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Anal. Chem. 1980, 52, 774-776
LITERATURE C I T E D
the two tests. If the overall significance level is not to exceed a , then it is sufficient for the significance levels (cy1 and cy2) of the two tests to be such that cy1 a2 5 a. For example, if the overall significance level is to be 0.05, perform the two tests a t a level of significance of 0.025. T h e last example of Kelter and Carr deserves a brief comment. It should be remembered that a significance level of 0.05 means that, over the long run, a true null hypotheses will be rejected 5% of the time. In addition, a significant 2-value indicates something is amiss statistically; hence the data should be investigated. This may result in the decision that, although the result is statistically significant, it is not of practical importance. For a discussion of statistical significance and piactical significance, see Daniel (6). In summary, we recommend that a test of hypothesis on the proportion of positive residuals be conducted before performing the runs test. Other tests may be performed as well, for example the techniques discussed by Draper and Smith (7) are, for t h e most part, suited to checking the goodness of fit of kinetic data to an hypothesized rate.
(1) Keiter, P. B.; Carr, J. D. Anal. Chem. 1979, 57, 1857. (2) Daniel, W . W. "Applied Nonparametric Statistics": Houghton Mifflin Co.: Boston, Mass., 1978; p 404. (3) Draper, N. R.; Smith, H. "Applied Regression Analysis"; John Wiley and Sons: New York, 1968 ; p 98. (4) Mendenhall, W. "Introduction to Probability and Statistics". 4th ed.; Duxbury Press: North Scituate, Mass., 1975; pp 130 and 199. ( 5 ) DraDer, N. R.; Smith, H. "Applied Regression Analysis": John Wiley and Sons: New York, 1968; p 13. (6) Daniel, W W. "Applied Nonparametric Statistics"; Houghton Mifflin Co.: Boston. 1978: 10. .. , Mass.. ~.~ ~, o r (7) Draper, N. R.; Smith H. "Applied Regression Analysis"; John Wiley and Sons: New York, 1968; pp 86-100.
+
~
Roger R. W. Ellerton* Eric W. Mayne Department of Mathematics and Statistics university of N~~ Brunswick, post Office B~~ 4400 Fredericton, N~~ ~ ~ ~E 3 ~5A3 ~ canada ~ ~ i ~
RECEIVED for review October 16, 1979. Accepted December 26, 1979.
AIDS FOR ANALYTICAL CHEMISTS Safe Handling and Purification of Aqueous Hydrazine J. W. Mitchell,* T.
D. Harris, and L. D. Blitzer
Bell Laboratories, Murray Hill, New Jersey 07974
High purity oxidizing and reducing agents are needed for t h e conversion of trace elements into appropriate oxidation states prior to their determination by physicochemical methods. For example, during our recent investigation of laser intracavity absorption spectrophotometry of species in aqueous solutions ( I ) , an aqueous solution of a reducing agent with extraordinarily low Fe contamination (50.1ng/mL) was required for the reduction of iron in the original sample to the ferrous state. Ultrapurification of a reagent with respect to a contaminant as commonly prevalent as iron can be an arduous and time consuming task. Therefore a reagent which would be potentially useful as a general purpose reducing agent in trace analysis was sought. Such a reagent would need to meet the following general criteria in addition to being extremely pure. The reagent should be (1)a reasonably powerful reductant and (2) excess amounts removable by decomposition or volatilization. (3) By-products from its oxidation should preferably be volatile low molecular weight gases, or (4) nonabsorbing, weakly or noncomplexing liquids. In addition, by-product species that are chemically and electrochemically inert towards a wide variety of trace elements would also be ideal. A survey list of the commonly used analytical reducing agents is provided in Table I. Few of these reagents possess a majority of the optimum properties mentioned previously a n d a t the same time are easily amenable to purification. All of them except hydrazine and its salts, hydroxylamine and its salts, formic acid, and hydrogen do not meet the criterion of general utility for a broad range of cationic reductions. Formic acid and hydrogen have relatively weak reduction potentials. Salts of hydrazine and hydroxylamine are not amenable to high efficiency zone refining methods because of thermal decompositions. A polymer resin coated with adsorbed chelating agent has been reported to remove 0003-2700/80/0352-0774$01 0010
Table I. Available Analytical Reducing Agents ascorbic acid arsenous acid
hypophosphorus acid
formic acid hydrazine hydrochloride sulfate
sodium dithionite sodium sulfite sodium thiosulfate
hydrogen
oxalic acid
s t a n n o u s chloride sulfurous acid
hydroxylamine hydrochloride
Fe, Co, Ni, and Cu quantitatively from hydroxylamine solutions ( 2 ) . However after treatment of the solutions, residual metal concentrations were reported to be -0.05,0.002,0.006, and 0.008 ppm for Fe, Co, Ni, Cu, respectively. While this method is quite convenient to execute, the reagent is still not sufficiently pure for our requirements. A low temperature sublimation technique described previously ( 3 ) ,can be applied to the high purity processing of this reagent. Thus a procedure for the safe handling and purification of aqueous solutions of hydrazine by low temperature sublimation has been applied and is described in this report. Properties. Anhydrous hydrazine is extremely toxic and explosive and should not be used as a chemical reagent. In contrast, the 85% aqueous solution is a colorless liquid which when handled with simple precautions does not present a safety problem. Eye goggles, rubber gloves, and protective clothing should be worn when handling it. T h e general physical and chemical properties of the anhydrous and hydrated forms are given in Table 11. The 85% reagent has a flash point of 90 "C and becomes noncombustible when diluted with water beyond 1:l hydrazine water mole ratio. Concentrated solutions react with oxygen in the
C
1980 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 4 , APRIL 1980
775
Table 11. Physical and Chemical Properties of Hydrazine and Its Aqueous Solutions property
NH,NH,'
mol. wt. state mP bp
flash p VP
density explosive hazard toxicity spontaneous combustion a
Ref. 2.
85% NH,NH, in H,O
NH,NH~,H,O~
50.06 colorless liquid
32.05
32.05
colorless fuming liquid
colorless liquid
1.4 "C 1 1 3 . 5 "C 37.8-52.2 "C 1 4 . 4 Torr, 25 "C 1.011 @ 15 "C
- 8 . 7 "C
severe via heat or chem. reac. very high in air with organics with strong oxidants
.__
-52 " C 118-120, 760 Torr
___ __-
-90 "C _._
1 . 0 1 6 @; 25 "C avoid exposure to heat
very high in air with organics with strong oxidants
1.032
avoid exposure t o heat very high
noncombustible
Ref. 3.
air and the reagent should be stored in closed containers, preferably under nitrogen ( 4 ) . Even dilute solutions undergo accelerated decomposition in air and thus should be protected. Storage vessels can be of glass or of most plastics except poly(vinylch1oride). As expected cationic impurities or metal surfaces of iron, copper, or zinc accelerate hydrazine decomposition and must be avoided. Hydrazine is a powerful reductant as indicated by the following calculated reduction potentials ( 5 ) of a variety of possible electrochemical reactions:
N2H5++ 3H+ + 2e-
1;1
2NH4'
+ 4 H 2 0 + 2e- s ZNH40H + 20HN2 + 5H+ + 4e- z N2H5+ N2 + 4 H 2 0 + 4e- s N2H4+ 4 0 H -
N2H,
E" =1.27 E" = 0.15 E" =-O.22
E" = -1.17
T h e full decomposition into nitrogen or ammonium provides the most common reaction route. Autooxidation has also been suggested as a common mode of decomposition. The basicity of the reagent is a disadvantage to its use in trace analyses since irreversible formation of hydroxides of trace metals could occur. Elimination of this interference has been accomplished and is discussed in the "Purification section". Other common chemical reactions of hydrazine have been covered comprehensively in a previous monograph (6). Precautions during Handling. The following general precautions and rules are recommended in the use of aqueous hydrazine ( 4 , 7 , 8). Hydrazine should be used only in a properly functioning exhaust hood. Glove bags of polyethylene filled with dry nitrogen are recommended for sampling, measurements, transfers, and general handling. Operations should be executed away from sparks, open flames, hot plates, oxidizing agents, organic materials, and congested areas. Any electrical equipment in the vicinity should be adequately grounded. Nitrogen, ammonia, or helium, not air or oxygen, should be used to bubble or pressurize hydrazine solutions. Spills should be flooded with copious quantities of water. All exposures to vapors or skin contact with the liquid should be avoided by using the protective shielding mentioned previously. Purification. The unique advantages of a low temperature sublimation technique for the ultrapurification of compounds that are liquid at ambient conditions were described previously ( 3 ) . An examination of the physical properties of the anhydrous reagent (Table 11) indicates that a rapid sublimation a t low temperature would occur. Additionally, the decreased chemical reactivity, lower vapor pressure, processing in a completely closed system under vacuum, and manipulation in the solid state a t low temperature are extremely attractive conditions for the safe purification of this potentially toxic reagent. T h e apparatus shown in Figure 1 was used for the
Figure 1. Low
temperature sublimation apparatus
production of up to two hundred milliliter batches of the reagent. The fused silica and Teflon parts of the cryogenic sublimator were precleaned by leaching for 48 h in 1 N H N 0 3 at -80 "C, followed by at least 24 h of leaching in -1 M HC1. After thorough rinsing with demineralized distilled-in-quartz water, the apparatus was dried with a heat lamp in a laminar flow hood located in a class 1000 clean room. The apparatus was then assembled in an all-plastics exhaust hood in the clean room. The collection vessel was partially submerged into a plastic insulated vessel containing a dry ice-isopropyl alcohol mixture. Approximately 20 mL of high purity water were collected first via sublimation from a 500-mL flask. Up to 200 mL of the 95% practical grade hydrazine (Eastman Kodak Co.) was transferred into a 5-L fused silica round bottom flask, then capped with a female 24/40 closed ended standard taper joint. After the closed flask was removed from a nitrogen filled glove bag, the liquid was frozen in a thin shell on the internal walls of the flask by rotating it in a quartz tray containing a dry iceisopropyl alcohol mixture. The flask was then attached to the sublimation vessel and -180 mL of the frozen material was sublimed and collected. After partially melting the sublimed material by exposure of the collection vessel to a heat lamp, the solid sublimate was broken up with a cleaned Teflon rod and the chunks of solid were poured into a precleaned wide mouth F E P bottle. Alternatively, the entire sample was melted and the solution was transferred by pouring the liquid from the vessel into the
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 4, APRIL 1980
Table 111. Transition Element Impurities in Reducing Agents,a p g / g or per mL sample
Fe
cu
co
Mn
Ni
Zn
Cr
hydroxylamine ascorbic acid hydrazine (95)c
0.667
N.D.b
0.060
N.D. N.D.
0.013
0.083
0.002
N.D. N.D. 0.002 N.D.
N.D. N.D.
hydrazined
0.073 0.039 0.003 0.003
N.D.
0.018
N.D. N.D. 0.127 N.D.
0.041
N.D. 0.040
N.D.
Analyzed by flameless atomic absorption spectrometry. K.D. = not detected, Co = 1 0 . 0 0 2 , hln
