Preparation of Volatile Carbon-1&Labeled Compounds for Counting Robert
H. Hamilton and
Donald E. Moreland, Field Crops Department, North Carolina State College, Raleigh, N. C.
OLATILE Cl4-labeled compounds are difficult to handle in GeigerNuller and proportional counters. Reproducible results cannot be obtained because of losses from planchets during storage and counting. The technique to be described greatly reduces losses from planchets during storage and eliminates contamination of counting chambers and windows. It reduced the volatilization of a C14-labeled herbicide, 2-chloro-4-isopropylamino-6diethylamino s - triazine (ipazine), and a C14-labeled nematocide, 0,Odiethyl - 0 - 2 - pgrazinylphosphorothioate (Zinophos), from counting planchets. The method conceivably can be employed with other radioactive, volatile, organic compounds. One-inch diameter, sand-blasted, glass planchets were plated initially with 0.25 pg. of CI4-ring-labeled ipazine in 10 X of absolute ethyl alcohol and with 1.15 p g . of C14-ethyl-labeled Zinophos in 10 X of hexane. Counting was performed with an aluminized-Mylar (1
-
mg. per sq. cm.), end-window, gas-flow, Geiger-Muller tube. Volatilization of C14-ipazine and C14Zinophos from uncoated planchets occurred rapidly and showed similar trends for both chemicals (Figure 1, lower curve). Since uncoated planchets could not be counted directly without contaminating the counting chamber and end window, acrylic plastic was applied to duplicate planchets a t the indicated times prior to counting. The activities measured were subsequently corrected for absorption by the plastic film with the relationship developed in Figure 2. All planchets were kept in a hood a t room temperature (30" C.) for 24 hours to restrict contamination evolving from the uncoated planchets. After 24 hours, coated planchets were stored in a constant-temperature room (22" C.). Planchets were coated with a clear acrylic plastic applied from a pressurized can. (Seymour's KO. 121, Seymour of Sycamore, Inc., Sycamore. Ill., was used, but Clear Finish KO. 54-115, Pittsburgh Plate Glass Co., Pittsburgh, Pa., was equally effective.)
100
The density thickness of the film was obtained by weighing tared planchets 20 minutes after application of the plastic. The weight of film applied to the planchets ranged from 0.4 to 0.8 mg. per sq. cm. Planchets coated a t zero time lost only a minor amount of activity in 72 hours (Figure 1, upper curve). Loss was delayed considerably, but was not completely eliminated. Twenty-eight days after the plastic was applied, the CI4-ipazine and C14Zinophos planchets had retained 88.9 and 82.9%, respectively, of their initial activities. At the end of 90 days, the residual activity measured 86.4y0 for ipazine and 79.6y0 for Zinophos. Effects of the thickness of the acrylicplastic coat on the relative activities of C14-labeled ipazine, Zinophos, and sodium carbonate are shown in Figure 2. Data for the figure were obtained by successively applying light coats of acrylate, weighing, and counting paired planchets for each of the chemicals. This sequence of operations was repeated four times. The radioactivity after each coat was divided by the uncoated activity (or the activity after one coat for the volatile chemicals) to obtain the relative actirity The ipazine and Zinophos planchets were coated immediatply after evaporation of the solvent, and the activity after
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Figure 1. Effect of coating with an acrylic plastic on loss of C14-2-chloro-4-isopropylamino-6-diethylamino-s-triazine (-0-) and C14-0,0-diethyl-O-2-pyrazinylphosphorothioate (-X-) from glass planchets
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0.8 1.6 DENSITY OF A C R Y L A T E (rnp./sg.crn.)
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Figure 2. Effect of the thickness of acrylic plastic on the relative activity of C14-labeled 2-chloro-4-isopropylamino6-diethylamino-s-triazine (-0-); 0,O-diethyl-0-2pyrazinylphosphorothioate (-X-); and sodium carbonate
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=-I VOL. 34, NO. 6, M A Y 1962
717
this initial coat was assumed to equal full activity. Consequently, density thicknesses shonn for the volatile organic rhemicals have had the weight of the initial coat subtracted (0.27 t o 0.48 mg. per sq. cm.). This mas the only way an initial activity determination could be made due to the volatile nature of the chemicals. The manipulation appeared t o bc valid since the rcxlationship brtn cen activity and thickness \vas linear to about 2.2 nig. per sq. c m . for both ipazine and Zinophos. A fimilar linear relationship was obtained for the low-volatile C'"ringlabeled 2-chloro-4,6-bis(ethylamino)-striazine (simazine), n hen full activity could be rrprwented by an uncoated
planchet. The absorption curve for C14-Zinophos (Figure 2 ) is essentially identical Ivith the one for ipazine. The absorption curve for sodium CI4-carbonate has a much steeper slope. Thc difference in slope may be attributed to solubilization of the labelrd organic chemicals in the constituents of the plastic aerosol preparations, v-hich resulted in a uniform dibtribution of the materials throughout the plastic coat. Sodium carbonate would probably be insoluble in the plastic solvents. and thus the ontire coat thickness nould hare to be penctrated by the 0-radiation from Ka2C140,. l h e sanic tcchnique has been used successfullj- w t h a n-indon-less propor-
tional c l-:L:nbcr and aluminum planchets (1.25 i n c ~ h cdiameter). ~ ACKNOWLEDGMENT
Thc authors are indebted t o the Geigy Chemical Corp., Ardslcy, S . Y., and the American Cyanamid Co., Stamford. Conn., for supplying the C1'-ipazine and the C'4-Zinophos uscd in this sturl:~. Support of this investigation by the Sational Cotton Council of iiiiic,rica and the Geigy Chemical Corp. is gratefully acknoivledged. COOPERATIVE investigations of the Crops Resenrch Uivision, Agricultural Research Service, U. 8. 1)epartment of Agriculture, and the Sorth Carolina -4gricultural Esperiment Station.
A Rapid Method for Volume Calibration Roy F. Putnam,' Stauffer-Aerojet Laboratories, Nimbus, Calif. for calibratanalytical vacuum systems either iiivolvc. filling the areas n-it,li known ainounts of mercury ( 1 ) or introducging a iwiglicd quantity of gas ( 2 ) . Khile thew iiictliods are quite a r ~1cmi tc, the in:] iiipu llt ions involved rcqi:irc. cwicider iI)k time atid are impracticd if tlil- volumcs nre frequently altcJrld. I n this 1.ihor tory a procedure originally ticvclopcd for the calibration of giiq cliromatopraphy sample loops h- s bctcn c~stc~iirlt~cl t.1 include volume dc~tcmiiri~ tions ot tlic incorporated v:ivuuu:-liii(> :I r i d the attached sample coiitaincrs. l'lic methncl descrihed in this 11!~)cr consicltwbl!. ciccwases the tiiiw involved. 7-ct it maintains the rcquiiwl accurac 7HI.: ACCEPTED 1II:THODS
1ing volumw in
column tcmperature of 60" C. calibration of peak area 2's. sample volume is obtained by injecting known samples (atmospheric pressure) of pure, dry, carbon dioxide into the chromatograph xith a highly accurate gas syringe. Corrections for temperature and baronietric pressure arc then applied. The system volume or the sample container to be determined is attached and evacuatrd to less than 10 microns. The volump is filled n ith carbon diovide gas, and the pressure is accurately measured. ;\fter isolating the caoiitainer and evacuating the system, thr carbon dioxide is transferred to the> sample loop which is immersed in liquid nitrogen. When the transfer i i coin-
pletBe,thc loop is isolated and allon.cd t o reach ambient temperature. The gas is then introduced into the gas chromatograph, and the peak area is rrcorded. Sin(*(. a direct rclationship exists hctn-ccii the recordrd peak area and thc molos of gas introduced from the cont'ainers. the 1.oluine is easily det'ermined. If tlic quaiitit!. of carbon tlioside injected for c:dibration and the quaiitity from the containers arc of the same order of magnitude, the volume can easily be rcyroduced n-ithin ~ k 0 . 2inl. Although rnrbon dioxide n-as used for iw, light h yd r o w rbons nbthis 1~rnc,c~l
APPARATUS r .
1h? q,pn;'atus consists of a Locnco
g a i clii~omatog:~a~ili, Jlodrl 1.1 (Lot, Enginwring r o . , .\lt:itlcna, Calif. 1, used in cwijunrtion \\.it11 a coniplet(~ gas
KI -3 disk intvgrator was used. Thr ( >h m n s tog1 ai 1hj. (dunin, p:ic ked \vith 20- t,o BO m w h silicas gc.1. was 6 fcet in lc~iigtli :ind cwistruc*tcd of inch 0.d. colq~cr tubing. Figure 1 shows the? vacuum nianifold and sample ucstion systc,ni. A\ny commercial ml'ling val\-c, hon-cwr, can c.asily lie incor~ior:it,c~l into this :irrangcment.
GLASS
TO E T AI. SEA.
PROCEDURE
The gas chroniatograpliy unit is -)10 crated in the convcntional manner IT ith a helium flow of 200 ml. per minutc and 1
Present
address,
Aerojet-General
Corp., Solid Rocket Plant, Sacramento,
Calif.
718
ANALYTICAL CHEMISTRY
Figure 1.
Vacuum manifold and sample introduction system
