Table 1. 98
rp
NBS Sample No. 1042
96-
a-
m 940
1043
YI
Analysis of National Bureau of Standards Steels
Per Cent Oxygen Vacuum fusion-gas NBS av. chromatography 0.017 0.019 0,019 0,018 0.002 0,001
92-
90
-
TIME, MINUTES
Figure 2. Adsorption of nitrogen ( 1 5.0 pg.), carbon monoxide (14.4 pg), and hydrogen (1.03 pg) on Linde 5 A Molecular Sieve at - 196" and -78" C.
flow rates and detector currents showed that these variables could be controlled so the total relative error arising from them should not exceed 3y0. A change of 1 ma. in the detector current caused relative errors of 0.9%, and a change of 0.2 p.s.i.g. in the inlet helium pressure caused relative errors of 1.O% for carbon monoxide and nitrogen. Thus, frequent calibrations are not necessary. As for sensitivity, 1 pg.. of carbon monoxide and 0.5 pg. of nitrogen gave 1% of full-scale deflection, and this sensitivity could be increased. Analytical results for some standard steel samples, Table I, demonstrate the acceptable accuracy and precision obtainable. The technique of using Molecular Sieves to concentrate gases rapidly and quantitatively for a chromatographic
1044
0.009
1045
0,007
0.002 0.002 0.008 0.008
0.007 0.007 0.007 0.007
separation and determination has other analytical applications. For example, as the data of Figure 2 indicate, the technique could be applied t o the determination of hydrogen by the hot extraction method. Preliminary work with the carrier-gas fusion technique in purified helium showed that oxygen and nitrogen in metals could be determined simultaneously by trapping the evolved carbon monoxide and nitrogen on a Molecular Sieve a t -196" C. and then running a chromatogram. The use of 'jlvinch Molecular Sieve pellets permitted a relatively rapid carrier-gas flow rate. (Whether or not the gases were adsorbed quantitatively was not studied.) I n addition, the carbon or oxygen content of a sample could be determined readily after a carrier-gas fusion by oxidizing the carbon monoxide formed t o carbon dioxide, trapping the carbon dioxide on a Molecular Sieve a t ambient temperature, and desorbing the carbon dioxide at about 300" C. for a chromatographic
Per Cent Sitrogen Vacuum fusion-gas NBS av. chromatography 0.014 0.012 0.013 0,015
0,005
0,004 0.004
0.004 0.003 0,003 0.003 0.003 0.003 0.003 0.005 0.005
determination. These procedures would have the advantages of simplicity, speed, and high sensitivity. ACKNOWLEDGMENT
The authors thank Robert Rapp for his assistance in the vacuum fusion determinations. LITERATURE CITED
(1) Brenner, N., Ettre, L. S., A x . 4 ~ .
CHEM.31,1815 (1959). (2) Feichtinger, H., Bachtold, H., Schuhknecht, W., Schweiz. Archiv. angew. Wiss. u. Tech. 25, 426 (1959). (3) Lesser, R., Gruber, H., 2. Metallk. 51,495 (1960). (4) .Martin, J. F., Friedline, J. E., Melnick, L. M., Pellissier, G. E., Trans. Am. Inst. Mining, Met., Petrol. Eng. 210,514 (1958). LYNNL. LEWIS LABEXM. MELNICK Applied Research Laboratory U. S. Steel Corp. Monroeville, Pa.
Decomposition of Oxygenated Terpenes in the Injection Heaters of Gas Chromatographs SIR: The feasibility of achieving plug flow during sample charging of the gas chromatograph has been pointed out by Porter, Deal, and Stross [ J . Am. Chem. Soc. 78, 2999 (1956)]. To facilitate plug flow, most of the newer gas chromatographs contain separately heated injection ports enabling operation a t temperatures sufficient to provide instant vaporization of charged samples. This feature, while highly desirable in approaching a plug flow pattern, can present serious problems when the sample contains compounds of questionable thermal stability. Isomerization of conjugated triene esters and dehydration of hydroxy esters of fatty acids in the heated injection port of gas chromato-
graphs have been reported by Morris, Holman, and Fontell [J.Lipid Research 1, 412 (1960)l. A similar problem developed in our laboratory during the separation of the flavor compounds of the loganberry ( R u b u s ursinus var. loganobaccus) which contains certain oxygenated terpenes. The purpose of this communication is t o illustrate the effect of flash heater temperatures upon terpenoid decomposition and the complicating effect of such decompositions on the chromatographic pattern of a flavor concentrate. Gas chromatographic separation of loganberry flavor initially was carried out with the flash heater temperature at 205" C. Other operating conditions
which were maintained throughout the work were: column, 9 feet X 1/16 inch i. d. with 2001, Apiezon M on 80- t o 100mesh Celite 545; flow rate, 29 ml. per minute; column temperature, 130" C.; detector cell temperature 250" C. I n Figure 1, chromatogram A depicts the pattern obtained. By accident, chromatogram B of Figure 1 was obtained where the flash heater was at 100" C. Examination of the chromatograms of Figure 1 led to the conclusion that chromatogram A depicts decomposition of slower moving fractions since these fractions are more evident in chromatogram B where a lower flash heater temperature was employed. If exponential flow or incomplete vaporization VOL. 34, NO. 7, JUNE 1962
869
CHROMATOGRAM ( A )
CHROMATOGRAM ( A )
Figure 1 . Effect of flash heater temperature on chromatograms of loganberry extract Flash heater: Chromatogram A, 205' C.; chromatogram 6, 100' C.
6
18
24
TIME
x)
(MIN)
56
di L 42
46
Figure 2. Effect of flash heater temperature on chromatograms of a-terpineol Flash heater:
of charged samples were a factor, the area of peak X, identified by infrared spectra as a-terpineol (p-menth-l-en-8-01), would be the reverse of that shown in Figure 1. Comparison of chromatograms A and B of Figure 2 shows that a-terpineol is aImost completely destroyed in A , whereas only slight decomposition was noted in B. The only difference in operating conditions for the two chromatograms was the flash heater tempera-
12
Chromatogram A, 205' C.;
ture. The fact that some decomposition was still evident, even a t 100" C. emphasizes the thermal lability of the compound. Similar results were observed for linalool. Oxygenated terpenes are not peculiar in this respect and, like many compounds, they present a problem in achieving plug flow because of their relatively high boiling points. Evaluation of flash heater temperatures for unknown mixtures, to avoid decomposition, may prove desirable in
chromatogram B , 100' C.
most cases. While low flash heater temperatures tend to give undesirable skewed peaks (Figure 1, chromatogram B ) , these are less objectionable than to devote time to the analyses of thermal artifacts. E.A. Day P.H. MILLER Department of Food Science and Technology Oregon State University Corvallis, Ore.
Spectrophotometric Determination of Iron in UraniumFission Efement Alloys SIR: I n studies connected with the processing of fuels for the Second Experimental Breeder Reactor (ERB-11)) i t has been necessary to determine less than 0.01% of iron in uranium alloys containing moIybdenum, ruthenium, palladium, rhodium, and zirconium. A simplified procedure for the spectrophotometric determination of iron in metallic uranium reported by Tomida and Takenchi (3) appeared to be adaptable for use on such samples. I n Tomida's procedure, iron in a uranyl chloride solution of 7.5N hydrochloric acid was extracted into butyl acetate. After washing the organic layer twice with 7.5N hydrochloric acid, the butyl acetate phase was diluted with 870
ANALYTICAL CHEMISTRY
an equal volume of methyl isobutyl ketone (hexone) and the mixed solvent layer was contacted with a 20% aqueous solution of ammonium thiocyanate. The absorbance of the iron thiocyanate complex was measured directly in the organic solution. A procedure reported by Evans, Hrobar, and Patterson ( I ) utilized an ammonium hydroxide precipitation of uranium and zirconium to separate zirconium from palladium and molybdenum contained in uranium-fission element dloys. Because molybdenum was considered a possible interference in the iron thiocyanate procedure, i t appeared that an ammonium hydroxide precipitation using uranium as a carrier
for iron would serve a two-fold purpose: It would separate the iron from molybdenum and i t would also furnish a precipitate which could be dissolved in 7.5N hydrochloric acid prior to the extraction with butyl acetate. As very little information was available on the details of the Japanese work, a study was made of the absorption spectra of the complex used, the effect of the hexone added, the time required for full color development, and the stability of the colored complex in the organic medium. The absorption spectra displayed a broad maximum centered about 500 mp, Full color development was obtained within 15 minutes and the color
