ferrule - part of fitting.

fittings - pieces of plumbing used to connect the column to the instrument by high pressure seal. See also column hardware.

flow rate - volume of mobile phase per unit time passing through the column. usually reported as millilitres per minute. See also fluorescence detector.

fluorescence detector - a very sensitive and selective HPLC detector which monitor an analyte fluorescence. Usually equipped with two monochrometers at right angles to one another. The flow cell is illuminated at one face, and compounds which are excited by that light (can fluoresce) emit light at a different wavelength. This emitted light is measured via the second monochromator using a photomultiplier tube.

frit - the porous element at either end of a column that serves to contain the column packing. It is placed at the very ends of the column tubes or, more commonly, in the end-fitting. Frits are made from stainless steel or other inert metal or plastic, such as porous PEEK or polypropylene.

frontal analysis - a form of chromatography where pure sample flows through the column; each component breaks through at a different time depending on its affinity for the adsorbent.

fronting - peak shape in which the front part of a peak (before the apex) in a chromatogram tapers in advance of the remainder of the peak. There is an asymmetric distribution with a leading edge. The asymmetry factor for a fronting peak has a value less than one. The opposite effect is tailing. Fronting is related to the shape of the adsorption isotherm.

gas chromatography (GC, GLC) - a form of chromatography where the mobile phase is gas.

Gaussian curve - a standard error curve, based on a mathematical function, that is a symmetrical, bell-shaped band or peak. Most chromatographic theory assumes a Gaussian peak. See also band broadening.

gel filtration chromatography (GFC) - size-exclusion chromatography carried out with aqueous mobile phases. Generally refers to separations carried out on soft gels such as polydextrans. Most gel filtration separations involve biopolymers.

gel permeation chromatography (GPC) - SEC carried out with organic mobile phases. Used for the separation and characterization of polymers. SEC with aqueous mobile phases is referred to as a aqueous GPC, or GFC.

ghost-peak - spurious signal due to the different sources such as sample carry over in a syringe or injection valve, or accumulated contamination on the column eluted as ghost in gradient elution.

gradient elution - technique for decreasing separation time by changing mobile phase composition over time during the chromatographic separation. Also known as solvent programming. Gradients can be continuous or stepwise. Binary, ternary, and quaternary solvent gradients have been used routinely in HPLC. See also gradient elution in RP HPLC or gradient hardware..

guard column - a small column placed between the injector and the analytical column. Protects the analytical column against contamination by sample particulates and, perhaps, by strongly retained species. The guard column is usually packed with the same material as the analytical column and is often of the same i.d. It is much shorter, costs less, and is usually discarded when it becomes contaminated.  Guard column is only useful for preparative separations in any other cases it is just waste of money and decrease of the system efficiency.

H - Same as HETP.

head pressure - the pressure above gravity at the head of the column. Expressed in psig, bar, atm, or MPa.

height equivalent to a theoretical plate (HETP) - value obtained by dividing the column length by the number of theoretical plates; taken as an indication of column quality. A carryover from distillation theory; a measure of a column's efficiency. For a typical HPLC column well-packed with 5-um particles, HETP (or H) values are usually between 0.01 and 0.03 mm. HETP = L/N, where L is column length, and N is the number of theoretical plates. See also band broadening.

hydrophillic - "water-loving"; refers both to stationary phases that are compatible with water and to water-soluble molecules in general. Most columns used to separate proteins are hydrophilic in nature and should not sorb or denature protein in the aqueous environment.

hydrophobic - "water-hating"; refers both to stationary phases that are not compatible with water and to molecules in general that have little affinity for water. Hydrophobic molecules have few polar functional groups; most are hydrocarbons or have high hydrocarbon content.

hydrophobic interaction - more rigorously called dispersive interaction. Intermolecular interaction based on the Van-der-Waals forces, very weak.

See also surface interactions.

hydrophobic interaction chromatography - a technique in which reversed-phase packings are used to separate molecules by virtue of the interactions between their hydrophobic moieties and the hydrophobic sites on the surface. High salt concentrations are used in the mobile phase; separations are effected by changing the salt concentration. The technique is analogous to "salting out" molecules from solution. Gradients are run by decreasing the salt concentration over time.