Anal. Chem. 1980, 52, 773-774
I +--I
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improvements, however, are evident. For example, a shorter hydrocarbon chain than octadecyl would permit the use of greater portions of the aqueous component in the mobile phase for comparable separations. Not only would this provide higher conductivity for the electrochemistry, but it would also have the effect of making the reduction potentials for peroxides more positive and thereby less prone to oxygen interference (8). Finally, considerable improvements in the design of thin-layer detector cells have recently been introduced ( 5 ) . By reducing the internal resistance of the cell, a matter of rearranging the electrode geometry. a greater dynamic range for the analysis would be available. These refinements are currently under investigation. We are also studying the general applicability of this method to other peroxide compounds, particularly those of biological importance.
LITERATURE CITED
0
5
10 min
Figure 2. Column: 4.6 X 250 m m , Zorbax BP ODS; mobile phase: 60/40, water/methanol, v/v; electrolyte: LiCIO,, 0.1 M; flow rate: 1 mL min-'. (A, B) tert-Butyl hydroperoxide, 5 wg. (C) tert-Butanol, 125 wg
might be anticipated by further eliminating this interference. One approach that has been employed involved enclosing the entire apparatus in a n inert atmosphere box (7). For the purpose of demonstrating feasibility, however, our rather crude approach was entirely satisfactory. In addition to the enhanced sensitivity, two dimensions of selectivity are available to this technique. First, variation of the applied potential should make possible the analysis of most if not all peroxides. Further, by judicious selection of potential, discrimination between the various classes of peroxides will be available. The second dimension in selectivity involves the chromatographic stationary phase. T h e extraordinary resolving power of reversed phase high performance liquid chromatography means that the analysis of mixtures of peroxides with closely related structures is for the first time an attainable goal. Further
(1) Mair, R. D.; Hail, R. T. "Determination of Organic Peroxides", Part 11. Vol. 14; Kolthoff, 1. M., Eiving, P. J., Eds.; Wiiey-Interscience: New York, 1971; pp 295-434. (2) Montgomery, F. C.; Larson, R . W.: Richardson, W. H. Anal. Chem., 1973, 45, 2258-60. (3) Mair, R . D.; Hall, R. T. "Organic Peroxides", Vol. I [ ; Swern, D., Ed.; Wiley-Interscience: New York, 1971: p 578. (4) Kissinger, P. T. Anal. Chem. 1977, 4 9 , 447A-456A. (5) Wightman. R. M.; Paik, E. C.; Borman, S.; Dayton, M. A. Anal. Chem. 1978, 50, 1410-14. (6) Ikenoya, S.; Abe, K.: Tsuda. T.; Yarnano, Y.; Hiroshima, 0.; O h m e , M.; Kawabe, K. Chem. Pharm. Bull. 1979, 27, 1237-45. (7) MacCrehan, W. A,; Durst. R . A. Anal Chem. 1978, 5 0 , 2108-12. ( 8 ) Levin, E. S.;Yamshchikov, A. V. "Progress in Electrochemistry of Organic Compounds", Vol. I ; Frumkin, A. N., Ershler, A. B., Eds.; Plenum: London, 1971, pp 411-40.
Max 0. Funk* Maggie B. Keller Bruce Levison Department of Chemistry University of Toledo Toledo, Ohio 43606 RECEIVED for review October 30, 1979. Accepted December 14,1979. This research was supported by the Susan Greenwall Foundation, Inc., Grant of the Research Corporation, and the University of Toledo Faculty Research Award Program.
Preliminary Statistical Analysis of Kinetic Data Sir: In a recent article, Kelter and Carr ( 1 ) concluded that the runs test should not be the only statistic used to test the goodness of fit of kinetic data to a rate law. (Kelter and Carr referred to this test as the Normal Variate or LJnit Normal Deviate. Many tests are based on the normal distribution. T h e usual name for this particular test is the runs test.) Unfortunately, the authors did not indicate what other possible procedures may be used. Our intention is to briefly review the runs test and present a procedure to be used in conjunction with the runs test that overcomes the difficulties mentioned by Kelter and Carr. Suppose n observations are taken resulting in n l positive residuals and n - n l negative residuals. If n l > 10 and n n l > 10, then the distribution of the number of runs can be approximated by a normal distribution as indicated by Kelter and Carr; otherwise special statistical tables are required ( 2 , 3 ) . In either case, the distribution of the number of runs is a conditional distribution, depending on the values of n and 0003-2700/80/0352-0773$01 O O / O
nl. That is, the statistical test checks to see if the number of runs is reasonable for given n and nl, too few runs indicating a lack of randomness. This procedure does not test whether the residuals come from a normal distribution. When working with kinetic data, we recommend that a test be conducted, prior to the runs test, to determine if nl is a reasonable number of positive residuals out of n. Or, in other words, is nl statistically different from n/2? This is the usual test of hypothesis for testing that a population proportion is equal to 0.5 (see ( 4 ) ) . For large n , the test statistic is approximately distributed as a standard normal and is given by (nl - 0.5n)/(n/4)112. Using this testing procedure before the runs test, clearly avoids the problem presented by the data of Case B in Table I of Kelter and Carr. In regression analysis, the above test is usually omitted; since for many fitted models the sum of the residuals is zero, hence forcing n l and n - n l to be approximately equal (see ( 5 ) ) . Care must be taken in selecting the significance levels of F 1980 American Chemical Society
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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.
+
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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
