Identification of 14C Nuclides in 14C-urea Capsules

Abstract

Helicobacter pylori is a type of bacteria that is commonly found in the stomach lining and is known to cause gastritis, gastric ulcers, and gastric cancer. Detection and diagnosis of Helicobacter pylori infection are crucial for effectively eradicating the pathogen. Currently, the 14C-urea breath test is widely considered the gold standard for detecting the infection. During the test, patients ingest capsules containing 14C-labeled urea. It is important to identify the active ingredient, 14C, in the 14C-urea capsules to ensure the quality and safety of the medication. Unfortunately, there is no clear method provided by the Chinese Pharmacopoeia or the United States Pharmacopoeia for identifying the 14C nuclide. To address this gap, a method for identifying the 14C nuclide in 14C-urea capsules using liquid scintillation counter measurement was developed in this paper. In the experiment, a solution of 14C-urea was mixed with ethanol and low-quenching scintillation cocktails, and then argon gas was used to remove oxygen and prepare a low-quenching sample. The liquid scintillation counter was used to measured the β spectrum, and five characteristic points were selected for comparison with the β spectrum of a standard non-quenched 14C source. The identified characteristic points included the maximum apparent energy value, the apparent energy value at the right end of the half-peak height, the apparent energy value at the right end of the 90% peak height, the 90% peak energy width, and half-height width. Successful identification of the 14C nuclides is achieved by comparing the β spectrum of the low-quenching sample with the standard non-quenched 14C source. Oxygen and ethanol are the main sources of quenching during the preparation of low-quenching samples. However, the experimental study shows that the dissolved oxygen in the scintillation cocktails could be effectively removed by flowing argon gas for 10 minutes, which significantly reduces the quenching degree and extends the validity period of the sample to 30 minutes. Furthermore, adding less than 1.67% ethanol to the sample results in no significant quenching. To avoid introducing new quenching sources, the distribution of 14C-urea in the capsule was analyzed, and it is found that more than 90% of the 14C-urea is located at the bottom of the capsule. The established nuclide identification method was used to identify 14C in three batches of 14C-urea capsules from a company in Shanghai, and the results are all qualified, validating the effectiveness and feasibility of the established method. In summary, the nuclide identification method developed in this paper can provide valuable experience for identifying nuclides in other radiopharmaceuticals, enhancing the safety and effectiveness of radiopharmaceuticals. Accurate identification of active ingredients in medications is essential for ensuring the safety of patients and improving the quality of healthcare.

Keywords

• nuclide identification
• liquid scintillation
• β spectrum