Multidimensional chromatography

The multidimensional chromatography is an efficient separation method for complex organic mixtures. In one-dimensional chromatography it can happen that two or more different substances to be separated move at the same speed and thus end up in the same place. To their further separation z. B. in two-dimensional thin layer chromatography, if in a second step the stationary phase is rotated by 90 ° and another mobile phase is used for renewed chromatography; in this way these substances can also be separated from one another.

nomenclature

The nomenclature for multidimensional chromatography was introduced during the first International Symposium on Comprehensive Multidimensional Gas Chromatography , 6. – 7. March 2003 agreed in Volendam , as well as the definition and use of the words “comprehensive” and “orthogonal” as well as the multiplex symbol “x” for the abbreviation for comprehensive two-dimensional chromatography.

Comprehensive

A two-dimensional chromatographic separation is said to be “comprehensive” if

1. Each sample component is subjected to two different separations:

2. Equal percentages (either 100% or less) of all sample components pass both separation columns and reach the detector;

3. the resolution achieved in the first dimension is essentially retained.

The third criterion can never be fully achieved. Nevertheless, the inevitable loss of resolution due to e.g. B. a reduction in peak broadening can be minimized.

The multiplex character "x"

abbreviation	meaning
GCxGC GCxGC-FID GCxGC-MS GCxGC-TOF-MS	Two-dimensional gas chromatography (2D-GC) 2D-GC with flame ionization detector 2D-GC with coupled mass spectrometer 2D-GC with coupled time-of-flight mass spectrometer
LCxLC LCxLC-MS LCxLC-TOF-MS LCxLC-MS / MS	Two-dimensional liquid chromatography ( HPLC ) (2D-LC) 2D-LC with coupled mass spectrometer 2D-LC with coupled time-of-flight mass spectrometer 2D-LC with coupled tandem mass spectrometer
LCxSEC	2D (liquid x size exclusion) chromatography
LCxGC	2D (liquid x gas) chromatography
LCxGC-MS	2D (liquid x gas) chromatography with coupled mass spectrometer
SFCxGC	2D (Supercritical Fluid x Gas) chromatography
GCxGCxGC	Three-dimensional gas chromatography (3D-GC)
LC-GCxGC	On-line LC - 2D-GC
SFC-GCxGC	On-line Supercritical Fluid Chromatography - 2D-GC

Orthogonality

In the literature, the term "orthogonal" is used very inconsistently in relation to the two-dimensional separation.

The word orthogonal is clearly defined in mathematics ( perpendicular ) and statistics ( independent ). It was used in chromatography to show different separation techniques or mechanisms. It was therefore necessary to formulate a definition for analytical chemistry:
Separating dimensions are orthogonal if the respective elution times of both dimensions can be viewed as statistically independent.