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June 22, 2016

Vocabulary of the chromatographer

By Tuomo Frigård, Scientist at GE Healthcare

Similar to other technical areas, chromatographers generate their own vocabulary, all with a good scientific purpose and for a common understanding. However, the same terminology can be used in other disciplines, but with an entirely different meaning.

10 words you must know

Here, I list the 10 words you must know when working with chromatography. If you have recently started to use chromatography, the terminology might seem unfamiliar. If so, the list can help you talk about chromatography with confidence. If you are an experienced chromatographer, the definitions can come in handy when teaching others.

1. Chromatogram

A graphical presentation of detector response(s), for example, absorbance (280 nm) against volume (mL). When a response is recorded, a peak will be displayed in the chromatogram.

2. Resolution

The ability of a packed column to separate two solutes (e.g., proteins). The solutes are monitored using detectors, most commonly UV.

3. Selectivity

The relative retention of two solutes (e.g., proteins) in a column. Selectivity is related to the distance between two peaks.

4. Column efficiency

The ability to elute narrow, symmetrical peaks from a packed bed. Relates to the peak broadening that occurs on the column and is frequently stated in terms of the number of theoretical plates (N). A column with a high number of theoretical plates will generate narrower peaks at a specific retention time than a column with a lower number.

5. Peak broadening

The widening of the zone of a solute (e.g., a protein) when passing through a column or a chromatography system, reducing resolution and resulting in dilution of the solute. The phenomenon is also termed band broadening or zone broadening. There are extensive theoretical explanations for the contributing components, such as longitudinal diffusion, eddy diffusion, and mass transport in the stationary and mobile phase.

6. Flow rate

Volumetric flow through a column and/or chromatography system, expressed in mL/min or column volumes (CV)/h.

7. Flow velocity

Linear flow through a column and/or chromatography system, expressed in cm/h. Flow rate divided by the cross-sectional area of a column.

8. CV flow

Flow rate expressed as column volumes (CV) per hour, a useful measure when scaling methods.

9. Delay volume

Fractionation delay volume is the volume in the tubing and system components between a monitor and the fraction collector. The gradient delay volume relates to the volume between the point where two solutions are mixed and the column.

10. Dead volume

Dead volume refers to the volume in a chromatography system, from the injector to the detector, except for the column volume.

Would you like to know more? The ÄKTA system handbook gives guidance on system usage and includes explanations to physical parameters related to system components (e.g., valve volumes and linearity of detectors).

Stay tuned for my upcoming blog post on tips when running an ÄKTA system.