Chromatographic response function
Encyclopedia
Chromatographic response function, often abbreviated to CRF is a coefficient which characterize in a quantitative manner, the quality of the separation in the result of a chromatography
.
The CRFs concept have been created during the development of separation optimization, to compare many simulated or real chromatographic separations and to choose best of them. Until now, there are many CRFs proposed and discussed.
In HPLC
the CRF is calculated from various parameters of the peaks of solutes (like width, retention time, symmetry etc.) are considered into the calculation. In TLC
the CRFs are based on the placement of the spots, measured as RF values.
The simplest criteria are
and 
product (Wang et al., 1996). They are the smallest difference between sorted RF values, or product of such differences.
Another function is the multispot response function (MRF) as developed by De Spiegeleer et al. It is based also of differences product. This function always lies between 0 and 1. When two RF values are equal, it is equal to 0, when all RF values are equal-spread, it is equal to 1. The L and U values - upper and lower limit of RF - give possibility to avoid the band region.
The last example of coefficient sensitive to minimal distance between spots is Retention distance
(Komsta et al., 2007)
The second group are criteria insensitive for minimal difference between RF values (if two compounds are not separated, such CRF functions will not indicate it). They are equal to zero in equal-spread state increase when situation is getting worse.
There are:
Separation response (Bayne et al., 1987)
Performance index (Gocan et al., 1991)
Informational entropy (Gocan et al., 1991, second reference)
Retention uniformity
(Komsta et al., 2007)
In all above formulas, n is the number of compounds separated, Rf (1...n) are the Retention factor of the compounds sorted in non-descending order, Rf0 = 0 and Rf(n+1) = 1.
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
.
The CRFs concept have been created during the development of separation optimization, to compare many simulated or real chromatographic separations and to choose best of them. Until now, there are many CRFs proposed and discussed.
In HPLC
High performance liquid chromatography
High-performance liquid chromatography , HPLC, is a chromatographic technique that can separate a mixture of compounds and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.HPLC typically utilizes different types of stationary...
the CRF is calculated from various parameters of the peaks of solutes (like width, retention time, symmetry etc.) are considered into the calculation. In TLC
Thin layer chromatography
Thin layer chromatography is a chromatography technique used to separate mixtures. Thin layer chromatography is performed on a sheet of glass, plastic, or aluminum foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose...
the CRFs are based on the placement of the spots, measured as RF values.
CRFs examples in thin layer chromatography
The CRFs in thin layer chromatography characterize the equal-spreading of the spots. The ideal case, when the RF of the spots are uniformly distributed in <0,1> range (for example 0.25,0.5 and 0.75 for three solutes) should be characterized as the best situation possible.The simplest criteria are
and product (Wang et al., 1996). They are the smallest difference between sorted RF values, or product of such differences.Another function is the multispot response function (MRF) as developed by De Spiegeleer et al. It is based also of differences product. This function always lies between 0 and 1. When two RF values are equal, it is equal to 0, when all RF values are equal-spread, it is equal to 1. The L and U values - upper and lower limit of RF - give possibility to avoid the band region.
The last example of coefficient sensitive to minimal distance between spots is Retention distance
Retention distance
Retention distance, or RD, is a concept in thin layer chromatography, designed for quantitative measurement of equal-spreading of the spots on the chromatographic plate and one of the Chromatographic response functions...
(Komsta et al., 2007)
The second group are criteria insensitive for minimal difference between RF values (if two compounds are not separated, such CRF functions will not indicate it). They are equal to zero in equal-spread state increase when situation is getting worse.
There are:
Separation response (Bayne et al., 1987)
Performance index (Gocan et al., 1991)
Informational entropy (Gocan et al., 1991, second reference)
Retention uniformity
Retention uniformity
Retention uniformity, or RU, is a concept in thin layer chromatography, designed for quantitative measurement of equal-spreading of the spots on the chromatographic plate and one of the Chromatographic response functions...
(Komsta et al., 2007)
In all above formulas, n is the number of compounds separated, Rf (1...n) are the Retention factor of the compounds sorted in non-descending order, Rf0 = 0 and Rf(n+1) = 1.