Photoelectric Fluorimeter RICHARD P. KREBS1 AND H. J. KERSTEN Department of Physics, University of Cincinnati, Cinoinnati, Ohio
T
HE alternating ourrenboperated fluorimeter shown in Figure 1 attains its sensitivity b y t h e use of vacuum photocells whose current is amplified by a n electronically stabilized feedback amplifier of conventional design, similar to t h s t described by Krebs, Perkins, Tytell, and Kersten (1). An ultraviolet lamp housed in s cylinder open at both endv (C, Figure 1) provides the baht which msses throwh four 0.47 X 2.5em. X 1 inch) vertioal slits and emerges Tn the direo-
tion of the white arrow. The cells for holding the liquid whose fluorescence is t o be determined are sumorted on two ulatforms of a n "elevator". One cell is shown in Dosition a t 6 and the ,
position a t D. b;re of the two windows through which the fluorescent light passes is shown at H and the other is opposite it. ~~~~~~
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with thk instrument. 82 is closed; after about a minute S1 is
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the platform at E. The door~isclosed i n d t h e meterb'rought t o zero by turning rheostats R12 and RQ (one is for coarse and the other for fine adjustment). Next, cell G is raised to a position formerly occupied by the one'on platform E by means of rod A which slides without rotating in tube B . The readinl. of the meter will then indicate anum-
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FIQQEE 2. DIAGR~M OF C U N N E C T I ~ N ~ 132
ANALYTICAL EDITION
February 15, 1943
133
The ultraviolet lamp is a Westinghouse BH-4, 100-watt with a natural red-purple bulb. A special transformer and socket for the lamp are also needed. The filters are Corning 5 em. (2 inches) square, polished; those used for the curve shown in Figure 3 were No. 4308, 3.14 mm. thick, and No. 3389, 1.51 mm. thick. The cell used for Figure 3 had a capacity of 25 ml. and was made of glass with one window of ultraviolet transmitting glass to permit a larger amount of the ultraviolet light to enter the liquid. Many liquids will fluoresce enough to give satiefactory readings when ordinary glass cells are used.
Acknowledgment I
0.I
0.3
0.2
MICROGRAMS
0.4
PER CC.
0.5
FIGURE3. GRAPHOBTAINED WITH FLUORIMETER T-SIYC. QVIKISESVLFATE IS 0.1 N SCLFERIC ACID T74C29 choke, 2'1, 283; 7'2, 2A3; T3, 12SJ7; 2'4, VR-105-30, 7'5, 523; T6, R. C:. A. 929; T7, R.C. A. 929;. T8, 12J7-GT. 7'9, 12SF5. See Figure 2 for diagram of connections.
T h e writers wish t o acknowledge the assistance of members
of t h e Department of Biologlcal Chemistry of t h e University of Cincinnati, who carefully prepared all t h e solutions used in testing t h e fluorimeter.
Literature Cited R. P., Perkins, Patricia, Tytell, A. A , and Kersten H Rev. Sci. Instruments, 13,229-32 (1942).
(1) Krebs,
A Constant Pressure and Flow Ratio Regulator for Continuously Mixing Two Gases N. L. HEIKES', Shell Development Company, Emeryville, Calif.
A
FLOW regulator was required which would introduce two components of a gas mixture into a reaction chamber at a constant predetermined ratio of flows and a constant reaction pressure, regardless of variations in reaction chamber pumping speed, rate of chemical reaction, initial pressures, and differential consumption rates of reactants. The following system meets these requirements, and while it was designed for flows of each gas in the range 0.40 to 20.0 cc. per second at 50 t o 200 mm. of mercury, it should be equally applicable t o other flow and pressure ranges. T h e design is such t h a t sparking regulator contacts are not exposed t o t h e mixed gases. T h u s even with a pair of gases which form a n inflammable mixture, there is no danger of spark ignition. A constant flow ratio is maintained on the principle that the ratio of flows through two resistances will remain constant regardless of changes in absolute values of pressure or flov, providing t h e ratio of t h e mean pressures remains constant. For a reactor feed system, where the reactor pressure is the common final pressure of the two gas inlet systems, this condition can be readily maintained b y establishing and maintaining a n equality of pressures between the inlet lines at some other point, for the ratio of mean pressures in t h e lines between this point and the reactor thus remains cons t a n t at 1. This can be accomplished by a control U-tube manometer.
Description A schematic diagram of the flow system and the electrical circuits is shown in Figure 1. The control manometer, F , has two fixed elertrical contacts on one limb. Valves A and B between the limbs of manometer F and the florvmeters, Jf and Q, provide the desired adjustment of ratio of resistances in the lines between F and the reactor. E is an open manometer, for control of presjure; it has a movable double contact arm in the open side. The contacts are slightly displaced vertically in E 1
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and F . Both manometers are sufficiently long to allow evacuation of any portion of the system, and both have a third contact sealed into the bottom. All manometer tubes should be a t least 10 mm. in inside diameter to prevent excessive sticking of the mercury meniscus. Manometer F is filled with mercury to a position midway between the contact points when both sides are balanced, The motor-driven valves C and D , details of which are shown in Figure 2, are a modified form of the valve described by Fowler ( I ) , and consist of a thin-walled brass tube, flattened and bent into a U. The valve is opened or closed by expanding or contracting the U by means of a rotating lead screw. For other flow ranges, different sizes of tubing from that shown will be necessary. An ordinary needle valve is satisfactory for the higher flow speeds. The lead screw of the U-type valve, or the stem of the needle valve, is turned by a 4 r. p. m. Telcchron motor, Type C2M. By reversing one of the pole pieces in each of the Telechron motors, the motors can be made to turn in either direction. The choice of valve operating speeds will be governed mainly by the resistances of the connecting gas lines and by the volume of the reactor. These lines should be as short as possible for the most rapid compensation without hunting. In the present system, it was necessary t o place the reactor about 360 cm. (12 feet) from the control apparatus and to make the lines of 0.6-cm. (0.25-inch) inside diameter tubing; thus, a rather slow valve operating speed was required. The reactor had a volume of about 500 ml. These figures may serve as a starting point for the selection of speeds for other conditions. Parts 1, 2, 3, and 4, in Figure 1, are battery-operated relays which require not more than 20 milliamperes current to energize, and have load capacities of 0.2 ampere. Double-pole doublethrow relays are used for 1, 2, and 4, and a single-pole doublethrow relay for 3. Part 6 is a double-pole double-throw switch with a neutral, or "off", position, for changing from manual to automatic control of the valves. Group 7 consists of four double-pole single-throw push-button switches for manual control of both motors in either direction.
Testing the Circuit T h e circuit may be tested b y shorting manometer contacts, as indicated in Table I, and observing the response of the valves.
