N-Nitroso N-desethyl sunitinib in Sunitinib capsules

Hello everyone

me and my team facing seperation issue on determining the N-Nitroso N-desethyl sunitinib in Sunitinib capsules by lcmsms and we are tried all kind of column chemistry and mobile phase and pH combination even though we are unable to seperate the API and Standard Analyte can anyone suggest me further proceedings