quired, a Clairex 603 low-resistance, fast-response photoconductor was chosen. The rapid response is essential because of the inevitable time delay in the transportation of the coolant through the exhaust line into the oven. If the response of the photoresistor is too slow, close regulation of the temperature is not possible. The line-valve solenoid, which is of the normally closed type, requires that the sensitive electronic relay be one that can be used in the reverse position-Le., the relay power is o n when the exciting signal is off. I n this way the solenoid is opened when the neon light is off and hence when no current is going to the heaters. The relay used in these laboratories is of the Fisher-Serfass type and it meets these requirements. Any other type of relay (solid-state or tube-type) can be used provided it is equipped with a "normally-of' outlet. A "normally-on" relay may also be used in conjunction with a "normally-open" solenoid line-valve.
Care should be taken to place the line-valve as close as possible to the oven. If exhaust tubes from the valve to the oven are long-e.g., more than 6 inches-coolant which is contained in the exhaust tube will continue to evaporate after the linevalve is closed and tend to drive actual temperatures beyond the control point. The above modification was effected o n a Varian-Aerograph Model 1520-1B, and experience in these laboratories indicates that very satisfactory temperature regulation (f1O C) can be achieved in this way. Components which we have found suitable for the control unit are: a n ASCO solenoid valve for C o n , 1000 psi., No. 8264C3; a Fisher-Serfass electronic relay; a Clairex 603 photosensitive resistor; and a miniature neon panel-light (NE23 ; 60-90 V starting voltage). RECEIVED for review May 8, 1967. Accepted June 20, 1967
Determination of Methyl Ethyl Lead Alkyls and Halide Scavengers In Gasoline by Gas Chromatography and Flame Ionization Detection Nestor L. Soulages
Laboratorio P e t r o t h i c o , Yacimientos Petroliferos Fiscales, Florencio Varela, Repu'blica Argentina THEDETERMINATION of lead antiknock compounds and halide scavengers in gasolines by gas chromatography and flame ionization detection was described in a previous paper ( I ) . The lead and halogenated compounds are catalytically hydrogenated, and the resulting methane and ethane are separated from gasoline hydrocarbons and measured. In the case of gasolines with the five methyl ethyl lead alkyls, the simultaneous determination of scavengers was not possible because of interference with the hydrogenolysis products of lead compounds. This limitation was solved using a 1,2,3 tris-(2-~yanoethoxy)propane(TCEP) partition column instead of a polypropylene glycol 400 column.
EXPERIMENTAL Equipment and Columns. The equipment employed was the same as described previously ( 1 ) The partition column was prepared by filling a 150-cm length of 0.4-cm id copper tubing with 20 % TCEP (laboratory-prepared) o n 30/60 Chromosorb P precoated with 1% KOH. The adsorption column was made from 80 cm of the same tubing charged with activated charcoal which was modified by the addition of 3 liquid petroleum jelly. The working temperature was 80' C and the hydrogen flow was 40 ml/minute. RESULTS AND DISCUSSION The excellent selectivity of TCEP is well known; a t temperatures over 50" C, dichloroethane (b.p. 83.5' C) is eluted after tetraethyl lead (b.p. 200" C), which is the lead compound of highest boiling point. The relative retention of dichloroethane as compared with tetraethyl lead rises with the temperature, and to attain a complete separation of both compounds it is necessary to work a t 80" C, which is the maximum recommended temperature for this stationary phase. The background is high, but despite this it is possible to work with a detector sensitivity that permits a good chromatogram to be obtained by injecting only 5 p1 of gasoline. According to ~~
ANALYTICAL CHEMISTRY
7
20
IS
IO
i
b
T i m * , Yinulss
Figure 1. Gas chromatographic separation of Tetramix components 150-cm X 0.4-cm id, 20 TCEP on Chromosorb P precoated with 1 % KOH. Temperature: column 8 3 T , injector 160°C. Carrier gas H1: 65 ml/minute 1. MerPb 2. Me3EtPb 3. Me2Et2Pb 4. MeEtsPb 5. EtaPb and toluene 6. EtCL 7. EtBr2 Table I. Analysis of Tetramix Mole % Wt % 3.23 4.38 MelPb 9.47 13.53 Me3EtPb 16.19 24.29 Me2Et2Pb 10.40 16.36 MeEt3Pb 2.09 3.43 EtaPb 39.68 19.94 Etch 18.94 18.07 EtBrz
Compound
Chovin ( 2 ) it is thought that tetracyanoethylated pentaerythritol can advantageously replace TCEP because of its greater stability with temperature.
~
(1) N. L. Soulages, ANAL.CHEW,38,28 (1966).
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3
(2) P. Chovin, Bull. SOC.Chim.,1964, 1800.
Table 11. Determination of Methyl Ethyl Lead Alkyls and Halide Scavengers in Gasolines Grams per liter Grams of lead per liter Compound Added Found Added Found Me4Pb 0.053 0.050 0.053 0.050 0.041 0.039 0.041 MeaEtPb 0.162 0.160 0.159 0.164 0.119 0.118 0.117 Me2Et2Pb 0.291 0.297 0.296 0.283 0.204 0.208 0.208 0.196 0.193 0.190 0.190 0.131 0.129 0.127 MeEtsPb EtaPb 0.041 0.043 0.043 0.040 0.026 0.028 0.028 0.239 0.231 0.248 0.245 EtC12 0.217 0.211 0.225 0.210 EtBr, Total 1.200 1.185 1.214 1.182 0.521 0.522 0.521
-
0.039 0.121 0.198 0.127 0.026 0.511
T C E P was employed by Barrall and Ballinger (3) and Bonelli and Hartmann (4) to avoid interference by the halogen derivatives in the determination of lead alkyls with electron capture detection. In both instances the column was made by employing silanized Chromosorb o r silanized Chromosorb W as the solid support. Observations in the course of the present work indicate that the lead alkyls are decomposed in columns of 20% T C E P o n silanized Chromosorb W a t 50" C. It is possible that this decomposition is one of the causes of the anomalous response factors found by the above authors. Chromosorb P alkalinized with 1 % KOH works satisfactorily up t o 100" C, the maximum temperature tested. Columns of polypropylene glycol 400 o n Chromosorb P which have not been alkali-treated d o not decompose these substances. Figure 1 shows the separation of the components of Tetramix (Du Pont) using conventional chromatographic apparatus. The overlapping of tetraethyl lead with toluene can be disregarded in this case because the latter is retained in the charcoal column. Analysis of gasolines containing Tetramix is made in 22 minutes (Figure 2), using for the calculations the peaks numbered 1,2,5,6,7,8, and 9 which are free of interferences. In the case of gasolines with high ethane and propane content (retention times indicated in the chromatogram), it may be advisable t o eliminate them partially to avoid interference with neighboring compounds; this is easily accomplished by bubbling nitrogen through the sample. This method can also be used to determine the composition of additives, the only limitation being that toluene is not determined. After convenient dilution with n-heptane they are handled as gasoline and d o not require previous calibration. F o r the calculations, the peak areas are corrected by factors which are theoretically deduced from the number of
moles of methane or ethane produced per mole of each component and by the relative molar response of ethane as related to methane (1.88). Table I shows the composition of Tetramix as determined by this method, working with a 1 :500 dilution in n-heptane. The toluene concentration which is not included in the result is 7.15 Z (wiw). Table I1 shows results obtained in three replicate analyses of a gasoline with 1.20 grams of Tetramix per liter, disregarding the toluene content. The quantitative calculations are made by comparison with standards using the procedure described in (1). The concentration of each lead compound and halogen derivatives in the standard are obtained from the data of Table 1.
(3) E. Barrall and P. Ballinger, J . Gas Chromafog., 1 , 7 (1963). (4) E. Bonelli and H. Hartmann, ANAL.CHEM., 35, 1980 (1963).
RECEIVED for review November 21, 1966. Accepted May 1, 1967.
I
,
20
10
IO
a
2
b
T i m a , Minutas
Figure 2. Analysis of Tetramix in gasoline 1. 2. 3. 4. 5. 6. 7. 8. 9.
CHI from Me4Pb CHI from MesEtPb CH4 from MesEttPb CH4 from MeEt3Pb and C2H6 from MesEtPb C2Hs from Me2Et2Pb c& from MeEt3Pb C2H6 from Et4Pb CPH6from EtC12 C2Hs from EtBr2
VOL. 39, NO. 1 1 , SEPTEMBER 1967
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