Kinetic performance factor - A measurable metric of separation-time-pressure tradeoff in liquid and gas...

A measurable dimensionless metric of tradeoff between separation, time and pressure in chromatography - the kinetic performance factor (e_c) is introduced. Measurable the same way for all LC and GC columns (open-tubular, packed, monolithic, pillar-array, etc.) regardless of retention mechanism, e_c supersedes metrics of a column structural quality such as dimensionless plate height (h), Bristow-Knox separation impedance (SI), Golay specific performance index (SPI) and others. Peak capacity, and other separation performance measures of a chromatographic system are proportional to e_c. To find e_c of a column, there is no need to know the column unmeasurable parameters such as h, stationary phase porosity, resistance factor, and others. To theoretically predict the separation-time performance of a particular column with known e_c, two measurable parameters - a column effective diameter (d_eff) and nominal diffusivity (D_n) were introduced in addition to e_c. Quantities e_c and D_n represent the properties of column classes while d_eff represents a particular column. The use of parameters d_eff, e_c and D_n for evaluation of relations between efficiency and void time (t_M) in columns of several types has been demonstrated. It is always more time-efficient to use maximum available instrumental pressure (Δp_max) for obtaining a predetermined column efficiency even if that efficiency is relatively low so that operation at Δp_max requires non-optimal flow. It has been also demonstrated that reducing the characteristic cross-sectional dimension (d_eff, particle size of a packed column, internal diameter of and open-tubular column, etc.) of a column operating at the same Δp_max reduces the column efficiency with the benefit of much larger reduction in the analysis time.