The stability of α‐bromophenylacetic acid (BPAA) in 50% aqueous methanol solution has been tested. CE in different running buffers was used to separate BPAA from the decomposition reaction products α‐hydroxyphenylacetic (mandelic) acid and α‐methoxyphenylacetic acid. Suitable CE separation of all three compounds and other product, bromide, was achieved in 60 mmol/L formate buffer (pH 3.0) at −30 kV in 50 μm (i.d.) poly(vinyl alcohol)‐coated fused silica capillary (30 cm/24.5 cm) with UV detection at 200 nm. The CE method was applied to determine the reaction order of the decomposition of BPAA (0.47 mmol/L) via nucleophilic substitution in 50% aqueous methanol. The first‐order reaction kinetics was confirmed by linear and non‐linear regression, giving the rate constants 1.52 × 10⁻⁴ ± 2.76 × 10⁻⁵ s⁻¹ and 7.89 × 10⁻⁵ ± 5.02 × 10⁻⁶ s⁻¹, respectively. Additionally, the degradation products were identified by CE coupled to mass spectrometric (MS) detection. The CE–MS experiments carried out in 60 mmol/L formate buffer (pH 3.0) and in 60 mmol/L acetate buffer (pH 5.0) confirmed the results obtained by CE–UV. Furthermore, the stability of BPAA in polar solvents was tested by ¹H NMR experiments. Our results provide strong evidence of the instability and fast degradation of BPAA in 50% aqueous methanol indicating that BPAA is not suitable as the model analyte for chiral separations.

中文翻译：

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α-溴代苯乙酸的稳定性研究：它代表手性分离的合适模型分析物吗？

已测试了50％甲醇水溶液中的α-溴苯乙酸（BPAA）的稳定性。在不同的运行缓冲液中使用CE分离分解反应产物α-羟苯基乙酸（扁桃酸）和α-甲氧基苯基乙酸中的BPAA。在30 kV的60 mmol / L甲酸缓冲液（pH 3.0）和50μm（id）聚乙烯醇包覆的熔融石英毛细管（30 cm / 24.5 cm），并在200 nm处进行UV检测。采用CE法测定了在50％甲醇水溶液中亲核取代双酚A（0.47 mmol / L）的反应顺序。一阶反应动力学通过线性和非线性回归确定，给出速率常数1.52×10 ^-4  ±  2.76×10^分别为-5 s ^-1和7.89×10 ^-5  ±  5.02×10 ^-6 s ^-1。另外，降解产物通过CE结合质谱（MS）检测进行鉴定。在60 mmol / L甲酸缓冲液（pH 3.0）和60 mmol / L乙酸盐缓冲液（pH 5.0）中进行的CE–MS实验证实了通过CE–UV获得的结果。此外，通过¹ H NMR实验测试了BPAA在极性溶剂中的稳定性。我们的结果提供了在50％甲醇水溶液中BPAA不稳定和快速降解的有力证据，表明BPAA不适合用作手性分离的模型分析物。