Only a rough optimization for the ashing step was performed to obtain these data. Figure 2 demonstrates the excellent linearity in a complex matrix without any difficult sample preparation steps. The relative standard deviations ranged from 4 to 16% with a sample population of 3. Since sample volumes are often limited in clinical situations, the automated sampler, with a dead volume of 150 pl, could not be used. A syringe was used to transport the sample, and the high relative standard deviation of individual points can be attributed to the difficulty of placing samples on the atomizer in a reproducible manner.
cases. Copper and lead were analyzed by atomic absorption, and detection limits of approximately 2 X gram were obtained. All of the analytical curves showed good linearity over two to three orders of magnitude in concentration. The relative standard deviation was usually between 4-770 at concentrations one order of magnitude greater than the detection limit. In Figure 1, typical recorder tracings of AF signals from 10 consecutive samples of 150 pg of Cd are shown. The relative standard deviation of the peak areas of these signals is 4%. These data were obtained without optimization of instrumental parameters. The detection limits and the dynamic range can probably be improved substantially if the system is optimized (8). The ability of a non-flame atomizer to utilize samples in complex matrices is one of its greatest assets. Because of its clinical significance, copper ( 1 3 ) in a serum matrix was chosen as a good test of the GBA in a practical analysis. When copper is analyzed by flame spectrometry, the serum matrix affects the results. probably because of changes in the transport parameters. The transport is nearly 100% efficient in the non-flame atomizers, and matrix effects are minimized when appropriate temperatures are used to desolvate, ash, and atomize the sample. Different amounts of aqueous copper were added to the tenfold diluted serum samples, and the standard addition analytical curve shown in Figure 2 was obtained by AA.
CONCLUSIONS The graphite braid non-flame atomizer has been shown to be a medium power alternative to the more commonly used graphite rods and furnaces. In addition to the high operating temperature and other advantages of non-flame atomizers which are preserved, the graphite braid provides a furnace-type environment with uniform temperature throughout the GBA. The atomizer requires relatively low power and no cooling system is necessary. The good detection limits and precision suggest that the GBA should have widespread application in AA and AF spectrometry. Further investigations of the GBA and its applications are being carried out in these laboratories. Received for review August 13. 1973. Accepted November 16,1973.
(13) Norbert W. Tietz. "Fundamentals of Clinical Chemistry," W. B. Saunders Go.. Philadelphia, Pa., 1970, p 663.
Double Modulation Atomic Fluorescence Flame Spectrometry W. K. Fowler, D. 0. Knapp, and J. D. Winefordnerl Department of Chemistry, University of Florida, Gainesville, Fla. 32607
A continuum source and double modulation-i. e., modulation of the source radiation and modulation of the spectral image over a small wavelength range-has been used previously in atomic absorption flame spectrometry by Elser and Winefordner ( I ) . Some of the advantages presented for such a system are applicable to atomic fluorescence flame spectrometry (AFFS). For example, emission radiation from the flame cell and incident radiation scattering can be minimized in AFFS by such a system. Modulation of the source radiation compensates for thermal emission from the flame cell, and wavelength modulation, which results in a derivative of the signal with respect to the wavelength, compensates for scattering from particles in the flame. A continuum source offers several advantages distinct from line sources among which are a savings in analysis time and cost of many sources and the convenience of having one source for all elements. Continuum sources unfortunately have rather low spectral radiance over an absorption line compared to the spectral radiance of intense line sources-e.g., thermostated electrodeless discharge lamps (EDL) (2). 1
Author to whom reprint requests should be sent.
( 1 ) R. C . Elser and J. D. Winefordner, A n a / . Chem , 44, 698 ( 1 9 7 2 ) . (2) R . F . Browner, B. M. Patei, T. H. Glenn, M. E. Rietta, and J. D. Winefordner. Spectrosc. Lett., 5 , 311 ( 1 9 7 1 ) .
In this work, the limits of detection of nine elements in an air-acetylene flame and three elements in a nitrous oxide-acetylene flame using a 900-watt xenon arc are measured by double modulated atomic fluorescence flame spectrometry (DMAFFS). Specifically, the spectral radiation from a 900-W xenon arc (XBO, 900 W/P, Osram, Berlin, Germany) enclosed in a suitable housing (LH 151 N, Schoeffel Instrument Co., Westwood, N.J.) and powered by a regulated dc supply (Sola Electric Co., Elk Grove Village, Ill.) was modulated a t 666 Hz by a mechanical chopper (Model 125, Princeton Applied Research, Princeton, N.J.) and focused on the center of the flame cell. The burner system, which utilized capillaries, has been described elsewhere ( 3 ) . Gas flow rates of 14.3 and 2.6 1. min-I and 12.0 and 6.4 1. min-l were used with air/CzHz and NzO/CzHz flames, respectively. All measurements were made approximately 2 cm above the burner top. The monochromator, refractor plate for wavelength modulation, and associated electrical components have been described previously ( 1 ) except that in the present case a low noise preamplifier (PAR, Model CR-4) and lock-in amplifier (PAR, Model JB4) were utilized. All aqueous solutions were prepared from reagent-grade chemicals . ( 3 ) L. M . Fraser and J. D. Winefordner, A n a / . Chem.. 43, 1693 (1971). A N A L Y T I C A L C H E M I S T R Y , V O L . 46, N O . 4 , A P R I L 1974
601
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 that 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, the 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 up to 200 "C and containing light ends (CI-C5 hydrocarbons) are often sampled at pressures up 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)
