Quantitation of a low level coeluting impurity present in a modified oligonucleotide by both LC-MS and NMR.This paper describes the use of two complementary techniques, LC-MS and NMR, to quantify a low level mono phosphate substituted impurity in an oligonucleotide drug substance.  With the use of a standard addition method it could be demonstrated that both analytical techniques show equivalency and furthermore, the LC-MS method alone with additional validation has the potential to perform this quantitative assay with a high degree of accuracy.
LC-MS
Quantitation of a low level coeluting impurity present in a modified oligonucleotide by both LC-MS and NMR.This paper describes the use of two complementary techniques, LC-MS and NMR, to quantify a low level mono phosphate substituted impurity in an oligonucleotide drug substance. 
NMR