termiiietl (Table I11j . The recovery of linoleic acid was somewhat lo^ in all samples except one, in which its content, was high and the apparent recovery m s too high. However, recoveries Ti-ere good for arachidonic acid at high proportions of arachidonate, and apparent recoveries incrmw-1 as the content of arachidonate decrwsed. L-nsaponifiable polyenic iiiaterials and wters n.hich are difficult to saponify may contribute to the inaccuracy of the measurement’ of polyenoic acids ( 2 ) . I t was therefore advisable to isomerize, for example. some cholesteryl esters and some nonsaponifiahle polyenes to rlrterniine t’o Tvhat extent t jugated and measurable saturated acids under the condit’ions of our niethocl. Table IT‘ lists tlie subFtancei tested and the extinction coefficients ~ l e ~ e l o p e dLinoleyl . and linolcnyl alcohols and aldehydes are a t lcast partly conjugated under the cnndition~ of t’he present method, .n-hereas octadecadiene \=,-as not isomerized. These results are apparently due to differences in solubilitj-. for octadccadirne was insoluble in the reaction niediuni, n-hereas tliP other substances n-ere readily dispersed in it. Chnlestq-1 linoleate and cholesteryl linolenate developed extinction coeffivients 64 and 82%, respectirely, of the values expected from their theoretical contents of linoleic and linolenic acids. 1-nrler tlie same conditions cholesterol it-clf th.rloped no significant absorption. Advantnges of the p r o p o 4 method :irp its npplirability to small quantities of lipirks. its simplified operations, and it$ stanrlartlizntion against pure polyiinsa~turntPilacids. The latter pertains p:irticul:wIy to the tetracnoic, pentncnoic, and hexaenoic acids. for which the conditions of isomerization have licen especially chosen. Janics and Insull ( 7 ) h a r e compared the present method with analysis hy gas phase chromatography for the measurement of dieiioic plus trienoic acid esters. Ynder their conditions of gas phase clironiatogrnpliy, linoleate and linole m t e cnierge together and are measured as one peak. A comparison of total tlienoic plus trienoic acids measured hy tlie two niethods in a series of anima,l lipides rcwaled no datistically significant differences. Tlic proper use of alkaline isomerization incsludes the recognition of its deficiencies. The method has greater inherent errors than a.re desirable, and it cannot’ he therefore used for studies
Table 111.
Recovery of Linoleic and Arachidonic Acids Linoleic .4cid, Mg. Arachidonic Acid, Mg. Recovery, Added Found Found Added Sample 70 ... ... ... ... 0.37 Rat fat, 2.28 mg. 157 ... ... linoleic acid 1.51 2.35 Rat fat ... ... 78 0.i4 0.95 ... ... 85 0.60 0.il 81 ... ... 0.51 0.41 87 ... 0.39 0.45 ... . . . . . . 0:002 Rat fat, 2.i6 nig. ... 101 . . . 0.89 0 90 ethyl arncliidonnte ... Rat fat 0.59 0.61 103 ... ... 102 ... ... 0 50 0 51 .. 112 ... 0 15 0 17 ... 0 06 0 08 130 ...
+
+
LITERATURE CITED
Table IV. Extinction Coefficients Developed by Nonacid Polyenes k?6j k?sa Linole?-l alcohol ... 59.2 T,inoleyl aldehyde (9) , . . 53.5 Octadecadiene ... .. Cholest’eryl linoleate ... 25 5 Cholesteryl linolennte 32.1 10.2 Linolenyl alcohol 71.9 34.8 Linolenyl aldehyde (9j 42.3 33.9
in m-hicli m a l l differentes are of great importance. lIethods based upon iqonierization do not distinguisli hetn ecn polyunsaturated acids which have the same number of double bonds but wvh~ch differ in chain length or in the positions of their nonconjugated double bonds. The result obtained-for example, in a n analysis for tetraenoic acid-15 a weighted average of all the tetruene; of various chain lengths and double bond positions, calculated and rcgorted as arachidonic acid. The method is highly empirical. and the directions for its use must be follolved carefully if one is t o obtain reproducible results which are comparable t o thoqe obtained in other laboratorie.. Severthelesq, such data are of value, and are particularly useful in studies d i e r e changes in composition of lipides is of niore iniportance than the absolute content of polyunsaturated fatty acids. ACKNOWLEDGMENT
The authors are indebted to Jean Labarrere for samples of cholesteryl linoleate and choleqteryl linolenate. to Helmut llaiigold for linoleyl and linolenpl alcohols arid aldehydes. to Orrille S. Privett for octadecadiene. and to Earl Hammond and Kalter 0. Lundberg for tlie concentrate of methyl docosahe\:teiioate.
(1) American Oil Chemists’ Society, Chicago, Ill,, Tentative Methods CD 7-48. M a r 1953. (2) Front, J. S., Dkubert, B. F., J . Ana. Chein. SOC.67, 1509 (1945). (3) Hammond, E. G., Lundberg, W.O., J . Am. 021 Chemzsts’ SOC.30, 433-8 (1953). (4) Herb, S. F . , Riemenschneider, R. IT., A X A L . CHEM. 2 5 . 953 11953). ( 5 ) Holman, R. T., dormel‘lnst. rniu. SIinn. Ann. Rept. 1955-56, 32. (6) Holman. R. T., “Methods of Biochemical Analysis” (D. Glick, editor) Vol. IV, pp. 99-138, Interscience, Ken- York, 1957. ( 7 ) J a m v , -1. T., Insull, W.,Rockefeller Institute of AIedical Research, LTew York, personal communication. (8) Lips, H. J., Tessier, H., J . d i n . Oil Chemists’ Soc. 26, 659 (1949). (9) Mangold, H. TI., J . Org. Chem. in mess. (10) Mang’old, H. K., Lamp, B. G., Schlenk, H . , J . Am. Chem. SOC. 77, 6070 (1955). i l l ) Nontag, IT,, Klenk, E., Hnyes, H.. Holman. R . T.. J . Bzol. Chem. 227, 53 (1957). (12) Schlenk, H., Gellerman, J. %., Tillotson, J. A,, Mangold, H. K., J . d i n . 021 C‘hemisfs’ SOC. 34, 37; (1957). (13) Kiese, H. F., Hansen, A . E., J . Biol. Cheni. 202, 41i (1953). RECEIVEDfor revim Octobrr 16, 1957. Accepted March 26, 1958. Study supported by grants fiom the Sational Live Stock and Meat Board, the Life Insurance Medical Research Fund, and the Horniel Foundation. Hormel Institute Publicntion KO. 164. ~-
Correction In the article on “High Temperature Thermal Conductivity Cell” [H. R. Felton and -4.-1.Beuhler, ASAL. CHESI.30, 1163 (1958)l line C under Figure 2 should read: C. Electrolytic condenser 500 mfd. 50 volts.
VOL. 30, NO. 8, AUGUST 1958
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