The solubility parameter theory has been used for the correlation
of infinite dilution activity coefficients of hydrocarbons
in mixed solvents (diethylene glycol and diethylphthalate) having
partial miscibility in the liquid phase. The calculated values were
in good agreement with those determined experimentally by GLC

Ireneo Kikic

Ljubomir Stele

Paolo Alessi

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CROATICA CHEMICA ACTA CCACAA 47 (1) 1-7 (1975) CCA-846 YU ISSN 0011-1643 545.84 OriginaL Scientific Paper Gas Chromatographic Investigation of Solvents with Partial Miscibility* Paolo Alessi, Ireneo Kikic, and Ljubomir Stele Istituto di Chimica Appiicata Universitci degli Studi di Tri este, Italy Received June 13, 1974 The solubility parameter theory has been used for the cor-relation of infinite dilution activity coefficients of hydrocarbons in mixed solvents (diethylene glycol and diethylphthalate) having partial miscibility in the liquid phase. The calculated values were in good agreement with those determined experimentally by GLC. INTRODUC'I'.ION Mixed solvents have been studied extensively wHh regard to the use of mixed liquid phases for analytical purposes1•2, as well as to the comparison between the igas-liquid chromatographic (GLC) performances of mixed station-ary phases and those of special couplings of GLC columns filled with pure stationary phases3•4 • · In this work we have inve,stigated a pair of polar solvents (diethylene glycol and diiethylphthalate) partially miscible 1in the liquid state with the aim to find a correlation between the activity coefficients of solutes in mixed solvents and those ~n p.ure solvents. The literature reports ,some iiinveshgations made by Maffiolo5, Renono and Wakzmundzki7•8 on this subject, but only mixtures with complete miscibility were taken .into consideration ,by these authors. The study of solvents with partial miscibility 'i!s of considerable interest from both a theo·retical and a practical point of view, because it cam throw some Light cm the behaviour of the solvents in liquid-liquid chromatog.raiphy9• EXPERIMENTAL The activity coefficients of hydrocarbons in the stationary phases were deter-m1ned according to the procedure of Desty and Swariton10• The various quantities appearing in the equation which gives the activity coefficients were evaluated as described before11 , 12 • The GLC apparatus was a thermal conductivity chromatograph (Erba, Fractovap mod. B). The solvents and solutes used were reagent grade products (Erba, Fluka, BDH). To prepare the saturated stationary phases the two solvents were equilibrated at 25 °c. RESULTS AND DISCUSSION Table I re:po·rts the experimental activity coefficients of some hydrocarbons at 25 °C, 50 °c, 75 °c in the following sta:tionary phases : diethylene glycol * This work has been supported by the National Research Council (CNR), Centro di Studi di Chimica Analitica Strumentale, Bari. Temperature/PC Compound n-pentane n-hexane n-heptane n-octane n-nonane n-decane 1-pentene 1-hexene 1-heptene 1-octene cyclohexane methylcyclohexane ethylcyclohexane benzene toluene ethyl benzene TABLE I. Natural logarithms of the ·experimental infinite dilution activity coefficients at 25 oC, 50 oc and 75 oC of hydrocarbons in the pure stationary phases and in the mixed stationary phases (saturated at ·25 °c): diethylene glycol (DEG), diethylene glycol with diethylphthalate (XoEP = 0.0353) (DEG-DEP), diethylene glycol saturated with diethylphthalate (DEGsat), diethylphthalate saturated with diethylene glycol (DEPsat> and diethylphthalate (DEP). DEG 25 50 DEG-DEP 25 50 75 I 75 DEPsat 25 50 DEG sat 25 50 75 75 4.49 4.16 3.90 4.10 3.83 3.62 3.89 3.63 3.43 1.69 1.37 1.21 4.91 4.52 4.22 4.60 4.23 3.92 ·4.34 3.99 3.71 1.88 1.51 1.33 5.37 4.92 4.56 5.05 4.60 4.25 4.76 4.36 4.04 2.04 1.66 1.46 5.81 5.34 4.94 5.57 5.02 4.57 5.20 4.76 4.38 2.20 1.81 1.60 6.22 5.71 5.30 6.02 5.46 4.90 5.63 5.12 4.70 2.36 1.95 1.72 6.64 6.10 5.66 6.50 5.80 5.22 6.07 5.51 5.04 2.52 2.10 1.86 3.66 3.42 3.24 3.50 3.23 3.03 3.35 3.12 2.95 1.10 0.95 0.89 4.17 3.90 3.66 3.91 3.62 3.37 3.76 3.48 3.26 1.31 1.10 1.00 4.71 4.34 4.04 4.40 4.03 3.73 4.17 3.84 3.57 1.51 1.25 1.12 5.22 4.77 4.43 4.92 4.45 4.07 4.64 4.20 3.84 1.68 1.40 1.26 4.02 3.72 3.47 3.73 3.45 3.20 3.65 3.35 3.10 1.46 1.13 0.95 4.53 4.19 3.90 4.29 3.96 3.65 4.07 3.72 3.43 1.60 1.29 1.13 5.00 4.57 4.26 4.83 4.32 3.95 4.44 4.03 3.70 1.75 1.44 1.26 2.06 1.94 1.83 1.95 1.80 1.67 1.75 1.62 1.53 0.10 0.04 0.10 2.60 2. 41 2.25 2.45 2.23 2.06 2.21 2.02 1.89 0.27 0.14 O.G7 3.09 2.88 2.70 2.94 2.65 '2.44 2.68 2.51 2.36 0.44 0.32 0.22 DEP 25 50 75 1.64 1.37 1.16 1.82 1.50 1.29 1.97 1.65 1.40 2.14 1.79 1.53 2.33 1.92 1.65 2.48 2.07 1.76 1.07 0.93 0.84 1.25 1.09 0.98 1.45 1.23 1.08 1.67 1.38 1.18 1.39 1.12 0.95 1.56 1.27 1.07 1.74 1.42 1.22 0.04 0.05 0.11 0.20 0.09 0.02 0.36 0.22 0.15 MIXED SOLVENT INVESTIGATION 3 (DEG), diethylene glycol with diethyliphthailate (DEG-DEP; XoF.P = 0.0353 eJCPressed as mole traction), methylene glycol saturated with diethylphthalate (DEGsa1), dieithyliphthalate saturated with diethylene glycol (DEPs.1) and di-ethyliphthalate (DEP). To give an example, the va:ria>tion of 'the activity coefficients of some solutes at 25 °c as a function of the ooncentration (expressed as mole fraction) of the mixed stationairy :phase is ipTesented in Fig. 1. It can b.e observed that no linear relation exists; this is a .consequence of the excess free energy of the binaTy mixture of the two ·Solvents and depends on the nature of the so.lute. 0,05 15 ° c n-hep lane 1-heplm melhylcyclohmne I I I l ol uene 0,1 X DEP 0,9 0,95 n-h1plan1 l-hl,1111 llHJ-blllll t1tm1 Fig. 1. Variation of activity coefficients of hydrocarbons at 25 °c as a function of stationary phase concentration (expressed as molar fraction) . In order to correlate the data ·Obtained 'iiil mixed solvents w1th those obtained iin pure solvents we have used the extension ;of the solubility :parameter theory of Hildebrand and Scott13- 15, according to which the activity coefficient can be eX!pressed as follows: ln 'Y ;' = ~(Cu+ C22- 2 C12) + ln ~ + ( 1- ~) RT Vi Vi (1) where (la) 4 or where P. ALESSI ET AL. cii = ;,; + rf C12 = (J.1 • J.2)' /2 (2) (2a) The superscripts 1 and 2 refer to the pure stationary phase and to the solute, respectively. When mixed s.tation ary phases are used, the solubility parameters j,1 and r 1 and the molar volume v 1 are replaced by },, r and v: 1 = q;>1 J.1 + q;>3 J.3 (3) V = q;>1 V1 + rp3 V3 where },1 , 23 , r 1 , r 3 are the solubility parameters of the pure solvents (1 and 3) and ({11 and ({13 are volume fractions . In Eq. (2) the cohesive ene.rgy of the solvents (C11) and the solutes (C22 ) is divided into a dispersional (/,) and a polar (r) contribution, and an empirical parameter (1jJ1 2) 15 (a function of the nature of the solute) is introduced, so that the deviations of the C1 2 term from the geometrical m ean y C11 • C22 can be taken into account satisfactorily (Eqs. la and 2a). We have assigned the solubility parameters to the various solutes and to diethylene glycol as descriibed before16 ; the sol1ibility parameters of diethylene glycol, of diethylphthalate and of the mixed solvents are reported in Table II ; TABLE II. Solubility parameters at 25 °C of the pure and mixed so lvents. v l T DEG 96.3 8.22 10.26 DEG-DEP 103.67 8.25 9.94 DEG sat 110.48 8.28 9.65 DEPsat 196.06 8.67 5.88 DEP 200.0 8.68 5.80 T e mperature = 25 •c the solubility parameters of the mixed solvents have been determined a's the volume mean of those of the pure solvents. Using these solubility parameters in Eq. 2, we have calculated the activity coefficients of the solutes: the values obtained were in good agreement with the experimental activity coefficients (Figs. 2 and 3). The deviations are, on the average, less than 60/o, and do not exceed 200/o; this value, according to Maffiolo et al.5 is still reasonable for the predfotion of activity coefficients. The error is .not enough to mask the effect due to the presence of the mixed solvent. MIXED SOLVENT INVESTIGATION 5 DlG sal. DEP o D£P sat. • DEG DEH EP o ' .~ . . I I ... 15 0 16 15 61 6 1s 0 c . ,. J .,. ~,.: "--r----.--.--, . Fig. 2. Comparison between experimental activity coefficients and those calculated in according to ref. 15, and to eq. 2 in DEG, DEG-DEP, DEG'"' at 25 •c. Fig. 3. Comparison between experimental activity coefficients and those calculated in. according to ref. 15, and to eq. 2 in DEP, DEP,,, at 25 'C. In order to overcome the difficulties i:nvolved (as various authorst5 still admit) in the choice of the suitable homom0irph for dividing a solubility para-meter into a polar and a non-polar contribution, we have adopted the treatment proposed by Maffio1o5. Accordingly, for the interpretation of the data relative to a series of solutes in a same solvent, the C1 2 term of eq. 1 can be expressed as follows: (4) where J. 2 is the solubility parameter of the solute, A and a are constants. On the basis of the experimental activity coefficients of n-pentane and n-octane we have calculated the A and a varues for the various stationary phases (Table 3). For the mixed stationary phases we have observed •that the A value can be calculated according to the equation: Ami xed phase = ADEG ' XDEG + ADEP • XDEI.' (x is the mole fraction), and that A and a are related by the following exp·res-sion : a = 0.00110847 A2 - 0.0630301 A + 1.51716 This relation is valid for each mixed phase within its field of miscibility. On the basis of these A and a values (Table III) we have estimated the activity coefficients for paraffins and cycloparaffi:ns in the mixed phases cansidered (Fig. 4). The agreement between calculated and experimental values is very good (the discrepancies are on the average < 4°/1>); only n-hexane and cyc1ohexane show anOlffialous discrepancies (> 100/o) in the mixed stationary phases. The method proposed by Maffiolo has the advantage of being more sensitive to small errors in the evaluation of the cohesive energy of the solvent and enables the use of the concept O·f homomorph to be avoided. It has, ho-wever, the Hmitation of not being applicable in the given form; to the pre-diction of activity coefficients of olefins and aromatics. In fact, we have found 6 P. ALESSI ET AL. TABLE III. A and a values of the eq. 4 for the pure and mixed stationary phases. C12 =A· ?cg I DEG DEG-DEP DEG531 A 29.4177 28.9176 28.4219 a 0.625008 0.621414 I 0.621152 Temperature ~ 25 •c 15.7951 0.798140 DEP 15.2542 0.813699 remankable differences fox olefins (abO'Ut 40°io) and for aromatics (more than 1000/o). The differenc;es could be due to the ex<istence ·in these so.lutes of a ,, polarity« (even through partial) , as already po~nted out by other authors14• 5 ' 6 D f G x Df P-D£G o D £ G sa t. D £ P sit. D £ P J ' "· 4 , s 3 . 15 ° c Fig. 4. Comparison between experimental activity coefficients of paraffins and cy cloparaffins and those calculated with the eqs. 1 and 4 in DEG, DEG-DEP, DEG, 0 , , D E P ,.,, DEP at 25 •c. Evidently, .in the case of olefins and aromatics the correlation with un-divided so1ubi1i!ty parameter of the so~ute ±s less signif.icant, whereas the method based on the div1idiing of the solubility parameter gives better 1resiults, and the discrepancies between calculated and e~perimental activity coef-ficients aire generally about or below 10°/(). REFERENCES 1. L. Rohrs c n eider, Z. anal. Chem. 170 (1959) 256. 2 . . W. H. Mc Fadden, Anal. Chem. 30 (1958) 479. 3. R. A . Ke 11 er, G . H. Stewart, Anal. Chem. 36 (1964) 1186. 4. C. L. You n g, J . Chromatog. Science 8 (1970) 103. 5. G. Ma ff i o Io, J . Lenoir, J . Vida I, Chim. Ind., Gen. Chim. 104 (1971) 1161. 6. P. Ve F n i er, C. R a i m b au 1 t, H. Reno n, J. Chim. Phys. 66 (1969) 960. MIXED SOLVENT INVESTIGATION 7 7. A. Waksmundzki, Z. Suprynowicz, J. Chromatog.18 (1965) 232. 8. A. W a ks mun dz k i, Z. Supry now i c z, I. Miedz i a k, J. Gas Chromatog. (1966) 74. 9. P. A 1 es s i, I. Ki k i c, Chromatographia 7 (1974) 299. 10. D. H. Dest y, W. T. Swanton, J. Phys. Chem. 65 (1961) 766. 11. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Mi"lano) 52 (1970) 1197. 12. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Mi"lano) 53 (1971) 9'25. 13. J. H. Hi 1 deb rand and R. L. Scott, The Solubility of Nonelectrolytes, Dover, N. Y. 1964. 14. R. F. Weimer, J. M. Pr au snit z, Hydrocarbon Process. 44 (1965) 237. 15. J. G. He 1 p i.n st i 11, M. Va n W i n k 1 e, I & C, Process. Des. Dev. 7 (1968) 213. 16. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Milano) 53 (1971) 1148. SAZETAK Ispitivanje otapala s ogranicenim mesanjem gasnom kromato~rafijom P. Alessi, I. Kikic i Lj. Stele Upotrebili smo teoriju parametara topivosti za korelaciju koeficijenata aktivi-teta beskonacno razredenih ugljikovih hidrata u mesanim razredivacima (dietilen-glikol, dietilftalat) sa ogranicenom stopom me5anja u tekucem sta11ju. Eksperimen-talne vrednosti postignute sa gas-kromatografijom dobro se slazu sa teoretskim racunima. ISTITUTO DI CHIMICA APPLICATA UNIVERSIT A DEG LI STUD I DI TRIESTE lTALIA Prispjelo 13. juna 1974. 

English

Gas Chromatographic Investigation of Solvents with Partial Miscibility

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CROATICA CHEMICA ACTA CCACAA 47 (1) 1-7 (1975) CCA-846 YU ISSN 0011-1643 545.84 OriginaL Scientific Paper Gas Chromatographic Investigation of Solvents with Partial Miscibility* Paolo Alessi, Ireneo Kikic, and Ljubomir Stele Istituto di Chimica Appiicata Universitci degli Studi di Tri este, Italy Received June 13, 1974 The solubility parameter theory has been used for the cor-relation of infinite dilution activity coefficients of hydrocarbons in mixed solvents (diethylene glycol and diethylphthalate) having partial miscibility in the liquid phase. The calculated values were in good agreement with those determined experimentally by GLC. INTRODUC'I'.ION Mixed solvents have been studied extensively wHh regard to the use of mixed liquid phases for analytical purposes1•2, as well as to the comparison between the igas-liquid chromatographic (GLC) performances of mixed station-ary phases and those of special couplings of GLC columns filled with pure stationary phases3•4 • · In this work we have inve,stigated a pair of polar solvents (diethylene glycol and diiethylphthalate) partially miscible 1in the liquid state with the aim to find a correlation between the activity coefficients of solutes in mixed solvents and those ~n p.ure solvents. The literature reports ,some iiinveshgations made by Maffiolo5, Renono and Wakzmundzki7•8 on this subject, but only mixtures with complete miscibility were taken .into consideration ,by these authors. The study of solvents with partial miscibility 'i!s of considerable interest from both a theo·retical and a practical point of view, because it cam throw some Light cm the behaviour of the solvents in liquid-liquid chromatog.raiphy9• EXPERIMENTAL The activity coefficients of hydrocarbons in the stationary phases were deter-m1ned according to the procedure of Desty and Swariton10• The various quantities appearing in the equation which gives the activity coefficients were evaluated as described before11 , 12 • The GLC apparatus was a thermal conductivity chromatograph (Erba, Fractovap mod. B). The solvents and solutes used were reagent grade products (Erba, Fluka, BDH). To prepare the saturated stationary phases the two solvents were equilibrated at 25 °c. RESULTS AND DISCUSSION Table I re:po·rts the experimental activity coefficients of some hydrocarbons at 25 °C, 50 °c, 75 °c in the following sta:tionary phases : diethylene glycol * This work has been supported by the National Research Council (CNR), Centro di Studi di Chimica Analitica Strumentale, Bari. Temperature/PC Compound n-pentane n-hexane n-heptane n-octane n-nonane n-decane 1-pentene 1-hexene 1-heptene 1-octene cyclohexane methylcyclohexane ethylcyclohexane benzene toluene ethyl benzene TABLE I. Natural logarithms of the ·experimental infinite dilution activity coefficients at 25 oC, 50 oc and 75 oC of hydrocarbons in the pure stationary phases and in the mixed stationary phases (saturated at ·25 °c): diethylene glycol (DEG), diethylene glycol with diethylphthalate (XoEP = 0.0353) (DEG-DEP), diethylene glycol saturated with diethylphthalate (DEGsat), diethylphthalate saturated with diethylene glycol (DEPsat> and diethylphthalate (DEP). DEG 25 50 DEG-DEP 25 50 75 I 75 DEPsat 25 50 DEG sat 25 50 75 75 4.49 4.16 3.90 4.10 3.83 3.62 3.89 3.63 3.43 1.69 1.37 1.21 4.91 4.52 4.22 4.60 4.23 3.92 ·4.34 3.99 3.71 1.88 1.51 1.33 5.37 4.92 4.56 5.05 4.60 4.25 4.76 4.36 4.04 2.04 1.66 1.46 5.81 5.34 4.94 5.57 5.02 4.57 5.20 4.76 4.38 2.20 1.81 1.60 6.22 5.71 5.30 6.02 5.46 4.90 5.63 5.12 4.70 2.36 1.95 1.72 6.64 6.10 5.66 6.50 5.80 5.22 6.07 5.51 5.04 2.52 2.10 1.86 3.66 3.42 3.24 3.50 3.23 3.03 3.35 3.12 2.95 1.10 0.95 0.89 4.17 3.90 3.66 3.91 3.62 3.37 3.76 3.48 3.26 1.31 1.10 1.00 4.71 4.34 4.04 4.40 4.03 3.73 4.17 3.84 3.57 1.51 1.25 1.12 5.22 4.77 4.43 4.92 4.45 4.07 4.64 4.20 3.84 1.68 1.40 1.26 4.02 3.72 3.47 3.73 3.45 3.20 3.65 3.35 3.10 1.46 1.13 0.95 4.53 4.19 3.90 4.29 3.96 3.65 4.07 3.72 3.43 1.60 1.29 1.13 5.00 4.57 4.26 4.83 4.32 3.95 4.44 4.03 3.70 1.75 1.44 1.26 2.06 1.94 1.83 1.95 1.80 1.67 1.75 1.62 1.53 0.10 0.04 0.10 2.60 2.41 2.25 2.45 2.23 2.06 2.21 2.02 1.89 0.27 0.14 O.G7 3.09 2.88 2.70 2.94 2.65 '2.44 2.68 2.51 2.36 0.44 0.32 0.22 DEP 25 50 75 1.64 1.37 1.16 1.82 1.50 1.29 1.97 1.65 1.40 2.14 1.79 1.53 2.33 1.92 1.65 2.48 2.07 1.76 1.07 0.93 0.84 1.25 1.09 0.98 1.45 1.23 1.08 1.67 1.38 1.18 1.39 1.12 0.95 1.56 1.27 1.07 1.74 1.42 1.22 0.04 0.05 0.11 0.20 0.09 0.02 0.36 0.22 0.15 MIXED SOLVENT INVESTIGATION 3 (DEG), diethylene glycol with diethyliphthailate (DEG-DEP; XoF.P = 0.0353 eJCPressed as mole traction), methylene glycol saturated with diethylphthalate (DEGsa1), dieithyliphthalate saturated with diethylene glycol (DEPs.1) and di-ethyliphthalate (DEP). To give an example, the va:ria>tion of 'the activity coefficients of some solutes at 25 °c as a function of the ooncentration (expressed as mole fraction) of the mixed stationairy :phase is ipTesented in Fig. 1. It can b.e observed that no linear relation exists; this is a .consequence of the excess free energy of the binaTy mixture of the two ·Solvents and depends on the nature of the so.lute. 0,05 15 ° c n-hep lane 1-heplm melhylcyclohmne I I I l ol uene 0,1 X DEP 0,9 0,95 n-h1plan1 l-hl,1111 llHJ-blllll t1tm1 Fig. 1. Variation of activity coefficients of hydrocarbons at 25 °c as a function of stationary phase concentration (expressed as molar fraction) . In order to correlate the data ·Obtained 'iiil mixed solvents w1th those obtained iin pure solvents we have used the extension ;of the solubility :parameter theory of Hildebrand and Scott13- 15, according to which the activity coefficient can be eX!pressed as follows: ln 'Y ;' = ~(Cu+ C22- 2 C12) + ln ~ + ( 1- ~) RT Vi Vi (1) where (la) 4 or where P. ALESSI ET AL. cii = ;,; + rf C12 = (J.1 • J.2)' /2 (2) (2a) The superscripts 1 and 2 refer to the pure stationary phase and to the solute, respectively. When mixed s.tation ary phases are used, the solubility parameters j,1 and r 1 and the molar volume v 1 are replaced by },, r and v: 1 = q;>1 J.1 + q;>3 J.3 (3) V = q;>1 V1 + rp3 V3 where },1 , 23 , r 1 , r 3 are the solubility parameters of the pure solvents (1 and 3) and ({11 and ({13 are volume fractions . In Eq. (2) the cohesive ene.rgy of the solvents (C11) and the solutes (C22 ) is divided into a dispersional (/,) and a polar (r) contribution, and an empirical parameter (1jJ1 2) 15 (a function of the nature of the solute) is introduced, so that the deviations of the C1 2 term from the geometrical m ean y C11 • C22 can be taken into account satisfactorily (Eqs. la and 2a). We have assigned the solubility parameters to the various solutes and to diethylene glycol as descriibed before16 ; the sol1ibility parameters of diethylene glycol, of diethylphthalate and of the mixed solvents are reported in Table II ; TABLE II. Solubility parameters at 25 °C of the pure and mixed so lvents. v l T DEG 96.3 8.22 10.26 DEG-DEP 103.67 8.25 9.94 DEG sat 110.48 8.28 9.65 DEPsat 196.06 8.67 5.88 DEP 200.0 8.68 5.80 T e mperature = 25 •c the solubility parameters of the mixed solvents have been determined a's the volume mean of those of the pure solvents. Using these solubility parameters in Eq. 2, we have calculated the activity coefficients of the solutes: the values obtained were in good agreement with the experimental activity coefficients (Figs. 2 and 3). The deviations are, on the average, less than 60/o, and do not exceed 200/o; this value, according to Maffiolo et al.5 is still reasonable for the predfotion of activity coefficients. The error is .not enough to mask the effect due to the presence of the mixed solvent. MIXED SOLVENT INVESTIGATION 5 DlG sal. DEP o D£P sat. • DEG DEH EP o ' .~ . . I I ... 15 0 16 15 61 6 1s 0 c . ,. J .,. ~,.: "--r----.--.--, . Fig. 2. Comparison between experimental activity coefficients and those calculated in according to ref. 15, and to eq. 2 in DEG, DEG-DEP, DEG'"' at 25 •c. Fig. 3. Comparison between experimental activity coefficients and those calculated in. according to ref. 15, and to eq. 2 in DEP, DEP,,, at 25 'C. In order to overcome the difficulties i:nvolved (as various authorst5 still admit) in the choice of the suitable homom0irph for dividing a solubility para-meter into a polar and a non-polar contribution, we have adopted the treatment proposed by Maffio1o5. Accordingly, for the interpretation of the data relative to a series of solutes in a same solvent, the C1 2 term of eq. 1 can be expressed as follows: (4) where J. 2 is the solubility parameter of the solute, A and a are constants. On the basis of the experimental activity coefficients of n-pentane and n-octane we have calculated the A and a varues for the various stationary phases (Table 3). For the mixed stationary phases we have observed •that the A value can be calculated according to the equation: Ami xed phase = ADEG ' XDEG + ADEP • XDEI.' (x is the mole fraction), and that A and a are related by the following exp·res-sion : a = 0.00110847 A2 - 0.0630301 A + 1.51716 This relation is valid for each mixed phase within its field of miscibility. On the basis of these A and a values (Table III) we have estimated the activity coefficients for paraffins and cycloparaffi:ns in the mixed phases cansidered (Fig. 4). The agreement between calculated and experimental values is very good (the discrepancies are on the average < 4°/1>); only n-hexane and cyc1ohexane show anOlffialous discrepancies (> 100/o) in the mixed stationary phases. The method proposed by Maffiolo has the advantage of being more sensitive to small errors in the evaluation of the cohesive energy of the solvent and enables the use of the concept O·f homomorph to be avoided. It has, ho-wever, the Hmitation of not being applicable in the given form; to the pre-diction of activity coefficients of olefins and aromatics. In fact, we have found 6 P. ALESSI ET AL. TABLE III. A and a values of the eq. 4 for the pure and mixed stationary phases. C12 =A· ?cg I DEG DEG-DEP DEG531 A 29.4177 28.9176 28.4219 a 0.625008 0.621414 I 0.621152 Temperature ~ 25 •c 15.7951 0.798140 DEP 15.2542 0.813699 remankable differences fox olefins (abO'Ut 40°io) and for aromatics (more than 1000/o). The differenc;es could be due to the ex<istence ·in these so.lutes of a ,, polarity« (even through partial) , as already po~nted out by other authors14• 5 ' 6 D f G x Df P-D£G o D £ G sa t. D £ P sit. D £ P J ' "· 4 , s 3 . 15 ° c Fig. 4. Comparison between experimental activity coefficients of paraffins and cy cloparaffins and those calculated with the eqs. 1 and 4 in DEG, DEG-DEP, DEG, 0 , , D E P ,.,, DEP at 25 •c. Evidently, .in the case of olefins and aromatics the correlation with un-divided so1ubi1i!ty parameter of the so~ute ±s less signif.icant, whereas the method based on the div1idiing of the solubility parameter gives better 1resiults, and the discrepancies between calculated and e~perimental activity coef-ficients aire generally about or below 10°/(). REFERENCES 1. L. Rohrs c n eider, Z. anal. Chem. 170 (1959) 256. 2 . . W. H. Mc Fadden, Anal. Chem. 30 (1958) 479. 3. R. A . Ke 11 er, G . H. Stewart, Anal. Chem. 36 (1964) 1186. 4. C. L. You n g, J . Chromatog. Science 8 (1970) 103. 5. G. Ma ff i o Io, J . Lenoir, J . Vida I, Chim. Ind., Gen. Chim. 104 (1971) 1161. 6. P. Ve F n i er, C. R a i m b au 1 t, H. Reno n, J. Chim. Phys. 66 (1969) 960. MIXED SOLVENT INVESTIGATION 7 7. A. Waksmundzki, Z. Suprynowicz, J. Chromatog.18 (1965) 232. 8. A. W a ks mun dz k i, Z. Supry now i c z, I. Miedz i a k, J. Gas Chromatog. (1966) 74. 9. P. A 1 es s i, I. Ki k i c, Chromatographia 7 (1974) 299. 10. D. H. Dest y, W. T. Swanton, J. Phys. Chem. 65 (1961) 766. 11. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Mi"lano) 52 (1970) 1197. 12. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Mi"lano) 53 (1971) 9'25. 13. J. H. Hi 1 deb rand and R. L. Scott, The Solubility of Nonelectrolytes, Dover, N. Y. 1964. 14. R. F. Weimer, J. M. Pr au snit z, Hydrocarbon Process. 44 (1965) 237. 15. J. G. He 1 p i.n st i 11, M. Va n W i n k 1 e, I & C, Process. Des. Dev. 7 (1968) 213. 16. P. A 1 es s i, I. Ki k i c, G. T 1 us to s, Chim. Ind. (Milano) 53 (1971) 1148. SAZETAK Ispitivanje otapala s ogranicenim mesanjem gasnom kromato~rafijom P. Alessi, I. Kikic i Lj. Stele Upotrebili smo teoriju parametara topivosti za korelaciju koeficijenata aktivi-teta beskonacno razredenih ugljikovih hidrata u mesanim razredivacima (dietilen-glikol, dietilftalat) sa ogranicenom stopom me5anja u tekucem sta11ju. Eksperimen-talne vrednosti postignute sa gas-kromatografijom dobro se slazu sa teoretskim racunima. ISTITUTO DI CHIMICA APPLICATA UNIVERSIT A DEG LI STUD I DI TRIESTE lTALIA Prispjelo 13. juna 1974. 

Gas Chromatographic Investigation of Solvents with Partial Miscibility

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