US EPA

8359676 

Journal Article 

Gas-liquid chromatography of the volatile components of onions 

Carson, JF; Wong, FF 

1957 

2 

4 

D-115 

English 

Gas-liquid chromatography columns were constructed from metal tubing, 5 ft. in length and 4.6 mm. internal diameter, coiled to fit into a Dewar vessel containing a heating fluid. Helium was used as the carrier gas and changes in the composition of the effluent gas were detected by a katharometer with two filaments maintained at the same temperature as the column. The design followed that described by Dimick and Corse (J. Food Technol. 10 , 360 (1956)) except that stainless steel rather than copper was used throughout. A number of liquid stationary phases were investigated with particular reference to their performance in the separation of aliphatic mercaptans, sulfides and disulfides. Apiezon M, Silicone SF 96-40, polystyrene glycol, octyl-phenoxypolyethyleneglycol and polyethylene glycol ("Carbowax") were studied. For the separation of saturated from unsaturated sulfides or disulfides, octylphenoxypolyethylene glycol and polyethyleneglycol were the most suitable. These materials separated completely a mixture of dipropyl disulfide, allyl propyl disulfide and diallyl disulfide at 140°C. with no evidence of decomposition, retention times increasing with degree of unsaturation. With polystyrene glycol, the retarding of unsaturated sulfides and disulfides was less pronounced and satisfactory separation could not be obtained. With Apiezon M or silicone, the order of emergence was reversed and followed the boiling points, but separation of saturated from unsaturated sulfides or disulfides was not complete. Volatile components of onions were isolated by steam distillation in vacuo through activated carbon followed by elution of the adsorbate with ether and stripping of the ether with a fractionating column. Gas-liquid chromatography of the oil on a polyethylene glycol ("Carbowax" 1540) column (I. D. 4.6 mm) at 140°, flow rate 45 cc/min. of helium, gave peaks for a minimum of 16 different components. Of these, di-n-propyldisulfide, methyl-n-propyl disulfide (two of the major components) and dimethyl disulfide have been identified by both chemical and physical methods. The finding of di-n-propyl disulfide confirms the recent reports of Niegisch and Stahl (Food Research 21, 657 (1956) and corrects statements in the literature that allyl propyl disulfide is the major component. Several of the other peaks are known to contain sulfur compounds but their identity has not been established.