Glossary of terms

Term

Definition

Analytical Column

Synonymous with Separator Column.

Auxiliary Valve

The auxiliary valve is a high-pressure valve used for in-line sample preparation. In Chromeleon CDS, the auxiliary valve may also be referred to as the HP_Valve.

Band Spreading

The broadening of the sample band as it travels through the column. Band spreading can also occur in the injection valve, detector cell, and interconnecting tubing.

Calibration Curve

A graph showing detector response in peak height or area versus analyte concentration.

Capacity Factor (k´)

The number of column volumes of eluent, pumped through the column, required to elute an analyte. Capacity factor is a dimensionless measure of retention which is independent of column length or eluent flow rate. It is calculated as follows:

k'' = tr- to/ to

Where: tr = retention time
to = retention time of unretained solute (column void volume)

Cell Constant (k)

A factor determined experimentally by measuring the conductance (G) of a standard solution of known equivalent conductivity (k).

k = κ / G

The value of k depends upon the surface area of, and distance between, the electrode faces in the conductivity cell.

k = l / A

Where: l = length
A = area of one electrode (the other electrode is equal to the first)

Channeling

The preferential flow of liquid along more open, less resistant paths through the column packing. This causes Band Spreading.

Column Efficiency (N)

A measure of the narrowness of analyte bands as they elute from the column. High efficiency is required as the resolution between closely spaced bands improves with greater efficiency. For a symmetrical (Gaussian) peak, column efficiency can be determined by:

N = 5.54(t1/W1/2)2

Where: t1 = the peak retention time (in seconds)
W1/2 = the peak width at 1/2 height (in seconds)

Column efficiency is proportional to column length: for a given resin and column diameter, increasing the column length increases the column efficiency. Synonymous with Theoretical Plates.

Column Selectivity (a)

Describes the relative separation of the band maxima between two adjacent peaks. Selectivity can be determined by the following:

a = (t2 - t0)/(t1 -t0)

Where: t1 and t2 = retention time of components 1 and 2, respectively
t0 = retention time of unretained components (void volume)

Concentrator Column

A short column used to retain and concentrate analytes from a measured volume of relatively clean sample. This allows large volumes of sample to be injected, lowering concentration detection limits.

Conductivity

A measure of the ease with which electrical current flows through a liquid contained between two opposite charged electrodes. Conductivity is a characteristic of ions in solution. Units are siemens.

Counterion

Ions carrying a charge opposite that of the sample ions (for example, Na+) may be the counterion of a Cl- analyte. These ions preserve electrical neutrality in solution.

% Crosslink

Divinylbenzene content in a polystyrene/divinylbenzene (PS-DVB) resin; this contributes to the mechanical strength of the resin and determines chromatographic properties.

Effluent

The stream flowing out of or exiting an analytical column.

Eluate

A mixture of solute and solvent exiting an analytical column. Similar to Effluent.

Eluent (Eluant)

The solution or mobile phase used as a solvent or ion extraction liquid in ion chromatography.

Eluite

The eluted species; also known as the sample or analyte.

Equivalent Conductivity (λ)

The contribution of an ionic species to the total conductivity of a solution as measured in a standard cell having electrodes 1 cm2 in area and exactly 1 cm apart.

Guard Column

A small column that prevents contamination of the separator column by absorbing organic contaminants and removing particulates. It is filled with the same packing as the separator column. Synonymous with Pre-Column.

HETP (H)

Height Equivalent to a Theoretical Plate. A measure of column efficiency which allows comparison between columns of different lengths.

HETP = H = L/N

Where: L = the length of the column (in mm)
N = the number of theoretical plates

Ion-Exchange Capacity

The number of active ion exchange sites in a given weight or volume of resin; this is usually expressed in meq/g or meq/mL.

Ion-Exchange Resin

An insoluble polymer matrix containing fixed-charge exchange sites (anionic or cationic). IC resins are formed into small spherical particles (beads).

Isocratic

A chromatographic method with a constant and uniform mobile phase composition; a regular phase that runs continuously.

Liquid Lines

Another word for tubing carrying liquids; gas tubing is not considered a liquid line, but a gas line.

Packing

The material that fills a chromatographic column; usually a resin or silica-based material.

PEEK

An acronym for polyether ether ketone. This is a type of hydrophobic, chemically-resistant plastic commonly used for tubing and other mechanically demanding applications.

Pellicular Resin

A resin with a solid, nonporous core coated with a thin layer of more porous material. The exchange sites of pellicular ion-exchange resins are located only on the surface layer of the bead. These resins have a low Ion-Exchange Capacity.

Pre-Column

Synonymous with Guard Column.

Regenerant

A dilute acid or base that converts ion-exchange sites in an electrolytically regenerated suppressor or chemically regenerated suppressor back to the form that suppresses the eluent conductivity.

Regenerant Pump

A peristaltic pump that performs several functions, including eluent regeneration, delivery of regenerant to a chemical suppressor, or delivery of water to an electrolytic suppressor being used in external water mode.

Resin

See Ion-Exchange Resin.

Resolution (R)

A measure of the separation between two sample components. This is expressed as the ratio of the distance between the two peak maxima to the mean value of the peak width at the baseline.

R = 2(t2 - t1)/(W2 + W1)

Where: t1 and t2 = the retention times of components 1 and 2, respectively
W1 and W1 = the baseline width of peaks 1 and 2, respectively (measured in the same units as the retention time)
R is proportional to the square root of efficiency (N). A value of R = 1.5 represents “baseline separation” of the two peaks.

Retention Time

The time from injection to peak maximum; the basis for identification of a species in chromatographic analysis.

Rotary Valve

A type of valve which regulates the flow of liquid or gas through a circular, rotating assembly. Also known as a rotary-motion valve.

Separator Column

The column used to perform a chromatographic separation; also called an analytical column.

Siemens (S)

Unit measure of conductance; the reciprocal of the electrical resistance of a solution.

Suppressor

A device used to minimize eluent conductivity and convert sample species to a common form, thus increasing detection sensitivity.

Temperature Coefficient

The percentage of change in the conductivity of a solution with a 1 °C change in temperature. Every solution has a characteristic temperature coefficient which is determined experimentally.

Theoretical Plates (N)

See Column Efficiency.

Void Volume (V0)

The volume occupied by the eluent in a packed column. This volume includes the volume between the injection valve and the column, and between the column and the conductivity cell. The components that are not retained are eluted in the void volume.