Gas Chromatographic Separation of Hydrazine Mixtures and Water Using a Stationary Phase That Is Chemically Similar to Hydrazine L. A. Dee and A. K . Webb Air Force Rocket Propulsion Laboratory, Research and Technology Diuision, Air Force Systems Command, Edwards, Calg.
CONSIDERABLE INTEREST exists in rapid and specific methods for the analysis of hydrazine mixtures. Malone (1, 2) developed several nonaqueous titration techniques for hydrazine mixtures ; however, they lack specificity for all components. Burns (3) determined that such titrimetric methods were no more accurate and less specific than a gas chromatographic technique. Gas chromatography of hydrazine mixtures, however specific, is difficult because of the strongly polar nature of these compounds. Sample adsorption and asymmetrical peaks generally result. Cain ( 4 ) and Hagstrom ( 5 ) developed chromatographic methods for various waterhydrazine mixtures using polyethylene glycol on diatomite supports. Noticeable water and hydrazine adsorption occurs at low concentrations. Jones (6) separated water, methylhydrazine (MMH), and hydrazine with Dowfax 9N9 on Teflon 6 (DuPont). This combination will not separate water and 1,l-dimethylhydrazine (UDMH). Asymmetrical hydrazine peaks are typical even with Teflon supports. Various authors (7-9) have described methods for reducing sample adsorption and peak tailing. Such techniques as carrier gas doping and stationary phase additives may produce better appearing chromatograms but frequently do not add to the quantitative accuracy or reproducibility of the method. Scholz (IO) and Brown ( I ] ) suggest that peak symmetry and selectivity for polar samples is increased when the stationary phase is chemically similar to the sample. This paper describes a study of two polar stationary phases on supports of varying reactivity. It demonstrates that through proper choice of column packing materials, water, UDMH, MMH, and hydrazine can be completely separated in all proportions with little or no adsorption and with symmetrical peaks.
Materials. The columns were prepared from 1- or 2meter lengths of l/r-inch 0.D. Type 316 stainless-steel tubing. The support materials were 90jlOO mesh Anakrom B (Analabs, Inc.), 35/60 mesh Teflon 6 (Perkin-Elmer Corp.), 40/60 mesh Fluoropak 80 (The Fluorocarbon Co.), and 40/60 mesh Teflon 5 (DuPont). The stationary phases were Carbowax 400 (Dow Chemical Co .) and 2-hydrazinopyridine (Aldrich Chemical Co .). Column Preparation. The columns were prepared by mixing the appropriate quantities of stationary phase dissolved in methyl alcohol (anhydrous, ACS grade) with the various support materials and evaporating the solvent in a flat tray. No special precautions were taken except for Teflon 6, which was chilled to 5” C prior to sieving and packing. All columns were thermally conditioned at 20”-30” C above operating temperature for several hours prior to use. Table I shows the various columns studied. A, D, E, F, G , and H represent the optimum packing composition and operating conditions for each column that would provide a reasonable analysis time ( 10 % Hypy”/Fluoropak 1 80 A 10% Hypy/Fluoropak 2 80 B C 2.5 % Hypy/Fluoropak 2 70 10 % Hypy/Teflon 6 2 80 D 10% Hypy/Anakrom B 1 80 E 30% CW 400/Anakrom B 1 115 F 20% CW 400/Fluoropak 2 112 G 10% Hypy/Teflon 5 1 80 H
He flow rate (cc/min) 100 100 120 80 100 120 100 120
= Hypy = 2-Hydrazinopyridine
Blend I I1
Table 11. Weight Composition of Blends H20 UDMH Z MMH Z NZH4
z
25.1 22.2
z
25.3 21.9
24.4 27.9
25.1 27.9
(11) I. Brown, J . Chromatog., 10, 284 (1963). VOL. 39, NO. 10, AUGUST 1967
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Figure 1. Chromatogram of Blend I1 using column A A . UDMH B . Hz0 C. MMH
Figure 2. Component area us. Blend I1 sample size
D. N2H4
RESULTS AND DISCUSSION
Where:
Ac Kc
= =
%C =
area of component sensitivity of component per cent of component in blend
Blend I was used to determine the sensitivity factors for the analysis of Blend 11. The analyzed composition of Blend I1 was calculated by the following formula:
”=
AcKc x 100 (AciKc,)
Table 111. Column Properties for NzHa Column HETP(mm) As Analysis time (minutes) A 3.8 1 .o 13 B C
D
...
E F G
1.5 6.3 2.5
H
Table IV. Mean Standard deviation Actual Mean error Sensitivity factor
1 .o 1.1 1.2 2 1.5 1.4 1.2
3.9 5.2 5.0
27 8 15
column degraded rapidly 9.5 14 16
Gas Chromatographic Analysis of Blend II ZUDMH ZHzO ZMMH ZNzH4 21.8
21.8
27.6
28.7
0.13 22.2 -0.4
0.08 21.9 -0.1
0.17 27.9 -0.3
0.17 27.9 +O. 8
1.OOO
0.803
0.926
Column Evaluation. Table I11 illustrates the interaction of the stationary phase and support with respect to the N z H ~ peak. The asymmetry values (As) were calculated according to the method described by Dal Nogare and Chiu (12). The As of the N2H4peak was used as a guideline for the determination of sample/column interaction. Columns A, B, and C gave base line separation of all components. Columns D and E only partially resolved MMH and HzO. Column F adequately resolved UDMH, HzO, and NzH4,but was inadequate for MMH-HzO separation when the water concentration exceeded 10% because of the peak asymmetry. Column G would not resolve HzO and MMH even though the water peak was symmetrical. Column H resolved all components well but the MMH and NzH4 peaks were asymmetrical. Column A was used for the following work because it offered the best compromise of analysis time, resolution, and peak symmetry. Quantitative Analysis. Table IV represents 10 replicate chromatographic analyses of Blend 11. The relative magnitude and sign of the mean errors probably results from vaporization losses of the blends during their preparation. The sample size was 2 pl. Figure 1 represents a typical chromatogram of Blend I1 chosen from the analysis series. The dashed line illustrates the trailing edge of the N z H peak ~ if the As value were 1.2. Response Linearity. Figure 2 is a plot of the peak area of each component LX. the total sample volume of Blend I1 injected. Response is linear for all corponents to their detectable limits, and all of the curves approach the origin thus indicating that sample adsorption is essentially non-
0.892 (12) S. Dal Nogare and J. Chiu, ANAL.CHEM., 34, 890 (1962).
1 166
ANALYTICAL CHEMISTRY
existent on this column. The retention times for the components also are constant regardless of sample composition. As little as 2 pg of MMH or NZH4in a 3-pl water sample was detectable, resolved, and produced symmetrical peaks on column A. This indicates that only normal solvent-solute interactions are responsible for the separation on this column. Other columns such as F and G showed appreciable adsorp~ the sample size was below tion of H20,MMH, and N z Hwhen 0.5 ,ul. Column Stability. 2-Hydrazinopyridine is a strongly alkaline material and reacts rapidly with COZ. Columns such as A, B, or C are stable for 6 to 10 days if some helium flow is maintained at all times; however, they deteriorate
rapidly if exposed to the atmosphere for several days. Thermogravimetric analysis of 2-hydrazinopyridine indicates that significant vaporization losses occur above 80" C. Solvents with higher boiling points would be an advantage; however, chemical similarity should be maintained. ACKNOWLEDGMENT
The authors are grateful to J. T. Nakamura and H. H. Martens for editing the original manuscript. RECEIVED for review February 13, 1967. Accepted May 26, 1967. This work was supported by the United States Air Force at the Rocket Propulsion Laboratory, Edwards, Calif.
Determination of Americium-241 in Pure Plutonium Using Extraction with Trioctylphosphine Oxide and Gamma Counting Joseph Bubernak, Marion S. Lew, and George M. Matlack Unicersiry of California, Los Alamos Scientific Laboratory, Los Alamos, N . M . RECENT WORK ON ELECTROREFINING methods at Los Alamos has resulted in the production of ultra pure plutonium containing less than 5 ppm of americium. For the determination of americium at this level, direct counting techniques such as combined alpha and gamma counting ( I ) proved to be inaccurate. This was due to the high plutonium contribution to total gamma activity, thereby requiring the use of a large correction factor, and to the effect of uranium-237 gamma activity present as a decay product of plutonium-241. Several chemical methods are available for the separation of americium from plutonium and uranium. One method involves oxidation of plutonium to the hexavalent state with ceric or dichromate ion, followed by the carrying of americium(II1) on a precipitate of lanthanum fluoride ( 2 ) ; plutonium (VI) and presumably also uranium(V1) remain in solution. Another method involves adsorbing plutonium(1V) from 8M nitric acid onto anion exchange Dowex-1 resin and eluting the americium(II1) through the column with additional acid (3). Alternatively, plutonium(1V) can be extracted from 1M nitric acid into 0.5M thenoyltrifluoroacetone (TTA) in xylene, leaving americium(II1) in the aqueous phase (4). Experience in this laboratory has shown that the lanthanum fluoride precipitation and TTA-extraction methods give insufficient decontamination from plutonium to allow measurement of americium by alpha or gamma counting. In the anion exchange method incomplete separation of americium from uranium-237 prohibited the use of gamma counting, while alpha counting was unsuitable because of salts present from adjusting the valence state of plutonium. (1) J. Bubernak, M. S. Lew, and G. M. Matlack, ANAL.CHEM., 30, 1759 (1958). (2) R. A. Penneman and T. K. Keenan, U. S. At. Energy Comm., Rept. NAS-NS-3006 (1960). (3) F. P. Roberts and F. P. Brauer, U. S. At. Energy Comm., Rept. HW-60552 (1959). (4) F. L. Moore and J. E. Hudgens, Jr., ANAL.CHEM.,29, 1767 ( 1957).
An extraction method which seemed suitable to the present problem involves the use of trioctylphosphine oxide (TOPO). Extraction coefficients between TOPO in an organic solvent and 6 M nitric acid have been reported to be above 600 for plutonium(1V) and about 100 for uranium(VI), while americium(II1) shows no extractability (5). The possibility of utilizing such a system whereby americium could be determined in the aqueous phase after extraction was therefore investigated. Recently the determination of americium by extraction into di(2-ethylhexyl) orthophosphoric acid in toluene from 0.05-0.1M nitric acid followed by stripping into 3M nitric acid has been described (6). Decontamination from plutonium and uranium were each greater than l o 4 and the americium was measured by counting its alpha activity. Although this method seemed applicable to the present problem, it was not evaluated. EXPERIMENTAL
Reagents and Equipment. Trioctylphosphine oxide (TOPO) was obtained from Eastman Kodak Co., Rochester, N. Y. Solutions for extraction contained 50 grams of this reagent per liter of octane. Gamma activity measurements were made using a welltype sodium iodide (TI) crystal. The high voltage on the multiplier phototube was set for the detection of gamma rays with energy above 30 keV. Procedure. Pipet an aliquot of sample into a 3-ml extraction tube, rinsing the pipet with 3 drops of 1M nitric acid, Add 2 drops of 1 M hydroxylamine hydrochloride, mix and allow the solution to stand for 20-30 minutes. Add carefully 6 drops of 1 M sodium nitrite, then 10-12 drops of concentrated nitric acid. Add about one rnl of 5 TOPO in octane to the tube and mix the phases thoroughly for 5 minutes. Discard the organic phase containing plu( 5 ) J. C . White and W. J. Ross, U. S. At. Energy Comm., Rept. NAS-NS-3102 (1961).
(6) M. H. Campbell, ANAL.CHEM., 36,2065 (1964). VOL. 39, NO. 10, AUGUST 1967
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