Extra Column Dispersion - Chromatographic Apparatus for Trace Analysis > Page 56

Chromatographic Apparatus for Trace Analysis

There are two very significant advantages to small bore columns and they are solvent economy and high mass sensitivity. Although the former is important when considering operating costs, the latter is the most important technically. The mass sensitivity of a chromatographic system does not depend on the properties of the detector only but on the associated column and, thus, indirectly, is related to extra column dispersion. It follows, that the factors that control mass sensitivity need to be understood.

The mass sensitivity of chromatographic system is defined as the mass of solute (mD) that will provide a peak with a height equivalent to twice the noise level.

 

Consider a peak with height equivalent to twice the noise level, being sensed by a detector with a concentration sensitivity of (XD) g/ml.

Let the peak-volume be (4sc) where (sc) is the volume standard deviation of the peak and the concentration at the peak maximum as twice the mean concentration of the solute in the peak.

Then,

or m =  2scXD