Chromatographic Analysis of Mixtures of Adipic, Glutar'ic, and Succinic Acids ANDREW 1. SMITH The Chemstrand Corp. Decatur, Ala.
$ A simple and accurate procedure
was needed for the analysis of mixtures of adipic, gigtaric, and succinic acids. Silicic acid columns containing water as a stationary phase were used. Two partition-type chromatoacgraphic procedures having + I % curacy and precision were developed. The first procedure involved extrusion of the column after development with a butanol-chloroform solution, then elution of each acid from its corresponding section of the column, The second procedure employed gradient elution with three butanol-chloroform solutions. An internal indicator in the column made it possible io collect each acid separately. Interferences due to nitric acid and copper were overcome with only a 4 to 5% loss of glutaric acid. This permitted accurate determinaticn of the acid yields when cyciohexanone-cyclohexa201 mixtures were oxidized. H E N adipic acid is prepared by the nitric acid oxidation of cyclohexanol-cyclohexanone mixtures using copper and vanadium as catalysts @), glutaric and succinic acids are formed as by-products. X simple and accurate procedure which was not time-consumirig was needed to determine the -synthesis yields of adipic and by-product acids. Marvel and Rands (3) and Yandenheuvel and Hayes (5) have shown that it is possible t o separate straightchain dicarboxylic acids by partition chromatography using water as a stationary phase on silicic acid. These methods, however, are not suitable for control procedures. The procedure of Marvel and Rands (3) requires 4 t o 4.5 hours for the analysis of a single sample, and the apparatus and operating procedure of Vandenheuvel et al. (6) are rather complicated. I n the present work two partitiontype chromatographic procedures for the quantitative separation of adipic, glutaric, and succinic acids were dei,eloped. The first, a n extrusion hilethod, is simiiar in several essential details to that developed by Smith, Mueller, and Rogers (4) for the determination oi the purity of chloroacetic acid. Separation of acids is achieved
with a two-component developing solution, on a silicic acid column containing water as the stationary phase. Quantitative determination of the three dibasic acids is carried out by eluting the appropriate section of the extruded, developed column and titrating each eluate with dilute base. The time required for duplicate analysis is 1.25 hours. The second method, involving gradient elution, is a modification of the procedure of Marvel and Rands (3). The column is developed and the acids are eiuted with chloroform-butanol solutions. Each acid is collected separately using a n internal indicator t o determine when to change the receivers. The individual eluates are then titrated with dilute alcoholic sodium hydroxide solution. .\bout 1.5 hours are required for duplicate analyses. EXPERIMENTAL
Apparatus. C h r o m a t o g r a p h i c tubes ( N o . 2, 19 X 200 mm., Scientific Glass Apparatus Co., Bloomfield, X. J.) were t h e only special pieces of apparatus used. These tubes were of uniform diameter t o allow extrusion of t h e wet absorbent. Reagents. T h e synthetic solution used in the determination of the accuracy and precision of t h e method contained 3.4853 grams of adipic acid, 1.0185 grams of succinic acid, and 1.010 grams of glutaric acid per liter. Commercial grade acids which were further purified wefe used t o make this standard solution. T h e adipic acid (nylon salt grade, 99.8% minimum purity) was distilled in vacuo and subsequently recrystallized from water. T h e glutaric acid (Eastman white label grade) was recrystallized twice from chloroform. T h e succinic acid (Eastman white label grade) was recrystallized twice, once from acetone a n d once from water. T h e purity of each acid was better than 99% as shown by titration. T h e neutral equivalents were: adipic acid found 73.02, theoretical 73.07; glutaric acid found 66.00, theoretical 66.06; succinic acid found 58.80, theoretical 59.05. Extrusion Method. Either a slurry or a d r y packing technique was m e d t o prepare t h e columns. For the slurry technique, 15 grams oi silicic acid (Mallinckrodt, 100-mesh chromaGographic grade), 7 ml. of water, and
1 A. of a 0.1% aqueous soiution of t h e desired indicator (usually m-cresol purple) were thoroughly mixed together in a beaker. Sixty milliliters of chloroform (reagent grade) were then added, and a homogeneous slurry was obtained by stirring. A small plug of cotton was inserted into t h e chromatographic tube and pushed to t h e bottom. T h e column was filled with t h e slurry which was then stirred with a long rod, reaching to t h e bottom of t h e column, to remove trapped air bubbles. As the chloroforni drained from the column, t h e remainder of the slurry was added in small increments to t h e top of t h e column. Reduction of the pressure in the receiver was necessary to maintain an appreciabie rate of flow of Iiquid from the column. When excess liquid disappeared from t h e top of the column; the silicic acid column was compressed in height to 125 mm., with a plunger which fit t h e inside of the tube. When t h e excess liquid which appeared on compression of t h e column had just disappeared, the liquid receiver was immediately vented t o the atmosphere. When the dry packing technique was used, silicic acid, water, and indicator, in the same proportions as used in the slurry method, were thoroughly mixed t o prepare a free flowing powder. The chromatographic tube was packed under reduced pressure (20 to 30 mm.), to a height of 125 mni. This dry packing technique was the preferred method of column preparation. Aliquots (10 ml.) of the synthetic sample solution were evaporated t o dryness on a steam bath in 20-ml. beakers and heated for 1 t o 2 hours. T h e dry acids were added t o t h e columns in a manner similar to t h a t of Bulen, Varner, and Burrell (I). Water (0.5 ml.) was used t o dissolve the dry acids instead of 0.5.V sulfuric acid :0.5 ml.). T h e water was added to the sample from B pipet and the acid residue was dissolved by warming on :I steam hath. One gram of dry silicic acid was mixed n i t h the sample soiut,ion. The resulting powdery miut,ure was then slurried with approximately !O mi. of chioroform and transferred t o the nolumn. Thirty-five miililiters of a lOyo (by volume) solut.ion c,t 1-hutanol in chloroform \vas useci ( r ) d(svcfiiop the columns. The pressure in the receiyer containing t h e I,luatc :vas reduced sufficiently 30 that the rate of elution \vas ab0u.t 2 t o S mi. per niinute. During the devclopnitnt, the YOL. 31,
do. i o ,
OCTOBER 1959
1621
lcwations of tlir acid fronts were shown ti!- tile internal indicator. .-ifter all of t h e developing solution harl entered the column! the suction. \vas continued on the column for about 60 seconds more in order t o dry the a d so r hen t part ia 11y and t !ierel-iy f a c i 1i tat(, its estrusion. I t \\as extruded, with the aid of a close-fitting cloxei, in one piece onto a clean slieet oi paper. The appearancc of the develolxd coiunin is indicated in Figure I . T h e shal-led arra.5 reprwvnt the acid z o n e . Thi. dotted lini,s indicatr thi. approxim:itt' points at n-hich the extruded silicic acid colunms w r e cut to separate thc J-arious acitb. Thc nude fnirly closc to the leading edges of each zone and well behind the trailing edgr of the zone ahead. The silicic acid which was used to adsorb the acids for addition to thc column was cut off and discarded.
solution of the indicator n e r e added to t h e adipic acid eiuate. T h e gradient elution procedure has t h e disadvantage t h a t tlie flow through the column of tlie 2 0 5 and larger butanol in chloroform solvent mi\tures is rather slon -1 drop per second-although the pressure in t h e receivers is . 3 to 4 redured to 20 t o 30 ~ I Uand pounds of air pressure are applied s i m u ~ a n e o u s l y to t h e top uf the column. RESULTS A N D DISCUSSIOti
-1 sjnthetic dibasic acid solution of h o n - n composition was used in the deveiopnient ivorh. The recol-ery of the acids was 99 f in the first analysis made u i n g the method of Man-el and Rank (.3). The time required for a single analysis %-a= about 4 h o u m To siiortcn the analysis time, an est m i o n method using the techniques employed by Smith, Mueller, and Rogers Each segment of t h e cut column (4) was developed. An indicator rras \vas crushed a n d spread out on a separate s h w t of paper t o hasten evapneeded n-hirh. n-hen added to t,he colorzition of the solvent. The adsorbumn. n-odd show t h r acid zones as e n t hccanie a free flon-ing po\\-der developnteiit progressed. after drying for 10 t o 13 minutes. Indiiators. Bromocresol green \vas Tht. rlrird adsorhrnt portions xvere the fii.st indicator tested (! mi. of a tiicn paikec! individually into clean 0.1$ solution per 15 Prams of silicic c 1 i r n m 3 t og ra 1111i c tubes and the d i ha sic acid). ;Ilthough t h e indicator solution acids were eluted from each portion was made basic-blue-green colorwith one 30-ni1. volunie of distilled before adtlition to the silicic acid, water. Tliv individual cluatm were collected in clcnn 125-nil. rewil-ers the color chanped to !-ellon- n-hen nixed usine a \'acuuni of 30 to 30 mni. t o with tlie silicic acid. During dehastrn the flon- of water through the velopment Kith 2. 5 . and 10% solutions column. of 1-butanol in chloroiorm. a yellonT h c dibasic acid vluates were transinheator hand \vas elutcd ahvat1 of the fer rccl (1 u a rl t i t a t ii.elv from the flasks adipic acid front. T h k s h o w d the to 135-;nl. beakcrs.' T h e flasks \\-ere position of the acid front so that no washrcl threc tinics with water. totaladipic acid n a s lost through the bottom in. about '70 nil. T h r solutions were of the column by overdrwlopmcnt. stirrt.ii a n d titrated with a sotlium hj.,lro\idv solution i 0 . C l . j t o 0.0:3.\') K h e n the amount of n-ntcr adtlcd to tn IJH s.5 using n Reckninn 3Iodc~l the silicic acid was decreased b!- 1 nd., H-2 nic,ter. B portion of the indicator \vas eluted Thtx titr:itirln 1-alucs 11 ere correctrd a h i ~ a t lof the glutaric acid front as \\-ell for the acidit!. of tlie solvents a n d as ahead of the adipic acid front. n h e n s i I i 1 , i p :lf.itl uscrl hy making a b l a n k run the watersilicic acid ratio n-as further n i t h no snnipie decreased by 1 ml. of water. the indiGradient Elution Method. T h e cator was present a t all threc acid columns ~vcrcip r e p u e d and the samfronts. p1c.s \v('pc' p i : i d on the columns as dcsc,rii)cd. Tlie columns :yere deK i t h bromocresol green indicator, vc~l~ipctlivitli 63 mi. of a iU$> ( b y it was necessary to streak the e.\truded volumtj) solution o i 1-l)utancl in column with the aqueous indicator ch:woform, follon.rd bh- 45 mi. of b solution to determine the position of 3 0 7 sclution of a 1-butanol in chloroform, and 2 5 nil. of I-butanol. ?'he rcc-ei\-ing flask n-:is chanpeci as each a c i f ! f r o n t approached within 0.5 Table 1. ElTect of Developer Cornincli of the bottom of the columr, as position on Acid Separation shown by t h r m-cresol purple indieator 1-Butanol, vol. yo 10 20 incorporated in thc column. -4dipic Chloroform, vol. 70 90 so acid was the first acid eluted from t h e Amount used, ml. 35 1 vol.0 CCJlumn, folloi\-ed hy glutaric a n d then Front travel, mm. suvc,iriic acids. Tlie indicator was Adipic 100 '77 eluded togrtfirr n-ith t h e glutwic and Glutaric 40 46 suc.cinic acids, but not with t h e adipic Succinic 20 23 Separation of fronts, mm. acid. Adipic-glutaric 60 31 T h e acid content of each fraction Glutaric-succinic 20 23 v,-as determinrr! by titration n-ith alcoholic sodium hydroside solution amount necessary to wet column t o the n-crpsol purple end point. completely. T w n t y drops of a 0.17, alcoholic 1622
ANALYTICAL CHEMISTRY
lc,
the acid zones, so that the column could be cut correct!j-. h n : : indicators were screened in order to find one or more n-hich, when incorporated into the column, would show all three acid fronts, when the maximum amount of water was used. Only two such indicators were found, metanii yellow and m-cresol purple. Tine latter n-as preferred because of grcattr contrast bet.n-rcn the acid nnd neutral zones. Developer Composition. I n t h e first esperiments, chloroform solutions containing 2, 5, and I-butanol (by volume) were used t:, d e w l o p t h e coiumns. It n-as found later t h a t a single solution would s f i c e . The amount of each particular solution needed depended ui:on the butanol The separation obconcentration. tained with chloroform solutions containing 10 and 2 0 5 but:ino: are given in Table I. Setter sq:aration of adipic from glutaric acid n-as obtained n-ith the 10% solution than with t,he 20% soiut ior.. Although a 5% butanoi solution also gave a good separaiiofi of the three acids, the amount necessary n-as 55 to 60 ml., whereas only 35 mi. of a 1Oy0 solution was required nith a consequent reduction ic the elution time. For these reasons, the lOyodeveloping solution was preferred. n h e n the 1Oyobutanol developer was used, 2@ to 25 ml. of solvent drained from the column. .-tc!. monobasic organic acids and higher dibasic acids n-hich might have been prrxsent mould have been removed by t h k effluent solvent. This eluate was not analyzed. Water-Silicic Acid Ratio. I n early experiments, different batches of silicic acid varied in their ability t o hold n-ater and still give a homogeneous slurry in chloroform n-hich settled only very slon-ly n-hen stirring n a s stopped. n ' h e r 10.5 ml. of ivater is mixed Kith 15 grams of one batch of silicic acid, a homogeneous slurry n-as obtained when chloroform was added and the mixture was stirred. 'Then silicic acid from another shipment was used, a homogeneous slurry could not be prepared although the same amounts were employed. The silicic acid-water mixeither clung to the side and bottom of the beaker n-hrn stirred or dropped immediately to the bottom of the beaker when stirring n-as stopped. 'Then dr;\--packed columns were prepared, the limit t o the amount of water which could be added to a given amount of silicic acid and still have a free-flowing powder m s the same as that which could he added and still make a good slurn- with chloroform, Several experiments were carried out to determne the effect of the watersilicic acid ratio on the separation of the acids. Table I1 shon-s the distance
the fronts moved from the top of a column containing 20 g r a m of silicic acid and varying amounts of water. The columns were developed with 35 ml. of 3 10% (by volume) solution of 1-butanol in chloroform. The weight and height of the silicic acid used to adsorb the acid ssniple were ®arded in the measurements. The results given in Table I1 show that the separation of the adipic and glutaric fronts is greatest for the highest water-silicic acid ratio. -4sadipic acid is the iuain component of the acid mk-tures t o be analyzed. a high n-atersilicic acid ratio was wed to obtain the maximum separation of the adipic and glutaric acids. The data c-f Table I1 also show that a certain minimum n-:iter-silicic acid ratio is newswry in order to separate glutaric and succinic acids. The ralue of this minimum ratio \vas not determined. Slurry and Dry Packing. The easiest way t o prepare silicic acidwater slurries in chloroform n-as to mix the water and silicic acid thoroughly 3nd remove all the lumps before adding the chloroform. Chloroform \vas apparently only a carrier for the adsorbent, because it wns removed while packing the column. K h e n the free-floffing ivater-silicic acid nk\?ure n-as added to the column without slurv i n g . the only difference noticed was that the flow rate of the solvent through the column was reduced. By reducing the pressure in the effluent receiver to 20 t o 30 nmi. the rate of solvent flow t h o u g h t.he dry-pwked colunins was increased to t.he desired rate of about 2 to 3 nil. per minute. Dr>--packed colunins were easier to prepare than slurrF-packed columns and were preferred for this reason. Accuracy and Precision. .I series of 15 analyses was made to determine t h e accuracy and precision of the extrusion method ( T a h l e 111). Two columns were prepared by the slurry technique, 13 b>- the dry-packing method. The precision of a single adipic acid determination was =O.S55. The amount of adipic acid found was 96.5% of the amount added. The precision of the glutaric ( = 2 . 5 5 ) and the succinic acids ("1.45) deternlinat.ions was lees than that of the adipic acid. The glutaric acid found n-as 93.8% of the amount, added. The amount of succinic acid found was 95.87c. Because the recoveries of the acids were low, several deternlinations were made with samples which did not evaporate t o dnness. Previously, the samples remained on the steam bath for 1 t.0 2 hours after completion of the evaporation of t.he water. The new determinations vere made by adding 1
~
Tabie It.
Silicic acid, g. Kater, g.
HTect of Water-Silicic Acid Ratio on Acid Separation 20 20 20 .a 10.3
8 0 0.40
Kater-siiicic ratio 0.525 Acid front, mm. from top of column Adipic 112 Glutaric 5'2 succinic .a Front separation, mm. .kiipic-glutaric 60 Glutaric-succinic 32
5.0 0.25
"0 0.10
s
112
100
65 27
64 31
35 35
47
36
1s
38
33
Sone
Table 111. Summary of Fifteen Determinations
SUCCINIC
.\rid .\dipic Glutnric Succinic 34 s 10 10 10 3) Actud, mg. 34.3 9 47 9.78 Found, mg. Std. dev. 0.29 0.24 0.14 Del-., yc 0 , s 2 53 1-44 Recovery, yo 98.5 93.S 95.S
GLUTAR IC
PI I
1
Table IV.
AMPIC
Controlled Evaporation Determinations
hcid hdipic Glutaric Succinic Actual, N g . 10.10
34,s
10 20
Found, lfg. Determination ,> 0
-
34 65 34,s
3*
34
46
35 1
5 b
35 0
10
Figure 1.
Developed column
a
gram of silicic acid to the acid saniple n-hen the 1-olunieof the solution reached about 0.5 1111. The rcsiilts given in Table show that the recoveries of all three acids were 100 =tlyc. Three deternlinations were made by the extrusion niethod and two by the gradient elution method. The loss of glutaric acid on prolonged heating on the steani bath \vas confirnied by anal\.ses of aliquots of a known solution of glutaric acid. Tennlillihter aliquots of a solution containing 1.00 gram oi glutaric acid per nd. were heated on the stenrn bath for 5 hours after dr!iiess n-as reached. During this heating period a white f i n fornied on the inside beaker walls. The aniount of acid remaining after the lienting \vas 9.1 mg.; the loss of acid n-ns 9S;. -4 siiiiilar set of experiments was carried out with a solution of succinic acid, The first tests Ivere inconclusi\.e, because of a variable loss of acid from 2.5 to T.2rc. Close eramination of the dn- samples showed that, the loss was due to spattering. Khen the evaporation was performed more carefully, the recoveries \yere 9 S 5 or better. These results indicate that the losses of adipic and surcinic acids from the 15 samples which were used t o determine the precision and accuracy of the
n-
s
10.1 10 1 10 2 10 2 10 0
Ill 10 10 10 10
1 1
1 1 2
Extrusion method. Grdient elution method
chronintoglnpliic iwthod \ \ ere due to sp:ittering durilig dr!-ing, The loss oi g1ut:iric wid w:is :ittrihuted to sp:ittering :11id. in sonie w s c s . tu loss I\ l i i h heating the dr!- e;iiiiple. Nitric Acid. \\-hen syiit!:c,t i c s i i i i ples contnininz nitric :icicl \\ c>i.e ci!ronintographcd. the rc,co\.t,ric.s o f the dibnsic acids \I CI'C lo\\, \I 1itL11 n 0.5gram sniuple of a :3.jrc nitric- .ci,id solution. coiitsininp ii total of 50 to 60 nip. of the dibasic :icids. \\;is c1iniili:itographed, npproxinintely 75% oi t w h acid \vas recoi-ered. The colunni eifluent nliend of the :idipic>acid effluent {vas found to be acidic. Presuninbly. monob:ieic esters were fomied b!. the reaction betwren the acids and the 1-but:inol in the developing sol\-elit. A 1O-ni1. aliquot of the stiiiidud solution containing added nitric acid, equivalent to 0.5 gram of 3 5 5 nitric acid solution, was anal!-zed ty- the usual procedure. The recovec. of acids \vas as follon-s: adipic acid 9S.5S;; glat.nric acid 9-12; and succinic acid 957,. When 10 nil. of this nitric acidcontaining solution were concentrated t o 0.5 nd.and then diluted with 10 nd. of water and re-evaporated to 0.5 nd., VOL. 31, NO. 10, OCTOBER 1959
1623
the recovery of succinic acid n-as not significantly increased. The recovery of adipic acid \vas better than 99%. When all the nitric acid was eliminated by heating nithout spattering on the steam bath for 1 t o 2 hours after dryness n-as reached, the recovery of adipic acid was 100 the recovery of succinic acid r a s a t least 98 to 99%, and that of glutaric 95 to 96%. This shows the necessity of completely removing the nitric acid before chromatographing the samples. Copper. Copper is t h e metal catalyst used in largrst a m o u n t in the synthesis of adipic acid from cyclohexanone-cyclohexanol mixtures; hence its effect on t h e determination of t h e dibasic acids n a s investigated. A known solution of the three dibasic acids and copper nitrate in dilute nitric n-as prepared. Anal!-sis of this solution b:+. the extrusion method, after removal of the nitric acid by evaporation. shon-ed that tjhe copper reacted preferentially m-ith the succinic acid. The amount of succinic acid missinp corresponded exactly t o the amount nxessnry to foim copper succinate
(CuC+"IO,) with the knon-n amount of copper present. The amount of succinic acid retained by the copper was determined b y eluting with water the top portion of the column containing the copper salt and titrating the eluate t o a p H of 9.0, The amount of base required for the titration was equal to the amount of acid missing from the succinic acid eluate. This technique of eluting the upper or catalystrcontaining section of the column and reporting the acid found as succinic acid n-ould probably not be accurate in the case of actual oxidation samples because of the possible presence of other acids. T h e formation of copper succinate during analysis was prevented by adding a n amount of oxalic acid slightly in excess of that necessary to react with the copper. It was easily calculated because the copper catalyst concentration in oxidized mixtures was known. A stock oxalic acid solution, 12 mg. of acid per ml., was prepared, a n d 0.5-d. portions were used t o dissolve all the dried copper-containing samples. T h e
excess of oxalic acia which did not react with the copper was eluted behind the succinic acid. This oxaiic acid was separated from the succinic acid by carefully cutting the extruded column after streaking i t with indicator. When the gradient elution method was used with acid samples containing oxalic acid, the developing solutions used were 65 ml. of a 10% solution of 1-butanol in chloroform, 45 nd. of a 20yo solution of 1-butanol in chloroform, and 35 ml. of a 60yosolution of I-butanol in chloroform. LITERATURE CITED
(1) Bulen, W. A . , Varner, J. E., BurreU, R. c., ANAL.CHEU. 24, 187 (1952). ( 2 ) Hamblet, C. H., Mc.4levy, A. (to E. I. du Pont de Kernours & Co.), U. S.Patent 2,557,282 ( J u n e 19, 1951). ( 3 ) Marvel, C. S., Rands, R. D., J. Am. C h m . SOC.72, 2642 (1950). (4) Smith, E. D., Mueller, W. A., Rogers, L. N., ANAL.CHEK,.24, 1117 (1952). (5) Vandenheuvel. F . A., Hayes, E. R., I&., 24, 960 (1952).
RECEIYED for review October 30, 1958. Accepted June 1, 1959. Division of Analytical Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
Gas Chromatography Analysis of the Reaction Products from the Hydroformylation of isobutene G. W. WARREN, J. F. HASKIN, R. E. KOUREY, and V. A. YARBOROUGH Development Department, Union Carbide Chemicals Co., Division of Union Carbide Corp., South Charleston, W. Va.
b A gas chromatographic method was developed for the analysis of the reaction products from the hydroformylatim of isobutene, because conventional chemical techniques and other instrumental methods were not directly applicable or were too time-consuming. Of the 20 compounds obtained, 15 were present in concentrations greater than 0.1%. With the exception of two bands (2-methyl- and J-methylbutanol; 2-methyl- and 3-methylbutanal), most of the major components were completely resolved. The ratios of these branched alcohols and aldehydes were determined by mass spectrometric analysis of trapped sampies representative of the particular chromatographic band. The water content was obtained by a chemical method.
T
technique of gas chromatography developed b y James, Martin, and Phillips (4, 6, 7 , 9) has been used by many investigators (9) for HE
1624
0
ANALYTICAL CHEMISTRY
the separation and quantitative determination of members of homologous series (9, 6). T h e application of the chromatographic technique to the analysis of a complex mixture which is produced by the coP1-flame combustion of the hydrocarbons has been demonstrated by Menapace, Kyryacos, and Boord ( 6 ) . Gas chromatography has been used in this laboratory for the analysis of complex mixtsres, which normally are difficult t o analyze b y conventional techniques. A unique application of this technique has been the analysis of the crude reaction products from t h e hydroformylation of isobutene and other olefins. This mixture is composed of at least 20 components boiling between 20" and 176" C. Normally, mass spectrometric or chemical methods or both are used for the analysis of fractions after distillation. Bowever, the chromatographic method gives a more complete analysis, requires much less time, and is equally precise a n d accurate.
PROCEDURE
The Perkin-Elmer Model 154 Vapor Fractometer was used for all determinations. A column, consisting of phenvlI-naphthylamine absorbed on Celite No. 545 (100 to 120 mesh, liquid phase 30% by weight), 4 meters by 6.3 mm. in outside diameter, and operated at 100" C. n-ith a helium flow (measured a t the column outlet) of 100 cc. per minute, was used to effect separations. Each sample was scanned at full sensitivity prior to the quantitative determination. If the presence of components having a boiling point above 150" C. was suspected to be in the sample, p higher column temperaturei.e., 125" C.-was used, provided ad+. quate resolution of the other components was also obtained. Liquid samples (0.01 to 0.02 ml.) were introduced with a hypodermic syringe and a 1.6-cm. N o 27 hypodermic needle through a sihcone-rubber diaphragm into the stream of helium. The detector response wm recorded on a Bronm 0 to IO-mv. strip-citsrt recorder. The signal was attenuated bv a known factor to maximize each &flection on
