Suitable Internal Standard for Tramadol HCl

[syx]

Dear Members,

Does anyone have an idea what substance is suitable to be internal standard for RP-HPLC determination of Tramadol HCl, C16H26ClNO2, in suppositories dosage form?

(1RS,2RS)-2-[(dimethylamino)methyl]-1-(3-methoxyphenyl) cyclohexanol . HCl
Solubility: freely soluble in water, methanol; very slightly soluble in acetone (BP2004)
Detector wavelength: UV 270 – 271 nm



Best regards,
SYX

[HW Mueller]

Is an ethoxy compound available, or an N-ethyl? A diastereomer would probably be too different (if available).