthermore, the absorbance of the reagent is not significant abore a wave length of 450 mp. Belon this nave length. honever, it exhibits appreciable absorption-i.e.. of the order of 0.1 abqorbance unit a t 425 mp and 1.6 absorbance units at 400 inp when measured versus a reference solution of water. The p H of the solutions vias adjusted n i t h a 10% solution of sodium earbonate, Sodium hydroxide should not be used because the reagent grade pellets contain sufficient impurities to VOL. 29, NO, 10, OCTOBER 1957
1427
cause poor results. Moreover, the dropwise addition of a solution of sodium hydroxide apparently causes localized hydrolysis of thorium. Effect of Variation of Quercetin Reagent and Alcohol. To determine t h e amount of reagent necessary t o produce maximum absorption, solutions were prepared t h a t contained approximately 50 y of thorium. T o these solutions various amounts of quercetin were added, following which the absorbance of each solution was measured. Maximum absorbance was attained when 2 ml. of a 0.1% solution of quercetin was present in a 25-ml. volume. Further tests revealed that this amount of reagent was sufficient to produce maximum color with up to 150 y of thorium. I n conjunction with these tests, the effect of varying the quantity of ethyl alcohol present was studied. Over a range of 5 to 20 ml. of alcohol in a total volume of 25 ml., no change in the absorbsnce of the complex was observed; however, if less than 5 ml. of ethyl alcohol is present, the quercetin tends to crystallize, thereby causing the color of the solutions to be unstable. A minimum amount of 6 ml. was chosen as the working volume because of the small solubility of some inorganic salts in ethyl alcohol. Stability studies revealed that the absorbance of solutions which contain 2 mg. of quercetin, a total of 6 ml. of ethyl alcohol, and up to 150 y of thorium does not change over a period of 5 hours. The absorbance of the complex is constant over a temperature range of 5' to 50" C. I n solutions which are allowed to stand for 15hours, the quercetin reagent crystallizes. Adherence to Beer's Law. A linear, Beer's law relationship exists over a range of 10 to 150 y of thorium under the working conditions described herein. The molar absorbance index for the thorium-quercetin complex is 33,000. Statistical analysis of a series of absorption measurements showed a coefficient of variation of 3y0, When the final test solutions contain less than 10 y of thorium, the absorbances are erratic and not reproducible. An evaluation of the optimum range for maximum precision was made by the method of Ayres ( 1 ) and Ringbom ( S I ) . I n order to define a suitable concentration range, per cent nbsorbance (or transmittance) is plotted us. log of concentration. The general form of the curve is S-shaped. The concentration range for greatest accuracy is the concentration corresponding to the steepest slope of the curve. Usually, a considerable portion of the curve around the inflection point is nearly linear and corresponds to the optimum range. The flat portion of the curve a t very high and low absorbance is the
1428
e
ANALYTICAL CHEMISTRY
I
I
00 500
I
I
450 425 W I V E LENGTH. m/L
475
400
390
Figure 1. Effect of pH on absorption spectrum of thorium-quercetin complex 75.5 y of thorium, 2.0 mi. of 0.1 yo quercetin, 2 5 4 . volume
0 80
t
I
I
I
IO CONCENTRATION OF VARIABLE
15 COMPONENT, M
20 I
10
'
23
Figure 2. Determination of quercetin-thorium molecular ratio by slope ratio method A. Quercetin constant, 5.7 X 1 O-5M B. Thorium constant, 5.7 X 1 O-5M
area of greatest inaccuracy. Maximum accuracy is defined as per cent relative error for each 1% absolute photometric error; this was found to be of the order of 3% over the optimum range of thorium from 1 t o 4 y per rnl. of final volume. Spectrophotometric Determination of Empirical Formula. T h e slope ratio method (18) was utilized to establish the empirical formula of the com-
plex formed between thorium and quercetin. I n this method, t x o series of solutions were prepared; in the first series, various amounts of thorium were added to a larger excess of quercetin. while in a second series, different quantities of quercetin were added to a large excess of thorium. The absorbance of the solutions in each series was measured and plotted versus the concentration of the variable component. The com-
bining ratio of the components in the complex is equal to the ratio of the slopes of the t\vo straight lines which are shown in Figure 2. The calculation of this ratio revealed a n n value of 1.92, 11-hich indicates that the complex is composed of 2 molecules of quercetin and 1 inolecule of thorium. Spectrophotometric Determination of Degree of Dissociation. DISSOCIATION COXSTAKT FOR THORIUM-QUERCETIN COMPLEX. Because 1 mole of thorium reacts with 2 moles of quercetin t o form 1 mole of complex, t h e dissociation of t h e complex can be expressed as : Th((2uercetin)2 = T h C
=
C(l
+ 2&
+ 0 (initial concentration) = cyC + 2aC (equilibrium 0
01)
concentration)
and Q represents 1 mole of quercetin. The dissociation constant is written as K = ( n C )( 2 4 2 = -4a3C* C(1 - a ) 1 - cy
n-hcre C is the concentration of the coniplcs in moles per liter and a is the dcgree of dissociation. The value of a is obtained from the relationship (18)
nhere E, is the ni 'mum absorbance of a given amount o ' thorium in the presence of a large esccss of quercetin, which absures t h a t all of the thorium is present as the complex. The absorbancy, E,, is the value obtained when the same amount of thorium is mixed with a stoichiometric amount of quercetin (2 moles of quercc%in to 1 mole of thorium). For a solution that was 2.3 X 10-6.1f in thorium, it was found that E , = 0.780 and E, = 0.520. The degree of dissociation was calculated to be 0.333. Substituting this value and the value of C which is equivalent to the concentration of thorium into the expression for the instability constant, the instability constant was calculated to be about 1.2 X 10.-'0 This is the same order in magnitude as the initability constant for the zirconiumquercetin complex (16) ( K = 1.3 X loF9), Iyhich also has a n empirical formula of Zr(Quercetin)z. Effect of Diverse Ions. T o determine t h e degree of interference of materials Tvhich are likely t o be encountered, measurements were made of t h e effect of various ions on the absorbance of solutions containing 50 y of thorium. If 10% is considered as the maximum permissible error, the following are the limiting quantities of the metals tested, in micrograms per microgram of thorium, that can be tolerated in the final solution in nhirh the color is developed:
Nickel(I1) 4 Chromium(V1) Iron(I1) 0.08 Chromium(II1) Iron(111) 0.04 Uranium( VI) Aluminum( 111)
0.06 3.2 0.12 0.04
The interference from chromium(V1) can be considerably lessened by reduction to chromium(III), while the interference from iron(II1) can also be decreased by reduction to iron(I1). Of the common anions, chloride was found to have no effect; hom-ever, sulfate, acetate, phosphate, and fluoride must be absent. The presence of nitrates results in erratic absorbance measurements and increases the coefficient of variation to some extent. For the best results, it is recommended that a perchlorate medium be substituted for nitrate. SEPARATION OF THOMUM
The methods tested for the separation of 15 to 130 y of thorium, prior to estimating it colorimetrically with quercetin, included anion exchange (WS), cation exchange (fo),chloroform extraction of the thorium cupferrate ( I S , 32), mesityl oxide extraction (3, 25), and thenoyltrifluoroacetone extractions (19). Of the separation methods tested, a combination of ion evchange and thenoyltrifluoroacetone extraction techniques proved to be the most successful. The anion exchange separation is based on the work of Kraus, Selson, who demonstrated that and Smith (El)> metals lvhich form chloro-complexes nhich are anionic can be absorbed on a strong base, anion exchange resin. This serves to separate thorium from such metals as iron, uranium, zirconium, cobalt, and tin. Conversely, such metals as aluminum, nickel, titanium, chromiuni(III), and the common anions are not absorbed by the resin and accompany the thorium in the effluent, Vanadium, when maintained in the pentavalent state, is absorbed quantitatively by the anion exchange column. I n order to assure that the vanadium remains in the pentavalent state, a small amount of chromate is added to the solution prior to the anion exchange separation. I n the absence of chromate, traces of vanadium are reduced by the resin and consequently accompany the thorium in the effluent. This constitutes a serious interference m-hich is not eliminated by the subsequent procedures. .4n extraction of the effluent ryith thenoyltrifluoroacetone \vas chosen to separate the thorium from the remaining interfering substances. Thorium can be extracted quantitatively into thenoyltrifluoroacetone from a n acetate solution at a pH of about 2. Titanium is partially extracted a t this pH, while aluminum ( 5 ) , nickel, and chromiuni(II1) are not. Attempts to achieve a separation of thorium from
titanium were made by re-extracting the thorium into 6M hydrochloric acid. Titanium was only partially separated by this procedure; however, when the titanium was complexed with Tiron (39) prior to the extraction, it was not re-extracted with 6M hydrochloric acid as was the thorium. Consequently, the addition of Tiron was essential for the final separation of titanium. The phosphate ion, a serious interference which prevents the quantitative extraction of thorium by thenoyltrifluoroacetone, is not removed by the anion exchange treatment under the conditions of the general procedure. I t can be removed, holvever, by first passing the test solution through a cation exchange column. The thorium is absorbed, while the phosphate remains in the effluent (14). The thorium can be eluted with about 35 ml. of 10M hydrochloric acid. The solution is then ready for the anion exchange thenoyltrifluoroacetone extraction treatment. The results of the separation of thorium from each of the various interfering subkinces are presented in Table I. DISCUSSION
From the data in Table I, the feasibility of separating small quantities of thorium from milligram amounts of most interfering substances is demonstrated. Because the purpose of this investigation was to devise a means to separate thorium from aqueous solutions which may contain appreciable quantities of diverse ions, the separation of thorium from larger quantities was not studied. I t appears probable, however, that by utilizing larger ion exchange columns, the upper limit of
Table 1. Recovery of Thorium after Removal of Diverse Ions b y Ion Ex-
change-Thenoyltrifluoroacetone
Ex-
traction
Thorium, -/ PresIonsa cmt Recovered Error F16 12 6 -3 4 F66 64 1 -1 9 Sod-16 16 4 $0 4 L T +6 16 16 5 +O 5 Po?--16 16 3 +O 3 Ti + 4 33 33 2 $0 2 \.+a Crt6 33 33 3 +O 3 Fe+++ 66 65 1 -0 9 Si-+ 66 65 1 -0 9 131 -2 Alf" 133 Zr +4 133 130 -3 Cr t6 133 130 -3 131 -2 Co'+ 133 132 -1 Mn + 133 -1 133 132 Sn + 4 133 133 0 Cd++ Cu+' 133 133 0 131 -2 110+& 133 1 mg. each except SOa-- and PO, - ( 5 mg.); V + 5 (0.2 mg ) , and becwnd F- determination (0.2 mg )
+
+
Q
VOL. 29, NO. 10, OCTOBER 1957
1429
the ions tested may be considerably extended. The recommended procedure can be utilized to separate thorium from the platinum metals and the rare earth elements. The platinum metals are absorbed by the anion exchange resin, whereas the rare earth elements are not. A separation from the latter group is achieved, hon-e17er, lvhen the thorium is extracted with thenoyltrifluoroacetone a t a p H of 2. The rare earths are not extracted a t this p H (6). The ability of thenovltrifluoroacetone to extract man!- metals depending upon the p H of the solution makes it a versatile reagent to utilize for analytical separations, Others (6, 6, 19) have taken advantage of this CharaCteristic p H dependence to achieve desired separations. Moreover, the extraction of many metals from the thenoyltrifluoroacetone phase depends upon the acid concentration of the extractant. This fact may also be taken advantage of in developing separation schemes. ACKNOWLEDGMENT
The authors acknobv1edge the assistance of C. D. Susano and h1. A. blarler in the preparation of this manuscript. LITERATURE CITED
( 1 ) Ayres, G. H., AN.4L. CHELI.21, 652 (1949). ( 2 ) Banks, C. V., Byrd, C. H., Ibid., 2 5 , 4 1 6 (1953).
( 3 ) Banks, C. V., Edwards, R. E., Ibid., 27, 947-9 (1955). ( 4 ) Banks, C. V., Klingman, D. R., Byrd, C. H., I b i d . , 25, 992 (1953). ( 5 ) Bolomey, R. A . , Wish, L., J . Am. Chem. SOC.72,4483 (1950). (6) BronaWh, H. J . J SUttle, J*F.9 S. Atomic Energy Comm. LA-1561 (1953). ( 7 ) Byrd, C. H., Banks, C. V., I o w u State Coll. ISC-456 (1953). ( 8 ) Clinch, J . 7 d n a l . Chim. Acta 14, 162 (1956). ( 9 ) Dhar, 8, K , , D~~ Gupta, A, K,, J . Sci. I n d . Res. ( I n d i a ) 12B, 518 (1953). ( 10) Dryssen, D., SL'ensh- Kenl. Tidsb. 62, 153 (1952). (11) Es-ivaranarayana, S.,Raghava Rao, B. S. V., Z . anal. Chem. 146,107-11 (1955). ( I 2 ) Fletcher, Lx. H., ?vlilkey, R. G . ~ ANAL.CHEX 28, 1402 (1956). (13) Foster, M. D., Grimaldi, F. S., Stevens, R. E., U.S. Geol. Survey,
Trace Elements Project,, Rept.
No. 2 (1944). (14) Goudie, ii. J., Rieman, W.,ANAL. CHEW24, 1067 (1952). (15) Grimaldi, F. S., Fletcher, 31. H., Ibid., 28, 812 (1956). (16) Grimaldi, F. S., White, C. E., Ibid., 25, 1886-90 (1953). (17) Hall, R. H., U. S. Atomic Energy Comm. AECD-2437 (1948). (18) Harvey, A. E., Manning, D. L., J . A"7n. Chenz. Soc. 72, 4488 (1950). J ' , u' S' (19) HYdeJ E' K . s Atomic Energy Comm., ANL4248 (1955). (20) Ingles, J. C., Can. Chein. Process I n d s . 35, 397-406 (1951). (21) Ishbashi, M.,Higashi, S., J a p a n Analyst 4 , 14-16 (1955). ( 2 2 ) Komenda, J., Chem. Listy 47, 531-3 (1953). (23) Kraus, K. A., Kelson, F., Smith, G. W.,J . Phys. Chem. 58, 11 (1954).
(24) Kronstadt, R., Eberle, A. R., U. S. Atomic Energy Comm. RMO-838 (1952). (25) Levine, H., Grimaldi, F. S., Ibid., AECD-3186 (1950). (26) Liska, K., Chem. Listy 49, 1656-60 (1955). (27) Moeller, T., Tecotzkey, M.,ASAL. CHEW27, 1056 (1955). (28) Murthy, T. K. S., Raghava Rao, B. S. V., Current Sci. ( I n d i a ) 8 , 2 4 8 (1949). (29) Oka, Y., Matsuo, S., J . Chem. SOC. J a p a n , Pure Chem. Sect. 74, 931-2 (1953). (30) Purushottam, A., Z . anal. Chem. 145, 245-8 (1955). (31) Ringbom, A , , Ibid., 115, 332 (1939). (32) Rodden, C. J., "Analytical Chemistry of the RIanhattan Project," 1st ed., pp. 176-7, McGraw-Hill, Xew Tork, 1950. (33) Ibid., pp. 188-9. (34) Sarma, D. V. S . , Raghava Rao, B. S . V., Anal. C h i m . Acta 13, 142 (1955). (35) Taylor, .4. E., Dillon, R. T., ANAL. CHEM.24, 1624 (1952). (36) Thomaeon, P. F., Perry, 11. A., Byerly, W. RI., Ibid., 21, 1239 (1949). (37) TomiEek, O., Holecek, V., Chem. Lidy 46, 11-14 (1952). (38) Willard, H. H., Horton, C. ANAL.CHEW22, 1190-4 (1950). (39) Yoe, J. H., Armstrong, A . R., Ibid., 19, 100 (1947).
I~ECEIVED for review January 26, 195;. Accepted RIay 31, 1957. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1957. Work carried out under Contract S o . W-7405-eng26 a t Oak Ridge Xational Laboratory, operated by Union Carbide Nuclear Co., a division of Union Carbide and Carbon Corp., for the U. S. Atomic Energy Commission.
Infrared Spectrophotometry of Sulfate Ion Combining Freeze-Drying with Potassium Bromide Disk Technique HAN TAI and A. L. UNDERWOOD Department of Chemistry, Emory University, Emory University, Go.
b By combining freeze-drying with the potassium bromide disk technique, it is possible to apply infrared analysis to samples presented in the form of aqueous solutions. These techniques will permit direct photometric determinations of common polyatomic anions which are often difficult to determine at low concentrations by existing methods. A study of the infrared spectrophotometry of the sulfate ion clearly demonstrates the feasibility of this approach. Under the conditions described here, the optimal analytical
1430
ANALYTICAL CHEMISTRY
range is 30 to 80 y of sulfate, where the standard deviation is 2 or 370.
T
spectra of many inorganic compounds have been recorded, but analytical chemists have not studied systematically the applicability of infrared methods to the determination of inorganic compounds. The catalogs of infrared spectra published b y Miller and Wilkins (6) and H u n t and associates (3, 4) point to the probable value of such a study. Until recently, it was difficult to apply infraHE INFRARED
red spectrophotometry to water-soluble compounds on a quantitative basis, but the potassium bromide disk technique (8-10) now provides a convenient method for observing the infrared spectra of such compounds. Hen-ever, to be of broad applicability, quantitative infrared methods for inorganic anions should be adaptable to analytical samples presented in the form of aqueous solutions. This requirement can be met b y combining lyophilization or freeze-drying with the potapsium bromide disk technique (11).
