deactivated adsorbent - adsorbent which has been chemically treated to reduce its surface activity; the most common treatments include silanizing with dimethyl dichlorosilane (DMCS) or thermal treatment of silica under vacuum.

See also surface chemistry and chemical modofication of the surface.

dead volume (Vo) dead time (To) - volume of liquid phase in the column.

See also dead volume theory.

degassing - the process of removing dissolved gas from the mobile phase before or during use. Dissolved gas may come out of solution in the detector cell and cause baseline spikes and noise. Dissolved air can affect electrochemical detectors (by reaction) or fluorescence detectors (by quenching). Degassing is carried out by heating the solvent or by vacuum (in a vacuum flask), or on-line using evacuation of a tube made from a gas-permeable substance, or by helium sparging.

See also degasing.

derivative(s) - compound(s) obtained from original sample, usually through chemical reactions which are more easily chromatographed; active protons such as those found in acids, amines, alcohols, and phenols are reacted to form more inert esters, ether, or silyl derivatives.