Glossary Of HPLC-LC Separation Terms – G

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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G

γ: The obstruction or tortuosity factor. Molecular diffusing term. See also tortuosity.

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. Using the peak maximum position as a measure of retention and the efficiency equations mentioned above assume Gaussian peak shape. See Figure 2.

Gaussian peak: A peak whose shape conforms closely to the equation: C = C max exp[–(t – t R)2/2σ2].

Gel: The solid packing used in gel chromatography or gel-permeation chromatography (GPC). An actual gel consists of two parts: the dispersed medium (solid portion) and the dispersing medium (the solvent). Also defined as a colloidal dispersion of a solid and liquid in which the solid is the continuous phase.

Gel-filtration chromatography (GFC): Also called aqueous size-exclusion chromatography. Performed with aqueous mobile phases. Generally refers to molecular size separation performed on soft gels such as polydextrans, but analysts also can use highly cross-linked polymers, silica gels, and other porous media. Most gel-filtration separations involve biopolymers and water-soluble polymers such as polyacrylic acid.

Gel-permeation chromatography (GPC): SEC performed with organic mobile phases used for the separation and characterization of polymers. SEC with aqueous mobile phases is called aqueous GPC, GFC, or aqueous SEC.

GFC: See gel-filtration chromatography.

Gigapores: See perfusion chromatography.

GPC: See gel-permeation chromatography.Gradient: A process to change solvent strength as a function of time (normally solvent strength increases) thereby eluting progressively more highly retained analytes. Typically gradients can be binary, ternary, and quaternary solvent mixtures in which solvents are blended to achieve the proper strength.

Gradient delay volume: See dwell volume

Gradient elution: Technique for decreasing separation time by increasing the mobile-phase strength 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.

Graphitized carbon: Graphitized carbon is a graphitic carbon with more or less perfect three-dimensional hexagonal crystalline order prepared from non-graphitic carbon by graphitization heat treatment; this packing material has a strong affinity for polar compounds in aqueous samples and water miscible organic extracts. Commonly used in pesticide analysis of food samples

Graphitized carbon packing: A reversed-phase packing material consisting of pure graphitic carbon. Possesses interesting sorbent properties such as preferential separation of geometric isomers such as o-, m- and p-aromatics and cis–trans isomers.

Guard column: A small column placed between the injector and the analytical column. It protects the analytical column from contamination by sample particulates and strongly retained species. The guard column usually is packed with the same material as that in the analytical column and is often of the same inner diameter. It is much shorter, costs less, and usually is discarded when it becomes contaminated. Integrated guard–analytical column systems often are preferred to minimize extracolumn effects caused by connecting tubing with separate guard and analytical columns.

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