804
ANALYTICAL CHEMISTRY
This paper is published with the permission of L. T. E. Thompson, technical director of the Naval Ordnance Test Station. LITERATURE CITED
(1) Dennis, L. M., and Nichols, M. L., “Gas Analysis,” rev. ed., p. 228, New York, Macmillan Co., 1929. (2) Fisher, R. A., “Statistical Methods for Research Workers,” 10th ed., London, Oliver &Boyd, 1948. (3) Giauque, W. F., and Kemp, J. D., J . Chem. Phys., 6,40 (1938).
(4) Jacobs, M. B., “Analytical Chemistry of Industrial Poisons, Hazards and Solvents,” 1st ed., p. 281, New York, Interscience Publishers, 1941. ( 5 ) Melvin, E. H., and Wulf, 0. R., J . Chem. Phys., 3,755-9 (1935). (6) Milligan, L. H., J.Phys. Chem., 28, 545 (1924). Gen. Elec. Rev., 41,106 (1938). (7) Stack, S.S., (8) Taylor, H. S., “Treatise on Physical Chemistry,” Vol. 1, p. 328, New York, D. Van Nostrand Co., 1924. (9) Yost, D. M., and Russell, H., “Systematic Inorganic Chemistry,” p. 78, New York, Prentice-Hall, 1944. RECEIVED October 4, 1948.
Determination of Fungicides in Varnishes and Wood Sealers Salicylanilide, Pentachlorophenol, and Mercurial Fungicides MELVIN H. SWANN Paint & Chemical Laboratory, Aberdeen Proving Ground, M d . Methods of analysis to ensure the presence of specified quantities of fungicides in wood preservative sealers are needed. In separating salicylanilide and pentachlorophenol from varnishes, use is made of their solubility in alkalies, insolubility in acids, and slight solubility in water. They are then determined colorimetrically. Mercurial fungicides can be reduced to the metallic state, separated and determined quickly and accurately without hazards or difficulties encountered in standard procedures for determining mercury in organic substances.
S
.iLICYLA?;ILIDE has been determined in mildew-proofing
materials for cotton duck webbing (6) by extraction with a suitable solvent and digestion with sulfuric acid by the usual micro-Kjeldahl method. This determination is based on the nitrogen content of the fungicide and is unsuitable for resinous materials, because the determination of salicylanilide by its nitrogen content would involve the tedious and difficult decomposition of organic matter. I n addition, the determination would be questionable where such resins as urea-formaldehyde or melamine-formaldehyde resins are present, because of their high nitrogen content. Pentachlorophenol, in isolated form, has been estimated by its hydroxyl or halogen content but must be extracted from resinous materials before such determinations can be made with accuracy. When pentachlorophenol is present there is no way of proving the absence of other halogen-bearing compounds, except in production contiol where the resin and solvents can be tested qualitatively for halogens before the fungicides are added. I n addition, pentachlorophenol must be extracted from the sealer for positive qualitative identification. The solubility propelties of the two fungicides permit their separation from oil and resin bases. They are extracted with strong alkali from an ether or benzene solution, then acidified and re-extracted with ether, from which they are re-extracted n i t h a weaker alkaline solution. The final purification is made by diluting an aliquot portion to sufficient volume to hold the fungicide in aqueous solution while the remaining impurities are precipitated and separated by filtration. The violet color of ferric salicylate that results when salicylic acid or its salts react with ferric chloride, is used to determine the salicylanilide colorimetrically following its extraction. Pentachlorophenol is determined colorimetrically in the extract by the yellow color of tetrachloroquinone, formed when pentachlorophenol reacts with nitric acid ( 2 ) . The colorimetric determina-
tion of either fungicide is not affected by the presence of the other. Simple qualitative tests will show the presence or absence of either fungicide in the extract. There are several mercury compounds used as fungicides in wood sealers-phenyl mercuric oleate, phenyl mercuric naphthenate, phenyl mercuric o-benzoic sulfamide, etc. When mercurial fungicides are used, they compose approximately 1% of the nonvolatile portion of the sealer. The ratio of organic matter to mercury is so great that relatively large samples must be used. The excess of organic matter present necessitates pr+ longed digestion when the usual methods of decomposing organ+ mercury compounds are employed. A method has been described by Rauscher (S),in which amines are used for the reduction of mercury to the metallic state in such compounds as oxides, salts, and isolated organomercury compounds. This method has been modified slightly to give excellent results with wood sealers. The method is relatively brief and may be used with standard laboratory equipment. High temperatures and the complete decomposition of organic matter are avoided. Relatively large samples may be used if desired. The metallic mercury that may separate in finely divided form is washed by decantation. Possible losses from volatility of mercury are avoided by never exposing the metal to air. The method is equally effective with all types of mercurial fungicides and results are accurate and reproducible to less than 0.1%. ANALYTICAL PROCEDURE
Extraction and Purification of Salicylanilide and Pentachlorophenol. A sample of the varnish, not exceeding 3.0 grams, is weighed by difference from a test tube into a 250-ml. pear-shaped separatory funnel containing 40 ml. of absolute ethyl ether (if the resin precipitates in ether, benzene is substituted in the first and second funnels). The sample and solvent are mixed by swirling and 20 ml. of 2.5y0aqueous sodium hydroxide solution are added. The funnel is vigorously shaken and the layers are allowed to seps-
V O L U M E 2 1 , NO. 7, J U L Y 1 9 4 9 rate completely. The aqueous layer is drawn off into a second separatory funnel and again shaken with 40 ml. of ether. After separation, the lower layer is drawn off and shaken a third time with ether. The aqueous layer is then filtered through paper (medium porosity) previously dampened with water, into a 400-ml. beaker. Four more extractions are made, using additional 20ml. portions of 2.5% aqueous sodium hydroxide. The same funnels and solvent are used for the washing. All aqueous layers are filtered through the same funnel and paper All portions of the aqueous layer6 are collected in the same beaker, along with the water used to wash the paper. h raised cover is placed on the beaker, a glass rod is inserted to prevent bumping, and the ether is driven off by immersing in a water bath. Volume is reduced to approximately 80 ml. on a steam bath and the sample is cooled. I t is then transferred to a 100ml. volumetric flask and brought to volume Rith water. One half of the sample, or 50 ml., are transferred to a 250-ml. separator funnel with a pipet, and acidified (pH 1.0) with 6 N hy&ochloric acid, added dropwise. Accutint indicator paper No. 20 is helpful in obtaining the desired pH. Bcidification of the aqueous solution precipitates the fungicides, which can then be taken up with ether. The fungicide is extracted with three 20-ml. portions of C.P. eth 1 ether, the combined ether extracts are washed with 5 ml. oYwater, and the water is discarded. The fungicide is next extracted from the ether with 100 ml. of 0.1 N sodium hydroxide, used in 20-ml. portions. Each alkaline layer is filtered through paper (medium porosity) previously dampened with water, into a 400-ml. beaker. The paper is finally washed with water. A raised cover is placed on the beaker, a glass rod is inserted, and the ether is driven off in a water bath. The beaker is transferred to a steam bath, the cover is removed, and the sample is evaporated to dryness. I t is then transferred to an oven and heated for 1 hour a t 110" C. Upon removal from the oven, 25 ml. of water are added and the sample is warmed on a steam bath until completely dissolved. I t is then cooled and transferred with water to a 50-ml. volumetric flask. The sample is brought to volume and held for final purification and qualitative or quantitative analysis. Qualitative Identification. To show the presence or absence of salicylanilide or entachloro henol, a 10- or 2 0 - 4 . portion of the sample is withi-am7.n anfacidified (pH 1.0) by adding 6 AT hydrochloric acid slowly and with constant stirring. I t is then warmed for a few minutes in a mater bath a t 50" C. and cooled in ice or cold running water. If as little as 3 or 4 mg. of either fungicide are present, it will precipitate from solution. I t is separated by filtration and identified qualitatively. Salicylanilide can be detected by the violet color of ferric salicylate formed when ferric chloride is added, or by the Tafel reaction for anilides ( 5 ) . The former is conducted by dissolving several milligrams of the salt in a few milliliters of ethyl alcohol, adding 80 to 100 ml. of water, and removing the alcohol by evaporating to a volume of 40 or 50 ml. When 1 ml. of ferric chloride solution (1.0 gram of ferric chloride hexahydrate in 100 ml. of 1.0 .V acetic acid) is added dropwise, a stable violet color forms immediately if salicylanilide is present. To apply the Tafel reaction for anilides, several milligrams of the fungicide are dried in an oven a t 50" C. and dissolved in 3 ml. of concentrated sulfuric acid in a small test tube and 1 drop of a saturated aqueous solution of potassium dichromate is added without agitation. An intense violet color appears for several seconds, finally changing to green when shaken. The presence of pentachlorophenol is readily detected by a strong positive reaction for halogens by Beilstein's copper wirc test ( 4 ) . Colorimetric Procedure for Salicylanilide. (Because the maximum amount that can be determined by the following procedure is 5 mg. of salicylanilide, it is necessary to withdraw several aliquots of different volumes from the extracted sample.) Aliquots of 2, 5, and 10 ml. are transferred to 250-ml. beakers and diluted to approximately 75 ml. with water. Each sample is then slowly and carefully acidified n i t h hydrochloric acid to exactly p H 5.0. A pH meter is used for the adjustment and 6 S hydrochloric acid is used first, followed by 0.1 N acid for the final adjustment, to avoid overdilution of the sample. The sample, are allowed to stand 1 hour, then filtered through double thicknesses of paper of fine porosity into 100-ml. volumetric flasks. The paper and beaker are rinsed with water. Exactly 2 ml. of ferric chloride solution (1.000 gram of ferric chloride hexahydrate in 100 ml. of 1.0 N acetic acid) are added, and samples are diluted to volume. The violet color is compared at once, preferably in a Fisher electrophotometer, against a tube of water, using a green light filter (approximate wave length 525 millimicrons).
805
The weight of salicylanilide in each aliquot taken is determined from a graph previously prepared as directed below. If the amount of salicylanilide in two of the three aliquots fails to agree proportionally, they are probably too large and smaller aliquots should be withdrawn.
PREPARATION OF GRAPH. If salicylanilide of known purity is not available, a quantity of the commercial product is dissolved in aqueous sodium hydroxide, diluted to 100 to 200 ml., acidified (pH 1.0) with hydrochloric acid, filtered, and washed with water. The fungicide is dried overnight in an oven at 50" C. A quantity is weighed nith fourth decimal accuracy, dissolved in absolute ethyl alcohol, C.P. grade, and diluted to definite volume with alcohol. Aliquots of 1 to 5 mg. are rvithdrawn into 250ml. beakers, diluted with water to 150 ml., and evaporated on a steam bath to approximately 75 ml. Each is transferred to a 100-ml. volumetric flask and color is developed as above. Colorimetric Procedure for Pentachlorophenol. (Because the maximum amount that can be held in solution during the final purification process is 5 mg. of pentachlorophenol, it is necessary to withdraw several aliquots of different volumes from the extracted sample.) Aliquots of 2, 5 , and 10 ml. are transferred to 600-ml. beakers and 400 ml. of distilled water are added. Each sample is acidified (pH 1.0) with concentrated hydrochloric acid and allowed to stand 1 hour. Accutint indicator paper No. 20 is helpful in obtaining the desired acidity. The samples are filtered through double thicknesses of paper of h e porosity into 600-ml. beakers and the filter papers are washed with water. Each is then neutralized with sodium hydroxide and an excess of 5 ml. of 10% sodium hydroxide is added. The samples are then placed in a boiling water bath and the volume is reduced to 20 to 30 ml. The samples are cooled, transferred with water to separatory funnels, and acidified (pH 1.0) with 6 N hydrochloric acidand the pentachlorophenol is extracted with three 20-ml. portions of C.P. benzene. The benzene extractions are combined and washed with 5 ml. of water. The combined benzene layers of each aliquot sample are filtered through paper (coarse porosity), previously dam ened with benzene, into glass-stoppered 250-ml. Erlenmeyer lasks. Ten milliliters of 10 N nitric acid and 1 ml. of 10% hydrochloric acid are added. A small strip of paper is inserted a t the side of each glass stopper and the flasks are placed in a water bath a t 70" C. for 20 minutes. Each sample is then cooled, transferred to a 250-ml. separatory funnel, and washed twice with 150 ml. of distilled water. The water washings are discarded and the benzene layers are filtered twice through paper of medium porosity, previous1 dampened with benzene. The second filtrsG tion is made direct& into 100-ml. volumetric flasks. The papers are washed with benzene and the yellow benzene solution is diluted to volume. The flasks are shaken thoroughly and allowed to stand from 10 to 30 minutes. The color is then compared in an electrophotometer against a tube of water, using a blue light filter (approximate wave length, 425 millimicrons). The m i g h t of pentachlorophenol in each aliquot taken is determined from a graph previously prepared as directed below. If the amount of fungicide in tR.0 of the three aliquots fails to agree proportionally, they are probably too large and an indefinite amount of pentachlorophenol has precipitated out during the final purification. PREPARATION O F GRbPH. If pentachlorophenol of known purity is not available, a quantity of the commercial product is dissolved in aqueous sodium hydroxide, diluted to 100 to 200 ml., acidified (pH 1.0) with hydrochloric acid, filtered, and washed with water. It is then dried overnight in an oven a t 50" C. A quantity is weighed with fourth decimal accuracy, dampened with absolute ethyl alcohol, dissolved in C.P. benzene, and diluted to a definite volume. Aliquots of 1 to 5 mg. are mithdrawn into 250-ml. glass-stoppered, Erlenmeyer flasks. Volume is made up to approximately 60 ml. with benzene and the color is d e veloped as in the colorimetric procedure. CALCULATIONS. If a = milligrams of fungicide in aliquot taken, b = size of aliquot in milliliters, c = size of original sample of sealer, in grams, and d = per cent of solids in sealer, evprcssed 10 X a decimally, then = % of fungicide in sealer, calculated b X c X d on the solids basis. ~
ANALYTICAL CHEMISTRY
806 If it is likely that phenolic fungicides other thao pentachloruphenol are present it will be necessary to separate the latter by precipitation. Fifty milliliters of the sample in 2.5% alkaline solution are acidified, to pH 1.0, with hydrochloric acid and diluted to 100-ml. volume. After standing a t least 12 hours, the 1O C. and the sample is filtered temperature is adjusted to 25" through porous glass crucibles of medium porosity, containing a layer of asbestos. The filtrate is used to make the transfer; no water is used. Three milligrams of pentachlorophenol will be lost because of its slight solubility, and correction must be made in calculating. Other phenolic fungicides, if present, will remain in the filtrate. The precipitated residue is dissolved while still wet, by passing 100 ml. of 0.1 ;V sodium hydroxide through the crucible several times, washing finally with water. The sample is then transferred to a 400-ml. beaker, evaporated to dryness on a steam bath, transferred to an oven, and heated for 1 hour a t 110" C The original procedure is followed from this point. Extraction of Metallic Mercury from Mercurial Fungicide Sealers. A sample of the sealer, not exceeding 5.0 grams, is carefully weighed by difference into a 100-ml. round-bottomed flask having a standard-taper, ground-glass joint. Five milliliters of mineral spirits are added to prevent coagulation of the varnish while the more volatile solvents are driven off by heating the open flask on a steam bath for 30 minutes. Five milliliters of diethanolamine and approximately 0.15 gram of sodium metal, cut into small pieces and wiped dry with absorbent paper, are added. Finally, several glass beads are added and a water-cooled condenser is attached. The sample is boiled gently for 45 minutes. The fungicide is reduced and metallic mercury collects in the bottom of the flask. After cooling, the condenser is m s h e d down with either C.P. acetone, or absolute methyl alcohol, whichever appears to be the better solvent for the products remaining after refluxing.
reagent is added to the filtrate and allowed to stand several hours. If precipitate appears, i t is added to the crucible. CALCULATION. Weight of precipitate X 0.2396 = weight of mercury in aliquot. ACCURACY OF METHOD
f
__
Table I . Fungwdr Solution
Varnish
Grams 3.0428 3.4629 1.1803
Grams 48.5016 68.7330 36.6071
Accuracy of Determination Type of Rerin
Alkyd
Linseed oil Phenolic
Sample Size Grama 4.8105 3.0322 5.2622
Fungmide b UrigiLidr Present Determined Gram
Gram
0.01188 0.01706 0.01928
0.0114c5
0.01683 n187n
n
The condenser is removed and the sample is diluted with acetone or methyl alcohol to approximately 50 ml. I t is mixed by swirling and the metallic mercury is allowed to settle into the bottom of the flask. h trap is connected to a source of vacuum and a curved glass jet is connected to the trap with vacuum tubing. With gentle suction, the solvent and resinous portibns of the sample are drawn off by holding the point of the jet against the side of the flask, near the bottom. All but a few milliliters are drawn off and the mercury is washed by adding 50-ml. portions of solvent, swirling, allowing the mercury to settle, and drawing off the washings. R h e n the washings appear free of resinous matter, the mercury is washed with distilled water by the same process. At all times, the mercury is covered with the washing liquid. It is then dissolved in a minimum amount of concentrated nitric acid, diluted to approximately 75 ml. with water, and filtered through paper into a 100-ml. volumetric Bask. The sample is then diluted to volume with water. Quantitative Determination of Extracted Mercury. The gravimetric determination of mercury in solution with Reinecke's salt ( I ) is the method best suited to complete the analysis. Bn aliquot estimated to contain from 2 to 20 mg. of mercury is drawn off into a 250-ml. beaker or flask. I t is diluted to 40 to 50 ml. with water and 0.1 S potassium permanganate solution is added to the first appearance of pink color. The sample is then made approximately 0.5 &V with hydrochloric acid (4 or 5 ml of 6 N hydrochloric acid). I t is heated on a steam bath and Reinecke's reagent is added dropwise-1 ml. of reagent per milliam of mercury estimated to be present. Reinecke's reagent ammonium tetrathiocyanatediamine chromate) is made by hydrochloric acid and dissolving 1.0 gram in 100 ml. of 0.05 filtering. A fresh solution is used. The Sam le is allowed to stand a t least 5 minutes and filtered through a ktted-glass crucible containing an additional mat of fine-fibered asbestos, previously dried for 1 hour at 110" C. and weighed. The precipitate is washed with hot water and the crucible is dried for 1 hour a t 110' C. and weighed. ;Idditionnl
r
To determine the accuracy of the method, weighed quantities of fungicide solutions of known composition were added to various types of varnishes so as to approximate the composition of wood sealers. Table I shows some of the results obtained from sealers made from 11.730/, solution of phenyl mercuric oleate. DISCUSSIOh
The recommended volumes of solutions and solveiits apecified in the purification process for salicylanilide and pentachlorw phenol are based on the partition of a compound soluble in two immiscible liquid media and must not be varied because i t would reduce maximum separation and accuracy. Large ether volumes are used in the ether extractions, so that the large particles of precipitated fungicides are dissolved in the first extract to prevent clogging of the qeparatorr funnel. Three such extractions are sufficient. T o develop the procedures fur extraction and purihcatioxi of salicylanilide and pentachlorophenol and to measure accuracy, known quantities (40 to 50 mg.) of the fungicides were dissolved in 40 ml. of benzene in separatory funnels. Weighed quantities of various types of resins were added in such proportions as to approximate the composition of wood sealers. The resins used were glyceryl phthalate alkyds, linseed oil, and modified phenolics as specified in U. S. Army Specification 3-186. The extraction and purification processes were then followed as outlined and the colorimetric procedure was conducted to determine the degree of recovery. Accuracy to 0.1% is obtained. The graphs for colorimetric determination of both tungicidee are straight lines. Under certain conditions, the graph for salicylanilide may curve slightly in the upper portions owing to the difficulty of obtaining a ferric chloride solution of exact composition. Ferric chloride hexahydrate is so hygroscopic that i t is advisable to weigh a lump of the salt in a closed weighing dish and calculate the amount of 1.0 S acetic acid that must be added to produce a solution of the concentration recommended. For the same reason, a large quantity should be made, sufficient to complete all samples under test. When a new quantity of ferric chloride solution is made, it is necessary to check it with known amounts of salicylanilide against the existing graph and to regraph the known quantities. This variation is due partially to the fact that the iron salt is always present in excess and imparts home of its own color to solution. If 0.05 molar ferric chloride solution is used in place of the recommended 1% solution, equivalent amounts of salicylic acid could be used in place of salicylanilide for preparing the graph. However, at this concentration of ferric chloride the range of the graph is reduced to such An extent that not more than 2 mg. of salicylanilide in R 100-ml. volume can be determined with accuracy. These methods of analysis were developed for use only on fungistatic varnishes and are not suitable, for example, for determining pentachlorophenol in treated wood LITERATURE CITED ( 1 ) Mellan, Ibert, "Organic Reagents in Inorganic p. 454, Philadelphia, Blakiston Co., 1941. I 21
(3) (4)
(5) (6)
.hiaIysis,"
Monsanto Chemical Co., private communication on modification of quantitative colorimetric determination of pentachlorophenol in permasan wood treating formulations. Kauscher, W. H., IND.ENG.CHEM.,AN.QL.ED..10,331 (1938). Kuigh, W. L., I b i d . , 11, 250 (1939). Tafel, J., B e y . , 1892, 412. U. S. Army Specification AXS-1247, "Mildew-Proofiiig of Cotton Duck Wehbing, Belting, and Thread" ( J u l y 24. 1945).
RECEIVEDMarch 5 , 1948
