reagent renders the chromatogram unsuitable for further analysis by overspraying with other reagents. By using the method described here no background colors are obtained. The chromatogram may be oversprayed with ninhydrin or other amino acid reagents, after sufficient time has been allowed for dissipation of the gaseous reagents from the paper. Only solvents
of the phenolic type interfere with the test and must be completely removed from the paper before gassing is attempted. An extensive study of the problem of removing phenolic types of compounds from paper has not been made. The last traces of phenol on air-dried paper strips can be removed without disturbing the tyrosine spot by washing the paper with ether that is
undergoing continuous extraction with an aqueous solution of a strong inorganic base. All other naturally occurring amino acids, with the exception of tryptophan, do not react. Tryptophan gives a weak test. The tyrosine derivatives 3,5diiodotyrosine, glycyltyrosine, tyrosine ethyl ester, and tyramine, all give strong positive reactions.
Transfer Cell for Gas Chromatography Douglas S. Russell and Marven E. Bednas, National Research Council, Ottawa, Canada
w;
RE the amount of s:imple is 1’ei-y imited (as in the study of photochemical kinetics), the whole sample must be transferred ynantitntively from a vacuum manifold to a commercial chromatographic unit. No convenient means of accomplishing this is recorded in the literature. Samples have been transferred by one of two methods: The chromatographic column mas connected directly to the system for which it was required or :t sample was drawn into n syringe or gas pipet and transferred a t atmospheric pressure. The former is not feasible for a general-purpose analytical instrument; the latter requires excess stmple a t atmospheric pressure. Simple and inexpensive transfer cells have been designed for this purpose. They may be easily made from two vacuum stopcocks and a hypodermic needle, attached with porcelain cement.
T o fill the cell from the vacuum manifold, the upper stopcock is turned so that the right arm of the cell may be evacuated. Then the sample is frozen into it by pouring liquid nitrogen into
P the cup. The cell is disconnected from the manifold, emptied of liquid nitrogen, and warmed to room temperature. Then with the stopcocks as illustrated, the carrier eas from a n auxiliarv line is flushed t h o u g h the extremiGes of the cell in order to remove the air. If
air does not interfere with the analysis of the sample, the cell may be simplified by omitting the left arm and employing simple vacuum stopcocks. With the carrier gas still flushing, the needle of the cell is inserted into the serum stopper of the column. The upper, then the lower, stopcocks are turned through a half turn to allow the sample to be swept into the column. Only a few seconds are necessary for a complete transfcr. The lower stopcock is closed :trid the needle is withdrawn. The cells may he made any size. For the authors’ purpose, a 1-ml. cell (10 cm. of tubing, 4 mm. in internal diameter) was ideal. Capillary tubing (1-mm.) was used in the extremities and the left arm to minimize the flushing time. The additional T in this arm is to evacuate the bulbs of the vacuum stopcocks. As little as 10-6 mole of sample has been transferred quantitatively with this design of cell. ACKNOWLEDGMENT
The authors are indebted to R. J. Cyetanovic for his helpful suggestions regarding the design of this cell.
Improved Contact Printing Frame for Ultraviolet light Absorbing Compounds Separated on Paper by Chromatography or Electrophoresis David S. Kinnory and Joseph Greco, Radioisotope Service, Veterans Administration Hospital, Hines, Ill., and Department of Biochemistry, Stritch School of Medicine, Loyola University, Chicago, 111.
ultraviolet light-absorbing propT erty of some compounds, like purines, pyrimidines, and their derivatives, HE
is useful in locating them after separation by paper chromatography or paper electrophoresis. Spraying the paper with a dye or a reagent which results in formation of a colored compound is avoided and the isolated compounds can be eluted from the paper in unchanged form, when needed for further investigation. A permanent record of the separation or identification of such compounds can be obtained by the ultraviolet light contact printing method suggested by Markham and Smith [Riochem. J.
1562
ANALYTICAL CHEMISTRY
294 (1949)l. A chromatography paper sheet containing spots of ultraviolet-absorbing compounds is held against a film and exposed to ultraviolet light. After developing, the film shows a black background with white spots where it was covered by the ultraviolet-absorbing compounds and shielded from ultraviolet light. The success of this printing method depends on correct exposure time and close contact between film and chromatography paper. A convenient way to assure a predetermined exposure time is to have the ultraviolet lamp operated by an automatic timer. Close contact between film and chromatography paper
45,
can usually be obtained by pressure. With ultraviolet photography, however, no ultraviolet-absorbing material (including glass) can be employed. Quartz sheeting is expensive and in such large dimensions unfeasible. Use of a nylon netting suggested by Crestfield and Allen [ANAL. CHEM. 27, 422 (1955)] leaves a definite and distracting net pattern on the film. For this reason, the contact printing frame suggested by Markham and Smith has been improved to accomplish close contact between the entire chromatography paper and film by downward tension against a curved surface. The frame is constructed of stainless
