Certified reference materials (CRMs) play vital roles in method validation and quality assurance
of assessment measurements. In this paper, a new CRM for sulfamethoxazole (SMZ) was prepared.
Purity determination and uncertainty evaluation methods were developed using mass balance
(MB) and differential scanning calorimetry (DSC) methods. Impurities including moisture, volatile components, and inorganic
components were accounted for and deducted from 100% using the MB method. Results were consistent between
DSC and MB. Certied value of SMZ was 991.6 ± 4.6 mg g-1 (k = 2, P = 0.95). This new CRM can be used to validate
analytical methods, improve the accuracy and comparability of measurement data, establish metrological traceability of
analytical results, and control the quality of SMZ in relevant pharmaceutical formulations.