Application to Chemical Impurities

Following the development of the technique and with the availability of commercial equipment, one of the first published real applications of HPLC-NMR was concerned with the identification of an impurity in a synthetic drug precursor [28], In this case, a 400 MHz HPLC-NMR system was tested with a small molecule typical of pharmaceuticals  

Having shown that the HPLC-NMR system could separate and characterise these three substances by using both continuous-flow and stop-flow approaches, a more realistic test was applied. This successfully characterised the two components shown below with the impurity at a level of 3 % using stop-flow HPLC-NMR  

In situations where impurities have low or no UV chromophores, HPLC-NMR provides a unique window on the separation process. This has been exemplified using a drug substance known as SKF-99085, where HPLC-MS, HPLC-NMR, refractive index, light scattering and gas chromatography methods were all used to quantify and identify impurities [30]  

HPLC with UV detection at 280 nm showed essentially only the required drug compound but a quantitative assay against a reference material showed a level of only 96.6% of that expected. A number of impurities were detected by using HPLC with MS and refractive index detection and the structures of the major components were elucidated by using 500 MHz H HPLC-NMR spectroscopy. 

The approach to characterisation of impurities in bulk drug materials from a production batch is also exemplified by a study on fluticasone propionate [31] which has the structure and numbering system shown below  

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