Optimization and validation of a gas chromatographic method for analysis of (RS,SR)-diastereoisomeric impurity in formoterol fumarate.

A gas chromatographic method for the determination of formoterol (RS,SR)-diastereoisomer, a process impurity, in formoterol fumarate was optimized and validated. The method involves silylation of formoterol fumarate with N-(trimethylsilyl)imidazole in N,N-dimethylformamide at room temperature in an autosampler vial to produce trimethylsilyl derivatives of the enantiomers prior to GC analysis. The optimized silylation and separation conditions, respectively, produced good yield and resolution of the analytes.