ANALYTICAL CHEMISTRY
722 food blender, cutter, or chopper samples could be dealt lvith. and the refluxing procedure with solvents are unnecessary. LITERATURE CITED
Basu, N.K., Z. Vitaminjorsch., 6, 106 (1937). Beadle, B. W., and Zscheile, F. P., J . B i d . Chem., 144, 21 (1942). Booher, L. E., Hewston. E. R.1.. and Marsh, R. L., Food Research, 6, 493 (1941).
Boot,h,V. H., J . SOC.Chem. Ind., 64, 162 (1945). Carter, G. P., and Gillam, A. E., Biochem. J . , 33, 1325 (1939). Cooley, M . L., Christiansen, J . B., and Schroeder, C. H., ISD. ENG.CHEM., ANAL. ED.,17, 689 (1945). De, N. C., I n d i a n J . .\fed. Research, 24, 751 (1937). Deleano, N . T., and Dick, J.,Biochem. Z . , 259, 110 (1933). Ferguson, IT. S., Analyst, 60, 680 (1935). Ferguson, W.S.,and Bishop, G., IbicE., 61, 515 (1936). Fraps, G. S.,and Keminerer, A . 11.. J . Assoc. Official A g r . Chem., 22, 190 (1939).
Fraps, G. S., illeinke, IT. W.,and Kemmerer, A. R., Ibid., 24, 739 (1941).
Fremy, H. E., Compt. rend., 61, 188 (1865). Guggenheim, K., Biochem. J . , 38, 260 (1944). Hickman, K . C. D., Harris, P. L., and Woodride, M.R.. S a t w e , 150, 91 (1942).
Hicknian, K. C. D., Kale)-, M. W., and Harris, P. I,., J . B i d . Chem., 152, 321 (1944). Holmes, H. N., and Leicester, 11. M.,G. S.Patent 1,967,121 (1934).
Kernohan, G., Science, 90, 623 (1939). Lease, E. J., and -Mitchell, J. H., ISD. EXG.CHEM.,.4sa~.ED., 12, 337 (1940).
Mann, T. B., Analyst, 69, 34 (1944). Miller, E. S., J . Am. Chem. Soc., 57, 347 (1935). Mitchell, H. L., and Hague, S . M.,J . B i d . Chem., 163, 7 : 164, 543 (1946).
Moore, L. 9., ISD.ENG.CHEW.,AN.4L. ED.,12, 726 (1940). Ihid.,14, 707 (1942). *Moore,L. A,, and Ely, R., Ibid., 13, 600 (1941): hlorgal, P. W.,Petering, H. G., and Miller, E. J., I n d . Eng. Chem., 32,1407 (1940).
(27) AIo~toli,R. A., "Application of Absorption Spectra to the S t u d y of Vitamins, Hormones and Co-enzymes." pp. 61, 103, London. Adam Hilrar. 1942. ( 2 8 ) Murri, I., cited f r o m ' S u t r i t i o n Abstracts & Rets., 14, 644 (1945). (29) Nelson, E. Bf., J . Assoc. Ofieial Agr. Chem., 28, 544 (1945). (30) O'Connor, It. J.. Heinaelman, D. C., and Jefferson, M. E., Isn. ENG.CHEM.,As.\L. ED., 18, 557 (1946). (31) Pepkowits, L. P.. J . Bid. Chem., 149, 465 (1943). (32) Petering, H. G., hlorgal, P. W., and Miller, F.: J., I n d . E/zg. Chem., 33, 1298 (1941). (33) Petering, H. G., Wolman, W.,and Hibbard, IT., IND.ESG. CHEM.,A~TAI,. ED.,12, 148 (1940). (34) Peterson, R.J.,Ibid.. 13, 212 (1941). (35) Peterson, IT. J., Hughes, J. S.. and Freeman, H. F., Ibid., 9, 71 (1937). (36) Raniasarma, G. B., and Hakim, D. N.. Satztre, 149, 611 (1942). (37) Raniasarma, G. B., Hakim, D. N., and Iiao, S. D., Current Sci. ( I n d i a ) 12, 21 (1943). (38) Ranganathan, S.,Sundararajan. A . E., and Swaminathan, M., I n d i a n J . M e d . Research, 24, 689 (1937). (39) Rao, S.D., S a t u r e , 156, 234, 449 (1945). (40) Sherman, W. C., J . Xutrition, 22, 153 (1941). I (41) Silker, R. E., Schrenk, IT. G . , and King, H. H., I n d . E W . Chcm., 3 6 , 8 3 1 (1944). (42) Silker, It. E., Shrenk, W. G., and King, H. H., IND.ENG.CHEM., ANAL.ED.,16, 513 (1944). (43) Snyder, W. W., and Moore, L. A , , J . Dairy Sci., 23, 363 (1940). (44) Sreenivasan, A , , and T'aidya, R. M., J . Sci. I n d . Research, 6B, 69 (1947). (45) Tswett, M., Ber. bot. Ges., 24, 316 (1906). ASAL. ED.,15, (46) Wall, M .E., and Kelley, E. G., TND. ESG.CHEW., 18 (1943). (47) Wall, M. E., Kelley, E. G., and Williaman, J. J., I n d . Eng. Chem.. 36. 1057 11944). (48) Weier, E., Am. J . Botany, 31, 537 (1944). ESG. CHEM.,ANIL. ED.,18, 702 (1946). (49) Wilkes, J. B., IND. (50) Witnah, C. H., Peterson, W. J., Atkeson, F. W.,and Cave, H. W., J . A g r . Research, 58, 343 (1939). (51) Zechmeister, L., and Tuzson, P., Biochem. J . , 32, 1305 (1938). (52) Zscheile, F. P., and Whitmole, 11. A , .%N%L. CHEU.,19, 170 (1947). RECEWED April 28, 1947.
Colorimetric Determination of Copper with Carbon Disulfide and Diethanolamine A n Improved Dithiocarbamate Reagent W A K K E S C . WOELFEL, Continental Oil C o m p a n y , Ponca C i t y , OkIa.
.4reagent prepared from carbon disulfide and diethanolainine reacts with the cupric ion to form a brow nish-yellow salt of bis(2-hj drox?eth?1)dithiocarbamic acid. The reaction has been made the basis of a colorimetric method for the determination of copper. As the colored compound is watersoluble, the use of a stabilizing colloid or extraction with an organic sol5ent is unnecessarj. Of the
4
metals whose compounds are soluble under the conditions used, bismuth, chromium, cobalt, iron, mercurj, nickel, silter, and uranium interfere seriouslj , Procedures are described for eliminating the interference of appreciable amounts of bismuth, chromium, ferric iron, and uranium. Among the anions studied, onl? c: anide, dichromate, nitrite, and sulfite interfered appreciahlj.
LTHOUGH sodium diethj ldithiocarbamate has bcen used estemively for the colorimetric determination of copper, the rcxagent possesse~the disadvantage that it forms an insolublc coppel' salt anti rcquiws the use of gum arabic for stabilization of
mination ot copper. It is suggested that the trivial name, ruprethol, bc applied to the n e v chromogenic agent.
the colloidal suspension (6) or extraction with a suitable organic solwnt (5) before colorimetric comparison can hc) made. Geiger and Muller ( 4 ) have shown that the bis(2-h>-drosyethyl)dithiocarbamate of diethanolamine reacts with the rupric ion to form a brownish-yellow salt vihich is soluble in water. They prepared the reagent by dissolving carbon disulfide and dicthanolamine in alcohol. The present paper describes the application of this reagent in slightly modified form to the colorimetric deter-
Hydrochloric acid, 1.2 S and 8 S. Sitric acid, 1.2 *V and 8 S. Sodium Pyrophosphate Solution. Dissolve 30 grams of sodium pyrophosphate decahydrate, (Sa4P20i10H20) in water and dilute to 1 liter. Sodium acetate Solution. Dissolve 200 grams of sodium acetate trihydrate in water and dilute to 1 liter. Acetate Buffer solution, pH 5 . Dissolve 96 grams of sodium acetate trihydrate and 17 ml. of glacial acetic acid in water, and dilute to 1liter.
REAGENTS
V O L U M E 20, NO. 8, A U G U S T 1 9 4 8 Ammonium hydroside, 15 -\. Standard Copper Solution. Disi.olve 0.1000 gram of pure comer in 5 ml. of 8 S nitric acid. add 1 ml. of concentrated sulfur& acid, and fume to dryness. ' Dissolve the residue in water and dilute t o 1 liter; 1 ml. cont.ains 0.100 mg. of copper. Dilute 50 ml. of this solution to 1 lit,er; 1 nil. of the solution contains 0.005 nig. of copper. Diethanolammoniuni Bis(2 - hydrosyethgl)dit,hiocarbamatc (Cuprethol) Reagent,. Solution A. Dissolve 4.0 grams of dicthanolamine in 200 ml. of methanol. Solution B. Dissolve 1.00 ml. of carbon disulfide in 200 ml. of methanol. Prepare sufficient reagent for one day'P use by mising equal volumes of Solutions ii and B. Standard solutions of various cations and anion? containing either 1 or 10 mg. of t,he ion per ml. A411chemicals were reagent gradcl. S o difference in results was noted when diethanolamine, Eastniari Kodak Company S o . 1598, \vas replaced by a conimerciakgrade. APPARATUS
Ihaviorof higher coppel' concentrations was not stuclicd. The effect of pH on the color intc'nsit>-aiid stability is shown in Table I.
Each solution contained 0.100 mg. of copper, 2 nil. of 1.2 .Y riilric acid, sufficient sodium acetate solution t,o give the final pH &,*ired, and 1 ml. of cuprethol reageut, in a total volume of 100 ml. LIeasurements of pH werc made with a Precision-Shell dual titrometvr, on which the glass ulcctrodes w r e calibrated against a staiidard phthalate buffer. Photomr>tcr rradings were corrected for traces of copper in the reagents by running appropriate blank dt.1erminations. .it pH 2 the color tended t o increasc gradually with timc, whereas at pH 4 the color decreased under the same conditions. The two effects appeared to be balanccd at pH 3, resulting in a coilstant color reading. -It pfI 5 the color was coilstant for at least 90 minutes, and was not changrd by increasing the pH t o 6.
723 Essentially the same results were obtained when hydrochloric acid was used instead of nitric acid. Effect of Cations. I t is often desirable to determine copper without preliminary removal of small amounts of iron which niay be present. Cuprethol, like sodium diethyldithiocarbamate, gives a dark brown color n-ith ferric salts. In the presence of sufficient pyrophosphate the brown color may appear on adding cuprethol, but fades out completely in 5 t o 10 minutes, and the copper determination can be made thereafter ivithout interferencc, from iron. Although 5 ml. of the pyrophosphate solution were found t o eliminate the interference of iron in concentrations up to 100 p.p.m., certain other cations may be precipitated. By using only 1 ml. of pyrophosphate solution, interference of 20 p.p.ni. of iron could be prevented, and a t the same time appreciable amounts of other metal ions could be tolerated. Large amounts of iron must he removed by careful precipitation with ammonia or by cstraction with isopropyl ether ( 2 ) . The cstent of interference for various cations in the presence of 1 p.p.m. of copper was studied by two procedures.
METHODI. h measured volume of solution containing the ion in question was added t o 20 nil. of the copper sulfate solution containing 0.005 mg. of copper per ml., followed by the addition of 2 ml. of 1.2 - \ nitric or hydrochloric acid. The solution was diluted t o approsimately 50 nil. with water, 1 ml. of sodium pyrophosphate solution was added, and the solution was brought to a pH of approximately 5 with sodium acetate solution. One inilliliter of cuprettiol reagent was added, the solution was diluted t,o 100 nil., and t'he dial readings were obtained a t intervals of 10, 30, and 60 minutes after color development. If interference was pronounced, smaller quantities of the ion were used successively until the limiting permissible concentration could be estimated, 2y0 error being set arbitrarily as a reasonable tolerance. L~ETHOD 11. The solution t o be tested contained 0.100 mg. of copper, a measured volume of solution containing the ion in question, and 5 ml. of 8 S nit>ric or hydrochloric acid. After dilution to approximately 50 nil. Tvitli n-ater, the solution was Table I. Effect of pH on Color Intensity and Stability with 1 P.P.M. of Copper Time after .idding Cupretliol, Min.
10 30 GO
90 210
. . . . . . Photometer . . . . . .Readings ........ P H ~ pH4
pH2
91 93
93 93 94 93 93
9.5
97
96
i>H5
94 94 94 94
94 94 91
89 83
pH6
94 9.5
94 94 94
91
Table 11. Effect of Cations on Determination of Copper by Method 1 3Iaxiniuni Perriiissible Concentration, P.p.m. 20 1000 1000 1000 1000 200 0 20
Inn Added as .iluniinuiii Amnioniniii Antin!ony .irsenic Arsenir Bnriiiiii Bismritli Cadmiri 111 Calciii i n Chromirini Cobalt Iron Iron Lead Litliiuni .\Iaenesirim llani?aneir Alercury llercury 31 olybdrnii 111 Nickel Pnta
