V O L U M E 25, N O . 4, A P R I L 1 9 5 3
659
Table VIII.
Comparison of Copper Content in Plant Samoles as Determined h v Different Methods Method
USDA-A.O.A.C. oarbarnate Improved cs.rb&mBte BiQ"in0ii"e
Comer Content. P.P.M. Alfhifa Timothy Buckwheat flour 10.0 5.0 3.3-4.0 10.5 5.5 3.6 10.8
6.0
4.0
ACKNOWLEDGMENT
(3) Callan, T., and Henderson. J., AnaZy$t, 54, 65R;i (1929). (4) Cheng. K. L., Bray, R. H., and Kurte, L.T., ANAL.CHEW.,25, %A7 ~-""-,. 114Y\
(5:1 Holmes, R. S.. Soil SCi., 59, 77-90 (1945). (6) Hoate, J., Anal. Chim. Acta, 4,23-37 (1950). (7) LaCoste. R. J., Earing. M. H., and Wiberley, S. E.; ANAL. CHEX..23. 871-4 (1951). . ~, (8) Lagerwerff. J. V.. Landbouwkund. Tijhch., 62, 282-90 (1950). (9) Lundblad, X.,Svmberg, O., and Ekmitn, P., Plant and Soil,1, 27-302 (1949). (IO) Pribil, R., Chimia (Switz).4, 160-3 (1950). (11) Pribil, R.,Collection Czechoslou. C h m . Communs.. 14, 320-30
~....,.
ilQ4Qj
The authors are grateful to K. C. Beeson for supplying some sail and plant samples and to L. T. XurB and S. W. Melsted for their interest and encouragement.
Robinson, J . C., J. Biol. Chem.. 179,1103-9 (1949). (13) Sandell, E. B.,"Colorimetric Determination of Traces 01 Metals," 2nd ed., New York. Intersoienoe Publishers, 1950. (14) Sohwaruenbach, G.. Chimia (Szu~tr.), 3, 1-9 (1949). (15) Sedivec, V., and Vasak, V.. Co22ection Csechosloa. Chem. (12)
Communs., 15, 260-6 (1950).
LITERATURE CITED
(1) Beeson, E.C., and Gregory, R. L., J. Assoc. 080. Agr. Chemists. 33, 819-27 (1950). ( 2 ) Breokenridge, J. G., Lewis, R. W. J.. and Quick, L. A , , Can. J . Reseaych, 17,258-65 (1939).
(16) Steenbjerg. F., and Boken. E., Plant andSoil, 2, 195-221 (1950). (17) Vermaat, J. B., and van der Bie, J., Plant and Soil, 2, 257-82
(1950). X&CEIVED lor review July 31, 1952. Aecested N o w mber 10. 1952
Identification of Organic Acids by Circular Paper Chromatograph] J. W. AIRAN, 6. V. JOSHI, J. BARNABAS, AND R. W. P. MASTER Wilson College, Bombay 7, India
et 0.1. (9)have employed the method of Lugg and Overell (6) for the resolution of organic acids by paper chromatog-
UCH
mphy, and then have used several spraying materials to enable them t o differentiate acids which are somewhat difficult to resolve. This has involved elaborate preparation and consi&eterahle
time. The method described in the present communication makes use of circular paper chromatography, which is a modificai tion by Giri and Raa ( 4 ) of earlier methods developed by Brown ($1 and Rutter (6). This technique has been found, in this instance, to be more direct and less time-consuming.
MATERIALS AND REAGENTS
Paper. VVhatman filter .namr No. 1. disk. shrtppd, 24 cm. in diameter. Solvent. 1-Pentanol-5 M aqueous formic acid was preparetI according t o Rueh et al. (9). However. it was found t,hat even if the mixture W&B prepared lestI than three hours before use it was equally effecltive. Surav Rea gents. Bromophenol blue was p r e parid &cord ing to Lugg and Overell (6). Mercuroch:rome. 0.1% solut.ion. was made in n m t r a i -.--hol. 2lonl This latter reitgent was tried since Airan ( I ) had already mentioned i t 85 an indicator in acid-alkali titrations. APPARATUS
A circular glass tank, 30 em. in diameter, which could be covered airtight by means of a elass d a t e was used. Inside. d l around the aircuhferekce, there was a suDDort for the rimer disk, 2 cm. from the hattbm. A Petri-dkh, 1.5 em. high, with & capacity of nearly 10 ml., was placed in the center to hold the solvent. METHOD AND RESULTS
Acids Using Bmmophenol
_.
_.
________/
.-.,
acids
S, succinic; M, mirtursoftheea
At the center of the filter ~ a u e disk r a Zcm. radius circle was drawn, along the circumference of which eight equidibtant points were taken. Five PI. 'of 1% aqueous, solutions of authentic samples of tartaric, citric, malic, malonic, and succinic acids were separately spotted a t five of these points. At the remaining three points, 25 d. of a mixture of equal parts of these five acids were spotted. The spota were made suf-
ANALYTICAL CHEMISTRY wick to take up the solvent onto the paper. The paper was kept in the glass tank in 8 horiaontal plane, only the wick dipping into the solvent. The tank was immediately covered, and the chromatogram was allowed to develop. Within about 3 hours the solvent front had reached the edge of the disk. Then the chromatogram was taken out, air-dried foor a couple of hours, and sprayed with the bromophenol blue reagent; yellow bands developed against the blue background. This chromatogram was photographed using red filter (Figure 1).
It is evident that this procedure makes the identification of these organic acids comparatively easier. Finer bands could be obtained by employing B multiple development technique. When, instead of bromophenol blue, a 0.1% alcoholic solution of mercurochrome was used as a spray reagent, white bands developed against a delicate pink background. When this chromatagram was placed in ultraviolet light, the pink background gave a greenish-yellow fluorescence, and the white bands became violet in color, thus making the distinction between the bands and the background even more pronounced. A prolonged exposure (3.5 minutes) under ultraviolet light gave a photograph of this chromatogram which makes this elem (Figure 2). Figure 2.
Chromatogram of Organic Acids Using Mercurochrome
ficiently large t o enable the bands later to spread out lengthwise so that they would nearly meet the bands developing from adjacent SpotB. This aided the identifioation of the individual acids in the separated mixture. See Figure 1. These spots were air-dried, and through a slit made a t the center of the disk a small strip of paper was inserted t o serve as a
LlTERATURE CITED
(1) .4iran, 3. W., Natum, 160,88 (1947). (2) Brown, W. G.. Nalum, 143, 377 (1939). (3) Buoh, M. L., Montgomery, R., and Porter, W. L.. ANAL. C ~ E M .24, . 489 (1952). (4) Giri, K. V., and Rao. N. A. N., J . I d . Inat. Sci., 34.35 (1952). (5) Lugg, J. W. H., and Overell. B. T.,Austmlian .I. Sci. Res. Phus. Sci., 1.98 (1948). (6) Rutter, L., Nature, 161,435 (1948). REOBIVED
for
August 18, ish% hcoeDtsd NovomhPr17. 19s~.
Amperometric Organic Sulfur Procedure CHARLES L. RULFS AND AHTI A. MACKELA Department of Chemistry, University of Michigan, Ann Arbor, Mich. end point has been applied for the indirect A microdetermination of sulfur in organic compounds. A N AMPEROMETRIC
Carius sealed-tube digestion using lead nitrate a8 the precipitant is employed. The lead sulfate is dissolved, and the resulting solution of lead ion is titrated amperometrically with standard bichromate solution. Chlorine, bromine, and nitrogen do not interfere; iodine is the only common interference. The complete procedure as described requires slightly less working time than does the' gravimetrio method. The precision rand accuracy of the technique are approximately equal to those of the gravimetric method. The average precision is better than f0.5Y0 sulfur, and the methodical error does not exceed 0.1%. The technique could be modified very readily for use in conjnnction with catalytic combustion t o give a rapid procedure. A suitable titrimetric procedure for the microdetermination of sulfur in organic compounds has long been needed. Two a p proaohes t o this problem are in current use; both proceeding, in general, from some modification of Pregl's catalytic combustion procedure. In the first method the measurement depends upon neutralization, and the end points are clearly defined, but halogens interfere. In the alternative method the sulfate is titrated with barium ion using tetrahydroquinone indicator, and halogens do not interfere, but the end point is very difficult to d e h e . Heroic measures involving the use of comparison standards, colorimeters, and spectrophotometers have been successfully applied in obviating the latter difficulty, but the resulting procedures leave something to be desired in the way of simplicity.
Amperometry has been a spectacularly successful solution t o the problem of applying electrochemical end point indications to precipitation titrations. Unfortunately, amperometric sulfur determinations are complicated by a number of factors; viz., the sulfate ion itself is polarographically inactive; the barium ion is polarographically active only a t very negative potentials, making its use inconvenient; and lead ion, while polarographieally active, doe8 not behave in a reproducible fashion us. sulfate ion amperometrically (e). These difficulties may be avoided by an indirect procedure based upon precipitation of lead sulfate, dissolution of the lead sulfate in acetate buffer, and amperometric titration of the resulting solution of lead ion with standard bichromate solution t o form lead chromate, which gives reproducible results amperometrically ( 1 ), Speed was not an object in the present investigation, and a Carius sealed-tube digestion was employed ae the starting point for the determination. Those. concerned with speed should find the technique readily adaptable to rapid catalytic combustion procedures. EXPERIMENTAL
Equipment and Reagents. A four-place electrically heated Carius furnace (A. H. Thomas Co.) was used for the digestion. A Tork time switch was set to turn the furnace on during the night, and off again after a period of 2.5 hours. A Fisher Elecdropode and the conventional dropping mercury electrode assembly were employed foor the amperometric titration. A 100-ml. electrolytic beaker served as the titration vessel. This was fitted with a five-hole rubber stopper containing nitrogen inlet and exit
