Table I s h o w data on the phenols and volatile oils investigated. Typical titration curves in the different solvents are shown in Figures 1 to 5. The most basic solvent, ethylenediamine, produced the greatest inflections. The end point may be obtained from the curves by inspection. Phenols are too weak to titrate in water, but they behave as weak acids in ethylenediamine. Although the inflections are not so marked with dimethyl formamide or acetonitrile as the solvent, the end point is readily obtained from a differential plot or even by inspection-for example, isoeugenol. Titration curves for thymol and thyme oil, the chief phenolic constituent of which is thymol, are shown in Figure 1. Thyme oil (red variety), K , F , VI1 (10) (containing not less than 20% phenols), was used in this investigation. According to N.F. X ( 2 1 ) thyme oil must contain not less than 40% phenols to meet official requirements. The results using the three solvents are in excellent agreement. The determination of thyme oil in dimethyl formamide by the procedure described was reported in an earKer paper ( 2 ) . A colorimetric method, the conventional procedure, and the titrimetric analysis yielded comparable results with the red and Iyhite varieties of thyme oil. Clove oil, bay oil, and eugenol (the main constituent in clove and bay oils) show similar titration curves (Figure 2) in the three solvents. The curves for eugenol and isoeugenol (Figure 5 ) compare favorably with those shown by Butler and Czepiel(3). The results in Table I for clove and bay oils and the nature of the curves demonstrate the applicability of nonaqueous titrations to the analysis of volatile oils of this type.
Bay oil (myrcia oil) contains 50 to 65% phenols. According to Palkin and Wells, as reported by Guenther (8), 89.3% of the phenol content is eugenol, while the remaining 10.7% is chavicol (p-allylphenol). The calculation of phenol content in bay oil shown in Table I is based on eugenol. hlethyl salicylate is the principal constituent of several volatile oils (wintergreen oil, sweet birch oil) or it may be prepared synthetically. Phenolic esters of this type were successfully titrated as weak acids in ethylenediamine by Glenn and Peake ( 5 ) . Typical titration curves in dimethyl formaniide and ethylenediamine are shown in Figure 3. Titration curves for origanum oil and carvacrol are shown in Figure 4, Origanum oil contains 63 to 74% phenols ( 7 ) consisting mainly of carvacrol. Isoeugenol occurs in varying concentrations in a number of volatile oils. Typical titration curves in the three soh-ents are shown in Figure 5 . The titrimetric procedure offers a number of advantages over the classical method for analyzing volatile oils ryhich contain phenolic constituents. Once the titrant has been prepared and standardized. routine analyses can be effected in a short time. Sample weights of less than 1 gram are needed, whereas the conventional method requires 10 ml. As volatile oils are generally rather expensive, this may he an important economic consideration. Percentage content is expressed in terms of weight in weight rather than volume in volume. The former is the usual manner for expressing the concentration of constituents. The accuracy and precision are superior to those obtainable by the extraction procedure. S o prob-
lems arise from difficulties in reading the meniscus or solubility of nonphenolic alkali-soluble substances. Although a Fisher Titrimeter was used, any suitable potentiometer may be employed. ACKNOWLEDGMENT
The author thanks Fritzsche Brothers, Inc., Kew York 11, K.Y., for kindly supplying the bay oil, isoeugenol, and origanum oil used in this investigation. He wishes to thank Jack Arndt for preparing the curves. LITERATURE CITED
Blake, ill. I., J . Am. Pharm. Assoc., Sci. E d . 46,287 (195i). Blake, M. I., Fibranz, L., Miller, C. E., Zbid., in press. Butler, J. P., Czepiel, T. P., -4s.~~. CHEM.28, 1468 (1956). Cundiff, R. H., hIarkunas, P. C., Ibid., 28, 792 (1956).
Glenn, R. A., Peake, J. T., Ibid., 27, 205 (1955).
Guenther, E., “The Essential Oils,” Vol. 1, p. 291, Van Nostrand, New York, 1948. Ibid., Vol. 111, p. 535, 1949. Zbid., Vol. IV, p. 395, 1950. Guenther, E., Langenau, E. E., ANAL.CHEM.27, 6 i 2 (1955). “Xational Formulary,” i t h ed.,, p. 306, American Pharmaceutical Association, Washington, D. C.,
1942. Zbid., 10th ed., pp. 385, 611, 612, 19.55.
(12) “U.-S: Pharmacopeia,” 15th rev., p. 163, Mack Printing Co., Easton, Pa., 1955. (13) Warner, B. R . , Haskell, W. W., ANAL.CHEX.26, 770 (1954).
RECEIVEDfor review June 3, 1957. -4ccepted Xovember 22, 1957.
Automatic Unit for Determination of Volatile Matter in Coal, Coke, and Char R. P. HENSEL and S. A. JONES Research and Development Division, Piffsburgh Consolidafion Coal Co., library, Pa.
b In determining the volatile content of coal, coke, and char, the American Society for Testing Materials designates a 7-minute heating period a t 950” C. with modification of the heating rate for certain nonagglomerating materials. Conventional manual control prevents close duplication of heating rates and results are often erratic. The apparatus described permits close control of the heating, is sufficiently flexible to b e adapted to a variety of
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ANALYTICAL CHEMISTRY
materials, and automatically controls the entire operation. It is designed to operate with one or two vertical tube furnaces.
I
N DETERMIKING the Volatile matter
of coals and cokes, the American Society for Testing Materials designates a 1-gram portion of sample weighed into a 10- or 20-ml. platinum crucible and lowered into a n electrical vertical tube
furnace or heated in a muffle to 9.50’ C. After a 7-minute residence time, the crucible and contents are removed, cooled, and weighed ( I ) . The volatile content is calculated from the weight loss. The shock heating effected by the above treatment is too extreme for certain types of samples and mechanical losses occur. These losses are manifested by “sparking” of the ejected particles in the hot portion of the furnace
Table 1.
-1
G
-E
Figure 1. A. 6. C.
D.
E. F. G. H. J. K.
Automatic volatile-matter unit
Preheat timer (Dimco-Gray Type 165) Heat timer Carriage-drive motor, 28 r.p.m. (Brown Synchronous, Type 7 7 3 1 1) Manual spring-loaded switch for carriage motor Screw-drive motor (Brawn Synchronous, Type 7 7 3 1 1) geared to a 4 to 1 ratio Screw drive, 0.5-inch diameter with a 1 3 pitch Stirrup support Crucible stirrups Hoskinr-Fieldner furnaces Pyrometers
immediately above the crucibles; in extreme cases ash deposits are visible on the lid of the crucible. Mechanical losses can he expected with materials that do not agglomerate or cake when heated and that evolve sufficient gas to carry some of the solid particles phj-sically from the crucible. Such materials are subbituminous coal, lignite, peat, anthracites, semianthracites, chars, and certain cokes (4). K i t h these materials the standard procedure has h e m modified by designating J. preliminary gradual heating of not less than 5 nor more than 10 minutes to reach a temperature of 950" C. This preliminary heating is done by the gradual lowering of the crucible into the furnace a t such a rate t h a t sparking does not occur. After this preliminary heating the crucible is lowered into its regular position in the furnace and heated for 6 minutes a t 950" C. (1). Volatile matter determination, as outlined in the ASTM methods, is dependent on operator technique and observation, and results not only varied between different operators but were often erratic \Tith the same operator making successive determinations. This was particularly true with materials requiring the modified procedure. Erratic results were probably due to lack of control of the heating rate. During the preliminary heating period the gradual temperature increase is effected by lowering the crucible manually into the hot zone. Conceivably, heating rates between successive runs could be different, re-
sulting in different values even if niechanical losses were avoided. GENERAL DESCRIPTION
OF
UNIT
To standardize the heating rate and to minimize human error, a mechanical lowering device was designed. The apparatus (Figure 1) consists of a motordriven screw drive for lowering the crucible a t a uniform rate into the hot zone. This drive is activated by a timer t h a t permits a n initial heating period a t the top of the furnace prior to the gradual lowering. After this preliminary heating period-which can be preset for any desired time interwlthe mechanical drive carries the crucible a t a uniform speed from the top of the furnace into the hot zone. At the end of the lowering cycle a second timer holds the crucible for a 6-minute period in the hot zone, then activates the return mechanism and the crucible is automatically carried up and out of the furnace, completing the cycle. The apparatus is designed to serve two volatile furnaces simultaneously, permitting duplicate runs. The entire operation is completely automatic; an alarm notifies the operator that the crucibles are out of the furnaces. OPERATING PROCEDURE
The procedure used depends on whether the material can be run according to the standard ASThl designation or requires the modified method. Standard Method. A 1-gram portion of the sample is veighed into
Comparison of Manual and Machine Operations
Volatile Matter, % Manual Machine operation operation High-Volatile Bituminous Coal4 38.68 38.60 39.22 38.54 38.50 38.60 38.28 38.70 Average 38.68 38.61 Probable error 0.27 0.04 ASTM permissible 0.5 0.5 difference ( 2 ) High Temperature Char" 2.99 2.60 2.65 2.60 2.45 2.54 2.62 2.58 Average 2.68 2.38 Probable error 0.16 0 02 ASTM permissible 02 0.2 difference ( 2 ) Low Temperature Chaf 18.32 18.17 G i .32 i7.80 18.26 18.00 18.33 17.76 ilverage 18.56 17.93 Probable error 0.34 0.11 ASTM permissible 0.5 0 5 difference ( 8 ) a Standard ASTM method. ASTPtl modified method.
each of tn-o tared volatile crucibles of platinum, and properly covered with the crucible cap. T h e crucibles are positioned in the stirrups, the positioning block is moved t o the bottom of the screw drive, and the heat timer is set for 7 minutes. Then, by means of the carriage lowering switch, the crucibles are carried immediately into the hot zone. The crucibles remain in the furnace until the end of the 7-minute period, when the drive motor is automatically activated and carries the crucibles to the top of the furnace. The crucibles are removed, cooled, and weighed. Modified Treatment. The samale is weighed and placed in the s t i r r u s . However, the positioning block is now moved to its top position on the drive screw, and the preheat timer is set. Experience has shon n that a 2-minute period a t the top of the furnace is ideal for most samples. The heat timer is then set for a 6-minute interval. Khen both timers are set. the carriage lowering switch is activated, lowering the entire unit. This positions the volatile crucibles approximately 0.5 inch9 into the furnaces, \\-here they are held for the preheat period. After this interval, the drive screw is automatically activated, which lowers the crucibles a t a gentle, uniform rate into the hot zone (4.5 minutes are required). The unit holds the crucibles in the hot zone for the required 6 minutes and then activates the drive motor, which returns the crucibles t o the top of the furnace. VOL. 30, NO. 3, MARCH 1958
0
403
COMPARISON OF RESULTS
The average results (Table I) obtained by manual and machine operation compare favorably, but the precision as shown by the probable error favors machine operation. Although the difference between the average results for a low temperature char is slightly larger than permitted by ASTM methods, the lomer value by machine operation indicatrs less possibility of mechanical losses. LOW TEMPERATURE CHAR
Pittsburgh Consolidation Coal Co. has devoted a considerable amount of research to low temperature carbonization. The result has been a heavy demand on the analytical laboratory
for volatile matter determinations on chars both for control operations and for material balance data. The automatic unit described was developed t o reduce errors, because as chars are nonagglomerating they are highly susceptible to sparking and are exceedingly difficult to run (6). DISCUSSION
While this unit was designed specifically for volatile matter determinations on coal and char as outlined by the American Society for Testing Materials, it has sufficient flexibility t o warrant its use for other operations requiring controlled time and temperature measurements. The unit has been used t o determine carbon residue on tars and
pitches. On several occasions the automatic unit has been used to make laboratory studies designed t o simulate specific carbonization conditions. LITERATURE CITED
(1) Am. SOC.Testing Materials, “ASTM Standards on Coal and Coke,” D271-48, 17-19 (1954).
(21 Ibid.. D. 36.
Invest. 3168, 1-2 (1932). (5) Selvig, W. A, Ibid., 3739 (1943). RECEIVED for review September 10, 1956. Accepted October 24, 1957. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1966.
Determination of Zinc and Separation from Ashed Biological Material J. A.
STEWART and J. C. BARTLET
Laboratories o f the Food and Drug Directorafe, Department of National Health and Welfare, Ottawa, Canada
b A method utilizing 4-chlororesorcinol is proposed for the colorimetric determination of zinc. The zinc-4-chlororesorcinol reaction obeys Beer’s law over the range of 0.1 to 5 p.p.m. o f zinc. Interference from cations is comparable to that with other reagents currently used. Use of a single reagent, sodium diethyldithiocarbamate, simplifies separation of zinc from other cations in the ash of biological material. Zinc and other cations which form diethyldithiocarbamates are extracted from buffered aqueous solution at pH 8.5 into chloroform. The zinc i s re-extracted with aqueous 0.1 6M hydrochloric acid, and determined colorimetrically with 4-chlororesorcinol or Zincon. With 4-chloresorcinol and standard zinc solution, the average recovery at the 15-7 level is loo%, and at the 50-7 level, 97%; the coefficients of variation are =k 1.4 and 12.2%, respectively. The mean recovery of zinc added to ash from agar-agar i s 95.470. Factors leading to variable blanks were investigated and means of reducing blank variation devised.
I
THE PRESEXCE of ammonium hydroxide, resorcinol reacts with zinc to produce a n indicator which is blue in alkaline and red in acid solution (4, 6). This reaction is the basis of a quantitative method for the coloripi
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ANALYTICAL CHEMISTRY
metric determination of zinc (11, 14, and has been used for the estimation of zinc in milk (18). Resorcinol also reacts with cadmium, calcium, copper, cobalt, manganese, and nickel (14)-no more cations than reported for dithizone (17) and a new reagent, Zincon (Z-carboxy-2’-hydroxy5’-sulfoformazylbenaene) (16). Because of the lack of specific reactions for the microdetermination of zinc, the nature of the resorcinol-ammonium hydroxide-zinc system rvas investigated. The colored dye from the reaction was isolated, and analyzed by infrared spectroscopy. The wave lengths of the absorption bands indicated that the dye contained benzene rings substituted in the meta positions. I n view of this, it was decided to examine the possibility of using other substituted phenols as a reagent for zinc in place of resorcinol. Particular attention mas paid to phenols with two hydroxy groups meta to each other. EXPERIMENTAL
A number of hydroxyaryl compounds were investigated t o establish their reactivity toward zinc in the presence of ammonia. Monohydroxy- and o-dihydroxybenzene compounds, and hydroxynaphthalene compounds reacted very slowly or not a t all. Mono-substituted resorcinols with the meta position relative t o each hydroxyl group occupied, such as orcinol and phloro-
glucinol, were nonreactive; those with the meta position unoccupied gave colored reaction products. These reactiye m-dihydroxylaryl compounds are listed in Table I, in order of decreasing rate of reactivity, with the absorbance data for the dye produced in the presence of zinc and aqueous ammonia. The compounds considered most promising as analytical reagents for zinc were 4chlororesorcinol resorcinol, 4-bromoresorcinol, 2,4-dihydroxyacetophenone, 2,4-dihydroxybenzaldehyde, and 2,4-dihydroxybenzoic acid, because in each instance the absorbance peaks of the blank and the test solution occur at different wave lengths. Bey and Faillebin (4) discovered that the reaction of resorcinol with certain cations in the presence of ammonium hydroxide required oxygen. I n the present investigation the effect of oxygen absorption from the atmosphere was controlled by use of reaction vessels of uniform shape containing a fixed volume of solution. S o attempt was made to prevent loss of ammonia from the reaction, because changes in ammonium hydroside concentration within defined limits do not affect the reaction. COMPARISON OF 4-CHLORORESORCINOL, 4-BROMORESORCINOL, AND RESORCINOL
The t h e e n i x t reactive compounds reported in Table I-resorcinol, 4bromoresorcinol. and khlororesorcinol --nere compared, to determine the
