Kill two birds with one stone: Analysis of [¹¹C]choline and [¹³N]ammonia with a single HPIC method

Introduction: [¹¹C]Choline and [¹³N]ammonia are widely used drugs for positron emission tomography (PET) imaging of recurrent prostate cancer and cardiac sarcoid/myocardial perfusion, respectively. Given their short half-lives and requirements for current Good Manufacturing Practice (cGMP) compliance, a robust and facile analysis is required for quality control. Both European and US pharmacopeias suggest using distinct methods for [¹¹C]choline and [¹³N]ammonia analysis, which requires two separate analytical systems with routine [¹¹C]choline and [¹³N]ammonia productions. In this study, we developed a single high pressure ion chromatography (HPIC) method for both [¹¹C]choline and [¹³N]ammonia analysis.

Methods: HPIC setup with shared column, mobile phase, suppressor, and conductivity and radioactivity detectors was employed for the analysis of both [¹¹C]choline and [¹³N]ammonia. HPIC method validation, including specificity and selectivity, linearity, precision, and accuracy, was determined by analysis of serially diluted choline, dimethylethanolamine (DMAE) and ammonia reference standard solutions. The HPIC system suitability tests were performed by collecting data from three consecutive injections of reference standard solutions. [¹¹C]Choline and [¹³N]ammonia were produced and tested to confirm the performance on this HPIC method.

Results: The HPIC setup and method provides qualitative and quantitative analyses information of [¹¹C]choline and [¹³N]ammonia. The HPIC peak and resolution results showed desired specificity and selectivity for choline, DMAE, and ammonia. HPIC validation data demonstrated a linear conductivity in the concentration ranges of 0.05-100 µg/mL for choline, and 1.56-100 µg/mL for DMAE and ammonia. The precision, shown as coefficient of variation of three repeated injections, was 1.7% ± 1.7%, 1.1% ± 0.9%, and 0.6% ± 0.5% for choline, DMAE and ammonia, respectively. The accuracy detection limit was 0.39 µg/mL, 6.25 µg/mL, and 6.25 µg/mL for choline, DMAE and ammonia, respectively. System suitability results of this HPIC method exhibited great resolution, plate number, and tailing factor for analysis of choline and ammonia reference standard. HPIC analysis of [¹¹C]choline and [¹³N]ammonia showed >99% radiochemical purity with retention times of 8.26 and 5.05 min, and <5% deviation of radioactive peak from the corresponding reference standard. The residual DMAE concentration in [¹¹C]choline product was 9-18 µg/mL. All the parameters meet European and US pharmacopeias requirements for PET drug release.

Conclusions: A single HPIC method was developed for the analysis of both [¹¹C]choline and [¹³N]ammonia with the same setup. The data suggested this HPIC system and method is validated for determining radiochemical/chemical purity and radiochemical identity of [¹¹C]choline and [¹³N]ammonia products in cGMP compliant manufacturing process.

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