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

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.