Determination of Anthraquinone in Capacitor Dielectrics PAUL D. GARN and MARY CAMPBELL BOTT Bell Telephone laboratories, lnc., Murray Hill, N. 1.
b A polarographic procedure was developed for determining anthraquinone in the common capacitor impregnants, mineral oil, chlorinated naphthalene, and chlorinated diphenyls. The impregnant i s dissolved in chloroform and aliquots are subsequently diluted with chloroformmethanol electrolyte solutions. The final solution i s ca. 3 to 2 chloroformmethanol. Hydrochloric acid i s used to shift the anthraquinone wave to a less negative potential. A solution with magnesium chloride as the electrolyte i s treated as the blank. Anthraquinone may now b e determined in any of the impregnants named b y a single method. Other chemical stabilizers may b e determined b y the same technique.
I
of paper capacitors, the assembly of paper and metal foil is vacuum-impregnated with a dielectric material to improve its dielectric characteristics. Under high operating temperatures or voltages, these capacitors undergo a progressive degradation, resulting eventually in failure of the component (6). This degradation can be retarded by the addition of a stabilizer to the impregnant. The impregnants commonly used are chlorinated diphenyls, chlorinated naphthalene, and mineral oil. Of the available stabilizers, anthraquinone is the most widely used in the Bell System. Solubility, gravimetric, and spectrophotometric methods are currently used for determination of anthraquinone in these impregnants. The first method involves adding known increments of anthraquinone until no more dissolves and is used to determine anthraquinone in the chlorinated impregnants. The gravimetric method consists of dissolving the sample in petroleum ether, and chilling the solution to precipitate the anthraquinone, which is then recovered and weighed. This method is used for determination of anthraquinone in mineral oils. The gravimetric data, particularly on mineral oil, are subject to uncertainty because the prolonged heating in the impregnating tanks solubilizes anthraquinone. The mechanism of this solubilization has not been determined. N
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THE
FABRICATIOS
ANALYTICAL CHEMISTRY
The anthraquinone can be determined polarographically in the filtrate. The third method depends on the formation of a colored complex with N,N-dimethylaniline. It requires a correction or special calibration for use with chlorinated naphthalene. This procedure appears to be suitable for chlorinated diphenyls and may be suitable, with the correction, for chlorinated naphthalene. It is not suitable for mineral oil because this oil, at least after some heating in the impregnating tanks, absorbs a t the wave length470 mp-used in the procedure. This accounts for our observation that the spectrophotometric data are significantly higher than polarographic results and considerably higher than gravimetric results. DETERMlNAl ION OF ANTHRAQUINONE CAPACITOR DIELECTRICS
IN
Anthraquinone yields a welldefined polarographic wave in several solvents. The reduction occurs in two steps, but the waves are not separated in all solvents. I n isopropyl alcohol, ethyl acetate-ethyl alcohol-water solvents, or glacial acetic acid (4)the waves appear as a single wave. I n dimethylformamide the waves are well separated (2, 6). Any of these solvent systems is satisfactory for the determination of
-2 I
,:-?
0
3.
A 1 1 3
Figure 1. Polarograms of anthraquinone in chlorinated diphenyl in chloroform-methanol-magnesium chloride 1. 2. 3.
Reference solution with HCl Sample solution with HCI Sample blank [no HCl)
anthraquinone but none is usable for all of the dielectric materials: The chlorinated diphenyls are insufficiently soluble in isopropyl alcohol; mineral oil is not sufficiently soluble in dimethylformamide; all three dielectrics are soluble in a solvent consisting of 20% ethyl alcohol and 2% nnter in ethyl acetate, but chlorinated naphthalene yields a wave which follows the anthraquinone wave too closely to permit quantitative determination of the anthraquinone. Within the limits stated, methods using the above solvents can be used. There are, however, obvious advantages in having a single method for the routine control of stabilizer concentration in all types of dielectrics. A solvent consisting of a 3 to 2 mixture of chloroform and methanol with magnesium chloride and with hydrochloric acid can be used. The function of the hydrochloric acid is to shift the wave of the anthraquinone to a less negative potential, thereby separating i t from any interference from the dielectric (Figure 1). Reagents. Reagcnts except anthraquinone are reagent grade. Hydrochloric Acid Diluting Solution. Dilute 500 ml. of chloroform and 50 ml. of hydrochloric acid to 1 liter with methanol. Magnesium Chloride Hexahydrate Solution. Heat magnesium chloride hexahydrate for 4 hours a t 110' to 130' C. Weigh out 11.9 grams of the dehydrated salt and dissolve in 200 ml. of methanol. Dilute to 1 liter with methanol. The salt should be almost completely soluble in 200 nil. of methanol. Magnesium Chloride Diluting Sohtjon. Dilute 250 ml. of chloroform to 500 ml. with the methanol-magnesium chloride solution. Anthraquinone Standard Stock Solution ( 5 mg. of anthraquinone per ml.). Weigh out 0.500 gram of anthraquinone. Dissolve in and dilute with chloroform to 100 ml. Anthraquinone Standard Solution (1 mg. of anthraauinone Der ml.). Transfe; 10.0 ml. o f t h e sto& anthraquinone solution to a 50-ml. volumetric flask, add 15.0 ml. of chloroform and 5.0 ml. of hydrochloric acid-methanol solution (1 l ) , and dilute to volume with methanol. Analytical Procedure. 1. Dissolve a n accurately weighed 3- to 5gram portion of the sample in 25 ml.
+
of chloroforin, transfer to a 50-ml. volumetric flask, a n d dilute t o t h e mark with chloroform. (The sample portion should contain no more t h a n 35 mg. of anthraquinone in t h e case of chlorinated naphthalene a n d no inore than 50 mg. in t h e case of inineral oil or chlorinated diphenyl.) 'rransfer 10.0-ml. portions of the sample to each of two 50-ml. volumetric flasks. Dilute one flask (flask A) to volume with the hydrochloric acid dilution and dilute the other (flask B) with the magncsiuni chloride dilution solution. Dcgas each solution. 2 . For the I-IC1-containing solution, drtermine the proper sensitivity setting of the polarograph so that a scale reading of betn-een 50 anti 80 divisions is obtained a t -0.4 volt. Using this srnsitivity obtain the reading a t -0.25 volt and then rim the entire curve betn-cen 0 and -0.8 volt. If a niaximum is found in the region of -0.2 to -0.4 volt, start again with a smaller .ample portion. 3. Using the sensitivity setting dctermincd in 2 , repeat 2 for the magntsium chloride-containing solution (flak l3). (Use the same aliauot as chosen in 2 . ) 4. Transfer aliquots (as chosen in 2 ) of the unstnbilized imareanant to two t50-ml. volumetric flasis. -To one add from a buret a portion of the standard :mthraquinone solution containing approximately the same amount of anthraquinone as the sample solution. This is flaqk C. Designate the other as flask D. Dilute both to volume with the hydrochloric acid diluting solution. Degas each solution. Measure each as directed in 2 , using the same sensitivity settings. 5 . Calculate the concentration of anthraquinone. I n the following equation the letter refers to the reading obtained for the corresponding solution c,orrectcd for the base reading.
diffusion current in the solution of the dielectric and comparison of this current with that obtained from a known amount of anthraquinone in the presence of the unstabilized impregnant. The current increases linearly with concentration. The presence of the unstabilized impregnant-Le., the mineral oil or chlorinated diphenyl or naphthalene without anthraquinone-is necessary because the diffusion current constant for anthraquinone in the pure solvent is a fern per cent greater than in the presence of the impregnant. This is presumably a viscosity effect. When determinations are to be made on several batches of the same impregnant, the same reference may be uijed so long as the sample size does not vary b y more than 25%, R I a ~ m aoccur in the polarogram TI ith ewessive concentrations of anthraquinone. Decreasing the sample size will elimin,zte the maxima. The function of the electrolytes is to shift the wave for anthraquinone so that materials not similarly affected by hydrogen ion concentration may be detected or their effects compensated for. A high base current in the acid solution should also appear in the magnrsium chloride solution, so that the effect is not measured. K i t h most instruments, the currents for each solution may be read and used simply as scale divisions. X Leeds & Korthrup Electrochemograph Type E with associated dropping mercury electrode was used in this work. The anthraquinone was of the purity used in production of the capacitors. The melting range was 286-7' C. a t ea. 1O per minute. Because of uncertainties inherent in using aged impregnant in
( A - B ) X mg. of anthraquinone in standard aliquot
% anthraquinone = ( C - D ) X grams of sample in sample aliquot X 10 DISCUSSION
Essentially the method comprises the measurement of the anthraquinone
a n y form of calibration procedure, only ten production line samples have been tested in this laboratory. Further,
because of lack of confidence in a n y known procedure for anthraquinone in these impregnants, no complrtely independent determinations were made. Instead, the possibility of any effect causing a nonlinear current-concentration response was excluded by determinations both by use of standards as described herein and by the standard addition technique. The results by the two techniques agreed within ea. 27,. rln electrolytic mechanism for the stabilization of dit3lectrics has been described (8). The data available in the literature lead to one genrral conclusion: The stabilization of direct current capacitors is a n electrolytic phenomenon and the materials which can be used as btabilizers must be easily reduced electrolytically. There are a few stabilizers which function by different mechanisms-Le.. fuller's earth by adsorption of degradation products ( 1 ) . From the evidence cited it can be predicted that except, for solubility problems and thc few materials which function by othcr mechanisms, any of the useful stabilizers for direct current capacitors can be determined in this system. Its usefulness has already been provcd for some other quinones, azo- and azo\ybenzme, and p-nitrodiphenyl. LITERATURE CITED
i l l Berberich. L. J.. Friedman., R.., Ind. ' Ens. Chem.40,11fj1918). (2) Edsberg, R. L., Eirhler, D., Garis, J. J., ANAL.CHEX 2 5 , TD8-800 (1953). (3) Garn, P. D., iinpitblished data. (4) Isshiki. T..Tach K.. Pharm. Bull. ( J a p a n )2,266-9 (1944). (5) Sauer, H. A,, 3IcLPnn. D. A., Egerton, L., Ind. Eng. Cheni 44,135-40 (1952). (6) Wawzonek, Stanley, Berkey, R., Blaha, E. IT.) Riinnrr, h l . E., J . Electrochem. SOC.103,4,56-9 (1956).
RECEIVEDfor review October 21, 1959. Accepted October 3, 1060. Division of Analytical Chemistry, Becknian Award Symposium on Chemical Instrumentation Honoring Howard Cars, 135th Meeting, ACS, Boston, Itlass., .ipril 1959.
Determination of Water in 1,l -Dimethylhydrazine, Diethylenetriami ne, and Mixtures HOWARD G. STREIM,l EGERTON A.
BOYCE, and JOSEPH R. SMITH
Liquid Propellant Section, liquid Rocket Propulsion Laboratory, Picatinny Arsenal, Dover, N. J. Minute quantities of water in some mixtures of alkylhydrazine and alkaline amines used as rocket fuels have an effect upon their ignition and combustion with nitric acid oxidizers in rocket engines. This paper describes investigations leading to the develop-
ment of a near-infrared and a gasliquid chromatographic method for determining water in 1,l -dimethylhydrazine, diethylenetriamine, and a mixture of these compounds. The precision and accuracy of both methods are compared.
D
of water in alkylhydrazine and alkaline amines used as rocket fuels are not easily acETERMINATIONS
1
present address, Stauffer ~ l , ~ ~ i ~ ~
Co., Chauncey, N. Y. VOL. 33, NO. 1, JANUARY 1961
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