j
6
P
o
5
10
IS
20
CONCENTRATION RATIO: P 0 4 / C o
Figure 3. Interference effect of phosphate on calcium absorption The data of David were taken from David, D. J., Analyrf 85, 495 (1 960).
is that concentration required to produce 1% absorption. Several significant conclusions can be drawn from the data presented in Table I. Although only 0.12 ml. of aerosol per minute passed through the plasma, the observed detection limits and sensitivities for the strong monoxide-forming elements (Al, Nb, Ti, W, Y) are comparable t o the best reported flame absorption values (2, 3 ) . Since aerosol flow rates for flames are commonly an order of magnitude greater, the comparable sensitivities observed indicate that either the degree of free-atom formation in the plasma is considerably greater or monoxide formation is greatly reduced.
-
'
The data in Table I also show that useful sensitivities are observed for absorption lines in the 4600 to 5200 A. spectral region. This wavelength interval is often avoided in flame spectroscopy because the strong CZband emission increases the d.c. noise component of the photomultiplier detector. The zone of the plasma examined in this study has virtually no band or continuum emission even when an aqueous aerosol is added. The only significant background emission, aside from the argon lines, in the zone of the plasma examined in this study is the 3064 A. OH system (see Figure 2). It is worth noting that the hollow cathode emission lines employed in this investigation produced photocurrents from 8 to 200 times greater than the band head a t 3063 A. Our expectations that chemical interferences would be markedly reduced in the plasma were confirmed, as shown in Figures 3 and 4, by the behavior of calcium in the presence of phosphate or aluminum ions. In contrast to the sharp depressive effect of these ions observed in flame absorption, the calcium absorption in the plasma shows a slight but surprising increase. Although this apparent enhancement invites speculation, it seems advisable to defer discussion until more definitive information on the various processes occurring in the plasma is available.
i
$40 I "01 :
L /
"
'INDUCTON COUPLED
-0
PLASMA
AIR-PIXTYLENE FLAME (DAVID1
a
AIR- ACETYLENE F L A M E (ISU)
0
s
IO
IS
20
CONCENTRATION RATIO: AllCo
Figure 4. Interference effect of aluminum on calcium absorption The data of David were taken from David, D. J., Analyst 85, 495 ( 1 960). LITERATURE CITED
(1) Greenfield, S., Jones, I. Ll., Berry, C. T., Analyst 89, 713 (1964). Manning, D. C., Atomic Absorption Newsletter 4, 267 (1965). (Perkin-
(2)
Elmer. Corp., Norwalk, Conn.).'
(3) Slavin, Walter, Atomic Absorption Newsletter, No. 24, 15 (1964), (Perkin-
Elmer Corp., Norwalk, Conn.).
(4) Wendt, R. H., Fassel, V. A., ANAL.
CHEM.37, 920 (1965). RICHARD H. WENDT VELMER A. FASSEL Institute for Atomic Research and Department of Chemistry Iowa State University Ames, Iowa RECEIVED for review September 27, 1965. Accepted December 13, 1965.
Gas Chromatographic Separation of Hydrazine, Monomethylhydrazine, and Water SIR: There has been no literature available describing a satisfactory method for the gas chromatographic separation of a mixture of hydrazine, monomethylhydraaine (MMH), and water, although a number of procedures for the separation of hydrazines, water, and various hydrazine mixtures have been published (I,%'). The method described here shows an excellent separation of water, MMH, and hydrazine on a column using 10% Dowfax 9N9 on Teflon 6 ( 3 ) . EXPERIMENTAL
Chemicals, The hydrazine and M M H are products of the Olin Chemical Corp., Lake Charles, La. The Teflon 6 (registered trademark for tetrafluoroethylene (TFE) fluorocarbon resin) is a product of E. I. d u Pont de Nemours & Co., Wilmington, Del. The Dowfax 9N9, a product 338
ANALYTICAL CHEMISTRY
of the Dow Chemical Co., Midland, Mich., has a chemical composition of
Apparatus. All analyses were performed with a Perkin-Elmer Model 154-C vapor fractometer using a dual chamber thermistor thermal conductivity cell. Chromatograms were recorded on a Leeds and Northrup 5-mv. recorder, a t a chart speed of l/z inch per minute. An Instron automatic integrator, two counter model, was used in integrating the peaks. A sample size of approximately 5 111. was used in each case. The column packing was prepared by air-drying a slowly stirred slurry of Dowfax 9N9 in methanol in amounts to produce a 10% Dowfax 9N9 coating, and subsequently was dried in a vacuum oven a t 100' C. The material was then chilled, screened through a 30mesh sieve, and carefully packed in a
l/d-inch o.d., 6-fooblong stainless steel column. The column was stabilized overnight a t 150' C. at a 20 ml. per minute helium flow rate. During analysis, a temperature of llOo C. and a helium flow rate of 40 ml. per minute were maintained. The column was conditioned prior to each day's use by one or more injections of approximately 10 pl. of hydrazine. Although separation required only about 7 minutes, an additional 10 minutes were allowed before the next analysis was performed. Sample Preparation. Samples of hydrazine and M M H were analyzed and an by an acidimetric method (4, 0.2% hydrazine analysis of 97.0 and 90.9 =t0.2y0MMH was obtained. Test mixtures were prepared by adding different amounts of water to hydrazine and to MMH, and by mixing hydrazine and MMH in various percentages. The per cent composition by weight of some of the mixtures is given in Table I.
*
‘I
3
1
13
i:
I
0
0 IO
II
09
I
-A 5
0 8
A 4
A 3-
06
0 H20: MMH
A
AI
H20: N2H4
07
0.6
A2 0.5 10
0
20
30
40
0
I
2
.3 4 5 6 7 RETENTION TIME- MINUTES
8
9 1 0
Figure 1 . Resolution of typical mixture ofhydrazines and water by 10% Dowfax 9N9 on Teflon 6 ldentiflcotion of peokr: 1, Air. 2, Ammonla. 3, Water. 4, MMH. 5, Hydrazine. lndividuol component run -Mixed component run ( 3 2 x 1 (25% water, 40% MMH, 35% hydrazine)
---
DISCUSSION
Two columns were prepared for the analysis of the hydrazine, and the MMH, and the water mixtures before a workable column was obtained. The first column, prepared as described in (3) with 10% Dowfax 9N9 and 1% sodium hydroxide on Chromosorb, did not separate the water from the MMH. A second column was prepared using 10% Dowfax 9N9 and 1% sodium hydroxide on Teflon 6. Although this column partially separated the water from the MMH, separation was not sufficient for a satisfactory analysis. The third column was prepared with 10% Dowfax 9N9 on Teflon 6, but without the sodium hydroxide. Although there was a slight increase in hydrazine tailing in this column, there was sufficient separation of the three components for a good analysis. Peaks appeared in the order of air, ammonia, water, MMH, and hydrazine; retention times were approximately 2 minutes for water, 3 minutes for MMH, and 4l/2 minutes for hydrazine (Table 11, Figure 1). Figure 1 also reveals that retention times shifted, depending upon whether each component was injected separately or in mixtures. This shifting of retention times is not clearly
Table I.
1 2 3 4 5 6 7 8 9 10 11
NZH4 98.64 97.03 88.50 69.36 49.51
80
30
I 100
...
... ... II.
Water
1 2 3
10 3 25
1 by definition
where R is the response, C is the integrator counts, A is attenuation, T is the reciprocal response ratio, h is hydrazine, m is MMH, w is water, and W is the weight of the sample. The, reciprocal response ratios (Table I, Figure 2) were determined from an average of a t least three analyses and showed only slight variations, with changes in water down to the 10% level. Below the 10% level, small errors in the calculated per cent water created large errors in the calculated response ratios. However, because the errors involved such a small percentage of the sample, the per cent composition
Reciprocal Response Ratios
1.36 2.97 11.50 30.64 50.49 0.64 9.15 16.59 35.76 54.35 72.43
...
Mixture
a
TO
calculations, reciprocal response ratios, the reciprocals of the relative response ratios, were used to calculate the composition of the samples being analyzed. The relative responses were calculated from
Component, % HzO
... ...
Table
I
Reciprocal response ratios of water to hydrazines
understood; however, it may be due to changes in concentration. The shifting of retention times was not detrimental to the separation of the components. Because retention time of unsymmetrical dimethylhydrazine (UDMH) was the same as that of water, the column proved to be inadequate for the analysis of hydrazine mixtures containing UDMH. The chromatogram disclosed the presence of nitrogen and ammonia, which could have been present either as impurities in the sample or as a result of the decomposition of hydrazine upon injection into the fractometer. The decomposition is particularly evident at a high injector temperature. The injector in this analysis was near the temperature of the column (110’ C.), Because the quantity of ammonia present was small, it had no significant effect on the relative response ratios. The relative response ratio of each component was determined from mixtures of known compositions of the hydrazines and the water. To simplify
Sample
60
I
HYDRAZINES (MMH O R NpH41
*/e
Figure 2.
50
1
Ratio, H20 = 1 H z O m
MMH
HzO/NzHd 0.74 0.56 1.05 1.06 1.04
... ... ... ...
. ...
99:36 90.85 83.41 64.24 45.65 27.57
... ... ... ... ...
...
...
... ..* ...
1.03 0.67 1.15 1.17 1.20 1.18
Variation of Retention Times with Composition (110’ C. at 40 ml./min.)
Component, % MMH 90 .I.
.
40
NzH;
... 97 35
Retention time, min.= Water MMH NzHi 2.0 2.0 2.2
3.2
...
3.4
...
4.4 5.0
Retention times measured from injection.
VOL. 38, NO. 2, FEBRUARY 1966
339
values obtained compared favorably with the acidimetric analysis. Percentage compositions for hydrazine were calculated by
yohydrazine
=
Analogous formulas were used for the other components. Calculated responses were based upon prepared mixtures of known composition and were dependent upon the acidimetric analysis of hydrazine and MMH, which is accurate to *0.2%. A chromatogram of a typical mixture of hydrazines and water is shown in Figure 1. The analysis was calculated by using the reciprocal response ratios obtained from the analysis of a previously prepared mixture of similar composition. The sample shown in Figure 1 had a calculated weight of 25.0% water, 40.4% MMH, and 34.6% hydrazine. The chromatographic analysis of this mixture, using the previ-
ously obtained res onse ratios, showed 24.2% water, 4 0 . 9 g MMH, and 34.9% hydrazine. Analyses of other mixtures by this procedure showed similar results. Because of the high reactivity of the hydrazine, the prepared column should not be used for the analysis of other materials. RESULTS
The statistical analysis of the data obtained in the analyses of hydrazine, MMH, and water mixtures indicated that 99% of all of the values collected should fall within f 0.71% of the average value of three data points a t the 95% confidence level. If the mean of three data points is used, the mean will be within 0.41% of the true value of each of the components as calculated by weight. The column described has been used for over 200 analyses with no apparent fatigue. The method employed in the study has the advantages of short
analysis time, minimal tailing, excellent resolution, and column stability. One of the disadvantages is the inability to separate UDMH and water. ACKNOWLEDGMENT
The author thanks W. R. Carpenter and E. M. Bens for their assistance and advice in the development and evaluation of this gas chromatographic procedure. LITERATURE CITED
(1) Cain, E. F. C;,, Stevens, M., “Gas Chromatography, p. 343, Academic Press, New York, 1961. (2) Kuwada, D. M., J . Gus Chromatog. 1, (3), 11 (1963). (3) O’Donnell, J. F., Mann, C. K., ANAL. CHEM.36,2097 (1964). (4) Penneman, R. A., Audrieth, L. F., Ibid., 20, 1058 (1961).
RICHARD M. JONES U. S. Naval Ordnance Test Station China Lake, Calif. 93557
Method of Proportional Equations for Analysis of Closely Related Mixtures by Differential Reaction Rates Where Concentration Reactants of Reagent
[Reactants], overcame most of the above mentioned limitations. The chief advantages associated with this kinetic method are (1, 2): Prior knowledge of total initial concentration of the species of interest need not be known; more than two components can be analyzed; and only a fraction of the total reaction time is required for analysis. However, because of the mathematical framework of this method, small ratio of rate constants-i.e., 4 to 1 or less-could not be tolerated (2). A Method of Proportional Equations (or double point method) which is applicable for reactions pseudo-firstorder with respect to the reagent is reported in this paper. This method has the above advantages of Garmon and Reilley’s method plus the additional advantage that small ratio of rate constants-i.e., 2 to 1 or less-can be used. The method was tested by the analysis of several different carbonyl mixtures using the reaction mentioned above. The method could be utilized, however,
for any closely related mixtures where the concentration of reagent can be followed experimentally as a function of time. PRINCIPLE
Roberts and Regan (6) presented a kinetic method for simultaneously determining two components, A and B, reacting with a common reagent, R. If the concentrations of A and B are much greater-Le. 50 to 1 or largerthan the reagent, R, the following pseudo-firsborder rate expression holds:
where K* is the overall pseudo-firstorder rate constant for both species which is given by where k A and kg are the second-order rate constants of A and B respectively reacting with R, and [AIoand [ B ] ,are the initial concentrations of reacting species A and B (the amount of A and B that reacts during the reaction is negligible as the concentrations of these species are in such great excess). The analysis is accomplished by measuring K* (as described by Papa,
