1198
ANALYTICAL CHEMISTRY
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ABSORBANCE i N MINERAL OIL Figure 2. Curve for conversion of absorbances of equivalent concentrations of ,&carotene in mineral oil at 436 r n p and in 10% acetone-90% hexane
WAVE L E N G T H I N MILLIMICRONS
Figure 1.
Comparison of absorptivity spectra of 8-carotene Mineral oil (0.3% benzene) (0.3% benzene)
_ _ _ - - Hexane
instiunie:it calibration for the pwticular determination of carotene. AIirieral oil standard solutions can he sealed in ampoules without danger of fire or loss of solvent. Stored in this manner they probably would be stable almost indefinitely if they xcre protected from strong light. Howver, i t is apparent that storage in screwcap vials is also entirely satisfactory. Because the absorptivity of 8-carotene in mineral oil is less than in 10% acetone-90yo hexane solutions, a conversion curve may be used t o obtain equivalent absorbances (Figure 2). These solut,ions obey Beer's law as do other solutions of 8-carotene. ACKNOWLEDG $1E S T
Table IT.
Stability of &Carotene in RIineral Oil Stored 9 Months in Darli
Conditions AIineraKoil not degassed, benzene not removed; stored in vials a t room temperature llineral oil degassed, benzene removed; stored in vials a t room temperature Sealed'ampoule, stored a t 7' C. Sealed.'ainpoule, stored a t r o o m temperature
Absorbance a t 436 mp Initial Final 0.612 0.595 0.370 0.360 0.378 1.60 1 GO
0.376 1.60 1,60
tions of hexane, R-ith about an 8-mp shift to longer wave lengths (Figure 1). T h e absorption spectrum in 10% acetone-90% hexane is shifted about 1 mp toward longer wave lengths from that in hexane solutions. The :ibsorbaiicee of mineid oil solutions indicated essential stability a t 436 mp (Table 11). The absorbances a t the wave lengths of maximum absorbance (487 and 459 mp) decreased somewhat with time and shifted dightly (1 mp) toward the ultraviolet, even when the absorbance at 436 mp remained unchanged. Probably this was a manifestation of some spontaneous trans to cis isomerization of the 8-carotene. T h e solutions appamntly !\*err as stable a t room teniper:iture in screw-cap vials as they were sealed under high vacuum in glass ampoules. Complete stabilit,y was not achieved when the mineral oil was not purified and degassed before dissolving the 8-carotene (Table 11). Because p-carotene exhibits stability at 436 mp in ~nineraloil solutions and because i t probably is determined most frequently at that wave length ( I I ) , i t should be possible t o utilize mineral oil solutions of p-carotene as standard solutions. There is adequate stahility for inttrlaboratory collaboration and for use in
The authors are deeply appreciative of the suggestions of F. \IQuackenbush . in promoting this study. LITERATURE CITED
(1) .-issoc. Offic. .igr, Cl,emists, J . Assoc. Oflic. A g r . Chemists 22, 79 (1939). ( 2 ) Rickoff, E;. AI., White. L. AI., Revenue. A , , Williams, K. T., Ihid., 31, 633 (1948). (3) Rlattni, J.. Krumphanalovd, J.. Sandrt. J-., Pritc?usr/lPotracin 5, 155-8 (1954). (4) Cooley, JI. I,., J . Assoc. O&. -4gr. Chemists 35, 487 (1952). (5) Cooky, AI. I,., Koehn, R. r.,ASAI.. CHEM.22, 322 (1950). (6) Guilbert. H. It., IND.ENU.CHEM.,ANAL.ED.6 , 452 (1934). (7) Kuhn, R., Brockmann, H., Z. physiol. C'he?n. 2 0 6 , 41 (1932). (8) SIunsey. V. E., J . Assoc. O f i c . -4gr. C'hemisfs 20, 459 (1937). (9) Ibid., 2 1 , 331 (1938). (10) Illid., p . 626. (11) Quackenhush, F. W., Ibid.. 33, 650 (1950). 112) Ibid.. 35. 738 (1952). (13j Russel, k. C'.,'Tayior, 11.TI-., Chicliestcr, D. I.'.. Piant Phusid l o ? 329 (1035). (14) Spragiie, T I . V., Science 67, 10T (1928). RECEIVED for review .January 9 , 1956. Accepted M a r c h 29, 1956. Journal Paper S o . 937 of the Prirdue Aericultural ExpPriment Station, Lafayette Ind.
Contents Page Omission Through a regrettable error, no listing was made on the contents page of the June issue of the article on "Semiquantitative Spectrochemical Analysis of Silicon" by P. H. Keck, A. L. MacDonald, and J. IT. Mellichamp, which was printed on page
995.
