Dielectric Percentage Saturation Detector E. J. Gelb and S. N. Steen L. S. G. Industries Corp., P.O.Box 928, Valley Station, Wayne, N.J. 07470 100
PERCENTAGE SATURATION is defined as the percentage ratio of the existing weight of vapor per unit weight of vapor-free gas to the weight of vapor that would exist per unit weight of vapor-free gas if the mixture were saturated at existing temperature and pressure. In reference to water vapor, the measurement of humidity may be accomplished by wet and dry bulb thermometry for static streams but for process stream analysis the expensive lithium chloride detectors and others are usually used. These devices are only for humidity determination, whereas the detector presented here has unlimited capabilities. By using the physical property of the dielectric constant of water vapor and its proportionality to capacitance change in an air condenser, a relatively inexpensive adiabatic per cent saturation detector was constructed. This detector is capable of many common industrial saturation analyses, such as solvent recovery in extraction processes. We are limiting ourselves, at this time, to the presentation of scientific data on its use as a per cent humidity device.
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Sensing cell Reference cell 20 pf silvered mica C4,s 1000 pf molded mica 8 mfd 450 V electrolytic C6 Inductor 28 turns with iron dust core L1 Same as L1 but with cathode tap 8 turns from BL, Ml 1 mA meter movement Ri 51K ohm 5% 1/2w 5lOK ohm 590 1/2w 33K ohm 5% 1/2w 51 megohms 5% 1/2w 10K ohm 5% 1 w lOOK ohm variable gain pot 1 w 10K ohm 5% 4.7K ohm 5% 1/2w 1/2w lOOK ohm 5% 4.7K ohm 5% 1/2w 51K ohm 5% lj2W 990
ANALYTICAL CHEMISTRY
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This method invulving the measurement of a change in the capacitance of a condenser is not new (1-3). The dielectric constant of water vapor is greater than that of oxygen, nitrogen, helium, carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen sulfide, methane, etc. Thus water vapor may be readily determined in the presence of the above gases. A simple circuit was designed and the reference cell of the detector filled with the gases to be normalized at their existing temperature and pressure. Upon changing the water vapor
(1) J. Griffith and A. Phillips, Analyst (London), 77, 897 (1952), (2) D. Turner, Nature, 181, 1265 (1958). (3) D. Winefordner, ANAL.CHEM., 33,515 (1961).
concentration in the sensing condenser, correlation of the percentage humidity was determined. The detector was separated from the electronic circuit and could be placed in a process stream at temperatures up to 300 “C and pressures up to 100 psi gauge. The detector exhibited a linear dynamic range of 0.5 to 90.0% humidity (at 25 “C, 1 atm) as typified in Figure 1. A response time of less than one second was recorded for the drift-free amplifier unit shown in Figure 2. The analysis is nondestructive, and the detector shown in Figure 3 is independent of changes in temperature and flow of the stream. RECEIVED for review December 3, 1968. Accepted January 29, 1969.
An Improved Procedure for Solid Scintillation Fluorography of Tritium Labeled Compounds Kurt Randerath The John Collins Warren Laboratories of the Huntington Memorial Hospital of Harvard University at the Massachusetts General Hospital, Boston, Mass. 02114
AUTORADIOGRAPHY of paper and thin layer chromatograms is an important analytical tool in many chemical and biochemical studies involving compounds labeled with a2P,35S, and particularly 14C. The standard autoradiographic technique is, however, 500-1000-fold less sensitive for 3H than for 14C. Because of their short range, only a few per cent of the primary @-particlesof tritium emerge from the surface of the chromatogram. Further losses occur not only in the gap between chromatogram and film, but also in the film itself because the range of the 3H @-particles in the film is shorter than the average distance between the silver halide grains. Organic and inorganic scintillators have been used to convert the energy of the 3H @-particlesto light, which in turn produces an image in the film (liquid or solid scintillation fluorography) (1-4). Although most literature data are not directly comparable, the sensitivity reported for procedures of tritium autoradiography and fluorography that permit the subsequent recovery of the compounds is 0.1-0.3 pc/cm2/day (5, 6). Sensitivity is increased to 0.03 pc/cm2/day if the chromatogram itself is treated with an X-ray emulsion, a procedure that precludes the recovery of the labeled compounds (6). This note describes a novel simple procedure for solid scintillation fluorography of 3H-labeled compounds. Its sensitivity is 0.006-0.008 pc/cm2/day. The technique has been applied so far only to 3H-labeled nucleotides and their derivatives separated on cellulose (Eastman 6064 sheets) (1) A. T. Wilson, Biochim. Biophys. Acta, 40,522 (1960). (2) E. V. Parups, I. Hoffman, and H. R. Jackson, Tahnta, 5, 75 (1960). (3) U. Liithi and P. G. Waser, Nature, 205, 1190 (1965). (4) S. Prydz and K. S. Skammelsrud, J. Chromatogr., 32, 732 (1968). ( 5 ) G. S. Richardson, I. Weliky, W. Batchelder, M. Griffith, and L. L. Engel, ibid., 12, 11 5 (1963). ( 6 ) J. Chamberlain, A. Hughes, A. W. Rogers, and G . H. Thomas, Nature, 201, 774 (1964).
and PEI-cellulose (7) thin layers, but there is no reason why its applicability should be restricted to this class of compounds or to cellulose-based thin layers. EXPERIMENTAL
A 7% (w/v) solution of 2,5-diphenyloxazole (PPO) in diethyl ether is rapidly poured over the entire chromatographic area and is distributed evenly by tilting. This operation should take no longer than 2-5 seconds depending on the size of the layer. The chromatogram is then immediately brought into a vertical position and allowed to dry for a few minutes. The volume of the PPO solution used for this treatment is 40 pl/cm2--i.e., 16 ml for a 20 X 20-cm layer. The layer is covered with Kodak RB-54 Royal Blue Medical X-Ray film and placed between two glass plates which are held together firmly with adhesive tape. Exposure is carried out in an insulated box over dry ice (-78.5 “C) in the dark for a few hours to a few days. The film is developed with Kodak Liquid X-Ray Developer and fixed with Kodak Liquid X-Ray Fixer according to the specifications of the manufacturer. RESULTS AND DISCUSSION
The sensitivity of this procedure was found to be 0.0060.008 pc3H/cm2/day. On one-dimensional thin-layer chromatograms (spot area 0.3 cmz) 0.002-0.003 pc3H can be clearly visualized after exposure for 24 hours. The sensitivity depends on (a) the concentration of the scintillator, (b) the solvent in which the scintillator is applied to the chromatogram, (c) the mode of application of the scintillator, (d) the temperature during the exposure, and (e) the film material. Because a systematic study of these factors except for (d) (3),has not been reported in the literature, we have (7) K. Randerath and E. Randerath in “Nucleic Acids,” vol. XI1 A of “Methods in Enzymology,” S. P. Colowick and N. 0. Kaplan, Eds., Academic Press, New York, N. Y., 1968, p 323. VOL. 41, NO. 7, JUNE 1969
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