tributions from the charging of the double layer. Thus it is not possible to check Equation 11 with the Fe(I1)-Fe(lI1) couple because the adsorption is not sufficiently pronounced. Nevertheless, it is to be expected that for cases where adsorption is more extensive and both adsorbed and diffusing forms of the reactants are simultaneously reduced (or oxidized), Equation 11 will be the best approximation for calculating true chronopotentiometric constants. LITERATURE CITED
(1) Anson, Fred C., ANAL. CHEM. 33, 934 (1961). (2) Anson, Fred C., Zbid., 33, 939 (1961).
(3) Anson, Fred C., J . -4111. C‘hem. SOC. 83, 2387 (1961). (4) Brdicka, R., 2. Elektrochem 48, 248 (1942); Collectzon Czechoslw. Chem. Cmmuns. 12, 522 (1947). (5) Deford, D. D., Div. of Analytical Chemistry, 133rd Meeting, ACS. San Francisco, 1958. (6) Delahay, P., Trachtenberg, I., J. Am. Chem. SOC.80, 2094 (1958). (7) Frumkin, A., Abstr. No. 172, Enlarged Abstracts of Papers of the Theoretical Section, Electrochemical Society Meeting, Philadel~hia.1959. (8) Eaitinen, H. A:, Mosier, B., J . A m . Chem. SOC.80, 2363 (1958). (9) . . Laitinen, H. A,, Randles. J. E. B..’ Trans. Faraday Soc. 51, 54 (1955). (10) Lingane, J. J., “Electroanalytical Chemistry,” Chap. XXII, Interscience, New York, 1958. (11) Lorenz, W., 2. Elektrochem. 59, 730 (1955).
(12) Lorenz, \Y., XIuhlbcre. El.. l b z d . . 59, 736 (195.5). (13) Lorenz, W., Xu1hlberg, H , Z.p h y s i k Chem. X.F. 17, 12:1 (1958) (14) Lorenz, W.,Schmalz, b. 0 , 2 . Elektrochem. 62, 301 (1958). (15) Matsuda, H., Delahay, P., Colleck~on Czechoslov C h e w Communp 12. 2977
(1960).
RECEIVEDfor review April 14, 1961 Accepted July 3, 1961. Division of Analytical Chemistry, 140th Meeting. ACS, Chicago, Ill., September 1961 Contribution KO.2665 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena, Calif. Work supported by the U. S. Army Research Office under Grant NO. DA-ORD-3 1-124-61-G91.
Potentiometric Titrations of Certain lnorga nic Substances by Titanium(ll1) Chloride and Chromium(I1) ChIo ride in N,N-Dimet hy Ifo rma mide JAMES F. HINTON and HAZEL M. TOMLINSON The Chemisfry Deparfmenf, Temple University, Philadelphia, Pa.
b Nonaqueous solvents are widely used in acid-base titrimetry and in titrations involving precipitations and complex ion formation, but few redox titrations involving inorganic substances in such solvents have been reported. This paper describes the procedures and results using Tic13 and CrClz in the titration of iodine, copper(ll), iron(lll), antimony(V), and bromine in N,Ndirnethylformarnide (DMF); CrClz also reduced titanium(1V) and iodine monochloride quantitatively. Other investigations in this field are currently in progress.
o
LITERATURE is available concerned with redox titrations in nonaqueous solutions except the studies in glacial acetic acid made by Stone (2, 3) and Tomicek (5-7) and their coworkers, and in liquid ammonia by Watt et al. (8-12). I n this laboratory, investigations not yet completed have included titrations of CuClz. 2H20, Iz, Br2, FeC13.6Hz0, and SbC& by TiCI, and CrCl? in DMF; in addition, IC1 and TiCL have been titrated with CrC12. Using Ti(II1) as titrant, potentiometric and visual titrations have a limit of error less than 10 parts per thousand. The limits of error in potentiometric titrations with CrClz are similar. Titanium chloride has been titrated by SbC15 in DRIF to a limit of error less
402
ANALYTICAL CHEMISTRY
than 1%. In each case in TiCl3 titrations, potentiometric and visual end points coincide and titrations may be made with nearly the same precision visually as potentiometrically. TITANIUM CHLORIDE AS REDUCTANT
Experimental. REAGENTS.Unless freshly opened, Fisher’s DMF (certified reagent grade, containing less than 100 p.p.m. of water) was stored for a t least 3 days ovei baked Linde Molecular Sieve 5A before use. All substances used for preparation of solutions were of Baker & hdamson reagent grade except the TiCla, with a typical analysis of 97% active reagent, which was kindly furnished by Union Carbide Co. Iodine and CuClz 2Hz0 were used as primary standards. APPARATUS. I n the titration setup, nitrogen of water-pump grade was passed successively through Burrell Oxsorbent, calcium chloride, magnesium perchlorate, past a lubricating oil manometer which served also as safety valve, into a closed glass cylinder encasing the upper parts of two burets with Teflon cocks, and hence through an exit needle between the burets. This needle was sufficiently flexible to effect stirring and providc a n atmosphere of nitrogen when placed in a 1-em. Beckman cell; this cell could be readily placed under either buret when a purely visual or spectrophotometric determination was made. Potentials were observed with either a Beckman Model G or a Leeds & LTorthrup Model 7664 pH meter.
A 20-ml. bulb and electrodes of 28gage B & 8 platinum wire were used. The buret-electrode ( I S ) assumes a definite potential in a given concentration of any one salt, but this value is unpredictable. A three-way stopcock permitted a continuous atmosphere of nitrogen whether or not the solution IWE stirred by this gas. CHARACTERISTICS OF TITANIUM CHLORIDE SOLUTIONS.Restandardizations of solutions of TiCla in DhSF were required each day of use. Very di1ut.e (0.0005F) solutions, prepared by adding TiCL by buret to DhIF in a I-em. Beckman cell, showed a marked decrease in absorbance over a 5-minute period; the extent of change >%-as not affected by the quantity of nitrogen used for stirring. When Tic12 solutions were titrated by I2 solutions, considerably more Tic13 was consumed for a given amount of iodine solution than. in the reverse titration. This was to be expected since transfer of TiC1, solution from one environment to another resulted in decrease in titer, and the reaction with iodine mas very slow, permitting a long exposure to the effect of the new environment. When Tic13 solutions were titrated rapidly by CuC12,2Hz0 solutions, the amount of TiC13 required above that required for the reverse titration was negligible. This was expected since the reaction of Cu(IT) and Ti(II1) is very rapid. Solutions of Tic13 mere undfected by standing in a buret for more than 4 hours in close proximity to 1 2 solution in the other hrirct. TVatcr in the iodine
solution was without appreciable effect in volumes up to 5% of the iodine titrated whcn 1 ml. of iodine was titrated mit'li 2 ml. of 0.08F TiC13. When 5 nil. of oxygen was bubbled through an iodine solution before titration, the titrant was oxidized to a quant,itative order corresponding to the oxygcn retained by the solution of iodine. PROCEDURE. Solutions were made up in containers filled with nitrogen. In transferring solutions, the containers were stoppered immediately after having removed the aliquot to minimize contact with air. I n the case of TiCb, samples m r e withdrawn through a rubber ampoule after injecting a volume of nitrogen from the syringe, corresponding to the quantity of sample to be withdrawn. All the titration cells were purged with nitrogen before saniples were added. All titrations were made without stirring during the initial addition of titrant. In every case. the init,ial volume of titrant added was a t least 90% of that required for quivalence. Copper(I1). Reagent grade CuC12. 2H20 was analyzed electrolytically; the total copper content corresponded to 99.9% CuC12.2H20. Solutions of CuC12.2H20in D M F were prepared by w i g h t . When the CuCl?.2H20 was used as a primary standard for TiCla solutions, a new primary standard was prtyared no less often than once a week. Iudine. Standard solutions of iodine in 13MF were prepared by weighing iodine in a small quantity of D M F vontained in a volumet'ric flask. followed by dilution. Iron(II1). Reagent grade FeC13. 61LO analyzed iodometricaliv was found to -rontaig iron(II1) corresponding to 99.0% FeC13.6H20. A solution of Il.Xl% FeCL.6H10 in D M F was prep&d on a k g h t basis, and aliquots of this solution were weighed in a titration cell purged with nitrogen just brfore its addition. The cell was imnicdiately placed in position for the titration and purged again by bubbling nitrogen through the sample. I n cases in which thiocyanate was used to obtain L: clcar end point, 5 ml. of D M F was Lidded to the weighed sample followed by 3.0 ml. of saturated (2M) K C S S , and t>hesolution was then purged with nitrogen. Jhoinine. Reagent grade prepurified h i m i n e was assayed iodometrically as (*ontxining100.0% reducible substances :is Br2. Bromine solutions were prcp n r d by weight, and calculations of nomality based on a specific gravity c~liaiige of 0.00096 per degree from a slwific gravity of 0.9445 a t 25" C. I ' i l ~ t s calibrated at room temperature with D M F were assumed to deliver the wnie volun:~a t any lower temperature. .I known \wight of DhIF was cooled to 5' ('. together with a bottle of bromine. l'lic DRlF IVRS opened momentarily rat room tcniperature in an atniosphere of nitrogen and then placed in a nat,er-ice niisture. Bromine was weighed in a 1-cm. Beckman cell which was fitted n-ith a Teflon plug. This cell was then dropped into the DRIF, and the con-
tainer was stoppered immediately and then shaken to remove the Teflon plug. After several minutes of shaking, the solution was placed in a water-ice mixture or cold bath of constant temperature. Aliquots were removed quickly and the ground glass stopper replaced as soon as possible after removing each aliquot. Antimony(V) Chloride. Iodometric analysis of the SbC15 showed 102.99;b reducible substances as SbC15. This reagent was found to contain 1%volatile oxidants calculated as chlorine, probably present as SbC15 2C12 (4), by passing nitrogen successively through an HCI solution which was then titrated to a starch end point with 0.1013N NazSz03 solution. Moreover, when platinum remained for more than 10 hours in contact with solutions of the SbCls prepared by breaking glass ampoules of the sample (by means of steel encased in smooth glass) in the reaction vessel containing D M F , loss in weight of the platinum resulted. This loss was considerably greater than that which occurred when the SbCls had been previously stirred with nitrogen before remaining in contact with platinum. Solutions of SbCls in D M F were prepared by rapid addition of more than 1 gram of reagent by pipet to 100-ml. volumetric flasks previously swept with dry nitrogen and containing weighed samples (approximately 75 ml.) of solvent. The solvent had been cooled thoroughly in a methanol-dry ice bath with intermittent opening of the flask in a stream of dry nitrogen; solute was added while the flasks remained in the bath, thrn the frozen SbC15-formamide mixtures werc :~110~wdto mrlt in the dark a n d I\ c.ighcd.
Table I.
RESULTS AND DISCUSSION
In Table I are presented the results of titrations together with the measures of their precision. Titration of Copper(I1). T h e reaction of C u C l 9 . 2 H 2 0 with t h e titrant is essentially immediate. K O consequential drift in voltage is encountered even upon addition of the increment of titrant at t h e equivalence point. T h e visible color change at t h e equivalence point is from yellnw t o colorless or very pale blue. This change IS discernible even when 0.01 ml. of 0.15M TiCla is added to 100 ml. of D M F containing a trace of cuc12. Titration of Iodine. Whenever total volumes were less than 15 ml. better results mere obtained when iodine solutions less than 0.1R were titrated by T i C b solutions more than 0.1N. T h e very slow reaction rate admits of loss of a significant amount of iodine due to nitrogen being passed through t h e solution; also, t h e less rapid transfer of titrant causes some decrease in its titer, an opposing effect. ,4 lapse of several minutes is usually necessary after the initial addition of a large quantity of titrant in order that a steady voltage reading be observed. I n the vicinity of the equivalence point, a n interval of at least 30 seconds is required after an increment of titrant has been added, and a very pale yellow color must be present just before addition of the small quantity of titrant required to reach the end point. At
Results of Titrations of Inorganic Substances with TiCI,
Milliequivalent TiCl?a c,I( 11)
0.6196 0 6195 l I e a n error 1/1000 0 6662 0 6675
TlCllh II C TlCl$ Fe( III)d
FdIII)'
0 6704 0 6707
0 2580
0 5180 0 5171
-__
0.7873 0 7872
0 4300 0 4305
mean and std dev 1/1000 0 2241 0 2242 0 2276 0 2239
0 4977 0 4981 0 2170 0 2181
mean dev 611000 std. dev. 9/1000 0 6129 0 5656 0 4346 0 6121
hIean error -2/1000 TiCIsb Br?
0 6227 0 6226
inean dev. Oil000 std. dev. l / l O O O
Mean error -3/1000 0 2585
llean error -16/1000 TlC13t
0.5686 0 5686
0.6829 0,6825
0 5662
mean and atd dev. I /lo00 0.6810 0.6810 0.6805 0.6805
0 4349
0.6782 0.6785
Mean error 1/1000 mean and std. dev. l/lOOO TiCl,?
0.3464 0.3464
0.33'76 0.3377
SbC'l,
1 I w n error - 1/1000
0 5901 0 5004
0.1887 0 1888
mean dev. 0 1000 std. (icv. 1 11000
Standardized with 1, solution. with Cu(I1) solution. Five i d . D M F added before titration. Without CXS- addition. e With CXS- addition.,
a
F,Standwdized
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the visual end point, the color is a light gray-blue which persists for considerably more than thirty seconds. The potentiometric end point is sharp and unmistakable, but often not a typical one. I n cases in which the end point is abnormal, a drift in voltage in the direction corresponding to the Ti(IV)/Ti(III) half cell takes place for the first time during the titration. This slow drift usually occurs approximately 15 seconds after stirring has been stopped. Repeated stirring results in more drift in the same direction. During each stirring, the potential returns to a value far removed from the Ti(IV/Ti(III) half cell, and then approaches the final equilibrium value of the reductant half cell. Titration of Iron(II1). Ferric chloride hexahydrate can be titrated directly b y TiC13, b u t the potentiometric break is very small; t h e end point found b y conventional inspection is much later t h a n t h e equivalence point, and cannot be located precisely because a n extended plateau rather than a sharp peak results when AE/ml. is plotted against milliliters of titrant added. A modified second derivative method permits precise location of a n end point which is close to or coincident with the equivalence point. A table showing milliliters of titrant added with corresponding AE/ml. values is made up in the conventional manner, and to this another column is added in which each AE/d. value is divided by the preceding value. When the d(M/ml.) following a n increment is less than one, it is assigned a value of one. The volume of titrant corresponding to the end point may then be obtained from the curve in which b(AE/ml.) is plotted against milliliters of titrant. The color change a t the visual end point when iron(II1) is titrated directly is a difficultly perceptible darkening due to the TiC13 color. It can rarely be located to a precision of better than 2%. Addition of more than 10 moles of KCNS for each mole of iron titrated greatly increases the change in voltage a t the equivalence point, and the titration becomes practical. The end and equivalence points coincide by conventional end point location. I n the titration procedure in which thiocyanate is added, the visual end point is very sharp and coincides with the equivalence point. A pale yellow precipitate forms during the titration. In the latter stages, the deep red color of the iron(II1) thiocyanate complex lessens, and just before the end point the solution is orange. The end point is a lemon or orange-yellow imparted to the nitrogen-stirred solution b y the precipitate. It can be located almost as precisely as by the potentiometric method. 1504
ANALYTICAL CHEMISTRY
Table I shows the results of typical titrations with and without thiocyanate addition. Titration of Bromine. Lon- and erratic results n-ere obtained when attempts w'ere made to titrate bromine b y t h e procedure of t h e other titrations. This was to be expected since solutions of bromine in D M F Exhave high vapor pressures. cellent results were obtained by taking aliquots of bromine solution a t 2' C. and titrating rapidly mith TiCla a t room temperature. T h e titrations were carried out in a 50-ml. volumetric flask with a piece of platinum wire inserted through its side to serve as the indicator electrode. The solution was stirred by gentle swirling. Upon addition of titrant just before the end point, the voltage may reach a value of the order of that a t the equivalence point and then drift rapidly back to an equilibrium value. At the end point increment, little or no drift will occur. Either a fairly steady value will be reached quickly, or else a drift will take place in the direction corresponding to a Ti(IV)/Ti(III) half cell. Successive stirring of the solution will usually accelerate the drift toward the voltage of the Ti(IV)/Ti(III) half cell indicating polarization. The change in potential a t the end point is often as large as 300 mv. per 0.01 nil. titrant, preceded by a change corresponding to less than 15 mv. per 0.01 ml. titrant added. The color change a t the end
Table II.
point is from light yellow to colorless or pale blue. In Table I are results of potentiometric and visual titrations a t 12" C. Titration of Titanium Chloride by Antimony Chloride. Titration of SbClj by TiC13 is unsatisfactory because of rapid voltage drift in and past the vicinity of the end point. I n the reverse titration, the SbClj solution must be added rapidly- for consistent results. T h e color change a t the visual end point is from blue t o pale yellow. CHROMIUM CHLORIDE AS REDUCTAN1
Experimental. REAGEXTS. I n addition t o the substances described above, CrClz kindly furnished by Union Carbide Co., Eastman iodine monochloride, and Tic14 from Fisher Scientific Co. were used for the preparation of solutions. APPARATUS.The titration apparatus included the buret-electrode as above; in addition a system for storage and delivery of Cr(I1) solutions was devised. Kitrogen, which passed successively through H2S04,Burrell Oxsorbent, and DMF in contact with solid CrC12 contained in a darkened gas-washing cylinder, was injected with a needle through a rubber ampoule to maintain a slight positive pressure when delivering the CrClz solution from reservoir and capillary supply line (also protected from light) to the buret provided with a Teflon needle valve. Injection of too little nitrogen per volume of D h l F
Results of Titrations of Inorganic Substances with CrCL
(Milliequivalent) CrClp Cu( 11)
0.3596 0.3598 0.3609 0.3601 0.3601 0.3601 Mean error 1/1000 mean and std. dev. 3/1000 0.2884 0.2883 0.2883 CrC1.P 0.2881 0.2886 0.2886 0.2886 12 0.2886 Mean error -1/1000 mean and std. dev. 1/1000 0.4205 0,4034 0.4014 CrClZb 0.4446 0,4194 0.4034 0.4011 Fe( 111) 0.4461 Mean error O/lOOO mean dev. 2/1000 std. dev. 3/1000 0.4107 0.4110 0.4118 CrCltb 0.4118 0.4112 0.4112 0.4112 IC1 0.4112 Mean error O/lOOO mean dev. and std. dev. 1/1000 0.2863 0.2858 0.2847 CrC1.p 0,2833 0.2843 0.2843 0.2843 Brs 0.2843 Mean error -3/1000 mean dev. 5/1000 std. dev. 6/1000 0 4144 0.4145 0 4143 CrClp 0.4189 0.4189 SbCls 0.4189 Mean error 11/1000 mean dev. 11/1000 std. dev. 13/1000 0.4147 0.4144 0 4133 CrC12b 0.4202 0.4202 SbC16 0.4202 Mean error 15/1000 mean dev. 10/1000 std. dev. 19/1000 0.2562 0 3409 0.2562 CrC12 0,2562 0.2569 0 3400 0 2551 0.2556 TiCL Mean error 8/lOOO mean dev. 3/1000 std. dev. 4/1000 5
b
0.3616 0.3601
Standardized with 1 2 solution. Standardized with Cu(I1) solution
results in an undesirable partial vacuum (1).
CHBRACTERISTICS O F CHROMIUM CHLORIDESOLUTIONS.The solubility of CrClZin DNF is such that concentrations exceeding 0.1F could not be prepared a t room temperature. Chromium (11) solutions, even when in contact with solid CrC12, decreased in titer when exposed to light; and in solutions not in contact with solid reagent stored and delivered as described, the decrease in concentration was approximately 0.2% per 24-hour interval over a period of more than 40 days. Whenever unsteady voltage readings constituting a definite drift from the Cr(III)/Cr(II) half cell were observed, results corresponded t o considerable more titrant than was needed for equivalence. This seemed to result from air oxidation because of insufficient nitrogen in the atmosphere of the titration. PROCEDURE. Stock solutions of samples were titrated less than 4 hours after preparation except in the cases of CuClz 2 H z 0 and 12,which were used as primary standards and prepared on the day of use. After the samples of solution had been prepared as stated in the Tic13 reductions, the cap of the titration vessel was replaced with a ground glass sleeve. The indicator electrode was inserted in the sleeve and tubing bearing a nitrogen stream forced well into the lower part of the sleeve near buret stem and electrode. More than 90% of titrant required for equivalence was added, then stirring was begun and continued throughout the titration except when voltage readings were taken in cases of Br2 and TiCL solutions. Analyses and preparations of solutions of Cu(II), Iz, Fe(III), Brq, and Sb(V) are identical with those above. Titanium(1V). The Fisher Scientific Co. product was reported b y the manufacturer to contain 99.8% Ticla. Results obtained b y precipitation of the hydroxide and ignition to TiOz (100.3 f 0.1% TiC14) were in excellent agreement. The Tic14 solvated violently in DRIF, and transfer without considerable and prolonged fuming could not be
made. To prepare a stock solution. a 100-ml. volumetric flask was filled with nitrogen and weighed; D l I F was added, the flask reweighed, then cooled to less than 0" in an ice-salt bath and opened in a nitrogen stream. Then a t least 1 gram of TiCl4 was added quickly by pipet and the solution shaken well. The flask was weighed approximately, wiped, then quickly weighed carefully. Stock solutions were stored in the dark. Iodine Xlonochloride. Iodine monochloride was analyzed iodometrically to contain 100.7y0 reducible substances calculated as IC1. Transfers of IC1 were made in glass ampoules having very thin capillary arms; capillaries as well as ampoules were crushed in preparing solutions in DMF.
perienced in locating the equivalence points. But when ampoules containing SbCl6 were thoroughly crushed by a quartz rod inserted in closed vessels (fitted with Quorn sleeves) containing D M F and the solution was immersed in a M e O H 4 r y ice mixture, no perceptible end points or uncertain ones were obtained. The SbCla content was invariably low. I n the titration of TiC14, it is important that true equilibrium be attained after the addition of the first (more than 90%) portion of the CrC12. This reaction is slow in the vicinity of the end point; 30 seconds may be necessary for obtaining a steady voltage reading. LITERATURE CITED
RESULTS AND DISCUSSION
The results of typical titrations are in Tab!e 11. Neither experimental errors in volumes transferred nor in sample weights taken incurred errors of as much as 1 part per thousand. All reactions are essentially instantaneous during the whole course of a titration except as stated below. The titrations of Cu(II), Izr Fe(III), and IC1 were without complication or distinguishing feature. Low results were obtained when Br2 solutions were prepared and titrated a t room temperature. More accurate results were obtained when stock solutions were made and aliquots transferred at temperatures below 0". The reaction is so slow in the vicinity of the end point t h a t a n interval of approximately 10 seconds may be necessary for equilibrium to be approximated. Upon addition of the volume increment required t o reach equivalence, a drift in potential toward that of the Cr(III)/Cr(II) half cell is observed for the first time. Table I1 shows that excellent precision was obtained in the titration of each individual SbCls solution prepared as stated above; no difficulty was ex-
(1) Du Pont Product Information Bull., A-aOllj, April 1, 1954. (2) Hinsvark, 0. S . , Stone, I(. G., AXAL.CHEM.27,371 (1955). ( 3 ) Ilinsvark, 0. N., Stone, I(.G., Ibid., 28,334 (1956). (4) Nellor, J. W., "A Comprehensive
Treatise on Inorganic and Theoretical Chemistry,'] Vol. IX, p. 487, Longmans, Green, New York, 1929. (5) Tomicek, 0.)Chem. l i s t y 44, 283 (1950). ( 6 ) Tomicek, 0.) Sbornik celostdtni prucovn?. konf. anal. chemiku, 1st Conf. Prague I, 246 (1953). (7) Tomicek, O., Heyrovsky, J., Collection Czechslov. Chem. Communs. 15, 997 (1950). (8) FTatt, G. K., Choppin, G. R., Hall, J. L., J . Electrochem. SOC. 101, 229 (1954). (9) Watt, G. W.,Gentile, P. S., J . '4m. Chem. SOC.77, 5462 (1955). (10) Watt, G. W.,Hall, J. L., Choppin, G. R., Ibid., 73,5920 (1951). (11) Watt, G. K., Hall, J. L., Choppin, G. R., J . Phys. Chem. 57,567 (1953). (12) Watt, G. W.,Hall, J. L., Choppin, G. R., Gentile, P. S., J. Am. Chem. SOC. 76,373 (1954). (13) Willard, H. H., Boldyreff, A. IT., Ibid., 51, 471 (1929).
RECEIVEDfor review March 27, 1961. Accepted July 10, 1961. Taken from a thesis submitted by James F. Hinton t o Temple University as partial requirement for the Ph.D.
Analysis of Aqueous Solutions by Gas Chromatography J. T. KUNG, J. E. WHITNEY, and J. C. CAVAGNOL Research Center, General Foods Corp., Tarrytown,
b Gas chromatographic analysis of solutions high in water on packed columns have been hampered seriously by the large tailing Of the water peaks. A technique has been develoDed usina an indeDendentlv heated precolumn calcium'carbide' to convert the water vapor to acetylene and eliminate.the effect of water entirely.
oT
N. Y .
Recoveries from alcohol mixtures containing Over 90% water, and aidehydes, esters, and alcohol mixtures containing 36% water are excellent. Recovery Of 's lower but reproducible. Organic acids are retained b y the calcium oxide formed and cannot b e detected.
HE COMBINATION O f gas ChromatoT g r a p h i c and spectrophotometric techniques provides an excellent method of analyzing complex mixtures found in natural and synthetic flavors. The mixtures are separated by gas chromatography and the fractions trapped for subsequent identification by infrarea spectrophotometry or mass spectrom-
VOL. 33, NO. 1 1 , OCTOBER 1961
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