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

Blumberg, Leonid M., Desmet, Gert
Journal of chromatography 2018
porosity, diffusivity, liquids, particle size, gas chromatography
A measurable dimensionless metric of tradeoff between separation, time and pressure in chromatography – the kinetic performance factor (ec) is introduced. Measurable the same way for all LC and GC columns (open-tubular, packed, monolithic, pillar-array, etc.) regardless of retention mechanism, ec 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 ec. To find ec 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 ec, two measurable parameters – a column effective diameter (deff) and nominal diffusivity (Dn) were introduced in addition to ec. Quantities ec and Dn represent the properties of column classes while deff represents a particular column. The use of parameters deff, ec and Dn for evaluation of relations between efficiency and void time (tM) in columns of several types has been demonstrated. It is always more time-efficient to use maximum available instrumental pressure (Δpmax) for obtaining a predetermined column efficiency even if that efficiency is relatively low so that operation at Δpmax requires non-optimal flow. It has been also demonstrated that reducing the characteristic cross-sectional dimension (deff, particle size of a packed column, internal diameter of and open-tubular column, etc.) of a column operating at the same Δpmax reduces the column efficiency with the benefit of much larger reduction in the analysis time.