ANALYTICAL CHEMISTRY
1546 operate, and give concentration os. volume relationships which are both reproducible and predictable. Analytical chromatography of nucleotides, amino acids, and organic acids in these laboratories has been simplified and improved by use of the described gradients. ACKNOWLEDGMENT
The authors are indebted to L. J. Gosting for helpful discussions of the theory, and to F. N. Hepburn and J. C. Alexander for testing some of these systems on amino acid mixtures and for pointing out some of the required concentration relationships.
LITERA’CURE CITED
(1) LUm, R. S., Williams. R. J. P., and Tiselius, A, Acta Chem. Scand., 6, 826 (1952). (2) Husch, H., Hurlbert, R. E . , and Potter, V. R., J . Rid. Chem., 196, 717 (1952). (3) Desreux, V., Rec. trav. chiin., 68, 789 (1949). (4) Hurlbert, R. B., and Potter, T’. It.. personal communication.
(5) Lakshmanan, T. K., and Lieberman. S., Arch. Biochem. arid Biophys., 45, 235 (1933). (6) Parr, C. W., Proe. Biochem. Soc., 324th meeting, XXVII. (7) Rohm and Haas Co., Form 20R,dmberlite IR-120. K E C E I Y Efor D review hpril 9, 1054. -4ccepted .July 26, 1954.
Determination of Tin, Iron, and Molybdenum in Titanium Using Paper Chromatography IRVING KOLIER
and
Picatinny Arsenal, Dover,
CHARLES RIBAUDO
N. 1,
Although paper chromatography has found wide usage in the separation of the elements, no application to the separation of elements from titanium metal and alloys has been reported. As part of a program to develop methods of analysis for titanium metals and alloys, an investigation of the separation of trace metals from titanium by paper chromatographic techniques was undertaken in this laboratory. Tin, iron, and molybdenum were successfully separated from a titanium metal sample and quantitatively determined by polarographic and colorimetric methods. If such separations can be performed with a wide variety of metals, the procedures should widen the scope of the techniques available to the analytical chemist.
T
I T A S I U M metal, in commercial form, may contain one or more of the following elements, usually in trace amounts: iron, chromium, maganese, alumillurn, molybdenum, magnesium, vanadium, tungsten, silicon, nickel, cobalt,, copper, zirconium, tiu, niobium, tantalum, beryllium, thorium, boron, sodium, calcium, lead, and silver. I n the determination of any of these elements a preliminary separation from titanium would bc most advantageous, and in many cases, necessary. A separation of the titanium is often carried out by chemical means Tl-ith very litt81euse of the physical means of separation. Although the chemical separation of titanium is satisfact,ory in some instances, the constant danger of coprecipitation of the trace elements, if t,he separation is one of precipitation, is aln-ays present. The use of paper chromatography as a means of separating metals from other metals has been a successful technique (6, 7 ) , although no work has been done toward its application t.o the separation of trace metals from titanium. Previous work involving the migration of tin, iron, molybdenum, and titanium using various solvent systems (6, 7 ) indicated that a separation \vas possible when these rnptals were present in more or less equal amounts; however, very little work had been done in the separation of trace metals from large amounts of another metal. An investigation was therefore initiated to explore the possibilities of finding a suitable solvent system, one in which titanium, the major constituent, would have little or no movement while the metals sought (tin, iron, and molyl~denum)would have sufficient movement for separation. Such a solvent system was found to be n-butyl alcohol saturated with 3 S hydrochloric acid. Titanium metal was dissolved in hydrochloric acid, and the dissolved metal oxidized with hydrogen peroxide and diluted to a specific volume. An aliquot was placed on a paper strip and
chromatographed. The separated mctals were determined by polarographic and colorimetric methods. APP.4RATUS
For the chromatographic separation of tin, iron, and molybdenum from titanium the following xere used: a Fisher chromatographic assembly (Catalog No. 5-724) containing a stainless steel support (painted with acidproof paint to prevent its corrosion by hydrochloric acid vapors), glass tray, Petri dish, four glass rods to hold t,he paper strips and a borosilicate glass jar, 2 feet high and 1 foot in diametrr: a roll (600 feet) of Fisher chromatographic filter paper Whatnian No. 1, 1.5 inches wide (Catalog S o . 5-716); a sprayer; and a micropipet calibrated to deliver 0.1 ml. The three elements were determined by use of a Sargent polarograph, Model SSI, ivith polarographic cell and a Beckman spectrophotometer, Model DU. CHROlM.4TOGRAPHIC SEPAKATIOS OF TIN, IRON, A S D MOLYBDENUM FROM TITANIUM
Reagents. Hydrogen peroxide, 30%; hydrochloric acid. n-BLtyl alcohol-hydrochloric acid solution. Add 3N hydrochloric acid to R volume of n-butyl alcohol in a separatory funnel. Shake and continue the addition of arid until two layers appear. Discard the lower layer. Alizarin-ammonia spray solution. Expose a 0.5% solution of alizarin in ethyl alcohol to ammonia vapors for 1 hour. The color of the solution changes from amber to violet. Procedure. Transfer quantitatively to a 50-ml. beaker an accurately weighed 0.50-gram portion of the titanium sample. Add approximately 7 ml. of coiiceiitrated hydrochloric acid, rover the beaker with a watrh glass and place on a steam bath. Add a few more milliliters of concentrated hydrochloric. acid if all thP t,itanium sample is not dissolved. When the entire sample has been dissolved, remove the beaker from the steam bath, cool to room temperature and add dropwise, with swirling, 30% hydrogen pewside. Continue the addition of hydrogen peroxide until the color of the solution changes from violet to yellow. Add 5 drops of hydrogen peroxide in excess and place o n a steam bath. Khen the dark red color obtained upon the addition of excess peroxide changes to yellow, remove from the steam bath, and cool to room temperature. Transfer to a 10-ml. volumetric flask and dilute to the inark with water. From a roll of I’/z inch Whatman S o . 1 chromatographic filter paper, cut 6 strips to i~ lrngth of 22 inches. Draw a pencil line horizontally across earh of the strips a t a distance of 5 inches from one end. Spread a 0.1-ml. portion of the dissolve‘d sample across the pencil line on each of five strips by means of a micropipet. Two of these strips are used in the determination of the elements sought, one strip is used for the determination of the hand location of the element hy spraying the strip with the Alizarin-ammonia spray solution, thr fourth and fifth strips are used for the colorimetric. determination of iron and molybdenum, if no separation is obtainrd, and the sixth strip is used for running a blank on the reagent and paper. -illow the spotted strips to dry in air for 1 hour. APPAR.ITL-S FOR CHROK~TOGRIPHING. Place the end of the
V O L U M E 2 6 , NO. 1 0 , O C T O B E R 1 9 5 4 strip, which is near& to the sample, in the tray. Hold the strip in position with glass rods. .4t the bottom of the jar, place a Petri dish containing 25 ml. of the n-butyl alcohol-hydrochloric acid solvent mixture. Place the rack, tray, and strips in the jar, and cover with a well-fitting glass plate. Allow the atmosphere in the jar to come to equilibrium relative to the butyl alcoholhydrochloric acid solvent. This requires about 2 hours. Remove the stopper from the center hole in the cover plate and pipet 50 nil. of the solvent mixture into the tray. Replace the stopper and allow the Chromatogram to develop for 16 to 20 hours a t constant temperature. Remove the strips from the rack. Blot the excess solvent mixture above the original sample spot with a piece of filter paper and allow the strips to dry in air for about 1 hour. When the strips are dry, spray one with the alizarin-ammonia reagent after first marking the position of the solvent front lightly with a pencil. The tin will appear just above and in some cases a t the mlvent front as a bright orange-red band, the intensity of the band being dependent upon the amount of tin present. Several applications of the spray reagent may be necessary to bring out the color. Spray with discretion so that the paper does not become saturated with the reagent. The R/ value of the tin band is approximately 0.93 and is measured by drawing parallel lines on both sides of the tin band and solvent front. The distance measured in determining Kj values is that distance from the penciled line, where the sample is Ppotted, to the point equidistant between the two parallel lines of the band in question. The same procedure is applied to the solvent front to determine the distance traveled. The iron band is above that. of tin and has an R/ value of 0.50 to 0.60. The band is easily located by its inherent yellow color. The rnolbybdenum band is just above, and sometimes overlapping, that of iron and has an I t , value of 0.45 to 0.55. The color of the molybdenum upon spraying the strip is a dark purple. The developed chromatogram will appear as shown in Figure 1. Cut from the strip of filter paper used for the determination the portions containing the tin, the iron, and the molybdenum or the iron and molybdenum together if the bands overlap. While the location of these portions can be determined from R / values, it is best measured by cnmparison wit,h the strip which has becii sprayed. TIN DETERMINATION
Polarographic. REAGENTS.Ammonium chloride; hydrochloric acid, 1111; perchloric acid, 70%; and gelatin solution, 0.05%. Standard stock tin solutions, containing 1 mg., 0.1 mg., and 0.01 mg. of tin per milliliter, respectively, were prepared. .4liquots of these solut,ions are taken for the standard graph and treated in the nianner described below, omitting the digestion step. PROCEDURE.Cut the portion of paper strip containinq tin into small pieces and place in a 30-ml. beaker. Add 5 to 7 ml. of concentrated nitric acid and 1 ml. of concentrated sulfuric acid, cover the beaker wit'h a watch glass, and heat on a hot plate to decompose the paper. When fumes of sulfur trioxide are observed, add, with caution, 1 to 2 ml. of concentrated nitric acid in small increments and again evaporate to sulfur trioxide fumes. Continue addition of nitric acid and subsequent fuming until the solution is colorless. Cool the solution, add 1 ml. of perchloric acid, and evaporate until a volume of 0.2 ml. (sulfuric acid) is obtained. Cool and transfer the contents of the beaker to a 10-ml. volumet,ric flask, containing 2.1 grams of ammonium chloride, with 111.1 hydrochloi,ic acid. Add 1 ml. of 0.05yo gelatin solution and dilute with 1-11 hydrochloric acid to mark. Polarograph a portion between -0.35 and -0.75 volt. Determine the diffusion current from the tin polarogram and refer the determined diffusion current to the standard graph to obtain the weight of tin in .solution. Calculate the per cent tin in the samplr as follow: Tin,
yo = 10d
TI where d = \wight of tin in milligrams found from standard graph l I * = {veight of sample in grams IRON DETER3lINATION
Colorimetric. REAGESTIS. Hydroxylamine hydrochloride, crystals; 0.1% of 1,lO-phenanthroline solution in water; hydrochloric acid, 3N and 6iY. Standard stock solutions containing 0.05 and 0.005 mg. of iron per milliliter, respectively, were prepared. Aliquots of these solutions are taken for the standard graph and the color is developed, omit't'ing the extraction step.
1547
PROCEUCRE.Cut that portion of the filter strip containing the iron (or the iron and molybdenum) into small pieces and place in a 30-ml. beaker equipped with a watch glass. Add 10 ml. of 6.Y hydrochloric acid and heat carefully, just to boiling. Boil for approximately 1 minute. Transfer the acid extract to a 100-ml. volumetric flask and repeat the extraction using 10 ml. of 3 S hydrochloric acid. Combine the acid extracts. Add 10 ml. of distilled water, heat to boiling again, and add this extract to the volumetric flask. Adjust the pH of the solution to 6.0 i 0.5 l)y adding concentrated ammoiliuni hydroxide. .4dd hydroxylamine hydrochloride (solid material IS satisfactory) to redure the iron completely to the ferrous state. Then, add an excess of 1,IO-phenanthroline solution. Dilute to the 100-ml. mark with water and measure the absorbance after 30 minutes, a t 510 mp with a spectrophotometer. Determine the iron present by referring the absorbance to the standard graphs. Calculate the per cent iron i n the sample as follou s:
rI
Iron,
10 4 yo = -:If
where
'i = weight of iron in milligram. =
weight of sample in grams
0
Polarographic. REAGESTS. Ovalic acid, 0.T5M; methyl orange, 0.1% solution; and gelatin solution, 0.05%. Standard stock solutions containing 0.5 and 0 05 mg. of iron per milliliter, respectively, were prepared. -4liquots of these solutions are C taken for the standard graph (appropriate aliquot,i were made up to 50-ml. volume, containing the appropriate amounts of electrolyte. acid, and gelatin, to give a concentration of iron in milligrams per 10 ml. of solution), and treat in the manner described, omitting the digestion strp. PROCEDLRE. Cut the portion of paper F i g u r e 1. strip containing iron into small pieces and T y p i c a 1 place in 30-ml. beaker. -4dd 5 to i ml. C h r o m a toof concentrated nitric acid, cover the beaker gram with a watch glasp, and heat the beaker A . Molybdenum and contents on a hot plate to decompose band the paper. Evaporate to dryness. If any B . Iron baud residual carbon is present, ignite it by C. T i n baud D . Solvent front means of a Bunsen flame. Allow the beaker to cool. add 0.5 nil. of c-onren.~. ..~~ trated hydrochloric acid, to diisolve the residue, 4 ml. of 0.75JT oxalic acid, and 1 drop of methyl orange. Add concentrated ammonium hydroxide dropwise to resulting solution until the methyl orange changes from red to orange color, pH 5 to ti. Transfer the solution to a 10ml. volumetric flask, add 1 ml. of 0.05% gelatin and dilute to mark with water. Polarograph a portion between -0.05 and -0.45 volt. Determine the amount of iron in 10 ml. bv refcrring the diffusion current to the Ptandard graph. Calcuiate the per cent iron in sample :iccsiJIdingto Equation 2. MOLYBDENUII DETERAIIK'ATION
Colorimetric. REACESTG. Stannous chloride, 10% solut,ion, in 1 t,o 9 hydrochloric acid (freshly prepared); ferric chloride, 10% solution; sodium nitrate, 5-If; ammonium thiocyanate, 10% solution; perchloric acid, 7 0 % ; hydrogen peroxide, 30%; sodium hydroxide, C . P . pellets. Isopropyl ether, purified by shaking in a separatory funnel with one tenth its volume of a mixture containing one third each of the stannous chloride solution, ammonium thiocyanate solution, and water. The reagent is prepared fresh each day. Standard stock solutions containing 0.05 and 0.005 mg. of molybdenum per milliliter, respectively, were prepared. illiquots of these solutions are taken for the standard graph and the color is developed, the standard solution being suhstituted for the strip paper. P R O C E D ~ RCut E . into small pieces that portion of filter paper containing the molybdenum (or thr molybdenum and ii,on). Place in a 30-ml. I)eaker and cover with a watch glass. ;idd 5 ml. of concentrated nitric acid and 1 ml. of perchloric acid. Place late and allow the digestion mixture to evaporate y. Add another 5-ml. portion of nitric acid and 5 ml. o f perchloric acid :ind again slowly evaporate to drynew.
1548
A N A L Y T I C A L CHEMISTRY
Place the beaker, after wiping the outside, into a 250-ml. beaker, add 70 ml. of water, and boil for 1 minute. Add 10 ml. of concentrated hydrochloric acid. Transfer the clear solution to a 100-ml. volumetric flask, wash the 30-ml. beaker and the inside of the 250-ml. beaker with 10 ml. of hot water, and add to the volumetric flask. Cool the flask to room temperature and dilute to the 100-ml. mark with water. (If the sample contains more than 0.04 mg. of molybdenum, take a 10-ml. aliquot of the clear solution, dilute to 100 ml., and continue.) Transfer the clear solution to a separatory funnel. Add 5 ml. of the ammonium thiocyanate solution, 1 ml. of sodium nit:ate solution, and 1 ml. of ferric chloride solution. Shake well, and add 5 ml. of the freshly prepared stannous chloride solution and shake well. Add exactly 10 ml. of the isopropyl ether reagent, and shake for 1 to 2 minutes, relieving the pressure in the funnel by means of the stopcock. Allow the two layers to separate. Draw off the aqueous phase and transfer the ether to a glassstoppered container. Repeat the extraction with another 10ml. portion of isopropyl ether and combine the ether extracts. After 10 minutes, measure the absorbance with a spectrophotometer a t 475 mp. Molybdenum,
10A lOOA 7O -- w or w
(3)
A = weight of molybdenum in milligrams found from graph W = weight of sample in grams The second formula is used if a 10-ml. aliquot of the sample solution is taken (as is in the case of higher amounts of molybdenum). Polarographic. REAGESTS.Sodium hydroxide, 20% solution; perchloric acid, 70%; and gelatin, 0.05y0 solution. Standard molybdenum stock solutions contained 1, 0.1, and 0.01 mg. of molybdenum per milliliter, respectively. Aliquots are taken for the standard graph and are treated in the manner described below. PROCEDURE. Cut the portion of paper strip containing molybdenum into small pieces, place in a 30-ml. beaker, add 7 to 10 ml. of concentrated nitric acid, and heat on a hot plate to decompose the paper. Add additional small increments of nitric acid to further decompose the paper. Evaporate to dryness and ignite by means of a Bunsen flame any residual carbon. (Avoid
Table I. Determination of Tin, Iron, and Molybdenum .4dded,
%
Found,
To
S o . of Detn.
Standard Deviation
Polarographic Methods Tin
0.096 10.0
0.084 9.9
8 8
0.006 0.26
Iron
0.11 9.4
0.14 9.9
6 6
0.026
0.10 10.0
0.14
6 6
0,012 0.54
Molybdenum
10.1
Colorimetric Methods 0.10 0.096
Iron Molybdsnum
0.28
10.0
9.8
6 R
0.000 0.07
0.10 10.0
0.096 9.8
0 G
0.007 0.10
Rf Values for Several Cations in Solvent Mixture (n-Butyl alcohol saturated with 3 S hydrochloric acid) Metal Rf Value 0.50-0.60 0.00-0.05
0.00-0.05 0.00-0.05 0.46-0.55 0.00-0.10 0.00-0.05 0.00-0.05 0.00-0.10 0.95-1.00 0.20 0.00-0.03 0.00-0.05 0 .oo-0 .05 0.00-0.06
0.00-0.05 0.00-0.10 0 .00-0.06 0
Molybdenum,
%
= 10d/TV
where
A W
= =
weight of molybdenum in milligrams found in 10 ml. Iveight of sample in grams
BLANKS.Take the strip of chromatographic paper reserved for the blank and cut strips equal in length to the strip containing the separated metallic ion and treat the blank paper in the same manner described for the determination of the respective metallic ion. If a blank does exist, subtract the amount found from the amount of the respective metal ion determined. RESULTS
where
Table 11.
excessive temperatures or loss of molybdenum trioxide though volatilization may occur.) Cool the beaker, add 1 ml. of 20% sodium hydroxide to dissolve the molybdic acid, and transfer the solution to a 10-ml. volumetric flask with water. Add 2.0 ml. of perchloric acid, cool, add 1 ml. of 0.05% gelatin and dilute to mark with water. Polarograph the resulting solution between +0.2 and -1.2 volts a t the appropriate sensitivity. Determine the amount of molybdenum present in 10 ml. by referring the resulting diffusion current to the standard graphs. Calculate the per cent molybdenum in sample according to Equation 2.
Rf values from literature.
A sample of powdered titanium metal, obtained from Metal Hydrides, Inc., was analyzed according to the described procedure. The analysis indicated the presence of 0.06% tin and 0.45% iron in the titanium: no molybdenum was detected. I n preparing the synthetics, known amounts of tin, iron, and molybdenum were added to the dissolved titanium metal prior to dilution to 10-nil. volume. The results, given in Table I, are the amounts receovered, after correcting for the determined amount of tin and iron in titanium. DISCUSSIOX
I n order for a solvent system to be useful in this particular analysis, the other metals present in the sample of titanium, as well as titanium itself, must have Ry values appreciably smaller than those. of tin, iron, and molybdenum. Table I1 shows the Rf values of the metals which may be encountered in a sample of titanium for the solvent mixture employed in this analysis. From the table it can be seen that a separation of tin(IV), iron(III), and molybdenum (as the molybdate ion) from titanium(IV), is possible. Using the solvent, system described in the procedure, the separation of the three metals from titanium was achieved in all instances. Remaining behind with titanium are those metals having values equal to or smaller than that of titanium. Although the separation of tin, iron, and molybdenum from titanium was always possible, a separation of iron from molybdenum was achieved in only 40% of the runs. The reason for this erratic behavior is not known a t the present time. However, the zone containing tin is so far below the iron and molybdenum zones that no interferences from these metals were encountered in the estimation of tin. While the R f values of t.he respective metals are a reliable indication of the positions of the metallic ions on the paper strip, a spray rcngerit was employed to detcwuine t,he exact location of the bands. I-?ing an alizarin-sinmoni;L rpr:ry, the tin appeared as a bright or:tngr-red colored band whereas the molybdenuni appeared as a dark-purple band. Sprx>-ing of the paper for the detection of thc iron band n-w not ncccwary because the ferric (yellox) color \vas sufficient For hand definit,ion. The deterniinat,ion of tin by t,he Godm and hlexander ( 4 ) polarographir method, slightly modified, indicated no interferences from other metals although int.erfereiice by tungsten and vanadium is possible if these two metal.. inigrilte with tin on the paper strip. The behavior of tungstcn and vanadium in the solvent syst,em employed has not been investigated as yet. The determination of iron and molyhdcnum by slightly modified methods of Knanishu and Rice (5) and Codell, Mikula, and hTorwitz ( 1 ) was possible when the two mct:tls were separated
V O L U M E 26, NO. 10, O C T O B E R 1 9 5 4 from each other hut difficult when no separation occurred. Upon ignition of the paper strip containing the two metals, the recovery of iron and molybdmum was not found to be quantitative. However, when the deterinination was made by the colorimetric methods of Fortune and Nellon (5’) and Evans, Purvis, and Bear ( 2 ) the quantitative determination of iron and molybdenum, in the presence of each other, was possible with good precision. ACKNOWLEDGMENT
The authors are indebted to E. F. Reese for the many helpful suggestions and encouragements tendered, and to E. F. Stevenson for the spectrophotometric determinations.
1549 LITERATURE CITED (1)
Codell, 11.. AIikula, J. J., and Norwitz, G., ANAL.CHEM.,25, 1441 (1953).
(2) Evans, H. J . , Purvis, E. R., and Rear, F. E., Ibid., 22, 1568
.
,
(1950).
Fortune. TV. R., and hlellon, 11. G., IND. ENG.CHEM.,ANAL. ED., 10, GO (1938). (4) Godar, E. 31.. and Alexander, 0. Ii., Ibid., 18, 681 (1946). ( 5 ) Knanishu, ,J., and Rice, T., I b z d . . 17. 444 (1945). (6) Lederer, E., and Lederer, AI., “Chromatography,” pp. 67, 317, London, Elsevier Publishing Co., 1053. (7) Smith, 0. C., “Inorganic Chromatography,” p. 57, New York, D. I‘an Nostrand Co., 1953. (3)
for review March 26, 1954. RECEIVED
Accepted August 12, 1951
Indicator Chromatographic Analysis of Organic Mixtures H. S. KNIGHT
and
SIGURD GROENNINGS
Shell Development Co,, Emeryville, Calif.
A n indicator-chromatographic methocl has been developed for the analysis of mixtures of polar organic liquids such as alcohols, ketones, and amines. The completeness of displacement of a sample by an eluent was found to depend on the ideality of the solution as well as on the relative adsorbabilities of the materials; in nonideal systems the sample is abnormally strongly adsorbed and may be bypassed by the eluent. Techniques for utilizing or avoiding bypassing by careful selection of eluent are described and examples of displacement development and frontal analysis by indicator adsorption methods are given. The equipment and mechanical procedure are adapted from the fluorescent-indicator chromatographic method of Criddle and LeTourneau for the deterniination of hydrocarbon types, but daylight dyes are used. The analysis requires 1 to 2 hours of elapsed time and about 15 niinutes of operator time. The accuracy varies from 1 0 . 1 to *4%, depending on the sisteni.
I
S THE: chromatographic analysis of colorless materials i t is often helpful to employ colored substances as indicators, whose locations on the column relative to the colorless materials are known. I n this way the course of the separation may be followed visually and often zones can be measured whose lengths are relntcd to the sample composition ( 2 ) . Criddle and LeTour~ieau(3) have described a fluorescent-indicator method for the deterniination of hydrocarbon types in gasoline and other petroleum fractions, in which a small sample containing traces of fluorescent dyes is forced through a long, narrow column of d i c a gel with alcohol as the displacing agent The sample components ai e aligned in the column on the basis of adsorbability, with saturate= hrst, followed by olefins, aromatics, and alcohol last. The bounciai ies between the zones are made visible in ultraviolet light by the fluorescent dyes, and the composition of the sample is determined by measuring the zones, the lengths of which are proportional to the concentrations of the types in the sample. Reclentlv L:llis and LeTourneau ( 4 ) have employed a mixturc of daylight .iud fluorescent dyes as indicators for the determination of hydi ocw-bon type and total ovygenated solvent content in lacquer thinners. I n the present work indicator adsorption methods were developed for the determination of individual compounds in oxygenated solvent and related systems of known qualitative coniposition. The eluotropic series or order of adsorbability of the components of each system was determined, and suitable oilsoluble dyes were selected to serve as indicators. The displace-
ment development technique, outlined above for hydrocarbons could usually be employed. However, in many nonideal systems the sample components failed to align themselves according to adsorbability; yet,, in most such instances the separation could be improved by using special eluents or by resorting to special techniques. A few systems were analyzed by frontal analysis where a larger sample is forced through the column without the use of developer, and at the liquid front the most weakly adsorbed component forms a zone, the length of which was indicated by the appropriate dj-e. The technique of indicator analysis is very simple; the theory, however, is complex and incompletely understood. I n this paper a qualitative theory is presented to explain the observed phenomena and assist analytical chcmists in establishing similar methods. APPARITUS AND PROCEDURE
The apparatus and procedure devised for hydrocarbon analysis ( 3 ) are suitable with certain modifications for other organic mixtures. The design of the analytical column employed in this work is shown in Figure 1. Specifications for the column truebore tubing are given in ASTM standards (1). The column is packed with about 7 ml. of Davison’s Gradc 923 (100- to 200-mesh) silica gel, and a few cubic millimeters of dyed gel-made by slurrying 0.1 gram of dye with 2 ml. of gel in a solvent and evaporating off the solvent-is inserted during the packing so that it appears somewhere in the separator section, below the surface of the adsorbent. For displacement development, the sample, usually 0.5 ml., is added to the surface of the adsorbent from a pipet, or a 1.00-ml. syringe for greater accuracy. Air pressure of 0.5 to 1 pound per square inch is applied until the sample is taken up by the adsorbent; then a 1- or 2-cm. layer of silica gel is added slowly to absorb any sample on thr walls of the column and prevent the eluent and sample from mixing. The eluent i3 added and pressure is again :tpplicd until the sample reaches the lower part of the analyzer wction. The sample component zones are niade visihle by the indicator dyes a t their boundaries. The zone Icngths a x measured and the sample composition in per cent by volume is calculated from the ratio of each zone length to the total sainple length, provided all the sample components are determined directly; otherwise the calculation is made from the equation Component, % v. =
zone length, mni. ~sample volume, ml.
where F is determined for the particular column design by displacing a known volume of a hydrocarbon such as iso-octane (2,2,4-trimethyl pentane) or benzene with isopropyl alcohol, and
