8. 9. i0.

ii. 12. 13.

14. 15. 16.

A. A. Bredikhin, V. A. Kirillovich, and A. N. Vereshchagin, Izv. Akad. Nauk SSSR, Ser. Khim., 1067 (1988). N. S. True and R. K. Bohn, J. Am. Chem. Soc., 98, No. 5, 1188 (1976); N. S. True and R. K. Bohn, J. Mol. Struct., 50, No. 2, 205 (1978). F. Daeyaert, F. Desseyn, and B. J. Van der Veken, Spectrochim. Acta, 44A, No. Ii, 1165 (1988); F. Daeyaert and B. J. Van der Veken, ibid., 45A, No. I0, 993 (1989); F. Daeyaert and B. J. Van der Veken, J. Mol Struct., 213, 97 (1989). V. L. Furer, A. A. Bredikhin, V. V. Alekseev, et al., Zh. Prikl. Spektrosk., 49, No. i, 7O (1988). A. N. Vereshchagin, Inductive Effect [in Russian], Nauka, Moscow (1987), p. 80. A. N. Vereshchagin, Inductive Effect, Constants of Substituents for Correlation Analysis [in Russian], Nauka, Moscow (1988); O. Exner, Correlation Analysis in Chemistry. Recent Advances, Plenum Press, New York-London (1978), pp. 439-540. A. A. Bredikhin, V. L. Polushina, and A. N. ~ereshchagin, Izv. Akad. Nauk SSSR, Ser. Khim., No. 12, 2720 (1985). A. A. Bredikhin, V. L. Polushina, A. I. Andreeva, et al., Izv. Akad. Nauk SSSR, Set. Khim., No. 5, 1038 (1987). A. A. Bredikhin, V. L. Polushina, V. A. Kirillovich, et al., Izv. Akad. Nauk SSSR, Ser. Khim., No. 5, 1041 (1987).

GAS-LIQUID CHROMATOGRAPHY OF SATURATED FLUORINATED CARBOXYLIC ACID ESTERS. I.

RETENTION IN HOMOLOGOUS SERIES E. P. Promyshlennikova, V. E. Kirichenko, K. I. Pashkevich, D. N. Grigor'eva and R. V. Golovnya

UDC 543.544.45:547.464.5'26

The retention times were determined for the first time for the members of 12 homologous and pseudohomologous series of polyfluorinated carboxylic acid esters on SE-30 and SKTFT-50Kh phases in isothermal conditions in the 60-160~ temperature range. It was found that the contributions of the methylene and difluoromethylene groups to the retention times change nonlinearly with an increase in the atomic number of the homolog. The suitability of three correlation equations for describing the chromatographic behavior of polyfluorocarboxylic acid esters was assessed.

Polyfluorinated carboxylic acids (PFA) and their esters (PFA E) are important products and intermediate products of synthesis in organic chemistry [I, 2]. Gas chromatography can be considered the basic instrumental method of analysis of these compounds in various objects involved in the preparation and use of PFA E (technology, biology, environmental protection). This is due to the high volatility and thermal stability of PFA E. The esters of a series of highly volatile lower polyfluorocarboxylic acids are used in reaction GLC: Many compounds containing a hydroxyl group are analyzed after acylation with fluorine-containing anhydrides with the formation of PFA E [3, 4]. However, there are only data in the literature on retention of saturated halogen-containing, including fluorine-containing, acid esters: the series of trifluoro- and trichloroacetates of n-alcohols and some PFA methyl esters [5-7]. The retention times (RT) for members of 12 homologous and pseudohomologous series of saturated polyfluorocarboxylic acid esters were obtained and the equations for describing Institute of Chemistry, Bashkir Scientific Center, Ural Branch, Academy of Sciences of the USSR, Sverdlovsk. A. N. Nesmeyanov Institute of Heteroorganic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 418-425, February, 1991. Original article submitted December 12, 1989. 0568-5230/91/4002-0359512.50

9

1991 Plenum Publishing Corporation

359

TABLE i. Retention Times of Polyfluorinated Carboxylic Acid Esters on Two Stationary Phases at 100 and 120~ SKTFT-5OKh (10%) Compound

SE-30 (10%)

t00~

t2o~

ioo~

i2o~

CF~CO=CH~ C=F~COzCH C~F,CO~CH~ C~F~CO~CH~ C~F,,CO~CH~ C~F,aCO:CH~

533,5 574,9 636,6 706.1 776,7 847,9

528,0 507,4 627,9 697,0 766,7 836,8

399,2 439,3 488,1 543,9 601.t 658,1

390,7 429,9 477,6 532,4 589,5 644,5

CF3CO~C2H~ C2F~CO2C~H~ CsF~CO~C~H~ C~F~CO~C~H~ C~F.CO~C~H~ C~F.CO~C:H~

613,7 649,0 7tl.0 776.7 845,4 9i4,9

607,7 64i,5 703.0 767,3 834,7 903,4

474,4 507,2 559.5 614,t 669,9 727,4

467,7 498,1 550,1 605,0 658.7 7t45

CF3COzCsH7 C~F~COzCaH~ C~H:CO~C~t{~

703.0 739.5 798,5 863,2 930,0 1000,5

697,3 732,4 789,5 852,7 918,4 987,5

563.3 594,2 646,8 701,2 756.1 812,3

557,4 585,t 635,6 688,8 74t,0 797,3

CsF,,CO2C4H9 C~FI3CO2C4H,

802,8 832,7 892,0 955.5 1021,7 t090,1

797,3 825,2 883,3 945,5 t010.7 1077,6

657,5 687,0 738,3 790,4 844.9 90t.0

649,5 677,6 727,7 779,1 832,4 887.0

CFsCO~C~H,t C2FsCO2CsH11 C,FTCO2CsH, C4F,CO2CsH,I CsF,,CO2C~HII CeFI3CO2CsH11

902,8 931,6 989,9 1052,0 ttt7,7 tt86,1

897,3 9243 98t,5 t042,5 t t06J 1173,4

756.0 784,7 833,2 884,6 937,9 993,3

748,3 776,6 824,2 875,5 927,4 98t,5

CFsCO2C6H18 C2FsCO2C,H~s C~FTCO2CsHt~

t002,8 1031.1 1088,6 1t49,6 1214_.8 t282,1

996,3 t023,8 t080.t 1t 40.0 1203.6 t269,4

854,t 881~1 929,2 979,9 1032,4 1087.0

847,5 873.2 920.4 970,4 i02t,7 t075.4

C;F,CO~C~H~ C~F,,CO2C~H~ C,F.CO~C~H~ CF3CO2C4H9 C=FsCO2C4H9

C~F~CO2C4H9 C4HgCO2C4H9

C4F~CO~C6H13 CsF.CO2C,HI~ C6F.CO2CeH13

the dependence of the retention times on the number of carbon atoms in the homologous alkyl, R = CmH2m+1 (m = i-6), and pseudohomologous polyfluoroalkyl, R F = CmF2m+1 (m = i-6), chain of the compounds were selected. The first six members of each series were investigated. EXPERIMENTAL The study was conducted on a Tsvet-164 chromatograph with a flame-ionization detector and glass columns (2 m • 3 mm) packed with Chromaton N-AW-HMDS (0.16-0.20 mm) with applied (in the amount of 5 and 10%) SKTFT-50Kh (methyltrifluoropropylsiloxane) and SE-30 (polymethylsiloxane) stationary phases. The stationary liquid phase (SLP) was applied on the solid support from solutions by the evaporation method. The carrier gas was argon, the flow rate was 30 cm3/min, and the hydrogen was electrolytic. The column thermostat temperature was 60, 80, 100, 120, 140, 160~ and the evaporator temperature was usually 40~ higher than the column temperature. All of the esters analyzed were synthesized from polyfluorocarboxylic acids and n-alcohols and identified by the boiling points when the constants were available in the literature [i] and by gas chromatography. Cs-C13 n-hydrocarbons were used as the standard series. The retention times were measured with a precision of up to 0.1 sec with an 1-05 integrator and the average was calculated from 5-7 determinations. The "dead" time was calculated with the Peterson and Hirsch equation. PFA E were added to the evaporator in the form of solutions (dilution of 1:50 by volume), and the sample size was 0.1 ~liter. The sample volume of standard n-alkanes was 0.02 Bliter.

360

~ ~(cH~I u.m. T

!

! ~ "U. . m .

66q 662 660 658

f

b'n -

~x~.x... ]),,

x I

I

I

lao

200

300

i~I

x I

500 600 A ' I0'~[%

0

l

2

J

q

5

m

Fig. 2

Fig. 1

Fig. i. Dependence of the retention time (I) of CsFTCO2CsH 7 on the mass (M, %) in the sample (i pliter) at a temperature of 80~ in a column with 10% SE-30; solvent: hexane. Fig. 2. Dependence of the contribution of the methylene group (~Im(CH2)) to the retention time on the length of the n-alkyl chain of the homologs (m) in six series of R F C(O)OCmH2m+1 at 120~ in a column with 10% SKTFT-50Kh. The numbers of the curves correspond to the following polyfluoroalkyl chain RF: i) CF2; 2) C2Fs; 3) CsF7; 4) C~Fg; 5) CsFlz;

6) C6Fis. RESULTS AND DISCUSSION It was found that the size of the sample introduced in the column significantly affects the retention characteristics of PFA E. The retention times decreased to their constant value with a constant sample volume (I pliter) and a decrease in the mass of PFA E in it. An example of this dependence is presented in Fig. i. This was observed for both SLP for a 5 and 10% concentration in the column. Samples in which the mass of substances corresponded to the horizontal segments of the curve, i.e., in the range of (0.12-0.60)~ were analyzed for calculating the RT for this reason. We calculated the values of the RT for members of six homologous series CmF2m+IC(O)OR, where m = 1-6, of polyfluorinated carboxylic acids. The values of the RT of all homologs for temperatures of 60-140~ with a 20~ interval and isothermal conditions are reported in Table i. Table 1 shows that the retention times in the column with SE-30 phase are 130-200 u.m. lower for all compounds studied than in the more polar SKTFT-50Kh. A nonlinear change in the RT with an increase in the number of homologous units (CH 2 or CF 2) is observed in both phases, especially for the first homologs. We examined six homologous series of polyfluorinated acid esters with the general formula CmF2m+zC(O)OR and a constant n-alkyl chain R for each series, and six series of the type RFC(O)OCmH2m+I with a constant polyfluorinated chain R F for a series to determine the changes in the retention times AIm(CX 2) with an increase in the alcohol or acid part of the polyfluorinated esters by one difluoromethylene (X = CF 2) or methylene (X = CH 2) unit, respectively. Each value of ~Im(CX2) was determined by comparing the RT of two successive homologs with each other: AIm(CX 2) = Im+ I - Im, where X = H or F; m is the number of the homolog in the given series, i.e., the number of C atoms in the propagating fluorinated or n-alkyl chain of the homologs; Im+ I and Im are the retention times of the neighboring homologs (m + i) and m. In both phases, the value of the contribution of the methylene group ~Im(CH 2) to the RT of the RFC(O)OCmH2m+I homolog increases in moving away from the RFC(O)O functional group, from 70 u.m. for the first methylene unit to 95-100 u.m. for the fifth one. The changes in

361

aZ~(cr2) u.m.

I

n ~ (:r~},u.-.

U

80 I

EY

6D

70

5D

50

~0

3

S

i i

I

T

I

I

2

4

5

Fig. 3

0~ m

I I

T

I

i

I

2

,7

~

5

m

Fig. 4

Fig. 3. Dependence of the contribution of the difluoromethylene group (AIm(CF2)) to the retention time on the length of the polyfluoroalkyl chain of pseudohomologs (m) in six series CmF2m+IC(O)OR at 120~ on a column with 10% SKTFT-50Kh. The numbers of the curves correspond to the following n-alkyl chain R: I) CH3; 2) C2Hs; 3) C3H7; 4) C~Hg; 5) CsH11; 6) C6HI~. Fig. 4. Effect of the temperature of the analysis on the dependence of the contributions of the difluoromethylene group (~Im(CF2)) to the retention times on the length of the polyfluoroalkyl chain of the homologous series CmF=m+IC(O)OCH 3 in a column with 10% SKTFT-50Kh. T, ~ i) 60; 2) 80; 3) 100; 4) 120.

the contributions of the methylene group to the retention of homologs in the series of trichloro- and trifluoroacetates of n-alcohols are similar [6, 7]. The contributions of the difluoromethylene units ~Im(CF 2) to the RT of PFA E are 1.5-2 times smaller than the corresponding contributions of the methylene units. They are also not constant, and vary from 30 to 70 u.m. in SKTFT-50Kh phase and from 20 to 60 u.m. in SE-30 phase. The curves of the dependences of AIm(CH 2) and ~Im(CF 2) on the number of the homolog m at a 120~ temperature of analysis for the SKTFT-50Kh stationary phase are presented in Figs. 2 and 3 as an example. As Fig. 2 shows, the contributions of the CH 2 units decreases sharply in approaching CHs and a functional group, observed for classic homologous series [8] and in the RFC(O)OCmH2m+I pseudohomologous series with constant fragments R F = CF 3, C2F s, ..., C6F13 for all series. Analogous changes are also observed in the CmF2m+IC(O)OR series with a propagating fluorinated chain (see Fig. 3). Approach of CF 3 and functional C(O)OR groups causes a sharp decrease in the values of AIm(CF2). The inconstancy of the values of ~Im(CF 2) is not only observed in the first difluoromethylene units, but the differences in the contributions are significant even between the fourth and fifth units. Without considering homologs with m > 6, it is not possible to draw any conclusions as to whether the tendency persists or the values of ~Im(CH2) and AIm(CF 2) are attained with sufficiently large m of some limiting value. The values of RT, AIm(CH2) , and AIm(CF 2 ) decrease with an increase in the temperature (Fig. 4), but the character of the change in these values with an increase in m does not change. It thus followed from the experimental data that the dependence of the retention times on the number of the homolog, i.e., the number of carbon atoms in the acid or alcohol parts of the polyfluorocarboxylic acid esters, is nonlinear and cannot be described by a simple linear dependence of the type I = a + bm. More complex equations have been proposed in the litera-

362

TABLE 2. Values of the Coefficients in Eq. (2) in Pseudohomologous CmF2m+iC(O)OR and Homologous RFC(O)OCmH2m+I i000; SMYr-5OKh (10%)

t20~ SE-30 {t0%)

R(R F) a

b

c

d

s

b

c

d

[

S

CmF=m+,C(0) OR CtI:~ CHt5 Call: CjI. C5}11, C~II~

3.q3.3 460,7 573,7 645,8 751.5 853,7

74,0 75,6 66.5 7313 70,1 69,0

66,2 77.0 6213 84,il 81j 803 )

-0.02 - 0,35 0/,7 -0.26 (LOl 0,03

0 45 0141 0.35 0,52 0,64 (},6~

303.8 335.9 430,0 52(L7 634.3 729,5

53,4 66,[; 62,8 61,3 57,8 57,4

33,2 66,0 65,0 6t,9 56,6 60,9

87,2 93,9 88,4 84,3 86,8 84,7

27,6 55,8 38,6 37,9 43,8 37.1

OA2 -0,89 -0,59 -0,50 -0.22 -0,24

1,00

0,61 0,93 0,63 0,35 0,53

Rr-C (0) OC.,tl2.~+ t (]1:~ C_,Fr, CaF7 C4F~, C~F~ C,;FH

399,5 441,2 511,~ 571.7 643,1 7()9,7

!)5,7 / 37,8 99 9 40,7 89,6 87.5 88,7

Z],9 45,0 .48,6

0,64 0,83 1,13 0,93 t.10 0,9(;

I t,21 [ I),5I / 0,,~'i [ 0,3(~ ~ (),/~'i [ 0,57

274,6 279,7 3.~9,7 4o9,7 458,6 521,7

t,25

0,60 0.95 1,38

0.99 1,11

I = a, -t- blm § cgn 2 -[- dFn a,

I = a2 + born. + c / m + d2rn ~', I = a + ~m q- 7 lg m/nz & ~l[(m - - 2) 2 q- 0.1].

ture to account for the nonlinear change in the retention parameters. quently used for this purpose [9].

0,62 0,87 0,61 2.17 1.03

0.78

(i) (2) (3) Power series are fre-

Equation (3) [9-11] most accurately described the gas chromatographic (GC) behavior of many homologous series in columns with phases of different polarity, beginning with the first members. It also satisfactorily describes the change in the retention times in homologous series in liquid chromatography and the distribution coefficients of homologs in two-phase systems [12, 13], and it can thus be considered universal. The possibilities of using Eqs. (1)-(3) for describing the GC behavior of members of homologous series of PFA E of the RFC(O)OCmH2m+I type and pseudohomologous series of PFA E of the CmF2m+l type were analyzed in the present study. The coefficients of Eqs. (1)-(3) were calculated by the method of least squares from the values of the retention times at i00 and 120~ and the results are presented in Tables 2 and 3. The values of the standard deviation (s) of the calculated RT from the experimental RT are comparable in all cases and are ~2 u.m., while 2 < s < 3 in only 6% of the cases. In the calculation with Eq. (3), the value of s for RT did not exceed 1.5 u.m. on both phases, i.e., the error of determination did not exceed 1%. We attempted to determine the physical meaning of the coefficients in order to select the equation which most precisely reflects the features of the GC behavior of our compounds. The first term of any of Eqs. (1)-(3) should basically reflect the contribution of the -C(O)OR or RFC(O)O- functional group to the RT of the compounds. As Tables 2 and 3 show, the values of al, a=, and a increase with an increase in the unchanged substituent R or RF, respectivley. The values of these coefficients increase with an increase in the polarity of the stationary phase, i.e., in going from SE-30 to SKTFT-50Kh. A comparison of the values al, a2, and a does not allow evaluating the advantages of each of Eqs. (1)-(3) for describing the features of the change in I = f(m). The physicochemical properties of the members in homologous series change with an increase in the number of homologous units, while the CH 2 units change in classic series and the CF 2 units change in pseudohomologous series of PFA E. The contributions of these units to the retention time of a compound are reflected by the coefficients in the second terms of Eqs. (1)-(3). For this reason, it should be predicted that coefficients b and ~ will be the most informative parameter for assessing the suitability of Eqs. (1)-(3). The values of the contributions of CH 2 units are positive and close to i00 u.m. in the Kovat system of retention times in classic homologous series [13]. The values of the coefficients of the second terms of Eqs. (1)-(3) should consequently also have the same character-

363

w

Cr,ll t I

C41[9

343.2 419,8 509,6 604.7 703,9 802.9

Clla C.jI~ C3II7

SE-3O (10%)

II v C

0,69 0,68 0.52 0,44 0,47 0,46

0,82 0,61 0.83 0,78 0,90 0,74

( O ) O C , , ~ H 2 , , , ,. t

0,63 0,t7 0,02 0,t2 0,31 0.26

140.6 -154,6 -151,7 -161,4 - 171,1 - 174,2

55,5 54,5 53,6 52,7 51.8 51,0 -

0.57 0,33 0.62 0,39 0,46 0,47

(;8,5

-214.6 -223,2 -227,6 -247,8 -255,1 -253.1

C,,F2~+ tC (0) OR

177,2 -213,6 -17t,7 - 177,1 - 180,7 - 179,4 -

- 17 t ,2 - 180,8 - 187.9 -20o,6 -21 [1,3 - 2 t 1,8

to0 ~

65,9 65,2 63,7 63,1 62,2

95,6 93.9 92,6 91,4 90,6 90,0

303,0 344,8 395,0 453,1 511.2 569,0 464,5 547,5 637.2 738,7 839,3 940, I

98,5 95,8 95,2 93,8 92,2 92,2

....

434,3 478,5 540,6 611,6 682,7 755,0

('.113 C,_,115 Czll? C~II~ C:,llu C,1Ii3

C~Fs C.W7 C4F9 CsFu C~FI3

CI:a

C3F? C~I% C.~Ft I

( ;~ I%

CI::~

I1F(R )

SKTFT-S0Kh ( 10 % )

SE-3t) (t0%)

SKTFT-50Kh (10%)

Stationary phase

0,16 0,58 0,36 0,81 0,80 0,78

1.26

1,25

0,23 0.75 !.16 0,95

1,16 1,00

1,28

0,82 0,84 0.98

t,37

1,03 1,03

I,I12

1,33

0,14

335,6 414.6 505,3 597,8 6(.)7,2 797,3

459,9 542,7 632,8 734,5 835,3 935.0

2(.!4.5 334.8 383,5 438,1 497,2 552,4

429, I 471,1 531,6 602,1 672,3 743,8

5P~.6 53,3 52. I 51.6 50,8 50.0

-

- f65, I 161,4 - 165.3 - 175,5

- 1 ~0.3 - 151.7

-251,7 -254,0 -2~7.6

- 2.11.(.!

--222.2 -222,2

- 165,8 -219,3 - 187,l - 225,3 -210,6 - 193,8

95,5 94A 93,4 93.6 91,(.) 91,2 67,6 6~,8 63.9 62,5 61,6 60,9

- 178,9 - 191,3 -211,4 - 233,9 -222,4

98,2 95,8 !t5,4 94,1 (.)3,2 92,2

- 167,9

120~

(),57 056

0,23

0,39 0,44 O,~(i 0,6(;

0,08 ().87 l, IO 0,91 !,t3 1,17

0,86 0,32 0,54 0,87

1,08

1,54

0,93 0,90 0,84 1.21

1,47

0,39

(1,2(;

0.63 D ().06 0.09

0,58 0,28 (I,68 0,37 0,38 0,44

0,97 0,90

t,35

0,72 0,76 0,80

054 0,59 0,94 0,8(.I 0,96 0,87

TABLE 3. Values of the Coefficients of Universal Equation (3) for Calculation of the Retention Times of Homologous RFC(O)OCmH2m+z and Pseudohomologous CmF2m+zC(O)OR Series

istics. However, the coefficients bl obtained with Eq. (i), which reflect the contributions of the CH 2 units in the RFC(O)OCmH2m+I series, are small, their values do not exceed 59.2 u.m., and they even have negative values in the case of CF 2 units [see the CmF2m+zC(O)OR series, Table 2]. In addition, the values of b I change arbitrarily, and there is no correlation between their values and the value of the constant substituent of the functional group. This allows excluding Eq. (I) from further use as not reflecting the real features of the GC behavior of the homologs. In contrast to Eq. (i), coefficients b 2 and ~ in Eqs. (2) and (3) are close to i00 u.m. They vary from 84.3 to 95 for Eq. (2) and from 90 to 98.5 u.m. for Eq. (3) in the RFC(O)OC mH2m+1 series. The values of b= decrease to 53.4-75.6 in the case of Eq. (2) and 50-68.5 for Eq. (3) with an increase in the polyfluorinated chain in the CmF2m+zC(O)OR series, as should have been expected from the values of the RT (see Table I). It follows from Figs. 2 and 3 that the values of the contributions of &Im(CH2) increase in the unchanged substituent R or R F of the functional group. The values of &Im(CH 2) should be correlated with the values of b 2 and 6. However, as Table 2 shows, the coefficients b 2 obtained with Eq. (2) can initially increase with an increase in R or RF, then decrease, or on the contrary, decrease and then increase, and no regularity is observed in these changes. The maximum values can correspond to the first and third units, and the minimum values can correspond to the first or fourth units. This behavior contradicts the experimentally observed change in the values of AIm(CX2)with an increase in m (see Figs. 2 and 3). Only coefficients ~ calculated with Eq. (3) (see Table 3) are rigorously correlated with the experimentally obtained regularity of the change in AIm(CH 2) as a function of m (see Figs. 2 and 3, Table 3). The precision of the calculation of the retention times for homologs and pseudohomologs with Eq. (3) corresponds to the experimental precision. It was previously shown on the example of classic homologous series that the value of coefficients 7 in universal Eq. (3) reflect the branching, length, and other features of the unaltered substituent and functional group of the series. Table 3 shows that coefficients ~ of Eq. (2) uniformly increase in absolute value with an increase in the mass of the unaltered substituents R and R F directly bound with a functional group in the case of PFA E. No dependence on the mass of R and R F is observed in Eq. (2), which indicates the noncorrespondence of Eq. (2) with the experimental findings. The advantage of Eq. (3) in describing the GC behavior of homologous and pseudohomologous series of organic compounds is obvious. Universal equation (3) thus best describes the character of retention of members of homologous and pseudohomologous series and allows calculating the retention times of polyfluorine-containing esters with a good precision, beginning with the first homologs. LITERATURE CITED I. 2. 3.

A. M. Lovelace, W. Postelnek, and D. A. Rauch, Aliphatic Fluorine Compounds, ACS Monograph 138, Reinhold, New York (1958). N. Ishikawa (ed.), Advances in the Technology of Fluorine Compounds [Russian translation], Mir, Moscow (1984). K. Blau and G. S. King, Handbook of Derivation for Chromatography, Heyden, London

(1978), p. 104. 4. 5. 6. 7.

V. G. Berezkin, Chemical Methods in Gas Chromatography [in Russian], Khimiya, Moscow (1980), p. 37. U. Muller, P. Dietrich, and J. Prescher, J. Chromatogr., 147, 31 (1978). K. Komarek, L. Hornova, and J. Churacek, J. Chromatogr., 244, 142 (1982). K. Komarek, J. Kriz, J. Churacek, and K. Tesarik, J. Chromatogr., 292, No. i, 105

8.

R. V. Golovnya and D. N. Grigor'eva,

(1984). Izv. Akad. Nauk SSSR, Ser. Khim., No. 6, 1240

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