At Pine Lake Laboratories, we have developed a standard methodology using Ion-Exchange HPLC-UV to quantitate therapeutic oligonucleotides and pegylated oligonucleotides in plasma.  This methodology has been adapted and optimized for multiple compounds across a wide variety of therapeutic areas.  For most compounds chromatographic resolution can be achieved between the parent compound and the N-1 to N-X metabolites.  Both gradient and column temperature are important in achieving good separation.  The sample preparation before HPLC analysis includes an overnight enzymatic digestion.  Carryover is a common problem but a strategy of including wash injections minimizes the impact of carryover.  All other validation parameters will meet the acceptance criteria.  One common area for instability is for the drug in plasma at room temperature.  Stability usually can be improved by keeping samples on ice during preparation or using higher concentrations of EDTA.  Validated methods have been used to support GLP and human clinical studies without any method related issues.  Most methods have column lives that exceed 1000 injections.