I
I I
d.5
I
710
I I
I
7:5
7 Figure 7. Time-averaged (225 scans) methyl region NMR spectrum in 95 : 5 (w :w) CCla :TMS of the monomethyltriphenylene fraction of amber petrolatum methyl derivative of triphenylene (VII). The N M R spectrum (Figure 7) of this fraction was dominated by a single peak at 7.46 T (TO= 7.3996 i 0.0021). Although shift data for neither methyltriphenylene isomer appear to be available, this peak can rather convincingly be assigned to the 2-isomer, since a
methyl group at the 1-position should appear roughly 0.7 ppm toward lower field by virtue of its angular orientation with respect to the benzo ring. The presence of at least five other compounds is evident from this spectrum. One of the two small peaks at 6.67 and 6.74 T, each of which integrates to roughly 2 of the mixture, might correspond to 1-methyltriphenylene. Alternatively, since chrysene (VIII) derivatives had been shown by UV to be present to the extent of about 10% in this fraction, these two peaks could be due to 4- and Smethylchrysene; the latter compound, while reported to be rather strongly carcinogenic (I7), would, however, be present in the whole petrolatum to the extent of only a few parts per billion. Finally, the noteworthy sensitivity of the N M R method described in this report can be illustrated using Figure 7. After time-averaging overnight, the peaks at 6.67 and 6.74 T , each of which corresponds to only 30-40 pg of sample, are quite suitable for quantitative analysis, and it seems likely that the limits of detection could be lowered even further with the appropriate use of Fourier transform and/or microcell techniques. RECEIVED for review April 12, 1971. Accepted May 19, 1971. Presented in part to the Midwest Regional ACS Meeting, Lincoln, Neb., October 29, 1970. The financial support of the U. S. Public Health Service, Contract No. 43-68-959, is gratefully acknowledged.
(17) G . M. Badger, Aduan. Cancer Res., 2, 73 (1954).
Gas Chromatographic Determination of Aqueous Trace Hydrazine and Methylhydrazine as Corresponding Pyrazoles L. A. Dee Air Force Rocket Propulsion Laboratory, Air Force Systems Command, United States Air Force, Edwards, Calg. 93523 A gas chromatographic technique is described in which hydrazine and methylhydrazine are determined simultaneously at concentrations of 0.1 to 50 parts-permillion in aqueous solution. Detector sensitivity to hydrazine and methylhydrazine is enhanced by quantitative formation of the substituted pyrazoles with 2,4-pentanedione prior to chromatographic separation. Unsym-dimethylhydrazine, urea, alanine, iron, copper, and aluminum do not interfere with the analysis.
HYDRAZINE, HYDRAZINE SALTS, and simple organic derivatives are used industrially as fungicides, antioxidants, reducing agents, and as rocket fuels ( I ) . A reliable method for the measurement of hydrazine and hydrazine derivatives in dilute (1) R. Kirk and D. Othmer, “Encyclopedia of Chemical Technology,” Vol. 11,2nd ed., John Wiley & Sons, New York, N. Y.,
1966, p 185. 1416
aqueous solution is necessary for both industrial and environmental control because even though low concentrations are often effective in processes, these concentrations may be quite toxic (2). Hydrazines are generally powerful reducing agents, and many sensitive tests for their presence are based on this property, Feigl and Dacorso (3) reported a number of spot tests based on reduction of metal ions by hydrazine. Sant ( 4 ) used the reduction of Ag(NH@+ to Ago to indicate the presence of hydrazine. Weakley et al. (5)applied the hydrazine reduction of Fe3+, present in excess, to Fez+and reaction of the remaining Fe3+ with 2,2-bipyridine to an indirect spectrophotometric
(2) N. Irving Sax, “Dangerous Properties of Industrial Materials,” 3rd ed., Reinhold Book Corp., Albany, N. Y . , 1968, p 819. (3) F. Feigl and G. E. Dacorso, Chemist-Analyst, 32, 28-30 (1943). (4) B. R. Sant, Mikrochim. Acta, 1958, 169-70. (5) F. B. Weakley et at., Microchem. J., 7(2), 185-93 (1963).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 11, SEPTEMBER 1971
determination of hydrazine. McKinnis and Yard (6) measured the nitrogen liberated when KIOBwas combined with dissolved hydrazine. Such methods are most adequate if the sample is well characterized, but they are sometimes subject to interference if other reducing substances are present. A number of direct colorimetric tests have been reported. Fuigl and Pdanhcimer (7) used the yellow hydrazone from salicylaldehyde t o test for hydrazine. Kul'berg and Cherkesov ( 8 ) and Riley (9) reacted hydrazine with picryl chloride to produce coiored products. Vanags et al. (10-12) studied the reaction of hydrazine with indanedione derivatives, and others (13-16) h::~t uscd p-dimrthylaminobenzaldehyde(PDAB) as a colorimetric reagent for hydrazines. Colorimetric methods for hydrazines, although generally more specific than oxidation/reduction methods, still are subject to a number of interferences. Hydroxylamine, urea, amino acids, other hydrazine derivatives, and some amines are typical interferences that have been reported. Preliminary separation of the desired hydrazine from interfering substances by paper chromatography has been reported by Bremner ( 1 7 ) and Hinman (18). Reynolds and Thomas (19) precipitated interfering proteins with trichloroacetic acid and measured the hydrazine or methylhydrazine content of the supernatant liquid with PDAB. Kalinina (20) also used PDAB but overcame the difficulty of interferences by dividing the sample and destroying the hydrazine in one portion prior to a differential spectrophotometric analysis. Still another approach to interference elimination is through a preliminary reaction followed by separation and measurement of the derivative. Such a method was reported by Neuman and Nadeau (21). NaClO added t o a n aqueous sample liberated methane in proportion to the methylhydrazine content, and the gas was separated and measured by a gas chromatographic technique. The following method is not affected by earlier reported interferences, and both hydrazine and methylhydrazine can be determined simultaneously. 2,4-Pentanedione is combined with aqueous hydrazine and/or methylhydrazine t o form the substituted pyrazoles. Separation and measurement of the pyrazoles from potentially interfering agents is accomplished by gas chromatography. This subsequent separation and measurement by gas chromatography allows the analyst somewhat greater freedom for adjustment of the method to his specific anarytical problems. (6) H. McKinnis and A. Yard, U. S. Dept. Com. Ofice Tech. Sew.. P. B . Rei),. 143,914, 13 pp, 1957. (7) F. Feigi and W . A. Manheimer, Mikrochim. Ver. Mikrochint. Actu, 40, 5C-2 (1952). (8) L. M. Kul'berg and A. I . Cherkesov, Z h . Anal. Khim., 6, 364-70 ( 195 1 ).
(9) J. P. Riiey, Anulyst, 79, 76-81 (1954). ( I O ) G. Vanags and M. Mackanova, Zh. Obshch. Khim., 25, 580-3 ( 1 955).
( I I ) G . Vanags and M. Mackanova, Zh. A m / . Khim., 12, 149-50
(1957). (12) G. Vanags and R. Shagata, Dokludy Akud. Nauk SSSR, 133, 362--3 (1960). (13) M. Pesez and A. Petit, Bull. Soc. Chim. Fr., 1947, 122-3. (14) H. McKennis and A. Yard, ANAL.CHEM., 26, 1960-3 (1954). (15) R. Freier and G . Resch, 2. A w l . Chem., 149, 177-81 (1956). (16) T. Dambrauskas and H. Cornish, Amer. Ind. H y g . Ass. J . , 23 (2), 151-6 (1962). (17) J . M. Bremner, Anulyst, 79, 198-201 (1954). (18) R . L. Hinman. A n d . Chim. Acta. 15, 125-8 (1956). (19) B. Reynolds and A. Thomas, Amer. Ind. H y g . Ass. J . , 26(5), 527-31 (1965). (20) N. M. Kalinina, Brergetik, 12(11), 41-2 (1964). 36, 6 W 1 (1964). (21) E. Neuman and H. Nadeau, ANAL.CHEM.,
EXPERIMENTAL
Reagents. p-Dimethylaminobenzaldehyde (Eastman) was used withcut further purification. 2,4-Pentanedione (Aldrich) was distilled through an 18-inch spinning band column (Nestor Faust) and the constant boiling (135 "C a t 690 mm) fraction was collected. The hydrazine and methylhydrazine ~ and ; (both from Olin Mathieson) assayed better than 99 ; were used without further treatment. 3,5-DIMETHYLPYRAZOLE. 3,5-Dimethylpyrazole was prepared by combining 0.16 mole of 2,4-pentanedione with 0.16 mole of hydrazine which had been dissolved in 100 ml of distilled water and cooled t o 5 "C. Isolation and purification of the pyrazole was accomplished by thc method dcscribed by Wiley and Hexner (22). The melting pOinK was 105-6 "C(found) with 106-7 "C (reported). 1,3,5-TRIMETHYLPYRAZOLE. Methylhydrazinc Wab substituted for hydrazine and 1,3,5-trimethylpyrazole was prepared and purified in a similar manner. The melting point was 36-7 " C (found) with 37 " C (reported). Infrared spectra of the pyrazoles also were used t o establish their identity. Apparatus. A Beckman Model GC-4 equipped with a n on-column inlet and a Beckman Model GC-M equipped with a flash vaporizer inlet were used. Both gas chromatographs had dual flame ionization detectors and were used in the conventional manner except that oxygen was used in the detectors instead of air for combustion of the hydrogen. The use of oxygen resulted in a fourfold increase in sensitivity. A Bausch and Lomb Spectronic 20 was used a t 460 nm for hydrazine determinations with p-dimethylaminobenzaldehyde. Procedure. STANDARD PREPARATION.Stock solutions of 1000 ppm hydrazine and 1000 ppm methylhydrazine were prepared by addition of appropriate amounts of each to separate 1000-ml volumetric flasks containing 150 ml of 0.1N H ? S 0 4 . Dilution t o the mark was made with distilled water. In addition, stock solutions containing 3000 ppm 3,Sdimethylpyrazole and 2390 ppm 1,3,4-trimethyIpyrazole in distilled water were prepared (equivalent t o 1000 ppm hydrazine and 1000 ppm methylhydrazine, respectively). Lower concentrations were prepared by further dilution of aliquots of these stock solutions with distilled water. CHROMATOGRAPHIC CONDITIONS.The columns were either three or six feet in length, constructed of 'Irc-inch stainless steel tubing, and were packed with 60-70 mesh Anakrom ABS (Analabs). The Anakrom ABS was coated with 3 0 z by weight of a mixture containing 16.7% Amine 220 (Applied Science) and e3.3 Apiezon L (Analabs). The flow rate of the helium carrier gas was 25 ml per minute. The temperature of the flash vaporizer inlet was 175 "C and that of the detector oven was 200 "C. The column oven was operated isothermally at 130 "C and the columns were preconditioned a t 170 " C with helium flow for 8 hours. SAMPLE PREPARATION AND ANALYSIS.The pH of an aqueous sample was adjusted t o between 6 and 9 with either 1 N NaOH or 1N H ? S 0 4and 50 pl of 2,4-pentanedione were added t o a 100-ml portion. The resulting mixture was shaken thoroughly and allowed to stand for a t least 1 hour a t room temperature. A 5-pl aliquot of the prepared sample or a calibration standard was injected into the gas chromatograph, and the peak height of the desired component was measured. RESULTS AND DISCUSSION
The 2,4-pentanedione (AA) reactions with hydrazine (N2H4) and methylhydrazine (MMH) to form 3,5-dimethylpyrazole (DMP) and 1,3,5-trimethylpyrazole (TMP), respectively, are illustrated by Equations 1 and 2. .
(22) R. H. Wiley and P. E. Hexner, "Organic Syntheses," Coll. Vol. IV, N. Rabjohn, Ed., 1963, p 351.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 11, SEPTEMBER 1971
1417
Table I. Detector Response to TMP and D M P Prepared from Concentrated Standards and from Aqueous Trace M M H and N,H4 Standards Peak height, divisions Pprn/wta MMH TMP N.HI DMP 0.1 130 140 1 70 160 0.5 710 730 390 380 1 .o 1440 1480 740 730 2.0 2900 1280 1300 2970 5.0 7600 7550 3300 3100 10.0 15100 15000 6310 6300 31200 20.0 30500 12600 12700 50.0 79700 77200 33003 31800 a TMP and DMP are calculated as ppmlwt M M H and N2HI, respectively. Table 11. Recovery of N,H, from Samples Which Contain Potential Interferences Recoiered Added N2HI.p p d w t NzHI, ppm/wt Interference, 100 ppmiwt GC PDAB 1 .o 1.1 1 .o Urea 1 .o 1,l-Dimethylhydrazine 10 1.1 1 .o DL-Alanine 1 0 1.1 1.o Fe::+ 0.90 0.80 0.80 1 .o 1.o CUI+ 1.o 1.o 1.o Ala+ 1.o Fe:* + Na?EDTA 0.97 0 82 1.o Cu2+ + Na2EDTA 0 97 1 .o
1.0
8
2
4
6
TIME (Min.)
Figure 1. Chromatographic separation of T M P and D M P A.
B. C.
H20 (320X) AA (320X) TMP (320X)
D. DMP(160X) 0
0
I1
H 3CC
N
\ / N I N
0
0
I I
I1
(DMP)
1
H3CCH2CCHz
+ NHzNHCHa
+
HC---CCHa
11
11
H 3CC
+ 2H20
(2)
\/” N
CH3 (TMP) A number of ketones and aldehydes may react with M M H and N2Ha quantitatively, but AA was chosen for a variety of rea-
sons. It is unlikely that either pyrazole is present in natural or industrial wastes, and both are relatively nonvolatile and can be easily separated from water, solvents, and volatile natural products. Also these pyrazoles are quite thermally stable and give symmetrical peaks even with only moderately polar substrates. Very dilute (
