INSTRUMENTATION
instrument abstracts
Cary Applied Physics
Corporation/Pasadena/California
Cary Vibrating Reed Electrometer simplifies C14, H 3 and S 3 S determinations
alternately opened and shut, in effect, reducing the reagent flow rate. W h e n the p H reaches the final end point, a pair of contacts in the p l l detector trig gers t h e stepping switch and t h e titra tion t a p closes finally. 9. T h e follower searches up the buret, and when the light beam reaches t h e level of the t o p of t h e titrant, t h e variation in o u t p u t of the photocell caused by t h e meniscus gives a signal to stop t h e follower, whose travel is simul taneously registered on t h e recorder chart, and t h e stepping switch is triggered back to its starting point. T h e sequence numbers given above do n o t correspond with the stepping switch positions: it is a 25-way t y p e . Some positions have been left unused for the addition of further actions if required. T h e sequence can be varied a t will, making the equipment very flexible in application. Titromatic Analysers can be supplied with interchangeable glassware in the following sizes: Sample flask. To measure from 1 to 100 ml. Water flask. To measure from 25 to 250 ml. Buret. To hold 25 or 50 ml.
DETECTS A S LITTLE A S 1 0 1 2 C U R I E S - T h e
high sensitivity and high precision of the Cary Model 31 Electrometer p e r m i t m i n i m u m a m o u n t s of costly "tagged" materials to be used in radio active isotope studies, saving enough to pay for the instrument in a short time and materially reducing the hazard to living experimental subjects. This greater sensitivity, plus the de velopment of simplified experimental procedures, make the Cary Model 31 particularly valuable in determination of C u and H 3 in biological and chemi cal samples. W i t h t h e s e n e w tech niques, the smaller samples may be used and the use of a precipitate with its inaccuracies and time-consuming preparation is eliminated. Instead, sam ples are directly converted into a gas which can be measured with an ioniza tion chamber and a Cary Model 31. The ionization chamber and vibrating reed electrometer offer the only conve nient accurate method of measuring radio-activity of COs-air mixtures in flowing systems, such as are encoun tered in ίη-vivo studies. One research group led by Dr. Bert M. Tolbert has had considerable suc cess in applying these procedures to a wide variety of samples and research problems, including studies of animals N E W R E V I E W PAPER
Dr. Tolbert, now at the University of Col orado, has authored a 46-page paper cover ing d e t a i l e d p r o c e d u r e s for C 1 4 a n d Tritium assays, ionchamber theory, samples and sample preparations, combustion of organic compounds to CO2, design and conFor further infonnation, circle number 62 A
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ANALYTICAL CHEMISTRY
struction of ion chambers and meas urement of ion chamber currents and approximate calibration data. Copies of the paper are available from Technical Reports Section, Department of Com merce, Office of Technical Services Washington 25, D. C , for 35 cents each. When requesting a copy, please ask for Bulletin UCRL-3499. OTHER USEFUL A P P L I C A T I O N S
Measurement of radioactivity is only one of many applications where the Model 31 can be used advantageously. Amplification and measurement of ion currents in mass spectrophotometry, p H determinations, measurement of e l e c t r i c a l p r o p e r t i e s w h e r e precise measurement of small charges, cur rents, or voltages from a high imped ance source is required, can all be made faster, simpler, less expensively and far more accurately using the Model 3 1 . BRIEF SPECIFICATIONS OF THE M O D E L 3 1 Accuracy —Measurements reproducible to within 1 % . Accuracy limited only by the accuracy of the recorder, potentiometer, or meter used. R e l i a b i l i t y - N o grid current, greater freedom from zero drift. Much more rugged than other types of electrometers. Stability —Open circuit input; less than 6 χ 10-' 6 coulombs rms short period noise; less than 5 χ 1 0 " amperes steady drift. Short circuit in put; less than 0.02 mv rms short period noise; less than 0.2 mv per day steady drift. 10 standard ranges —Ranges provided on the Model 31 are 1, 3, 10, 30, 100, 300, 1,000 mv, and 3, 10, 30 volts. The output of the Model 31 will operate a 1 ma recording milliammeter or a standard recording potentiometer. Accessories —Ionization chambers, recorders and various special modifications and accessories are available for all types of electrometer uses.
A new catalog on the Cary Model 31 is available. Write for your copy today to Applied Physics Corporation, 362 West Colorado St., Pasadena 1, California. Ask for Data File A9-117. 62 A on Readers' Service Card, page 83 A
T h e accuracy of the titration can be held a t ± 1 % for a 24-hour period, for a n y b u t the smallest volume. W i t h these very small quantities t h e accu racy will be lower. Alternative gearing for t h e follower drive is provided, so t h a t the recorder scale can represent either t h e full length of the buret, or only a quarter of this length. T h e follower is provided with limit switches to prevent it from travel ing too far. T h e range of the analyser (end point setting) can be adjusted between p H 2 t o 12. T h e end point anticipation has a m a x i m u m a t approximately p H 4. T h e sequence cycle can be varied between 1 and 100 ml., diluent volume between 25 and 250 ml., and the b u r e t either 25 or 50 ml. T h e end point anticipation feature permits good accuracy and reproduci bility is of t h e order of ± 0 . 0 2 5 ml. of t i t r a n t . Inasmuch as this seems to be a fixed error, over-all precision can be deduced from the choice of original sample volume and concentration of the titrant. T w o Unit Assembly T h e a p p a r a t u s is fitted into two separate, matching cubicles, 6 feet 2 inches high, connected by multicore and coaxial cables. T h e cubicles are free-standing steel cabinets, with a pro tective finish. T h e y have air-tight panels and doors and are fitted with connections for air purging. Other external connections required are the
