Spectrophotometric Determination of Aluminum with Eriochromecyanine W. E. THRUN Valparaiso University, Valparaiso, Ind. Composite reagent, prepared by mixing 3.volumes of dye solution, 2 of the buffer, and 1 of the gum solution. Upon standing, the red color becomes lighter, but no effects upon the results were noted. Uniform Pvrex test tubes. of 25-1111. caDacitv. calibrated a t 15 . and 20~ml. Ostmld pipets to deliver desired volumes of standard sample or solutions. Coleman universal model 11spectrophotometer, with matrhed, round cuvettes of 16-mm. inside diameter.
has not been much used in ERIOCHROMECYANINE this . country as a reagent forR aluminum because it has not been available, nor have papers on its use been published in thib country. Its advantages over the most commonly used reagent for aluminum, aurintricarboxylic acid, notably a lower sensitivity to ferric ( 3 )and phosphate ions, made it desirable to determine the conditions under which it can be used for aluminum determinations with an electrospectrophotometer. Eegrine ( 3 ) first suggested this dye as a reagent for aluminum. Other papers on its use were published by Alten et ul. ( 1 , 21, Xfillncr (.5),and Richter (6, 7'). PREPARATION OF ERIOCHROiMECYANINE
The dye was prepared according to U. S. Patent 877,052 (1908). In a 500-ml. round-bottomed, short-necked Pyrex flask, 42 g r a m of Eastman T-3543 50% sodium salt of o-sulfobenzaldehyde were dissolved in 200 grams of 50% sulfuric acid. Then 31 g r a m of Eastman T-838 cresotinic acid were stirred in. The flask was fitted with an air condenser and a thermometer, immersed in an oil bath, and heated to keep the mass a t 120" to 125" C. for 12 hours. The cooled mass was filtered through asbestos fiber on a Biichner funnel. The leuco base was washed from the filter with a minimum of water into a beaker. Enough sodium chloride (about 2 grams) was added to begin precipitation. The precipitate was stirred thoroughly, especially against the walls of the beaker. A black stickv mass collected on the stirring rod and the walls. The solution was decanted and the remainder of the leuco base salted out, filtered off, and allowed to dry. The leuco base was oxidized by nitrosyl sulfuric acid, prepared by adding slowlv 1.7 grams of sodium nitrite to 31.7 grams of concentrated sulfuric acid and cooling to 20 O C. Ten grams of the leuco base were added t o the acid slowly while the temperature was kept to 20' or lower. The melt was allowed to stand 4 hours to complete oxidation. Three milliliters of water were added slowly with stirring. The dye was filtered off on asbestos and dissolved in a minimum of water. Some of the dark substance was again removed by fractional salting out. The dye solution was then shaken for a few minutes with 3 grams of activated black (Darco), filtered, and tested for the dark substance. The test was performed by adding a few drops of the solution to 12 ml. of water and 3 ml. of the p H 5.4 buffer described below, and heating. When the color became a clear amber (not suggesting licorice) no further treatments with smaller amounts of Darco were given. The remainder of the dye was then salted out, filtered off,.washed with very little water, and dried in a desiccator. The yield was about 4 grams. The ash content of the product was 36.0%. The trisodium salt of the dye was calculated to have 37.2y0 ash as sodium sulfate plus sodium carbonate. The treatment with activated black removed a variety of dye, also mentioned by Millner (6),which gave a red aluminum lake without a violet tinge. An impure eriochromecyanine preparation, obtainable from the Hartmann-Leddon Co. of Philadelphia, yields 70% ash and contains some aluminum lake and the black substance. To prepare a solution which is equivalent to a 0.3% solution of the pure sodium salt of the dye, dissolve 0.8 gram of it in 100 ml. of water, add 8 drops of concentrated ammonia, 4 grams of powdered silica gel No. 8595-12, obtainable from the Davison Chemical Corp., Baltimore, and 1.5 grams of Darco. Shake moderately for 5 minutes, filter, and keep in a Pyrex vessel. REAGENTS AND APPARATUS
Aqueous 0.300j0, eriochromecyanine solution, in a Pyrex vessel. Standard solution of aluminum chloride hexahydrate containing 0.010 mg. of aluminum per ml. Gum arabic solution, prepared by dissolving 0.1 gram of powdered gum and 0.5 gram of ammonium benzoate in 100 ml. of water. Buffer solution, prepared by dissolving 25 grams of ammonium acetate and 0.5 gram of ammonium benzoate in 50 ml. of water, adding 2 ml. of glacial acetic acid, and adjusting the solution with acetic acid or ammonia so that 2 ml. of it plus 1 ml. of the gum solution diluted to 20 ml. have a pH of 5.4.
I
.
L_
PROCEnCRE
Pipet an aliquot of 10 ml. or less of the sample aoiution containing 0.005 to 0.07 mg. of aluminum into a calibrated test tube To neutralize the solution add 10% ammonium carbonate solution drop by drop until no more carbon dioxide is evolved. Pipet 5 ml. of the composite reagent into the tube and make up with water to the 15-ml. mark. Mix and heat in water bath for 10 minutes a t 70" C., taking the time from the moment water in a similar tube shows the desired temperature on the immersed thermometer. Cool in water to room temperature, make up to the 20-ml. mark with water, and mix. After 1 hour, determine the per cent of transmittance a t a wave length of 600 mu relative t o that of xater. Obtain the weight of the aluminum in the aliquot from a standard curve prepared by plotting the weight of the aluminum against the logarithm of the per cent transmittance. DISCUSSION
Gpon heating, a blank changes color from red to amber, and the lake solutions turn to a brown-red. The cooled blank retains its color, but the lake solutions turn to a red, violet-red, or violet with increasing amounts of aluminum. The standard curve is a straight line Rhen the amounts of aluminum are from 0.01 to 0.07 mg. Below 0.01 mg. of aluminum the transmittance is too high, possibly because small amounts of the lake stick to the walls of the test tube in which it was developed. Above 0.075 mg. of aluminum the transmittance is also too high, probably because the molecular ratio of dye to aluminum is not high enough. It is suggested that a neiy standard curve be prepared for each new supply of the dye until a source of constant purity is established. The per cent transmittance of the lake was measured on two occasions with different solutions and using 0.02, 0.04, and 0.05 mg. of aluminum 10 minutes after they had been made up to volume and again 50 minutes later. An average increase in per cent transmittance reading of 1.65, 1.60, and 1.57 occurred. So to measure the per cent transmittance of solutions within the above range of aluminum content after 10 minutes, 1.6 should be added to the per cent reading, using the same standard curve obtained after 1 hour. After 30 minutes 0.45 should be added to the reading. After the six lake solutions had stood 90 minutes the per cent transmittance readings increased less than 0.1% as compared with those taken after 1 hour. The wave length setting a t 600 mp gives a desirable slope to the curve. Below this wave length the curve becomes steeper, lowering the range. Above that setting the curve becomes too flat, thus making the ratio of change in transmittance to the amount of aluminum too small. The ammonium acetate is preferred to a sodium acetate buffer because the effect of the magnesium ion is less. At high pH, the effect of ferric ions is greater. Richter (6) prefers a pH of 3.8 for lake development because a t room temperature the color intensity becomes constant in 4 hours, or in 1 hour if the solution is first brought to boiling. The p H of 3.8 has the disadvantage that the blank remains much more deeply colored, and this affects the linearity of the curve. 1117
ANALYTICAL CHEMISTRY
1118 INTERFERENCES
If the above procedure is used, the phosphate ion does not give low results when present in amounts less than 29 times the weight of the aluminum. The chromate ion does not interfere. Silicate and fluoride ions should be a t a minimum. Manganous, zinc, and nickel ions do not affect the results. Ferric ions may give positive errors when present in amounts greater than 0.05 mg. Chromic ions give large positive errors. Magnesium ions give small positive errors, and should not be present in an amount greater than 0.05 mg. Copper, reported previously (4) along with titanium (IV) and zirconium as giving similar reactions, doeq not give positive errors unless more than 0.5 mg. is prwrnt. PRECISION
Duplicate results obtained a t different times and with vanoub solutions, with aluminum aliquots running from 0.01 to 0.07
mg., showed average negative deviation from the curve of 1.64% and average positive deviation of 1.48% of the amount of aluminum present. Maximum deviation was -3.07, with 0.01 mg. of aluminum. LITERATURE CITED
Alten, F., Wandrowski, B., and Hille, E., 2. angew. Chem., 48, 273-5 (1935).
Alten, F., Weiland, W., and Knippenberg, E., Z . anal. Chem., 96, 91-8 (1934).
Eegriwe, E., Ibid., 76, 43843 (1929). International Committee on New Analytical Reactions and Heagents of Union Internationale de Chimie, Tables of Keagents for Inorganic Analysis, First Report, p. 117, Leipzig, .ikademische Verlagsgesellschaft,1938. Millner, Theodor, 2. anal. Chem., 113,83(1938). Richter, F.,Ibid., 126, 438-43 (1944). Ibid., 127, 113-39 (1944). RECEIVED .4ugust 1, 1946.
Determination of the Insect Repellent, Dimalone JEROME GOLDENSON AND SAMUEL SASS Chemical Corps, Technical Command, Army Chemical Center, Md. S COSKECTIOS \vith \\\orE; u11 the dimethyl ester of c~s-3,6-
I endomethylene- A'-tetrahydrophthalic acid (6),an efficient insect repellent known also as Dimalone, it became necessary to
devise methods of analysis suitable for various development operations and applicable to clothing impregnated with the compound. A choice of methods is desirable during development stages of work when fixatives and other materials are used which may interfere in one method but not in another. The methods described in this paper, involving determination of methoxyl groups, bromination of the double bond in the compound, saponification, and colorimetric estimation of the methyl alcohol formed by treating the compound with alkali, were found satisfactory for determination of the compound, which has the following structure: CH
Reagents for Saponification Method. Alcoholic potassium hydroxide solution, 0.1 N. Sulfuric acid solution, 0.1 N . Phenolphthalein indicator solution. Reagents for Bromination Method. Carbon tetrachloride, C.P. Hydrochloric acid, C.P. concentrated. Potassium bromatepotassium bromide solution of 3.5 grams of C.P. potassium bromate and 13.0 grams of C.P. potassium bromide, made up to 1 liter with water. Reagents for Colorimetric Method. Potassium permanganate solution prepared by dissolving 3 grams of C.P. potassium permanganate and 15 ml. of C.P. phosphoric acid 85%, in water to make 100 ml. oxalic-sulfuric acid solution prepared by dissolving 5 grams of oxalic acid in 100 ml. of 1 to 1 sulfuric acid solution. Schiff's reagent, prepared as follows: Dissolve 0.2 gram of basic fuchsin in 120ml. of hot water, cool, and add 2 grams of anhydrous sodium sulfite dissolved in 20 ml. of water. Add 2.0 ml. of concentrated hydrochloric acid, dilute to 200 ml., and place in a refrigerator a t least 24 hours before using. Store in an amber bottle.
BUBBLE COUNITER APPARATUS
Methoxyl apparatus, essentially the same as used by Clark (3) with an absorber similar to one described by Niederl ( 6 ) and used in the determination of halogens (Figure 1). This apparatus has also been used by Alexander Sadle at the Army Chemical Center for the determination of dimethyl phthalate (7). Klett-Summerson photoelectric colorimeter with green filter KO.55 (maximum transmittance 520 to 600 millimicrons) and standardized colorimeter tubes.
I2MM.DIA
REAGENTS
Dimalone, obtained from Sowa Chemical Co., 30.5 East 46th St., New York 17, K. Y., and purified by distillation; boiling point a t 9 mm. 130-131.5", n2z 1.4853.; Reagents for Methosyl Method. Hydriodic acid, Merck grade for methoxyl determination (when reagent darkens, shake with small amount of mercury to pale yellow color). Bromine, C.P. or redistilled. Sodium acetate-acetic acid solution made by dissolving 10 grams of c . ~ sodium . acetate trihydrate in 100 ml. of glacial acetic acid. Sodium acetate solution made by dissolving 10 grams of C.P. anhydrous sodium acetate in 90 ml. of distilled water. Potassium iodide, C.P. Formic acid, C.P. Sodium thiosulfate solution, 0.1 X. Starch indicator solution. Carbon dioxide from cylinder. Cadmium sulfate solution made by dissolving 15 grams of c . ~anhydrous . cadmium sulfate in 100 ml. of distilled water. Red phosphorus, powdered. The hydriodic acid may also be prepared or purified as described by Clark ( 2 ) .
ABSORBER SPIRAL 12 TURNS QF4MM.DIA ROD
I BMMDIA.
60MM.DIAM. REACTION
FLASK2 Figure 1. Diagram of Apparatus
