Detection of Pentachlorophenol in Treated Wood S. S. SAKORNBUT and H. L. MORRILL Monsanto Chemical Co., Saint Louis, M o .
Pentachlorophenol in treated wood was detected by formation of cry stal violet (hexamethylpararosaniline chloride). Sections of treated wood were exposed to chlorine dioxide and sprayed with a 1% solution of crystal \iolet leuco base, p,p’,p’’-methylidynetris(iV,Ndimethy laniline), in xylene-Skellj solte E. Pentachlorophenol was con\erted to chloranil (tetrachloro-pquinone), w hich oxidized the leuco base to crystal ~ i o l e t . During color debelopment, oxidation by air was aioided by the use of an enclosure filled with nitrogen or carbon dioxide gas. The minimum pentachlorophenol concen tration detectable in treated Ponderosa pine sapwood was estimated as 0.022YG.
T
HE deterinination of penetration of pentr:tchlorol)henol solution in treated wood generally has not heen simple iiccause of the esac:ntially colorless nature of the compound and the small quantifies in ivhich it is found. When the solvents of the darkened ~ - o o dtissue. Oil-soluble dyes have been used for intensifying the color of preservative solutions, and fluorescent additives for dctection in ultraviolet light. I’olvdered dyes have been used to impart color to the penetrated t k u e of wood treated with a, prwervutive solution of low volatility (4). These method3 are based on the assumption that pentachlorophenol penetration is the same as that of other components of t,he solution. Determination of penetration of a clean, paintable type of formulation without a fluorescent additive iiiiiqt he through tletec*tion of peiitachlorophenol itself.
7
Pattern for cutting timber into block specimens
Pentachloropheiiol foimis colored salts with iron, nickel, cobalt, copper, etc., the, dark red-purple color of copper peiitachlorophenate is probably most easily detectable. -111 alcoholic solution of cupric acetate sprayed on the surface of treated Ivood \vi11 readily foi,iii copper pentachlorophenate, hut the color formation is not cliwernilile except when the pent:tc.hloroI)heiiol content is above 1%. Pentachlorophenol is oxidized by nitric acid to a yellon-red inixture of tetrarhloro-c- and -p-qtIinones ( 1 , 2 ) . \Then this reaction is (wried out on wood, the wood substance itself is also darkened hy nitric :wid, which renders the similarly colored quinone3 uiidetertithle except a t higher concentrations. Sandermann and Jonas (3) osidized pentachlorophenol in d cliloranil (tetrachloro-p-quinone) by exposing it treated ~ o o to
--
.
~
--
v‘]’:
_ - --
itre dark-colored, penetration can be determined by observation
Figure 1.
to chlorine dioxide, and ol)tainetl the violet,-bliir color of ~iietliyl violet by subsequent spraying with a benzine solution of .\-,LYdimethylaniline. S,.~--Diniethylaniline can d a o \)e converted to methyl violet by iodine, cupric salts, etc., as shown by \Vic.helhaus ( 5 ) . The sensitivity of the Sanderm~tnri and .Jon:t:: iiiethod was found by this laboratory to he approsimntely O.ii% with respect to pent:ichlorophenol concentratiou in n.ooil. Although riii.2 method 1wovides a more sensitive tle. tection than that by the -, .I t copper ~~~~it:ichloro~~liea * I N nate method, it lenvea -~ .- ! I much t o be desired. 6”
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-
\.
THEORETICAL CONSIDER.4TION
In R - O O ~preserviiig industries, preservative allb sorption or retention has usually been espressed in terms of pounds per cul)ic t , foot of wood. Since the ‘.. L preservative solution is -6’e usually not uniformly disFigure 2 tributed throughout e:wh a. Derivation of blochs 1’ and piece, nctiial preservative U ’ from blochs 4 and I ) b. Derivation of blocks B’ and concentration in ~ o n i e C’ from blocks B and C parts is lower than the average preservative content, For esaniple, in a piece of timber treated to a retention of 6 pounds of 5% pent:ichloropheiiol solution per cubic foot of wood, the over-all prepervative content is 0.96% of pentachlorophenol by weight (based on wood with a specific gravity of 0.5). If this tinilier i.=treated by one of the coninionly used metliod.. t h e preserv:it ive concent ratioii of the outer zone \vi11 exreed 0.96%, n-hile that of the inner zone will be consiclerahly IoLver, iiich 0.17~ or less. To determine tlie estell t of pelletration to the.;cs low lei-els, n sensitive te.st is reqiiired. The detailed renetions involved during the convewion of lY,,Ydimethylanil i n e l>y chloranil to methyl violet are not fully understood. I t has been postulated that a methyl Figure 3. Apparatus for exposing group in one ,V,lVwood sections to chlorine tlinxide
1259
1-
ANALYTICAL CHEMISTRY
1260 dimethylaniline molecule is oxidized to formaldehyde, which condenses with the resulting A17-methylanilineand two molecules of unaltered S,S-dimethylaniline to form pentamethylpararosaniline (the carbinol base of niethyl violet). The dyes methyl violet and crj-stal OUTLET violet (hexamethylNITROGEN INLET pararosaniline chloride) are converted by alkali to carbinol bases, which can be reduced t o colorless 1,; 1 S t D C Q l l leuco bases. These
q+
L E . - - -
reactions are reFigure 4. Kitrogen chamber used versible. Thereduring calor development fore, it seemed probable that the use of a leuco base instead of S,,V-dimethylaniline as a color-forming reagent 1% ould produce three times as many moles of dyestuff per mole of chloranil, according t o the following equation.:
/ + [OI
H C/- - - ~ ( C H ~ ) ~
chloranil
\ O X (
U
Carbinol base of methyl violet
estimate of pentachlorophenol in each increment of the block. I n treating, the blocks were suspended vertically at the same level, and a 2.5y0 solution of technical pentachlorophenol in 1 t o 1 (by volume) xylene-mineral spirits was brought into contact with the lower ends so that they mere immersed t o a depth of 0.25 inch for 3 minutes. A4fterthe treatment, the blocks yere left suspended in air for 5 days to condition to equilibrium. The conditioned blocks were then “shelled” by sawing off 0.5-inch slabs from all four sides, leaving blocks A‘, B’, C‘, and D’ BJ shown in Figure 2 (solid lines). The crystal violet color reaction was carried out on longitudinally split sections of blocks A’ and D’ (not shown in drawing). The wood sections were exposed for 30 minutes to chlorine dioxide gas, generated by the action of glacial acetic acid on sodium chlorite. This treatment was made in a glass casserole (household type) approximately 7 inches in diameter (Figure 3). Ten grams of sodium chlorite was placed in the casserole and sufficient water was added t o form a paste, to which approximately 8 ml. of glacial acetic acid was added. The reactants were then covered with a 6-inch Petri dish, the bottom of which had been perforated a t 1-inch intervals around the circumference. The perforated dish, which rested on the curved sides of the casserole about 1 inch from the bottom, also served as a support for wood specimens. Sfter treatment with chlorine dioxide, the n-ood specimens were aired for 0.5 hour before they were sprayed with a 1% solution of crystal violet leuco base in 1 to 1 (by volume) xylene-Skellj-solve E. Immediately after spraying, the specimens were placed in a nitrogen chamber (Figure 4). A violet color soon developed, starting a t the dipped ends, and within 5 minutes the color formation extended to its maximum length of approximately 2.3 inches. The pentachlorophenol concentration at this point was found to be approximately 0.022% by analysis as shon-n later. A slight coloration eventually developed on the remainder of the specimens, and even on untreated, unoxidized controls. This might have been caused by traces of air that were alrendjpresent in the wood.
(2)
CH3)2
Leuco base of methyl violet Since the leuco base of methyl violet was not readily available, whereas that of crystal violet, 4,4’,4”-methylidynetris(N,Sdimethylaniline), could be obtained from chemical supply companies (Eastman Kodak Co. KO. 3651), the latter compound was chosen for study. EXPERIMENTAL
To determine the sensitivity of the color reaction, it was necessary to develop a method of treating and sampling wood so that the pentachlorophenol concentration at the limit of detection could be accurately estimated. Preliminary experiments included analysis of treated wood sections on which pentachlorophenol was barely detectable by the color renction. Such analytical samples were taken from the interior of commercially treated lumher of large cross section (4 X 4 inch lumber or larger). The detection and analyses were also made on several specimens treated in the laboratory with both pressure and nonpressure methods. It was found that by dip-treating the ends of carefully duplicated specimens rut from even-grained, clear-grade Ponderosa pine sapwood, the duplicates could be treated to the same preservative retention with practically the same concentration gradient from the dipped ends. Wood blocks were cut from a piece of timber according to the pattern shown in Figure 1; blocks A and D were 2 X 2 X 6 inches and blocks B and C, 2 X 4 X 6 inches. -4lthough the A-D pair differed from the B-C pair in cross-sectional area, they were essentially duplicates with respect t o preservative concentration gradient. The uniformity of the grain was readily verified because of the cutting pattern and the pairing of specimens in detection and analysis. The blocks for analysis ( B and C) were cut larger than A and D. Cross sections of the larger blocks provided sufficient pentachlorophenol for accurate quantitative determination a t the limit detectable by the color reaction. Very thin cross-sectional slices ( 2 mm.) were taken to assure an acrurate
-’
I
6 ‘I
Figure 5 .
0.07
I
Zoning of blocks B’ and C‘
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0 03 0 02
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A\
I I
0 01
Figure 6.
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1
-3
Distribution and detectable limit of pentachlorophenol in wood
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1
1261
V O L U M E 27, NO. 8, A U G U S T 1 9 5 5 The pentachlorophenol concentration in planes 1, 2, 3, 4, 5, and 6 of blocks B’ and C’ (Figure 5 ) !vas estimated by analysis of a composite of adjacent cross sections, 2 mm. thick, on either side of these planes. The two sections for each analysis were pulverized together in a Kenmore liquidizer and digested in 2.57, sodium hydroxide. Pentachlorophenol was recovered by acidification with hydrochloric acid and steam distillation. The isolzted pentachlorophenol was determined by the nitric acid oxidation method (2). The results are given in Figure 6, in which the extent of penetration, as revealed by the color of crystal violet, is also shown. From these results it is estimated that 0.022% is the limit of pentachlorophenol concentration detectable by the crystal violet method in the kind of wood studied.
It was found that the degree of sensitivity determined was reliable only when applied to freshly exposed surfaces of wood sections. The amount of pentachlorophenol, and consequently of chloranil, to react with the leuco base is very small in the vicinity of the detectable limit, probably in the order of a fraction of a microgram per square millimeter. L‘olatilization of pentachlorophenol is likely to cause a significant reduction of the surface concentration upon prolonged exposure. Carbon dioxide from a cylinder or from sublimation of dry ice is a satisfactory substitute for nitrogen as a means of excluding air during color development.
DISCUSSION
LITERATURE CITED
Clear-grade Ponderosa pine s a p ood vias used in the experiment because of the uniformity of its grain and color. It x a s found that, for all practical purposes, the degree of sensitivity estimated is also applicable t o other species of light-colored wood, and to other types of pentachlorophenol formulations. Obviously, the sensitivity a-ould be considerably lower for darkcolored wood. I t is also conceivable that extractives of some species of wood and some ingredients used in pentachlorophenol formulations might interfere with the color reaction.
(1) Deichmann, W., and Schafer, L. J., IND. EKG.CHEY.,ANAL.ED., 14, 310 (1912). (2) Monsanto Chemical Co., Tech. Bull. C-24 (1955). (3) Sandermann, W., and Jonas, G. Z., Nolz Roh- u m’erkstof’, 9, 298
(1951).
c. S., W o o d , 5 , 31 (1950). (5) Wichelhaus, H., B e y . , 19, 107 (1886).
(4) Walters,
RECEIVEDfor review February 21, 1955. Accepted April 18, 1955.
Chromatographic 2,4=Dinitrophenylhydrazone Method for Determination of Allethrin NATHAN GREEN and M. S. SCHECHTER Entomology Research Branch, Agricultural Research .Service,
U. 5. Department
o f Agriculture, Beltrville,
Md.
The hydrogenolysis method ( I d ) for pyrethrins has also been adapted to the analysis of allethrin (4). I t was used for the assay of allethrin until it was discovered that chrysanthemummonocarboxylic anhydride was present in allethrin and that an adequate correction for the anhydride could not be made by this method. Hogsett, Kacy, and Johnson (IO) have recently proposed a method in which allethrin reacts with ethylenediamine. N 1949 Schechter, Green, and LaForge ( 2 3 ) discovered a This splits the ester and forms an equivalent of chrysanthemummethod of synthesizing esters of the pyrethrin type. One monocarboxylic acid, which is then titrated in a nonaqueous of these esters, dl-2-allyl-4-hydroxy-3-methyl-2-cyclopenten-1-medium. At present it is the preferred procedure for the assay one esterified with a mixture of cis- and trans-dl-chrysanthemumof allethrin, for it has the advantages of reproducibility and monocarboxylic acids and called allethrin ( d o ) , is now being adaptability to the running of many samples in a reasonable time; produced commercially a t the rate of about 50,000 pounds per in addition a number of acidic impurities found in technical year ( 2 2 ) . I t now costs about $32 per pound. samples are determined. I t does, however, have certain dieadvantages, such as the number and quantity of solvents and CH, I standard solutions required, some difficulty with the end points found with dark-colored samples, and the need for large samples (5.3 to 8.6 grams per single analysis). I n some of these methods it is necessary to make separate determinations of acidic impurities, such as chrvsanthemummonocarboxylic acid, its anhydride, and its acid chloride, in order to correct for the presence of these materials. .4 number of other methods have been proposed-some (CH,),C=CH-CH chromatographic (15, 29)) some colorimetric ( 2 , 5, I S , 14, 26), and H2Cc=o others modifications of existing methods. h polarographic Allethrin method has been presented by the Japanese workers Yamada, Sato, and Iwata ( 5 0 ) and an infrared method by Freeman (6). As Rith all ne17 chemicals, it is important to have a number The authors’ method is based on the formation of the 2,4of methods of analysis available. The development of analytical methods for allethrin has been difficult because of the complexity dinitrophenylhydrazone derivative of allethrin, its chroniatographic separation on a silicic acid column, and gravimetric deof the molecule. Allethrin is similar to the pyrethrins in structermination of the main band thus separated. A colorimetric ture, and some of the methods used for the analysis of pyrethrins, determination can also be used for smaller amounts where less such as the rlOAC ( 1 ) and Sei1 ( 2 7 ) methods, can be adapted for certain purposes. However, the accuracy and precision of these accuracy is tolerable. Since the derivative is colored, its progress methods leave something to be desired in spite of attempts to down the column can be readily observed. Some impurities, such as allethrolone, form bands which easily separate from the improve them i n recent rears.
A method is described fox the determination of allethrin
based on its conversion to the 2,4-dinitrophenylhydrazone derivative, chromatographic analysis of the derivative on silicic acid, and gravimetric or colorimetric determination of the main band.
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