isothermal operation of the column at 25" and 40' C. Kieselbach has given a modified form of this equation and a detailed discussion of the terms involved (1). If i t is assumed t h a t the partitioning agent is present on the packing material of the column as a solid at room temperature and as a liquid a t the elevated temperature used in these studies, a preliminary consideration would suggest that the diffusion coefficient of the gaseous sample into the liquid phase might be a controlling factor in determining the HETP. Proceeding with this idea, the WET? of the eicosane column \vas found to be 0.60 a t room temperature and 0.42 a t 40' C. for nbutane. Within the accuracy of our data this quantity may be given b y HETP
=
.4 f B Dgo -f
:
UO
p--
(1
-
(pL?po)
where the terms conform to the nomen-
clature of Kieselbach (1). The terms A and B Dg,/% were determined experimentally under the two isothermal conditions and the various parameters evaluated for our conditions of flow rate, pressure, etc. These data then led t o the relationship
ions about the factors involved in column operation. T h e inverse programming method, however, appears t o be a useful analytical technique, and its extension t o other types of columns where feasible operating temperatures straddle the melting point of the substrate may improve column efficiency. LITERATURE CITED
I n view of published values for diffusion coefficients for analogous systems, this ratio appears too low t o attribute the change in column resolution primarily to the difference in the rate of diffusion of the gaseous sample into the . effecpartitioning phase. Since d ~ the tive film thickness, probably is not very different for these two conditions, the constant C, the coefficient of resistance to mass transfer in the partitioning agent, is apparently a n important factor in this phenomenon. The extent of the data obtained is insufficient to allow any further conclus-
(1) Kieselbach, R., ANAL. CHEM. 33, 23
(1961).
(2) Meyer, R. A., in "Gas Chromatogr a p h y , " ~ 93, . V. J. Coates, H. J. Noebels,
I. S. Fagerson, eds., Academic Press, New York, 1958. (3) Taramasso, M., Ric. Sci. 2 6 , 887 (1956). T. 0. TIERNAN J. H. FUTRELL
Chemistry Research Laboratory Aeronautical Research Laboratories Office of Aerospace Research Wright-Patterson Air Force Base, Ohio
RECEIVEDfor review August 31, 1962. Accepted October 11, 1962.
Analysis of Ferrocenes by Mass Spectrometry SIR: Aromatic and olefinic compounds have been analyzed b y low voltage mass spectrometry for several years (1-3). Attempts have been made recently a t this laboratory to apply the same technique to ferrocene compounds. At the outset, i t was desired to determine whether the iron t o cyclopentadienyl ring bonding in ferrocene would be cleaved under the conditions used in low voltage analysis, thus yielding fragment ions rather than molecule ions, which are normally produced at low electron energies. Spectra of several substituted ferrocenes were obtained using a Consolidated Electrodynamics Corp. Model 21-103 mass spectrometer at a n inlet temperature of 350" C. and a nominal ionizing voltage of 8 e.v. After examining these spectra, i t became apparent that in all cases very intense molecule ion peaks n-ere produced with little or no fragmentation. This fact would allow the determination of molecular weights of substituted ferrocenes for identification and qualitative determination of purity. Quantitative estimations could be made by a comparison of peak intenqities. However, accurate quantitative results could not be obtained because low voltage sensitivities had not been studied. This latter study is made difficult b y the lack of a large number of very pure compounds. It is possible that the low voltage sensitivities of substituted ferrocenes depend upon the nature and posi-
tion of the substituent groups, as has been found with substituted benzenes (1).
Table I lists the compounds for which low voltage spectra were obtained. Also included are the mass number of the molecule ion containing the most abundant isotope and the intensity of this peak. Since unequal sample sizes were used in obtaining the various spectra,
Table
I.
Intensities of Ferrocene Molecule Ions
Intensity of molecule mle of
chart divi-
186 370 254
811.0 222.0 307.0 708.0 646.0 594.0 399.0
ion
Ferrocene Biferrocenyl 1,l'-Dichloroferrocene 1,l'-Diethylferrocene
242
1,l'-Di-n-butylferrocene 298
1,l'-Dibutyrylferrocene Trimethylsilylferrocene 1,l'-Bis( trimethylsily1)ferrocene Triphenylsilylferrocene Dimethylethoxysilylferrocene 1,l'-Bis( dimethylethoxysily1)ferrocene Vinyldimethylsilylferro.~
cene 1,l '-Bis(vinyldimethy1sily1)ferrocene
ion,
molecule
326 258
sions
444
330
2244.0 439.0
288
3740.0
390
3210.0
270
1226.0
354
436.0
the intensities observed do not indicate a measure of the sensitivities of the compounds. These d a t a are included only to show that very large intensities can be obtained in this class of compounds. Compounds containing acid substituents [COOH, SOaH, B(OH)2] decomposed in the mass spectrometer and spectra could not be obtained. The use of mass spectrometry in analysis of ferrocenes was demonstrated by a n examination of the product from an ethylation of ferrocene. The product was found t o contain predominantly mono- and diethylferrocene and a small amount of triethylferrocene. Further, i t appears that ferrocenes would be easily identified in the presence of other types of compounds which do not contain any iron, if use is made of the existence of the four iron isotopes having atomic weights of 54, 56, 57, and 58. LITERATURE CITED
(1) Crable, G. F., Kearns, G. L., Norris, M. S., ANAL.CHEM.32, 13 (1960).
(2) Field, F. H., Hastings, S. H., Ibid., 28, 1248 (1956). (3) Lumpkin, H. E., Ibid., 30, 321 (1958). DONALD J. C L A N C Y ~ ILGVARS J. SPILNERS Gulf Research & Development Co. Pittsburgh 30, Pa. 1 Present address, Research Division, W. R. Grace & Co., Clarksville, Md. RECEIVED for review September 10, 1962. Accepted October 18, 1962. VOL 34, NO. 13, DECEMBER 1962
0
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