1760
ANALYTICAL CHEMISTRY
pH due to the release of hydrochloric acid which constitutes the basis of the analysis, and then there is a small change in pH which accompanies the change in environment resulting from the dilution of the “blank solution” with a nearly equal volume of sample solution. This latter effect constitutes an error in the analysis which amounts to about +0.05 pH unit \There the solvent is water and about -0.02 pH unit where the solvent is methanol, Keither benzene nor dioxane appears to have any effect on the pH. This error is practically negligible when working in the range of 0.01 millimole per milliliter where the total pH change is about 1.16 pH units. If desired, however, a correction may be made by running a blank analysis on 10 ml. of carbonyl-free solvent. A significant “change of environment” error may be introduced in the analysis, if one uses hydroxylamine hydrochloride reagent which contains an appreciable amount of free hydrochloric acid. For example, the use of 0.05 S hydroxylamine hydrochloride reagent containing but 0.3 X 10-6mole of free hydrochloric acid per milliliter resulted in an error of more than twice that normally encountered. The sensitivitv of the analysis was checked using varying concentrations of hydroxylamine hydrochloride. I n the range 0 to 0.023 millimole per milliliter of carbonyl the best results v.-ere obtained xith a 0.5 Ksolution. More concentrated solutions were
less sensitive to small changes in pH while the less concentrated solutions showed poor stability, tending to hydrolyze rapidly to release hydrochloric acid. A 0.5 A! solution is stable for about 3 days. The pH change is not appreciably affected by variations in temperature between 20” and 30” C., provided the pH meter is adjusted for this change. Some heat results from the addition of methanol or dioxane to the aqueous blank solution, causing the temperature to rise as much as 5” C. above room temperature. ’VCTith stirring, the temperature normally returns to room temperature in the 5 minutes allowed for the reaction. This investigation was limited to systems involving benzene, dioxane, methanol, and water. Cndoubtedly analyses may be performed in many other solvent systems. However, for each solvent the standard working curve should be checked by analysis of known concentrations of carbonyl compounds. LITERATURE CITED
(1) Byrne, R . E., A N ~ LCHEM., . 20,1245-56 (1945).
(2) Huckabay, W. B., Newton, C. J., and hletler, A . V., Ibid., 19, 8.15-41 (1947). RECEIVEDhiaroh 30, 1951,
Analysis of Technical Pentachlorophenol J. B. LACLAIR California State Department of Agriculture, Sacramento, Calif Existing methods of analyses were inadequate for the proper enforcement of the Agricultural Code of California pertaining to the sale and labeling of products containing pentachlorophenol which are widely used as wood preservatives, fungicides, herbicides, and defoliants. An ultraviolet spectrophotometric method was developed for the quantitative determination of the individual components of technical pentachlorophenol, adaptable to most com-
T
HE use of technical pentachlorophenol as a fungicide and
herbicide has been increasing during the past few years. The task of enforcing the Agricultural Code of California pertaining to labeling and sale of technical pentachlorophenol and its formulations is difficult because of the lack of an accurate, specific method of analysis. A literature search disclosed methods of analysis based on determining pentachlorophenol from total chlorine ( 4 ) , and colorimetric procedures (1, 3,4,6, 7 ) which are not specific for pentachlorophenol, but include many phenolic substances. EXPERIJIE5T4L
Using a Beckman hlodel Dli spectrophotometer, an ultraviolet absorption study of the components of technical pentachlorophenol, separated by vacuum sublimation and compared with the most probable components (Figures 1, 2, and 3), disclosed only pentachlorophenol, 2,3,4,6tetrachlorophenol,and an unidentified, dark brown, high melting, chlorophenol containing 58.3% chlorine (Figure 3), which is probably a polymerization product produced during process of manufacture. An examination of the absorption spectra of pentachlorophenol and tetrachlorophenol (Figure 1) showed that a t 255 millimicrons tetrachlorophenol absorption offered the least interference to
mercial pentachlorophenol products. The use of ultraviolet spectrophotometric methods for the analysis of substituted phenolic compounds has apparently not been developed. By using spectrophotometric methods, in conjunction with appropriate separation procedures, i t is possible to identify and quantitatively determine phenolic compounds which are too closely related structurally for ordinary chemical methods.
pentachlorophenol absorption. The best point for tetrachlorophenol absorption was found a t 285 millimicrons. After determining the extinction coefficients for pentachlorophenol and tetrachlorophenol a t these two wave lengths a series of known mixtures was analyzed (Table I) using these data. Close adherence to the Lambert-Beer law was noted for the concentrations tested.
Table I. Analysis of Prepared Mixtures of Pentachlorophenol and Tetrachlorophenol Pentachlorophenol Added, Found, Recovery, mg. mg. % 96.0 0.48 0.5 104.0 1.04 1.0 100.8 2.52 2.5 102,2 5.11 5.0 99.6 7.47 7.5 94.1 8.47 9.0 100.2 9.52 9.5 0.09 0.0 104 2 10.42 10.0 99.3 2.58 2.6 102.6 5.85 5.7 98.2 9.82 10.0 95.2 14.08 14.8 99.1 1 1 58 11.7 Av. recovery 99.6
:
Added, mg. 9.5 9.0 7.5 5.0 2.5
1 .o
0.5 10.0 0.0 11.4 15.5 11.8 4.2 2.1
Tetrachlorophenol Found, Recovery, mg.
%
9.60 8.99 7.51 5.10 2.50 1.02 0.54 9.87 0.06 11.47 15.88 11.82 4.06 2.06
101.1 99.9 100.1 102.0 100.0 102.0 108.0 98.7 l06:6 102.3 100.e 96.8 98.1 100.8
V O L U M E 23, NO. 12, D E C E M B E R 1 9 5 1
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100
solution is extracted six times more using 5-mL portions of tetrasodium pyrophosphate solution, collecting the aqueous extracts in the second separatory funnel. The aqueous extracts are then shaken with about 10 ml. of petroleum ether and allowed to separate. The lower aqueous la er is drained into a third separatory funnel, and the petroleum etler layer is washed twice with a few milliliters of distilled water. The water washings are added to the pyrophosphate extracts in the third funnel. The petroleum ether layer is then added to the oil solution in the first separatory funnel.
80
e 60
2i 9
100 r-
40
a E
80
//
ii
I '
PO
0 220
240 P60 280 WAVE LENGTH, m p
300
320
Figure 1. Absorption Spectra of 2,3,4,6-Tetrachlorophenol ( A ) and Pentachlorophenol ( B ) , 0.1 Mg. per Ml., in E t h y l E t h e r Solution Technical pentachlorophenol is often formulated with chlorophenylphenols, and as they have very strong absorption a t 255 and 285 millimicrons it was necessary to separate pentachlorcphenol and tetrachlorophenol from these compounds. I t has been claimed that pentachlorophenol could be completely separated from phenylphenols by steam distillation a t p H 9 ( 4 ) ,but this separation was not complete enough to use. Extraction m-ith a 5% solution of tetrasodium pyrophosphate is used to remove pentachlorophenol from weakly acidic phenolic compounds (4). This extraction completely separates pentachlorophenol and tetrachlorophenol from any of the phenylphenols commonly used in conjunction with technical pentachlorophenol (Table 11), and also from the polymerized chlorophenol normally found in technical pentachlorophenol.
Table 11. Separation of Pentachlorophenol and Tetrachlorophenol f r o m Phenylphenols by Extracting with 59" S o d i u m Pyrophosphate Solution
-
Phenylphenol Added,
Name 6-Chloro-2-phenylphenol Chloro-2-phenylphenol o-Phenylphenol 4-Chloro-2-phenylphenol
mg.
9.6 15.4 9.4 41.4
Pentaohlorophenol Added, Found, mg. mg. 8.7 9.19 18.2 18.12 6.8 5.92 8.2 8.15
Tetrachlorophenol Added, Found, mg.
mg.
5.5 6.6 7.5 8.1
5.52 6.90 7.40 8.09
,
