sorb generally gave an enlarged air peak indicating negligible retention of the solute. In contrast, the glass column gave very small air peaks indicating that the solutes were not being eluted with air, but only carbon disulfide and petroleum ether could be detected as a result of coming off the column within an hour. Furthermore, the peaks tailed severely, a clear indication of adsorption. Tailing for the - to 150-mesh glass was less than for 60 to 80 but it was still severe. Studies are being initiated to determine how much, if any, of the retention can be attributed to Molecular Sieve action C., Boord, 6.E., ANAL. 787 (1957)j as opposed to simple adsorption. Comparison of the impregnated supports also raised interesting questions. In the first place, the retention volume
on 60- to $@mesh Vycor for petroleum ether, when corrected for its retention volume on unimpregnated Vycor, was nearly seven times larger than the corresponding value for impregnated Chromosorb. From this, one might conclude that the liquid was being used more efficiently on the porous Vycor. Bowever, the Bituation is not simple. Colu r n of 100- to 150-mesh unimpregnated Vycor required about 50% larger volumes than 60- to $@mesh for the air and petroleum ether peaks to emerge. More important, impregnation resulted in a retention volume for petroleum ether that was smaller than on the uncoated support, whereas that for carbon disulfide appeared to behave normally. As indicated above, studies are being directed toward elucidation of the retention mechanism for different solutes by the unimpregnated Vycor because
it may prove to be a useful adsorbant for removing or separating volatile compounds. In addition, study of lightly impregnated Vycor may be helpful in understanding how surface factors, particularly porosity, influence column efficiency. L. B. RocfpE6sP JEFFREYC.SPITZ~RP De artment of Chemistry and Lafomtory for Nuclear Science Massachusetts Institute of Technology Cambridge 39, Mass. 1 Present address, Department of Chemistry, Purdue University, Lafayetfe Ind. 2 Present address, Department of &hemistry, University of Arizona, Tucson, Ariz. review August 14, 1961. Accepted October 19 1961. Work supported in part by tke U. S. Atomio Energy Commission under Contract
RECEIWD for
AT(30-1)-906.
ete rmina tio SIR: Podometric procedures for peroxide determination are based on the ability of peroxides to oxidize iodide salts to free iodine, with subsequent measure of the latter giving, indirectly, the amount of peroxide originally present in the sample. In conventional procedures, titration of iodine by sodium thiosulfate requires the presence of an aqueous phase, and vigorous shaking is required a t the end of the titration to ensure removal of all iodine from the nonaqueous phase. Air oxidation of iodide i s reported to take place readily in acetic acid but not in alcoholic solvents
(4).
We have found that a solvent mixture of 50% absolute ethyl alcohol, 3Q% glacial acetic acid, and 20% chloroform containing 0.2% octyl thioglycolate (pleasant odor) easily dissolves lipides and provides the necesTable 1.
sary medium for rapid oxidation of iodide by lipide peroxide. The presence of octyl thioglycolate in this mixture provides for the immediate titration of iodine as it is liberated. A backtitration of the excesa thioglycolate by a standard iodine solution indicates the amount of iodine that was liberated by the peroxide. This procedure provides the advantages of a single-phase solution, the elimination of “oxygen error” due to air oxidation of iodide, and the immediate titration of iodine as it is liberated, thus circumventing its possible addition to o l e h s . Wagner, Smith, and Peters (6) cited evidence to show that in the presence of peroxide, iodine will add to conjugated diolefms. Since the formation of conjugated &olefins occurs in the autoxidation of polyunsaturates (1, s),this effect could lead
Standardization of Method on Pure Peroxides
Sample,
Weight,
Peroxide, pmoles % Found Theoretical Error 1.1 1.15 4.6 1.75 1.7 1.72 1.87 1.9 1.6 1.02 0.98 4.0 Lauroyl peroxide 2.2 2.26 2.7 Bis (a-hydroxyheptyl) peroxide 2.86 2.91 2.1 1.69 1.53 3.9 Weighta obtained by (2iss0l~$g given weights of peroxide in a deiini6 volume of 8OlVeRt and taking appropnate "a. Peroxide teerbButyl hydroperoxide
e
B
Mg. 0.124’ 0.186 0.202 0.39 0.90 0.74 0.40
ANALYTICAL ~ ~ ~ M ~ § T R Y
to lowered peroxide measurements in the conventional iodometric procedure, but it is eliminated in the proposed method. PROCEDURE
A standard iodine solution is prepared by weighing accurately approximately 0.1 gram of iodine in a 100-ml. glassstoppered volumetric flask, dissolving in 70% ethyl alcohol, and making up to volume. The lipide-solvent mixture comists of 50% absolute ethyl alcohol, 30% glacial acetic acid, and 20% chloroform, and to this is added 0.2% octyl thioglycolate, a lipide-soluble sulfhydryl compound (Evans Chemetics, Inc., 250 East 43rd St., New York 17, N. Y.). Depending upon its state of oxidation, from 1 to 100 mg:of the lipide sample is dissolved in 1 ml. of the solvent mixture. Two drops of a saturated aqueous solution of potassium iodide is added and mixed. ,After 15 minutes, the mixture is titrated with the standard solution of iodine, by means of a micsoburet, to a perceptible yellow. A repetition of the procedure, eliminating the lipide sample, serves as a control blank, twt-Butyl hydroperoxide (go), lauroyl peroxide, and bis(a-hydroxyheptyl) peroxide (Lucidol Division, Wallace & Tiernan Corp., 1740 Military Road, Buffs10 5, N. Y.) were measured by this procedure to assess its accuracy. The values given in Table I indicate the new procedure measures up to 8 pmoles of these synthetic peroxides within 5y0 of their theoretical value.
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. To 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. The Beckman Model DU flame spectrophotometer has been
described (3). The following instrument settings were employed:
E M , % adjust Phototube resistor, megohms Multiplier phototube (RCA 1P28), volts per dynode Acetylene flow, cu. ft. per hr. Oxygen flow, cu. ft. per hr. Oxygen pressure, Ib. per sq. in. Slit width, mm.
60 22
60 2.25 7.38 10.0
0.030
Method. Yttrium was extracted with a 0.lM solution of T T A from a n aqueous phase, 0.1M in total acetate 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. The 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
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