Validation of a Multiwell γ-Counter for Measuring High-Pressure Liquid Chromatography Metabolite Profiles

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FIGURE 1.
Simulated HPLC curve resembling an early ¹¹C-flumazenil plasma sample. The curve was generated using a ⁵⁷Co stock solution. Shown is the mean cpm for 55 repeated measurements together with the SD corresponding with each measurement. (SD bars are almost invisible as they are the same size or smaller than the size of the circles).
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FIGURE 2.
Plot of the mean (n = 55) minimum and maximum cpm values for a simulated HPLC curve resembling a late ¹¹C-flumazenil plasma sample. The curve was generated using a ⁵⁷Co stock solution. Shown is the mean cpm for 55 repeated measurements together with the SD corresponding with each measurement.
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FIGURE 3.
Measured cpm as a function of the volume of ⁵⁷Co in 1.5 mL for 2 concentrations of ⁵⁷Co stock solution. The cpm values for the low-activity curve are on the right y-axis, and those for the high-activity value curve are on the left y-axis. All samples were counted in the same well with a counting time of 1 min for each sample. The correlation coefficients for the lines were 0.99868 and 0.99986 for the low- and high-activity curve, respectively.
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FIGURE 4.
Measured cpm as a function of the absolute amount of radioactivity (kBq). The insert shows an enlargement of the low-activity range.

TABLE 1

Repeated Well Counter Measurements of Background Levels and a ¹³⁷Cs Source

TABLE 2

Well Counter Reproducibility for Simulated (Flumazenil) HPLC Metabolite Curves (55 Repeated Measurements)