10.3.3 Dynamic Flow HPLC-RFD
A dynamic flow radiodetection technology has been recently developed to
enhance the performance of the stop-flow RFD (Lee, 2006). The new Dynamic
Flow device (AIM Research Inc,) employs a dynamic flow mode added to the
original stop-flow RFD system. The dynamic flow mode operates at a
consistent HPLC flow rate, while the ratio of liquid scintillation cocktail to the
HPLC flow rate varies. As a result, the total flow rate in the radiodetection cell
varies. A decrease of the total flow rate in the RFD detection cell increases the
counting time of a radioactivity peak. Therefore, radiodetection sensitivity of
the dynamic flow RFD is improved. Figure 10.6 shows comparison of
radiochromatograms from the analyses of the conventional HPLC–RFD
versus the dynamic flow HPLC–RFD. A sample with a total radioactivity of
130 DPM was analyzed separately using the nonstop mode or the dynamic flow
mode with the same run time (26 min). The dynamic flow RFD analysis clearly
detected two major radioactivity peaks (Fig. 10.6b), while the RFD failed to
detect any radioactivity components (Fig. 10.6a). Dynamic flow HPLC–RFD
(actual run time: 26 min)
(actual run time: 26 min)
Bkg
0.00 2.00 4.00 6.00 8.00 10.0012.0014.0016.0018.0020.0022.0024.0026.0028.00
0
20
40
60
80
100
120
140
160
ChA(CPM) Sample: RP3014_6hr NSF, Vial: 16, Inj.# 1
Min
1
2 3
Bkg
0.00 2.00 4.00 6.00 8.00 10.0012.0014.0016.0018.0020.0022.0024.0026.0028.00
0
10
20
30
40
50
60
ARC(CPM) Sample: RP3011_3hr, Vial: 13, Inj.# 1
Min
Nonstop method
Dynamic Flow method
Applied: 130 DPM
Applied: 130 DPM
FIGURE 10.6 Analysis of radiolabeled metabolites using HPLC-RFD (top panel,
nonstop mode) and dynamic HPLC-RFD (bottom panel). The same amount of sample
was injected, and the total HPLC run times were the same in both analyses.
300 APPLICATIONS OF LIQUID RADIOCHROMATOGRAPHY TECHNIQUES