Glossary Of HPLC-LC Separation Terms – F

The listing should be helpful to those just starting in HPLC but it also can serve as a refresher for long-time users in the field.

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F

F: See flow rate.

φ: See flow resistance parameter.

Fast LC: Use of HPLC of short columns (1.5–7 cm) with conventional inner diameters (2–6 mm) packed with small particles (3- or 5-μm d p). Separation times in the range of minutes, or even seconds, are common.

Fast protein LC (FPLC): A termed coined to cover the specific use of HPLC for separating proteins. Generally, glass columns, moderate pressure, and spherical microbeads are used for FPLC.

Flash chromatography: A very fast form of classic LC used by synthetic organic chemists for rapid purification. Performed primarily in the normal-phase mode, sometimes with reversed-phase chromatography.

Flow rate (F): The volumetric rate of flow of a mobile phase through an LC column. Typical flow rates are 1–2 mL/min for a conventional 4.6-mm i.d. HPLC column.

Flow resistance parameter (φ): φ = d p 2 /B o, where B o is permeability. See also permeability.

Fluoro phase: One of a family of aliphatic and aromatic reversed-phase materials in which a substantial fraction of the bonded phase is fluorinated. Sometimes called fluorous phases or perfluoro phases. Typically these phases have different selectivities than hydrocarbon phases.

Foley–Dorsey equation: A correction of the plate count and retention time for peak tailing from extracolumn sources of broadening. See reference B.

FPLC: See fast protein LC.

Fractionation range: Refers to the operating range of a gel or packing in SEC. This range is where a packing can separate molecules based on their size. At one end of the range, molecules that are too large to diffuse into the pores are excluded. At the other end of the range, molecules that can diffuse into all of the pores totally permeate the packing and are eluted (unseparated) at the permeation volume.

Frit: The porous element at either end of a column that contains the column packing. It is placed at the very ends of the column tube or, more commonly, in the endfitting. Frits can be stainless steel or other inert metal or plastic such as porous PTFE or polypropylene. The frit porosity must be less than the smallest particle in the HPLC column; otherwise particles will pass through the frit, and the packing will be lost.

Frontal analysis: A chromatographic technique that involves continuous addition of sample to the column with the result that only the least sorbed compound, which moves at the fastest rate, is obtained in a pure state. The second-least-sorbed compound is eluted with the first-eluted compound, the third-least-sorbed compound with the first and second compound and so on until the original sample is eluted at the column exit. Frontal analysis is seldom used and is mainly a preparative technique.

Frontal chromatography: Same as frontal analysis.

Fronting: Peak shape in which the front part of the peak (before the apex) in a chromatogram tapers in advance of the remainder of the peak; that is, the front is less steep than the rear. The peak has an asymmetric distribution with a leading edge. The asymmetry factor for a fronting peak has a value of less than one. Tailing is the opposite effect. Fronting can result at high sample loads because of positive curvature in the isotherm and from using poorly packed columns.

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