Specific Determination of Monomethyl Hydrazine in Dilute Aqueous Solutions Containing Other Hydrazine Derivatives EDWARD W. NEUMANN and HERBERT G. NADEAU Olin Research Center, O h Mathieson Chemical Corp., New Haven 4, Conn.
b Monomethyl hydrazine (MMH) in dilute aqueous solutions containing hydrazine and small amounts of other hydrazine derivatives, specifically unsymmetrical dimethyl hydrazine (UDMH), methylene dimethyl hydrazine (MDMH), and trimethyl hydrazine (TMH), is determined by a combined oxidative procedure and gas chromatographic determination for methane. The method described is applicable to mixtures of hydrazines containing monomethylamine.
M
can be determined in dilute aqueous solutions by the usual oxidative procedures such as those incorporating sodium hypochlorite or chloramine-?' ( I ) . However, these oxidants are not specific, and any oxidizable materials present will also be included as apparent monomethyl hydrazine (MMH). A method by Clark and Smith (1) differentiates between hydrazine and MhlH, but does not provide for the differentiation of other oxidizable materials such as unsymmetrical dimethyl hydrazine (UDMH), methylene dimethyl hydrazine (MDMH), and trimethyl hydrazine (TMH). A method was desired which would allow for the specific determination of MMH in research samples where many different types of hydrazine compounds could be expected. An attempt to utilize gas chromatography for the separation and analysis of M M H in the presence of other compounds, especially hydrazine, was not successful. Complete separation of M M H , hydrazine, UDMH, and M D M H in aqueous solution was readily obtainable, but no quantitative data for M M H and/or the other components could be obtained. It appears that both absorption and degradation take place. -45% Quadrol (tetrabishydroxypropyl ebhylenediamine) on Chromosorb W, 80to 100-mesh column was employed in conjunction with a chromatograph which provided for temperature programming and a flame ionization detector. Other column substrates and supports were tried with no apparent advantage. 640
ONOMETHYL HYDRAZINE
ANALYTICAL CHEMISTRY
In these laboratories, while studying various reactions of MMH, it was discovered that the gaseous products resulting from the reaction of M M H and sodium hypochlorite were nitrogen, methane, carbon monoxide, and traces of alkyl chlorides. Identifications were made by both gas chromatography and mass spectrometry. It was previously reported by Clark and Smith ( I ) that nitrogen and carbon monoxide were the only gases found. They reported no methane but they did postulate a reaction in which an oxidation of M M H occurs with an 8-electron change. The reaction which they postulated was based on the infrared spectra of the gaseous products. In this work, it was demonstrated by gas chromatography that the CH4content of the gas phase was always greater than that of the CO, possibly because the reaction is not driven to completion. Further gas chromatographic studies of the hypochlorite-MMH reaction indicated the possibility of an analytical method for aqueous solutions of h l h l H based on
4
E I t
-s 1 min
Figure 1.
A typical chromatogram
the determination of the CHI produced. A few trials indicated that, under certain conditions, the amount of methane produced in the reaction is proportional to the amount of M M H present. The methane produced represents only about 25% of theoretical if it is assumed that one mole of methane is produced for each mole of X M H reacting. EXPERIMENTAL
Reagents. Sodium hypochlorite, 5.25% (Clorox); monomethyl hydrazine, 98.0% by weight (Olin Mathieson Chemical Corp.). Apparatus. ilerograph gas chromatograph A-90P-2, equipped with a 3foot aluminum '/(-inch diameter column packed with Molecular Sieves SA, 60- to 80-mesh. The chromatographic conditions were as follows: helium flow, 45 ml. per minute; injection port, 100" C.; column, 60" C.; detector, 120" C.; detector current, 200 ma. Preparation of Solutions for Calibration Curve. Ten solutions of M M H were prepared by pipetting 98.07, 1 I M H into 100-ml. volumetric flasks. Solutions of 0.40, 0.50, 0.80, 1.00, 1.50, 2.00, 2.50, 3.00, 3.50, 4.00, and 4.50 volume 70mere made, using freshly boiled, distilled water. Dissolved air, because of its carbon dioxide content, seriously affects the reaction. Therefore, freshly boiled water was used. Method. Three grams of KC1 (hO.1 gram) are weighed into a 60-cc. serum bottle, and 3 ml. of Clorox are added by pipet. The bottle is sealed with a serum cap. One milliliter of a standard solution of N M H is then injected through the serum cap with a 1-cc. tuberculin syringe. The syringe is removed immediately so as not to allow the escape of the gases produced. The reaction occurs in a few seconds. il clean, dry, 1-cc. tuberculin syringe is used to remove 0.50 cc. of gas from the serum bottle. This gas is immediately injected into the gas chromatograph. When a sample of gas is removed from the serum bottle, it is advisable to move the syringe plunger up and down several times to obtain a representative sample of gas, because a small amount of air resides in the syringe needle, and this is introduced into the bottle when the needle is inserted.
Oxygen, nitrogen, methane, and carbon monoxide are eluted in 34, 53, 101, and 154 seconds, respectively. A standard calibration curve is prepared by plotting the ratio of C H I / N ~peak heights us. the volume % MMH. RESULTS AND DISCUSSION
A typical chromatogram is shown in Figure 1. The relationship b e x e e n the ratio of methane to nitrogen and the MMH concentration was determined on six different occasions and had the following slopes: 1.70, 1.75, 1.70, 1.64, 1.64, 1.69. The data are tabulated in Table I, together with the stand,trd deviations for those concentrations where there were enough determination3 for a statistical calculation. It was fe t that four or less determinations were insufficient. The ratio of CH4 to Nz has been plotted, rather than the CHh value itself. This eliminates the va aiations in day-today instrument respor se and any variations in the size of the 0.50-cc. gas sample which is injected. The calibration curve intersects the x-axis a t a concentration of 0.3y0, which possibly is
the limit of detectability under these conditions. Nitrogen is produced in the reaction; however, it is negligible compared to that present in the air in the serum bottle. Potassium chloride is used in the reaction to decrease the solubility of methane in the liquid phase. The molar ratio of sodium hypochlorite to M M H on the average is 5 to 1, so that there is always an excess of hypochlorite present. The stoichiometry of the reaction of M M H and sodium hypochlorite in aqueous solution, as well as the mechanism for the production of both carbon monoxide and methane is not known. Possibly under the conditions of the reaction, dealkylation occurs to produce a methyl radical which can abstract hydrogen to form methane. Methane in turn may be oxidized to carbon monoxide. The presence of alkyl chlorides certainly would lend credence to this type of reaction. No attempt has been made to study this reaction further. Under the conditions used in this
Table 1.
MMH,
%
0.4 0.5
Reproducibility Data
No. of
detns.
0.8
3 4 3
4.0 4.5
4 2
CHdN2 X lo2, average 0.17 0.34 0.82
Std. dev.
... e . .
...
6.53 7.05
method, the maximum concentration of M M H permissible would be of the order of 5%. It certainly would not be suitable as a method of assay for MMH. LITERATURE CITED
(1) Clark, J. D., Smith, J. R., ANAL.
CHEW33,1186 (1961). RECEIVED for review October 14, 1963. Accepted December 6,1963. The authors thank the Olin Mathieson Chemical Corp. for permission to publish, especially the personnel of the Chemicals Division, who supported the study.
A Simplified Routine Method for X-Ray Absorption Edge Spectrometric Analysis EUGENE P. BERTIN, RITA J. LONGOBUCCO, and RITA J. CARVER Radio Corporation of America, Electron Tube Division, Harrison, N.
b A simplified routine method for x-ray absorption edge spectrometric analysis was developed for use on standard flat-crystal x-ray spectrometers with only minor modifications. The only x-ray measurements required are the intensities transmitted by the sampIe(s), an empty sample cell, a correction standard, and the open x-ray secondary beain tunnel at each of two wavelengths bracketing an x-ray absorption edge of the element determined. Sample concentration is calculated from these measurements and from certain other data derived from the literature, Tables of such data were compiled and are presented. No standards or calibration are required, and matrix effects are usually absent. The bracketing wavelengths are x-ray spec:traI lines excited in secondary targets placed in the sample drawer. The procedure is most readily applied to solutions, but is also useful with pciwders, briquets, thin slices, foils, and films. Cells for all these sample fcirms and other accessories were designed and made, and are described. The simplified
J.
procedure was evaluated for 10 elements having a wide range of atomic number in a variety of sample forms. The results are only a little less satisfactory lhan those reported in the literature for the more elaborate procedures.
T
HE ANALYTICAL CHEMIST is most frequently called upon to strive to increase the accuracy of his methods. However, there are still many types of analysis for which some accuracy may be sacrificed in the interest of increased speed and convenience. The objectives of this project were to eliminate the preliminary experimental work and some of the refinements involved in the x-ray absorption edge procedures described by Barieau (1) and Dunn ( 6 ) , to incorporate certain techniques reported by various other workers, and to evaluate the resulting simplified procedure for elements having a wide range of atomic number in a variety of sample forms. X-ray absorption edge spectrometry has been known for nearly 40 years (IC), and reviews of its progressive
development have appeared regularly ($0, 21). Routine procedures of general applicability and high precision and accuracy have been described by Barieau ( I ) , Dunn (6), Hakkila and Waterbury (15), Knapp, Lindahl, and Mabis (I@, and others. I n view of the many advantages of absorption edge spectrometry, it is difficult to understand why the method is not more widely used. The preparation of standards and calibration curves for x-ray fluorescence spectrometric analysis of a multicomponent system is warranted if there are many samples to be analyzed from time to time, but usually not for one or a few samples on a single occasion. Absorption edge spectrometry eliminates the need for preparation and storage of standards and for their measurement each time a n analysis is made. The method is applicable to liquids, solids, briquets, powders, foils, thin films, and even gases. Liquid volumes as small as 0.2 ml. are usually sufficient. Matrix effects are usually absent because only the element determined undergoes a marked change in absorption coefVOL. 36, NO. 3, MARCH 1964
641
