Michael E. Swartz

Ira S. Krull

This three-part column describes how statistically rigorous QbD principles can be put into practice to accelerate each phase of LC instrument method development. The column is presented in three parts. In this first part, we address column screening. We examine current method development approaches in terms of design space coverage — a key element of process knowledge. In Part II, we will present QbD data treatments to both accelerate and bring quantitation to the column-screening effort. The final installment will focus on integrating quantitative method robustness estimation into formal method development.

Reversed-phase LC is by far the most widely used LC separation method in the pharmaceutical and biotechnology industries. Reversed-phase LC is therefore the basis of the discussions and examples used in this paper. However, the reader will recognize that the instrumentation, software, and QbD-based methodologies presented here are applicable to other LC approaches such as normal-phase LC and hydrophilic interaction liquid chromatography (HILIC).

The traditional approach to LC method development is to systematically vary one factor across some experimental range while the level settings of all other controllable factors are held constant. This "one-factor-at-a-time" (OFAT) approach, still widely practiced today, is carried out by selecting one instrument parameter to study while holding all other parameters fixed. The "best" performing level of the study parameter is identified normally by visual inspection of the trial chromatograms; the parameter is then fixed at this level, and a new instrument parameter is selected for the next iteration. The OFAT process is repeated parameter by parameter until an adequately performing instrument method is obtained.

Table I: Historical phasing of method development workflow