initial descent of W . A toothed wheel, U (Figure 2), against which the rubber face of a soft iron bar, N , is forced by a spring, acts as a brake which may be released by energizing the solenoids, GG. The pulley, spindle, and flywheel shafts are all ball-bearing mounted to ensure smooth operation. The electrical controls, housed in the steel chassis at the bottom of the apparatus, consist of a thyratron relay and stabilized power supply as shown in Figure 3. As long as contact is maintained between 2 and P, the thyratron, VI, cannot fire. (The secondary leads from T may have t o be reversed if the tube does not cut off when first tested.) Breaking this contact removes the bias and VI can pass a current through GG. Sz may be closed to hold the brake on n-hen refilling, etc. The voltage reference tube, Ti2, maintains a constant voltage, independent of line fluctuations, across the voltage divider, Rd, P I , Pz, and R. The values shon-n are for use with a 20-mv. Brown Electronik recorder (Brown Instruments Division, XinneapolisHoneywell Regulator Co., Philadelphia] Pa.) recording from left to right. Maximum voltage is fed into the recorder when the buret is full but as it empties and R is turned, the voltage is reduced (the contact on R moves upward in Figure 3). In the resulting recording the vertical axis represents the amount of solution delivered rather than the amount in the buret a t any time. PI is adjusted by means of a screwdriver, to give a total deflection to the recorder needle for total emptying of the buret. Once the buret has been calibrated, PI should not be changed. P f , on the other hand, adjusts the zero setting of the recorder, so is provided
with a knob for adjustment after each filling. The components on which the fidelity of the recording depends and their tolerances are as follows: Buret tube B is made of precision bore Pyrex tubing, l/4 inch &0.10/, inside diameter (catalog 30. 9600, Corning Glass Works, Corning, N.Y.). The ten-turn potentiometer has a linear accuracy to = t O . l % . The 5651 voltage reference tube maintains a potential of about 87 volts with a variation of less than 0.1 volt for normal line voltage fluctuations. The theoretical accuracy of this apparatus then should be 0.3%. To test this, the buret )vas charged with 0.liV hydrochloric acid and fed through a Radiometer Titrator (Welwyn International, Inc., 3355 Edgecliff Terrace, Cleveland 11, Ohio) into a beaker containing 500 ml. of distilled water. A 0.1N sodium hydroxide solution was leaked a t constant rate from a Xariotte bottle into the beaker and the level of solution kept a t a constant height by sucking off the extra liquid through a water aspirator. The titrator was set a t pH 7.00 and a recording made of the acid consumed as a function of time over the total range of the buret. This was repeated five times, giving six lines, none of which varied from linearity by more than 0.27, of the total volume of the buret, a value which should be the lowest limit of accuracy for the apparatus.
or two such determinations are sufficient. When alkali is used as the titrant, nitrogen gas or carbon dioxide-free air may be passed through the side arm, K , to prevent carbon dioxide diffusing into the solution. For weak electrolytes, such as acetic acid, for which the resistance of the solution is too high to operate the relay because of the distance between P and 2,both contacts may be brought in through P , so that they are about 1 mm. apart. Contact of the probe with the solution will then bridge this gap. The buret described has been in operation almost continuously for a year and has given a minimum of trouble, because of its simplicity of operation. A previous model operating with a motor was more complex, and, having a fixed speed, unable t o follow the wide varieties of titration rates it was called upon to record. The only disadvantage to the system is the stepwise motion of the recorder, which is determined mainly by the surface tension of the titrant-Le., the ease with which the meniscus pulls away from the probe. Because the platinum tip is relatively fine, these steps do not exceed 0.2% of full scale, and under optimum conditions they are less than the thickness of the pen line. ACKNOWLEDGMENT
Because the recording is linear, calibration is simplified. The easiest method of calibration is to fill the buret with standard acid and titrate a measured volume of standard alkali. One
The author wishes t o thank R. A. Latimer and B. L. Huston for their assistance in the development of this apparatus.
Direct Print Photographic Paper for Rapid Analysis of Paper Chromatograms Containing UltravioletAbsorbing Materials
.
Frank M. Ganis, Department of Biochemistry, University of Rochester School of Medicine and Dentistry, Rochester, N. Y. LTHOUGH
various
photographic
A methods have been utilized for ob-
taining permanent records of the movement of materials on paper chromatograms, the photographic films or prints of the paper chromatograms must be processed by development, fixation, and drying before being useful. When there are large numbers of chromatograms to be analyzed, or immediate reproduction of a chromatogram is desirable, the processing procedure takes more time and effort than the actual photography of the chromatogram. The method described offers the investigator an immediate print of a chromatogram without the delay or necessity of chemical processing. It has been used successfully in this laboratory for routine analysis of large numbers of chromatograms containing 2068
ANALYTICAL CHEMISTRY
quantities of ultraviolet-absorbing materials, particularly steroids, in the order of 5 y or more per square centimeter of paper. METHOD A N D DISCUSSION
The ultraviolet scanner-camera and the techniques employed to obtain prints of chromatograms are similar to those described by Haines (“Recent Progress in Hormone Research,” Vol. 7, pp. 255-305, Academic Press, KenYork, 1952). The following modifications were found essential. Over a thoroughly dried chromatogram is placed a sheet of Kodak Linagraph direct print single weight photographic paper which is exposed for 15 seconds t o 1 minute, depending upon the concentration of the chromatographed material. A 15-watt ultra-
violet lamp (General Electric germicidal lamp, G 15T8) is mounted approximately 25 em. from the filter glass. The photographic paper must be held in close contact 71 ith the chromatogram by a pressure plate cover. After exposure, the paper is removed and the latent image is developed by holding the emulsion side of the paper 18 inches from a 30-watt fluorescent bulb until a real image of a desirnble contrast is obtained. The development process is thus observed and overexposure compensated for by shorter exposure to the developing lamp. An underexposed print may be darkened by longer exposure to the developing lamp. The method allows for immediate observation of the development process and judgment of errors and correction of these errors, or for repetition of the printing process.
If the original exposure time is extended, development with the fluorescent bulb will not be required. I n this case a real image will immediately appear upon the Linagraph print. When nanow-strip chromatograms or chromatograms containing several limbs are photographed, it is desirable to cut a thin opaque mask to fit between limbs to avoid possible overexposure of the paper. The developed print image of the areas of the chromatogram containing ultraviolet-absorbing materials appears white to light gray in contrast to the darker background of the print. The print is then superimposed upon the original chromatogram and fractions of the latter are cut in subdued room light. Alternatively, the prints may he saved in a lighttight container for future analysis of the chromato-
grams or for reference. Further viewing of the print, however, should he done under subdued room light. Such prints will not serve as permanent records, as continued exposure to light will darken them. To secure permanent records, it is better to employ a high contrast paper to obtain prints of the paper chromatograms. The best print is obtained when the original chromatogram is exposed to Kodak Azo F-5 single weight paper for 1 second. The paper is developed with Versatol developer diluted l to 10 with water, fixed, and dried as usual.
Losses due to even 1-minute exposure of the ultraviolet-absorbing materials to the ultraviolet light are not significant if the paper is thoroughly dry before exposure. In no case is the loss greater than that which results from conven-
tional spot test analysis of representative strips of the paper chromatogram. ACKNOWLEDGMENl
The author would like to acknowledge with appreciation support received from Grant HF-6137 National Institutes of €Iealth, National Heart Institute. Thanks are also due to J. T. Groet, Graphic Reproduction Division, Technical Service Center, Eastman Kodak Go., Rochester, N. Y., for supplying information concerning the use of Kodak Linagraph direct print paper, and to W. F. Swann and W. T. Swanton, Industrial Sales Division, EastmanKodak Co., forgeneronsly supplying the photographic paper for this study.
Rapid Evaporation of Solutions in Test Tubes Charles E. Pierce and Theodore D. Perrine, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare, Bethesda, Md.
purification proceINdures, such asorcolumn chromatogANALYTICAL
raphy, a large series of fractions is often obtained. These fractions, as obtained b y an automatic fraction collector, usually consist of equal volumes of solution stored in individual tubes. The evaporation of the solvent from these fractions, which is often the prerequisite to further work, is tedious. To improve the efficiency of this operation, a number of experiments were carried out. The practice has been to warm the tube in a heated bath and blow a stream of gas into the tube, evaporate the liquid in vacuo, or use a combination of both. With many solvents, practical evaporation rates can be achieved only vhen one of these methods i s employed. With one of the more effective devices (R. R. Williams and T. D. Spies, “Vitamin B, and Its Use in Medicine,” p. 141, Maemillan, New York, 1938) it was possible to evaporate 10 ml. of water in 1 hour (at an unstated bath temperature). This required a fairly large gas stream, and experience shovs that it works best when the gas inlet jet i. continually adjusted to maintain the tip close to the liquid surface. Unless the gas stream strongly riffles the liquid surface, this method of evaporation is not efficient. Difficulty arises becanse the geometry of test tubes is such that the free liquid surface is small and bumping occurs readily. Radin [ANAL.CHEM.28, 542 (1956)l described an evaporator designed to overcome this. Experiments were designed to agitate or whirl the tubes so that the free sur-
face would he greatly increased and humping reduced. The methods included high and low speed rotation of the tube about ita axis, low frequency agitation, and slow rotation of a series of tubes symmetrically placed about an i n c h e d vertical axis. Only high speed rotation gave a film thin enough to prevent undesirable bumping unless the volume of the liquid in the tube was very small, in which case any of the methods was reasonably satisfactory. Unfortunately, the power requirements and heat generation necessary to operate a high speed rotary vacuum seal are such that high ~. meed rotation is not practical. A Eecond objection is that this type of motion, while i t produces a thin film, induces no movement. of the liauid relative to the tube wall, and hence produces a “dead” surface as opposed to the rolling surface found, for example, in a falling-film still. (The rolling surface can he obtained if the speed of rotation is continuously varied.) The Evapo-mix, manufactured by the Lahoratory Glass and Instruments Carp., New York 31, N. Y., is designed to oscillate a series of 10 tubes about an axis perpendicular to the axis of the tubes, at frequencies up to 125 cycles per second. This device can impart a rolling motion to the liquid similar to that obtained in a falling-film still, and has a centrifugal component which should Serve to minimize humping or spraying during rapid distillation. Theoretically, this should provide excellent evaporation rates, and tests indicate that within certain limits this type of agitation is satisfactory. ~
Figure 1. Evopo-mix showing springloaded tube holders and modified manifold and tube covers
The machine, as supplied, requires certain modifications to protect the sample from conta.mination. Other modifications have been made for convenience in use. (Figure 1). An improved model now availiable is much the same as the one described here, except for the stopcocks. Stopcocks are superior to pinch clamps, which are affected by instrument vibration. Also one does not always have 10 tubes to he evaporated a t one time. DESCRIPTION OF APPARATUS
The Evapo-mix machine consi rack to hold a maximum of 10 ti to u) mm. in diameter and 120 VOL. 30, NO. 12, DECEMBER 1958
