melted, stirred, and cooled. The results of these determinations showed a standard deviation of *2%. Table I1 compares results from the analysis of unknown blends by three methods. Mass spectrometry, utilizing a heated sample system, while able to detect Ionol a t a concentration of 2 p,p.m., has a precision of only about &20% of the amount present for the concentration range shown in this table. For that reason, the agreement between the mass spectrometry results and the infrared and ultraviolet results is poor. The agreement between infrared and ultraviolet analysis is considerably better and on the order of 4% of the amount present. This method was applied to the determination of other additives and
etermi nati
certain impurities in polyethylene. To determine unknowns, about 50 grams of polyethylene were shaken overnight with 100 ml. of solTrent. After the solvent was separated, it was examined spectroscopically. When necessary, the solvent was evaporated to concentrate the extracted unknowns. ACKNOWLEDGMENT
(2) Klute, P. J., Franklin, P. J., J . Polymer Scz. 31, 162 (1958). (3) LeBlano, R. B., “New Techni ues in
the Infrared-Mass Spectrometrylaboratory,” Gulf Coast Spectroscopic Meeting, Beaumont, Tex., September 1957. (4) Miller, R.G. J., Willis, H. A,, Spectrochim. Acta 14, 124 (1959). (5) Myers, A. W., Rogers, C . E., Stsnnelt, V., Szwarc, M., Modern Plastics 34, No. 9, 157 (1957). (6) Nawakowski, -4. C., ANAL. CHEU. 30,1868(1958).
The authors acknowledge assistance furnished by L. C. Shepard and T.V. M. Weddell. They also thank J. R. Davis for supplying the standard material.
(7) Pinsky, J., Modern Plastics 34, 145 (April 1957). (8) Richards, R. B., Trans. Faraday Soc.
LITERATURE CITED
RECEIVEDfor review Bpril 18, 1960. Accepted August 1, 1960. Pjttsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1960.
( 1 ) Hilton, C. L., ANAL. CHEM.32, 383 (1960).
42, 10 (1946).
etramethyllead and Tetraethyllead ss Spectrometry
H. E. HOWARD, W. C. FERGUSON, and L. 8. SNYDER Research Department, Union Oil Co. of California, Brea, Calif. Standard procedures in the oil industry for determining tetraethyllead additive in gasoline are based on determination of the lead and calculation of a tetraethyllead concentration from the lead value. These procedures cannot be used when both tetraethyl- and tetramethyllead fluids are used as additives and where a knowledge of the concentration of either or both of them is required. An accurate mass spectrometric procedure has been developed which permits the rapid analysis of gasoline for tetramethyl- and/or tetraethyllead. Of the literature pertinent to tetraethyllead (TEL) indicates that its determination in gasolines has not been carried out as a direct procedure. The amount of lead in a sample of known volume is determined and the TEL concentration is calculated from this value. Lead may be determined by polarographic ( I ) , chemical (8, 6),colorimetric (7), x-ray spectrometric (6),and x-ray absorptiometric (5, 4) procedures. Use of the foregoing procedures is contingent upon knowledge of the nature of the compound of which lead is a part. If the compound is TEL, any of these methods Fill give adequate results. The use of TML (tetramethyllead) as an additive has been noted recently in the petroleum industry, both by itself and in conjunction with TEL. Where B knowledge of the N EXAMINATION
1814
e
ANALYTICAL CHEMISTRY
concentrations of the two lead compounds individually is required, none of the standard methods for determining lead are useful since they all determine lead without respect to its origin. A mass spectrometric method has been developed in this laboratory for the direct determination of both TML and TEL in gasolines, regardless of whether only one or both of these compounds is present. The Concentration of TML and T E L fluid in gasolines is determined in milliliters per gallon by comparing the mass spectrum of the sample with mass spectra of two synthetic gasoline blends, one having a known concentration of
Table I. Mass Spectrometric Results on Known Blends of TML and TEL in Gasoline
(411 values in milliliters of TML or TEL fluid per gallon) TML TEL SynsynBlend M.S.= thetic M.S. thetic 1
2
x
4 5
6
7 8
0.14 0.50 n 74
i.18 1.52 2.27 2.52 2.91
0.14 0.50
o
75
i.20 1.50 2.25 2 50 2.86
Mass spectrometry.
2.92 2.51 2.21 1.88 1.52 0.75 0.51 0.17
2.86 2.50 2.25 1.80 1.50 0.75 0.50
0.14
TML and the other a known concentration of TEL. EXPERIMENTAL
Apparatus. A Consolidated Electrodynamics Co. mass spectrometer Model 21-102 modified to 21-103C1 with a high speed amplifier, was used. The magnet current was 1.05 amperes and the isatron temperature was 270’ C. The ionizing voltage was carried a t 70 volts and the ionizing current a t 100 pa. A constant volume pipet (0.002 ml.) and a mercury orifice system were used to introduce samples into the mass spectrometer. Calibration. Prepare two synthetic blends, one with 3.0 ml. of TML fluid per gallon (in any normal gasoline stock), and the other with 3.0 ml. of T E L fluid per gallon. Obtain the mass spectrum of each blend, scanning through m/e+ 295. On the TEL mixture, measure the peak height of m/e+ 295; on the TML mixture, measure the peak height of m/e+253. Procedure. After calibration runs are completed, scan the sample in exactly the same manner. Sample size must be identical to t h a t of the standard. Measure the peak heights at m/e+ 253 and 295. Calculate TML and TEL concentrations as follows:
TML in ml./nallon - = sample 253 peak X 3.00 standard 253 peak TEL in ml./gallon = eample 295 peak X 3.00 standard 295 peak
Accuracy. Eight synthetic mixtures of T M L fluid, TEL fluid, and gasoline were prepared and analyzed by the mass spectrometric method. The results, given in Table I, show excellent agreement. Three ASTM cooperative samples of T E L in gasoline and seven service station gasolines of various brands were analyzed by the new method and ASTM Method D-526. These results, shown in Table 11, are in good agreement, illustrating the compatibility of the two methods where only T E L is present. DISCUSSION
One possible limitation regarding the ability of the new method to differentiate between T M L and T E L in gasoline could be the use of some additive which might mask the presence of T M L a t m/e+ 253 or T E L a t m/e+ 295. Even if an additive of this sort were used, its presence would be easily recognized and appropriate corrections could be made. Analysis of gasolines containing T M L and T E L was attempted with a high
Table 111. TEL Content of ASTM Cooperative Samples and Commercial Gasolines
(All values in milliliters of TEL per gallon; samples 4 to 10 are commercial gasolines) ASThl M.S. D-526 ASTM-1 4.68 4,750 ASTM-2 0.49 0 . 46a ASTM-3 2.97 2 , SAa 4 0.54 0.52 0.55 0.55 5 2.75 2.78 2.82 2.94 6 2.48 2.75 2.50 2.77 7 0.44 0.45 0.44 0 46 8 2.84 3 02 2.91 9 0.94 0.91 0.98 10 3.14 3.28 3.30 3.39 a Average of 22 separate determinations on each sample by six different laboratories.
molecular weight mass spectrometer. The sample was inserted by capillary dipper through a liquid gallium valve into an inlet system heated to 300” 6. No TRIL or TEL peaks were observed. The lead compounds either decomposed under these conditions or did not pass through the gallium. LITERATURE CITED
(1) rlm. SOC. Testing Materials, Phil-
adelphia, Pa., “ASTPYI Standards on Petroleum Products and Lubricants,” Designation D 1269-58, p. 716, 1959. (2) Am. SOC. Testing Materials, Philadelphia, Pa., “ASTM Standards on Petroleum Products and Lubricants,” Designation D 526-56, p. 267, 1959. (3) Calingaert, George, Lamb F. IT., Miller, H. L., Koakes, G. h., ANAL. CHEM.22, 1238 (1950). (4) Hughes, Harold K., Hochgesang, Frank P., Ibid., 22, 1248 (1950). (5) Lamb, F. W., K’iebylski, L. AI., Kiefer, E. W., Ibid., 27, 129 (1955). (6) Russ, John J., Reeder, Wendell, Ibid., 29, 1331 (1957). (7) pmith, V. A., Dilaney, W.E., Tancig, M , J., Bailie, J. C., Ibid., 22, 1230 (1950). RECEIVEDfor review June 27, 1960. Accepted September 19, 1960.
Instrumental Measurement of Total Ionization in the Mass Spectrometer H.
E. LUMPKIN and J. 0.BEAUXIS
Humble Oil & Refining
Co., Baytown, rex.
b The successful development of quantitative analytical procedures with the mass spectrometer requires that the amount of calibrant materials charged to the instrument be known. Equipment has been designed and installed in a commercial analytical mass spectrometer which allows direct instrumental measurement of a signal proportional to the amount of sample charged. The electrodes normally used to repel ions from an ionization chamber are biased negative with respect to the chamber body and the total ion current collected is amplified and measured. Data on pure compounds indicate that the observed peak height/total ionization ratio is more reproducible than replicate charges with a constant-volume pipet.
I
of mass spectrometric methods for the analysis of high boiling liquid or solid samples of petroleum and petroleum-derived mateN THE DEVELOPMEST
rials, a major difficulty has been the inability to determine accurately the amount of sample introduced into the inlet system of the mass spectrometer. Although micromanometers are used to measure pressures in inlet systems operating up to 150” C., they are not designed t o function a t the higher temperatures (ca. 250” to 300” C.) required for complete vaporization of high boiling fractions. The use of total-delivery, constant-volume pipets (9) for charging liquid calibrants and samples has resulted in many procedures ($, 3, 7 ) . The accuracy of these procedures is dependent on the reproducibility of the charging technique and, although the Humble Laboratories claim a reproducibility to about 1 to 1.5yG, most groups have not achieved this value. Hood (4) expects a possible error of 1 5 to 10% in determining peak heights per unit volume of sample, and Kearns, ilIaranomski, and Crable (6) quote sample volume reproducibility as “within 37&” Otvos and Stevenson (8) suggest that
*
the total ion intensity (21) is an approximate measure of the liquid volume of hydrocarbons containing eix or more carbon atoms per molecule charged to the mass spectrometer. In two more recent papers Hood (4) and Crable and Coggeshall (1) have independently used total ionization principles as a means of standardizing mass spectia and as the basis for compound type analyses for naphthas and higher boiling petroleum fractions. Measuring and summing the peak heights of each peak above mass 38 are required for each spectrum in order to determine 21. In a series of articles Tate and Smith (IO) determined ionization potentials and relative ionization cross sections for a number of mono- and diatomic gases. A parallel plate on one side of their ionization chamber mas electrically biased to collect ions. Otvos and Stevenson (8) and Lampe, Franklin, and Field (6) modified commercial mass spectrometers to allow measurement of total ion currents from which ionizaVOL. 32, NO. 13, DECEMBER 1960
o
1815
