It might be expected that lipide peroxides would oxidize octyl thioglycolate directly, thus obviating the necessity of an iodide salt. However, preliminary experiments indicated this reaction t o be extremely slow under these conditions, showing no measurable reduction in the amount of titratable octyl thioglycolate in 15 minutes. T o test the effect of air oxidation of iodide, the apparent peroxide content of autoxidized corn oil methyl esters was measured a t intervals by our procedure and by that of Wheeler (r). The peroxide increased a t rates of 0.001 and 0.020 fimole per minute in the two methods, respectively, indicating that air oxidation is a minor factor in our proccdure. Samples of autoxidized corn oil methyl esters and autoxidized cottonseed oil methyl esters were subjected to both procedures for peroxide measurement. The comparison of values obtained by both procedures on these esters (Table 11) indicatrs that the method of Wheeler gives slightly higher values, more than might be accounted for by “oxygen error.” Wagner (6), considering the formation of cyclic intramolecular peroxides in autoxidation of diolefins, found that ascaridole, a cyclic peroxide, was incompletely reduced by iodide in acetic acid media, and even less reduced in alcoholic media. The presence of this type of cyclic intramolecular peroxide in the autosidized esters would be reflected
Table II. Comparison of Two Methods for Determination of Peroxide Number
Lipide Corn oil methyl esters
Peroxide Number. Sample, Meq./Kg. ‘ Weight, ’ New Wheeler Gram method method 0.0198 0.0210 0.0220 0.0207 0.0384 0.1232 0.1293
AY.
Cottonseed oil methyl esters Lot I
159
0.0828 0.0428 0.0189 0.0200 0.0146 0.0179
AY.
Lot I1 (new procedure scaled up to meet sample size) Av.
158 166 160 168 156
0 0573 0.0579 I
n . n777
0.0379 0.0752 0.0594 0.0439 0,0938 0.0563 0.1283
532 524 532 540 532 469 465
172 170 171 520 564
542
47 -. 1 -
495 500
480 -
510 475 474 499 490 490
has been used here on a semimicro scale (1 to 100 mg. of lipide sample), but it can be scaled up easily for use in macroanalysis, as indicated in Table 11. In our laboratory, this method has been found to have advantage in analysis of biological material. For example, our solvent system completely dissolvea erythrocyte stroma, thereby facilitating the measurement of peroxide in the lipides thereof. LITERATURE CITED
(1) Bolland, J. L., Koch, H. P., J . Chem. SOC. 1945, 445. (2) Dickey, F. H., Raley, J. H., Rust, F. F., Treside, R. S., Vaughan, W. E., Znd. Eng. Chem. 41, 1673 (1949). (3) Holman, R. T., “Progress in the Chemistry of Fats and Other Lipids,” R. T. Holman, W. 0. Lundberg, T. Malkin, eds., p. 53, Pergamon Press, London. 1954. _. - .~ (4) Kokatnur, V. R., Jelling, M., J . Am. Chem. Soc. 63, 1432 (1941). (5) Tobolsky, A. V., Mesrobian, R. B., “Organic Peroxides,” pp. 52-4, Interscience, New York, 1954. (6) Wagner, C. D., Smith, R. H., Peters, E. D., IND.EIW. CHEM,,ANAL. ED. 19, 976 (1947). (7) Wheeler, D. H., Oil & Soap 9, 89 (1932).
LELANDK. DAHLE RALPHT. HOLMAN
I
in slightly lowered values given by the new procedure. Our procedure measures lipide peroxides within the limits of peroxideiodide reactivity encountered in iodometric methods (8, 6). The method
Department of Physiological Chemistry University of Minnesota Minneapolis, Minn. Hormel Institute Austin, Minn. WORKsupported by The Hormel Foundation and the National Institutes of Health (H-3662)
lame Spectrophornetric Study of Yttrium SIR: We wish t o extend the information previously reported for the flame spectrophotometric characteristics of yttrium (2). Rodden and Plantinga (6), using the spark-in-flame spectrographic method, gave 0.0001M as the limit of detection of yttrium, but reported an unsteady emission below 0.001U (equivalent to 89 fig. of yttrium per ml.) Direct current arc procedures are limited to the 50- to 100-pg.per-ml. range as a minimum. Vndoubtedly, the low emission intensity of yttrium in aqueous solution has detracted from its applicability. However, with a n organic medium, the emiesion intensity of yttrium from an oxygen-acetylene flame is increased about 400-fold. Consequently, of the methods available for the determination of yttrium in concentrations greater than about 2.5 pg. per ml., flame spectrophotometry has a number of advantages. The effects of flows of oxygen and acetylene, ratios of these flows, different regions of flame mantle viewed, I
and various cations and anions have been studied. EXPERIMENTAL
Reagents. Yttrium nitrate, C.P. grade, was precipitated as the oxalate, washed, and ignited to the oxide. A standard solution of yttrium, 1.OO ml. equivalent to 4.00 mg. of yttrium, was prepared by dissolving 1.270 grams of Y20ain the minimum amount of HNOs and 30% HzOz to cause dissolution. After the excess peroxide was removed by boiling, the volume was adjusted to 250 ml. with demineralized water. Less concentrated solutions were prepared by appropriate dilution. A 0.1M solution of Zthenoyltrifluoroacetone (TTA) was prepared by dissolving 5.5 grams of the technical grade reagent in 4-methyl pentan-2-one, then diluting to 250 ml. with additional solvent. Apparatus. T h e Beckman Model DU flame spectrophotometer has been
described (3). The following instrument settings were employed:
E M , % adjust
60 Phototube resistor, megohms 22 Multiplier phototube (RCA 1P28), volts per dynode 60 Acetylene flow, cu. ft. per hr. 2.25 Oxygen flow, cu. ft. per hr. 7.38 Oxygen pressure, Ib. per sq. in. 10.0 Slit width, mm. 0.030 Method. Yttrium was extracted with a 0.lM solution of T T A from a n aqueous phase, 0.1M in total acet a t e and a t p H 5 . 5 . The phases were shaken gently for 2 minutes. Extraction began a t p H 1.3, became quantitative a t p H 4.2, and remained quantitative up t o at least p H 10. T h e p H value at 50% extraction was 2.8 as compared with the value of 3.2 reported for nonoxygenated solvents (I). The effect of aqueous-organic volume ratios on the percentage of yttrium recovered was identical with the study reported for aluminum (4). VOL. 33, NO. 13, DECEMBER 1961
0
19611
Table 1.
Tolerance Limits of Other Elements and Ions
Aqueous phase contained 20 pg. of yttrium per mi. An equal volume (5 ml.) of 0.1M ITA in 4-methyl pentan-2-one used a5 extractant.
Diverse Tolerance Limit, Mg. Material Present 597 mM 613 mp AlurninWl 200 20" Barium 20a 204 Calcium 200 20" Cerium(1x1) 2 4 Cobalt 2 2 Copper 0.05 0.05 Chromium(I11 ) 20; 20; Gadolinium Iron( 111) 2 2 Lanthanum 0.2 20" Magnesium 204 200 Manganese 0.2 20" Nickel 204 205 Potassium 205 204 b b Bcandium Sodium 20; 20; Terbium f 2 Thorium Uranium 2cQ 205 Vanadium 2.5 2.5 Zinc 0.2 20 Zirconium 0.1 0.05 Bromide 206 Chloride 20" Fluoride 0.2 Iodide 205 Nitrate 2Qm Oxalate
