reaction of the elements. Peak assignment was made by comparing retention times with chromatograms of separate components. These hexafluorides are readily prepared quantitatively and are particularly easy to handle gas chromatographically. Extensive column conditioning is not required for the quaptitative elution of these compounds. Peaks of SiFl and BF3, prepared from Bz03 and powdered quartz which were added to the mixture, were unresolved a t this column temperature. Since Kel-F oil No. 10 begins to solidify at -6' C., separation of SFe, SeF8, and TeFo a t dry ice-acetone temperatures is apparently due to gas-solid adsorption rather than to partitioning. Elution of VF6. Attempts to determine vanadium compounds quantitatively failed owing to oxyfluoride formation and reaction of the fluoride with the packing material. The elution behavior of vanadium is shown in Figure 5 , The peaks labeled V F j and VOFI mere shown t o contain vanadium by standard spot tests ( 3 ) . The peak labeled VOFI was formed only when oxygen was present. This niaterial condensed as needle-like colorless crystals in the exit tube of the chromatograph when eluted in large quantities. VOF3 is the only known oxyfluoride which would give this behavior. The
yield of VFs (b.p., 47.9" C.) is greatly dependent upon the reaction conditions. When the heating element is maintained a t red heat during the one-minute reaction period and the reactor block is maintained a t 50" C., small amounts of VF6 are produced by reaction of Fz with VeOa. If the reactor block is increased in temperature to 125" C. or if the heating element is lowered in temperature, no VF6 is produced. In the reaction of F2 with VC, VF6 is formed in small yields when the reaction block is maintained below 50" C.; at higher temperatures, no VFs is formed. The formation of a dark gray coloration in the column suggests reaction between JTF5and the packing material. Conclusions. This work demonstrates that gas chromatography is readily adaptable to the quantitative analysis of many inorganic compounds and alloys. The procedure is rapid, often requiring no more than 20 minutes per sample. Relative errors approaching 1% are common with well - behaved systems. -4 thermodynamic study of the solutesolvent interactions of these systems will be published elsewhere. LITERATURE CITED
(1) Dennison, J. E., Freund, H., AUL.
CHEM.37, 1766 (1965).
Quantitative Analysis of Aqueous by Gas Chrornatogruphy
(2) Feigl, F., "Spot Tests," Vol. I, p. 137, Elsevier, New York, 1954. (3) Ibid., p. 118. (4) Hamlin, A. G., Iveson, G., Phillips, T. R., ANAL.CHEM.38,306 (1963). (5) Juvet, R. S., Durbin, R. P., Ibid., p. 565. (6) Juvet, R. S.,Fisher, R. L., Ibid., 37, 1752 (1965). (7) Mattraw, H. C., Hawkins, N. J., Carpenter, D. R., Sahal, W. W., J . Chem. Phys. 23, 985, (1955). (8) Meites, L., ed., 'Handbook of Snalytical Chemistry," p. 2-17, &ICGraw-Hill. New York., ~1863. - - (9) Philli s,' C. S. G., Timms, P. L., Ax.4~.&EM. 35, 505 (1963);( (10) Rodden, C. J., ed., Analytical Chemistry of the Manhattan Project," Div. TIII, Vol. 1, p. 40, RIcGrawlain Hill, New Yo&*-,..-"". (11) Sie, 8.T., EUeumer. J. P. 9.. R.iinders. G. R. A., Separation Sci. 1, 41 (1966): (12)- Sievers, R. E., Wheeler, G., Ross, m.D., ANAL.CHEM. 38, 306, (1966). (13) Simons, J. H., ed., "Fluorine Chemistry," 1'01. VI p. 106, Academic Press 1964. (14) Zado, F. &I., Juvet, R. S., ANAL. CHEM.38, 569 (1966).
RECEIVEDfor review July 29, 1966. Accepted October 4, 1966, Research supported by the National Science Foundation (Grant NSF-GP-2616 and continuation grant NSF-GP-5151). Presented in part at the 6th International Symposium on Gas Chromatography and Associated Techniques, Rome, Italy, September 20-23, 1966.
Alcohol
Mixtures
CLAIRE BLUESTEIN and HOWARD N. POSMANTER Cenfral Research, Witco Chemical Co., Inc., Oakland, N . J.
b An improved gas chromatographic procedure for determination of water and C1 to Cg alcohols in mixtures was developed. The mixtures were separated on a 12-foot X I/d-inch column packed with 5% Triton X-305 on Teflon using helium carrier gas and a thermal conductivity detector. The lower limit of detection of any component by this procedure was of the mixture. The about upper limit of water which this column will effectively handle is about 8 mg. Even at high water concentrations, the peaks show negligible tailing. The calculation of unknown samples was made by u new variation of the internal normalization method which is applicable to any three or mare component systems. A table of area fractions vs. weight fractions based on a known standard was constructed. The sample composition range for
o.3Y0
such a table must be limited to obtain accurate results with unknowns. This calculation procedure has advantages over usual internal normalization methods in that sample size and method of area computation can be variable. Also, it is readily utilized for routine control of plant process mixtures. This general procedure was adapted also for aqueous alcohol extracts of nonvolatile compounds.
N
gas chromatographic procedures for the analysis of aqueous alcohol mixtures have been published. I n the quantitative analysis by gas chromatography of polar mixtures containing water, a major problem had existed because of tailing, particularly in the water peak (8,Q).When the direct determination of water in a sample was not necessary, many turned to the use UXEROUS
of the flame ionization detector which is purportedly unaffected by water in samples, though this is not strictly true (4). Where a direct determination of water 13-as required and the usual thermal conductivity detector was available, it has been generally accepted that a Teflon column packing has been the best solution to the problem of tailing ('J
R1
6)'
For the substrate, we have preferred to use Triton X-305 because this improved the separation of the ternary mixtures with which we were working, decreased the relative retention time of the water peak, and allowed for more rapid elution of the higher boiling components a t a relatively lorn column temperature. The thermal conductivity detector response was used to calculate quantitative amounts of water and alcohols in the mixtures. Present quantitative calculation VOL. 38, NO. 13, DECEMBER 1966
e
1865
0.140
0 .I 30
4
L!"
0.120
s ::
0.1 10
0
0.100
9)
lx
0.090 0.080
0.00
1.0
2.o
3.0 Weight
Figure 1 .
~~
I.
Relative Retention Times
Compound Benzene Water Methanol Ethanol 1-Propanol 1-Butanol 1-Pentanol 2-Propanol 2-Methyl-1-propanol 3-Methyl-1-butanol 2-Methyl-2-propanol
1866
e
Relative retention time on 5% Triton X-305 on Teflon, He carrier 75" c. l l o o 6. 1.65 1.47 2.24 1.00 1.32 2.24 4.43 8.54
1.38 1.00 1.14 1.62 2.52
3.26
2.09 4.38
1.35
6.87
1.29
ANALYTICAL CHEMISTRY
of
6 .O
5.0 Water
in
Injected
7.0
8.0
9 .o
I 0.0
11.0
Sample (mg.)
Constancy of response factors of water for aqueous alcohol mixtures
methods depend upon the accuracy of obtaining area measurements for each component peak eluted. Improvement in accuracy will be forthconiing as some of the newer, more automated measuring devices become more common. However, the basic quantitative calculation froni the area measurement should remain the same. The simplest method, area proportionality, gives a rough quantitative estimate where insufficient information about components is known. When the components are known and known mixtures can be tested, the method of internal normalization has been used with some success; but sample size has to be determined carefully to obtain a good degree of accuracy. The method of using an internal standard has made further
Table
4.0
4.38
1.17 1.16
improvement in accuracy. However, this procedure is limited to mixtures which allow selection of an appropriate internal standard. In considering some mixtures with three or more components in which me were interested, we were not able to find a suitable internal standard. Therefore, we developed the calculation procedure described below to eliminate as many excess measurement parameters as we could. A primary objective of the development of this method was to set up a quantitative determination which could be handled by a routine control laboratory without the use of any elaborate instrumentation such as computers. EXPERIMENTAL
Apparatus. Equivalent analyses were obtained on a 12-foot, 1,14-inch Cu column packed with 570 Triton X-305 (Rohm and Haas Co.) on Teflon 6 under the following conditions: IF and hl. Model 720 chromatograph using He carrier gas a t 60 ml.iminute; injection port, 140' C.; column, 75' C.; detector, 300' C.; bridge current, 150 ma.; or Wilkens herograph Model 1520 using He carrier gas a t 50 nil./niinute; injection port, 140' C.; column, 80' C.; detector, 300' C.; bridge power, 200 ma, Responee was measured on either instrument with a 1.0-mv. Honeywell recorder equipped with a Disc integrator to measure response areas. Procedure. Calibration standards were prepared from MC&B Chromatoquality alcohols, which were checked on the chromatograph and
found to have 0.1% or less impurity. The weight composition of all mixtures was known by direct weighing. The density of a mixture was determined from the weight contained in a calibrated 50-ml. volumetric flask a t 25' C. All samples injected were measured with a 10-11. Haniilton syringe. The volume injected was determined by a difference reading between before and after injection, and each sample determination was the average of two duplicate injections. Retention tinies relative t o the first component eluted, methanol, are given in Table I. Calculations. The method of calculation used was developed and derived from the standard equations of the internal normalization method. Therefore, each substance in the mixture-for example, component i in a solution of 12 components--was assigned a specific substance response factor, Ra defined by Equation 1, where A , is the area of the peak generated by the known weight, TV$, of the substance.
W , is known because we can calculate it from the volume of sample injected, using the composition of the mixture represented by the weight fraction, W F a , and the density of the mixture. Further we can relate weight fractions to measured chromatogram areas by Equation 2: R,A, TVF, = ___ (2)
5R A
Area fractions, AFi, in the entire chromatograni trace of the multicomponent mixture are defined by
AFi
Ai
= -
Table II. Compound
(3)
2 Ai
Relative Thermal Response per Mole Literature values (5 ) 100 27 63
Benzene Water hIethanol Ethanol 1-Propanol 1-Butanol 1-Pentanol 2-Propanol 2-Methyl-1-propanol 3-Methyl-1-butanol 2-31ethyl-2-pr opanol
Combining Equations 2 and 3, we can relate area fractions and weight fractions of individual components by either
Detd. values
(7) 100 21 55 72 83
82 95
100 33 56 70 85 100 112 86
95
108 121
(1;;)
96
(95)
107 96
110 94
or RESULTS AND DISCUSSION
Our response data were checked with the previous literature t o confirm the validity of our analysis. The plot of relative retention times us. carbon number gives the straight line relationships of the normal and iso-alcohol series as described by Crippen and Smith (3). Relative substance response factors to benzene obtained under the described experimental conditions were calculated for each alcohol and for mater using Equation 1. The values were converted to relative molar response by the equation in Kaiser (6) and are shown in Table 11. Our results are compared with the literature values (6,7 ) . The assumption that the thermal response should be the same for any isomer of a primary alcohol of given niolecular
We can use these facts to set up a calculation table that is always valid for a known concentration range of a multicomponent sample, whenever such a sample needs to be analyzed. To construct the table we applied the basic 11.
niatheniaticai principle that if C A F i = n
1, x ( A F i - AFI*) = 0 , where dFd* is another set of area fractions which would be obtained from a similar mixture to a standard sample, but one which differs slightly in proportion of components. By starting with i l F , obtained from a sample of known TVFi, the AFI* can differ by arbitrary increments and each corresponding TVFc can be obtained using Equation 5 .
weight appears to be not strictly true. We have found sinall differences in the response between 1-butanol and 2methyl-1-propanol and betveen l-pentanol and 3-methyl-1-butanol. We have not investigated the secondary alcohols in this respect. For the most part, our results agree well with Messner's ( 7 ) . However, the water response which we obtain is significantly higher than both reported values. We be1ie.i-e that the higher value for water represents a truer response. Keither Teflon or the low loading of Triton X-306 causes much adsorptive hold-up. Samples containing as little as 0.2% water show a detectable peak even at the higher attenuations used for analysis of the other components. Also, Karl Fischer water analyses were run on some of the
n
iso-
x
P F OH a
LL
x
X
0.1'20
..
*.
McOH
0.
'
e
oaso I
I
0.0
'1.0
2 .o
I
3.0 Weight
Figure 2.
4.0 of
5 .O
6.O
Alcohol in lnjoctod
I
7.0 Somplo
8.0
I
9.0
10.0
11.0
(mg.)
Constancy of response factors of alcohols in aqueous and nonaqueous alcohol mixtures V8L. 38, NO. 13, DECEMBER 1966
D
'1
Table ill. Table for Conversion of Area Fraction to Weight Fraction MeQH RuOH
0.290 0.280 0,270 0 I260 0.255 0.260 0.245 0.240 0.230 0.220
0.262 0.254 0.246 0,237 0.233 0.229 __ 0.224 0.220 0.211 0.203
0,340 0,360 0.380 0.400 0.490 0,420 ___ 0,430 0.440 0,460 0.480
aqueous alcohol unknown mixtures, and these agreed with the results obtained by gas chromatography. The constancy of each response factor (Equation 1) was checked by plotting the component weight in a sample us. the experimentally determined response factor. Figure 1 shows this plot for water and Figure 2 shows this plot for three of the alcohols, methanol (MeOH), %propanol (iso-PrOH), and 2methyl-1-propanol (iso-BuOH) Data were plotted from gas chromatographic determinations on injects of the same sample mixture of different sizes, different sample mixtures, and different column temperatures. Kevertheless, the response factor for each substance remains constant over a nide weight range. The scatter of data points becomes greater for low component weights. K e believe this is mainly due to inaccuracy in the area nieasurement. Therefore, for better precision of analysis it is best to use a sample or attenuation range that produces a large enough peak area, to minimize the area measurement error caused by imprecise base line. R a t e r analyses by gas chromatography are less reliable than those for usual organic components in mixtures. This is graphically shown by the wider scatter of points on the constancy curve in Figure 1. Theoretical plate calculations were made on the column under the described conditions. All of the I
Table IV.
AF
0,300 0.290 0,285 0.280 0.275 0.270 0.260 0.255 0.250 0.245 0.240 0.230
e
0.370 0,360 0.350 0.340 0.335 0.330 0.325 0.320 0.310 0.300
__.
0,427 0,416 0.405 0.395 0.389 0.386 __ 0,379 0.373 0.363 0.352
alcohols gave similar values averaging 625 theoretical plates. However, water analyses averaged 400 theoretical plates. Relative retention times shown in Table I indicate that we did not intend to separate all of the alcohols in one sample. However, by increasing the substrate loading and shifting temperature, one could readily make a similar column suitable for separating any of the aqueous alcohol mixtures. Our aim was to ensure reproducible quantitative analysis for routine series of specific samples, and we developed the tabular calculation procedure based on the derivation described above. Two examples of such tabulations are shown in Tables 111 and IV. By holding the AF of one component constant, the AP of the other components were n
varied by 0.010 or 0.005 such that C A F , = 1. Each corresponding TVF was calculated from Equation 5 . This procedure was repeated until the table covered the desired range of AF and WF values. The total procedure mag be shortened by calculating only selected TT F ' values, such that by appropriate subtraction from unity the remaining ones may be obtained. These tables illustrate three-component systems. However, the general procedure is applicable to 4,s or multicomponent analyses. Alternatively, this can be applied to any number of components in a mixture by normalizing
Comparison of Similar Tables for Conversion of Area Fraction to Weight Fraction
iso-PrOH A, TBF
-
~
0.311 0.330 0 349 0.368 0.378 0,385 0.392 0,407 0.426 0.446
the group of components whose weight fraction of the total sample is known independently, Table 111 is in a form which can be used for routine analyses of samples in the composition range of about 20 t o 26% methanol, 31 to 45% water and 35 to 43y0 1-butanol. The composition of the standard on which this was based is indicated by the underlined values. For good analyses, particularly when water is present, i t is advisable not t o exceed a range of about 15% variation in composition for any one component from the standard mixture on which the table is based. Even with this precaution, samples containing 1 to 10% water will probably show relative errors of about 10% in the water content. For better accuracy than that, we run a Karl Fischer analysis. It should be possible to consider a wider composition range table when water is not expected in samples. HOWever, we advise checking this with several standards prior to setting up any table. For the mixture in Table I11 we mould also advise the use of about a 5 4 . sample at an attenuation suitable for good area measurement on the recorder. -4n operator can then compute area fractions and read weight fractions from the adjacent column, interpolating values when needed. -4s an added check, the sum of the weight fractions should be one. If this is not true, either an error was made, or the unknown mixture contained a component not shown on the chromatogram trace. For sets A and B, Table IV, we illustrate the variation in a tabulation possible when the empirical response factors vary slightly for two standards of similar compositions. Sets A and B response factors were obtained from the standard samples shown by the underlined compositions. Although they were both obtained under the experimental conditions described above, insufficient operator experience with technique produced the variations shown. For niany analytical applica-
B, W F (RA 0.132) (RB= 0.130) 0.318 0,309 0.305 0.300 0,295 0.291 0.281 0.276 0.272 __ 0,267 0.262 0.252
ANALYTICAL CHEMISTRY
0.315 0.306 0.302 __ 0.297 0.293 0.288 0.279 0.274 0.269 0.264 0.260 0.250
AF 0.400 0.420 0.430 0.440 0.450 0.460 0.480 0.490 0,500 0.510 0.520 0.540
H2Q -4, WF B, WF ( R A = 0.107) (Rs = 0.106) 0.344 0,363 0.373 0.382 0.391 0.401 0,421 0.431 0.440 0.450 0.460 0.4'79
0.343 0.361 0.371 0.381 0.390 0.400 0.419 0.429 0.439 0.449 0.459 0.479
iso-BuQH
AP 0.300 0.290 0.285 0.280 0.275 0.270 0,260 0.255 0.250 0.245 0.240 0.230
A,W F
B, WF (R.4 = 0,140) (RB = 0,141) 0.335 0 330 0.323 0.318 0.313 0.308 0.295 0.293 0.288 0.283 0.278 0.26'7 I
I _
0,342 0.332 0.327
0.322 0.317 0.312 0.302 0.291 0.292 0.287 0.282 0.271
tions, the two sets of compositions obtained for an unknown would not be significantly inaccurate. If better precision were required, a large number of runs could be accumulated to evaluate statistically the best factor for each component. When empirical response factors are determined, in addition to standard column and sample handling techniques, some of the more important precautions to watch for are temperature changes, flow rate variation, and base line overlap. It is not always possible to transfer a precise table directly to a different Chromatographic instrument.
We have also observed the effect of aging of the thermal conductivity wires in both of the instruments over a period longer than 6 months. In general, the magnitude of response diminishes gradually while the relative proportionality of the various components remains the same. The relative proportionality of various components also remains the same when a new Triton x-305 on Teflon column replaces an old one. LITERATURE CITED
(1) Bennett, 0. F., ANAL. CHEM. 36, 684 (1964). ( 2 ) Casazza, W. T., Steltenkamp, R. S., J. Gas. Chromatog. 3, 253 (1965).
(3) CriPPen, R.
c.,
Smith,
c. E., Ibid.,
*?! 37. (4) Foster, J. S.,Murfin, J. W., Analyst 90, 1;s (1965).
(5) Kaiser, R., “Gas Phase Chroma-
tography,” Vol. 3, chap. 8, Butter1963*
(6) Kirkland, J. J., ANAL. CHEM.35, 2003 (1963). (7) Messner, A. L., Rosie, D. AI., Argabright, P. A., Ibid., 31, 230 (1959). (8ksSom!;$$5gy*~ Acta Chem. Stand* 1 3 1 (9) Zarembo, J. E., Lysyg, I., ASAL. CHEW31, 1833 (1959). RECEIVEDfor review May 31, 1966. Accepted September 19, 1966. Presented
at the First Middle Atlantic Regional Meeting, American Chemical Society, Philadelphia, Pa., Feb. 3, 1966.
Extraction of Metal Ions with IsooctyI Thioglycolate JAMES S. FRITZ, ROBERT K. GILLETTE, and H. E. MISHMASH‘ lnstitufe for Atomic Research and Deparfment of Chemistry, Iowa State University, Ames, lowa lsooctyl thioglycolate (IOTG) is a water-immiscible organic complexing agent that quantitatively extracts bismuth(lll), copper(ll), gold(lll), mercury (II), and silver(1) from aqueous nitric acid solutions. Antimony(ll1) and tin(lV) are partially extracted, but other metal ions studied are not extracted from 0.1M acid. The extraction of bismuth(ll1) and silver(1) from 3M and 7M nitric acid, respectively, was accomplished. Bismuth, copper, mercury, and silver are easily back-extracted into aqueous hydrochloric acid and can be determined by standard analytical methods. Several additional metal ions are extracted from solutions of higher pH. Overlapping curves were obtained for the extraction of lead(l1) and zinc(l1) plotted as a function of pH. However, these metal ions are separated quantitatively at pH 4 on a column packed with a solid Columns support containing IOTG. can also be used in more acidic solutions to isolate small amounts of extractable elements from larger amounts of nonextracted substances.
and it does not have an objectionable odor. It is a complexing or chelating agent, reacting with the metal ions that form insoluble sulfides when reacted with hydrogen sulfide. It can be made selective by making adjustments in the acid concentration. IOTG is immiscible with water and only slightly soluble in water. It has a fairly high boiling point and is not highly viscous. These properties make it possible to use IOTG alone for solvent extractions, or it can be diluted with an organic solvent such as cyclohexane, chloroform, or ethyl acetate. It is one of the few complexing organic liquids that can be used in solvent extraction without a diluent. Of the metal ions studied, bismuth (111), copper(II), gold(III), mercury (11), and silver(1) are extracted quantitatively from aqueous solutions 0.1M or greater in nitric acid. Antimony(II1) and tin(1V) are partially extracted from acidic aqueous solutions. Other common metal ions studied are not extracted from 0 , l M acid, although some are extracted from less acidic solutions.
A
Apparatus. Absorption spectra were measured with a Bausch and Lomb 600 spectrophotometer. A Nuclear - Chicago scintillation well counter, Model DS 5, was used as the detector for experiments involving radioactive tracers. A Nuclear-Chicago spectrometer, Model 1820, isolated the gamma emission from the tracers used. A decade scaler counted the pulses received from the spectrometer. Reagents and Solutions. Commercial isooctyl thioglycolate (IOTG) , b.p., 125’ C. a t 17 mm., sp. gr. 0.9736 a t 25’ C. and thioglycerol (both from Evans Chemetics, Inc.)
EXPERIMENTAL
a number of sulfur-containing analytical reagents such as dithieone, dialkyldithiocarbamates, and thiophosphorous compounds (3) have been used for separation of metal ions b y precipitation or solvent extraction, most of these are broad-spectrum reagents that react with a rather large number of metal ions. This paper describes the use of isooctyl thioglycolate, HSCH2COOCSHU,as a selective reagent for the solvent extraction of certain metal ions. Isooctyl thioglycolate (IOTG) is available commercially as a pure liquid LTHOUGH
were used without further purification. A11 acids and organic solvents were analytical reagent grade. Solutions of metal nitrates were 0.05M and contained enough nitric acid to prevent hydrolysis. Solutions of tin(1V) and antimony(II1) chlorides were 0.05M and contained 2 X hydrochloric acid. An aqueous solution of O.05M chloroauric acid was prepared. A 0.05M aqueous solution of EDTA was prepared from reagent grade disodium (ethylenedinitri1o)tetraacetate and standardized by titration with ainc nitrate (pure zinc metal as primary standard) a t pH 6 using NAS indicator [0.5% aqueous solution of 7-(6-sulfo-2naphthylazo) - 8 - hydroxyquinoline - 5sulfonic acid, disodium salt (@I. The Teflon4 was a special type, 70 to 80 mesh, obtained from Analytical Engineering Laboratories, Inc. Extraction Procedure. Add exactly 10 ml. of 0.05M metal ion in 0 , l N or 1 . O X nitric acid to a 125ml. separatory funnel. Add 1 ml. of isooctyl thioglycolate and shake for 2 minutes. Add 10 ml. of chloroform, cyclohexane, or ethyl acetate and shake for 1 minute. I n some cases more chloroform vas necessary to keep the complex in solution. Use cyclohexane when a solvent lighter than water is desirable; it is satisfactory for all metals except copper. After the final shaking allow a few minutes for the phases to separate. Run off the lower phase, add a little chloroform (or water if cyclohexane or ethyl acetate is used), swirl gently and again run off the lower phase. To recover the extracted elements, back-extract the organic phase with an equal volume of aqueous hydrochloric acid. Use a t 1 Present address, Department of Chemistry, Kansas State University, Manhattan, Kan.
VOL. 38, NO. 13, DECEMBER 1966
1869
