ASCARITE P R E-TR A P
Y 1 INTEGRATOR
z
TRAP
GAS CHROMATOGRAPH
I_
Figure 1. Flow diagram for Nitrox 6 At both temperatures, a significant but reproducible blank was present due t o the reaction of the carbon black packing and the quartz reaction tube: SiOz
+ 2C
-
2CO
Table 11. Low Temperature Oxygen Analysis Furnace temperature, 1700 OC. Benzoic acid standard, platinum-tin flux Theory, Experimental, Compound 7z Acetanilide 11.8 11.7,11.7 Urea 26.6 27.0 o-Iodobenzoic acid 12.9 12.9,12.7 Sulfanilamide 18.6 18.7 Cystine 26.6 26.9 4,4'-Dichlorodiphenylsulfone 11.2 11.3, 11.5 5,5-Methylene-bis-salicylaldehyde 25.0 25.0 Ethylene-MMA copolymer 5 5.35 (Total CHO = 100.273
C~~HDBMON~O~ C~~H~~BMON~O~ CaF;CONHC,Hii' C;Fl sFe(CO)Ja BajFe4PtOlj Sr2FeRuOs a Fluorine interference.
8.15
7.9 5.4
9.7 16.8 22.4
8.2 7.9 10.7 11.8
17.1,16.9 22 8
+ Si
The blank was estimated to be between 10 and 25 pg of CO. Compensation was made for this blank by using the total integrator count (CO area due to blank and sample) in both standard and sample runs. The sample size chosen should contain 0.1 t o 2 mg oxygen per run (generally 5-20 mg sample). Large samples of organic matter (25-50 mg) flash back in the furnace and prevent quantitative flushing of the off-gases to the collection trap. Therefore, organic samples containing 3 2 or less oxygen are best determined at a higher sensitivity setting (e.g., 8 cs. the usual 32), using a smaller amount of sample. Chlorine and fluorine can both interfere with the above oxygen determination. The Ascarite trap effectively elimi-
nates chlorine interference. Without this pre-trap, chromatograms of CI- or F-containing compounds, especially organics, show considerable tailing of all peaks. Subsequent samples, even those containing no fluorine or chlorine, also exhibit tailing. Apparently HC1 and HF or similar species are formed in the sample decomposition and are bled off the collection trap each time it is heated. Fluorine also interferes by reaction with the quartz furnace assembly to ultimately give CO, as indicated by a greatly increased blank. This has led to high results for all fluorine-containing samples analyzed t o date. RECEIVED for review May 29, 1968. Accepted August 15, 1968.
Use of Alkylphenol Surfactants for Liquid Scintillation Counting of Aqueous Tritium Samples Ronald C. Greene, Michael S . Patterson, a n d Alice H. Estes V A Hospital and Department of Biochemistry, Duke University Medical Center, Durham, N . C. USE OF Triton X-100 (Rohm & Haas Co., Philadelphia, Pa.) to solubilize or emulsify aqueous samples for liquid scintillation counting has been described ( I , 2 ) . These reports only considered counting at temperatures near 0 "C and the systems described are not useful in ambient liquid scintillation counters. We have extended these studies t o other members of the Triton series of surfactants and have defined mixtures in which aqueous samples can be solubilized o r emulsified that are suitable for counting tritium from below 0 " C t o above room temperature. We have shown the presence of impurities in Triton emulsifiers which emit light when mixed with alkaline solutions and have devised a procedure for removing them.
and tritiated toluene were obtained from the Packard Instrument Co.; the Triton surfactants were obtained from Rohm & Haas Co., and all other chemicals were analytical reagent grade from standard commercial sources. The scintillation solution used in all experiments contained 4 grams of 2,5diphenyloxazole (PPO) and 100 mg of 1,4-bis-2-(5-phenyloxazo1yl)-benzene (POPOP) per liter of toluene. Aqueous samples were mixed with Triton and scintillation solution in counting vials and emulsification was effected either by vigorous shaking or, as suggested by Benson ( 2 ) by adjusting the sample t o the temperature where a homogeneous solution is formed followed by adjustment to the counting temperature. Comparable results are obtained by either procedure.
EXPERIMENTAL
Luminescence of Triton Emulsifiers. In our original paper ( I ) , we reported that Triton X-100 contained a luminescent
Low temperature counting was done with a Packard TriCarb Model 3375 liquid scintillation spectrometer. A Packard Tri-Carb Model 574 liquid scintillation spectrometer was used for counting at ambient temperature. Scintillators, glass counting vials, and standard solutions of tritiated water
RESULTS AND DISCUSSIOK
(1) M. S. Patterson and R. C. Greene, ANAL.CHEM.,37, 854 (1965). (2) Royal H.Benson, ibid., 38, 1353 (1966). VOL. 40, NO. 13, NOVEMBER 1968
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Table 1. Effect of Triton Surfactants on Counting Efficiency of Toluene 3Ha Counting efficiency, % Vol Triton Triton Triton Triton Triton x-45 X-114 X-100 added, ml x-102 0 47 47 47 48 1 43 43 44 44 2 41 41 42 42 3 40 40 40 40 4 36 37 37 38 5 34 35 35 37 a Each vial contained 10 ml of scintillation solution 9.5 x 106 dpm of tritiated toluene, and indicated volumes of Triton surfactants. Samples were counted at 0 "C with a Packard Tri-Carb Liquid Scintillation Spectrometer Model 3375; gain, 50%; lower discriminator, 50; upper discriminator, 1000.
Table 11. Counting Efficiency of Tritium in Triton Toluene Water Mixtures at Low Temperature" Counting Physical state Counting efficiency, Triton of mixture rate, cpm % x-100 Viscous 14,151 19.5 translucent emulsion x-102 Viscous 14,082 19.4 translucent emulsion X-45:X-114 (1 :1) Clear mobile 12,771 17.6 solution Each vial contained 17 mi of a mixture of one volume of Triton to two volumes of scintillation solution and 5 ml of water containing 7.25 X lo4 dpm of tritiated water. Samples were counted at 0 "C with a Packard Tri-Carb Liquid Scintillation Spectrometer Model 3375; gain, 80%; lower discriminator, 50; upper discriminator, 1000.
impurity which could be removed by treatment with silica gel. Benson ( 2 ) recommended that the Triton be further purified by treatment with activated charcoal. Subsequently we have observed that such luminescence is a function of the particular lot of Triton X-100 and is not shown by any of the lots that we have tested during the past two years. However, all of these lots of Triton surfactants exhibit luminescence when alkaline solutions are added to solutions of the emulsifiers in toluene. This base induced luminescence varies between the different types and batches of Triton but, generally, immediately after mixing aqueous alkali with a toluene solution of Triton, there is a n intense light emission which rapidly declines reaching background levels in a few hours. The luminescence of a typical batch of Triton X-100 and its rate of decay was measured by adding 1 ml of 0.1N NaOH to a vial containing 15 ml of a precooled solution of Triton X-100 in toluene (1 part of Triton, 2 parts of toluene). The solution was rapidly mixed and placed in a Packard Tri Carb Model 3375 liquidscintillation counter within 10 seconds. A series of 25 one-minute counts were recorded with only a single channel (set up for tritium) printing out so that the interval between counts was 10 seconds. A semilog plot of the counts L'S. time could be resolved into three first order processes, one with a n initial intensity of 1.6 X l o 6cpm and a half life of 0.5 min, another with an initial rate of 2.5 X 10' cpm and a half life of 2 min, and a third with an initial rate of 2.5 X l o 3cpm and a half life of 10 min. Treatment with a variety of agents (silica gel, charcoal, activated alumina, sodium hydroxide 2036
ANALYTICAL CHEMISTRY
pellets, extraction with hexane and chloroform) had no appreciable affect on the alkali induced luminescence. However, treatment with freshly prepared Dowex-l hydroxide (stirred for 2 days with 0.1 gram of moist Dowex-1 X-8 hydroxide per ml of Triton) removes the luminescent impurity. Triton X-100 treated in this fashion regains its alkali inducible luminescence on prolonged storage although the rate is very slow if it is protected from the light and kept in the cold. After 5 months' storage, the counting rate during the first minute after mixing 1 ml of 0.1N NaOH with 15 ml of a 2:l mixture of toluene and Triton X-100 was 1.2 x 105 cpm for a sample that had been stored a t room temperature in the light, 6.8 x l o 3cprn for one that had been stored at room temperature in the dark, and 1.2 X l o 2 for one stored in the dark at 4 "C. The luminescence of all these samples had decayed t o background levels by 45 minutes after addition of alkali. Although by use of this treatment it is possible to remove the luminescent material and to retard its reaccumulation, we have found it inconvenient to d o so, preferring to acidify alkaline samples before counting. If acidification of samples is undesirable, storage of the samples for a few hours before counting to allow decay of the luminescence is also acceptable. It is convenient t o cool the samples during this storage period. Phase Transitions in Mixtures of Toluene, Triton, and Water. Benson (2) reported that mixtures of toluene, Triton X-100, and water form a single clear phase when heated slightly above room temperature. We have investigated the temperature dependent phase transitions of mixtures containing 20% water and 80% of a solution of one part of Triton in two parts of toluene. A typical mixture is milky and mobile at high temperature, as the mixture is cooled a single clear mobile phase forms which persists for a few degrees and then becomes cloudy and viscous. On further cooling, the mixture becomes clearer and more viscous till the freezing temperature is reached and the emulsion breaks. Either the clear mobile solution or the translucent viscous emulsion may be used for counting. The temperatures at which these transitions occur are a function of the length of the polyethylene glycol chain of the Triton surfactant and thus differ with each member of the series. The homogeneous solution is formed between 46 and 51 "C with Triton X-102, between 31 and 39 "C with Triton X-100, between 15 and 23 "C with Triton X-114 and between -2 and 3 "C with a 1 :1 mixture of Triton X-45 and Triton X-114. The translucent emulsion is formed between - 1 and 30 "C with Triton X-102 and between -5 and 8 "C with Triton X-100. The mixtures containing Triton X-114 and Triton X-45 freeze before a translucent emulsion is formed. The composition of mixtures of Triton X-100, toluene and aqueous solution which give optimal counting properties have been carefully investigated (3, 4) and mixtures with higher water contents than used here and acceptable counting efficiencies have been defined. These studies have shown that the appearance and counting properties of the Triton X-100, toluene, water system at low temperature are quite composition dependent. Thus, it would be expected that the phase transitions described above would also be affected by changes in composition. Our limited experience indicates that increasing the water content of mixtures with the 2:1 to1uene:Triton solution tends to narrow the acceptable temperature ranges. (3) J. D. Van Der Laarse, Itit. J. Appl. Radiat. Isotopes, 18, 485 (1967). (4) P. H. Williams, ibid., 19, 377 (1968).
Counting Properties of Toluene Triton Water Mixtures. Because the greatest difficulties are found in the counting of weak /3 emitters, tritium has been used to evaluate the various mixtures. As shown in Table I, addition of the several Triton surfactants t o toluene solutions of scintillator in the absence of water has relatively small effects o n the counting efficiency of tritium. Mixtures of Triton and scintillation solution are useful for solubilizing small amounts of biological material for counting ( 5 ) . F o r example, we have used these mixtures to count E. coli cells precipitated with trichloroacetic acid. Tables I1 and I11 show the counting efficiencies of tritiated water in suitable mixtures of Triton, scintillation solution, and water in the cold and at room temperatures, respectively. The differences in counting efficiencies between the two sets of conditions may be caused by a variety of factors such as differences in instrumentation and differences in light yield from the phosphors at the different temperatures. Within each group, however, the counting efficiencies of the solubilized samples are similar to those of the emulsions even though many of the emulsions are quite murky. The temperature range over which the mixtures form homogeneous solutions can be adjusted to any desired value by the use of appropriate mixtures of Triton surfactants as illustrated by the mixtures of Triton X-45 and X-114 in Table I1 and Triton X-100 and X-114 in (5) R. C. Meade and R. Stiglitz. I t i t . J . Appl. Radial. Isotopes, 13, 11 (1962).
Table 111. Counting Efficiency of Tritium in Triton Toluene Water Mixtures a t Ambient Temperature" Counting Physical state Counting efficiency, Triton of mixture rate, cpm % X-114 Clear mobile 7670 10 solution X-114 :X- 100 (2 :1) Clear mobile 7133 9.4 solution x-102 Viscous 7934 10.4 translucent emulsion a Each vial contains 5 ml of water with 7.6 X 104 dpm of tritiated water and 17 ml of a mixture of 2 parts ofscintillation solution to 1 part of Triton. Samples were counted at approximately 22 "C with a Packard Tri-Carb Model 574 liquid scintillation spectrometer; gain, 65 %; lower discriminator, 35; upper discriminator, 1000. The mixture containing Triton X-114 was clear between 17 and 21 "C and the mixture containing both Triton X-100 and Triton X-114 was clear between 22 and 28 "C. Table 111. For emulsion counting, Triton X-102 has the greatest utility for it can be used over a much wider temperature range than the others. RECEIVED for review June 24, 1968. Accepted August 14, 1968. Work supported in part by Grant No. G M 10317 from the National Institutes of Health.
High Precision Activation Analysis of Sodium with an Internal Standard Technique R . H. M a r s h a n d W. Allie, Jr. Ford Motor Co., Scientific Research Staff, Dearborn, Mich. 48121
MANYWORKERS have used activation analysis t o determine sodium in a variety of materials employing radiochemical separations. Reuland and Voight ( I ) analyzed tungsten bronzes for sodium nondestrictively, by coincident y counting. Lightowlers ( 2 ) determined sodium in a diamond with a pulse height analyzer. Schroeder and Winchester ( 3 ) determined sodium in silicate rocks nondestructively by discriminating against y rays having energies less than 2.6 meV, and using sodium carbonate as a standard. Kawashima ( 4 ) determined dysprosium in yttrium oxide using the yttrium as an internal standard. Standard deviation for a single determination was about 10%. Recently, Lutz and DeSoete (5)employed sodium as a n internal standard for the determination of carbon in sodium by photon activation analysis. The problem under consideration here was that of the determination of macro amounts of sodium in a material which could only be readily solubilized by a basic fusion. Because of the possibility of contamination, loss of sample, dilution error, etc., to which the usual methods used for the deter(1) R. J. Reuland and A. F.Voigt, ANAL.CHEM., 35, 1263 (1963). (2) E. C. Lightowlers, ibid., 35, 1285 (1963). (3) G. L. Schroeder and J. W. Winchester, ibid., 34, 96 (1962).
(4) Toshi Kawashima, Deriki Tsushin Kendyusho Keiikya Jitsuyoka Hokokir, 13, 1835 (1964). (5) G. J. Lutz and D. A. DeSoete, Anal. Chem., 40, 818(1968).
mination of sodium can be subjected, a n attempt was made to develop a neutron activation technique which would be highly precise and accurate. Although neutron activation is usually thought of as a trace method, proper care should allow the technique to be used for macro quantities. One of the severest limitations t o the precision of activation analysis is nonuniform neutron fluxes which are found in reactors and which require flux mapping in order t o apply corrections. Also, the maintenance of strictly uniform irradiation and counting geometry is difficult. The use of a n internal standard obviates the necessity of mapping neutron fluxes in reactors and maintaining strictly uniform counting geometry. EXPERIMENTAL
Apparatus and Reagents. The following special equipment and reagents were used: a cooled, lithium-drifted germanium detector and 400-channel analyzer with a resolution of 5-6 keV F W H M for cobalt-60 radiation, and a lithium-drifted germanium detector and 2048-channel analyzer with a digital spectrum stabilizer having a resolution of 3.5 keV F W H M . Potassium carbonate containing less than 2 ppm of sodium, obtained from United Mineral and Chemical Corporation. All other materials used are common t o a n analytical laboratory. Procedures. The first procedure employed was as follows: the standards were prepared by weighing 10-mg portions of AS203 and 20-mg portions of N a 2 C 0 3 into 1-cm long polyVOL. 40, NO. 13, NOVEMBER 1968
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