Defining Method Types and Goals

HPLC methods are developed for single-analyte or for multiple-analyte assays. Methods can be categorized into three major method types qualitative, quantitative, and preparative. 

A qualitative method is primarily an identification test that confirms the presence (or absence) of a certain analyte(s) in the sample by matching retention time with that of a reference standard. UV spectral data from a photodiode array detector are often used as a secondary confirmation technique. This type of method can be a limit test to evaluate whether the level of the analyte is above or below a certain preset limit or to generate a chromatographic profile for comparative purposes. 

A quantitative method generates information on the concentration or amount of the analyte (s) in the sample. System calibration (standardization) typically using external standard(s) is required. A quantitative method can also be adopted as a qualitative method. For instance, an assay method can often also serve as an identification method. A quantitative method is more difficult to develop and requires extensive effort for validation. This method type is the focus of this chapter. 

A preparative method is used to isolate purified components in the sample. This method often requires large-diameter columns and high flow rates to increase yield for each run. Method validation is typically not required since the goal is to generate purified components or enriched fractions. 

---