100-fold
are seen
in the phosphores-
cent intensity.
To adapt this technique to RFF, the two scientists built a reservoir of phosphoric acid, from which a controlled amount of the acid bleeds through a porous membrane into a fine volume of sample right at the end of a fiber. Deaton says that eventually he will use a sapphire lens to couple the emitted phosphorescence back into the fiber. “The problem is properly controlling the diffusion of phosphoric acid and uranyl into a fine volume of sample right at the end of a fiber, so an equilibrium is set up,” explains
Deaton. Optrodes have also been developed for a number of physical measurements. There are optrodes sensitive to salinity, redox potential, even temperature and pressure. But the development of optrodes for analytical applications has but barely begun. “Ten years from now,” predicted Hirschfeld, “we will still be devising new optrodes.” There can be little doubt that, as the decade progresses, RFF and the optrodes that serve to make the technique more powerful will become increasingly important in the analytical repertoire.
Mobile Mass Spectrometer for Nuclear Analyses A mass spectrometer on wheels, designed specifically with nuclear applications in mind, was on display at the 25th Conference on Analytical Chemistry in Energy Technology, held in Gatlinburg, Tenn., this past October. The mobile mass spectrometer, developed by Joel A.Carter and his research group at Oak Ridge National Laboratory /Union Carbide, with funding from the Department of Energy’s Office of Safeguards and Security (OSS), will make it possible to perform onsite determinations of U and Pu in fuel rods and in process or effluent streams at nuclear power plants or at other sites where nuclear fuel is processed. The mass spectrometer’s mobility will minimize the need to use expensive mass spectrometers at each site for routine analysis. The mass spectrometer itself is a $90,000 quadrupole instrument equipped for thermal ionization and featuring a direct insertion probe. To make it mobile, the spectrometer was built into a $26 000 camper van. The
van
has also been outfitted with
a
icated laboratory, complete with a fume hood and a centrifuge, in addition to hot plates and vortex mixers. Preconcentration of the U and Pu contained in nuclear samples will be performed with a simple but powerful anion exchange bead technique prior to mass spectral analysis. The pH of a liquid sample from the nuclear power plant is first adjusted with concentrated nitric acid, and internal standards (frequently U-233 and Pu-244) are added to the sample to aid in quantitation. Under strong acid conditions, U and Pu in the sample become adsorbed to the beads, but other solution constituents, including potential interferents, do not. (The only elements adsorbed to any significant extent, besides U and Pu, are Th and Np, but these elements do not interfere with the mass spectral determination of U and Pu). After the U and Pu have adsorbed to the beads, a single bead is placed on the rhenium filament of the direct in-
Quadrupole mass spectrometer and dedicated computer are housed inside standard recreational vehicle 1618 A
•
ded-
ANALYTICAL CHEMISTRY, VOL. 53, NO. 14, DECEMBER 1981
sertion probe. The probe is inserted into the quadrupole mass spectrometer, and the U and Pu atoms are volatilized and ionized in the thermal ionization source, detected at an electron multiplier, and quantitated with the aid of a dedicated computer. Determination of concentration values and Pu/U isotopic ratios is accomplished with reference to the U-233/Pu-244 internal standard. There are a number of advantages to the resin bead technique. The selectivity is excellent. The technique is safe, since only a small fraction of the U and Pu actually present in the original sample adsorbs onto the beads. And the amounts of U and Pu handled after the resin bead adsorption step are typically in the nanogram range, affording a wide safety margin for the chemists involved, and for the mass spectrometer as well. As Jack Fassett of the National Bureau of Standards put it, “If you introduce pg amounts of U and Pu into your mass spectrometer, what happens is you get a radioactive mass spectrometer.” The new mobile mass spectrometer will make it easier for OSS to determine the U and Pu concentration of a wide range of liquid samples at nuclear sites. The resin bead technique’s specificity and its ability to safely isolate these two elements is particularly valuable, in light of the fact that dissolver solutions from nuclear fuel rods may contain perhaps 50-75 different fission products and other constituents, many of them highly radioactive. Considering the recent Reagan Administration decision to go ahead with the breeding and reprocessing of nuclear fuel (as France, West Germany, Japan, and the U.S.S.R. are already doing), the mobile unit could well see service in safeguarding the materials balance at reprocessing plants. According to Joseph A. Goleb of OSS, the mobile van has already been employed domestically for inventory verification, and the resin bead/mass spectrometric technique has also been used to assay reprocessing solutions from Japan’s nuclear facilities. Fears about possible diversion of fissionable materials suitable for the fabrication of atomic bombs were what originally delayed implementation of commercial nuclear fuel reprocessing in this country. The resin bead/mass spectrometric technique will help in monitoring for such diversion. And the mobile van will not have far to go if it is to be used in such an application. The first U.S. breeder reactor is presently under construction in Clinch River, Tenn., just a few miles down the road from Oak Ridge, where the mobile mass spectrometer was born. Stuart A. Borman
