TABLE YII. Carotene M zcro-
COUP.lRISOX O F
Cryptoxanthol Carotene Ratio
Clark, G. L., and Gring, J. L., IND.ENG.CHEM.,ANAL. ED., 9, 271 (1937). Comar. C. L.. and Zscheile. F. P.. Plant Phwsiol.. 17. 198 (1942). Fraps, G. S.,’and Kemmerer, A. R., IND.-ENG. CHEW, ANAL. ED., 13,806 (1941). Hogness, T. R., Zscheile, F. P., Jr., and Sidwell, A. E., Jr., J . Phys. Chem., 41, 379 (1937). Kuhn. R., and Brockmann, H., Ber., 66, 407 (1933). Kuhn, R., and Grundmann, C., Ibid., 67, 593 (1934). Peterson, W.J., Hughes, J. S., and Payne, L. F., Kans. Agr. Expt. Sta., Tech. Bull. 46 (1939). White, J. IT., Jr., and Zscheile, F. P., J . Am. Chem. SOC.,64, 1440 (1942). White, J. IT., Jr., Zscheile, F. P., and Brunson, A . M.,Zbid., in press. Zscheile, F. P., and Comar, C. L., Bot. Gar., 102, 463 (1941). Zscheile, F. P., White, J. W.,Jr., Beadle, B. W.,and Roach, J. R., Plant Physiol., 17, 331 (1942).
RESULTS
.
Carotene plus Cryptoxanthol .If icro-
Total CarotenoIs Micro-
gramslo.
grams/g.
grams/y.
Buxton (aj 0,34-0.85 Clark and Gring ., ...., 14) Kuhn and Grundman n ( 9 ) 0.5-0.7 Peterson, Hughes, and Payne (IO) . . . . Fraps enrl W o r n mer( This paper (mature samples) 2.0-8.9
5,9-13,5
,....
4.2-9.3
.......
0.10-1.11
2.2-33.0
6.5-14.0
5,l-7.5
12.7-14.5
.....
0 . S-9.4
0.1-26.0
0.73-2.14
0.9-7.7
0.7-1.2
3.7-19.6
....... 18.2-35.9
A comparison of the results of several investigators is shown in Table VII. Kide variation is found among corn varieties with respect to pigment content. All varieties studied here were inbreds; this was not true of the other work reported in Table VII. The grain of inbred lines usually has a higher proportion of pigmented hard starch than the grain of hybrids, which may account for the relatively high values obtained in this study. Clark and Gring (3) found an inverse relationship between grain size and carotenoid content. The outstanding differences between the results presented here and those of other workers are the higher values for carotene and the consequently lower rryptoxanthol-carotene ratio. The method of separation of carotene and cryptoxanthol used here tends to give slightly high results for carotene because of the inclusion of about 10 per cent of the cryptoxanthol in the carotene fraction. Since a corresponding percentage of the carotene is found in the cryptoxanthol fraction, error is introduced by incomplete separation only when the cryptoxanthol-carotene ratio deviates appreciably from unity. The results of Fraps and Kemmerer show ratios of the same order of magnitude as those reported here. Approximation of the amount of unnamed carotene 1 in the inbreds from R , values in Table I11 gives results varying from 5 to 35 per cent of the total carotene fraction. Fraps and Kemmerer ( 5 ) reported K carotene in 22 corn varieties to average 15 per cent of the total carotene fraction. Summary
X method is presented for the determination of the carotenoids of corn grain which involves a separation of the pigments into three fractions by partition between immiscible solvents and spectrophotometric estimation of the pigment concentration. The analysis of the carotene and cryptoxanthol fractions of corn-grain carotenoids in terms of normal and neo-type pigments was not highly successful, but it is probable that analyses of thg fractions for total pigment content aze reliable a t 4325 A. for the carotene fraction and a t 4375 A. for the cryptoxanthol fraction. Analysis of the carotenol fraction for luteol, zeaxanthol, and total neocarotenols was made by spectrophotometric method:. Analysis for total pigment in this fraction was made a t 4275 A. Four inbred corn lines were studied. Variations in content of mature grain were as follows: total carotenols twofold, total carotenes fourfold, total cryptoxanthols sixfold, luteol fourfold, and eeaxanthol twenty-five fold. Literature Cited Beadle, B. W.,and Zscheile, F. P., J . Biol. Chem., 144, 21 (1942). ‘ 2 ) Buxton, L. o., 1ND. ENQ.C H E M . , ANAL.ED., 11, 128 (1939).
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801
ANALYTICAL EDITION
October 15, 1942
I
JOINT contribution from the Departments of Agricultural Chemistry and Botany of the Purdue University Agricultural Experiment Station and the Division of Cereal Crops and Diseases, Bureau of Plant Industry, U. 8. Department of Agriculture. Journal Paper No. 35 of the Purdue Univeraity Agricultural Experiment Station. Studies on the Carotenoids No. 5.
Apparatus for Iodometric Determination of Tin WILLIAM M. RUJIBERGER Titan Metal nlfg. Company, Bellefonte, Penna.
I
?: T H E volumetric determination of tin it is necessary to keep the solution of stannous chloride under an atmosphere of a neutral gas, such as carbon dioxide, while the solution is being reduced and then titrated with a standard oxidizing solution such as potassium iodate. A 500-ml. 3-necked d i s t i l l i n g flask has AIR CONDENS€R been found to be a 15 T O to CM.LONG v e r y s u i t a b l e container for the solution during reduction and titration. The middle neck accomcq modates the buret, and carbon dioxide is supplied through one of the side necks. The other side neck serves not only as an outlet for the gas but also as a c o n v e n i e n t avenue for the introduction of potassium iodide and starch indicator. If the side neck acting as the entrance for the carbon dioxide is supplied with a glass tube projecting below the surface of the solution as shown in the accompanying sketch, carbon dioxide will bubble through the solution, indicating the rate of flow of gas, and solution will be thoroughly agitated at all times. The use of a 90-cm. (36-inch) length of rubber tubing (longer if necessary) to connect the distilling flask and the carbon dioxide generator will greatly facilitate moving the flask from the hot plate to the sink for cooling purposes. After the entire unit has been assembled, the complete procedure may be carried out 1%-ithouttaking the apparatus apart and without interrupting the flow of carbon dioxide.
