drides which may be encountered in environmental analysis. This is because of the different physiochemical response characteristics of the three detectors. For example, an FPD response a t 546 nm indicates the presence of boron, an electron capture response indicates a n electron deficient compound, and a microcoulometric response using the iodine system indicates the presence of a reducing material. This combined information can indicate the presence of a boron hydride as opposed to some other boron compound type as, for example, a saturated organo boron compound. For tentative identification purposes, the three detectors can be used simultaneously to detect the effluent from a single GC column. This can be done by splitting the column effluent with a toggle valve and diverting sample to the FPD and electron capture detector. Since the electron capture detector is a nondestructive detection system, the sample effluent from this detector can be passed on to the microcoulometer. This approach can provide a readout from one sample on three detectors with a dual split. Quantitative analysis for the boron hydrides requires a verification of standard curves due to potential variability in detector response as a function of slight changes in operating conditions. This can be accomplished by using an external standard ratio. In this method, a known amount
of boron hydride (for example, 1.0 p1 of 10-4M B10H14 in cyclohexane which is equivalent to 12 ng of B10H14) is injected and detected chromatographically before and after an unknown boron hydride sample. This response is then compared with a previously determined standard curve for the same compound and detector, and an adjustment in the standard curve intercept, if necessary, is made corresponding to the ratio in response observed. A confirmatory analysis should be made of any boron hydride which is tentatively identified by relative retention times on different columns, by Kovats retention indices, or which is detected by FPD, electron capture, or microcoulometric detectors. For this purpose, a direct GC-MS interface utilizing a single stage Llewyllen silicone separator can be used. This experimental system is designed to confirm the identity of boron hydrides which can occur as by-products from industrial operations in which diborane is used a t elevated temperatures and a t atmospheric pressure or the reaction products of boron hydrides under environmental conditions as, for example, in the presence of oxygen and water vapor a t atmospheric pressure. Received for review December 31, 1973. Accepted March 21, 1974. This research was made possible by a grant from the Western Electric Company to Drexel University.
Neutron Capture Gamma Ray Spectrometry for Determination of Sulfur in Oil A. Reza Pouraghabagher and A. Edward Profio Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, Calif. 93706
Neutron capture gamma ray spectrometry has been applied successfully for instrumental analysis of the sulfur content of fuel oil in the per cent range. Source-associated background and detection efficiency were studied to select a 7-cm source-detector spacing, using a 0.24-microgram 252Cf source and 7.6-cm by 7.6-cm Nal(TI) scintillation detector, with no gamma ray attenuator. This is probably the weakest neutron source that has been used for capture gamma ray analysis. The signal-to-background ratio was about 0.04 at 1 % sulfur; hence, background had to be measured precisely in a run with a blank (pure fuel oil), and subtracted. Calibration against standard solutions gave 22.9 cpm per wt % sulfur. The lowest concentration measured with this source was 0.48%. The statistical precision of the net count rate was 41% at this concentration, decreasing to 8 % error at 3.53 wt % sulfur, for a 33.33-minute run. A stronger source, e.g., 5 p g 252Cf, will permit shorter data accumulation times or better sensitivity and precision.
Crude petroleum may contain 0.1% to 6% sulfur. depending on origin. Desulfurization of fuel oil and other distillates is often necessary to meet air quality standards or to reduce corrosion of equipment. Blending may be undertaken to provide a range of product concentrations
from about 0.1% on up, according to regulations. Power plants may have to burn low-sulfur fuel on certain days, while favorable meteorological conditions may permit combustion of cheaper and more abundant high-sulfur oil on other days. Thus, a rapid and reliable analyzer for sulfur content of oils is needed a t refineries and possibly a t electric power plants. On-line, instrumental analytical techniques offer practical advantages over standard chemical analyses. X-Ray absorption instruments are in use, but are expensive and suffer from interference from the nickel and vanadium also present in most petroleum ( I ) . Neutron activation analysis ( 2 ) is not well-suited for determination of sulfur (especially with the weak neutron sources available for field use) because most captures in sulfur lead to stable isotopes or a pure beta-ray emitter. The 5-min 37Sgamma ray activity can be counted, but a nuclear reactor is required because of the small abundance and cross section of 36S. However, neutron capture gamma ray spectrometry, in which the gamma rays emitted promptly upon neutron capture are measured, is suitable. The present work shows that sources emitting on the order of lo6 neu(1) 0. I . Milner, "Analysis of Petroleum for Trace Elements," The Macmillan Company. New York, N . Y . , 1963. (2) Paul Kruger, "Principles of Activation Analysis." Wiley-lntersoence, New York. N . Y . , 1971
ANALYTICAL CHEMISTRY, VOL. 46, NO. 9, AUGUST 1974
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Table I. N e u t r o n C a p t u r e in S u l f u r Isotope
Abundance,
?S
95.0 0.76 4.22 0.0136
3
33 s
3 4 s 3%
Yo
