Literature Cited (1) Molina, M. J., Rowland, F. S., Nature, 249,810 (1974). (2) Singh, H. B., Lillian, D., Appleby, A., Lobban, L., Enuiron. Lett., in. - - 2.59 , - -1197.5). - -, ( 3 ) Singh, H. B., Salas, L., Cavanagh, L. A., Paper No. 76-15.2, presented at the 69th Annual Meeting of the Air Pollution Control
(6) Afifi, A., Azen, S. P., “Statistical Analysis: A ComDuter Oriented Approach”, Academic Press, New York, N.Y., 1972. (7) Saltzman, B. E., Burg, W. R., Ramaswamy, G., Enuiron. Sci Technol., 5,1121 (1971).
\ - -
Association, Portland, Ore., June 1976. (4) Halocarbon Workshop, Boulder, Colo., March 1976. (5) O’Keeffe, A. E., Ortman, G. C., Anal. Chem., 38,760 (1966).
Received for review April 26, 1976. Accepted December 16, 1976. Project financed in part with federal funds from the Enuironmental Protection Agency under Grant No. EPA 803802010.
Loss of 14C and 3H from Liquid Scintillation Counting Vials Joseph L. Thompson’
and David A. Olehy
Chemical Research and Analysis Branch, Allied Chemical Corp., Idaho Falls, Idaho 83401
Observations of significant losses of 14C-C02 and 3H-H20 from liquid scintillation counting solutions under certain conditions are reported, and evidence is presented for migration of these radioactive species through the walls of polyethylene counting vials. Weimer and coworkers ( I ) recently reported that dilute lost activity, aqueous solutions of 32P-Po4-3and 14c-co3-2 as measured by liquid scintillation counting, because of precipitation or volatilization of the radioactive species from a dioxane base cocktail. A similar observation concerning loss of activity from dilute aqueous ‘4C-HC03- solutions in Aquasol (a premixed cocktail available from New England Nuclear Corp.) was reported by Iverson and coworkers ( 2 ) .In the present communication, observations corroborating those of Weimer and Iverson with respect t o volatilization of 14C-C02 are reported, and evidence is presented which indicates that there is appreciable migration of 14C-C02 and :’H-H20 through the walls of polyethylene counting vials. Liquid scintillation counting is a standard technique for monitoring levels of :IH and I4C in the environment (3, 4 ) . Such environmental samples are typically of low specific activity and require long counting times. Migration of 3H or 14C from the counting vials can introduce serious counting errors and cause contamination of equipment. Work in our laboratory involved the counting of dilute solutions (about M) of 14Cas Na2C03 and of 3H as H2O in commercially prepared cocktails (“Ready-Solv VI” from Beckman Instruments; “Insta-Gel” from Packard Instruments Co.) or in a dioxane base cocktail (8 g butyl-PBD, 100 g naphthalene, diluted t o 1 L with dioxane). Low potassium glass vials and polyethylene “Poly-Q” vials (both from Beckman Instruments) were used to contain the counting solutions. T h e dilute NaZCO3 solutions stored in glass vials (which were opened periodically t o withdraw samples) lost 14C activity a t rates u p t o 90% in a one-month period. As Weimer suggests, this loss is probably due to volatilization of COP.The
Present address, Department of Chemistry, Idaho State Uni-
versity, Pocatello, Idaho 83209.
addition of ethanolamine in a cocktail (either Insta-Gel or Ready-Solv VI) caused the activity level t o remain constant over periods of several months. This observation agrees with that of Iverson who used phenethylamine as a COz absorbant. We further found that if Ca(OH)2 was added so that CaC03 was formed, no loss of 14Cactivity was observed. Thus, it apsolutions d o not retain pears t h a t dilute aqueous 14c-co32their activity unless some steps are taken t o prevent volatilization of 14C02.In contrast with this experience with 14C02, we have observed no loss of 3H activity from HzO stored in glass vials. Appreciable losses of I4C and 3H activity from unopened polyethylene vials were also observed, both from dilute aqueous solutions and from cocktails containing small aqueous samples. Typical loss rates from Insta-Gel or Ready-Solv VI spiked with 50 X of dilute I4C-Na2C03 and 50 X of 3H-H20 were about 10%of the 3H activity and about 50% of the 14C activity in a three-day period. These loss rates were sufficiently severe to preclude the use of polyethylene vials for low activity samples requiring long counting times if either commercial cocktail were used. As noted above, loss of 14C02 was prevented if ethanolamine or Ca(OH)2 was added to the vial contents. Several experiments were performed to determine whether the activity was escaping from the polyethylene vials or being removed from the solution by a n adsorption phenomenon. When the vial was immersed in Ready-Solv VI t o a level slightly below the cap, appreciable quantities of the 3H and 14Cfrom the contents of the vial appeared in a few days in the surrounding fluid. T h e arrangement used prevented any material leaking through or around the vial cap from getting into the cocktail surrounding the bottom part of the vial. Thus, the activities were migrating through the vial wall when it was immersed in the cocktail. T o learn whether this migration would occur if the vial were not in external contact with the cocktail, a vial loaded with Ready-Solv VI and 14C and 3H aqueous spikes was placed in a closed vessel containing a reservoir of Ready-Solv VI which was not in contact with the vial. After standing at room temperature for five days, both 14C and 3H were found in the cocktail in the reservoir. T h e results of these experiments led us to conclude that the previously observed losses of activity from the polyethylene vials were due to migration of the radioactive material through the walls of the vials. Apparently, this migration is in part a Volume 11, Number 5, May 1977
513
function of thgcocktail composition, because we did not observe loss of 14Cor 3H activity from aqueous solutions mixed with the dioxane base cocktail described above. Our experience indicates that with certain cocktails, polyethylene vials may not be satisfactory containers. Care should be exercised in the selection of counting cocktails and vials to avoid measurement errors and contamination problems due to migration of activity through the vial walls.
Literature Cited (1) Weimer, W. C., Rodel, M. G., Armstrong, D. E., Enuiron. Sci.
Technol., 9 (lo),966 (1975). (2) Iverson, R. L., Bittaker, H. F., Myers, V. B., Limnol. Oceanogr., 21,756 (1976). ( 3 ) Budnitz, R. J., Health Phys., 26,165 (1974). (4) Cantelow, H. P., et al., ibid., 23,384 (1972).
Receiued for review August 27, 1976. Accepted December 20,1976.
Further Developments in Oxidation of Methane Traces with Radiofrequency Discharge Daniel L. Flamm’’ Department of Chemical Engineering, Texas A&M University, College Station, Tex. 77843
Theodore J. Wydeven NASA Ames Research Center, Moffett Field, Calif. 94035
The radiofrequency discharge, previously shown to oxidize trace levels of methane in oxygen, was studied with contaminated air a t 50,600, and 760 torr. As with oxygen, the concentration of methane traces could be reduced by several orders of magnitude, and no organic reaction products were detected in the effluent; however, substantial concentrations of NO, (0.1-6%) were formed during treatment. The concentration of NO, was decreased by using a large diameter electrode. There is evidence that the process will oxidize N2 and NO as well as organic impurities in oxygen or oxygenlinert gas atmospheres. Recently, we reported that a radiofrequency glow discharge could be used to effect almost complete removal of contaminative methane traces from oxygen ( I ) over a wide range of pressure (50 torr to 1atm) and concentration (70-8000 ppm). Unlike many other methods of purification, the fraction of methane removed was insensitive to concentration within this range, even a t high degrees of removal (99%) and very low concentration. The device was proposed as a means for removing trace contaminants from closed environments such as spacecraft or from “zero gas” used as a standard for monitoring equipment. In the previous investigation, only contaminated oxygen was studied. We have now extended that work to air, which contains methane traces, and report the formation of NO, in air which is so treated. An analysis of the thin film which forms on the reactor wall ( I ) is also given.
this purpose, a sample of the reactor effluent was collected in an evacuated bomb containing 25 cm3 of 0.003 N HzS04/0.3% H2Oz solution and chilled to 0 “C with an ice bath. The samples collected a t subambient pressure were back-filled to atmospheric pressure with oxygen and set aside for 24 h. NO and NO2 are thus converted into nitrate in solution. T o each sample was added 0.5 ml of 5 M K F ionic strength adjuster, and an Orion Model 93-07 ion selective electrode was used to determine the nitrate concentration. An attempt was made to analyze ozone from two oxygen discharges a t atmospheric pressure by iodometry (Table I). The treated stream passed through an extra coarse gas dispersion tube immersed in 300 ml of 0.2 M KI solution buffered with 0.1 M boric acid. The iodine thus formed was titrated with 0.1 N Na2S203. During these experiments the TC filament detector was operated a t high current giving increased sensitivity over that of our previous investigation. This enabled us to detect and thus confirm the presence of COz, CH4, and NO2 with the TC detector, although these chromatograms were not quantitative or entirely reproducible due to the consequent oxidation of the filament.
NEEDLF VALVE VENT
Experimental The basic apparatus and reactor have been described in detail (1,2).A mixture of dry air or dry oxygen and methane is formed in a dynamic dilution system (Figure 1)and metered into the reactor. The reactants and products have been analyzed by use of a gas chromatograph with a dual thermal conductivitylflame ionization detector. In addition to this analysis, the product stream from the air discharges was routinely analyzed for total nitric oxides. For
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Environmental Science 8 Technology
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Present address, Bell Laboratories, Room 63-216, Murray Hill, N.J. 07974.
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