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Use of kovats indices for prediction of retention temperatures in linear temperature-programmed capillary gas chromatography
Journal of Chromatography, 407 (1987) 65-77 El&er Science Publishers B.V., Amsterdam -
Printed in The Netherlands
CHROM. 19 807
USE OF KOVATS INDICES FOR PREDICTION OF RETENTION TEMPERATURES IN LINEAR TEMPERATURE-PROGRAMMED CAPILLARY GAS CHROMATOGRAPHY
J. KRUP&C*,
r>. REPKA and T. HkVESI
Depmtment of Analytical Chemistry, Fuculty of Chemistry, Slovak Technical University, Radlinskeho 9,812 37 Bratislava (Czechoslovakia) and G. ANDERS Academy of Science8 of the GDR, Institute of Organic Chemistry, Leipzig (G.D.R.) (Received May 2&h, 1987)
SUMMARY
Over 100 hydrocarbons present in gasoline have been identified by linear temperature-programmed capillary gas chromatography on OV-101 on the basis of experimental, TRE,and predicted, TRP,retention temperatures. For the calculation of TRP, both isothermal retention data (Kov&ts indices and their temperature coefficients) and temperature-programmed retention data (retention temperatures of nalkanes) were used.
INTRODUCTION
Retention temperatures are often used for the characterization of solutes separated by linear temperature-programmed capillary gas-liquid chromatography (LTPGC). This parameter is the column temperature at which the maximum solute concentration is eluted from the column. It is calculated from the retention time, tR, the initial temperature of the LTPGC experiment, To, and the oven temperatureprogramming rate, r: TR =
To i- rtR
(1)
The repeatability of TR measurements, under constant working conditions including the column and GC instrument, is comparable with that of isothermal measurements of retention data when appropriate instrumentation is used. However, the reproducibility of TR measurements, i.e., of interlaboratory retention data, is generally not sufficient for identification purposes since the data depend on many variables which are problematic during LTPGC, e.g., heat transport through the oven and the column walls, carrier gas flow-rate in capillary GC. This is why published retention temperatures are not normally employed for identification purposes in LTPGC. 0021-9673/87/$03.50
IQ
1987 Elsevier Science Publishers B.V.
J. KRUPt5fK et al.
66
a
*RP
%E.z+1
T
Fig. 1. Dependences of the isothermal (a) and temperature-programmed perature. For details see text.
(h) retention indices upon tem-
For the prediction of retention temperatures from isothermal retention data, published procedures are available’. One recent procedure predicts retention temperatures from Kovhts retention indices, Z(Y’),their temperature coefficients, dZ/dT, and retention temperatures of n-alkanes, TRE,z and TRE,=+ 1, obtained experimentally by LTPGC*. The retention temperature can be predicted graphically, as seen in Fig. 1. The dependence of the Kovats index on temperature (line a in Fig. 1) dZ Z(T) = Z(TJ + (T - Ti).dT crosses the dependence of the temperature b in Fig. 1)
z=
1ooz +
T T RE,Z+I
programmed
index on temperature
(line
TREJ -
TREJ
at a point P which is characterized by Z(TRp) and TRpvalues. An equation equivalent to the graphical procedure was derived for the prediction of retention temperature:
TRp
=
@a+
1 -
TR&)[Z(TI) - Tl(dZ/dT) - 100~1+
~OOTRE,~
(4) 100
-
(dZ/dT)(Tm,z+i
-
TRE,Z)
Further it was shown that a11predicted retention temperatures were slightly higher than the corresponding experimental values3. The aim of this paper is to describe an empirical procedure with which experimental and predicted retention temperatures coincide within the precision of common laboratory temperature measurements. This procedure has been tested by the identification of hydrocarbons in premium gasoline separated on a polydimethylsiloxane capillary column (OV-101) via LTPGC.
PREDICTION
OF RETENTION
TEMPERATURES
67
IN GC
EXPERIMENTAL
A Fractovap 2350 gas chromatograph (Carlo Erba, Milan, Italy) equipped with a flame ionization detector and an all-glass inlet split system was used. Nitrogen was used as a carrier gas. The separation of gasoline was performed on a glass capillary column (270 m x 0.25 mm I.D.) coated dynamically with OV-101 stationary phase using a 15% solution of the stationary phase in dichloromethane as described elsewhere4. The separation power of the capillary column was tested isothermally at 60°C and for the capacity factor k = 2.56 it exhibited 750 000 theoretical plates using nitrogen as a carrier gas at a rate of zi = 10 cm s-l. A 0. l-pi volume of gasoline was injected into the column by an l-p1 Hamilton microsyringe. All analyses were performed by linear temperature-programmed capillary gas chromatography starting from 40°C and with increases of 0.5, 0.9, 1.4, 2.4 and 2.9”C mine1 respectively. The inlet pressure of the nitrogen carrier gas was kept constant, pi = 380 kPa. The oven temperature was measured at S-min intervals by a carefully checked mercury thermometer. The temperature-programming rate, P, was determined by a linear regression analysis of the oven temperature (read from the mercury thermometer) versus time
T= To + rt where T is temperature
(5) in “C and t is the time in min.
RESULTS AND DISCUSSION
Fig. 2 shows the separation of gasoline in a glass capillary column coatedwith OV-101 under LTPGC conditions, from 40°C at 0.9X! min-‘. Experimental values of the retention temperatures, TRE,were calculated for each peak from the retention rate, r, by substitution time, tR, and the corresponding temperature-programming into eqn. 1. Values of the retention temperatures were predicted from published Kovats indices, I, and their temperature coefficients, dl/dT, as well as from experimental retention temperatures of n-alkanes, TRE,zand TRE++Ir obtained by LTPGC at each temperature-programming rate, according to eqn. 4. Peaks on the chromatograms were “identified” by comparing their experimental, TRE,and predicted, T RP,retention temperatures, and considering the composition
m
4
to
50
40
m
Fig. 2. Chromatogram of gasoline on a glass capillary column coated with OV-101 under the conditions of LTPGC (from 40°C at O.YC min-I).
J. KRUF’CfK er
al
Fig. 3. Dependences of the isothermal and temperature-programmed retention indices on temperature for hydrocarbons between n-pentane and n-heptane in gasoline separated on the OV-101 capillary column.
of gasoline estimated by its separation on squalane6-s and polydimethylsiloxanesg~lo both isothermally and by LTPGC. The graphical prediction of retention temperatures, according to Fig. 1, is illustrated in Figs. 3-6 for compounds expected to be present in gasoline. The graphs demonstrate the changes in elution orders with the temperature-programming rates in LTPGC. The dashed lines in Fig. 6 correspond to the extrapolated dependences of the temperature-programmed retention indices, I, upon the retention temperatures, TRE, of n-nonane and Pr-decane. As shown previously2, the slope of this dependence for n-alkanes at a given temperature-programming rate is not constant and therefore the slopes of the extrapolated lines differ from those found for n-decane and n-undecane. However, the dashed lines can be used to estimate the elution order of compounds which at higher temperature-programming rates are eluted after ytdecane.
J. KRUPcfK
72
er al.
TABLE I EXPERIMENTAL, TRY, AND PREDICTED, Tnp, RETENTION TEMPERATURES IDENTIFIED IN GASOLINE BY CAPILLARY TEMPERATURE-PROGRAMMED GRAPHY ON OV-101
FOR HYDROCARBONS BUS CHROMATO-
Be = Benzene; Bu = butyl; Cy = cytlo; Dee = &cane; Et = ethyl; Hep = heptane; Hex = hexane; Me = methyl; Non = nonafie; Oet = octane: Pe = pentane; Pro = propyl. Peak No.
3 4 5 6 7 8 9 10 11 12 13 14 15 I6 17 18 19 20 21 22 23 24 25 26
.27 28 29 30 ~ 31 32 ‘. 33’ 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Abbreviation
2,2-DiMeBu CyPe 2,3-DiMeBu 2-MePe 3-MePe n-Hex MeCyPe 2,CDiMePe Be 3,3-DiMePe CyHex 2-MeHex 2,ZDiMePe l,l-DiMePe 3-MeHex I-cis-3-DiMeCyPe 3-EtPe I-trans-3-DiMeCyPe I-mm-2-DiMeCyPe n-Hep MeCyHex 1,1,3-TriMeCyPe 2,4-DiMeHex EtCyPe 2,5-DiMeHex l-tram-2-cis-4-TriMeCyPe 3,3-DiMeHex 1-tram-2-cis-3-TriMeCyPe 2,3,4_TriMePe MeBe 2,3-DiMeHex 2-Me-3-EtPe I,1 ,ZTriMeCyPe +feHep CMeHep 3,4-DiMeHex 3-MeHep 3-EtHex 1-cis-@ms-4-TriMeCyPe 1-cis-3-DiMeCyHex 1-trum-4-DiMeCyHex 1, I-DiMeCyHex I-Me-tram-2-EtCyPe I-Me-cis-3-EtCyPe 1-Me-tram-J-EtCyPe I-trans-2-DiMeCyHex
O.YC min-’ TRE
T RP
53.4 53.5 53.5 53.5 53.7 54.0 54.5 54.5 55.0 55.2 55.2 55.4 55.5 55.6 55.7 56.0 55.9 56.0 56.0 56.8 57.2 57.3 57.8 57.7 57.8 58.1 58.2 58.4 58.6 58.8 59.1 59.2 59.2 .59.5 59.6 59.6 59.9 59.9 60.0 60.1 60.1 60.4 60.6 60.8 60.9 60.9
53.3 53.3 53.6 53.6 53.8 54.8 54.8 55.4 55.6 55.7 55.9 55.9 56.1 56.1 56.3 56.4 56.4 56.5 57.9 58.0 5x.4 58.4 58.3 58.9 58.8 59.1 59.3 59.5 59.7 59.8 59.9 60.0 60.0 60.2 60.3 60.4 60.4 60.5 60.6 60.9 61.2 61.1 61.2 61.4
1.4”C minT RE 80.1 80.1 80.1 80.1 80.4 80.8 81.7 81.7 82.7 82.7 83.1 83.2 83.4 83.7 83.7 84.1 84.2 84.4 84.4 84.9 86.3 86.4 87.0 87.0 87.0 87.6 87.6 88.1 88.3 88.7 89.0 89.2 89.4 89.5 89.5 89.6 89.8 90.1 90.2 90.5 90.6 91.2 91.3 91.5 91.6 91.8
1
TRP 79.6 80.2 80.2 80.2 80.5 82.2 82.1 83.2 83.3 83.6 83.6 83.8 83.8 84.0 84.4 84.4 84.5 84.7 87.2 87.2 87.6 87.9 87.4 88.4 88.4 88.9 89.1 89.6 89.7 89.9 90.3 89.9 90.0 90.4 90.5 90.7 91.0 91.3 91.5 92.0 92.3 92.2 92.2 92.9
2.4”C mi?l-’
2.9”C minm’
TRE
TRP
TRE
TRP
115.5 115.5 lj5.5 115.5 f16.0 116.5 117.7 117.7 118.9 118.9 119.4 119.6 119.8 120.0 120.0 120.8 120.7 121.0 121.0 121.5 123.4 123.4 124.2 124.2 124.0 125.0 125.0 125.5 125.8 126.4 126.9 127.0 127.1 127.1 127.1 127.1 127.7 127.9 128.1 128.5 128.7 129.6 129.7 129.9 129.9 130.2
116.0 115.9 115.8 115.8 116.2
137.8 137.8 137.8 137.8 139.3 139.7 141.0 141.0 142.3 142.3 142.8 142.8 143.0 143.3 143.3 144.2 144.0 144.2 142.2 144.7 146.6 146.6 147.5 147.5 147.3 148.2 148.2 148.8. 148.8 149.6 149.6 149.6 150.2 150.2 150.2 150.2 150.8 150.8 150.8 151.7 151.9 152.8 152.8 153.2 153.2 153.5
138.3 139.2 139.0 139.0 139.4
118.5 118.1 119.7 119.8 120.4 119.9 120.3 120.8 120.4 121.2 121.0 121.4 121.5 125.2 125.0 124.9 125.8 124.6 126.3 126.2 127.0 127.1 127.9 127.6 127.9 128.9 127.6 127.8 128.6 128.5 128.8 129.7 130.2 130.3 131.2 131.2 131.0 131.1 132.4
141.9 141.4 143.2 143.2 143.9 143.2 143.6 144.3 143.7 144.6 144.3 144.8 144.9 148.9 148.5 14X.2 149.4 147.8 149.8 149.6 150.5 150.6 151.3 150.9 151.3 152.5 150.8 151.0 152.0 151.7 152.1 153.3 153.8 153.9 154.9 154.7 154.3 154.8 156.1
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
73
TABLE I (conrimed) P&Zk
Abbreviation
U.5”C iftin-’
1.4”C rniK’
2.4”C mine’
2.9”c min-
TRE
TM
TKE
TRE
TRP
TRE
TRP
61.8
92.2 92.4 92.7 92.7 92.9 93.5 94.1 94.1 94.5 94.9 95.2 95.5 95.5 95.1 95.5 96.3 96.3 96.3 96.7 96.9 97.0 97.6 97.7 97.7 98.0 98.3 98.7 98.7 98.8 99.2 99.2 99.2 99.8 Kg.3 100.3 100.4 101.5 101.5 104.0 105.7 107.8 107.8 108.3 108.3 108.8 109.8 109.8 110.8 111.1
130.7 130.7 131.5 131.5 131.2 132.3 132.3 132.9 133.4 133.7 134.0 134.6 134.8 134.8 134.0 135.5 135.2 135.5 136.1 136.1 136.2 136.9 137.0 136.9 137.5 131.9 138.2 137.9 138.2 139.2 139.2 138.9 138.9 138.9 140.0 140.0 14-1.4 141.9 143.8 146.0 148.2 148.2 148.7 148.7 149.2 150.4 150.4 151.6 151.9
132.7
153.8 153.8 154.7 154.7 154.3 144.5 154.3 156.1 156.7 156.8 157.6 157.8 158.4 158.2 157.6 158.8 157.6 158.8 159.3 159.3 159.3 160.3 160.6 160.3 161.0 161.3 161.7 161.3 161.7 161.7 161.7 162.5 142.7 162.5 163.5 163.5 165.2 165.8 168.0 170.4 173.1 172.3 173.7 173.7 174.1 175.7 175.7 177.1 177.1
156.5
’
NO.
“. ;
49 50 51 52 53 54 55 56 51 58 59 60 61 62 63 64 65 66 67 68 69 JO 71 72 73 74 75 16 77 78 79 80 82 83 85 86 87 88 95 100 106 107 108 109 110 111 112 113 114
I-cis-Zcis-3-TriMeCyPe n-act I-c&CDiMeCyHex I-tram-3-DiMeCyHex I-tram-2-DiMeCyHex IsoProCyPe 2,3,5-TliMeHex 1-h$&@-2-EtCyPe 2;4-DiMeHep 4,4-DiMeHep I -cis-2-DiMeCyHex 2,6-DiMeHep n-ProCyPe EtCyHex 2,5-DiMeHep 1,1,3-TriMeCyHex 3,5-DiMeHep 3,3-DiMeHep 2,4-DiMe-3-EtPe 2,3,3-TriMeHex l,l,CTriMeCyHex 2,2,3,3_TetMePe EtBe 2,3,4-TriMeHex 3,3,4-TriMeHex 1-cis-3-cis-STriMeCyHex 1,3-DiMeBe 2,3-DiMeHep 1,CDiMeBe 3,4-DiMeHep 3,QDiMeHep 4-EtHep 4-MeOct Z-MeOct J-EtHep 3-MeOct I,2-DiMeBe 1,l ,ZTriMeCyHex n-Non i-ProBe 3,5-DiMeOct 3,5-DiMeCkt n-BuCyPe EtCyHep 2,dDiMeOct n-ProBe 2-Me-3-EtHep 1-Me-3-EtBe l-Me-4-EtBe
61.2 61.6 61.6 61.6 61.6 62.1 62.6 62.7 62.9 63.3 63.3 63.7 63.7 63.7 63.8 64.1 64.3 64.4 64.5 64.6 64.8 65.1 65.2 65.2 13 65.4 65.5 65.9 66.0 66.1 66.3 66.3 66.5 66.8 66.9 67.4 67.6 68.0 68.6 70.5 71.4 73.2 73.4 13.7 73.9 14.4 74.8 75.1 75.7 75.9
62.0 61.9 61.4 62.5 63.1 63.4 63.7 64.0 64.0 64.3 64.3 64.4 64.8 64.9 65.0 65.1 65.3 65.4 65.5 66.0 65.9 66.0 66.3 66.5 66.7 66.9 66.8 66.9 66.9 67.1 67.4 67.6 67.9 68.0 68.7 68.9 12.0 74.0 73.X 74.4 74.7 74.9 75.6 15.8 76.5 76.8
TRP
93.4 93.9 93.9 93.2 94.1 94.8 95.7 95.4 95.9 96.8 96.0 96.4 97.1 97.1 97.8 97.1 97.5 98.0 98.2 98.3 99.3 99.2 9x.9 99.7 100.3 100.0 99.4 loo*0 100.0 99.7 99.7 100.1 100.1 100.9 101.1 102.9 103.6 107.0 109.6 108.1 109.8 109.9 109.4 111.4 110.8 112.4 112.7
133.8 133.7 133.0 134.8 133.8 135.7 134.2 13.5.2 137.4 134.7 135.6 137.4 136.6 138.2 136.3, 137.0 138.2 138.2 138.3 140.0 139.8 139.0 140.5 141.7 140.5 138.9 140.4 140.0 139.3 139.2 139.6 139.4 140.4 140.7 144.3 145.7 148.9 152.1 148.8 151.8 151.7 150.2 154.0 152.1 154.9 155.4
158.0 151.9 157.2 159.1 157.4 160.0 157.7 159.0 162.1 158.1 159.4 161.9 160.6 162.9 160.1 160.9 162.6 162.6 162.7 164.8 164.5 163.4 165.4 167.0 165.1 162.8 165.0 164.3 163.4 163.0 163.5 163.2 164.4 164.8 169.5 171.5 174.9 178.8 173.8 178.1 177.8 175.4 180.8 177.8 181.2 182.4
74
J. KRUPCiK
et al.
TABLE I (cor&wd)
Peak No.
115 116 117 118 119 121 122 I23 124 125 131 132 133
Abbreviation
4-EtOct 1,3,5-TriMeBe 2,3-DiMeOct 5-MeNo 4-MeNo 2-MeNo 3-EtOct 3-MeNo tBuBE 1,2,4-TriMeBe IsoBuBe sec.-BuBe iZ-Dee
0.5”C mifl-l
1.4”C min-’
2.4”C min-l
2.9”C min-’
TRE
TRP
TRE
TEP
TRB
TRP
TRE
TRP
76.1 76.7 77.0 77.6 77.8 78.2 78.6 79.0 79.7 79.7 81.5 82.0 82.9
77.0 77.5 77.8 78.0 78.3 78.6 79.0 79.4 80.4 80.6 82.3 82.7
111.1 111.7 112.0 112.4 112.8 113.1 113.7 114.1 115.6 115.6 117.3 117.8 118.4
111.7 113.5 114.3 112.8 113.2 113.6 114.1 114.5 117.0 117.4 119.3 119.6
151.9 152.4 152.8 153.3 153.5 154.0 155.0 155.0 157.1 157.1 158.5 158.8 160.0
152.7 156.2 157.7 153.7 154.4 154.7 155.3 155.8 160.4 160.9 163.0 163.2
177.5 178.0 178.5 178.5 179.3 179.7 180.9 180.9 183.3 183.8 185.5 185.5 186.4
178.1 183.5 185.4 179.2 180.1 180.4 181.1 181.8 188.2 189.0 191.2 191.3
to compound, indicating that their values depend not only on temperature differences between the oven and column but “inter ah” also on the nature of the compounds and other factors. It should also be noted that the Kovats indices, I, and their temperature coefficients, dl/dT, are valid only in a narrow temperature region1 l and their extrapolation to higher temperatures can be a source of serious errors. The Kovats indices published by Lubeck and Sutton5 were obtained at 6O”C, and their use for prediction of retention temperatures above 120°C is very problematic; the data for above 120°C given in Tables I and II have high errors. The knowledge of the coefficients A, B and C enabled us to predict retention temperatures for the temperature-programming rates of 0.9 and 1.9”C min- r using the rearranged eqn. 6: TRC
= A + BTRp + Cr
(7)
The values of TRC found are in very good agreement with experimental data, as shown in Table II, with’the exception of overlapped peaks and retention temperatures above 120°C. CONCLUSIONS
Relation temperatures, TRp, were predicted for the main constituents found in gasoline by linear temperature-programmed capillary gas chromatography on OV101 from isothermal Kovats indices, I, their temperature coefficients, dI/dT, and experimental retention temperatures for n-alkanes, TRE,z and TRQ+ 1. The values were in relatively good agreement with experimental data, TRE. From experimental, TRE, and predicted, TRp, retention temperatures obtained at four different programming rates, r, the coefficients A, B and C of the equation TR, = A + BTRp + Cr were calculated by multiple linear regression analysis. Using these coefficients it was
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
75
TABLE II COEFFICIENTS OF EQN. 6 CALCULATED FROM THE DATA GIVEN IN TABLE I BY MULTIPLE LINEAR REGRESSION ANALYSIS, AND COMPARISON OF RETENTION TEMPERATURES FOUND EXPERIMENTALLY, TRE,AND THOSE CALCULATED FROM EQN. 6, TRc Peak No.
3 4 5 6 7 9 10 11 12 13 14 15 16 17 18 19 20 21 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 41 48 49 51 52 53 54
A
2.463 4.026 3.592 3.592 -0.387 -0.152 -0.590 0.042 -0.676 0.473 0.136 0.150 2.345 0.020 -0.188 0.564 1.771 1.257 2.066 1.386 -0.482 0.925 -0.412 1.347 0.195 0.845 2.186 0.395 2.373 3.735 2.425 0.602 0.025 1.199 -0.931 1.815 4.111 1.456 1.096 2.242 0.783 - 1.536 0.437 0.856 2.183 3.617 3.217 6.473 38.738
B
0.945 0.890 0.901 0.901 1.009 l.ooo 1.008 0.992 1.011 0.979 0.982 0.987 0.930 0.990 0.998 0.972 0.945 0.956 0.939 0.955 0.998 0.966 0.999 0.951 0.985 0.968 0.934 0.979 0.929 0.898 0.933 0.974 0.992 0.964 1.015 0.948 0.900 0.965 0.969 0.942 0.973 1.034 0.989 0.979 0.944 0.918 0.929 0.866 0.092
c
1.572 3.400 3.086 3.086 -0.325 -0.241 -0.330 0.088 -0.616 0.487 0.698 0.404 2.279 0.366 0.024 1.075 1.898 1.529 1.613 1.154 0.027 0.744 0.005 1.480 0.236 0.754 2.033 0.354 2.458 3.479 1.896 0.930 0.136 0.865 -0.753 1.665 2.995 0.640 0.557 1.566 0.512 - 1.665 -0.039 -0.091 1.351 2.081 1.650 4.040 34.685
OYC min-I
1.9”C min-’
7kE
TR.8
66.1 66.3 66.3 66.3 66.5 67.5 67.5 68.3 68.4 68.7 68.8 68.9 69.1 69.1 69.6 69.5 69.7 69.7 71.2 71.3 71.9 71.4 71.9 72.0 72.4 72.8 73.0 74.0 73.7 73.8 73.8 74.0 74.0 74.2 74.3 74.6 74.7 74.8 75.0 75.4 75.6 75.8 75.9 75.9 16.3 76.8 76.8 76.9 77.5
TRC
66.31 66.14 66.12 66.12 66.40 61.41 67.47 68.14 68.31 68.46 68.63 68.79 68.97 69.02 69.39 69.29 69.46 69.44 71.03 71.18 71.89 71.66 71.83 72.13 72.30 72.69 72.78 74.05 73.50 73.65 73.71 74.00 74.14 74.05 74.49 74.49 74.51 74.86 74.88 75.28 75.49 75.76 75.84 75.98 76.26 76.65 76.72 76.67 77.14
99.5 99.8 99.7 99.7 100.0 101.5 101s 102.6 102.7 103.1 103.3 103.5 103.8 103.8 104.3 104.5 104.7 104.7 106.8 106.8 107.7 107.7 107.5 108.3 108.3 108.9 109.1 109.6 110.0 110.2 110.4 110.4 110.4 110.6 110.9 111.1 111.2 111.6 111.8 112.5 112.7 112.9 113.0 113.2 113.8 114.2 114.2 114.4 115.1
TRC
99.43 99.36 99.33 99.33 99.86 101.54 101.52 102.63 102.67 103.11 103.31 103.52 103.81 103.73 104.46 104.39 104.64 104.61 106.82 106.91 107.75 107.68 107.60 108.34 108.37 108.88 109.10 109.66 109.95 110.08 110.30 110.39 110.48 110.47 110.98 111.13 111.18 111.67 111.78 112.57 112.69 112.97 112.97 113.30 113.67 114.25 114.24 114.99 115.42 (Continued on p. 76)
Peak
A
3
c
0.9-c #tin-’
I.932 w&l-’
TkE
TRC
TRE
78.0 78.1 78.4 1.8 78.9 79.4 79.4 79.4 79.7 79.9 80.0 80.2 80.4 80.5 80.6 81.1 81.2 81.2 81.4 81.6 82.0 82.0 82.0 82.1 82.3 82.3 82.9 83.0 83.7 83.8 84.5 85.1 88.3 89.6 89.6 90.7 91.0 91.4 92.0 92.3 93.0 93.3 93.7 94.0 94.2 94.8 95.1 95.4 95.8 96.3 97.4 97.5 99.3 99.9
77.71) 77.98 78.34 78.40 78.73 79.22 79.30 79.23 79.40 79.67 79.76 79.94 80.09 80.19 80.34 80.74 80.98 80.93 81.14 81.26 81.78 81.74 81.97 82.07 82.1-l 82.49 82.81 83.05 83.48 83.69 84.22 84.64 87.97 89.92 90.08 90.51 90.67 91.28 91.75 92.09 92.78 92.91 93.31 93.66 93.94 94.72 95.02 95.36 95.93 96.25 97.07 97.07 98.99 99.34
-115.1 115.8 116.2 116.5 117.0 117.2 117.6 117.6 117.2 118.2 118.0 118.2 118.7 118.8 118.9 119.6 119.7 119.6 120.1 120.4 120.8 120.7 120.8 121.0 121.2 121.2 121.7 121.7 122.6 122.6 124.0 124.6 128.8 130.1 130.1 131.7 131.7 132.2 133.1 133.1 134.7 135.0 135.0 135.5 135.8 136.4 136.7 137.1 137.6 138.2 140.0 140.2 142.1 142.4
No.
55 56 57 58 59
60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 z 77 78 79 80 82 83 85 86 87 88 100 IO6 107 108 109 110 111 112 113 114 115 116 117 118 119 121 122 I23 124 125 131 132
10.453 3.852 0.m 4602 4.558 0.843 -0.725 4.851 0.208 6.714 9.236 1.595 6.038 6.189 6.541 6.690 4.792 5.491 6.568 9.273 5.942 4.306 6.008 12.077 11.741 1.247 2.221 5.574 2.886 2.971 7.983 6.702 9.729 9.853 8.340 7.064 5.348 1.960 8.643 1.758 7.696 11.246 -0.973 9.049 9.383 2.387 -0.538 -0.807 -1.381 0.733 9.833 7.027 4.676 6.944
0.759 0.910 0.982 0.878 0.899 0.965 1.003 0.888 0.983 0.846 0.786 0.954 0.859 0.856 0.851 0.849 0.894 0.873 0.852 0.796 0.866 0.892 0.867 0.733 0.733 0.960 0.943 0.877 0.929 0.931 0.834 0.874 0.813 0.817 0.839 0.869 0.898 0.958 0.843 0.961 0.861 0.797 1.002 0.841 0.841 0.952 1.004 i ,009 1.016 0.983 0.835 0.881 0.928 0.894
8.413 2.320 0.666 4.348 2.512 1.539 -0.249 3.295 -0.196 4.934 7.771 I.290 4.720 4.827 4.950 4.712 3.030 4.201 4.670 6.607 ,4.426 4.039 4.367 10.104 10.216 1.678 2.134 4.729 2.733 2.435 5.446 3.221 6.384 5.914 6.238 4.098 2.978 1.404 5.032 1.043 4.450 7.056 -0.002 5.005 4.562 1.917 -0.336 -0.495 -0.595 0.469 5.586 3.527 1.131 2.589
T RC 115.02 115.78 116.31 116.45 116.93 117.32 117.56 117.51 117.25 118.10 117.72 118.24 lL8.64 118.73 118.82 119.42 119.67 119.52 120.05 120.25 120.75 120.57 120.84 120.69 121.14 121.50 121.83 121.90 122.63 122.64 123.78 124.29 128.32 130.60 130.55 131.20 131.30 131.96 132.86 133.02 133.98 134.45 134.59 134.85 135.24 135.85 136.34 136.73 137.60 137.83 139.25 139.45 141.24 141.56
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
77
possible to calculate retention temperatures, TAC,which coincide with experimental values, TRE, within the errors of laboratory temperature measurements ( f G!T). This precision allowed us to identify over 100 hydrocarbons in gasoline analyzed by LTPGC using published isothermal Kodts retention indices. REFERENCES 1 J. Curvers, K. Knauss, P. Larson, .I. Rijks and C. Cramers, in P. Sandra and W. Bertsch (Editors),
2 3 4 4 6
Proceedings of the Vlth International Syrnposittm on Capillary Chromatography, Riva de! Garda, May 1985, Htithig, Heidelberg, 198.5,p. 744. J. Kru#ik, P. Cell&r, D. Repka, J. Garaj and G. Guiochon, S. Chromatogr., 351 (1986) 1 il. J. Q-up&k, D. Repka, T. Hevesi and J. Garaj, J. Chrmatogr.. 406 (1987) 117. J. Krup&k, M. Kristin, M. Valachovicovi and $.Janiga, J. Chromatogr., 126 (1976) 147. A. J. Lube& awl D. L. Sutton, J. High Resolwt. Chrwnatogr. Chromatogr. Commun., 6 (1983) 328. I. M. Whittemxe, in K. H. Alget and T. H. Gouw (Editors), Chromatography in Petroleum Analysis,
Marc& Dekker, New York, 1979, p. 50. 7 E. M&so&, J. KrupEik, P. CelIlr and J. Garaj, J. Chromatogr., 303 (1984) 151. 8 E. Matisoti, J. KrupCik, P. Cell&r and A. K&an, 1. Chromtogr., 346 (1985) 177. 3 N. G. Jahansen, L. S. Ettre and R. L. Miller, J. Chrwmtogr., 2% (1983) 393: 10 R. L. Miller, L. 9. Ettre and N. G. Jahansen; d. Chronmtogr., 259 (1983) 393. 11 L. S. Ettre, Chramatagraphia, 7 (1974) 39.
Printed in The Netherlands
CHROM. 19 807
USE OF KOVATS INDICES FOR PREDICTION OF RETENTION TEMPERATURES IN LINEAR TEMPERATURE-PROGRAMMED CAPILLARY GAS CHROMATOGRAPHY
J. KRUP&C*,
r>. REPKA and T. HkVESI
Depmtment of Analytical Chemistry, Fuculty of Chemistry, Slovak Technical University, Radlinskeho 9,812 37 Bratislava (Czechoslovakia) and G. ANDERS Academy of Science8 of the GDR, Institute of Organic Chemistry, Leipzig (G.D.R.) (Received May 2&h, 1987)
SUMMARY
Over 100 hydrocarbons present in gasoline have been identified by linear temperature-programmed capillary gas chromatography on OV-101 on the basis of experimental, TRE,and predicted, TRP,retention temperatures. For the calculation of TRP, both isothermal retention data (Kov&ts indices and their temperature coefficients) and temperature-programmed retention data (retention temperatures of nalkanes) were used.
INTRODUCTION
Retention temperatures are often used for the characterization of solutes separated by linear temperature-programmed capillary gas-liquid chromatography (LTPGC). This parameter is the column temperature at which the maximum solute concentration is eluted from the column. It is calculated from the retention time, tR, the initial temperature of the LTPGC experiment, To, and the oven temperatureprogramming rate, r: TR =
To i- rtR
(1)
The repeatability of TR measurements, under constant working conditions including the column and GC instrument, is comparable with that of isothermal measurements of retention data when appropriate instrumentation is used. However, the reproducibility of TR measurements, i.e., of interlaboratory retention data, is generally not sufficient for identification purposes since the data depend on many variables which are problematic during LTPGC, e.g., heat transport through the oven and the column walls, carrier gas flow-rate in capillary GC. This is why published retention temperatures are not normally employed for identification purposes in LTPGC. 0021-9673/87/$03.50
IQ
1987 Elsevier Science Publishers B.V.
J. KRUPt5fK et al.
66
a
*RP
%E.z+1
T
Fig. 1. Dependences of the isothermal (a) and temperature-programmed perature. For details see text.
(h) retention indices upon tem-
For the prediction of retention temperatures from isothermal retention data, published procedures are available’. One recent procedure predicts retention temperatures from Kovhts retention indices, Z(Y’),their temperature coefficients, dZ/dT, and retention temperatures of n-alkanes, TRE,z and TRE,=+ 1, obtained experimentally by LTPGC*. The retention temperature can be predicted graphically, as seen in Fig. 1. The dependence of the Kovats index on temperature (line a in Fig. 1) dZ Z(T) = Z(TJ + (T - Ti).dT crosses the dependence of the temperature b in Fig. 1)
z=
1ooz +
T T RE,Z+I
programmed
index on temperature
(line
TREJ -
TREJ
at a point P which is characterized by Z(TRp) and TRpvalues. An equation equivalent to the graphical procedure was derived for the prediction of retention temperature:
TRp
=
@a+
1 -
TR&)[Z(TI) - Tl(dZ/dT) - 100~1+
~OOTRE,~
(4) 100
-
(dZ/dT)(Tm,z+i
-
TRE,Z)
Further it was shown that a11predicted retention temperatures were slightly higher than the corresponding experimental values3. The aim of this paper is to describe an empirical procedure with which experimental and predicted retention temperatures coincide within the precision of common laboratory temperature measurements. This procedure has been tested by the identification of hydrocarbons in premium gasoline separated on a polydimethylsiloxane capillary column (OV-101) via LTPGC.
PREDICTION
OF RETENTION
TEMPERATURES
67
IN GC
EXPERIMENTAL
A Fractovap 2350 gas chromatograph (Carlo Erba, Milan, Italy) equipped with a flame ionization detector and an all-glass inlet split system was used. Nitrogen was used as a carrier gas. The separation of gasoline was performed on a glass capillary column (270 m x 0.25 mm I.D.) coated dynamically with OV-101 stationary phase using a 15% solution of the stationary phase in dichloromethane as described elsewhere4. The separation power of the capillary column was tested isothermally at 60°C and for the capacity factor k = 2.56 it exhibited 750 000 theoretical plates using nitrogen as a carrier gas at a rate of zi = 10 cm s-l. A 0. l-pi volume of gasoline was injected into the column by an l-p1 Hamilton microsyringe. All analyses were performed by linear temperature-programmed capillary gas chromatography starting from 40°C and with increases of 0.5, 0.9, 1.4, 2.4 and 2.9”C mine1 respectively. The inlet pressure of the nitrogen carrier gas was kept constant, pi = 380 kPa. The oven temperature was measured at S-min intervals by a carefully checked mercury thermometer. The temperature-programming rate, P, was determined by a linear regression analysis of the oven temperature (read from the mercury thermometer) versus time
T= To + rt where T is temperature
(5) in “C and t is the time in min.
RESULTS AND DISCUSSION
Fig. 2 shows the separation of gasoline in a glass capillary column coatedwith OV-101 under LTPGC conditions, from 40°C at 0.9X! min-‘. Experimental values of the retention temperatures, TRE,were calculated for each peak from the retention rate, r, by substitution time, tR, and the corresponding temperature-programming into eqn. 1. Values of the retention temperatures were predicted from published Kovats indices, I, and their temperature coefficients, dl/dT, as well as from experimental retention temperatures of n-alkanes, TRE,zand TRE++Ir obtained by LTPGC at each temperature-programming rate, according to eqn. 4. Peaks on the chromatograms were “identified” by comparing their experimental, TRE,and predicted, T RP,retention temperatures, and considering the composition
m
4
to
50
40
m
Fig. 2. Chromatogram of gasoline on a glass capillary column coated with OV-101 under the conditions of LTPGC (from 40°C at O.YC min-I).
J. KRUF’CfK er
al
Fig. 3. Dependences of the isothermal and temperature-programmed retention indices on temperature for hydrocarbons between n-pentane and n-heptane in gasoline separated on the OV-101 capillary column.
of gasoline estimated by its separation on squalane6-s and polydimethylsiloxanesg~lo both isothermally and by LTPGC. The graphical prediction of retention temperatures, according to Fig. 1, is illustrated in Figs. 3-6 for compounds expected to be present in gasoline. The graphs demonstrate the changes in elution orders with the temperature-programming rates in LTPGC. The dashed lines in Fig. 6 correspond to the extrapolated dependences of the temperature-programmed retention indices, I, upon the retention temperatures, TRE, of n-nonane and Pr-decane. As shown previously2, the slope of this dependence for n-alkanes at a given temperature-programming rate is not constant and therefore the slopes of the extrapolated lines differ from those found for n-decane and n-undecane. However, the dashed lines can be used to estimate the elution order of compounds which at higher temperature-programming rates are eluted after ytdecane.
J. KRUPcfK
72
er al.
TABLE I EXPERIMENTAL, TRY, AND PREDICTED, Tnp, RETENTION TEMPERATURES IDENTIFIED IN GASOLINE BY CAPILLARY TEMPERATURE-PROGRAMMED GRAPHY ON OV-101
FOR HYDROCARBONS BUS CHROMATO-
Be = Benzene; Bu = butyl; Cy = cytlo; Dee = &cane; Et = ethyl; Hep = heptane; Hex = hexane; Me = methyl; Non = nonafie; Oet = octane: Pe = pentane; Pro = propyl. Peak No.
3 4 5 6 7 8 9 10 11 12 13 14 15 I6 17 18 19 20 21 22 23 24 25 26
.27 28 29 30 ~ 31 32 ‘. 33’ 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Abbreviation
2,2-DiMeBu CyPe 2,3-DiMeBu 2-MePe 3-MePe n-Hex MeCyPe 2,CDiMePe Be 3,3-DiMePe CyHex 2-MeHex 2,ZDiMePe l,l-DiMePe 3-MeHex I-cis-3-DiMeCyPe 3-EtPe I-trans-3-DiMeCyPe I-mm-2-DiMeCyPe n-Hep MeCyHex 1,1,3-TriMeCyPe 2,4-DiMeHex EtCyPe 2,5-DiMeHex l-tram-2-cis-4-TriMeCyPe 3,3-DiMeHex 1-tram-2-cis-3-TriMeCyPe 2,3,4_TriMePe MeBe 2,3-DiMeHex 2-Me-3-EtPe I,1 ,ZTriMeCyPe +feHep CMeHep 3,4-DiMeHex 3-MeHep 3-EtHex 1-cis-@ms-4-TriMeCyPe 1-cis-3-DiMeCyHex 1-trum-4-DiMeCyHex 1, I-DiMeCyHex I-Me-tram-2-EtCyPe I-Me-cis-3-EtCyPe 1-Me-tram-J-EtCyPe I-trans-2-DiMeCyHex
O.YC min-’ TRE
T RP
53.4 53.5 53.5 53.5 53.7 54.0 54.5 54.5 55.0 55.2 55.2 55.4 55.5 55.6 55.7 56.0 55.9 56.0 56.0 56.8 57.2 57.3 57.8 57.7 57.8 58.1 58.2 58.4 58.6 58.8 59.1 59.2 59.2 .59.5 59.6 59.6 59.9 59.9 60.0 60.1 60.1 60.4 60.6 60.8 60.9 60.9
53.3 53.3 53.6 53.6 53.8 54.8 54.8 55.4 55.6 55.7 55.9 55.9 56.1 56.1 56.3 56.4 56.4 56.5 57.9 58.0 5x.4 58.4 58.3 58.9 58.8 59.1 59.3 59.5 59.7 59.8 59.9 60.0 60.0 60.2 60.3 60.4 60.4 60.5 60.6 60.9 61.2 61.1 61.2 61.4
1.4”C minT RE 80.1 80.1 80.1 80.1 80.4 80.8 81.7 81.7 82.7 82.7 83.1 83.2 83.4 83.7 83.7 84.1 84.2 84.4 84.4 84.9 86.3 86.4 87.0 87.0 87.0 87.6 87.6 88.1 88.3 88.7 89.0 89.2 89.4 89.5 89.5 89.6 89.8 90.1 90.2 90.5 90.6 91.2 91.3 91.5 91.6 91.8
1
TRP 79.6 80.2 80.2 80.2 80.5 82.2 82.1 83.2 83.3 83.6 83.6 83.8 83.8 84.0 84.4 84.4 84.5 84.7 87.2 87.2 87.6 87.9 87.4 88.4 88.4 88.9 89.1 89.6 89.7 89.9 90.3 89.9 90.0 90.4 90.5 90.7 91.0 91.3 91.5 92.0 92.3 92.2 92.2 92.9
2.4”C mi?l-’
2.9”C minm’
TRE
TRP
TRE
TRP
115.5 115.5 lj5.5 115.5 f16.0 116.5 117.7 117.7 118.9 118.9 119.4 119.6 119.8 120.0 120.0 120.8 120.7 121.0 121.0 121.5 123.4 123.4 124.2 124.2 124.0 125.0 125.0 125.5 125.8 126.4 126.9 127.0 127.1 127.1 127.1 127.1 127.7 127.9 128.1 128.5 128.7 129.6 129.7 129.9 129.9 130.2
116.0 115.9 115.8 115.8 116.2
137.8 137.8 137.8 137.8 139.3 139.7 141.0 141.0 142.3 142.3 142.8 142.8 143.0 143.3 143.3 144.2 144.0 144.2 142.2 144.7 146.6 146.6 147.5 147.5 147.3 148.2 148.2 148.8. 148.8 149.6 149.6 149.6 150.2 150.2 150.2 150.2 150.8 150.8 150.8 151.7 151.9 152.8 152.8 153.2 153.2 153.5
138.3 139.2 139.0 139.0 139.4
118.5 118.1 119.7 119.8 120.4 119.9 120.3 120.8 120.4 121.2 121.0 121.4 121.5 125.2 125.0 124.9 125.8 124.6 126.3 126.2 127.0 127.1 127.9 127.6 127.9 128.9 127.6 127.8 128.6 128.5 128.8 129.7 130.2 130.3 131.2 131.2 131.0 131.1 132.4
141.9 141.4 143.2 143.2 143.9 143.2 143.6 144.3 143.7 144.6 144.3 144.8 144.9 148.9 148.5 14X.2 149.4 147.8 149.8 149.6 150.5 150.6 151.3 150.9 151.3 152.5 150.8 151.0 152.0 151.7 152.1 153.3 153.8 153.9 154.9 154.7 154.3 154.8 156.1
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
73
TABLE I (conrimed) P&Zk
Abbreviation
U.5”C iftin-’
1.4”C rniK’
2.4”C mine’
2.9”c min-
TRE
TM
TKE
TRE
TRP
TRE
TRP
61.8
92.2 92.4 92.7 92.7 92.9 93.5 94.1 94.1 94.5 94.9 95.2 95.5 95.5 95.1 95.5 96.3 96.3 96.3 96.7 96.9 97.0 97.6 97.7 97.7 98.0 98.3 98.7 98.7 98.8 99.2 99.2 99.2 99.8 Kg.3 100.3 100.4 101.5 101.5 104.0 105.7 107.8 107.8 108.3 108.3 108.8 109.8 109.8 110.8 111.1
130.7 130.7 131.5 131.5 131.2 132.3 132.3 132.9 133.4 133.7 134.0 134.6 134.8 134.8 134.0 135.5 135.2 135.5 136.1 136.1 136.2 136.9 137.0 136.9 137.5 131.9 138.2 137.9 138.2 139.2 139.2 138.9 138.9 138.9 140.0 140.0 14-1.4 141.9 143.8 146.0 148.2 148.2 148.7 148.7 149.2 150.4 150.4 151.6 151.9
132.7
153.8 153.8 154.7 154.7 154.3 144.5 154.3 156.1 156.7 156.8 157.6 157.8 158.4 158.2 157.6 158.8 157.6 158.8 159.3 159.3 159.3 160.3 160.6 160.3 161.0 161.3 161.7 161.3 161.7 161.7 161.7 162.5 142.7 162.5 163.5 163.5 165.2 165.8 168.0 170.4 173.1 172.3 173.7 173.7 174.1 175.7 175.7 177.1 177.1
156.5
’
NO.
“. ;
49 50 51 52 53 54 55 56 51 58 59 60 61 62 63 64 65 66 67 68 69 JO 71 72 73 74 75 16 77 78 79 80 82 83 85 86 87 88 95 100 106 107 108 109 110 111 112 113 114
I-cis-Zcis-3-TriMeCyPe n-act I-c&CDiMeCyHex I-tram-3-DiMeCyHex I-tram-2-DiMeCyHex IsoProCyPe 2,3,5-TliMeHex 1-h$&@-2-EtCyPe 2;4-DiMeHep 4,4-DiMeHep I -cis-2-DiMeCyHex 2,6-DiMeHep n-ProCyPe EtCyHex 2,5-DiMeHep 1,1,3-TriMeCyHex 3,5-DiMeHep 3,3-DiMeHep 2,4-DiMe-3-EtPe 2,3,3-TriMeHex l,l,CTriMeCyHex 2,2,3,3_TetMePe EtBe 2,3,4-TriMeHex 3,3,4-TriMeHex 1-cis-3-cis-STriMeCyHex 1,3-DiMeBe 2,3-DiMeHep 1,CDiMeBe 3,4-DiMeHep 3,QDiMeHep 4-EtHep 4-MeOct Z-MeOct J-EtHep 3-MeOct I,2-DiMeBe 1,l ,ZTriMeCyHex n-Non i-ProBe 3,5-DiMeOct 3,5-DiMeCkt n-BuCyPe EtCyHep 2,dDiMeOct n-ProBe 2-Me-3-EtHep 1-Me-3-EtBe l-Me-4-EtBe
61.2 61.6 61.6 61.6 61.6 62.1 62.6 62.7 62.9 63.3 63.3 63.7 63.7 63.7 63.8 64.1 64.3 64.4 64.5 64.6 64.8 65.1 65.2 65.2 13 65.4 65.5 65.9 66.0 66.1 66.3 66.3 66.5 66.8 66.9 67.4 67.6 68.0 68.6 70.5 71.4 73.2 73.4 13.7 73.9 14.4 74.8 75.1 75.7 75.9
62.0 61.9 61.4 62.5 63.1 63.4 63.7 64.0 64.0 64.3 64.3 64.4 64.8 64.9 65.0 65.1 65.3 65.4 65.5 66.0 65.9 66.0 66.3 66.5 66.7 66.9 66.8 66.9 66.9 67.1 67.4 67.6 67.9 68.0 68.7 68.9 12.0 74.0 73.X 74.4 74.7 74.9 75.6 15.8 76.5 76.8
TRP
93.4 93.9 93.9 93.2 94.1 94.8 95.7 95.4 95.9 96.8 96.0 96.4 97.1 97.1 97.8 97.1 97.5 98.0 98.2 98.3 99.3 99.2 9x.9 99.7 100.3 100.0 99.4 loo*0 100.0 99.7 99.7 100.1 100.1 100.9 101.1 102.9 103.6 107.0 109.6 108.1 109.8 109.9 109.4 111.4 110.8 112.4 112.7
133.8 133.7 133.0 134.8 133.8 135.7 134.2 13.5.2 137.4 134.7 135.6 137.4 136.6 138.2 136.3, 137.0 138.2 138.2 138.3 140.0 139.8 139.0 140.5 141.7 140.5 138.9 140.4 140.0 139.3 139.2 139.6 139.4 140.4 140.7 144.3 145.7 148.9 152.1 148.8 151.8 151.7 150.2 154.0 152.1 154.9 155.4
158.0 151.9 157.2 159.1 157.4 160.0 157.7 159.0 162.1 158.1 159.4 161.9 160.6 162.9 160.1 160.9 162.6 162.6 162.7 164.8 164.5 163.4 165.4 167.0 165.1 162.8 165.0 164.3 163.4 163.0 163.5 163.2 164.4 164.8 169.5 171.5 174.9 178.8 173.8 178.1 177.8 175.4 180.8 177.8 181.2 182.4
74
J. KRUPCiK
et al.
TABLE I (cor&wd)
Peak No.
115 116 117 118 119 121 122 I23 124 125 131 132 133
Abbreviation
4-EtOct 1,3,5-TriMeBe 2,3-DiMeOct 5-MeNo 4-MeNo 2-MeNo 3-EtOct 3-MeNo tBuBE 1,2,4-TriMeBe IsoBuBe sec.-BuBe iZ-Dee
0.5”C mifl-l
1.4”C min-’
2.4”C min-l
2.9”C min-’
TRE
TRP
TRE
TEP
TRB
TRP
TRE
TRP
76.1 76.7 77.0 77.6 77.8 78.2 78.6 79.0 79.7 79.7 81.5 82.0 82.9
77.0 77.5 77.8 78.0 78.3 78.6 79.0 79.4 80.4 80.6 82.3 82.7
111.1 111.7 112.0 112.4 112.8 113.1 113.7 114.1 115.6 115.6 117.3 117.8 118.4
111.7 113.5 114.3 112.8 113.2 113.6 114.1 114.5 117.0 117.4 119.3 119.6
151.9 152.4 152.8 153.3 153.5 154.0 155.0 155.0 157.1 157.1 158.5 158.8 160.0
152.7 156.2 157.7 153.7 154.4 154.7 155.3 155.8 160.4 160.9 163.0 163.2
177.5 178.0 178.5 178.5 179.3 179.7 180.9 180.9 183.3 183.8 185.5 185.5 186.4
178.1 183.5 185.4 179.2 180.1 180.4 181.1 181.8 188.2 189.0 191.2 191.3
to compound, indicating that their values depend not only on temperature differences between the oven and column but “inter ah” also on the nature of the compounds and other factors. It should also be noted that the Kovats indices, I, and their temperature coefficients, dl/dT, are valid only in a narrow temperature region1 l and their extrapolation to higher temperatures can be a source of serious errors. The Kovats indices published by Lubeck and Sutton5 were obtained at 6O”C, and their use for prediction of retention temperatures above 120°C is very problematic; the data for above 120°C given in Tables I and II have high errors. The knowledge of the coefficients A, B and C enabled us to predict retention temperatures for the temperature-programming rates of 0.9 and 1.9”C min- r using the rearranged eqn. 6: TRC
= A + BTRp + Cr
(7)
The values of TRC found are in very good agreement with experimental data, as shown in Table II, with’the exception of overlapped peaks and retention temperatures above 120°C. CONCLUSIONS
Relation temperatures, TRp, were predicted for the main constituents found in gasoline by linear temperature-programmed capillary gas chromatography on OV101 from isothermal Kovats indices, I, their temperature coefficients, dI/dT, and experimental retention temperatures for n-alkanes, TRE,z and TRQ+ 1. The values were in relatively good agreement with experimental data, TRE. From experimental, TRE, and predicted, TRp, retention temperatures obtained at four different programming rates, r, the coefficients A, B and C of the equation TR, = A + BTRp + Cr were calculated by multiple linear regression analysis. Using these coefficients it was
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
75
TABLE II COEFFICIENTS OF EQN. 6 CALCULATED FROM THE DATA GIVEN IN TABLE I BY MULTIPLE LINEAR REGRESSION ANALYSIS, AND COMPARISON OF RETENTION TEMPERATURES FOUND EXPERIMENTALLY, TRE,AND THOSE CALCULATED FROM EQN. 6, TRc Peak No.
3 4 5 6 7 9 10 11 12 13 14 15 16 17 18 19 20 21 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 41 48 49 51 52 53 54
A
2.463 4.026 3.592 3.592 -0.387 -0.152 -0.590 0.042 -0.676 0.473 0.136 0.150 2.345 0.020 -0.188 0.564 1.771 1.257 2.066 1.386 -0.482 0.925 -0.412 1.347 0.195 0.845 2.186 0.395 2.373 3.735 2.425 0.602 0.025 1.199 -0.931 1.815 4.111 1.456 1.096 2.242 0.783 - 1.536 0.437 0.856 2.183 3.617 3.217 6.473 38.738
B
0.945 0.890 0.901 0.901 1.009 l.ooo 1.008 0.992 1.011 0.979 0.982 0.987 0.930 0.990 0.998 0.972 0.945 0.956 0.939 0.955 0.998 0.966 0.999 0.951 0.985 0.968 0.934 0.979 0.929 0.898 0.933 0.974 0.992 0.964 1.015 0.948 0.900 0.965 0.969 0.942 0.973 1.034 0.989 0.979 0.944 0.918 0.929 0.866 0.092
c
1.572 3.400 3.086 3.086 -0.325 -0.241 -0.330 0.088 -0.616 0.487 0.698 0.404 2.279 0.366 0.024 1.075 1.898 1.529 1.613 1.154 0.027 0.744 0.005 1.480 0.236 0.754 2.033 0.354 2.458 3.479 1.896 0.930 0.136 0.865 -0.753 1.665 2.995 0.640 0.557 1.566 0.512 - 1.665 -0.039 -0.091 1.351 2.081 1.650 4.040 34.685
OYC min-I
1.9”C min-’
7kE
TR.8
66.1 66.3 66.3 66.3 66.5 67.5 67.5 68.3 68.4 68.7 68.8 68.9 69.1 69.1 69.6 69.5 69.7 69.7 71.2 71.3 71.9 71.4 71.9 72.0 72.4 72.8 73.0 74.0 73.7 73.8 73.8 74.0 74.0 74.2 74.3 74.6 74.7 74.8 75.0 75.4 75.6 75.8 75.9 75.9 16.3 76.8 76.8 76.9 77.5
TRC
66.31 66.14 66.12 66.12 66.40 61.41 67.47 68.14 68.31 68.46 68.63 68.79 68.97 69.02 69.39 69.29 69.46 69.44 71.03 71.18 71.89 71.66 71.83 72.13 72.30 72.69 72.78 74.05 73.50 73.65 73.71 74.00 74.14 74.05 74.49 74.49 74.51 74.86 74.88 75.28 75.49 75.76 75.84 75.98 76.26 76.65 76.72 76.67 77.14
99.5 99.8 99.7 99.7 100.0 101.5 101s 102.6 102.7 103.1 103.3 103.5 103.8 103.8 104.3 104.5 104.7 104.7 106.8 106.8 107.7 107.7 107.5 108.3 108.3 108.9 109.1 109.6 110.0 110.2 110.4 110.4 110.4 110.6 110.9 111.1 111.2 111.6 111.8 112.5 112.7 112.9 113.0 113.2 113.8 114.2 114.2 114.4 115.1
TRC
99.43 99.36 99.33 99.33 99.86 101.54 101.52 102.63 102.67 103.11 103.31 103.52 103.81 103.73 104.46 104.39 104.64 104.61 106.82 106.91 107.75 107.68 107.60 108.34 108.37 108.88 109.10 109.66 109.95 110.08 110.30 110.39 110.48 110.47 110.98 111.13 111.18 111.67 111.78 112.57 112.69 112.97 112.97 113.30 113.67 114.25 114.24 114.99 115.42 (Continued on p. 76)
Peak
A
3
c
0.9-c #tin-’
I.932 w&l-’
TkE
TRC
TRE
78.0 78.1 78.4 1.8 78.9 79.4 79.4 79.4 79.7 79.9 80.0 80.2 80.4 80.5 80.6 81.1 81.2 81.2 81.4 81.6 82.0 82.0 82.0 82.1 82.3 82.3 82.9 83.0 83.7 83.8 84.5 85.1 88.3 89.6 89.6 90.7 91.0 91.4 92.0 92.3 93.0 93.3 93.7 94.0 94.2 94.8 95.1 95.4 95.8 96.3 97.4 97.5 99.3 99.9
77.71) 77.98 78.34 78.40 78.73 79.22 79.30 79.23 79.40 79.67 79.76 79.94 80.09 80.19 80.34 80.74 80.98 80.93 81.14 81.26 81.78 81.74 81.97 82.07 82.1-l 82.49 82.81 83.05 83.48 83.69 84.22 84.64 87.97 89.92 90.08 90.51 90.67 91.28 91.75 92.09 92.78 92.91 93.31 93.66 93.94 94.72 95.02 95.36 95.93 96.25 97.07 97.07 98.99 99.34
-115.1 115.8 116.2 116.5 117.0 117.2 117.6 117.6 117.2 118.2 118.0 118.2 118.7 118.8 118.9 119.6 119.7 119.6 120.1 120.4 120.8 120.7 120.8 121.0 121.2 121.2 121.7 121.7 122.6 122.6 124.0 124.6 128.8 130.1 130.1 131.7 131.7 132.2 133.1 133.1 134.7 135.0 135.0 135.5 135.8 136.4 136.7 137.1 137.6 138.2 140.0 140.2 142.1 142.4
No.
55 56 57 58 59
60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 z 77 78 79 80 82 83 85 86 87 88 100 IO6 107 108 109 110 111 112 113 114 115 116 117 118 119 121 122 I23 124 125 131 132
10.453 3.852 0.m 4602 4.558 0.843 -0.725 4.851 0.208 6.714 9.236 1.595 6.038 6.189 6.541 6.690 4.792 5.491 6.568 9.273 5.942 4.306 6.008 12.077 11.741 1.247 2.221 5.574 2.886 2.971 7.983 6.702 9.729 9.853 8.340 7.064 5.348 1.960 8.643 1.758 7.696 11.246 -0.973 9.049 9.383 2.387 -0.538 -0.807 -1.381 0.733 9.833 7.027 4.676 6.944
0.759 0.910 0.982 0.878 0.899 0.965 1.003 0.888 0.983 0.846 0.786 0.954 0.859 0.856 0.851 0.849 0.894 0.873 0.852 0.796 0.866 0.892 0.867 0.733 0.733 0.960 0.943 0.877 0.929 0.931 0.834 0.874 0.813 0.817 0.839 0.869 0.898 0.958 0.843 0.961 0.861 0.797 1.002 0.841 0.841 0.952 1.004 i ,009 1.016 0.983 0.835 0.881 0.928 0.894
8.413 2.320 0.666 4.348 2.512 1.539 -0.249 3.295 -0.196 4.934 7.771 I.290 4.720 4.827 4.950 4.712 3.030 4.201 4.670 6.607 ,4.426 4.039 4.367 10.104 10.216 1.678 2.134 4.729 2.733 2.435 5.446 3.221 6.384 5.914 6.238 4.098 2.978 1.404 5.032 1.043 4.450 7.056 -0.002 5.005 4.562 1.917 -0.336 -0.495 -0.595 0.469 5.586 3.527 1.131 2.589
T RC 115.02 115.78 116.31 116.45 116.93 117.32 117.56 117.51 117.25 118.10 117.72 118.24 lL8.64 118.73 118.82 119.42 119.67 119.52 120.05 120.25 120.75 120.57 120.84 120.69 121.14 121.50 121.83 121.90 122.63 122.64 123.78 124.29 128.32 130.60 130.55 131.20 131.30 131.96 132.86 133.02 133.98 134.45 134.59 134.85 135.24 135.85 136.34 136.73 137.60 137.83 139.25 139.45 141.24 141.56
PREDICTION
OF RETENTION
TEMPERATURES
IN GC
77
possible to calculate retention temperatures, TAC,which coincide with experimental values, TRE, within the errors of laboratory temperature measurements ( f G!T). This precision allowed us to identify over 100 hydrocarbons in gasoline analyzed by LTPGC using published isothermal Kodts retention indices. REFERENCES 1 J. Curvers, K. Knauss, P. Larson, .I. Rijks and C. Cramers, in P. Sandra and W. Bertsch (Editors),
2 3 4 4 6
Proceedings of the Vlth International Syrnposittm on Capillary Chromatography, Riva de! Garda, May 1985, Htithig, Heidelberg, 198.5,p. 744. J. Kru#ik, P. Cell&r, D. Repka, J. Garaj and G. Guiochon, S. Chromatogr., 351 (1986) 1 il. J. Q-up&k, D. Repka, T. Hevesi and J. Garaj, J. Chrmatogr.. 406 (1987) 117. J. Krup&k, M. Kristin, M. Valachovicovi and $.Janiga, J. Chromatogr., 126 (1976) 147. A. J. Lube& awl D. L. Sutton, J. High Resolwt. Chrwnatogr. Chromatogr. Commun., 6 (1983) 328. I. M. Whittemxe, in K. H. Alget and T. H. Gouw (Editors), Chromatography in Petroleum Analysis,
Marc& Dekker, New York, 1979, p. 50. 7 E. M&so&, J. KrupEik, P. CelIlr and J. Garaj, J. Chromatogr., 303 (1984) 151. 8 E. Matisoti, J. KrupCik, P. Cell&r and A. K&an, 1. Chromtogr., 346 (1985) 177. 3 N. G. Jahansen, L. S. Ettre and R. L. Miller, J. Chrwmtogr., 2% (1983) 393: 10 R. L. Miller, L. 9. Ettre and N. G. Jahansen; d. Chronmtogr., 259 (1983) 393. 11 L. S. Ettre, Chramatagraphia, 7 (1974) 39.