Simplified Method for Microdetermination of Iodine in Eggs H. J. ALMQUIST AND J. W. GIVENS Division of PouItry Husbandry, Agricultural Experiment Station, University of California, Berkeley, Calif.
T
HE iodine content of eggs has been a matter of much
interest in recent years, because eggs with a high iodine content are a convenient source of iodine in the human dietary and may be of value in the cure or prevention of iodine deficiency diseases. Iodine may easily be incorporated in eggs b y adding iodine compounds to poultry feeds. The principal problem in the microdetermination of iodine in eggs is the removal of large quantities of organic material without a n appreciable loss of iodine. Various methods given in the literature for the microdetermination of iodine in biological substances were found to be unsuitable or inconvenient in the analysis of eggs. The digestion w-ith sulfuric acid and hydrogen peroxide, as described by Pfeiffer (S), is unsatisfactory because of incomplete oxidation, the distillation of fatty acids and other substances, and the inability t o use large quantities of material. The fusion with potassium hydroxide and nitrate, as described by Kelly and Husband ( I ) , requires such large quantities of reagents as t o introduce considerable danger of contamination and difficulty in handling. Liquid eggs are not adaptable t o combustion tube methods such as have been devised b y McClendon ( 2 ) ,while a thorough drying of the eggs previous to combustion is undesirable.
a sample of mixed liquid eggs was found to contain 250 gammas (millionths of a gram) of iodine per egg b y the alcoholic potash digestion method, while the ashing of the dried egg after a n intimate mixture with a large excess of alkali gave a n average value of 210 gammas, or only 84 per cent of the first value. The treatment with alcoholic potash probably converts the organically bound iodine into iodide ion and thus stabilizes i t to the attion of ashing. The efficiency of the alcoholic potash digestion method in tho recovery of iodine was tested b y adding a number of inorganic and organic iodine compounds to liquid egg material of known iodine content and determining the total iodine in the mixtures. The results of these recovery experiments are given in Table I. By the alcoholic potash digestion method the iodine content of eggs has been determined over a range of 2 t o 1750 gammas, with consistently good check results, during the routine analysis of eggs at this laboratory. This method may prove of value in the analysis of other biological materials. TABLE I. RECOVERY BY ALCOHOLIC POTASH DIGESTION METHOD O F IODINE ADDEDTO E G G 0 IODINE
IODINE IODINE DETER- IODINE CONTENT ADDED MINED REPER EQQ PER EGG PER EGG C O V E R ~ D
COMPOUND ADDED
IODINE
PROCEDURE A procedure developed in this laboratory is simple and re-
Gammas Gammas
Potassium iodide
quires no costly or complicated apparatus.
;4 C
The liquid contents of a number of eggs are placed in a flask, an equal volume of 95 per cent ethyl alcohol and 10 grams of c. P. potassium hydroxide per egg are added, and the mixture is boiled gently under a good reflux condenser for 16 to 24 hours. The boiling takes place without foaming or bumping. The product is a dark brown liquid containing very little solids. An amount of this liquid equivalent to 1 egg is placed in a 500-cc. nickel crucible and evaporated to dryness on a hot plate. Nickel crucibles are to be preferred, but may be replaced by Pyrex beakers. The crucible (or beaker) and contents are placed in a muffle furnace and ashed for about 4 hours at about 600” C. The ash is extracted with 50 cc. of hot water, the extract filtered off, and the residue washed with hot water, the washings being run into the filtrate. The filtrate is acidified carefully with 6 N sulfuric acid t o the acid point of methyl red. Five drops more of acid are then added. Saturated bromine water is added to the solution until it has a permanent, strong yellow color. The excess bromine is boiled off and the solution evaporated to about 15 cc. on a steam bath, cooled, and transferred to a small separatory funnel. Any crystalline material formed during cooling and eva orating is removed and washed. The washings are added to tEe solution. A crystal of potassium iodide is added and the iodine formed is extracted with five I-cc. portions of purified carbon tetrachloride in a small separatory funnel. The iodine in the carbon tetrachloride is determined colorimetrically by comparison with standard solutions of iodine in carbon tetrachloride. Corrections for the iodine content of the reagents used are determined by following the same procedure. The colorimeter used is the Bausch and Lomb 3650-1 hydrogen-ion colorimeter. The capacity of the colorimeter cells is about 5 cc. Light is provided by a 75-watt frosted lamp in the Bausch and Lomb colorimeter lamp 2414. A blue glass filter is included in the eyepiece of the colorimeter. The digestion of liquid eggs in alcoholic potash before ashing insures a more complete recovery of iodine. For example,
12 12 12
Potassium iodate
b”
Iodosalicylio acid
a . b
50
50
Qammas
%
61 63 61
98 102 98 100 98
62 61 62
100 98 100
61 62
98 100
0
12 12 12
Iodobenzoio acid
a b
12 12
50
Desiccated thyroid gland
a b
12 12
50 50
63 61
102 98
Potassium iodide
Av. 3 dets.
6
100
106
100
Iodosalioylic acid
Av. 3 dets.
6
30
36
100
Desiccated thyroid gland
Av. 3 dets.
3
40
41
96
50
50
LITERATURE CITED (1) Kelly and Husband, Biochem. J., 18, 951 (1924). (2) McClendon et al., J. Am. Chem. Soc., 50, 1093 (1928); 51, 394 (1929); 53, 1245 (1931). (3) Pfeiffer, Biochem. Z . , 228, 146 (1930). RECEIVEDMarch 6, 1933. Contribution 17, Division of Poultry HUEbandy, Agricultural Experiment Station, University of California.
Correction In the paper on “Use of the Slide Rule in Calculating Hydrogen-Ion Concentration and pH Values” [IND. ENG.CHEM.,5, 218 (1933)l the second sentence in the second example should read: ‘‘0.477 is read on the L scale under 0.3339 on the Cl scale.” M. C. SANZ,JR.
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