certain for rare earths present in snialler amounts. The data are all based on readings a t the primary index peak positions. Analyses based on the subsidiary index peaks of Table I (data not shon-n) were generally in fair agreement. The subsidiary praseodymium peaks a t 432.5 and 590 mp, however, are of little value when a small amount of t h a t element is associated with a larger aniount of neodymium. The presence of neodymium caused a marked interference viith the primary erbium peak a t 523.5 nip. Only a single sharp peak was seen, bnt, as erbium was known to be present in the greatest concentration, the reading a t this peak TTas taken 3s the erbium d u e and corrected for neodyniiuni, a pro-
cedure which gave satisfactory results.
An attempt to take a neodymium reading on the side of the peak and correct it for erbium n as unsuccessful, however. Tf a large amount of neodymium were present n ith a small amount of erbium, the recommended primary peak of the latter a t 523.5 nip nould be very unreliable. As anticipated, the presence of a large amount of erbium made the ytterbium determination more uncertain. S o particular reason can be giren for the high samarium and holmiuni results in the 11-component mixture. LITERATURE CITED
I-.,Klingman, 1).R-., S n a l . Chztx. Acta 15, 356 (1950).
(1) Banks, C.
Hoogschagen, J., Gorter, C. J., Physica 14, 197 (1048). IIoeller. T.. BrantleT-. J. C.. ANAL. CHE\;. 22, 433 (1Yk)). lloeller, T , l l o e s , P. J., Ibzd.,
23, 3149 (1951). Prandtl, T I - , Scheiner, K., 2.anorg. u. allgem. Chenz. 220, 107 (1034). Rodden, C. J., J . Research S a t l . Bur. Standards 26, 557 (1011). Ibzd., 28, 265 (1942). Stenart, L). C., U S. ;\tomic Energy Commission, Aecd- 2389 (Sept. 22, 1018); ANL- 4812 (February 1952); ANL- 5624 (October 1956). ( 9 ) Stewart. 11. C.. Faris. J. P.. J . Itaoro. Suciehr Chein. 3, 64 (1‘356).
RECEIITDfor revieiv January 15, 1957. dccepted July 31, 1057. Based on work performed under the auspices of the U. S. Atomic Energy Commission.
Absorption Spectra of Terbium Perchlorate and Terbium Chloride Solutions E. I. ONSTOTT and C. J. BROWN’ University of California, los Alamos Scientific laboratory, los Alamos, N.
The spectra of terbium perchlorate and terbium chloride solutions have been recorded in the range of 200 to 1200 mp with the Cary recording spectrophotometer. An intense absorption at 219.8 mp follows Beer’s l a w and i s usable for accurate determinption of terbium at low concentrations. The molar extinction coefficient for perchlorate solutions was calculated to be 320. There are a number of minor absorptions in the range of 240 to 380 mp, and a minor absorption a t 487 mp, but no significant absorptions a t other wave lengths up to 1200 mp, ‘8eer’s law i s followed for most of the absorptions; notable exceptions are the absorptions at 263 my and at 265 mp.
I
x THIS LABORATORY a recording spectrophotometer has proved indispensible for the rapid, accurate analysis of rare earth mixtures. Stenart and Kat0 (9) describe the advantages of a recording spectrophotometer for this purpose, and report that terbium absorption a t 219 mp has analytical utility. The present paper reports a detailed study of this absorption for both terbium perchlorate and terbium chloride solutions by means of a Cary recording spectrophotometer. The anal>-tical utility of this absorption is confirmed. The selection of a particular absorp1 Present address, The University of Texas, Austin, Tex.
172
ANALYTICAL CHEMISTRY
M.
tion peak for determining a lanthanon in a mixture of lanthanons depends 011 the relative concentrations present. Thus a profitable approach to the accurate analysis of complex mixtures of lanthanons is to learn as much as possible about the spectra of individual pure lanthanons. rl start has been made by obtaining comprehensive data on pure terbium solutions. Emphasis was placpd on determining the adhcrence to Beer’s law for all the absorptions and on accurate positioning of the absorption maxima. Work of terbiuni absorptions has been reported by Sten-art (7, 8), Prandtl and Scheiner (j), and Holleck and Hartinger ( 3 ) . Banks and Klingman ( 2 ) recorded the spectrum of a terbiuni perchlorate solution, but did not give details. A number of minor absorptions are reported here TI hich have not been previousl>- reported. Possibly some of these m r e not observed by S t e n a r t because they n ere not resolved by the Beckman instrument (8),but they ma\- have been niissed simply because of their low intensity. The ability of the Cary instrument to resolve the r e r y sharp absorptions of the lanthanons has been demonstrated by LIocller and lloss ( d ) , who studied gadolinium absorptions. The Model 14 Cary spectrophotometer has better resolution in the ultraviolet region than the Beckman DK instrument. It has less stray light and better ultraviolet optics ( I ) , so
t h a t it is usable to about 200 mp whereas the Beckman DK probably does not have utility below 210 m,u. EXPERIMENTAL
The ultraviolet and visible measurements \?ere made m-ith a Cary recording spectrophotometer, Model 14X. Serial KO.1, range 200 to 800 mp. For the range of 800 to 1200 nip, a Model 14, Serial S o . 5 , was used. Just prior t o making the measurements. the niachines were adjusted for optimum performance by a Car? Co. reprcsentative. I n most of the experiments, the machine was run at the s l o w s t scanning speed and fastest chart speed. The slit amplifier was set a t 30. For the range of wave lengths above 300 mp, the light amplifier was set a t dynode 2 or 3. A t 240 to 300 mp, the setting \vas dynode 3 or and below 240 mp, a setting of dynode 4 or 5 was generally used, t o get a small slit opcning. The tungsten lamp was used above 350 nip, and the hydrogen lamp n a s used beloiv 350 mp. Spectra nere recorded by running the machine from the high end of the spectrum t o t h e loiv end. Both 1-cm. square cells and 10-em. cylindrical cells w r c used. A duplicate cell containing distilled water was placed in the reference beam. The 1-em. cells ~ i r r eplaced in the center of the beam, as recommended by the Car- Co. The terbium oxide used, purchased from the T’arlacoid Chemical Co., S e w York, N. Y., n a s specified as 99.9% pure. Spectrographic analysis showed no detectable lanthanon impurities (limit of detection 0.5% each element),
I
[--
30
___ 7
I
cerium present, the spectrophotometric det,ermination is more sensitive and considered more accurate than the spectrogiaphic determination of terbium. Stew-irt and Kato (9) point out that europium and prascodyniium also iiiterfere.
I
25t
1
, i
2o W
0
a
1
i 15:-
Table I.
I
Data for 2 19.8-Mp Absorption
JIolaritya x 103 Perchlorate Solutiolis 219.8 4.88 219. 8 3.25 219 9 2.44 210.8 1.22 219.8 0 610 219.9 0 , :305 Av. 219.8 219.5 0.1721 210 5 0 O512b 219.3 0 0172" 0 . 006P 219.5 Chloride Bolutioni 219. 6 4 40 219,s 2 20 Am.,,,
lip
1
05
' 0 L200
.
I
J' 220
\
L, 240
260
300
280
320
360
340
380
400
X-rnp
Spectrum, 200 to 400 mp First absorption (210.8 mp)) 3.25 X 10-3J1 Th(C10~hin l.-cni. cell, dynode 5, Remaining ahsorptioiis, 1.91121 Th( C104)3 in l.-cni. cell. dyiiode 2. Tungsten lamp used above Figure 1.
344 mp
:mtl no sljec~trol)liotoriictricahsorptioas ~ v i ~or lt ~~ ~ c r n-liic*li v ~ l c o ~ l d attributed to iriipuritics. Tlic terliuni as prvcipitat,cd twice us t h e oxalatr,, u i t h subscqueiit, ignition t,o the ositlc for
Solutions for analJ.sis \ ~ c r cpri,l,nrccl osicle, lT.ciglle,tl nc'itl! follon.c(i 17y cmove t,he F'XCPSS acid. I t ry to add a fm drops of 30% hytIl,ogen pcrositlc to sp(>td the tlissolutioii ~ ~ O C T S S The . chloride salt PI^ n.ith great (-are and a little hydrocliloric acid must be adtlcd for clcnr solutiolis xftw tlic funiiiig. H o x c ~ tc~r1)iuiii p ( ~ r ( ~ h l t ~ is r a t rathrr ~~ stable aiid c:m lie I i ~ ~ t eto d rciiiow e s c c ~ s acitl viithout, npprrciablc The pcwliloratc phould he ec.trophotometric dcterniinatioiia, if at all 1)ossiljlc. d lIotl(~1C; Rwknian p H m c t u was u s i d for thr. acidity mcasurcmeiits. 3Icasurcnicnts w r p iiiade in an aircontlit,ioiicd room a t 21-2" C.
ljecaiisc> the Bcclmiaii DII spectrophoto11ietc.r failetl to rccorcl accllratply tile aljsorl,tiolis at, lo\T. iengt,ll. \Tith use of 1 0 - ~ ~ ~ ~ it ,is possihle t,o make the tletcmiiinations at vtry low conccmtrnt'ions, hut accuracy suffers Iwcausi~of the t~tniolcl incrense in l~acl~grouii~1 absorption and loss in light intcmity. Cerium intclrfercs seriously \\-it11 the terbium detcrmination, as it absorbs strong]y in tllis region (8). Ho\yever, even n.itll a relatively large Rnloullt, of
2 10 . 3 21!) 5 219 5 AiT7, 219, 5
1 10 2 20 1 10
E
319 316
320 :324 320 32:3 320 289 200 230 340
:323 315
206
306 :303 308
219.7 0.055h 271 pH of pcwliloric sam1)lc~s\rap. 5.25 t o 5,80;chloride san,l,ir,s, 4,50 to 4,$)0. 10-c1xl. cell used; for otiler determin:ttiolis, I - ~cell. ~ , (1
~
DlSCUSSlON OF RESULTS
The s p t ~ % r u min the raiige of 200 to 400 niu is shon-n in Figure 1. The absorpt'inn at' 487 nip is small, and is not, included. S o appreciabk absorjstioiis i w r e fouiid in the range of 500 to 1200 nip. S t e x a r t liken-ise fouiid 110 absorptions in this r q i o n (7, 8). The :rl)sorption at 219.6 nip can be uscd t o determine tcrl>iuni accurately a t lo\\concciitratioiis (Talile I), Perchlorate Solutions give molar extinction coefficient, E , values n-liich slion- less variation than those for chloride solutions; consequcntly~ perchlorate solut'ions should be uscd for hettcr accuracy. Tlie value of e obtained by St'ervart and Iinto (9) for tlic 219 n1p chloride solution al,sorl,tioli is larger tilaIl tile ralue obtained in this work. Evidently these investigators were unable to correct for background absorptions,
Table
Ill
Terbium 1'cwhlor:ite Solutions" nip CC 487.2 0.034 ;377 9" Inflection
,,,A,
,
3 7 < i tj. . ;374.fide 367 7
0 169 0.164
0.2ti3 0,103
357, 7 351 . : j d :350,3
Inflection 0.215
341.7
0.086 0 074
339.1d 336.4d
327. 226. 320 6 d 3li 8
Inflertion 0,023 0 023 Inflect ion 0.091
:303 . 1
0.066
295. I
d
285. 8 d
0.016 Inflection 0.220 0.223 0.122 See T:il,le I11 See Table I11 0.083
Minor Absorptions
Terhiuni Chloride ~ ~Solutionsh _ _ An,,,, nip
187.3 377. ti
Inflection
375.5 374.8 3 0 7 . ti
0.166 0 270
351.4 350.2
Inflection 0 221
357.6
1.7 0.1
6.5
327.8 32ti. 6
295. 0 286.0
_
ec
0.034 0.1ti9
0 106
0,086
0 ,072 Inflection 0.024 0.02g Iii flection 0.087 0.058 ...
Inflection 0.208 0.210 0.122 S r e Tal~leI11 See Table 111
284.2J 284.3 283.7dCj 283 3 272.3 272 3 264.8 2ti5.0 263 . :3 262.8 254.P 254.8 0.115 247. O d 0 018 248.1 0.0:30 244.2d 0 023 244.5 0.02; 241.3 0.120 241.3 0,124 a Concentration rangc studied 1.910 t o 0.0049JT; pH 5.05 to 6.48. Concentration range studicLd 0.279 to 0.008851; pH 2.47 to 4.25. c E = loglo (Zg/I)(Cl)is an average value for 3 t o 5 of values of absorbance for most concentrated solutions where Beer's lan- \vas obeyed. .4lisorhance is logio (ZcdI). Concentration, moles per liter; cell length, em. Ahsorptions not previously r e p o r t d . e i ~ estinetioll ~ lcoeficient ~ decrease ~ ~ at 1 , 9 1 0 ~ f . f Jlolar extinction coefficient increase at I. E., private comniunica-
tion. (2) Banks, C. Y., Klingman, .)I W., A i d . C h h . Acta 15. 356 11950). ( 3 ) Holleck, L., Hartingbr, L’., Angeui. Chenz. 67, 648 (1965). (4) lloeller, T., Moss, F. d. J., J . A m . Chem. Soc. 73, 3149 (1951). ( 5 ) Prandtl, IT.,Scheiner, K Z. anory. u. allgem. Cheni. 220, 105 (1934). (6) liosenbaum, E. J., A N ~ L . CHEM. 26,20 (1954). (7) Stewart, I). C., Argonne Xational Laboratory, Doc. ANL-5624 (October 1956). (8) Steaart, D, C., University of California Radiation Laboratory, Doc. UCRL-182 (Sentember 1938). Kato, Dorothy, ( 9 ) Stewart, I).‘ ,ZAAL.CHEII.30, 104 (1958).
e.,
RECEIVEDfor review May 28, 1957. Akccepted Koveniber 12, 1957. Work done under the auspices of the Atomic Energy Commission.
Colorimetric Method for Determining Dialdehyde Conte nt of Perio date - Oxidize d St a rc h C. S. WISE and C. 1. MEHLTRETTER Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture, Peoria, 111.
b Micro quantities of periodate oxystarch have been determined colorimetrically. This rapid method i s particularly suited to the precise estimation of low percentages of carbonyl groups in periodate-oxidized starches. A p-nitrophenylhydrazone of oxystarch i s precipitated from aqueous solution, dissolved in ethyl alcohol, and determined spectrophotometrically.
D
an investigation on the industrial applications of periodate ox!-starches, it became necessary to deterniine very sinal1 amounts of periodate oxystarch having rarious extents of oxidation. A marc preciv procrdure than either the sodium borohydride (3) or the alkali consumption ( I ) method was desired which could also be used for the analysis of oxystarchcs of low dialdeh ~ d ccontent. Kcuberg and Strauss (b) showed that dicarbonyl compounds in niicro quantitivs can b(1 determined by convrrting
174
URISG
ANALYTICAL CHEMISTRY
them t o insoluble nitrophenylhydrazones, which in ethanolic sodium hydroxide solution produce a violet color capable of spectrophotometric evaluation. Applying this procedure t o periodate-oxidized starches produced results of low precision because of color instability. Improved precision was obtained by eliminating the ethanolic sodium hydroxide treatment and by measuring direetly the yrllon- color of ethyl alcohol solutions of the p-nitrophenylhydrazones of the 0x1 starches. The absorbance n i e a s u r d a t 445 mg nas as intense as the maximum blue lriolet color obtained with ethanol alkali a t 575 inw and was constant for a t least 3 days. An\- foreign substance present t h a t can form a n insoluble p-nitrophenylhydrazone n ill interfcre n ith the method. APPARATUS A N D REAGENTS
Spectrophotonieter, Coleman Junior Xodel G A .
Fritted glass filter funnel, 3.5-cm. inside diameter, medium porosity. Borosilicate glass tubes, 18 X 150 mm., selected for uniforniity in spwtrophotometric measurements. p-Sitrophenylhydrazine (East man). Stock solutions are made by dissolving 0.25 gram (Procedure A) or 0.50 gram (Procedure B) in 15 ml. of glacial acetic acid. C(.lite hltcr aid, analytical grade. PROCEDURE
Procedure A. Analysis of Oxystarches Containing Less Than One Dialdehyde Unit per Hundred Repeating Units. Weigh out oxystarch samples approximately equivalent t o 0.25 nig. of 1007, osystarch. For example. a 25-mg. sample of 1% oxystarch \vas taken and a 250-nig. sample (dry \wight basis) of 0.17, oxystarch was used. After placing the weighed sample in a trst tube, add 20 nil. water and heat in the &am bath for one-half hour. Occasionally agitate the mixt’ure TYith a
