Determination of Salicylanilide in Varnishes by Ultraviolet Spectrophotometry M. H. SWANN and M.
L.
ADAMS
Coating and Chemical laboratory, Aberdeen Proving Ground, Md.
,A
fairly rapid method of high accuracy was developed for the determination of salicylanilide in fungusresistant varnishes. The absorption of an alkaline extraction solution a t 336 mp is measured and is free of interference from other varnish constituents.
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Table 1. Determination of Salicylanilide in Laboratory Samples of Fungistatic Varnishes
Present, c-
/c
5.96 5.02 5.19 9.32
F
varnishes are used as wood preservatives and for the treatment of electrical equipment. Specification MIL-V-173 ( 1 ) is of this type and covers a varnish consisting of a p-phenylphenolformaldehyde resin in combination with tung oil and suitable solvents, made fungistatic by the addition of salicylanilide. -4 colorimetric method ( 2 ) was deyeloped for salicylanilide based on the violet color formed by its reaction with ferric chloride following a n alkali extraction of the fungicide. The tendency of p-phenylphenolformaldehyde to sublime in the preparation of varnishes has caused some interference with this method. A more rapid method of high accuracy and free of interference from other varnish constituents is presented which utilizes the ultraviolet absorption of salicylanilide a t 336 nip. The complete spectrum is shown in Figure 1. Although stronger absorption occurs at 220 and 270 nip, these \$are lengths are unsuitable in this method because of interference from impurities extracted by aqueous alkali. X Beckman Model DU spectrophotonieter with ultraviolet accessories n-as used. Details for calibrating are given, but the authors believe that the absorptivity calculjted for salicylanilide is sufficiently high that analysts using an instrument that has been given a wave length calibration can use this factor with suitableaccuracy. UNGUS-RESISTANT
PROCEDURE
Calibration. 9 small quantity of salicylanilide is spread out in a shallow dish and dried in a desiccator over calcium chloride for several days. Approximately 0.1 gram is weighed accurately, dissolved in 60 nil. of 2.5% sodium hydroxide solution, and diluted with water t o 250 ml. in a volumetric flask. After thorough mixing, a 5-ml. aliquot is m-ithdrawn
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230
250
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270 290 310 WAVE LENGTH m y
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330
Figure 1. Ultraviolet spectrum salicylanilide in sodium hydroxide
of
and diluted to 250 ml. with water. The absorbance of this solution is determined a t 336 mb using a slit width of 0.4 mm. with water in the blank cell. A cell correction is applied if necessary, or the cells are reversed and the absorbances averaged. Absorptivity is calculated as follows:
R-here aZ38 = absorptivity ~ 4 3 3 6 = absorbance after cell correction b = cell length in cm. c = concentration of salicylanilide in grams per liter
A minimum of tiyo standards should be used for calibration and a n average absorptivity value calculated. An absorptivity of 41.2 was obtained with commercially available salicylanilide of practical purity from two different sources. Determination in Varnishes. From a dropping bottle, a sample of t h e varnish weighing approximately 2.5 grams is weighed accurately into a 250-ml. pear-shaped separatory funnel containing 40 ml. of ethyl ether a n d mixed. If t h e varnish precipitates instead of dissolving in t h e ether, benzene is substituted in t h e first funnel, using ether in t h e second, d f t e r 20 ml. of 2.5y0aqueous sodium hydroxide are added, the funnel is agitated
Found, % 593 4.98 5,l5
9.23
thoroughly and allowed to stand until complete separation of the solvent layers results. The lower aqueous layer is drawn off into a second funnel containing 40 ml. of benzene and agitated. A total of three such extractions are made with 20-ml. portions of sodium hydroxide. Each aqueous layer froin the second funnel is dra-ivn off without filtering into a 400-ml. beaker, and the combined portions are diluted with n-ater to approximately 150 ml. The beaker is then placed in a water bath a t 80" to 85" C. for at least 1 hour and cooled to room temperature, and the contents are diluted to 250 ml. with water in a volumetric flask. After thorough mixing, approximately 100 ml. of this solution are filtered through paper and the first 50 ml. discarded. This filtration may be omitted if the sample solution is completely free of cloudiness or separation. A 5-ml. aliquot is withdrawn from the filtered sample and diluted to 250 ml. with Tvater in a volumetric flask and thoroughly mixed. The absorbance of t h k solution is determined a t 336 mp using a slit width of 0.4 mm. with viater in the blank cell. The value of this absorbance reading should lie betryeen 0.2 and 0.5; if it does not fall in this area, a ne\v aliquot of appropriate size is withdran-n from the filtered sample and the absorbance determined. Cell corrections are applied if necessary, or the cells are reversed and the absorbances averaged. The per cent salicylanilide is calculated as follows:
where Aa3s = absorbance after cell correction = absorptivity (obtained in calibration) VOL. 30, NO. 1 1 , NOVEMBER 1958
1807
b
8.w. al.
= = =
cell length in cm. sample weight size of aliquot in ml. DISCUSSION
Salicylanilide was added to tung oil varnishes of various oil lengths, extracted, and determined. Some results of these determinations are shown
in Table I. As the entire sample was used in most cases, duplicate results are not Dresented. T i e entire procedure is simple to conduct, and the relatively high absorptivity of this fungicide is responsible for the high accuracy (error less than 1%). Other-types of varnishes, based on alkyd resins and rosin esters, have been analyzed with equal accuracy.
LITERATURE CITED (1) Specification pVIIL-V-173, “Varnish,
Moisture- and Fungus-Resistant, for the Treatment of -Communications, Electronic, and Associated Electrical Equipment,,, Jan, 23, 1952,
(2) Swarm,
804 (1949).
H
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A ~ A L . CHEM.
21,
RECEIVED for review February 6 , 1958. Accepted May 27, 1958.
DifferentiaI Voltammetry Using the Hanging Mercury Drop Electrode KENNETH J. MARTIN and IRVING SHAlN Chemistry Department, Universify of Wisconsin, Madison, Wis. The general techniques of voltammetry with continuously varying potential have been applied to a differential method in which two electrolysis cells are used, each with a hanging mercury drop electrode. Using this method, it is possible to determine 10+M solutions with increased precision, and also to analyze solutions as dilute as 10F6Mwithout removing oxygen from the electrolysis cells. Mixtures can be analyzed easily by adding individual components of the mixture to the reference cell.
0
to the problem of increasing the sensitivity and convenience of polarographic and related analytical methods, perhaps the most important have involved attempts to compensate for the residual current (3, 5, 8). Cancellation of this residual current rvould improve the accuracy of determinations a t low concentration levels and eliminate the need for pre-electrolysis of the indifferent electrolyte (6). Furthermore. compensation of unwanted electrolysis currents would permit the rapid analysis of all constituents in a mixture. I n some cases it would be possible to perform analyses without removing dissolved oxygen from the solution. A method of obtaining compensation of this type is the differential technique (2, 8 ) . Two cells are used, one containing the unknown solution with the indifferent electrolyte, the other containing only the indifferent electrolyte. The circuit is constructed so that the difference in current between the two cells is measured, Application of this technique to conventional polarography has had only limited success because of difficulty in synchronizing two dropping mercury electrodes (1, 4). F THE ~ . I A N YAPPROACHES
1808
ANALYTICAL CHEMISTRY
It was found that many of the difficulties encountered when using dropping mercury electrodes can be avoided by using hanging mercury drop electrodes in a two-cell differential circuit, using the general techniques of voltammetry with continuously varying potential. EXPERIMENTAL
Apparatus. T h e apparatus was similar t o t h e schematic diagram given by Delahay ( 2 ) . The polarization unit and load resistors have been described (9). The difference in potential developed across the two load resistors was amplified by a Leeds & Northrup direct current microvolt amplifier and recorded as a function of time on a Bristol potentiometer recorder. The chart speed was 20 inches per minute. The rates of voltage scan were 0.0278 volt per second and 0.0417 volt per
second, corresponding to 36 seconds for a 1.000- and 1.500-volt sweep. Cells and Electrodes. T h e hanging mercury drop electrode assembly was similar t o t h a t described previously ( 7 ) . I n preliminary experiments, separate reference electrodes were connected to each cell by means of a salt bridge, but differences in potentials of these reference electrodes resulted in large errors in matching the cell potentials when different currents were passed. A single silver-silver chloride (saturated potassium chloride) reference electrode was constructed with two salt
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VOLTS
Figure 1 . Current-voltage curves for reduction of air-free solution of 1 .OO X 10-4M thallium and 2.00 X 10-6M cadmium A. B.
Figure 2. Current-voltage curves for reduction of air-free mixture of 2.00 X 1OF4Mthallium, 1.00 X 10-4M lead, 1 .OO X 1 OU4Mbismuth, 0.33 X 1 O-4M iodate, and 1.00 X 10-4M zinc
Nondifferentially Differentially, with thallium compensated
A. 6. C.
D. E.
Differentially, with only indifferent electrolyte in reference cell Differentially, with thallium compensated Differentially, with thallium and l e a d compensated Differentially, with thallium, lead, and birmuth compensated Differentially, with thallium, lead, bismuth, and iodate compensated
