I
placed on the glass plates. At the end of 4 to 5 hours, the drops had changed completely to hard gel deposits slightly larger in diameter than the original spread liquid drops. The gel deposits were quite uniform in thickness. Under the microscope they were seen to consist of numerous adherent flakes of irregular shape but of roughly uniform size. This reticulated feature is caused by the shrinkage of gel on drying. The deposits readily adsorb trypaflavine from aqueous solution. Aqueous solutions cause some flaking off of the deposits. Hydrocarbon solutions of other dyes, however, do not cause these deposits to flake off. Silica Gel Coating. The second general method of silica gel plate preparation was one of coating glass by use of silica sol A, B, or C. The spin-dryer shown in Figure 1 was effective for the desired coatinp. A clean glass plate dipped in silica sol was placed in the receptacle of the spin-dryer and spun for 10 minutes. A very thin uniform coating of silica gel was spread over almost the entire area of the glass plate, with excessive deposits appearing only at the corners. The more concentrated the sol, the greater should be the spinning speed for uniform coating. Concentrated sols give coatings which adsorb more dye per plate. The pH of aqueous solution has a strong influence on the degree of adsorption from that solution. For example, trypaflavine is not adsorbed from 2.5 x l 0 P M solution with a pH of 4, but is adsorbed from 10WMsolution with a pH of 6.
SPECTRAL RESULTS
The t~ypaflavine in cellophane was tested by its carbon-arcexcited phosphorescence in vacuo. Although this phospnorescence was bright, it was not quenched noticeably by oxygen until the oxygen pressure exceeded 1 torr. These plates were considered unsuitable for the intended study (4) of trypaflavine phosphorescence which is sensitively quenched by oxygen. The trypaflavine adsorbate in the silica gel deposits was tested for phosphorescence excited by carbonarc radiation. Under vacuum, the phosphorescence was bright and was quenched by very small pressures of oxygen (millitorrs in magnitude). ACKNOWLEDGMENT
This work toward the author’s Ph.D. thesis was conducted at the University ofMinnesota and Lawrence College. R ~ c ~ ~ v ~ ~ f o r rMay e v i 11,1972. ew AcceptedJuly28,1972. (4) J. J. Sjoblom, Dim. Abstr., 16(4), No, 15,959 (1956).
A Simple Disposable Teflon-Capped Reaction Vial Robert L: Wolen filly Laboratory for Clinical Research, Marion Counfy General Hospital, Indianapolis, Ind. 46202
WITHTHE INCREASING use of derivatization in gas chromatographic procedures and the increased chemical reactivity of derivatizing reagents, a need arises for an inexpensive simple Teflon (Du Pont fluorocarbon resin) -capped reaction chamber. A number of screw-capped vials with Teflon-lined caps are available, as are special reaction vials with Teflon-lined caps. We have found these useful but relatively expensive, and they exhibit some difficultyin washing because of size and shape. We have devised a method utilizing inexpensive vials and Teflon tape in a manner making the cost per unit low enough to effecta single use of the vial a practical reality. The procedure utilizes ampoules (Kimble Ampoule No. 12012-L) of appropriate volume, that are sealed with a double layer of tightly stretched Teflon sealing tape (Applied Science Laboratories, Inc.), (Figure l), of the type used as a sealant with threaded fittings. The ampoules are well adapted to solvent drying under a nitrogen stream and, following addition of derivatizing reagents, to incubation in a heating block (Figure 1). Their shape facilitates refluxing of volatile reagents during heating, while the Teflon tape serves as an adequate flexible seal which will not permit pressure to build up and create an explosion hazard should the block temperature control fail. In recovery of the derivatized material, the user has the choice of using a Pasteur pipet or long needle syringe to recover material at the bottom of the intact ampoule, or of breaking the ampoule at the constriction and using a syringe equipped with a short needle. The Teflon covering is readily pierced, negating the need for its removal. The technique has been successfully utilized in the derivatization of amines with highly reactive acid anhydrides and other 2418
Figure 1. Illustration of technique described. Front: (left to right) Teflon (DuPont flnorocarbon resin) tape; vial; sealed vial. Rear: Typical incubation setup similar reactions requiring heating of the reaction mixturf during derivatization. The total cost per unit including cost of the tape and am poule varies from 3.5 to 5 cents each, depending on type quantity, etc. This cost is low enough to make disposal afte use practical.
RECEIVED for review July 27, 1972. Accepted September 11 1972.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
