GC calibration as per USP

CHROMATOGRAPHY

INTRODUCTION

Chromatographic separation techniques are multistage separation methods in which the components of a sample are dis-

tributed between two phases, of which one is stationary and the other is mobile. The stationary phase may be a solid or a

liquid supported on a solid or a gel. The stationary phase may be packed in a column, spread as a layer, distributed as a film,

or applied by other techniques. The mobile phase may be in a gaseous or liquid form, or a supercritical fluid. The separation

may be based on adsorption, mass distribution (partition), or ion exchange; or it may be based on differences among the

physicochemical properties of the molecules, such as size, mass, and volume. This chapter contains general procedures, defini-

tions, and calculations of common parameters and describes general requirements for system suitability. The types of chroma-

tography useful in qualitative and quantitative analyses employed in

USP

procedures are column, gas (GC), paper, thin-layer

(TLC) [including high-performance thin-layer chromatography (HPTLC)], and pressurized liquid chromatography [commonly

called high-pressure or high-performance liquid chromatography (HPLC)].

GENERAL PROCEDURES

This section describes the basic procedures used when a chromatographic method is described in a monograph. These pro-

cedures are followed unless otherwise indicated in the individual monograph.

Paper Chromatography

STATIONARY

PHASE

The stationary phase is a sheet of paper of suitable texture and thickness. Development may be ascending, in which the

solvent is carried up the paper by capillary forces, or descending, in which the solvent flow is also assisted by gravitational

force. The orientation of paper grain, with respect to solvent flow, is to be kept constant in a series of chromatograms. The

machine direction is usually designated by the manufacturer.