Table I. Limits of Detection of Several Elements by Double Modulation Atomic Fluorescence Flame Spectrometry (DMAFFS) Limits of detection, pg/ml Element
Wavelength, nm
Flamea
328.1 396.2 422.7 357.9 324.8 285.2 279.8 313.3 232.0 405.8 377.6 318.4
A/A A/"
Ag A1
Ca Cr cu Mg
Mn Mo Ni Pb T1 V
DMAFFS~
0.03 0.8 0.3 0.6 0.05 0.03 0.09 1. 4. 5. 0.6 6.
Previous work,c continuum
0.001 ( 4 ) d
... 0.02 ( 7 ) d
... 0.2 (9)d 0.002 ( 1 1 ) d 0.003 i l l ) d
... 1. ( 7 ) d 0.2 (15)d 0.07 ( 7 ) d
...
Previous work, line
0.0001 (5) 0 . 1 16) 0.02'(5)d 0.005 ( 8 ) 0.0005 0.0001 (12) 0 . 0 0 1 l(13) 0 . 5 (6) 0 . 0 0 3 (14)d 0 . 0 2 116)d 0 . 0 0 8 15)d 0 . 0 7 (6)
*
a A/A = acetylene/air flame. A / N = acetylene/nitrous oxide flame. Source was 900-W CW xenon arc. Only references to non-laser line sources are given. Flame used was Hllentrained air or H,/argon/entrained air.
The limits of detection (LOD) defined as t h a t concentration giving a signal to (rms) noise ratio equal to two are given in Table I for twelve elements and compared with other limits of detection for both continuum sources and line sources. A 1000 p g ml-I zirconium solution was indis(4) D. W. Ellis and D. R. Derners, Anal. Chem.. 38, 1943 (1966). ( 5 ) K. F. Zacha, M. P. Bratzel, J. M. Mansfield, and J. D. Winefordner, Anal. Chem.. 40, 1733 ( 1968). ( 6 ) R. M. Dagnali, G . F. Kirkbright. T. S . West, and R. Wood, Ana/. Chem.. 42, 1029 (1970). (7) D. W. Ellis and D . R. Demers, "Atomic Fluorescence Flame Spectrometry," Chapter in "Trace lnorganics in Water," H. A. Beller, Ed., Advan. Chem. Ser. No. 73, Government Printing Office, Washington, D.C., 1968. ( 8 ) J. D . Norris and T. S. West, Anal. Chim. Acta, 59, 355 (1972). (9) M . P. Bratzel, R . M. Dagnall, and J. D. Winefordner, Ana/. Chim. Acta, 52, 157 (1970). (10) H . G. C. Human, Spectrochim. Acta, 2 7 8 , 301 (1972).
tinguishable from the blank signal in all cases. Although the present detection limits are inferior to those obtained in AFFS with line sources, t h e double modulated continuum source AFFS system compensates for scattering which is difficult to correct for in resonance fluorescence with line sources and allows the determination of several elements with only one source. Received for review July 30, 1973. Accepted November 21, 1973. Research supported by AF-AFOSR-70-18801. ( 1 1) A. Hell and S . Ricchio, Talk given at Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. Cleveland, Ohio, 1970. (12) P. L. Larkins, Spectrochim. Acta, 2 6 8 , 477 (1971). (13) L. Ebdon, G . F. Kirkbright, and-T. S. West, Talanta. 1 7 , 965 (1970). (14) J. Matousek and V. Sychea, Anal. Chem., 41, 518 (1969) (15) R. Smith, C. M . Stafford, and J. D . Winefordner, Can. Spectrosc., 14, 2 (1969). (16) V. Sychra and J. Matousek, Taianta, 1 7 , 363 (1970).
Direct Mass Spectrometric Analysis of High Pressure Gasoline Streams Containing Light Ends Dirk V. Rasmussen Gulf Oil Canada Limited, Research and Development Department, Sheridan Park. Ontario, Canada
Hydrocarbon process streams boiling u p to 200 "C and containing light ends (CI-C5 hydrocarbons) are often sampled at pressures u p to 500 psi. Conventional mass spectrometric techniques require the venting of the sample cylinder, transfer of the liquid to a glass bottle, depentanization ( I ) , and analysis of the depentanized fraction (2, 3 ) . Depentanization is required because of calibration limitations. but it also introduces errors and much additional work. This paper describes a high pressure liquid introduction system for mass spectrometers and a method of analysis in which depentanization is eliminated. Constant volumes (1 ) American Society for Testing Materials, "Standards on Petroleum Productsand Lubricants." Vol. 17, 712 (1970). ( 2 ) American Society for Testing Materials, "Standards on Petroleum Products and Lubricants." Vol. 17, 1103 (1970) (3) American Society for Testing Materials. "Standards on Petroleum Products and Lubricants," Vol 17, 589 (1970)
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of gasoline type samples containing large amounts of c1-C5 hydrocarbons a t pressures up to 500 psi are introduced by means of a four-port slide valve. The high ionizing voltage mass spectrum is mathematically depentanized ( 4 ) using the gas chromatographic light ends analysis ( 5 ) of the sample.
EXPERIMENTAL Instrumental. S p e c t r a were o b t a i n e d o n a C o n s o l i d a t e d E l e c t r o d y n a m i c s C o r p o r a t i o n M o d e l 21-103C mass spectrometer. m o d i f i e d by t h e a d d i t i o n of a B e n d i x G r e e n b r i e r f o u r - p o r t slide v a l v e . T h e v a l v e has a s a m p l e v o l u m e of 1 PI a n d is a c t i v a t e d by 40 p s i n i t r o g e n and a f o u r - w a y S k i n n e r solenoid valve. A h i g h pressure h e l i u m s u p p l y was i n s t a l l e d so t h a t s a m p l e c l - l i n d e r s c o u l d h e pressurized at t h e m a s s s p e c t r o m e t e r . T h e c o n f i g u r a t i o n o f t h e m o d i f i c a t i o n i s s h o w n in F i g u r e 1. ( 4 ) H. E. Howard and W . C Ferguson, Ana/. Chem.. 3 1 , 1048 (1959). ( 5 ) R . D Beckham and R . J. Libers, J . Gas Chromatogr.. 6, 188 (1968)
TO VACUUM PUMPS
)I\
A
Figure 1. High
’Ac
SKINNER SOLENMO VALVE
WASTE SAMPLE RECEtVER
pressure liquid sampling system
Table 11. Analytical Results of Reformer Reactor Product
Table I. Mass Spectrometric Calibration for Paraffinic Light Ends
High pressure full renge analysis
Constant volume sencitivities (peak heightlinjection) m/e
CzHs
i-C~Hio
n-C1Hlo
i-CsHli
n-CaHl?
41
549 897
2047 4899 26 149
1331 4187 52 109
1949 2685 161 1554 1
1856 4250 151 558
1
1 22
43 55 57 67 68 69 71
50
2
P r o c e d u r e . High pressure gasoline range process streams a r e normally sampled in stainless steel cylinders. T h e sample p r m sure is measured a n d a constant volume (1 @I) is injected into $.he mass spectrometer by means of the Bendix slide valve. The 70-eV mass spectrum is obtained. A stainless steel cylinder. containing a benzene standard. is pressurized with helium to a value equivalent to the sample pressure. T h e benzene is injected by the slide valve, and from the mass spectrum. the constant volume benzene sensitivity associated with the sample io obtained. When a series of samples is analyzed. the pressures a r e generally similar and only a small number of benzene s t a n d x d s is required. T h e c 1 - C ~hydrocarbons present in t h e sample are determined by the conventional gas chromatographic procedure (31. Calibration. Calibration requirements for this method consist of t h e constant liquid volume sensitivities of each C3-CS hydrocarbon of interest a t tbach of the matrix peaks. T h e peak heights at m / e 41. 43. 55. 57. 67. 68. 69. 71 due to fixed .;olumes of propane. isobutane. n-butane. isopentane. and n-r)entane are required. Each standard is run as a liquid by means 0 ; the liquid sampling valve. T h e gaseous standards, obtained i n lecture bottles. are further pressurized to 300 psi with helium, The liquid standards (n-pentane, benzene I are placed in 30C)-ml stainless steel cylinders and are similarly pressurized t o 300 psi. Benzene is used to supply a reference sensitivity. T h e contribrition of each hydrocarbon standard to each matrix peak is expressed in “peak height per unit volume” a t a benzene parent peak sensitivity of 7000. A typical light ends calibration is shown in T a b l e I. Previously published calibration d a t a a r e used for the hydrocarbon type analysis of the C g + hydrocarbons. Calculations. T h e contributions of the C3-CS hydrocarbons a t m j e 41, 43. 55, 57. 67. 68. 69, 71 are calc,ulated from the gas chromatographic light ends analysis and thf: mass spectrometric calibration d a t a (Table I ) . T h e sum of #ihe contributions at each mass number is removed from the re‘,pective “full range“ peak.
Light ends Methane Ethane Propane Isobutane n-Butane Isopentane n-Pentane P a r affin s Monocycloparaffins Dicycloparaffins A1kylbenzenes Benzene Toluene
cs
CI
c
10
c 1 1
Total liquid vol. %
(16.4) 0.5 2.3 3.8 1.6 2.8 3 .O 2.4
35.5 5.6 0.3 (42 .2) 0.9 5.7 15.5 15.6 4.2 0.3 100 .o
Corrected, ASTM D 2789
(16.4) 0.5 2.3 3.8 1.6 2.8 3 .O 2.4
35.8 5.7 0.2
(41.9) 0.8 5.6 15.6 15.6 4 .O 0.3
100 .o
Conventional, ASTM D 2789
(16.4) 0.5 2.3 3.8 1.6 2.8 3 .O 2.4 36.5 5.6 0.2 (41.3) 0.8 5.5 15.4 15.4 3.9 0.3
100 .o
resulting in the light ends corrected mass spectrum. The latter is subjected t o matrix analysis for paraffins, cycloparaffins. and dicycloparaffins a n d direct volume calculations for alkylbenzenes. T h e results are combined with the GC light ends to complete the analysis. T h e calculations are easily computerized and in this laboratory. an on-line IBM 1800 computer system performs all the required GC and M S computations.
RESULTS AND DISCUSSION The liquid sampling valve was extensively evaluated. The repeatability of sample volumes was 0.2% at the 95% confidence level and proved to be considerably better than the repeatability obtained by a constant volume capillary dipper. Sample volumes were found to be somewhat dependent on sample pressure. This was attributed to the dilation of the Teflon sample cavity and not the isothermal compressibility of the liquid. The pressure dependence amounted to 0.01% per psi and, though not desirable. did not present a problem since the benzene standard was run a t the same pressure as the sample. The procedure described is used extensively in this laboratory. Samples of reformer reactor products and straight A N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 4, A P R I L 1974
603
run naphthas are routinely analyzed using this technique. A typical analysis is shown in Table I1 and is compared to the results of the conventional procedure. A comparison is also made with the results of the conventional method after correction for errors introduced h y the depentanization. These errors include approximately 1.5% light ends that are habitually left in the depentanized fraction and approximately 3.5% CS components that are often cut out of it. The corrections are based solely on the gas chromatographic analyses of the overhead and bottoms of the depentanizations. The analytical results ot the new technique are in good agreement with those of the corrected conventional method. but differ significant11 from the uncorrected one.
The repeatability of the new method was determined to be 0 . 6 7 ~a t the 95% confidence level and compares favorably to the 2.470 obtained for the conventional procedure. The analytical technique presented here is therefore more accurate and precise than the conventional mass spectrometric method of analysis. Furthermore. the lengthy depentanization procedure is no longer required and high pressure process streams may be analyzed at their sampling pressures. T o date. the technique has been applied solely to lowolefinic stocks. It should also be applicable to olefinic streams. Received for review August 21, 1973. Accepted Sovember 5, 1973.
Semimicro Procedure for the Determination of Hydrocarbon Types in Shale-Oil Distillates Larry P. Jackson,l Charles S. Allbright,* and Howa,rd B. Jensen U.S. Department of the Interior. Bureau of Mines. Laramie E n e ~ g yResearch Center. Laramie. Wyo. 82070
The characterization and analysis of crude shale oil:< and their various distillate fractions have been objectives of the work carried out a t the Laramie Energy Research Center. Analysis of the crudes usually involves the quantitative determination of five general compound types: t a r acids, tar bases, saturates, olefins. and aromatics. For the purposes of this paper. t a r acids and t a r bases are referred to as polars; saturates, olefins, and aromatics are hydrocarbons. The limited quantities of sample frequently encountered in research and development make it very difficult to apply, with accuracy. standard methods of analysis such as acid absorption ( I ) , bromine number (2), and silica gel chromatography ( 3 ) because of the subjective judgments that must be made in each test. This paper describes a n analytical procedure based on a new application of the reaction of olefins with diborane in the quantitative determination of saturates, olefins. and aromatics in shale oil. Two major sources of difficulty in the analysis of shaleoil distillates are the high concentrations of nitrogen compounds and olefins. In the procedure reported here, the first of these problems is circumvented by the removal of the nitrogen compounds and the other polars from the hydrocarbons by column chromatography on Florisil ( 4 ) . For the purposes of this study. no further characterization was done on the polars. Because of the high concentration of olefins in the hydrocarbon fraction, accurate analysis by
* Present address, Department of Biochemistry. University of Wyoming, L a r a m i e . R y o . 82070. Correspondence should be addressed tn this author at the Laramie Energy Research Center. (1) "ASTM Book of Standards, 1971," Part 17, Method D 1019-68, "Olefinic and Aromatic Hydrocarbons in Petroleum Distiliates." pp 34251. ( 2 ) Ref. 1, Method D 1159-66, "Bromine Number of Petroieum Distillates and Commercial Aliphatic Olefins by Electrometric Titration." pp 378-89. ( 3 ) Ref. 1. Method D 1319-70, "Hydrocarbon Types in Liquid Petroieum Products by Fluorescent Indicator Adsorption," pp 474-79. ( 4 ) G. U. Dinneen, J. R Smith, R A. Van Meter, C. S Allbright. and W. R. Anthoney. Anal. Chem.. 27. 185 (1955).
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fractionation on silica gel is difficult, especially on small samples (5). In the present analytical scheme. the wellknown reaction between olefins and diborane is used as the key step in the selective, destructive removal of olefins from the hydrocarbon fraction (6). The reaction is carried out on a sample consisting of a 1:l mixture of the hydrocarbons from a shale-oil distillate fraction and a suitable internal standard made u p of n-alkanes and nalkylcyclohexanes whose boiling points are a t least 25 "C removed from that of the hydrocarbon fraction. Gas chromatography (GC) is used as the d a t a readout to determine the ratios of sample to internal standard before and after treatment to remove the olefins. The difference in the two ratios is a measure of the olefin content. The percentage of saturates is determined on another portion of the same sample solution by selective removal of both the olefins and aromatics with a modification of the HzSO4P205 acid absorption procedure ( I ) . The resulting raffinate is a:ialyzed by the same gas chromatographic technique. T h r value obtained for saturates is combined with the olefin \,due and the result is used to calculate the percentage of aromatics in the sample. The procedure which we propose uses modern GC techniques for wiiich the precision of any given quantitative measurement is about *l%. This degree of precision is seldom attainable in classical methods of analysis where a subjective judgment often has to be made in tests that give no clearly defined end points or separations and where cornpetink; chemical reactions give erroneous results. SpecificalilJ, acid absorption end points are frequently diffuse when samples are rich in aromatics and olefins; bromine number values are affected by nitrogen compounds and alpha olefins, both of which occur in high concentrations in
