Simple Liquid Scintillation Counting of 14C02 To determine the rate of "COX uptake in photosynthesis experiments we employ an extremely simple method that is suitnblo for class use. While 'similar t o the methods of other workers' ours does not require any speeinl equipment or visl caps other than s scintillalion counter. A 10-ml gas sample is taken from the photosynthesis chamber with a syringe having a 5-em lung number 25 needle. The sample is slowly expelled into a vial coniaining 10 ml scintillation solution (0.4% PPO and 0.017, POPOP in t o h e n e ) aud 0.1 ml Hyamine 10-X. Approximately 90 sec is required t o expel1 10 ml gas ss a gentle flow of bobbles. Thevials are immediately ready for counting. The resulbs of a t,ypieal photosynthesis experiment are shown in Figure 1. To test the accuracy of this method ten 10-ml sl~mpleswere taken with nn ordinary syringe from a chamber containing "CO. but not any plauts. The average count was 42,022 cpm; t h e coefficient of variahiliby was 1.77, (S.1). 697). Even better repeatability should be possible with gas-tight syringes. A diagram of our chambers, made from Plexiglas, is given in Figure 2. T o obtain a tight seal we use a 5-em wide flange an t h e lower section and a closed cell rubber easket. 1 CUPPY,D. AND CRI:YASSK, L., Annlyt. Bioehem, 5 , 462 (1963). G o o ~ n r x P. , A N D S N Y D F., ~ , Analyt. Bioehem., 4 , 310 (1962). WOE> m:a, F. II., Analgt. Hioehcm., 2 , 508 (1961). GORDON,B. E., LUKISNS, H. It., JR., A N D TI:.% IIOVE,W., Internal. J . Appl. Rad. Isotopes, 12, 14.5 (1961).
m-.
fl,....~ . .
Figure 1. " C 0 2 decrease during photosynthesis. 2 5 0 ps " C 0 1 was released into a 40-1 chornber containing four plants.
Figure 2. Diogram of photosynthesis chamber. chromstoThe graphic septa for taking gas rompler and adding solutions ar well or the ride ports for Aurhing the chornber have beenomitted.
Volume 46, Number 3, March 1969
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