V O L U M E 2 5 , NO. 10, O C T O B E R 1 9 5 3
1557
to construct. However, contact of the eluent with a mercury surface is often undesirable. Readjustment of the mercury contart was found to be necessary with 5-ml. fractions when the eluent density changed. With larger fractions (20 ml. or greater) the mercury differential should be such that one adjustment will tw sufficient unless the density variation is very large. The pipet sxitch of Gibson (S), activated by a change in capacitance, is a more universally adaptable although somewhat more expensive form of a pipet switch. This capacity pipet switch o as redesigned to eliminate evaporation by the addition of glass joints, side arm, and suction flask in the same manner as the pipet first described (Figure 2). For greater sensitivity, a plate of copper or platinum foil instead of the single wire (3) was use 1 for the inside electrode. The outside plate n’as of copper foil. The resulting increased surface area of the electrode and the improved circuit increased the sensitivity to the extent
that liquids as nonpolar as chloroform will activate the switch. Any increase of polarity thereafter will activate the switch a t a lower liquid level. The improved, more sensitive circuit developed for this pipet switch is shown in Figure 3. The components cost about $40. Similar capacity controllers are sold commercially for about $200. LITERATURE CITED
(1) Briniley, R. C., and Snow, A., J . Sci. Instr. and Phys. zn Ind., 26, 73 (1949). (2) Donaldson, K. U., Tulane, V. J., and Marshall, L. &I., AKAI.. CHEM.,24, 185 (1952). ( 3 ) Gibson, A. R., Chemistry & Industry, 1951, 185. (4) Grant, R. X.,and Stitch, S. R., Ibid., 1951, 230. (5) Mader, Charles, and l l a d e r , George, Jr., ANAL.CHEM.,25, 1423 (1953). (6) Stein, W. H., and Moore, S., J . BioE. Chem., 176, 337 (1948).
RECEIVED May
1 1 , 1953.
Accepted June 15, 1953.
Electrolytic Determination of Copper with an Isolated Anode DUNCAN G . FOSTER Swarthmore College, Swarthmore, Pa.
IN
THE electrolysis of copper by controlled cathode potential methods, a frequent difficultyarisesout of thereoxidation of the cuprous ion a t the anode, substantially slowing the procedure. Oxidation of deposited copper from circulation of liberated oxygen also occurs, causing results by this method to run 0.4 to 0.5% high. In 1947 Diehl(1) reported a series of experiments in which he attempted to obviate these difficulties by placing the anode inside a porous cup. His results were promising, but he was unable to obtain adequate stirring with the motor-and-propellor type stirrer which he used, and abandoned the method as calling for apparatus too complicated to be worth while. The writer has succeeded in obtaining satisfactory results with this method by the simple expedient of using a magnetic stirrer of the type now widely sold [as was also done by Lingane (311, and by the considerable simplification of the apparatus which this allowed. The apparatus is shown diagrammatically in Figure 1, and details are fully described in t h e legend a t t a c h e d . The potentiostat u s e d h a s been described elsewhere (a).
I
Z Y
A . 26-mm. o.d., borosilicate glass tubing, 30 c m . long B. Lucite cell cover C. 250-ml. electrolytic beaker D . Rubber collars E. Alundum thimble: Norton Co., R.A. 84, m e d i u m porosity, cut to length F.
of anode Platinum gauze cathode, 35 X 50 mm.
G. Platinum gauze anode. 15 X 50 mm. H . Magnetic stirring bar. 1 i n c h I . 250-ml. leveling bulb J . Saturated eafomel electrode K . 4-mm. diameter soft glass t u b e with anode sealed into lower end
Table 1. Duplicate Analyses of Brasses Samplea Pb content, % Cu found, %
Mean Manufacturer’s ralue
1 2 3 4 5 0.90 0.94 5.32 5.88 7.83 6 0 . 0 7 70.85 78.01 7 6 . 3 6 82.14 59.96 7 0 . 8 2 7 8 . 0 2 76.43 82.14 60.02 70.84 78.02 76.40 82.14
6 11.10 80.96 81.12 81.00
6 0 . 0 0 7 0 . 7 8 78.01
81.00 6 9 . 0 4
7 6 . 3 9 82.16
7 19.36 69.18 69.22 69.20
PROCEDURE
A stock solution of an anolyte was made up, consisting of 135 ml. of concentrated hydrochloric acid and 14 grams of hydrazine dihydrochloride per liter. The brass samples were dissolved in 15 ml. of 2 t o 1 hydrochloric acid with the aid of 5 ml. of 30% hydrogen peroxide (4). After boiling out the excess hydrogen peroxide, the solution was cooled, and 1 or 2 grams of urea were added. Anolyte was introduced into the leveling bulb, the weighed cathode was clamped in place, and the level of liquid in the vertical tube adjusted to approximately 25 cm. above the top of the cathode. The beaker containing the solution of brass was then set in place over the electrodes and supported by the magnetic stirring motor. The solution was diluted until its level was about ‘ / z inch below the top of the cathode. With the control set a t -0.22 volt us. the saturated calomel electrode (S.C.E.), the stirrer was started, and the current was raised until the controls operated. This took place a t a current of from 4 to 8 amp., depending on the concentration of salts in the solution. The instrument was left to operate automatically until the current had dropped t o 2 amperes, which took from 5 to 8 minutes. During this time there mas very little deposition of copper, and the color of the solution gradually disappeared. The “up” control was then turned off, and the control potential was set a t -0.30 volt us. S.C.E. The instrument was left to reach this value of its own accord, after which the “up” control was turned on again and the electrolysis continued until the current had fallen t o below 10 ma. and had become essentially constant. RESULTS
Table I shows a series of duplicate determinations of copper in brasses varying in lead content from less than 1% to nearly 20%. Half-gram samples mere taken. Results are both precise and accurate within about 2 parts per thousand or better, for the samples studied. Oxidation appears to be negligible as shown by the light pink color of all
ANALYTICAL CHEMISTRY
1558
deposits obtained. Separation from lead is satisfactory if the control potential is not above -0.30 volt us. S.C.E. The method is distinctly more rapid than the conventional one. total time for reduction and deposition of weights of copper from about 175 to about 800 mg. being from 20 to 30 minutes. This is to be compared with about 45 minutes for the conventional method plus 15 or 20 minutes additional time for reduction with hydrazine or hydroxylamine hydrochlorides. The writer’s students have performed a number of satisfactory analyses on brass samples as large as 1 gram, which are not reported here. A minor disadvantage is the dilution of the solution with the anolyte. This amounts to 50 m]., a t most, and the author has not found it serious.
One rough determination of current efficiency was made by noting the current a t intervals, plotting this against timc. and integrating graphically. A value of 96% was obtained. LITERATURE CITED
( I ) Diehl, H., “Electrochemical Analysis with Graded Cathode Potential Control,” pp. 27-30, Columbus, Ohio, The G. Frederick Smith Chemical Co., 1948. (2) Foster, D. G., J . Chem. Edzic., 28, 626 (1951). (3) Lingane, J. J., Anal. Chim. Actu, 2, 554 (1948). (4) Willard, H. H., quoted by Dich!, H., “Electrocheniiral Analysis with Graded Cathode Potentia! Control,” p. 39, Columhus, Ohio, The G. Frederick Smith C‘hemica! Co., 1948. RECEIVED for Icrirw 11arch 20. 3453.
Arcented June 11. 1953.
Distillation of Micro Quantities of Iodine Application t o Determination of Protein-Bound Iodine in Bovine Blood S e r u m GORDON H. ELLIS’ AND GORDON D. DUh-CAK* U . S. Plant, Soil, and iyutrition Laboratory, Bureau of Plant Industry, Soils, and .4gricultural Engineering, U. S . Department of Agriculture, Ithaca, S. I-. HE
catalytic effect of iodine on the rate of reaction between
Tcerium( IV) and arsenic( IT) first described by Sandell and
Kolthoff ( 8 ) and adapted to a colorimetric procedure by Chaney (3) has proved very satisfactory for the determination of the small quantities of iodine found in blood serum. -4fter osidation of the organic matter and of the iodine to iodate with a mixture of sulfuric and chromic acids, the iodine is distilled after the addition of a suitable reducing agent. I n this distillation much time can be saved if the volume of distillate can be kept low, and Chaney (3) has described a widely adopted procedure by whirh this may be accomplished. The apparatus, however, is fairly comples, and gives somewhat erratic recoveries approximating 85%. The borosilicate glass distillation apparatus illustrated in Figure 1 is simple in design, and with it more consistent recoveries approximating 96% are obtained (see Table I). Both aeration and distillation are utilized to effect rapid transfer of the iodine to the distillate, thus keeping the volume of distillate small. The application of this still to the determination of the proteinbound iodine in bovine serum is described below. The protein precipitant of Somogyi (9) is used to separate the protein-bound iodine which consists largely if not completely of thyroxine iodine ( I d ) . This method is widely used (1, 7 , 10, 11). The widely used chromate oxidation procedure ( 3 , 6 )is modified by using a stream of air to aid in defining the point a t which heating should be stopped. I n the colorimetric determination, chloride ions are used to increase the sensitivity (1,d , 4 , 5,8).
Sodium Arsenite. For a 0.1 ;V solution, dissolve 0.2166 gram of sodium arsenite in 50 ml. of solution. Sodium Chloride. Make solution containing 20 grams per liter. Sodium Hydroxide. Use a 0.75 N solution and a 1% solution. Concentrated Sulfuric Acid. Add 10 ml. of concentrated hydrochloric acid per liter of C.P. sulfuric acid and boil for 30 minutes. 70% Sulfuric Acid (by Weight). Slowly add 470 ml. of sulfuric acid (sp. gr., 1.84) to 270 ml. of water. Zinc Sulfate. Dissolve 12.5 grams of zinc sulfate heptahydrate in 125 ml. of 0.25 sulfuric acid and make up t o a volume of 1 liter. Iodine Standard. Dissolve 0.032i gram of C.P. potassium iodide (dried overnight a t 135’ C.) in water, and make up to 250 ml.; dilute 1 t o 1000 for working standard of 0 . 1 iodine ~ per milliliter. PROCEDURE
Precipitation of Protein-Bound Iodine. ridd 32 ml. of thr zinc sulfate solution to 1 ml. of srrum in a 50-ml. centrifuge tube and
REAGENTS
Iodine-Free Water. Add 1 gram of sodium hydroxide to 3 liters of distilled water and redistill in all-glass still. Arsenious Acid. Dissolve 2.636 grams of C.P. arsenious trioxide in a solution of 150 ml. of water and 13.4 ml. of sulfuric acid (sp. gr., 1.84) b y heating on a hot plate, cool, and make t o a volume of 200 ml. Ceric Ammonium Sulfate. Dissolve 12.65 grams of the C.P. salt in a hot solution of 125 ml. of water and 19.6 ml. sulfuric acid (sp. gr., 1.84),cool, and make t o a volume of 200 ml. Chromic Acid. Dissolve 300 grams of chromium trioxide in 300 ml. of water. (Grasselli’s chromium trioxide was found t o be low in iodine.) Phosphorus Acid. Boil Baker’s C.P. 50% phosphorus acid for 30 minutes, maintaining constant volume by adding water from time t o time. 1 Present
address, Wyeth Institute of Applied Bioahemistry, Philadelphia
30, Pa. Present address, Elgin State Hospital, Elgin, 111.
I25 ml
DlSTlLLlHQ FLASK
0.4 mm IDJ
Figure 1. Distillation Apparatus for Determination of Iodine
