1345
V O L U M E 24, N O . 8, A U G U S T 1 9 5 2 The mean value t'or tlie chromium recovery is 93 to 94%) n o matter in which form the chromium is added. The st:indard reference curves established with 1 nil. of blood (dry-ashing procedure) and with 10 1111. of blood (x-et-ashing procedure) TWIT identical. The standard deviation for the clcxtcrmination of chromium was calculated on the b&s of a great numher of data obtained \Then amounts of chroniium ranging from 0.2 to 3.2 micrograms were added to blood samples of 1 t o 10 ml. If the dry-ashing procedure is wed, the standard deviation is 1 0 . 0 6 micrograni of chromium; if the !vet-ashing procedure is used, the standard deviation is 1 0 . 0 5 microgram of chromium. REFERENCES
-Lkatsuka, h.,and Fairhall. L. T., J . Iiid. fl!iu., 16, 1 (1934). -Uwens, TV., Ber. l ' l l l l n t e r i ~Korbg?'. Cnfa.llrned. u . Berujskrankh., Frankfurt/M., September 1938, p. 97'3, Leipzig, Georg Thieme, 1939. Baetjer, 1.31.. A / d f . I n d . Huu. 0 c c i i i ) u t l o u u l .Wed., 2 , 487 (1950). Ihid., p. 505. Ridstrip, L., i l r c h . bclaes 7ithd. . s w i , i / ~( t hyg., 8, 500 (1950). Bourne, H. G., Jr., and Tee, H. T., Iiid. M e d . and Surg., 19, 563 (1950). Arard, Daniel, ";lctualitbs Scientifiqur.: et Industriellcs," S o . 225, Paris, Hernmn et Cie., 1935. Caster, W. O., .Is.u..CHEAT., 23, 1229 (1051). Caeeneuve, P., Bull. suc. chiin., [ 3 ] 23, 701 (1900); [3] 25, 761 (1901). Davis. 1%C., and Bacon, d.,J . SOC.C ' h i m . Itid., 67, 316 (1948). Dingwall, .L.,and Heans, H. T . , A m , J . Cariwr. 16, 1490 (1932). P , T., Proc. .\-r!tl. .Icad. Sci., 20, 416 Dingwall, A , , antl U ~ N I I [I. (1934). Dingwall, 9.. ('ioaeii. K.G., arid Beans, H. T., -4m. J . C ' U J I C W , 21, 606 (1934). Doerner, H. -4., L-. ,S.Dt,pt. Interior, liur. Mines, Ttcii. Paper 577 (1937). Ege, J. F., Jr., and bSilrernian.L., AA-.LL. CHEAL,19, 693 (1047). Feigl, F., personal comniunication. Gray, S. J., and Sterling, I- he done satisfactorily in a Nett-Summerson colorimeter. using the proper blue filter, or more precisel). with a spectrophotometer at 420 nip. T h e time of standing depends upon the amount of iodine in the blank and must be determined empirically. Prepare a graph, showing iodine concentration against extinct,ion.
V O L U M E 24, NO. 8, A U G U S T 1 9 5 2
1347
Results. Table I givcs a feLv examples to illustrate reproducibility and recovery \\ ith this method. DISCUSSION
The small amount of serum required, the rapidity of the method, and its adaptability to the simultaneous analysis of several samples are evident from the description of the technique. The accuracy is illustrated by the t,abulated results. Trichloroacetic acid proved t o be the most suitable agent for protein separation because it produced a precipitate that could be packed by centrifugal force into a small, cohesive, rubbery mass, from which the supernate could be decanted with ease. The two treatments with trichloroacetic acid Pufficed to separate protein-bound from inorganic iodine, as shown by the fact that further washing with distilled water, followed by centrifugation, did not alter results significantly, even when iodine had been added t o the sample just before precipitation. The prevention of iodine loss during evaporation, particularly in the stage of fuming, depends upon maintenance in the form of iodate. Iodic acid is not volatilized a t the temperatures employed, as shown by the recovery data in Table I . Slthough the presence of chloric acid will maintain iodine in the oxidized form, this acid disappears during the fuming stage, partly by decomposition to volatile products, partly by conversion to perchloric acid. Loss of' iodine oxurR in fuming mixtures of iodic and perchloric acids in the absence of chromium. Hot and concentrated perchloric acid will oxidize triv:dent chromium to chromate arid the presence of the latter will maintain iodine as iodate throughcut the procedure. The 5-mg. amounts of sodium chromate employed are adequate for keeping iodine in the oxidized form. Kevertheless, it was found advisable to add one or t\vo drops of cliloric acid reagrnt when the first fumes of perchloric a(-id appear or whenever there is any indication of reduction of chromium t o the green-colored trivalent state. Glass beads must be present t o avoid low of sample by bump-
Table I.
Determination of Protein-Bound Iodine Iodine Added (a- I 2 2 2 3
3
12
Iodine r o u n d , y 0 0 0 0
34 77 34 13 0 43
00 o 00 0 18
n n
0 00 0 00 0 on
0 I8 0 16
o on o no o on n n
18 18 0 00 0 18
28 30 0 48
n 20
0 17 0 17 0 ''8 0 .52 0 50 0 25 0 42
2 2
0.00
> >
n no
0.18
0 25 0 40
2
0 18
n no
n
2
2
0 no 0 18
0 17 0 35
Serum I(
3 3
0 18
n oo
Ferun, L
3 3
n on
Serum 31
2 2
0 00 0 18
0 0 0 0 0 0
2
n oo
Seruin 1% Srrrinl I
Serum J
8i.riim
N
2
6eiurn 0
2 2
0.18
n 18
n 18 n oo 0 18
0 23 0 14
28 0 48
08 28 11 30 34 52 n 20 0 34 0 20 0 37
ing. Toward the end of the digestion, there is a distinct crackling of the solution, which is probably due t o t h e decomposition of chloric acid. This occurs irrespective of whether or not organic material was originally present. The elimination of sample transfer throughout a procedure is an important consideration in any analytical method. This is particularly true in submicro techniques. T h e only transfer made in this process is t o the volumetric flask for accurate dilution, preparatory to removal of the aliquot for final measurement of iodine. For routine determinations, it was found that transfer to the volumetric flask for dilution could be eliminated by the experienced worker. SuccesE of this modification depended upon the ability t o carry the evaporation of each sample and standard t o a uniform volume, as judged visually. Ten milliliters of distilled water were then added to each beaker from a pipet and, after mixing, aliquots were removed for analysis. After some experience, it was found that tilk short cut could be carried out with a volume error of only +2y0in the final dilution. Strani distillation is required in most acid oxidation method3 to separate iodine from the large salt concentration, but is rendered unnecessary in this procedure by the lo^ salt concentration in the chloric acid digest. Even though the amount of perchloric acid in the final residue may be subject t o variation, this does not influence the subsequent colorimetric estimation of iodine. hpproxiniatrly 15% of the chromate ion is lost during digestion and evaporation. A1 though the decrements in chromate were found to be fairly constant, it became necessary to determine the inHuence of variations in the anicunt of chromate on the colorimetric ePtimation of iodine in the cerium(1V)tem. Twice the customary amounts of chromate caused no significant change in the values for iodine. A n e v calibration curve must be established whenever new reagents itre introduced. Blank determinations of the trichloroacetic acid reagent have shown n o iodine. As the procedure for samples and standards w a . ~identical in other respects, blank corrections were the same. The reduction of iodate in the residue is accomplished by a measured excess of arsenic(II1). The amounts of arsenious acid employed are large enough to provide the needed excess in the event of variable amounts of chromate or other oxidizing agents in the treated suniple. T o demonstrate the effectiveness of the reduction of iodatc, by the use of arsenic(TI1) in acid solution, amounts of iodatr and excess potassium iodide in association with starch 1vei.e treated with 2 ml. of 2 S arsenic(III), ivhich was 1.5 S in sulfuric w i d . Immediate discharge of the starch-iodine complex !vas noted. T o two 5-nil. samples of a solution of iodate (0,028A') in 1 AV acid were added 10 ml. of standard arsenic(II1) solution of the eame normality. T h e mixtures were permitted to stand for 3 and 20 minutes, respectively. T h e mixtures were then neutralized with sodium hicarhonate and the excess arsenic(II1) \vas titrated with standard iodine (0.0073 .V). Five milliliters of the arsenic(II1) alone in sodium bicarbonate buffered solution required 19.3 ml. of standard iodine. T h e values ot)t.ained in t,he back-titration of the excess arsenic(II1) were 19.34 and 19.35 nil. of standard iodine. T o carry the experiment to I o w r values. a curve based upon potassium iodide as a primary source of iodine covering the range from 0.00 to 0.74 microgram of iodine was prepared. Recovery of 0.59 microgram of iodine as potassium iodate under the conditions of the procedure described Tvas then made. Percentage recovery values were found to he 100.4, 100.4, and 90.6 on three separate samples. This \vas considered to be within the range of accuracy of the cerium(1V)-arsenic(II1) end point. T h e precautions t o be observed in estimating iodine by its catalytic effects on the cerium(1V)-arsenic(II1) system have been brought out adequately by Sandell and Kolthoff (16) and others ( 1 , 6 ) . Minute traces of mercury, silver, fluoride, or cyanide are known t,o check the reaction. T h e amounts of mercury present in the blood after a therapeutic dose of a mercurial diuretic: may interfere with the determination of iodine. Osmium,
1348
ANALYTICAL CHEMISTRY
chloride, and bromide are known to be positive catalysts in this system. It is not likely that osmium would be encountered in human serum. Chloride and bromide are removed in the digestion process. SUMMARY
A rapid method for the determination of protein-bound iodine in multiple 2- t o 3-ml. samples of serum involves protein precipitation by trichloroacetic acid, protein destruction and simultaneous oxidation of iodine to iodate by chloric acid in the presence of sodium chromate, evaporation to a small volume for removal of acid and organic matter, dilution of the residue, and colorimetric estimation of iodine by catalytic action on the cericarsenite system. The principal advantage of the method is that all steps in preparation of the sample up to colorimetric estimation are carried out in the same container, thereby eliminating losses of iodine through transfer or distillation. The accuracy to be expected by this procedure, as shown by addition, is in the neighborhood of *15’%. This error is reduced considerably by analyzing duplicates. LITERATURE CITED
(1) Barker, S. B., J. BWZ. Chem., 163, 313 (1946). (2) Barker, S. B., and Humphrey, hl. J., J . Clin. Endocrinol., 10, 1136 (1950). (3) Barker, S. B., Humphrey, 11. .J., and Soley, M. H., J . Clin. Invest., 30, 55 (1951).
(4) Chaikoff, I. L.,Taurogg, A , , and Reinhardt, W. O., Endocrinology, 40, 47 (1947). (5) Chaney, A. L.,IND. ENG.CHEM.,A h a ~ ED., . 10, 326 (1938). (6)Ibid., 12, 179 (1940). (7) Conner, A. C.,Swenson, R. E., Park, C. W., Gangloff, E. C., Lieberman, R., and Curtis, J. >I., Surgery, 25, 510 (1949). (8) Leipert, T., B w c h e n . Z., 261, 437 (1933). (9) McClendon, J. F.,and Foster, W. C., J . Bwl. Chem., 154, 619 (1944). (10) Man, E. B., Smirnow, A. E., Gildea, E. F., and Peters, J. P , J . Clin. Invest., 21, 773 (1942). (11) Riggs, D. S., Lavietes, P. H., and Man, E. B., J . BioE. Chena., 143, 363 (1942). (12) Riggs, D.S.,and Man, E. B., Ibid., 134, 193 (1940). (13) Rosenberg, I. X., J . Clin. Ilazlest., 30, 1 (1951). (14) Salter, W. T., Baseett, -4.M., and Sappington, T. S., A m . J . Med. Sei., 202, 516,527 (1941). (15) Sandell, E., and Kolthoff, I. M., Mikrochiwi. Acta, 1, 9 (1937). (16) Sappington, T. S.,Halpirin, N.,and Salter, W. T., J . Pharrn. Ezptl. Therap., 81, 331 (1944). (17)Shahrokh. B. K..J . Biol. Chem.. 154. 517 (1944). (18j Talbot, N. B., Butler, A. M., Salsrnan, A. H., and Rodriguez, P. M., J. Bid. Chem.,153,479 (1944). (19) Taurogg, 9., and Chaikoff, K., Ibid., 163, 313 (1946). (20) Winkler, A. W., Riggs, D. 8.. and Man. E. B., J . Clin. Invest., 24, 732 (1945). (21) Winkler, A. W., Riggs. D. S., Thompson, K. W,, and .Man, E. B , Ibid., 25,404 (1946). RECEIVED for review August 27, I951 Accepted June 9, 1952. Work supported in part by grants from trhe Hational Heart Institute and the Michigan Heart Association.
Progress Report of Committee on Nomenclature, Division of Analytical Chemistry, June 1952 T
HE ikst progress report of the Committee on Somenclature of the Division of Analytical Chemistry, published in 1947 [ A s a L . CHEM.,19, 931 jl947)], outlined the geneml direction in which further work should be undertaken. The following report on specific defhitions is an effort to carry out this commission. Every effort has been made to consider the findine and advice of other nomenclature Committees working on scientific definitions. The committee has tried to avoid coining new definitions, perhaps a t times to the point of not being consistent. The advice of the ACS Committee on Nomenclature has been sought and incorporated in this report. While every effort has been made to consider all points of view-.this report is not to be considered final. The following terms commonly used by American chemists and in the publications of the AMERICAN CHEUICAL SOCIETY have been studied by the committee. They had the assistance and advice of specialists on nomenclature in the - ~ V E R I C A XCHElTIChL SOCIETY.The committee realized when the study was undertaken that because of the uncertain and conflicting usage of many of these terms no completely acceptable definition for all chemists would be possible. With due regard to the action of other standardizing bodies to generally accepted usage and with the hope of achieving some greater degree of consistency, the following definitions are recommended. Accuracy is a measure of the approach of a given value to what is considered to be the most probable value of the quantity on the basis of analyses carried out by skilled investigators. Acidimetry is the measurement of the concentration of an alkali by titration m-ith a standard solution of an acid. Alkalimetry is the measurement of the concentration of an acid by titration with a standard solution of an alkali. Analysis is the separation, the identification, or the determination of the concentration of part or a11 of the constituents or components of a sample.
Chromatographic AnaIysis is the analysis of a solution by the use of solid sorbents, such as paper or alumina, to separate substances in solution by selective sorption. Dissolution is the process by which two or more phases become homogeneous. Determination is the act, process, or result of any measurement. Electroanalysis is the use of electrical energy for the separation, precipitation, detection, or determination of elements and compounds in chemical analysis. It is distinguished from other electrical methods of analysis by the fact that it depends upon the consumption of significant amounts of electrical power.
report i t is hoped that constructive B criticism will ofbethis sent to the new expanded committee Y PUBLICATION
xhich is charged with the task of continued study in this controversial field. Close cooperation with other nomenclature committees will continue, especially with those working outside the United States which have expressed an interest in working with this new committee, which is ss follows:
S.E. Q. ASHLEY,Chairman,
General Electric Co., Pittsfield, Mass. H. C. DIEHL P. J. ELVING
N.H. Fu~n1.m
R. P. GRAHAM L. T. HALLETT E. B. SANDELL E. J. SERFASS E. R. SWIFT F. D. TUEMMLER G. T. WERNIMONT H. H. WILLARD
