Abstract: To ensure accurate determination of organic impurities in certified reference materials for organic purity, we studied the brominated flame retardant tetrabrombisphenol A (TBBPA). Using the area normalization and standard curve methods, we quantified its primary organic impurity, tribromobisphenol A, and evaluated the associated uncertainties. Additionally, the impurity's content was measured using quantitative nuclear magnetic resonance (qNMR). The impurity levels derived from the area normalization and standard curve methods were 0.70% ± 0.04% and 1.16% ± 0.09%, respectively. A combined purity estimate yielded 0.93% ± 0.24%, encompassing the qNMR result of 0.76% ± 0.03%. When significant discrepancies (>0.1%) arise between the area normalization and standard curve methods, their combined result can be adopted to guarantee the accuracy of the measurement.