The paramount problem in performing absorption, distribution, metabolism, and excretion (ADME)/pharmacokinetic studies of therapeutic oligonucleotides revolves around inefficient and labor-intensive sample preparation. These traditional methods require multiple steps - liquid–liquid extraction (LLE) and solid-phase extraction (SPE) - to extract therapeutic oligonucleotides from serum and plasma for liquid chromatography–mass spectrometry (LC–MS) analysis and thus are not practical for clinical studies with large numbers of samples. Furthermore, these methods tend to yield low recoveries and poor reproducibility. This article presents a revolutionary new method for performing sample cleanup of therapeutic oligonucleotides from serum and plasma. The method extracts many types of therapeutic oligonucleotides from biological matrices in a rapid four-step SPE protocol that eliminates the need for LLE and can be automated for large sample sets. In the testing presented, different..