fate caused rapid disappearance of iododimethylarsine and therefore was not suitable to dry extracts. Although the preparation of standard iododimethylarsine was not difficult, the compound must be recognized as VOLATILE AND POISONOUS, and both standards and derivatized samples should be handled with adequate ventilation and precautions against skin contact. Typical recoveries (Table I) were based on the standard curve derived directly from cacodylic acid. Attempts to determine the exact yield of the derivatization step with a standard curve based on iododimethylarsine gave recoveries greater than 10070,due to instability of the standard solution. Interferences in the water analyses were not serious (Figure l), and the detectability limit of 0.05 ppm or less could be lowered further by derivatization of a larger water sample. Attempts to lower the detectability limit in soil (about 0.5 ppm) by prior extraction of the cacodylic acid with methanol or aqueous methanol failed, probably because of its binding to soil particles (13). Previous methods for determination of arsenic in soil have avoided this problem by converting the bound cacodylic acid to arsenic trioxide, which is then removed as arsine. Major advantages include simplicity and rapid analysis; dried soil samples can be weighed, derivatized, and analyzed in less than 10 minutes, and water samples, once evaporated, require a similar amount of time. The instability of iododimethylarsine was circumvented by using a standard curve based on fortification, and by analyzing each sample in triplicate. Other Arsenic Derivatives. Trimethylsilyl (TMS) derivatives (Figure 2) of arsenite, arsenate, cacodylate, and methanearsonate were prepared (16) from 5 mg of the ar(16) W C Butts and W T Rainey. Anal Chern, 43, 538 (1971)
senical, 200 r l of bis(trimethylsily1)trifluoroacetamide (BSTFA), and 200 p1 of dimethylformamide in a septum capped vial. While the four derivatives were separated by GLC (5 ft, 5% SE-30), the reaction was never reproducible, perhaps because of the hydrolytic instability of the products. Cyanoethylated derivatives (Figure 2 ) were prepared by trapping the effluent of a nitrogen-swept arsine generator (7, 17, 18) in chilled acrylonitrile containing sodium methoxide catalyst. Although the previously described methanearsonate derivative (17) and the cacodylate derivative were separated by GLC (5 ft, 5% OV-17), the reaction proved too slow for practical use. Heating and/or additional catalysis produced chromatograms obscured by polymerization products of acrylonitrile. The major impediment to the development of a general procedure for arsenicals was the gas chromatography of the highly reactive arsenic derivatives. Work is in progress on solving this difficulty so that the hydriodic acid procedure may be extended to methanearsonic acid and the inorganic arsenicals.
ACKNOWLEDGMENT We thank Clay Reece and Ken Carroll for their assistance in various aspects of this work. Received for review April 30, 1973. Accepted July 25, 1973. Research was supported in part by NIH Grant ES00054. (17) R. C. Cookson and F. G. Mann, J. Chem. SOC..1949,67. (18) R. E. Hawk and E. F. Girling, Abstracts 163rd National Meeting of the American Chemical Society, Boston, Mass., April 1972, No. Pest. 28.
Detailed High Resolution Gas Chromatography-Mass Spectrometry Analysis of a Pyrolysis Naphtha E. J. Gallegos, I .
M. Whittemore, and R .
F. Klaver
Chevron Research Company, Richmond, Calif. 94802
Modern gasolines are complex blends of many hydrocarbon streams which are, in turn, complex mixtures. Most of these blending components are explicitly manufactured for gasoline production. Occasionally a by-product stream from an unrelated process is of such boiling range and octane number that with little or no processing it can be utilized as a gasoline blending stock. The liquid recovered from the pyrolysis of naphtha to make ethylene is such a product. It consists of unconverted hydrocarbons of the feed naphtha and large quantities of olefins and aromatic compounds formed during the pyrolysis step. This paper describes use of mass chromatography ( M e ) to make compound-type identifications so that a routine high resolution capillary gas chromatography (HRCGC) method could be used to make analyses of pyrolysis naphthas. The MC method (1-5), when combined with known HRCGC retention data, provided a uniquely rapid way to correctly analyze pyrolysis naphthas whose compositions were unlike those of the typical gasoline blending components.
EXPERIMENTAL D a t a presented here were obtained using a 1000-ft squalanecoated 0.02-in. i.d. capillary c o l u m n in a Hewlett-Packard F a n d M 810 gas chromatograph. T h e c o l u m n i s interfaced t o a N u c l i d e 12-90-G mass spectrometer through a single-stage 3-mm o.d., 1-mil t h i c k d i m e t h y l silicone membrane enricher. T h e enricher i s m a i n t a i n e d a t about 150 "C. A comparison o f t o t a l i o n m o n i t o r ( T I M ) a n d flame ionization detector (FID) traces shows negligible resolution loss due t o interfacing. T h e c o l u m n was programmed f r o m 30 t o 100 "C a t 1 "C/minute. H e l i u m was used as carrier gas.
(1) T. J. Mayer, D. L. Camin. and A. J. Raymond, "The Development of Instrumental Methods for the Analysis of Gasoline Components." Amer. Chem. SOC.. Div. Petrol. Chem. Prepr.. August 27-September 1. 1972, F 14. (2) J. C. Holmesand F. A. Morrell, Appl. Spectrosc., 11, 86 (1957). (3) R. A. Hites and K. Biemann, Anal. Chem., 40, 1217 (1968). (4) R. D. McCoy, G. T. Porter, and B. 0. Ayers, Amer. Lab.. September 1971. (5) D. V. Rasmussen and I . P. Fisher, "Identification and Analysis of Predominant Hydrocarbon Group Types in Pyrolysis Gasolines," Amer. Chem. SOC.,Div. Petrol. Chern. Prepr., August 27-September 1, 1972, F 38.
ANALYTICAL CHEMISTRY, VOL. 46, NO. 1, J A N U A R Y 1974
157
Table I. Identification of Peaks in Figure 3 1. 2. 3. 4.
5. 6. 7 8. 9. 10. 11. 12. 13. 14. 15. 16. 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.
Ethylene Unknown 1-Butene, isobutene, 1,3-butadiene n-Butane trans-2-Butene cis-2-Butene 1-Butyne 3-Methyl-1 -butene 1,4-Pentadiene I sopentane 1-Pentene 2-Methyl- 1-butene Isoprene n-Pentane trans-2-Pentene cis-2-Pentene 2-Methyl-1 -butene trans-l,3-Pentadiene Cyclopentadiene c i s - l S 3 - P e n t a d i e n e( a small 2 = - 2 ) 2,2-Dimethylbutane Cyclopentene 3-Methyl-1 -pentene Diene 2,3-Dimethyl-l -butene 2-Methyl-l,3-pentadiene ( + cyclopentane) 2,3-Dimethylbutane 2-Methylpentane 2-Methyl-1 -pentene ( + diene) 3-Methylpentane ( + 1-hexene) 1,5-Hexadiene Hexenes ( 3 ) 2-methyl-2-pentene trans-2-Hexene n-Hexane ( + 3-rnethylcyclopentene cis-2-hexene) 2-Methylcyclopentene Diene trans-4-Methyl-2-pentene 2-Methylcyclopentadiene 1-Methylcyclopentadiene Met hylcyc Iopentane Hexadienes ( 2 or 3 ) Benzene Hexadiene 1 -Methylcyclopentene Unknown (diene) 1,3-Cyclohexadiene (shoulder on left -2) Diene 3,3-Dimethylpentane Cyclohexane 2-Methylhexane Cyclohexane 2,3-Dimethylpentane 1 , l -Dimethylcyclopentane 3-Methylhexane Unknownb 1 ,cis-3-Di methylcyclopentane Unknownh 1 ,trans-3-Dimethylcyclopentane 3-ethyl-pentane Unknownb 1 ,trans-2-Dimethylcyclopentane Olefin? Unknown trans-2-Heptene Heptane Dirnethylcyclopentene
+
+
z=
47. 48. 49.
50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63 64. 65.
158
+
66 67 68 69 70 71 72 73 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86.
z=o z = -2 Diene larger
Resolved HRCGCa
87. 88. 89. 90. 91, 92. 93. 94. 95. 96. 97.
Resolved HRCGC
z = -2 z=o
m,le 82,
z= z= z= z=
Z=
-2
-2 -2 -2 -4
z = -2 z = +2 Resolved HRCGC Resolved HRCGC Resolved HRCGC Resolved HRCGC Resolved HRCGC m:e 96, Z = - 2
m,'e 96, Z = - 2
z=
-2
z=o m / e 96, Z = - 2
z=o
z
= -2
Comment
Name
Comment
Name
98. 99. 100. 101, 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112. 113. 114. 115. 116. 117. 118. 119. 120. 121. 122. 123. 124. 125. '1 26. 127. 128. 129. 130. 131.
ANALYTICAL CHEMISTRY, VOL. 46, NO. 1, JANUARY 1974
Dimethylcyclopentene Dimethylcyclopentene Unknownb 1 ,cis-2-Dimethylcyclopentane
1,1,3-Trimethylcyclopentane Met hylcyclohexane Cyclic diene Cyclic diene Unknownb Ethylcyclopentane 1 ,trans-2,cis-4-Trimethylcyclopentane Cyclic diene Toluene ( + Z = 0) Cyclic diene Unknownb Cyclic diene 2,3-Dimethylhexane ( + on right, cyclic diene Z = - 4 ) 2-Methyl-3-ethylpentane Unknown 2-Methylheptane 4-Methylheptane ( + unknownb z = -2) 3-Methylheptane Cyclic diene Cyclic diene 1 ,cis-3-Dimethylcyclohexane 1 , l -Dimethylcyclohexane Trimethylcyclohexane Unknownb n-Octane Unknownb Unknownb 1 ,trans-2-Dimethylcyclohexane ( + on right Z = 0) 1-trans-3-Dimethylcyclohexane 2,4-Dimethylheptane Unknownb 2,6- Di methyl heptane 2,5-Dimethylheptane n-Propylcyclopentane Ethylcyclohexane Ethylbenzene
z
= -2
z = -2 z = -2 z=o z=o z= z=
-4 -4 m / e 96, Z
z=o z = -4 z = -4 z = -2 z = -4 z=f 2
z=
-2,z=
z=
-4
z=
-2
z= z=
-2 -2
-4
z= -4
m / e 110, Z
1,1,3-Trimethylcyclohexane Trirnethylcyclohexane p-Xylene rn-Xylene 4-Methyloctane 2-Methyloctane Styrene 3-Met.hyloctane ( + unknown m / e 98) o-Xylene Trimethylcyclohexane Tri rnethylcyclohexane Trimethylcyclohexane Trimethylcyclohexane 1 -Methyl-cis-3-ethylcyclohexane Nonane 1-Methyl-trans-4-ethylcyclohexane Cumene a-Methylstyrene n-Propylbenzene Unknownb 1-Methyl-3-ethylbenzene 1-Methyl-4-ethylbenzene Unknown Propenylbenzene 1-Methyl-2-ethylbenzene Propenylbenzene
= -2
z=o
m / e 104
z=o z=o z=o z=o
m / e 118 m / e 120 z = -2 m / e 120 m / e 120 = -4 m / e 118 m,/e 120 m / e 118
z
= -2
Table I (continued) Name
Comment
132. 133. 134. 135. 136. 137. 138. 139. 140. 141. 142.
1,3,5-Trimethylbenzene Unknown o-Methylstyrene rn-Methylstyrene p-Methylstyrene 1,2,4-TrimethyIbenzene Clo-vinyl aromatic Decane Alkylbenzene (rn-Cymene?) Propenylbenzene? Cyclopentadiene Dimer
143. 144. 145. 146. 147. 148. 149. 150. 151. 152.
1,2,3-Trirnethylbenzene Clo-vinyl aromatic lndane Indene Unknown Alkylbenzene Unknown Cyclopentadienemethylcyclopentadiene dimers
[
r n l e 120 z = -4 r n j e 118 m l e 118 r n / e 118 rn e 1 2 0 r n l e 132 rn ' e 142 rn, e 132 rn e 1 1 8 rn e l 3 2 Fragment r n l e 66 rn / e 120 m l e 132 r n l e 118 r n ' e 116
Mass chromatograms presented in this work were obtained by monitoring m / e fragments 77, 71, 69, 67, and 65, For a sample such as pyrolysis naphtha, these peaks are characteristic of vinyland/or alkylbenzenes, paraffins, monocyclics or monoolefins, cyclic olefins or diolefins, and cyclic diolefins or triolefins, respectively. T h e rising baseline on the m / e 71 a n d 69 mass chromatograms in Figure 2 is due to squalane bleed into the mass spectrometer. The mass chromatograms displayed here were produced hy repetitive accelerating voltage scanning a t 50-msec intervals.
RESULTS F i g u r e 2 shows t h e TIM GC-MS t r a c e and t h e f i v e mass chromatograms. T h e l a t t e r mass chromatograms serve t o i d e n t i f y t h e h y d r o c a r b o n t y p e for m o s t of t h e
I \
3-1116
rn!e 134 m / e 146 Fragments rn 'e 80
High Resolution Capillary Gas Chromatography. Z = - 2 parent indicated: most probable assignments are diene or cyclic monoolefin.
The column inlet pressure was maintained a t 40 psi; a typical sample size used for GC-MS was 1 pl. Complete mass spectra were obtained on all components separated by the gas chromatograph. Data were gathered a t 4-sec intervals using magnetic scanning. These d a t a were used to verify MC and GC d a t a . T h e peak selecting device which produces the mass chromatograms consists of five gating channels which can he manually set t o continuously monitor the intensity of any five preselected fragment or parent ions. Peak selection is accomplished by allowing the mass spectrometer signal to pass to the galvanometer amplifier only when the spectrometer sweeps through the mass of interest. Since t h e gating circuitry, shown in Figure 1, is synchronized with the oscilloscope sweep. the peak selector can only he used when the spectrometer sweep, either magnetic or electrostatic. is synchronized with the oscilloscope. T h e diagram shows only one of the channels. T h e circuitry within t h e dotted lines.is in actuality repeated five times to allow selection of u p t o five different peaks or combination of peaks to he displayed on five different galvanometers. P11 triggers A11 which, with a 15-volt pulse. opens Gate $1 when the oscilloscope sweep reaches a voltage corresponding to a desired m / e peak. With Q1 open. the mass spectrometer signal is allowed to he recorded on Galvanometer GI. P12 then triggers A12 which closes Gate Q1.
,
D I M E R S OF CYCLOPENTADIENE A N D METHYL C Y C L O Q E ~ T A D I E I E
- 13u
I ( 1 A D I E N E DIMER BENZENE
,=--
,20
t
>
ClDlENE
-
HEPTANE
-
I
6 1 I 6 Figure 1. Simplified mass spectrometer peak selector diagram
Figure 2. Pyronaphtha T I M GC-MS trace and the five mass chromatograms ANALYTICAL CHEMISTRY, VOL. 46, NO. 1, JANUARY 1974
159
PI
5:’
152
98
}
- 99
95
93
) 151 90
}
150
5e=-; 81
80
J 78
79
159 b
I98
I97 I 96
P
p 52
53/
5u
50
Q
I30
127
126
1’42 r
r3 124
37
-
35
20
19
I IV
17, 18 I13
13- 15
I I2
Ill I IO
L L
-
-
7-
7
=u-5
109
6
3
105
I
i
Figure 3. GC-MS analysis of pyronaphtha 160
-
IO8
6
ANALYTICAL CHEMISTRY, VOL. 46,
NO. 1, JANUARY 1974
peaks shown on the TIM trace. Shaded TIM peaks are those which required a more complete identification. In order to do this, complete mass spectra were obtained on these and other GC peaks shown in the TIM trace. The detailed peak identifications are shown in Figure 3 and Table I. Each measurable peak is identified as to name or compound type. Exact identification and/or molecular weight, where indicated. have been obtained from complete mass spectra analysis and standard gas chromatographic retention times. Many of the smaller and/or unresolved peaks are only identified as to compound type from the mass chromatograms. This analysis establishes the identification of 1,3-butadiene, isobutene, 1-butene, and the likely position of 1butyne, 1,4-pentadiene, cyclopentadiene. cis-1,3-pentadiene, cyclopentane. and 2-methyl-1,3-pentadiene.Starting with Peak 55, Figure 3, there are several unknown peaks whose mass chromatograms indicate their molecular type to be 2 = -2. The most probable molecular assignments for these peaks would be either diolefins or cyclomonoolefins. The liquid volume per cent represented by the sum of these peaks is less than 1% of the pyronaphtha.
Dicyclopentadiene was positively identified for the first time in this kind of sample. This component has a parent ion a t mle 132 and a fragment ion a t mle 66. In addition, cross dimers between cyclopentadiene and methyl cyclopentadiene were observed. These compounds show parent ions a t mle 146 and tell-tale dimer fragment ions a t m / e 80. Several Cs vinyl aromatics were also identified including a-methylstyrene and the three vinyl toluenes. The related compounds, indane and indene, were also found in the heavy ends of the pyronaphtha. The ability to obtain complete mass spectra not only allows the identification of new components in this sample but also demonstrates the validity of hydrocarbon type identification using the powerful and rapid mass chromatographic technique. The detailed results of the MC and GC-MS runs were used to provide qualitative identifications for routine HRCGC. The HRCGC analysis was carried out on a similar but somewhat higher resolution 1000-ft by 0.02-in. squalanecoated capillary. HRCGC was then used to follow the effects of processing variables. Received for review ,June 20, 1973. Accepted .July 23, 1973.
lsobutane Chemical Ionization Mass Spectra of Volatile Lanthanide Chelates T. H. Risby, P. C. Jurs, and F. W. Lampe Department of Chemistry, The Pennsylvania State University, University Park, Pa. 76802
A. L. Yergey Scientific Research Instruments Corporation, 6 7 0 7 Whitestone Road, Baltimore, Md. 21207
The separation and analysis of the lanthanide elements pose many problems because of their similar chemical and physical properties. Among the various procedures which have been used to separate and purify these elements are fractional crystallization, liquid-liquid extraction, and ion exchange. All these procedures are extremely complicated. Classical chemical techniques for the qualitative and quantitative analysis of the lanthanides are even more difficult because of their chemical similarity. Emission, absorption, and fluorescent measurements in the X-ray, ultraviolet, or visible region of the electromagnetic spectrum are all very complicated, and often it is found that many of the lines and bands of the lanthanides overlap each other. This overlapping of peaks makes selective identification very difficult and often impossible. Also, these metals form stable diatomic monoxide molecules in flames (refractory oxides), a fact which makes analytical flame spectrometric methods almost impossible. In recent years, there has been considerable interest in the use of gas-liquid chromatography and a number of chelates have been found which exhibit thermal stability and volatility. In the course of this work, various chelates of the lanthanide elements were found which can be chromatographed successfully-notably the chelates based on the ligands 1,1.1,2,2.3,3-heptafluoro-’i,’i-dimethyloctane4,6-dione H(fod) and 2,2,6,6-tetramethyl heptane-3.5dione H(thd) (1-7). The lanthanide chelates unfortunately have not so far been successfully resolved completely by gas-liquid chromatography.
These volatile chelates have also been analyzed by electron ionization mass spectrometry uia the direct insertion probe (8-13). However, the results of these studies, although they are useful in terms of the analysis of individual lanthanides, are not very useful when mixtures of the lanthanide elements are to be examined. This is due to the fact that the fragmentation of the chelate is complex, and together with isotopic peaks these fragments often obscure peaks due to other lanthanide elements. A typical fragmentation before the mass spectrum becomes too complicated is as follows (13):
K. J. Eisentraut and R . E. Sievers, J . Amer. Chem. SOC..87, 5254 (1965). C. S. Springer, D. W. Meek, and R. E. Sievers, / n o r g . Chem.. 6 , 1105 (1967). T. Shigematsu, M. Matsui, and I . Utsumomiya, B u / / . Chem. SOC. Jap., 42, 1278 (1969). W . C . Butts and C. V. Banks, Ana/. Chem.. 42, 133 (1970). J. W. Mitcheil and C . V. Banks, Anai. Chim. Acta. 57, 415 (1971) C . A . Burgett and J. S. Fritz, Anal. Chem.. 44, 1738 (1972). R. F Sieck and C. V.Banks, Anal. Chem.. 44, 2307 (1972). R. J. Mayer, Sci. Toois, 15, 11 (1968). R. Belcher, R. J. Mayer, R. Perry. and W. I . Stephens, Ana/. Chim. Acta, 43, 451 (1968). J. D. McDonald and .J. L. Margrave, J. Less Common Metals. 14, 236, (1968) R. Belcher, I?. J. Mayer. R. Perry. and W. I . Stephens, J. Inorg. Nucl. Chem. 31, 471 (1969). 8. Kowalski, T. L. Isenhour. and R . E. Sievers, Ana/. Chem.. 41, 998 (1969). T. H. Risby and T. L. Isenhour, unpublished data.
ANALYTICAL CHEMISTRY, VOL. 4 6 , NO. 1, JANUARY 1974
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