Gas Chromatographic Analysis of Nitriles IHOR LYSYJ Food Machinery and Chemical Corp., Chemical Research and Development Center, Princeton, A ,n attempt was made to resolve a mixture of close-boiling nitriles by gas chromatography. Single columns different in nature and length were tried without much success. During the experimental part of this work, it was observed that the order of elution of nitriles on a nonpolar column i s different from that on a polar one, and this phenomenon formed a basis for the technique described.
T
HE METHOD utilizes two modes of gas chromatographic separations. One is based on the separations obtained on a nonpolar column, where analyzed materials are resolved according to their boiling points. The other is based on the separations obtained on a polar column n-here order of separations is influenced not only by the boiling points of analyzed materials but also by the degree of their polarity. The stationary liquid phase of a polar column has a higher degree of affinity for the polar materials than for nonpolar and because of it retains the former to a greater extent than the latter. Two materials of different polarity. boiling a t approximately the same boiling point, can be separated gas chroniatographically if a stationary liquid phase of proper polarity is used. The complex mixtures containing materials of different polarity and boiling points can be analyzed if complementary separations on the nonpolar and polar columns are undertaken. Utilizing such complementary separations, mixtures of acrylonitrile, acetonitrile, methacrylonitrile and propionitrile were analyzed in less than 20 minutes.
N. J.
COLUMN COKDITIONS Polar h-onpolar Instrument Fisher Gulf Partitioner Cenco gas chromatograph Recorder Leeds & Northruu Sueedomax. 5- Same mv., speed i&h/min. Column 20% (w./w.) Carbomax 400 de- 15yo Craig polyester succinate posited in a conventional manner (Wilkers Instrument and Research Corp.) deposited in (1) on Chromosorb W 30 t o 60 conventional manner (1) on mesh size and packed under vibraChromosorb 30 to 60 mesh tion into a 12-foot long, '/r-inch diameter aluminum tube size and packed under vibration into a 24-foot long, '/,inch diameter aluminum tube Gas Helium, 100 nil./min. Same Temperature 70" C. 100" c. Sample size 0.01 ml. a t sensitivity 1.5 0.01 ml. a t sensitivity 6
The samples were injected in a conventional manner using a microliter hypodermic syringe for injection in the Crnco instrument and a constant volume capillary pipet for injection in the Fisher Gulf Partitioner. Table I indicates the order of elution and retention times for nitriles on the polar and nonpolar columns. The areas under the peaks were integrated using a polar planimeter, added and calculated in terms of area percentages for each chromatograph. The final calculation of composition of mixture n a s made as follows: propionitrile, average of per cent values rcpresented by last peaks of polar and nonpolar columns; methacrylonitrile, per cent value represented by the second peak of nonpolar column; acetonitrile, per cent value represented by the second peak of polar column; acrylonitrile, difference obtained by subtracting per cent value of acetonitrile (second peak polar column) from per cent value representelrl by the first peak of nonpolar column.
Table 1.
Retention Times of Nitriles
Polar Column (Carbomax 400) Retention Time, Minutes First peak Methacrylonitrile 8.1 (Double) Acrylonitrile 8.2 Second peak Acetonitrile 10.1 Third peak Propionitrile 12.0 Nonpolar Column (Craig Polyester Succinate) First peak Acrylonitrile 10.8 (Double) Acetonitrile 11.5 Second peak Methacrylonitrile 15.7 Third peak Propionitrile 18.2 Table 11.
Analysis of Synthetic Mixtures of Nitriles Pres-
ent, DifferWt. Found, ence, Compound % %a % Acetonitrile 11.0 11.9 -0.9 Acrylonitrile 23.4 24.8 +1.4 Methacrylonitrile 41.9 39.8 - 2 . 1 Propionitrile 23.7 23.4 -0.3 0 Results represent duplicate analysis.
A synthetic mixture containing all four nitriles was analyzed (Table 11). The gas chromatographs obtained on polar and nonpolar columns are presented in Figure 1. Figure 1. columns
Separation of nitriles on polar and nonpolar
Peaks in order of appearance Carbowox 400 (methacrylonitrile and acrylonitrile, acetonitrile, propionitrile) Craig polyester succinate (acrylonitrile and acetonitrile, methacrylanitrile, propionitrile)
-
----
LITERATURE CITED
(1) Keulemans, A. I. M., '(Gag Chromata aphy," p. 60, 2nd ed., Reinhold, New Fork, 1959. RECEIVED for review December 29, 1959. Accepted March 2, 1960. VOL. 32, NO. 7, JUNE 1960
0
771
