The type of correlation shown in Figure 5 has also been reported by Dal Nogare and Safranski ( 1 ) and Giddings (2). Dal Nogare et al. showed the linear relationship between the relative retention time us. the number of carbon atoms for a series of alcohols (CZ-C,) and hydrocarbons (C5-Clo). By extrapolation (using Table I data and Figure 3), it was estimated that di-p-tolyl carbonate should have a boiling point near 335' C. A boiling point of 342" C. was determined for this solid with an isoteniscope. This is in good agreement with the estimated value. Therefore, it seems very probable that good boiling point estimates for the ortho- and meta-tolyl isomers are also possible by this method. Quantitative Studies. Having established that carbonic acid esters can be resolved, several four-component mixtures were analyzed using the Perkin-Elmer 154C chromatograph. Figure 6 is a chromatogram
of these mixtures with n-tetradecane added as internal standard. These mixtures were resolved with a 9-foot by 1/4-inch diameter column operated a t 210" C. and packed with 20% by weight of Apiezon L loaded on 30 to 60-mesh Chromosorb W. The helium flow rate was 123 cc. per minute. The weight % results based on corrected area measurements are listed in Table 11. Although the average relative error for these determinations is nearly f 2.3% using area weight % correction factors, the average error based on area measurements alone was +11.5%. The area correction factors for weight % data as determined for the chromatographic conditions cited above were as follows: di-n-propyl, 0.95 0.02; di-n-butyl, 1.02 f 0.03; di-n-amyl, 1.13 f 0.03; di-n-hexyl, 1.28 + 0.03. These were based on 8 to 10 observations for each component.
*
ACKNOWLEDGMENT
The authors acknowledge the assistance of John Piser, Monsanto Research Corp., for determining the di-p-tolyl carbonate boiling point. LITERATURE CITED
W.,in "Organic Analysis," Vol. 4, p. 201, Interscience, New York, 1960. (2) Giddings, J. C., J . Chromatog. 4 , 11 (1) Dal Nogare, S.,. Safranski, L.
(1960). (3) Goldenson, J., %SI,S., ANAL.CHEM. 20,730 (1948). (4) Gudzinowicz, B. J., Campbell, R. H.,
Ibid., 33, 1510 (1961). (5) Gudzinowicz, B. J., Smith, W. R., Ibid., 32, 1767 (1960). (6) Ibid., 33, 1135 (1961). (7) Smith, W. R., Gudsinowics, B. J.,
Preprints Third International Gas Chromatography Symposium, p. 111-115, East Lansing, Mich., June 13-16, 1961.
RECEIVEDfor review April 27, 1961. Accepted July 31, 1961.
High Temperature Gas Chromatographic Separations of Aryl Phosphines and Phosphine Oxides 8. J. GUDZINOWICZ and R. H. CAMPBELL
Boston laboratories, Monsanto Research Corp., Everett, Mass. b Investigations have been performed showing that high boiling, high molecular weight, substituted aryl phosphines and phosphine oxides can b e separated b y high temperature gas chromatography. Furthermore, using triphenylmethane as internal standard, triphenylphosphine in mixtures can b e quantitatively analyzed.
phines (6), phosphonium salts (Q),or phosphoranes (9). No gas chromatographic methods TEMPERATURE.
OC
have been reported for separating high boiling, high molecular weight, substituted aryl phosphines and phosphine oxides. It is the purpose of this paper to show that such compounds, all solids at room temperature, can be resolved rapidly by high temperature chromatography. RESULTS AND DISCUSSION
I
more frequent applications of gas chromatography to the separation and analysis of volatile inorganic phosphorus and organometallic compounds have been reported (1, 2, 10, 11). Furthermore, higher boiling samples containing mixtures of triphenyl phosphate-tris(m-tolyl)phosphate (7) and (PNF2)3-(PNF2)4 (8) have been resolved. With the availability of commercial quantities of triphenylphosphine for the production of phosphorus ylides, important intermediates for the synthesis of complex olefins and aldehydes, greater emphasis has been placed recently upon the use of this organometalloid, which is a white, free-flowing, crystalline powder, melting a t 79" C. and boiling near 360" C. a t atmospheric pressure. Normally, titrimetric methods using perchloric acid are employed for the analysis of either triarylphosN RECENT YEARS,
15 10
ANALYTICAL CHEMISTRY
I
I
0
3
I
1
I
Figure 1. Chromatogram phosphine mixture 1. 2. 3. 4.
5.
I
I
6 9 12 15 RETENTION TIME, MINUTES
of
18
aryl
Benzene Triphenylphosphine p-Methoxyphenyldiphenylphosphine Di(p-methoxypheny1)phenylphosphine Tri(p-methoxypheny1)phosphine.
Qualitative Studies. Using temperature-programming for the resolution of the phosphines and phosphine oxides shown in Table I, preliminary investigations were undertaken with the modified high temperature BarberColman Model 10 instrument (4, 61. The temperature-programmed gas chromatograms for the phosphine and phosphine oxide samples shown in Figures 1and 2, (and see Figure 4) were obtained with a 6-foot by 1/4-inch diameter stainless steel column packed with 5% by weight dimethyl silicone polymer (General Electric S E 3 0 silicone gum rubber) as liquid stationary phase impregnated upon 80- to 100-mesh Chromosorb W, and an argon flow rate of 39 cc./minute. In all exploratory studies using this sensitive argon detector instrument, the detector temperature was maintained at 400" C., the flash heater a t 405' C., and a cell voltage of 1250 volts was used.
Table 1.
Aryl Phosphines and Phosphine Oxides
;#;YE
COMPOUND Triphenylphosphine
MOL. WT
M.t?,'C
262
79
278
105-106
p-H phosphine ydroxyphenyldiphenfl-
H O G P C Q 1 2
p-Methoxyphsnyldipheylphosphine
CH~O~PCQ)~
Di(p-methoxyphenyl)pen~phosphine
292
( C H 3 0 0 $ G
Tri(p-methoxyphenyl1phosphine
Triphenylphosphine oride p-Methoxyphenyldiphnnylphosphine oxide
(QfSp.0
Trl(p,-methoxyphenyl)phaphine oxide
(CH30Q.0
CH30GCQ),
78-79
322
87-89
352
129-131
278
153
308
116-118
368
144-145
Figure 3. rings
t
I
Figure 2. mixture 1.
2. 3. 4. 5.
I
1
I
I
I
Plot of retention time vs. number of phenyl 0-0
I
a-•
Phosphines Phosphine oxides
Chromatogram of aryl phosphine oxide Benzene p-Hydroxyphenyldiphenylphosphine Triphenylphorphine oxide p-Methoxyphenyldiphenylphosphine oxide Tri(p-methoxypheny1)phosphtne oxide
Using the retention time data for the phosphines and phosphine oxides resolved and identified in Figures 1 and 2, respectively, a linear plot of the retention time us. the number of remaining phenyl rings in each compound that has not been substituted by a p-methoxyphenyl group is obtained (Figure 3) for both these series of homologous compounds. A similar linear relationship between retention time and number of carbon atoms has also been reported by Giddings (3), whereas, in isothermal runs, the rcxtention time increases exponentially. With nearly linear temperature-programming, members of homologous series are eluted as uniformly spaced peaks. Figure 4 clearly shows the applicability of gas chromatography to the separation of multicomponent phosphinephosphine oxide mixtures. Quantitative Studies. For the
Figure 4. Chromatogram of aryl phosphine-phosphine oxide mixture 1.
Benzene
2. Triphenylphosphine 3. p-Methoxyphenyldiphenylphosphine 4. Di(p-methoxypheiiy1)phenylphosphine 5. p-Methoxyphenyldiphenylphosphine oxide 6. Tri(p-methoxypheny1)phosphine 7. Tri(p-methoxypheny1)phorphine oxide
quantitative determination of unreacted triphenylphosphine in mixtures obtained from syntheses of ylide adducts, an F & M Model 124 gas chromatograph was used. With triphenylmethane added as internal standard to establish the area correction factor necessary to provide weight yo data, these mixtures were resolved with a 6-foot by '/r-inch diameter copper column operated a t 275" C. and packed with 20y0 by weight of Apiezon L on 40- to GO-mesh, acidwashed C-22 firebrick. The helium inlet pressure and flow rate were 18
p.s.i. and 107 cC./minute, respectively.
Peak areas were measured by multiplying peak heights by half-band widths. To esta1)lish the area correction factor of tri 3henylphosphine relative to the triphenylmethane area, four synthetic blends of these compounds were prepared and chromatographed. Over triphenylphosphine concentration ranges of 25 to 7Oy0by weight, a linear plot was obtained for the ratios of the areas us. the ratios of the weights for triphenylphosphine to triphenylmethane. The area correction factor for the phosphine was 1.01 using the chromatoVOL. 33, NO. 1 1 , OCTOBER 1961
0
151 1
Table II. Quantitative Analysis of Triphenylphosphine in Mixtures
(Average of two determinations) Weight % Sample Known Found Difference 39.6 -2.0 E 41.6 -0.5 F 22.0 21.5 G
55.8 46.3
H
58.4 46.3
f2.6 0.0
graphic conditions cited above. The fact that it is nearly 1.00 indicates that the uncorrected arms would be closely related to the weight % of both triphenylphosphine and triphenylmethane in these known samples. The results for triphenylphosphine in several synthetic triphenylphosphinetriphenylphosphine oxide mixtures with
tetrahydrofuran as solvent are shown in Table 11. ACKNOWLEDGMENT
The authors thank C. N. Matthews, Monsanto Research Corp., for the samples of triphenylphosphine and triphenylphosphine oxide and A. E. Senear, W. Valent, and J. Wirth, Boeing Airplane Co., Seattle, Wash., for the substituted aryl phosphines and oxides noted in Table I and the melting point data. LITERATURE CITED
(1) Abe, Y., J a p a n Analyst 9 , 795 (1960). (2) Abel, E. W., Nickless, G., Pollard, F. H., Proc. Chem. SOC. (London) 1960, 228. (3) Giddings, J. C., J . Chromatog. 4, 11 (1960). (4) Gudzinowicz, B. J., Smith, W. R., ANAL. CHEM.32, 1767 (1960).
( 5 ) Ibid., 33, 1135 (1961). (6) Henderson, W. A., Streuli, C. A.,
Buckler, S. A., Abstracts, p. 47-0, 137th Meeting, ACS, Cleveland, Oho, April 1960. (7) Lewis, J. S., Pa..ton, H. W., in “Gas Chromatography, V. J. Coates et al., eds., p. 149, Academic Press, New York, 1958. (8) Mao, T. J., Dresdner, R. D., Young, J. A,, J . Am. Chem. SOC. 81, 1020 (1959). (9) Rose, S. T., Denney, D. B., . ~ N A L . CHEM.32, 1896 (1960). (10) Shipotofsky, S. H., Moser, H. C., Ibid., 33, 521 (1961). (11) Stanford, F. G., J . Chromatog. 4, 419 (1960).
RECEIVEDfor review May 4, 1961. Accepted August 10, 1961. Division of Analytical Chemistry 140th Meeting, ACS, Chicago, Ill., September 1961. Work supported in part by the Air Research and Development Command, U.S. A.F., under Contract No. AF 33(616)6950.
Preparation of Methyl Esters of Fatty Acids for Gas-Liquid Chromatography Quantitative Cornpa rison of Methylation Techniques MARIE L. VORBECK, LEONARD R. MATTICK, FRANK A. LEE, and CARL S. PEDERSON New York Sfafe Agricultural Experiment Station, Cornel1 University, Geneva, N. Y.
b A quantitative comparison of four methods for the preparation of methyl esters of fatty acids for gas chromatography has been made. The reagents used were: diazomethane, methanolhydrochloric acid with sublimation, methanol-hydrochloric acid on ion exchange resin, and methanol-boron trifluoride. The data show that the choice of a methylation procedure depends on the nature and composition of the sample. The greatest variation among the methods occurred in the mixture of lower molecular weight acids. Esters of mixtures containing lower molecular weight acids are best prepared b y reaction with diazomethane. N o si,gnificant loss of polyunsaturated fatty acids was found as a result of treatment with diazomethane. The methods are comparable when only the higher molecular weight fatty acids are present. A method is presented for the analysis of complex mixtures containing low and high molecular weight fatty acids. The standard deviation of the method is &0.72%.
G
A5LIQUID
CHROMATOQRAPHY
Of
methyl esters provides a rapid and convenient method for analyzing fatty acids and the acidic moiety of complex
1512
ANALYTICAL CHEMISTRY
lipides. Procedures have been described (6, ?’, 9, 13) for the preparation of methyl esters from fatty acids and from the free fatty acids liberated from lipide material; however, little has been reported on the comparison of the various methods. To apply these methods to the analysis of unknown samples, data giving a quantitative comparison are essential. Diazomethanolysis is rapid, but it has been suggested that quantitative results may be poor where polyenoic acids are involved due to the formation of addition products of diazomethane a t ethylene bonds (pyrazolines) (8). Other procedures involve the use of anhydrous methanol containing a c a b alyst and refluxing for varying periods of time. After the addition of water, the esters are extracted with petroleum ether, Usually it is necessary to remove excess solvent prior to gas chromatographic analysis. In this investigation four methods for the esterification of fatty acids have been compared on a quantitative basis. The methods employed diazomethane (9); methanol-hydrochloric acid with microsublimation (19); methanol-hydrochloric acid on ion exchange resin ( 5 ) ; and methanol-boron trifluoride (7).
EXPERIMENTAL
Quantscation of Detector Response. Few reports have appeared
in the literature concerning quantification of the response of the highly sensitive ionization detectors. Esters used for quantification of the detector response were obtained from various commercial sources. Each standard was checked for impurities by gas chromatography. Peak areas were measured by triangulation. Calculations were made on the basis of mole per cent and weight per cent added. Preparation of M e t h y l Esters. Acids were obtained in guaranteed purity of 99% or greater. Butyric and valeric acids were obtained from Eastman Kodak Co., Rochester, h-. Y. Caproic, caprylic, myristic, palmitic, stearic, and oleic acids were obtained from Applied Science Laboratories, State College, Pa., and linoleic acid from the Hormel Foundation, Austin, Minn. The amounts of the various acids used were in the range of 20 to 30 mg. The most highly unsaturated acids of menhaden body oil were recovered according to the method of Stoffel and Ahrens (12). (The menhaden oil was supplied by Dr. T. Miller, Marine Chemurgics, Morehead City, N. C.) Five grams of menhaden oil were
