Channels ratio quench correction curve

Using the data obtained from samples 1 to 4, the known number of 14C disintegrations per minute added to each of these samples, and considering the counts per minute data obtained from the widest window as a reflection of overall counting efficiency (the total possible number of counts per minute that can be detected in each sample), construct a channels ratio quench correction curve similar to that shown in Figure 3-9. 

Figure 3-17. Channels ratio quench correction curve. This curve was constructed using the sample and discriminator settings described in Figure 3-16. (Courtesy of Beckman Instruments, Inc.)...

Figure 3-20. External standard channels ratio quench correction curves. These data were obtained using the procedures outlined in steps 3-50 to 3-57 of the experimental section.

Fignre 3-39, Channels ratio quench correction curves for C and H. 

The following channels ratio quench correction curve was obtained for C... 

Figure 3-9 Channels ratio quench correction plot for 14C. Quench correction data may curve slightly up or down depending on the make and model of counter used.

The radioactivity of samples was measured by liquid scintillation with toluene+POPOP or with Triton X-100 (Isocap-300).Counting efficiencies,determined via the channel ratio method and quench correction curve,were sufficiently constant (about 70-80%).Gas exchange measurements of respiration of leaf were conducted by manometric tech-nique(9).It was found that the chosen concentrations of exogenous substrates had no effect on dark respiration of leaves studied plants. 

Once these standard curves have been prepared the multiply labeled sample may be counted in the presence and absence of the external standard. The counting rate in channel B (cpm C). and the channels ratio value may be used in conjunction with the quench correction cutve (Figure 3-20) to calculate the absolute dpm of C using equation 3-24. 

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