Functional Group Analysis in Gas Chromatography SIR: The gas chromatographic analytical scheme of Hoff and Feit ($) brings the vapor of the sample to be analyzed into contact with classification reagents. It is limited in its applicability to compounds with boiling points up to about 200' C. We present a more general method for the identification of the functional groups present in mixtures of acids, alcohols, aldehydes, esters, and ketones in which the sample need not be vaporized and which, therefore, can be applied to compounds with much higher boiling points even in presence of low boiling solvents. EXPERIMENTAL
Reagents. T h e classification reagents used were sodium borohydride (saturated solution in ethanol), po-
Procedure. The liquid reagent (0.5 pl.) was spread b y means of barrel action onto the wall of a 10-p1.
tassium permanganate (satmurated solution in acetone), sodium hydroxide (saturated solution in ethanol), a n d methanol with 517, boron trifluoride.
Table I.
Hamilton microsyringe.
One micro-
Classification Reagents and Conditions for the Reaction
Exposure time Reagent (minutes) Effect of reagent Saturated ethanolic sodium borohydride 2 Reduces carbonyl compounds and produces corresponding alcohol Saturated acetone soln. of potassium 10 Oxidizes aldehydes to carboxylic acids, permanganate primary alcohols to aldehydes or acid and secondary alcohols to corresponding ketones Saturated ethanolic sodium hydroxide 15 Hydrolyzes esters and produces corresponding alcohols Methanol/517, BFI 5 Esterifies acids to corresponding methyl ester
Table 11.
Per Cent Recovery and Classification Chart
Column after reaction Initial column
Compound Acids Oxalic acid Malonic acid Succinic acid Glutaric acid Adipic acid
Boiling Pt. 150 sub d. 235 d. 304 d. 26510°
Column and temp. Acid" column 180-200" C. temp. programmed
Retention time, minutes
Classification reagent
Column and temp.
decom- hIeOH/BFa LBCb column pose 4.1 5.6
l75O C.
Retention time, minutes 1.8 2.8 3.5 4.9 7.0
Identity of new peaks Dimethyl Dimethyl Dimethyl Dimethyl Dimethyl
oxalate malonate succinate glutarate adipate
Conversion into new Decrease comof original pound, peak, % 5% 60-70 60-70 6G70 60-70 60-70
60-70 60-70 60-70 60-70 60-70
Pimelic acid 272Ia0 7.1 9.5 Dimethyl pimelate 60-70 60-70 Suberic acid 279loo 13.1 Dimethyl suberate 60-70 60-70 8.7 1" C./30 seconds Azelaic acid 10.7 1 8 . 1 Dimethyl azelate 60-70 360 d. 60-70 25.1 Dimethyl sebacate Sebacic acid 295100 13.1 60-70 60-70 Ketones 2-Decanone 156 11.9 17.8 2-Decanol 100 80-90 156 10.2 3-Decanone LACb 80-90 16.0 3-Decanol LACb 100 156 column 4-Decanone column 8 . 9 NaBH4 80-90 15.2 4-Decanol 100 2-Octanone 173 3.4 80-90 5 . 7 2-Octanol 100 2-Nonanone 195 5.5 115' C. ll5O c. 80-90 6 . 9 2-Nonanol 100 Cyclohexanone 156 4.3 80-90 5 . 7 Cyclohexanol 100 Aldehydes %-Hexaldehyde 137 LAC5 2.6 LACb 4 . 4 1-Hexanol 100 80-90 n-Heptaldehvde 4 . 3 iYaBH4 column 155 column 7 . 2 1-Heptanol 100 80-90 n-Octaldehyae 163 7.5 11.7 1-Octanol 100 80-90 n-Nonaldehvde 13.0 190 19.1 I-Nonanol 100 80-90 n-Decaldehyde 22.8 208 90" c. 114' C. 31.5 1-Decanol 80-90 100 Alcohols 1-Decanol 231 LBCb 31.5 LAC5 1 1 . 7 n-Decaldehyde 80-90 50 2-Decanol 210 column 17.8 KMn04 column 11.9 2-Decanone 50 80-90 3-Decanol 210 16.0 10.2 3-Decanone 80-90 50 4-Decanol 210 15.2 115" C. 115" C. 80-90 8.9 4-Decanone 50 1-Nonanol 213 19.1 80-90 6 . 4 n-Nonaldehyde 50 1-Octanol 195 11.7 2 . 8 n-Octaldehyde 80-90 50 Esters 2-Decyl butyrate 1308 L.4Cb 6.3 5 . 0 2-Decanol 80-100 80-100 n-Decyl butyrate 1358 column 10.4 NaOH LACb 11.1 1-Decanol 80-100 80-100 n-Octyl heptoate 290 lk0 column 80-100 4 . 6 1-Octanol 80-100 116" C. 10.2 4-Decyl hexoate 190so >130° C. 4 . 6 4-Decanol 80-100 8.0-100 4-Decyl valerate 290 7.0 4 . 6 4-Decanol 80-100 80-100 80-100 80-100 n-Butyl decoate 123 10.0 ... . . .c a 5% Isophthalic acid 5% Carbowax on acid washed embacel. 10% Diethylene glycol adipate linked with pentaerythritol on EmButanol coincided with ether peak (the solvent used) at this temperature. bacel. 0
VOL. 38, NO. 13, DECEMBER 1966
1961
liter of an approximately 0.1% ether solution of the sample was then introduced into the syringe and left to react the appropriate time depending on the reagent used, as indicated in Table I. The sample was then injected into a gas-liquid chromatograph. Instruments. Two flame ioniaation chromatographs were used in our work: for the acids, a Pye Series 104 Model 4 and, for all the other compounds, a Perkin Elmer F11. I n the Pye machine where samples were injected straight into the column, a 0.25-inch 0.d. 4-fOOt glass column
was used. The packing was 5y0 isophthalic acid 5% Carbowax on acid washed Embacel (1). I n the Perkin Elmer machine a glass tube was fitted into the injection port; the 0.25-inch 0.d. 2-meter copper tube was packed with LAC 2R-446 (10% diethylene glycol adipate linked with pentaerythritol on Embacel). These columns remain stable and useful for about 500 injections and are renewed when the retention time of standard samples begins to change. I n both cases nitrogen was used as carrier gas a t 7 5 ml. minute.
RESULTS
A summary of the results of analyses carried out in this laboratory is shown in Tables I and 11. LITERATURE CITED
(1) Clarke J. R. P.! Fredericks, K. M., J . Gas dhromatog. in press. ( 2 ) Hoff, J. E., Feit, E. D., ANSL. CHEM. 36, 1002 (1964).
K. M. FREDRICKS
ROBERT TAYLOR Imperial Chemical Industries Ltd. Petrochemical & Polymer Laboratory Runcorn Heath Runcorn, Cheshire
A Simple Versatile Collection Programmer for Preparative Gas Chromatography Bruce H. Kennett, Commonwealth Scientific and Industrial Research Organization, Division of Ryde, N.S.W., Australia
for the automatic collection of material emerging from a preparative gas chromatograph may be considered to have two distinct parts. The function of one part is to govern the timing for changing the collection traps, and the other part is the actual trapchanging mechanism. Two methods in general use for automatically actuating the trap-changing mechanism utilize, respectively, either a switch fitted to the recorder and actuated by movement of the recorder pen, or mechanical or electronic timers preset to operate at the required times. Both methods have limitations, the first lacking flexibility when collecting components that are either not well resolved or are minor constituents in a complex mixture, while simple electronic or mechanical timers, though they may be programmed to any chosen pattern, are generally limited by the number of set points available on them. Examination of food volatiles in this laboratory involves the use of preparative gas chromatography to separate the complex mixtures into fractions which are then examined on high resolution columns. However, since the relative concentration of the coniponents in the volatiles from frozen peas was found to extend over a range of at least 10,000: 1 the recorder-actuated switch used to effect trap changing on an available Aerograph Autoprep ‘705 was not applicable, and the present programming system was therefore developed. The effectiveuse of the programmer is dependent on reasonable reproducibility of replicate chromatograms, and the Autoprep 705, whether isothermally
Food Preservation, P.O. Box 43,
QUIPMENT
1962
ANALYTICAL CHEMISTRY
Figure 1. 1. 2. 3. 4. 5. 6.
Tape drive
Sensing head (see Fig. 2) Tape Drive roller Pressure roller Fixed idler rollers Adjustable idler roller
operated or temperature-programmed, has given acceptable reproducibility. The programmer is operated by driving a continuous loop of punched tape around a set of rollers (Figure 1). The holes in the tape correspond to the injection and trap-changing points transcribed directly from a chromatogram of the material under investigation. When a punched hole corresponding to a trap-changing point passes through the sensing head (Figure 2), it actuates the trap-changing mechanism. Similarly the punched hole corresponding to the injection point either initiates injection of another sampIe, or, with gas chroma-
tographs having inbuilt automatic repetitive injection systems, causes the tape to pause until the next sample is injected. The drive roller 3 (see Figure 1) is machined to give tl tape speed identical with the recorder chart speed, and is attached to the shaft of a 10 r.p.h. motor. The pressure roller 4 is made from brass rod sleeved with soft rubber tubing, pressure being applied by a helical tension spring, Fixed idler rollers 5, together with an adjustable idler roller 6, allow the use of different lengths of tape; up to 3 meters can be accommodated in a space of 20 X 25 cm.
