Reduction of Current Fluctuations in the Farrand Spectrofluorometer Delmar J. Mahler and Fred L. Humoller, Medical Research Laboratory, Veterans Administration Hospital, Omaha 5, Neb., and Harold G. Beenken and Ronald D. loch, Cardio-Vascular Research, University of Nebraska College of Medicine, Omaha, Neb.
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RECEXT
years spectrofluurometers,
1 such as the Farrand Model 104243
(Farrand Optical Co., Inc., Bronx Boulevard and East 238th St., New Tork 70, N. Y.), have found increasing use in determinations of minute quantities of serotonin, 3-(2aminoethyl)-indol,%ol, epinephrinc (adrenaline), and similar fluorescing substances. T o obtain the necessary sensitivity, the manufacturer h a incorporated into thr instrument a microammeter capable of measuring 0.0002 pa. However, this high sensitivity was not fully utilized because it was accoinpanird by random fluctuations of the meter. When the batteries supplying the potential for the multiplier phototube and the nniineter (RCA ultrascmitive direct current microainmet~r) w r e replaced with line-operatcd components, the in4rument operated nithout hindrance from random fluctuations. A11 batteries of thc instrument were eliminated in two step‘ to make it fully line operated. First Beckman Ilt- pon-er supplj- ( T k k m a n Instruments Inc., Fullrrton. Calif.) was used 3s 3 source of voltagc for the phototube. Although otlicr line-operated power supplies may also provide satisfactory service. thP Reckinan power supply was chowi hcc:ius? fJf previous
favorable experience with it in this laboratory. The Beckman unit was modified with relative ease to supply
Figure 1 . Circuit diagram for adapting Beckman power supply to Farrand spectrofluorometer
the phototube voltage for the Farrand spectrofluorometer. Two Amphenol
receptacles were mounted in the end (opposite the lamp terminals) of the Beckman Power Supply cabinet and ired as shown in Figure 1; it is recommended that deposited carbon low noise precision resistors be used. The existing cord and plug from the phototube was then connected to the AN 3102 A-22-14S receptacle and the ammeter. Secondly, a Keithley hIodel 410 micromicroammeter (Keithley Instruments, Inc., 12416 Euclid Avc., Cleveland 6, Ohio) \\as utilized. This amnicter has the advantage over the original meter in that it is line operated and has 20 ranges covering 10 decades from 10-3 to IO-’3 amperc. Therefore, it adequately compcrisntes for the reduction of the original power supply of 900 to 640 volts supplied by the Beckman unit. The Keithley micromicroammeter nas connected to the 83-1R receptacle by means of RG/U coaxial cable containing a polyethylene inner insulation. The modifications describctl here markedly improved the operation of the Farrand spectrofluorometer. Meter needle fluctuations of the original instrument ranging from 20 to 30% of full scale nere reduced to 1 to 2% of full scale in the modified system.
Differential Thermal Analysis and Simultaneous Gas Analysis C. B. Murphy, J. A. Hill, and G. P. Schacher, General Engineering Laboratory, General Electric CO., Schenectady, N. Y.
thermal :inalysis most often requires coupling with other analytical techniques, to provide meaningful interpretation of thermograms. X-ray diffraction and thermobalance itudies have been most frequently used to augment differential thermal data. Although instrumentation has been described that provides simultaneous thermogravimetric and differential thermal data (S), general practice is to resort to separate instrumental techniques. Difficulties are cncountered using separate techniques because of different heating rates, atmosphere control, etc. Not2 and Jaffe (2) have pointed out difficulties in correlation of differential thermal
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ANALYTICAL CHEMISTRY
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TO VACUUM PUMP-
Figure 1. Differential t h e r m a I a n a Iy s i s adapted for gas sampling
GAS SAMPLE DLEADoUT*T
3.WAY j
G E.THERMOC0UPLE VACUUM GAUGE TUBE
SAMPLING MANIFOLD
GAS SAMPLE COLLECTION B E L L JAR FURNACE
D.T& SAMPLE H O L M R
I M A NU F A C T ~ 0E BV STONE CCll
and therniogravimetric analyses reactions in the decomposition of uranyl sulfate and uranium trioxide, Although an “air atmosphere” was employed in both cases, the nature of the
gas in direct contact with the samples was markedly different. This condition was responsible for a shift in thermal decomposition temperature for the same reaction.
