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Integration of the peak areas was taken as an indication of mass. In order to study the stability of the parent compound, a solution of 50 micrograms of both radiolabeled and stable fluoro ascorbic acid in 4-5 mL of water for injection was analyzed by HPLC at 7-15 minute intervals.In the absence of fluorine-18, the FAA appears to undergo decomposition in aqueous solution at a relatively slow rate, however, the radiolabelled FAA decomposition rate is significantly accelerated as shown in Fig. 2. Further, the decomposition of the carrier-added FAA results in a compound without ultraviolet absorbance as indicated in the figure. Based upon both the decrease in mass of the carrier product and the radioactivity analyses of the 18 F-FAA and the I8 F-dehydro compound as summarized in Table 1, the rate of decomposition of the parent compound appears to follow first-order decomposition kinetics. AcknowledgementA preliminary report of this work was presented orally at the Eleventh International Symposium on Radiopharmaceutical Chemistry, held August 13-17, 1995 in Vancouver, B. C. Canada. The manuscript is dedicated in memory of Professor Edward Rack. The authors gratefully acknowledge the cyclotron staff for their assistance in the preparation of the fluorine-18 radionuclide. Chromium(VI) oxide / Perchloric acid / Acid reduction / Chromium determination SummaryA study of the behavior of 5, Cr0 3 in 70% HC10 4 over the temperature range from 20 to 194°C by means of Cr-51 labelling, UV-VIS spectrophotometry and ion exchange chromatography, shows that the solubility of 5 'CrO, depends on a competition between the dissolution process and the acid reduction of solution phase Cr(VI). These processes occur simultaneously and are dependent on both the temperature and the concentration of Cr(VI), as shown by comparison between radiometric measurements (where total chromium can be accurately determined) and spectrophotometric measurements (where only the Cr(VI) is detectable at the wavelengths studied). These conclusions are confirmed by PbCr0 4 precipitation of 51 Cr(VI), where at 194 °C, 97% of the total chromium appears as Pb"Cr0 4 while at 86 °C only 5% does. Cation exchange chromatography of the solution after brief contact of 51 CrO, with concentrated HC10 4 at 20 °C shows only traces of 5l Cr(VI), most of the radioactivity eluting as "Cr(H 2 0)6 + , with smaller amounts of species with +2 and +1 charges. These results imply serious limitations to the spectrophotometric determination of low concentrations of total chromium in alloys or in biological material which use dissolution in 70% HC10 4 as a primary analytical step.

The speciation of the products from the reaction of 51Cr(VI) with concentrated perchloric and trifluoromethanesulfonic acids was carried out by ion chromatography, using HC104 and Ca(C104) 2 as eluents. The reaction (1 h) of high specific activity 51Cr(VI) with 99% CF3SO3H produces 47.6% of the 51Cr as a 3+ species (hexaaquochromium(III)), 27.6% as a 2+ species and 1.7% as a 1+ species. The reaction with 70% HC104 gave 82.5% of the 51Cr as a 3+ species, 14.0% as a 2+ species and 2.9% as a 1+ species. The 1+ and 2+ species undergo slow reactions to give the hexaaquo form.