EDC
EDB
-
tative analysis is based on the size of the sample introduced onto the column and on responses t o a series of different quantities of pure TEL standards as shown in Table I. An internal standard, chlorobenzene, serves to verify this procedure. Studies of the resolution and response factors of other iead alkyl compounds are in progress. A detailed account of the experimental technique will be presented later. LITERATURE CITED
(1) Clark, S. J., Abstracts,
63B, 140th Meeting, ACS, Chicago, IE:, September 1961.
(2) Goodwin, E. S., Goulden, R., Richardson, A., Reynolds, J. G., Chem. & Id.
in parallel using pure TEL containing a chlorobenzene marker. The relative electron absorption coefficient of TEL was 115, indicating it to be a strongly absorbing compound. The reference standard, chlorobenzene, was assigned the value of unity. The photoionization detector served a dual purpose in computing the coefficient and in determining the elution time of the TEL. Figure 3 shows typical chromatograms with samples of leaded and unleaded gasolines. Lead scavengers, ethylene dibromide (EDB) and ethylene
dichloride (EDC), are present in the gasoline. They are strong electron absorbers and could also have been analyzed by this same technique. At the retention time of TEL in the leaded gasoline, a well resolved peak is absent in the unleaded gas. The photoioniaation detector records unresolved components and is complementary to the electron capture detector. The time for complete analysis of TEL in gasoline can be shortened to less than 2 minutes, simply by increasing the linear gas velocity through the column. Quanti-
(London) 1960, (3) Lovelock, J. 162 (1961). (4) Lovelock, J. (1961). ( 5 ) Lovelock, J. Proceedings, p.
1220. E., ANAL. CREM.33,
E., Nature 189, 729 E., Gregory, N. E., 151, International Gas
Chromatography Symposium, Lansing, Mich., June 1961. (6) Lovelock, J. E.,Lipsky, S. R., J. Am. Chem. Soc. 82,431 (1960).
(7) Parker, W. W., Smith, G. E.,Hudson, R. L., ANAL.CHEW33, 31170 (1961). J. E.LOVELOCK A. ZLATKIS Department of Chemistry University of Houston Houston, Tex. RECEIVED for review September 5, 1901. Accepted October 6, 1961.
nfused Vycor as a Support for Gas Chromatography SIR: Crushed unfused Vycor appears
to have interesting properties which merit further investigation for its use as a filling for gas chromatographic columns. First, samples of several volatile organic liquids "disappear" when injected into a column a t 25" C.; many do not appear even at 60" C. Second, comparison of a porous glass column with one of firebrick showed in one case that the distribution ratio, for a given amount of liquid, was considerably higher when glass was used, thereby indicating a more efficient use of the liquid. EXPERIMENTAL
Supports. Unfused Vycor rods (Corning Glass Co.) were crushed in a diamond mortar and the was sieved. The 60- to 80- ancf%?~~ 150- fractions were leached overnight with concentrated hydrochloric acid,
rinsed with distilled water, and dried. The amount of support required to fill a 1/1 X 30 inch copper column (previously degreased with benaene) was impregnated with methanol contaidhg 29.1 mg. of Carbowax 400. After evaporation of solvent, the material was stored overnight in a vacuum oven at 110" C. After the column had been packed, it was placed in a water bath a t 25' C. and hehum carrier passed through it overnight to remove traces of solvent. A column of untreated 60- to 80-mesh Chromosorb P (Johns-Manville firebrick) was impregnated and packed in the same way. It appeared to require virtually no preconditioning to attain constant response to solutes. Similar columns were packed with unimpregnated glass and Chromosorb, respectively. Apparatus and Procedures. Simple home-made equipment, based upon thermal conductance, was used [Duffield, J. J., Rogers, L. B., ANAL.
CEEM.32, 340 (1960)l. Most of the comparisons, were made a t 25' C. using flow rates that were optimum for Chromosorb: a helium flow of 105 cc. per minute under an inlet pressure of 20 cm. of mercury above atmospheric. An air peak required about 3.5 seconds. Similar flow rates were maintained at 60" and 87' C. RESULTS
Comparison of two 60- to $@mesh columns, one of porous glam and the other of firebrick, showed that, as expected, the pressure drops and the retention volumes and peak shapes for air were nearly identical. There the resemblance ended. qjection of a variety of 2p1. samples of liquids, including carbon tetrachloride, carbon disulfide, eis-1,Wichloroethylene, 4-methyl-cis-%pentane, acetone, benzene, and petroleum ether onto a column of unimpregnated ChromoMOL. 33, NO. 13, DECEMBER 1961
@
1959
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 olehs. 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 teerbButyl hydroperoxide
Mg. 0.124’ 0.186 0.202 0.39 0.90 0.74 0.40
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.
e
B
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.
