bility on the Kave length scale is not affected because the wave length setting can be checked before each run. The pens are stored partly submerged in colored writing ink. For this purpose 0.8-em. holes are drilled centrally in the screw caps of the ink bottles; under each cap is fitted a rubber washer with a 0.2-cm. central hole for the pen and another small hole for an air leak. In this way the pens are prevented from drying out and kept loaded with ink. Unlike the pen supplied with the instrument, the glass pen described seldom blocks. Khen it does, the blockage is removed by flushing with water. Although it has been possible to test these pens only nith the Model DK-2 spectrophotometer, no doubt they could be used with any similar instrument.
1
PEN
r ?
PEN
-
SPECTRO PHOTOMETER
POINT OF NARWING
MICRO BURNER
PEN CARRIAGE
1
\ /
'-/
,
-
Figure 1. Formation of capillary tip on glass pen
Figure 2. Glass pen ottached to pen carriage
Device for Measuring Rf Values Robert
v
L.
Clements', Department of Agricultural Biochemistry, The Ohio State University, Columbus, Ohio
have been used for the rapid determination of Rfvalues on paper chromatograms. The following instrument is particularly useful for small chromatograms, but larger versions can be constructed to accommodate papers of any size. The device does not cover the paper during measurements; thus notations can be made directly on the chromatogram. It is easily constructed, and a high degree of precision is possible without special machining or engraving. ARIOCS DEVICES
The instrument consists of a rigid right angle with a straight pointer pivoted a t the end of one leg and a decimal scale laid out along the other. The scale, A, is positioned along the vertical leg, so that the zero point lies on the upper edge of the horizontal leg. The pointer, B , is pivoted from a point, C, which lies on the upper edge of the horizontal leg, and is located one scale length from the vertical scale-i.e., 2 = y. A small sliding indicator, D, is attached to the horizontal leg, and a reference line, E, is engraved through the pivot parallel to the scale. In use, the slide indicator is first set so that the distance, f, from the slide to the pivot is equal to the frontal distance. This may be done by measuring off the distance by superimposition, or by placing the upper edge of the horizontal leg on the starting line of the Chromatogram, setting the pointer t o R , = 1, and setting the slide t o correspond to the point a t which thp pointer crosses the front. Readings are then made with the upper edge of Present address, Department of Plant Biochemistry, University of California, Riverside, Calif. 160
ANALYTICAL CHEMISTRY
the horizontal leg on the starting line of the chromatogram, and with the slide indicator at the point of application of the sample. The pointer is positioned over each spot (resulting from that particular application) and the corresponding R f values are read from the points at which the pointer crosses the scale. When there is a slope in the solvent front, Rfvalues may be determined by adjusting the slide indicator for each application (as though it were an individual chromatogram). The instrument can be modified for measurement
of distances on chromatograms on which the solvent front has been allowed to run off the paper and a value based on a reference compound is used -e.g., Rglucose. For this application the decimal scale should extend t o 2.0 (or greater, as dictated by the particular case). The slide indicator distance, f, would then be set with the pointer a t 1.0 on the scale for the particular reference compound. The existing models were constructed of aluminum, but any rigid material should suffice. The pointer consists of
A. Decimal scale
-
Chromatogram
-
Front
-
Starting line
a strip of transparent plastic with a line engraved lengthwise through the center of the pivot, and with a metal bushing inserted a t the pivot to prevent wear and consequent loss of alignment. The sliding indicator was also constructed
of aluminum, and secured by spring action or a set screw. For small chromatograms (with a frontal distance of less than 10 inches), the scale consists of a 10-inch strip of graph paper inscribed with 10 lines per inch. For a
larger instrument, a longer strip of appropriate graph paper can be adapted, or a meter stick or photographic enlargement of a 10-cm. scale can be used. The author is indebted to Harold Krohne for the illustration.
Water-Curtain Enclosure for Spraying Paper Chromatograms E. C. Fiebig and H. Siegel, Shell Development Co.,Emeryville, Calif.
compounds are frequently S detected on finished paper chromatograms by spraying the paper with EPARATED
color-forming reagents. When reagents are sprayed, inherent hazards such as toxicity are increased because they are dispersed in air. The area in which the spraying is carried out becomes coated with unsightly stains and undesirable and sometimes dangerous chemical deposits. A water-curtain enclosure for spraying paper chromatograms has been designed to minimize such hazards and contamination. A flowing film of water, maintained on all surfaces of the enclosure exposed to the spray, has proved effective in trapping and washing away in a diluted state a variety of reactive and intensely colored spray reagents, both aqueous and nonaqueous. Aqueous reagents include ammoniacal silver nitrate (S), potassium permanganate (d), and 2,Pdinitrophenylhydrazine in 30% perchloric acid (4). Trifluoroacetic acid in ether (5) and an ethanolic solution of benzidine ( 1 ) are examples of nonaqueous spray reagents. This enclosure is particularly recommended when reagents which leave dangerous or noxious residues are used, as they are continuously removed by dilution. The water-curtain enclosure is usually in a conventional laboratory hood. It can be located on a standard laboratory bench if hazardous spray reagents are not employed. The watercurtain enclosure described is portable and of convenient size. The basic design can be scaled up or down to meet individual needs. The water-curtain enclosure consists of a stainless steel cabinet, A, 30 inches high, 7 inches deep, and 16 inches wide across the open front. The sides taper to a back width of 12 inches. The sides and top of the open front have a 0.5-inch lip, B; the bottom has a 2-inch lip to confine the flowing water. The top panel has five holes, 1 inch in diameter, for ready venting of vapors when the enclosure is installed in a conventional laboratory hood. A metal baffle, C, is supported from the top, so its saw-toothed edge (25 teeth per inch) presses firmly against
the sides and back of the enclosure to distribute the water over the vertical surfaces. The water is supplied to the metal baffle through a copper tube, D, which is perforated along its length (l/la-inch holes, inch apart). The enclosure is lined with glass cloth, E , whose edges are fused with a gas torch to minimize fraying. The upper edge of the glass cloth is held by the metal baffle, and when the glass cloth is wet, it adheres closely to the vertical surfaces. Attached to the base is a 3/4-inch copper tube coupled with a rubber hose to conduct the run-off water to the laboratory drain, F . The bottom panel of the base is tilted for better drainage of the water.
Two clamps, G, are mounted on the rear vertical panel of the enclosure to hold the rectangular metal frame, H , used for supporting the paper chromatograms. The frame has a fixed width of 10 l/z inches, but its length can be adjusted to accommodate paper chromatograms up to 20 inches long. DISCUSSION
I n early attempts to establish a water curtain over the vertical inner surfaces,
the perforated copper tube did not provide even and continuous distribution of the water. Satisfactory distribution of the water was achieved by using the serrated metal baffle described. Difficulty was encountered in securing a continuous film of flowing water on the stainless steel. Etching the surfaces with aqua regia provided surfaces which remained wet when sprayed with aqueous reagents. When nonaqueous reagents were used, dry spots developed on the surfaces of the enclosure which were difficult to rewet. The glass cloth surface, finally adopted, remains wet even when sprayed with nonaqueous reagents, so that a continuous flowing film of water is maintained. Water and sewer are the only laboratory services required. In use, a continuous film of water is established a few minutes after the water is turned on. Very little attention is required to maintain the film in a satisfactory condition. The efficiency of the water-curtain enclosure for trapping spray was not measured. Such experiments would involve the construction and efficiency of spray guns. However, the efficiency of the watercurtain enclosure is believed to be high when the geometry of the setup is considered. In usual chromatographic technique, the spray gun is held about 6 inches from the paper chromatograms. 4 small gun is generally employed which delivers a fog of about 2 inches in diameter a t this distance. Finally, the water curtain has a tremendous rate of flow of water relative to the rate of spraying. LITERATURE CITED
J. L4., Smith, F., .%SAL CHEM.26, 1113 (1954). (2) Drummond, A. Y., Waters, W. -4., J. Chem. Soc. 1953, 435. ( 3 ) Hough, L., Nature 165, 400 (1950). ( 4 ) Neuberg, C., Grauer, A,, Pisha, B. V., Anal. Chim. Acta 7,238 (1952). (5) Siegel, H., Bullock, A. B., private (1) Cifonelli,
communication.
VOL. 30, NO. 1, JANUARY 1958
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