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Effect of temperature on the gas chromatographic separation of halogenated compounds on polar and non-polar stationary phases
Journal of Chromatography, 431 (1988) 3345 Elsevier Science Publishers B.V., Amsterdam -
CHROM.
Printed
in The Netherlands
20 166
EFFECT OF TEMPERATURE RATION OF HALOGENATED LAR STATIONARY PHASES
GIANRICO
CASTELLO*
and TOMASO
ON THE GAS CHROMATOGRAPHIC COMPOUNDS ON POLAR AND
SEPANON-PO-
C. GERBINO
Istituto di Chimica Industriale, Universitri, Corso Europu 30, 16132 Genova (Italy) (Received
October
7th, 1987)
SUMMARY
The effect of column temperature on the gas chromatographic separation of chloro-, bromo- and iodo-methanes, -ethanes and -ethenes with one or more of the same or different halogen atoms in the molecule was investigated by using non-polar (OV-1) and polar (SP-1000) stationary phases. Retention indices, Z, at 75, 100 and 125°C were measured and their correlation with the structures and boiling points of the compounds was examined. A linear correlation between vapour pressure and Z was found for the nonpolar stationary phase, which permits the peak separation at any temperature to be predicted. On the polar column, this correlation is too poor for extrapolation of retention values at different temperature. An Antoine-type equation, the constants A, B and C of which can be calculated starting from experimental values, was found to be useful for the calculation of Z values at any temperature on both the polar and non-polar stationary phases.
INTRODUCTION
The analysis of haloalkanes in the environment, mainly in drinking water supplies, has previously been carried out by gas chromatography (GC) by using different extraction methods1-4. Mixed-phase polar and non-polar columns has been used for the separation of many chloro-, bromo- and iodo-methanes, -ethanes and -ethenes with one or more of the same or different halogen atoms in the molecule. The optimum phase composition was determined by using the window-diagram methods-‘. A column containing 60% of OV-1 and 40% of SP-1000 [both 10% (w/w) on Chromosorb W DMCS (So-100 mesh)] was found useful for separation of 33 different halogenated compounds*. Some experiments have been carried out at various temperatures in order to permit the separation of closely eluted peaks, which not only depends on the difference in retention times, but also on the peak width, i.e., on the number of theoretical plates of the column (about 2600 for trichloroethylene for the mixed-phase column described previously*). Two groups of closely eluted peaks were found to be difficult to resolve: the 0021-9673/88/$03.50
0
1988 Elsevier Science Publishers
B.V.
34
G. CASTELLO,
T. C. GERBINO
rapidly eluted compounds CH3CHC12, CHzClz and CHJCHJ, with an average adjusted retention time (t;O of about 4 min (at 6O”C!, and a slowly eluted group of five compounds (Cl& = CC12, trans-BrCH = CHBr, CHBrC12, BrCH2CH2Cl and CH2Br2), with ti values of about 18-20 min at the same temperature. The best resolution was achieved at 59°C by applying the window method to the ratios of log Yor of the retention index, Z, as a function of temperature, and was verified experimentallys. However, this procedure is time consuming and therefore a simple and general relationship is necessary for predicting the retention of various compounds on pure or mixed stationary phases as a function of temperature. Some experiments were therefore carried out in order to investigate the effect of temperature on the retention of different halogenated compounds on polar and non-polar liquid stationary phases. Retention indices, I, were calculated and used because they depend only on the stationary phase and temperature, and permit the elimination of the influence of other parameters of the analysis (column length and diameter, amount and mesh size of the stationary phase, carrier gas flow-rate, etc.). For practical purposes, approximation of the Z values to within 1 index unit (i.u.) is sufficient, but in the tables given here two decimal figures have been included in order to permit the order of elution of closely eluting peaks to be identified, and to permit a comparison between experimental and calculated values, which sometime differ by less than 1 i.u. EXPERIMENTAL
Non-polar OV-1 and polar SP-1000 stationary phases [both 10% (w/w) on Chromosorb W DMCS (80-100 mesh)] were used, packed in stainless-steel columns (3 m x l/S in. O.D.). A Varian 3760 gas chromatograph was used with thermal conductivity detection (TCD) in order to obtain approximately the same response from compounds having different numbers of halogen atoms in the molecule, while the sensitivity of electron-capture detection (ECD), generally used in the analysis of these compounds, can differ by two orders of magnitude or more. Therefore, when using ECD, standard solutions of different concentration have to be prepared in order to obtain comparable peak heights on the chromatogram, and variations in the size of the sample may affect the peak shape of the compound injected in the largest amount and cause tailing or asymmetry. Further, the determination of retention indices by comparison of the retention time of each compound with those of linear alkanes is easily achieved by using TCD, whereas more complicated methods, e.g., the use of linear iodo- or bromoalkanes as intermediate reference compounds detectable by ECD, have to be applied with specific detectorsgTlO. Helium was used as the carrier gas at a flow-rate of 30 cm3 min-‘, which was maintained constant and checked after every change of the column temperature. RESULTS
AND
DISCUSSION
Tables I and II list the adjusted retention times, tk, and the retentions, r, relative to trichloroethylene at 75, 100 and 125°C on OV-1 and SP-1000 columns. Table
GC OF HALOGENATED
35
COMPOUNDS
TABLE I ADJUSTED RETENTION TIMES, t;, AND RETENTIONS RELATIVE TO TRICHLOROETHYLENE, I, OF HALOALKANES ON A NON-POLAR STATIONARY PHASE Stationary phase, OV-1, 10% (w/w) on Chromosorb W DMCS (So-100 mesh); stainless-steel column, 3 m x l/8 in. O.D.; carrier gas, helium; flow-rate, 30 cm3 min-‘. NO.
8 9 10 II 12 13 14c 14t 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
100°C
75°C
Compound
CH&HC12 CH2 = CC12 ClCH = Ccl2 ClzC = ccl* cc14 CICH2CH2CI CHC& CHBr,Cl CHBrCl, CHBr3 CH&C& CHlClz CHjCHZI cis-BrCH = CHBr rrans-BrCH = CHBr BrCHZCHZBr C13CCHC12 CH,I C1$ZCHZCl trans-CICH = CHCI cis-ClCH = CHCI BrCHzCHzCl CHzIz CBrC& &H,Br Cl#ZHCHC12 Br&HCHBr, CHzBrCl CHzCII CH2Br2 CI~CCC13 CBr4 CH13 ICH&HzI CH,CH,CI
125°C
tk
r
IR
I
1X
Y
1.42 0.94 3.17 8.92 3.01 2.41 1.88 7.11 3.72 13.46 2.56 0.99 1.99 6.27 5.06 7.77 28.36 0.98 11.06 1.33 1.87 4.28 18.09 6.10 0.97 16.06 185.79 1.89 4.17 3.56 57.93 50.67 143.89 36.64 0.52
0.376 0.249 1 2.366 0.798 0.639 0.498 1.885 0.986 3.570 0.679 0.262 0.527 1.663 1.342 2.061 7.522 0.260 2.933 0.352 0.496 1.135 4.798 1.618 0.257 4.260 49.28 0.501 1.106 0.944 15.366 13.440 38.167 9.718 0.138
0.81 0.56 1.91 4.12 1.58 1.30 1.04 3.40 1.90 6.02 1.37 0.58 1.12 3.06 2.53 3.69 11.15 0.60 4.95 0.76
0.424 0.293 1 2.157 0.827 0.680 0.544 1.780 0.994 3.152 0.717 0.303 0.586 1.602 1.324 1.932 5.838 0.314 2.591 0.398 0.523 1.136 3.780 1.554 0.314 3.539 3 1.623 0.549 1.110 0.963 11.329 9.837 25.916 7.434 0.172
0.50 0.37 1.08 2.08 0.92 0.70 0.63 1.82 1.08 3.04 0.80 0.37 0.68 1.65 1.39 1.97 5.24 0.39 2.53 0.47 0.59 1.23 3.63 1.63 0.38 3.28 23.43 0.64 1.20
0.463 0.342 1 1.926 0.852 0.648 0.583 1.687 1.000 2.814 0.740 0.342 0.629 1.527 1.287 1.824 4.852 0.361 2.342 0.435 0.546 1.138 3.361 1.509 0.352 3.037 21.69 0.592 1.111 0.981 8.750 7.787 19.074 6.046 0.203
1.oo 2.17 7.22 2.97 0.60 6.76 60.4 1.05 2.12 1.84 21.64 18.79 49.50 14.20 0.33
1.06 9.45 8.41 20.60 6.53 0.22
III lists the retention indices of the same compounds on both columns. The dependence of the Z values on temperature and on the structures and physical properties of the sample compounds can be correlated with the behaviour of absolute retention values, e.g., retention volumes. From the general equation used for the calculation of I1 l the following is deduced for every stationary phase (s.p.): (s)
=
e.pvJ - 1ooz 100
’
b%” + ln vR (z)
36 TABLE
G. CASTELLO, II
ADJUSTED RETENTION TIMES, Q, AND RETENTIONS ENE, r, OF HALOALKANES ON A POLAR STATIONARY Stationary I.
T. C. GERBINO
phase, SP-1000,
10% (w/w) on Chromosorb
RELATIVE PHASE
W DMCS (80-100
TO TRICHLOROETHYL-
mesh). Conditions
as in Table
_ Compound No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14c 141 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
100°C
75°C tk
i-
2.74 0.94 5.97 7.13 2.72 9.22 6.66 41.07 16.66 100.93 2.83 3.59 2.81 28.98 13.70 31.96 94.28 1.68 32.06 2.26 5.49 17.33 _
0.459 0.157 1 1.194 0.455 1.544 1.115 6.879 2.790 16.906 0.474 0.601 0.470 4.854 2.295 5.353 15.792 0.281 5.370 0.378 0.919 2.903 _
9.14 1.23 153.88 _
125°C r
d
r
1.531 0.206 25.77 _
1.34 0.52 2.54 3.18 1.35 3.86 2.84 14.57 6.48 32.55 1.37 1.65 1.34 10.83 5.58 12.13 30.02 0.77 11.60 1.10 2.41 6.87 44.58 3.92 0.70 45.35 _
0.527 0.204 1 1.252 0.531 1.519 1.118 5.736 2.551 12.815 0.539 0.649 0.527 4.263 2.197 4.775 11.819 0.303 4.567 0.433 0.949 2.705 17.55 1.543 0.275 17.85 _
0.84 0.37 1.48 1.88 0.84 2.12 1.60 7.06 3.37 14.71 0.87 0.99 0.83 5.51 3.05 6.26 13.94 0.49 5.80 0.69 1.40 3.66 19.65 2.29 0.48 18.53 _
0.567 0.250 1 1.270 0.567 1.432 1.081 4.770 2.277 9.939 0.587 0.668 0.561 3.723 2.060 4.229 9.419 0.331 3.919 0.466 0.946 2.472 13.27 1.547 0.324 12.52 _
8.12 22.19 18.01 91.13 _ _ _
1.360 3.717 3.017 15.264 _ _ _
3.44 8.55 7.00 30.12 112.80 _ _
1.354 3.366 2.756 11.858 44.409 _ -
1.91 4.44 3.70 14.54 45.33 _ _
1.290 3.000 2.500 9.824 30.628 _ _
0.55
0.092
0.33
0.129
0.24
0.162
where V, is the retention volume and (s) refers to the sample compound and (z) to a linear alkane having z carbon atoms and bgP. is the slope of the linear part of the plot of n-alkane retention versus z. As In VR (s) is linearly correlated with the number, n, of functional units in the molecule 12, from the definition of I this value depends linearly on n and I and can be considered to be an additive function. This is true not only for homologous series where n is the number of methylene groups in the linear part of the molecule, but also in other instances. Fig. 1 shows f he regular behaviour of the I values of some haloalkanes as a
GC OF HALOGENATED TABLE
37
COMPOUNDS
III
RETENTION STATIONARY Columns Compound
INDICES, PHASES
and conditions
I, OF HALOALKANES
as in Tables
ON NON-POLAR
(OV-1) AND POLAR
(SP-1000)
1 and II.
SP-1000
ov-I
No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14c 14r 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
75°C
100°C
12s’c
75°C
100°C
12yc
565.53 516.86 691.37 803.74 661.99 633.04 602.0 1 774.89 689.64 859.27 640.49 518.46 607.41 758.31 730.02 786.61 957.20 518.17 832.79 557.17 597.20 707.95 894.78 754.13 516.86 882.09 1205.66 601.95 703.85 683.19 1052.72 1034.75 1172.55 983.67 431.12
567.76 517.34 696.32 808.62 667.41 637.87 604.40 782.73 694.66 870.35 645.92 519.10 614.11 766.32 737.78 795.11 965.19 523.44 840.00 558.38 597.65 715.60 902.89 761.99 523.78 887.76 1225.59 606.87 712.35 690.17 1067.53 1045.56 1195.98 1001.98 431.17
569.50 519.14 701.98 814.23 672.72 641.22 608.30 791.53 701.52 881.85 650.55 519.69 621.29 774.33 744.26 804.57 977.64 527.94 849.97 559.15 598.01 722.81 911.06 772.19 529.14 895.27 1244.51 610.98 718.31 697.85 1081.31 1059.63 1221.27 1014.87 431.23
886.92 734.18 1007.14 1036.20 886.54 1077.64 1027.69 1304.75 1167.37 1441.60 897.56 926.65 896.49 1252.54 1139.04 1267.79 1431.59 818.02 1267.53 863.21 998.32 1174.97 _ 1075.59 777.51 1511.30 -
900.52 744.9 1 1010.70 1050.23 900.66 1084.20 1030.11 1316.36 1174.75 1456.67 904.35 935.70 901.65 1266.33 1150.25 1286.00 1143.17 804.33 1276.65 867.61 1003.60 1186.26 1510.47 1087.48 792.57 1513.66 _
901.48 750.44 1012.45 1059.96 902.20 1084.96 1028.95 1322.01 1175.89 1467.06 909.11 932.62 899.84 1274.70 1157.92 1299.71 1454.62 802.99 1283.29 866.47 1003.47 1192.67 1522.18 1101.23 795.84 1515.59 _
1057.80 1212.53 1175.95 1426.53 _ _ _
1064.58 1224.48 1189.98 1444.17 1677.81 _ -
1066.29 1231.23 1196.47 1461.57 1690.77 -
661.48
661.08
661.45
function of the number of chlorine and bromine atoms in the molecule. The numbers refer to the compounds listed in Tables I-III. In the series CHCls, CHBrC12, CHBr2Cl, CHBr3 (compounds 7, 9, 8 and 10, respectively) an increment of about 88 i.u. is observed on the OV-1 column when a chlorine atom is replaced with a bromine atom. This regular behaviour can be used to predict the retention of compounds that are not available as pure standards. The I values of CBrzClz and CBr&l (open circles) can be obtained by interpolation of the straight line calculated with the I values of CCL,, CBrC13 and CBr4 (compounds 5, 23 and 31, respectively).
38
G. CASTELLO, T. C. GERBINO
0
1
2-3
Chlorine
4
5
atoms
Fig. 1. Retention index, I. on an OV- 1 column at 1WC of halogenated methanes and ethanes as a function of the number of Cl atoms that replace Br atoms. For compound numbers, see Table I. 0, Interpolated I values of CHBr&& and CBr,Cl; *, extrapolated I value of CHBr2ClZ (see text).
A linear dependence of the I values on the boiling point is also observed. Fig. 2 shows the behaviour of compounds with different numbers of chlorine and bromine atoms in the molecule as a function of the boiling point at 760 Torr. A regular behaviour is also observed here: the points that represent compounds 5 (Ccl& 7 (CHC13) and 12 (CHICI,) and those of compounds 23 (CBrCl& 9 (CHBrC12) and 27 (CH2BrCl) lie on straight lines (dashed lines). Linear extrapolation (dotted line) from the Z values of compounds 29 (CH,Br2) and 8 (CHBr2Cl) permits the approximate Z value of CBr2C12 (asterisk) to be predicted, with a suitable coincidence with the point calculated by interpolation on the line of bromochloromethanes in Fig. 1 (open circles) or with tabulated boiling points (150.2°C)13 from line C in Fig. 2. Similar graphs and linear correlations can be obtained at various temperatures and permit the Z values of non-available standards to be predicted with reasonable accuracy. Linear correlations are also obtained between the Z values and vapour pressure on both the non-polar and polar columns. As an example, Fig. 3 shows the plot of Z on SP-1000 columns at 100°C as a function of the logarithm of vapour pressure, p”, at the same temperature, calculated from tabulated data14 by using the correlation’ between p” and the boiling point, Bp15:
GC OF HALOGENATED
39
COMPOUNDS
llO( I-
I
901D-
701 O-
501 0,
3(I
70
110 Boiling
150 point
190
(“C)
Fig. 2. Retention index, I, on an OV-I column at 100°C of halogenated methanes and ethanes as a function of their boiling points. For compound numbers, see Table I. *, Extrapolated I value of CHBr& (see text).
1300 t 1100 I
Fig. 3. Retention vapour pressure,
index, I, on an SP-1000 column at 100°C of halogenated For compound numbers, see Table 1.
p”, at IWC.
compounds
as a function
of
40
G. CASTELLO.
T. C. GERBINO
log p0 = K1 + K2Bp
(2)
or by taking into account the ratio between the retention values on non-polar OV1 stationary phase and the vapour pressure, measured experimentally16. The linearity of the Z values as a function of log p” is represented by the equation p
(T)
=
100 (z -
log rs.q + bFP.)
(3)
s with respect to a reference comwhere r,,q is the relative retention of compound pound q and the other symbols have the same meaning as in eqn. 1, and the correlation* 7
log rs,q= lo@;@X/P3
+ h3
(Y&s)
(4)
where yq and yS are the activity coefficients of the substance s and of the reference compound in solution in the stationary phase. Eqn. 4 is suitable for application with very dilute solutions such as occur in gas-liquid chromatography. For many homologous series of compounds the following relationships were found18,rg: log p” = K3 + K4n
(5)
log y = K5 + K6n
(6)
where, as stated above, n is the number of structural units in the molecule (i.e., carbon atoms, methylene groups, chlorine atoms, etc.) and K3, K4, KS and KS are constants for each homologous series at a given temperature. For such compounds log y and log p” are approximately linearly related: log y = a + h log po
(7)
where a = K5 - (K3K6/K4) and b = KS/K+ tion for the retention volume, VR: v,
Taking
into account
the general
NIRT = ~ YPO
equa-
(8)
where Nr is the number equation is derived:
of moles of stationary
log V, = log (N,RT)
-
a -
phase in the column,
(b + 1) logp’
the following
(9)
showing that the different values of y for different compounds, temperature and volumes injected do not affect the linearity of log I/,/log p” plots for homologues, but only changes their slope. As a consequence, the r/log p” and Z/log p” plots are also linear. Eflect of temperatwe
on retention
index
The dependence of Z on temperature can be calculated by starting from the general gas chromaLtographic equations, i.e., the definition of the specific retention
.
CC OF HALOGENATED
volume,
Vg, and of the retention
p
B TS
(T) = A +
where constants from’ z A = Cl
41
COMPOUNDS
index itseWO, obtaining
the equation
C
A, B and C depend
on solute and stationary
phase and are obtained
1ooz
+
B = Ci(dH),
-
C = (AfOz -
(11) (OH),+,
+ C&W
z-
C&W
(AH) z+i+
W0z.1
z- (AH)
(12) (13)
c5
where Cl-C5 are constants, AH is the differential molar heat of evaporation of the solute from the stationary phase and z and z + 1 refer to the number of carbon atoms of the n-alkanes eluted before and after the sample compound s. AH values theoretically depend on temperature, but it has been reported that they can be considered to be constant in a suitable temperature rangezl and, therefore, eqn. 10 may show a linear region within the temperature range used in gas chromatographic determinations22-24. In this instance, this can be confirmed by the least-squares determination of the linearity of Z values as a function of temperature: E.p. (r)
= PT + Q
(14)
The values of the slope, P, and the intercept, Q, are listed in Table IV, with the correlation coefficient, R, for non-polar (OV-1) and polar (SP-1000) stationary phases, showing a fair linear dependence on temperature on non-polar phase21,25,26. The values of the constants in eqn. 10 can be deduced from the experimental values of Z at different temperatures T, and three series of measurements at suitable temperatures (75, 100 and 125°C) permit their calculation by means of the following equations: c
=
(7’2
-
Td
V3T3
-
Td
(12
ZITI)
+
CT3
-
TI)
VITI
-
(T2
-
T,)
(13
-
Z27’2)
(15) (T3
A =
Z3T3
-
ZITI
+
CC13
-
11) -
-
II>
I,> (16)
T3
-
B = Z3T3 + Z3C -
TI
A (T3 + C)
(17)
By using a personal computer, the values of the constant are easily calculated. If the divisor of eqn. 15 becomes equal to zero owing to the approximate knowledge of Z values, an error message and aborting of the running program can be avoided by automatically increasing the I2 value by a small amount (e.g., 0.1 i.u.) that does not appreciably influence the final results but permits the calculation to be carried out without computing errors due to division by zero.
42 TABLE
G. CASTELLO, IV
COEFFICIENTS OF THE LINEAR EQUATION POLAR (SP-1000) STATIONARY PHASES Correlation Compound No.
I 2 3 4 5 6 7 8 9 10 11 12 13 14c 14t 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
T. C. GERBINO
coefficients,
F+(r)
= PT + Q ON NON-POLAR
(OV-1) AND
H, are also given.
ov-I
SP-1000
P (i.u./‘C)
Q (ia.)
R
0.079 0.070 0.212 0.209 0.214 0.163 0.126 0.332 0.237 0.451 0.201 0.025 0.277 0.320 0.284 0.359 0.408 0.195 0.343 0.039 0.016 0.297 0.325 0.361 0.245 0.263 0.776 0.180 0.289 0.293 0.571 0.497 0.974 0.623 0.002
537.98 490.95 617.04 730.60 587.32 576.35 557.97 658.91 606.64 702.04 570.60 509.91 510.72 646.81 631.12 661.44 814.19 450.29 712.75 543.46 591.57 604.59 781.46 628.04 431.65 790.05 935.43 539.23 603.63 581.03 853.90 861.04 833.14 767.42 430.30
0.998 0.999 0.999 0.999 0.999 0.994 0.990 0.999 0.996 0.999 0.998 0.999 0.999 1.00 0.998 0.999 0.992 0.998 0.995 0.992 0.997 0.999 1.00 0.997 0.997 0.996 0.999 0.998 0.994 0.999 0.999 0.997 0.999 0.995 1.00
P (i.u.rC)
Q (i.u.)
R
0.291 0.325 0.106 0.475 0.313 0.146 0.025 0.345 0.170 0.509 0.231 0.119 0.067 0.443 0.377 0.638 0.460 0.300 0.315 0.065 0.103 0.354 _
787.68 621.87 970.48 871.54 779.64 1027.58 1019.51 1185.61 1109.11 1265.17 817.51 887.12 874.33 1099.20 1008.22 1046.37 1271.32 920.57 1158.25 841.44 963.37 1052.59 _
0.894 0.983 0.981 0.994 0.907 0.909 0.520 0.980 0.921 0.994 0.994 0.649 0.639 0.990 0.994 0.996 0.999 0.903 0.995 0.713 0.855 0.987 _
0.512 0.366 -
896.82 652.13 _
0.999 0.937 _ _
_ _
999.55 1083.24 1034.38 1282.76 _ _
0.945 0.987 0.978 0.999 _ _ -
-0.001
661.12
0.998
_ 0.169 0.364 0.410 0.700 _
Tables V and VI show the values of the constants A, B and C calculated from the experimental Z values on OV-1 and SP-1000, respectively, shown in Table III, and the Zvalues calculated by using these constants in eqn. 10 at 75, 100 and 125°C. The reasonable correspondence between these data and the experimental values in Table III shows that both eqns. 10 and 14 permit the calculation of the retention indices of haloalkanes on a non-polar stationary phase at any given temperature, while the linear correlation between Z and T (eqn. 14) may in some instances result in considerable errors when polar stationary phases are used, as shown by the low correlation coefficients for some compounds on SP-1000 in Table V.
GC OF HALOGENATED TABLE
43
COMPOUNDS
V
VALUES OF THE CONSTANT IN EQNS. 15,16 AND 17 AND ZVALUES BY REPLACING THESE CONSTANTS IN EQN. 10 These I values should Compound No.
1 2 3 4 5 6 I 8 9 10 11 12 13 14c 141 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
be compared
with the experimental
Constants
ON OV-1 CALCULATED
results in Table III. Calculated
I values
A (i.u.)
B (i.u. K)
C IK)
At 75°C
At 100°C
AI 125°C
583.1 412.9 617.3 733.6 1190.7 659.7 592.0 638.9 657.2 263.6 708.8 534.2 413 553 816.3 621 920 585 781.9 562 601.2 966.3 _ 1305.7 693.4 571.3 841.4 1972.2 656.8 152.2 537.0 1463.8 952 558.8 1089.1 430.56
- 3208 - 153990 - 29484 - 26954 - 1276078 -3021 - 1285 - 62284 - 6042 -815516 - 19759 -9289 - 144903 - 142022 -21852 -78351 -5111 - 19539 -8106 -476 -810 -211680 - 149010 - 13221 -9358 - 8288 -718036 -13915 - 5677 -80191 - 274988 - 17803 -417221 - 12533 -165
- 170.4 - 1848.0 - 746.6 - 132.2 2065.6 -234.8 -477.1 - 806.3 - 534.4 - 1717.0 -58.6 242 - 1096 - 1039.7 -94.9 -840.7 -487 - 55.8 - 528.6 -260.5 - 148.0 471.3 -7156.3 - 565.9 - 176.2 -552 588.6 -94.3 -230.7 - 896.6 320.9, - 563.8 - 1027.8 -229.1 - 648.0
565.45 515.57 691.22 803.78 662.12 633.05 601.97 774.85 689.64 859.37 640.55 518.44 606.75 758.36 730.02 786.07 956.81 518.17 832.82 556.56 597.15 707.98 894.89 754.09 516.88 882.06 1205.68 601.98 703.74 683.11 1052.84 1034.48 1172.68 983.81 431.15
567.68 517.31 696.16 808.67 661.53 637.86 604.37 782.69 694.67 870.45 645.98 519.08 613.46 766.07 737.77 794.58 964.89 523.43 840.04 557.17 597.60 715.63 903.00 761.95 523.78 887.74 1225.61 606.89 712.26 690.08 1067.65 1045.28 1196.13 1002.05 431.20
569.41 519.11 701.82 814.29 672.84 641.21 608.29 791.50 701.54 881.95 650.60 519.67 620.64 774.37 744.25 804.04 971.52 527.93 850.04 558.54 597.96 722.83 911.17 712.17 529.14 895.27 1244.52 611.00 718.24 691.75 1081.42 1059.34 1221.43 1014.91 431.26
In contrast, the use of eqn. 10 with A, B and C leads to satisfactory results, even if the trend of the I values as a function of temperature is almost horizontal or shows appreciable curvature. By using simple computer programs, the temperature for the best resolution of any mixture of compounds can be calculated when the values of A, B and C are known on pure or mixed-phase columns. A possible flow of the program is as follows: a list of the available halogenated compounds is shown on the screen; the operator selects those probably contained in the sample; the I values are calculated with eqn. 10 by using the stored values of the constants and
44 TABLE
G. CASTELLO,
T. C. GERBINO
VI
VALUES OF THE CONSTANT IN EQNS. 15, 16 AND 17 AND I VALUES LATED BY REPLACING THESE CONSTANTS IN EQN. 10 These I values should Compound
be compared _
with the experimental
Constants
ON SP-1000
CALCU-
results in Table III. Calculated
I values
No.
1 2 3 4 5 6 7 8 9 10 II 12 13 14c 14t 15 16 17 18 19 20 21 23 24 25 27 28 29 30 34
A (i.u.)
B (i.u. K)
C (Kl
At 75°C
At 100°C
At 125°C
902.6 767.7 1017.6 1113.7 904.1 1085.9 1028.5 1338.3 1177.4 1523.6 936.2 931.1 898.9 1308.9 1198.8 1396.9 3483.0 801.4 1325.5 865.8 1003.3 1215.9 911.7 800.9 1534.8 1069. I 1255.5 1214.1 3898.2 661.5
-60.2 - 1784.0 - 504.9 -8771.0 - 107.6 - 54.2 - 14.6 - 1593.6 - 92.0 -9100.5 -4529.3 56.5 32.2 -4353.4 - 6476.9 - 19676.8 -9034219.5 90.4 - 7758.6 26.63 6.04 - 2689.4 -60582.4 -325.1 - 5284.0 - 191.4 -2789.2 - 1643.2 - 8596597.6 -0.374
-344.1 -294.8 - 299.6 -234.8 -341.8 -341.4 -363.8 - 300.6 -338.8 -236.9 -230.7 - 360.7 - 360.9 - 270.8 - 239.6 - 195.7 -4055.8 - 342.6 -214.1 -358.2 - 349.2 -282.3 -717.6 ~ 334. I -123.6 -331.1 -283.1 - 304.9 3129.9 -372.2
887.73 734.26 1007.20 1036.32 886.98 1077.87 1027.59 1304.89 1167.56 1441.80 897.62 926.60 896.37 1252.61 1139.13 1267.88 1431.61 817.68 1267.62 863.15 997.55 1175.06 1075.68 777.85 1511.32 1057.87 1212.62 1176.11 1426.53 661.51
900.53 744.93 1010.73 1050.30 900.67 1084.19 1030.07 1316.43 1174.72 1456.81 904.39 935.64 901.53 1266.36 1150.30 1286.06 1143.19 804.36 1276.12 867.58 1003.55 1186.30 1087.58 792.66 1513.68 1064.55 1224.53 1190.02 1444.17 661.17
901.49 750.44 1013.48 1060.00 902.20 1084.94 1028.94 1322.06 1175.85 1467.16 909.14 932.61 899.76 1274.71 1157.95 1299.76 1454.64 803.03 1283.34 866.47 1003.42 1192.69 1101.34 795.91 1515.60 1066.24 1231.26 1196.48 1461.56 661.48
listed in increasing order; and the AZ values between adjacent compounds are also calculated. This procedure is repeated at many temperatures (increments of 2 or 5°C are suitable, within the usable temperature range of the column or within the range previously selected by the operator) and the temperature that ensures the greatest AZ values is eventually selected. By applying this procedure to the compounds previously analysed on a mixed-phase columns, a temperature of 60°C was calculated, compared with the experimental value of 59°C. When the linearity is fair, the constants P and Q can be used for qualitative analysis: the value of the slope, P, can confirm the identification of a substancez7J8, being correlated with structure 29. As an example, the P values of CHC13, CHBrCL CHBrzCl and CHBr3 are regularly spaced on replacing chlorine with bromine atoms
GC OF HALOGENATED
COMPOUNDS
45
(AP = 0.11, 0.10 and 0.12) and the same interval (0.11 i.u./“C) is found between CHzBrCl and CHzBrz (see Table IV). ACKNOWLEDGEMENTS
The authors thank Mrs. Graziella Bitossi for her cooperation in the preparation of this paper. This work was supported by the Minister0 Pubblica Istruzione, Italy. REFERENCFS 1 The Analysis of Trihalomeihanes in Finished Waters by the Purge and Trap Method, Method 501.1, United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, OH, 1979. 2 The Analysis of Trihalomethanes in Drinking Water by Liquid/Liquid Extraction, Method 501.2, United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, OH, 1979. 3 G. Castello, T. C. Gerbino and S. Kanitz, J. Chromafogr., 247 (1982) 263. 4 G. Castello, T. C. Gerbino and S. Kanitz, J. Chromafogr., 351 (1986) 165. 5 R. J. Laub and J. H. Purnell, J. Chromatogr., 112 (1975) 71. 6 R. J. Laub, Int. Lab., May/June (1981) 16. 7 J. H. Purnell, in F. Bruner (Editor), The Science of Chromatography, Elsevier, Amsterdam, 1985, p. 362. 8 G. Caste110 and T. C. Gerbino, J. Chromatogr., 366 (1986) 59. 9 G. Caste110 and G. D’Amato, J. Chromatogr., 54 (1971) 157. 10 G. Caste110 and G. D’Amato, J. Chromatogr., 58 (1971) 127. 11 E. Kovats, Helv. Chim. Acfa, 41 (1958) 1915. 12 H. Purnell. Gas Chromatography, Wiley. Chichester, 1962. p, 39. 13 R. C. Weast (Editor), CRC Handbook of Chemisfry and Physics, Chemical Rubber Co., Cleveland, OH, 5lst ed., 1970-71, p. C-367. 14 G. G. Schlessinger, in R. C. Weast (Editor), CRC Handbook of Chemistry and Physics, Chemical Rubber Co.. Cleveland. OH. 5lst ed., 1970-71, p. D-146. 15 H. Purnell, Gas Chromatography, Wiley, Chichester, 1962, p. 44. 16 T. C. Gerbino, Doctorate Thesis, Genova University, 1987. 17 E. F. G. Herington, in P. H. Desty (Editor), Vapour Phase Chromatography, Butterworths, London, 1957, p. 5. 18 G. J. Pierotti, C. H. Deal, E. L. Derr and P. E. Porter, J. Am. Chem. Sot., 78 (1956) 2989. 19 D. A. Leathard and B. C. Shurlock, in J. H. Purnell (Editor), Progress in Gas Chromatography, Wiley, New York, 1968. p. 1. 20 J. Takacs, P. Rajcsinyi, L. KBplar and 1. OIBCSI, J. Chromafogr., 41 (1969) 438. 21 E. B. Molnar, P. Moritz and J. Takacs, J. Chromatogr., 66 (1972) 205. 22 J. Takacs, M. Rockenbauer and I. Olacsi, J. Chromafogr., 42 (1969) 19. 23 L. S. Ettre and K. Billeb, J. Chromatogr., 30 (1967) 1. 24 M. C. Saha and G. D. Mitra, J. Chromatogr. Sci., 8 (1970) 84. 25 F. Riedo, D. Fritz, G. Tarjan and E. Kovlts, .I. Chromatogr., 126 (19876) 63. 26 M. Dimov, J. Chromatogr., 347 (1985) 366. 27 L. Sojak and J. Janak, Anal. Chem., 45 (1973) 293. 28 L. Sojak, J. KrupEik and J. Janak. J. Chromatogr.. 195 (1980) 43. 29 G. Castello, M. Berg and M. Lunardelli, /. Chromatogr., 79 (1973) 23.
CHROM.
Printed
in The Netherlands
20 166
EFFECT OF TEMPERATURE RATION OF HALOGENATED LAR STATIONARY PHASES
GIANRICO
CASTELLO*
and TOMASO
ON THE GAS CHROMATOGRAPHIC COMPOUNDS ON POLAR AND
SEPANON-PO-
C. GERBINO
Istituto di Chimica Industriale, Universitri, Corso Europu 30, 16132 Genova (Italy) (Received
October
7th, 1987)
SUMMARY
The effect of column temperature on the gas chromatographic separation of chloro-, bromo- and iodo-methanes, -ethanes and -ethenes with one or more of the same or different halogen atoms in the molecule was investigated by using non-polar (OV-1) and polar (SP-1000) stationary phases. Retention indices, Z, at 75, 100 and 125°C were measured and their correlation with the structures and boiling points of the compounds was examined. A linear correlation between vapour pressure and Z was found for the nonpolar stationary phase, which permits the peak separation at any temperature to be predicted. On the polar column, this correlation is too poor for extrapolation of retention values at different temperature. An Antoine-type equation, the constants A, B and C of which can be calculated starting from experimental values, was found to be useful for the calculation of Z values at any temperature on both the polar and non-polar stationary phases.
INTRODUCTION
The analysis of haloalkanes in the environment, mainly in drinking water supplies, has previously been carried out by gas chromatography (GC) by using different extraction methods1-4. Mixed-phase polar and non-polar columns has been used for the separation of many chloro-, bromo- and iodo-methanes, -ethanes and -ethenes with one or more of the same or different halogen atoms in the molecule. The optimum phase composition was determined by using the window-diagram methods-‘. A column containing 60% of OV-1 and 40% of SP-1000 [both 10% (w/w) on Chromosorb W DMCS (So-100 mesh)] was found useful for separation of 33 different halogenated compounds*. Some experiments have been carried out at various temperatures in order to permit the separation of closely eluted peaks, which not only depends on the difference in retention times, but also on the peak width, i.e., on the number of theoretical plates of the column (about 2600 for trichloroethylene for the mixed-phase column described previously*). Two groups of closely eluted peaks were found to be difficult to resolve: the 0021-9673/88/$03.50
0
1988 Elsevier Science Publishers
B.V.
34
G. CASTELLO,
T. C. GERBINO
rapidly eluted compounds CH3CHC12, CHzClz and CHJCHJ, with an average adjusted retention time (t;O of about 4 min (at 6O”C!, and a slowly eluted group of five compounds (Cl& = CC12, trans-BrCH = CHBr, CHBrC12, BrCH2CH2Cl and CH2Br2), with ti values of about 18-20 min at the same temperature. The best resolution was achieved at 59°C by applying the window method to the ratios of log Yor of the retention index, Z, as a function of temperature, and was verified experimentallys. However, this procedure is time consuming and therefore a simple and general relationship is necessary for predicting the retention of various compounds on pure or mixed stationary phases as a function of temperature. Some experiments were therefore carried out in order to investigate the effect of temperature on the retention of different halogenated compounds on polar and non-polar liquid stationary phases. Retention indices, I, were calculated and used because they depend only on the stationary phase and temperature, and permit the elimination of the influence of other parameters of the analysis (column length and diameter, amount and mesh size of the stationary phase, carrier gas flow-rate, etc.). For practical purposes, approximation of the Z values to within 1 index unit (i.u.) is sufficient, but in the tables given here two decimal figures have been included in order to permit the order of elution of closely eluting peaks to be identified, and to permit a comparison between experimental and calculated values, which sometime differ by less than 1 i.u. EXPERIMENTAL
Non-polar OV-1 and polar SP-1000 stationary phases [both 10% (w/w) on Chromosorb W DMCS (80-100 mesh)] were used, packed in stainless-steel columns (3 m x l/S in. O.D.). A Varian 3760 gas chromatograph was used with thermal conductivity detection (TCD) in order to obtain approximately the same response from compounds having different numbers of halogen atoms in the molecule, while the sensitivity of electron-capture detection (ECD), generally used in the analysis of these compounds, can differ by two orders of magnitude or more. Therefore, when using ECD, standard solutions of different concentration have to be prepared in order to obtain comparable peak heights on the chromatogram, and variations in the size of the sample may affect the peak shape of the compound injected in the largest amount and cause tailing or asymmetry. Further, the determination of retention indices by comparison of the retention time of each compound with those of linear alkanes is easily achieved by using TCD, whereas more complicated methods, e.g., the use of linear iodo- or bromoalkanes as intermediate reference compounds detectable by ECD, have to be applied with specific detectorsgTlO. Helium was used as the carrier gas at a flow-rate of 30 cm3 min-‘, which was maintained constant and checked after every change of the column temperature. RESULTS
AND
DISCUSSION
Tables I and II list the adjusted retention times, tk, and the retentions, r, relative to trichloroethylene at 75, 100 and 125°C on OV-1 and SP-1000 columns. Table
GC OF HALOGENATED
35
COMPOUNDS
TABLE I ADJUSTED RETENTION TIMES, t;, AND RETENTIONS RELATIVE TO TRICHLOROETHYLENE, I, OF HALOALKANES ON A NON-POLAR STATIONARY PHASE Stationary phase, OV-1, 10% (w/w) on Chromosorb W DMCS (So-100 mesh); stainless-steel column, 3 m x l/8 in. O.D.; carrier gas, helium; flow-rate, 30 cm3 min-‘. NO.
8 9 10 II 12 13 14c 14t 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
100°C
75°C
Compound
CH&HC12 CH2 = CC12 ClCH = Ccl2 ClzC = ccl* cc14 CICH2CH2CI CHC& CHBr,Cl CHBrCl, CHBr3 CH&C& CHlClz CHjCHZI cis-BrCH = CHBr rrans-BrCH = CHBr BrCHZCHZBr C13CCHC12 CH,I C1$ZCHZCl trans-CICH = CHCI cis-ClCH = CHCI BrCHzCHzCl CHzIz CBrC& &H,Br Cl#ZHCHC12 Br&HCHBr, CHzBrCl CHzCII CH2Br2 CI~CCC13 CBr4 CH13 ICH&HzI CH,CH,CI
125°C
tk
r
IR
I
1X
Y
1.42 0.94 3.17 8.92 3.01 2.41 1.88 7.11 3.72 13.46 2.56 0.99 1.99 6.27 5.06 7.77 28.36 0.98 11.06 1.33 1.87 4.28 18.09 6.10 0.97 16.06 185.79 1.89 4.17 3.56 57.93 50.67 143.89 36.64 0.52
0.376 0.249 1 2.366 0.798 0.639 0.498 1.885 0.986 3.570 0.679 0.262 0.527 1.663 1.342 2.061 7.522 0.260 2.933 0.352 0.496 1.135 4.798 1.618 0.257 4.260 49.28 0.501 1.106 0.944 15.366 13.440 38.167 9.718 0.138
0.81 0.56 1.91 4.12 1.58 1.30 1.04 3.40 1.90 6.02 1.37 0.58 1.12 3.06 2.53 3.69 11.15 0.60 4.95 0.76
0.424 0.293 1 2.157 0.827 0.680 0.544 1.780 0.994 3.152 0.717 0.303 0.586 1.602 1.324 1.932 5.838 0.314 2.591 0.398 0.523 1.136 3.780 1.554 0.314 3.539 3 1.623 0.549 1.110 0.963 11.329 9.837 25.916 7.434 0.172
0.50 0.37 1.08 2.08 0.92 0.70 0.63 1.82 1.08 3.04 0.80 0.37 0.68 1.65 1.39 1.97 5.24 0.39 2.53 0.47 0.59 1.23 3.63 1.63 0.38 3.28 23.43 0.64 1.20
0.463 0.342 1 1.926 0.852 0.648 0.583 1.687 1.000 2.814 0.740 0.342 0.629 1.527 1.287 1.824 4.852 0.361 2.342 0.435 0.546 1.138 3.361 1.509 0.352 3.037 21.69 0.592 1.111 0.981 8.750 7.787 19.074 6.046 0.203
1.oo 2.17 7.22 2.97 0.60 6.76 60.4 1.05 2.12 1.84 21.64 18.79 49.50 14.20 0.33
1.06 9.45 8.41 20.60 6.53 0.22
III lists the retention indices of the same compounds on both columns. The dependence of the Z values on temperature and on the structures and physical properties of the sample compounds can be correlated with the behaviour of absolute retention values, e.g., retention volumes. From the general equation used for the calculation of I1 l the following is deduced for every stationary phase (s.p.): (s)
=
e.pvJ - 1ooz 100
’
b%” + ln vR (z)
36 TABLE
G. CASTELLO, II
ADJUSTED RETENTION TIMES, Q, AND RETENTIONS ENE, r, OF HALOALKANES ON A POLAR STATIONARY Stationary I.
T. C. GERBINO
phase, SP-1000,
10% (w/w) on Chromosorb
RELATIVE PHASE
W DMCS (80-100
TO TRICHLOROETHYL-
mesh). Conditions
as in Table
_ Compound No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14c 141 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
100°C
75°C tk
i-
2.74 0.94 5.97 7.13 2.72 9.22 6.66 41.07 16.66 100.93 2.83 3.59 2.81 28.98 13.70 31.96 94.28 1.68 32.06 2.26 5.49 17.33 _
0.459 0.157 1 1.194 0.455 1.544 1.115 6.879 2.790 16.906 0.474 0.601 0.470 4.854 2.295 5.353 15.792 0.281 5.370 0.378 0.919 2.903 _
9.14 1.23 153.88 _
125°C r
d
r
1.531 0.206 25.77 _
1.34 0.52 2.54 3.18 1.35 3.86 2.84 14.57 6.48 32.55 1.37 1.65 1.34 10.83 5.58 12.13 30.02 0.77 11.60 1.10 2.41 6.87 44.58 3.92 0.70 45.35 _
0.527 0.204 1 1.252 0.531 1.519 1.118 5.736 2.551 12.815 0.539 0.649 0.527 4.263 2.197 4.775 11.819 0.303 4.567 0.433 0.949 2.705 17.55 1.543 0.275 17.85 _
0.84 0.37 1.48 1.88 0.84 2.12 1.60 7.06 3.37 14.71 0.87 0.99 0.83 5.51 3.05 6.26 13.94 0.49 5.80 0.69 1.40 3.66 19.65 2.29 0.48 18.53 _
0.567 0.250 1 1.270 0.567 1.432 1.081 4.770 2.277 9.939 0.587 0.668 0.561 3.723 2.060 4.229 9.419 0.331 3.919 0.466 0.946 2.472 13.27 1.547 0.324 12.52 _
8.12 22.19 18.01 91.13 _ _ _
1.360 3.717 3.017 15.264 _ _ _
3.44 8.55 7.00 30.12 112.80 _ _
1.354 3.366 2.756 11.858 44.409 _ -
1.91 4.44 3.70 14.54 45.33 _ _
1.290 3.000 2.500 9.824 30.628 _ _
0.55
0.092
0.33
0.129
0.24
0.162
where V, is the retention volume and (s) refers to the sample compound and (z) to a linear alkane having z carbon atoms and bgP. is the slope of the linear part of the plot of n-alkane retention versus z. As In VR (s) is linearly correlated with the number, n, of functional units in the molecule 12, from the definition of I this value depends linearly on n and I and can be considered to be an additive function. This is true not only for homologous series where n is the number of methylene groups in the linear part of the molecule, but also in other instances. Fig. 1 shows f he regular behaviour of the I values of some haloalkanes as a
GC OF HALOGENATED TABLE
37
COMPOUNDS
III
RETENTION STATIONARY Columns Compound
INDICES, PHASES
and conditions
I, OF HALOALKANES
as in Tables
ON NON-POLAR
(OV-1) AND POLAR
(SP-1000)
1 and II.
SP-1000
ov-I
No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14c 14r 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
75°C
100°C
12s’c
75°C
100°C
12yc
565.53 516.86 691.37 803.74 661.99 633.04 602.0 1 774.89 689.64 859.27 640.49 518.46 607.41 758.31 730.02 786.61 957.20 518.17 832.79 557.17 597.20 707.95 894.78 754.13 516.86 882.09 1205.66 601.95 703.85 683.19 1052.72 1034.75 1172.55 983.67 431.12
567.76 517.34 696.32 808.62 667.41 637.87 604.40 782.73 694.66 870.35 645.92 519.10 614.11 766.32 737.78 795.11 965.19 523.44 840.00 558.38 597.65 715.60 902.89 761.99 523.78 887.76 1225.59 606.87 712.35 690.17 1067.53 1045.56 1195.98 1001.98 431.17
569.50 519.14 701.98 814.23 672.72 641.22 608.30 791.53 701.52 881.85 650.55 519.69 621.29 774.33 744.26 804.57 977.64 527.94 849.97 559.15 598.01 722.81 911.06 772.19 529.14 895.27 1244.51 610.98 718.31 697.85 1081.31 1059.63 1221.27 1014.87 431.23
886.92 734.18 1007.14 1036.20 886.54 1077.64 1027.69 1304.75 1167.37 1441.60 897.56 926.65 896.49 1252.54 1139.04 1267.79 1431.59 818.02 1267.53 863.21 998.32 1174.97 _ 1075.59 777.51 1511.30 -
900.52 744.9 1 1010.70 1050.23 900.66 1084.20 1030.11 1316.36 1174.75 1456.67 904.35 935.70 901.65 1266.33 1150.25 1286.00 1143.17 804.33 1276.65 867.61 1003.60 1186.26 1510.47 1087.48 792.57 1513.66 _
901.48 750.44 1012.45 1059.96 902.20 1084.96 1028.95 1322.01 1175.89 1467.06 909.11 932.62 899.84 1274.70 1157.92 1299.71 1454.62 802.99 1283.29 866.47 1003.47 1192.67 1522.18 1101.23 795.84 1515.59 _
1057.80 1212.53 1175.95 1426.53 _ _ _
1064.58 1224.48 1189.98 1444.17 1677.81 _ -
1066.29 1231.23 1196.47 1461.57 1690.77 -
661.48
661.08
661.45
function of the number of chlorine and bromine atoms in the molecule. The numbers refer to the compounds listed in Tables I-III. In the series CHCls, CHBrC12, CHBr2Cl, CHBr3 (compounds 7, 9, 8 and 10, respectively) an increment of about 88 i.u. is observed on the OV-1 column when a chlorine atom is replaced with a bromine atom. This regular behaviour can be used to predict the retention of compounds that are not available as pure standards. The I values of CBrzClz and CBr&l (open circles) can be obtained by interpolation of the straight line calculated with the I values of CCL,, CBrC13 and CBr4 (compounds 5, 23 and 31, respectively).
38
G. CASTELLO, T. C. GERBINO
0
1
2-3
Chlorine
4
5
atoms
Fig. 1. Retention index, I. on an OV- 1 column at 1WC of halogenated methanes and ethanes as a function of the number of Cl atoms that replace Br atoms. For compound numbers, see Table I. 0, Interpolated I values of CHBr&& and CBr,Cl; *, extrapolated I value of CHBr2ClZ (see text).
A linear dependence of the I values on the boiling point is also observed. Fig. 2 shows the behaviour of compounds with different numbers of chlorine and bromine atoms in the molecule as a function of the boiling point at 760 Torr. A regular behaviour is also observed here: the points that represent compounds 5 (Ccl& 7 (CHC13) and 12 (CHICI,) and those of compounds 23 (CBrCl& 9 (CHBrC12) and 27 (CH2BrCl) lie on straight lines (dashed lines). Linear extrapolation (dotted line) from the Z values of compounds 29 (CH,Br2) and 8 (CHBr2Cl) permits the approximate Z value of CBr2C12 (asterisk) to be predicted, with a suitable coincidence with the point calculated by interpolation on the line of bromochloromethanes in Fig. 1 (open circles) or with tabulated boiling points (150.2°C)13 from line C in Fig. 2. Similar graphs and linear correlations can be obtained at various temperatures and permit the Z values of non-available standards to be predicted with reasonable accuracy. Linear correlations are also obtained between the Z values and vapour pressure on both the non-polar and polar columns. As an example, Fig. 3 shows the plot of Z on SP-1000 columns at 100°C as a function of the logarithm of vapour pressure, p”, at the same temperature, calculated from tabulated data14 by using the correlation’ between p” and the boiling point, Bp15:
GC OF HALOGENATED
39
COMPOUNDS
llO( I-
I
901D-
701 O-
501 0,
3(I
70
110 Boiling
150 point
190
(“C)
Fig. 2. Retention index, I, on an OV-I column at 100°C of halogenated methanes and ethanes as a function of their boiling points. For compound numbers, see Table I. *, Extrapolated I value of CHBr& (see text).
1300 t 1100 I
Fig. 3. Retention vapour pressure,
index, I, on an SP-1000 column at 100°C of halogenated For compound numbers, see Table 1.
p”, at IWC.
compounds
as a function
of
40
G. CASTELLO.
T. C. GERBINO
log p0 = K1 + K2Bp
(2)
or by taking into account the ratio between the retention values on non-polar OV1 stationary phase and the vapour pressure, measured experimentally16. The linearity of the Z values as a function of log p” is represented by the equation p
(T)
=
100 (z -
log rs.q + bFP.)
(3)
s with respect to a reference comwhere r,,q is the relative retention of compound pound q and the other symbols have the same meaning as in eqn. 1, and the correlation* 7
log rs,q= lo@;@X/P3
+ h3
(Y&s)
(4)
where yq and yS are the activity coefficients of the substance s and of the reference compound in solution in the stationary phase. Eqn. 4 is suitable for application with very dilute solutions such as occur in gas-liquid chromatography. For many homologous series of compounds the following relationships were found18,rg: log p” = K3 + K4n
(5)
log y = K5 + K6n
(6)
where, as stated above, n is the number of structural units in the molecule (i.e., carbon atoms, methylene groups, chlorine atoms, etc.) and K3, K4, KS and KS are constants for each homologous series at a given temperature. For such compounds log y and log p” are approximately linearly related: log y = a + h log po
(7)
where a = K5 - (K3K6/K4) and b = KS/K+ tion for the retention volume, VR: v,
Taking
into account
the general
NIRT = ~ YPO
equa-
(8)
where Nr is the number equation is derived:
of moles of stationary
log V, = log (N,RT)
-
a -
phase in the column,
(b + 1) logp’
the following
(9)
showing that the different values of y for different compounds, temperature and volumes injected do not affect the linearity of log I/,/log p” plots for homologues, but only changes their slope. As a consequence, the r/log p” and Z/log p” plots are also linear. Eflect of temperatwe
on retention
index
The dependence of Z on temperature can be calculated by starting from the general gas chromaLtographic equations, i.e., the definition of the specific retention
.
CC OF HALOGENATED
volume,
Vg, and of the retention
p
B TS
(T) = A +
where constants from’ z A = Cl
41
COMPOUNDS
index itseWO, obtaining
the equation
C
A, B and C depend
on solute and stationary
phase and are obtained
1ooz
+
B = Ci(dH),
-
C = (AfOz -
(11) (OH),+,
+ C&W
z-
C&W
(AH) z+i+
W0z.1
z- (AH)
(12) (13)
c5
where Cl-C5 are constants, AH is the differential molar heat of evaporation of the solute from the stationary phase and z and z + 1 refer to the number of carbon atoms of the n-alkanes eluted before and after the sample compound s. AH values theoretically depend on temperature, but it has been reported that they can be considered to be constant in a suitable temperature rangezl and, therefore, eqn. 10 may show a linear region within the temperature range used in gas chromatographic determinations22-24. In this instance, this can be confirmed by the least-squares determination of the linearity of Z values as a function of temperature: E.p. (r)
= PT + Q
(14)
The values of the slope, P, and the intercept, Q, are listed in Table IV, with the correlation coefficient, R, for non-polar (OV-1) and polar (SP-1000) stationary phases, showing a fair linear dependence on temperature on non-polar phase21,25,26. The values of the constants in eqn. 10 can be deduced from the experimental values of Z at different temperatures T, and three series of measurements at suitable temperatures (75, 100 and 125°C) permit their calculation by means of the following equations: c
=
(7’2
-
Td
V3T3
-
Td
(12
ZITI)
+
CT3
-
TI)
VITI
-
(T2
-
T,)
(13
-
Z27’2)
(15) (T3
A =
Z3T3
-
ZITI
+
CC13
-
11) -
-
II>
I,> (16)
T3
-
B = Z3T3 + Z3C -
TI
A (T3 + C)
(17)
By using a personal computer, the values of the constant are easily calculated. If the divisor of eqn. 15 becomes equal to zero owing to the approximate knowledge of Z values, an error message and aborting of the running program can be avoided by automatically increasing the I2 value by a small amount (e.g., 0.1 i.u.) that does not appreciably influence the final results but permits the calculation to be carried out without computing errors due to division by zero.
42 TABLE
G. CASTELLO, IV
COEFFICIENTS OF THE LINEAR EQUATION POLAR (SP-1000) STATIONARY PHASES Correlation Compound No.
I 2 3 4 5 6 7 8 9 10 11 12 13 14c 14t 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
T. C. GERBINO
coefficients,
F+(r)
= PT + Q ON NON-POLAR
(OV-1) AND
H, are also given.
ov-I
SP-1000
P (i.u./‘C)
Q (ia.)
R
0.079 0.070 0.212 0.209 0.214 0.163 0.126 0.332 0.237 0.451 0.201 0.025 0.277 0.320 0.284 0.359 0.408 0.195 0.343 0.039 0.016 0.297 0.325 0.361 0.245 0.263 0.776 0.180 0.289 0.293 0.571 0.497 0.974 0.623 0.002
537.98 490.95 617.04 730.60 587.32 576.35 557.97 658.91 606.64 702.04 570.60 509.91 510.72 646.81 631.12 661.44 814.19 450.29 712.75 543.46 591.57 604.59 781.46 628.04 431.65 790.05 935.43 539.23 603.63 581.03 853.90 861.04 833.14 767.42 430.30
0.998 0.999 0.999 0.999 0.999 0.994 0.990 0.999 0.996 0.999 0.998 0.999 0.999 1.00 0.998 0.999 0.992 0.998 0.995 0.992 0.997 0.999 1.00 0.997 0.997 0.996 0.999 0.998 0.994 0.999 0.999 0.997 0.999 0.995 1.00
P (i.u.rC)
Q (i.u.)
R
0.291 0.325 0.106 0.475 0.313 0.146 0.025 0.345 0.170 0.509 0.231 0.119 0.067 0.443 0.377 0.638 0.460 0.300 0.315 0.065 0.103 0.354 _
787.68 621.87 970.48 871.54 779.64 1027.58 1019.51 1185.61 1109.11 1265.17 817.51 887.12 874.33 1099.20 1008.22 1046.37 1271.32 920.57 1158.25 841.44 963.37 1052.59 _
0.894 0.983 0.981 0.994 0.907 0.909 0.520 0.980 0.921 0.994 0.994 0.649 0.639 0.990 0.994 0.996 0.999 0.903 0.995 0.713 0.855 0.987 _
0.512 0.366 -
896.82 652.13 _
0.999 0.937 _ _
_ _
999.55 1083.24 1034.38 1282.76 _ _
0.945 0.987 0.978 0.999 _ _ -
-0.001
661.12
0.998
_ 0.169 0.364 0.410 0.700 _
Tables V and VI show the values of the constants A, B and C calculated from the experimental Z values on OV-1 and SP-1000, respectively, shown in Table III, and the Zvalues calculated by using these constants in eqn. 10 at 75, 100 and 125°C. The reasonable correspondence between these data and the experimental values in Table III shows that both eqns. 10 and 14 permit the calculation of the retention indices of haloalkanes on a non-polar stationary phase at any given temperature, while the linear correlation between Z and T (eqn. 14) may in some instances result in considerable errors when polar stationary phases are used, as shown by the low correlation coefficients for some compounds on SP-1000 in Table V.
GC OF HALOGENATED TABLE
43
COMPOUNDS
V
VALUES OF THE CONSTANT IN EQNS. 15,16 AND 17 AND ZVALUES BY REPLACING THESE CONSTANTS IN EQN. 10 These I values should Compound No.
1 2 3 4 5 6 I 8 9 10 11 12 13 14c 141 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
be compared
with the experimental
Constants
ON OV-1 CALCULATED
results in Table III. Calculated
I values
A (i.u.)
B (i.u. K)
C IK)
At 75°C
At 100°C
AI 125°C
583.1 412.9 617.3 733.6 1190.7 659.7 592.0 638.9 657.2 263.6 708.8 534.2 413 553 816.3 621 920 585 781.9 562 601.2 966.3 _ 1305.7 693.4 571.3 841.4 1972.2 656.8 152.2 537.0 1463.8 952 558.8 1089.1 430.56
- 3208 - 153990 - 29484 - 26954 - 1276078 -3021 - 1285 - 62284 - 6042 -815516 - 19759 -9289 - 144903 - 142022 -21852 -78351 -5111 - 19539 -8106 -476 -810 -211680 - 149010 - 13221 -9358 - 8288 -718036 -13915 - 5677 -80191 - 274988 - 17803 -417221 - 12533 -165
- 170.4 - 1848.0 - 746.6 - 132.2 2065.6 -234.8 -477.1 - 806.3 - 534.4 - 1717.0 -58.6 242 - 1096 - 1039.7 -94.9 -840.7 -487 - 55.8 - 528.6 -260.5 - 148.0 471.3 -7156.3 - 565.9 - 176.2 -552 588.6 -94.3 -230.7 - 896.6 320.9, - 563.8 - 1027.8 -229.1 - 648.0
565.45 515.57 691.22 803.78 662.12 633.05 601.97 774.85 689.64 859.37 640.55 518.44 606.75 758.36 730.02 786.07 956.81 518.17 832.82 556.56 597.15 707.98 894.89 754.09 516.88 882.06 1205.68 601.98 703.74 683.11 1052.84 1034.48 1172.68 983.81 431.15
567.68 517.31 696.16 808.67 661.53 637.86 604.37 782.69 694.67 870.45 645.98 519.08 613.46 766.07 737.77 794.58 964.89 523.43 840.04 557.17 597.60 715.63 903.00 761.95 523.78 887.74 1225.61 606.89 712.26 690.08 1067.65 1045.28 1196.13 1002.05 431.20
569.41 519.11 701.82 814.29 672.84 641.21 608.29 791.50 701.54 881.95 650.60 519.67 620.64 774.37 744.25 804.04 971.52 527.93 850.04 558.54 597.96 722.83 911.17 712.17 529.14 895.27 1244.52 611.00 718.24 691.75 1081.42 1059.34 1221.43 1014.91 431.26
In contrast, the use of eqn. 10 with A, B and C leads to satisfactory results, even if the trend of the I values as a function of temperature is almost horizontal or shows appreciable curvature. By using simple computer programs, the temperature for the best resolution of any mixture of compounds can be calculated when the values of A, B and C are known on pure or mixed-phase columns. A possible flow of the program is as follows: a list of the available halogenated compounds is shown on the screen; the operator selects those probably contained in the sample; the I values are calculated with eqn. 10 by using the stored values of the constants and
44 TABLE
G. CASTELLO,
T. C. GERBINO
VI
VALUES OF THE CONSTANT IN EQNS. 15, 16 AND 17 AND I VALUES LATED BY REPLACING THESE CONSTANTS IN EQN. 10 These I values should Compound
be compared _
with the experimental
Constants
ON SP-1000
CALCU-
results in Table III. Calculated
I values
No.
1 2 3 4 5 6 7 8 9 10 II 12 13 14c 14t 15 16 17 18 19 20 21 23 24 25 27 28 29 30 34
A (i.u.)
B (i.u. K)
C (Kl
At 75°C
At 100°C
At 125°C
902.6 767.7 1017.6 1113.7 904.1 1085.9 1028.5 1338.3 1177.4 1523.6 936.2 931.1 898.9 1308.9 1198.8 1396.9 3483.0 801.4 1325.5 865.8 1003.3 1215.9 911.7 800.9 1534.8 1069. I 1255.5 1214.1 3898.2 661.5
-60.2 - 1784.0 - 504.9 -8771.0 - 107.6 - 54.2 - 14.6 - 1593.6 - 92.0 -9100.5 -4529.3 56.5 32.2 -4353.4 - 6476.9 - 19676.8 -9034219.5 90.4 - 7758.6 26.63 6.04 - 2689.4 -60582.4 -325.1 - 5284.0 - 191.4 -2789.2 - 1643.2 - 8596597.6 -0.374
-344.1 -294.8 - 299.6 -234.8 -341.8 -341.4 -363.8 - 300.6 -338.8 -236.9 -230.7 - 360.7 - 360.9 - 270.8 - 239.6 - 195.7 -4055.8 - 342.6 -214.1 -358.2 - 349.2 -282.3 -717.6 ~ 334. I -123.6 -331.1 -283.1 - 304.9 3129.9 -372.2
887.73 734.26 1007.20 1036.32 886.98 1077.87 1027.59 1304.89 1167.56 1441.80 897.62 926.60 896.37 1252.61 1139.13 1267.88 1431.61 817.68 1267.62 863.15 997.55 1175.06 1075.68 777.85 1511.32 1057.87 1212.62 1176.11 1426.53 661.51
900.53 744.93 1010.73 1050.30 900.67 1084.19 1030.07 1316.43 1174.72 1456.81 904.39 935.64 901.53 1266.36 1150.30 1286.06 1143.19 804.36 1276.12 867.58 1003.55 1186.30 1087.58 792.66 1513.68 1064.55 1224.53 1190.02 1444.17 661.17
901.49 750.44 1013.48 1060.00 902.20 1084.94 1028.94 1322.06 1175.85 1467.16 909.14 932.61 899.76 1274.71 1157.95 1299.76 1454.64 803.03 1283.34 866.47 1003.42 1192.69 1101.34 795.91 1515.60 1066.24 1231.26 1196.48 1461.56 661.48
listed in increasing order; and the AZ values between adjacent compounds are also calculated. This procedure is repeated at many temperatures (increments of 2 or 5°C are suitable, within the usable temperature range of the column or within the range previously selected by the operator) and the temperature that ensures the greatest AZ values is eventually selected. By applying this procedure to the compounds previously analysed on a mixed-phase columns, a temperature of 60°C was calculated, compared with the experimental value of 59°C. When the linearity is fair, the constants P and Q can be used for qualitative analysis: the value of the slope, P, can confirm the identification of a substancez7J8, being correlated with structure 29. As an example, the P values of CHC13, CHBrCL CHBrzCl and CHBr3 are regularly spaced on replacing chlorine with bromine atoms
GC OF HALOGENATED
COMPOUNDS
45
(AP = 0.11, 0.10 and 0.12) and the same interval (0.11 i.u./“C) is found between CHzBrCl and CHzBrz (see Table IV). ACKNOWLEDGEMENTS
The authors thank Mrs. Graziella Bitossi for her cooperation in the preparation of this paper. This work was supported by the Minister0 Pubblica Istruzione, Italy. REFERENCFS 1 The Analysis of Trihalomeihanes in Finished Waters by the Purge and Trap Method, Method 501.1, United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, OH, 1979. 2 The Analysis of Trihalomethanes in Drinking Water by Liquid/Liquid Extraction, Method 501.2, United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, OH, 1979. 3 G. Castello, T. C. Gerbino and S. Kanitz, J. Chromafogr., 247 (1982) 263. 4 G. Castello, T. C. Gerbino and S. Kanitz, J. Chromafogr., 351 (1986) 165. 5 R. J. Laub and J. H. Purnell, J. Chromatogr., 112 (1975) 71. 6 R. J. Laub, Int. Lab., May/June (1981) 16. 7 J. H. Purnell, in F. Bruner (Editor), The Science of Chromatography, Elsevier, Amsterdam, 1985, p. 362. 8 G. Caste110 and T. C. Gerbino, J. Chromatogr., 366 (1986) 59. 9 G. Caste110 and G. D’Amato, J. Chromatogr., 54 (1971) 157. 10 G. Caste110 and G. D’Amato, J. Chromatogr., 58 (1971) 127. 11 E. Kovats, Helv. Chim. Acfa, 41 (1958) 1915. 12 H. Purnell. Gas Chromatography, Wiley. Chichester, 1962. p, 39. 13 R. C. Weast (Editor), CRC Handbook of Chemisfry and Physics, Chemical Rubber Co., Cleveland, OH, 5lst ed., 1970-71, p. C-367. 14 G. G. Schlessinger, in R. C. Weast (Editor), CRC Handbook of Chemistry and Physics, Chemical Rubber Co.. Cleveland. OH. 5lst ed., 1970-71, p. D-146. 15 H. Purnell, Gas Chromatography, Wiley, Chichester, 1962, p. 44. 16 T. C. Gerbino, Doctorate Thesis, Genova University, 1987. 17 E. F. G. Herington, in P. H. Desty (Editor), Vapour Phase Chromatography, Butterworths, London, 1957, p. 5. 18 G. J. Pierotti, C. H. Deal, E. L. Derr and P. E. Porter, J. Am. Chem. Sot., 78 (1956) 2989. 19 D. A. Leathard and B. C. Shurlock, in J. H. Purnell (Editor), Progress in Gas Chromatography, Wiley, New York, 1968. p. 1. 20 J. Takacs, P. Rajcsinyi, L. KBplar and 1. OIBCSI, J. Chromafogr., 41 (1969) 438. 21 E. B. Molnar, P. Moritz and J. Takacs, J. Chromatogr., 66 (1972) 205. 22 J. Takacs, M. Rockenbauer and I. Olacsi, J. Chromafogr., 42 (1969) 19. 23 L. S. Ettre and K. Billeb, J. Chromatogr., 30 (1967) 1. 24 M. C. Saha and G. D. Mitra, J. Chromatogr. Sci., 8 (1970) 84. 25 F. Riedo, D. Fritz, G. Tarjan and E. Kovlts, .I. Chromatogr., 126 (19876) 63. 26 M. Dimov, J. Chromatogr., 347 (1985) 366. 27 L. Sojak and J. Janak, Anal. Chem., 45 (1973) 293. 28 L. Sojak, J. KrupEik and J. Janak. J. Chromatogr.. 195 (1980) 43. 29 G. Castello, M. Berg and M. Lunardelli, /. Chromatogr., 79 (1973) 23.