Limit of detection, dilution factors, and technique compatibility in multidimensional separations utilizing chromatography, capillary electrophoresis, and field-flow fractionation

The theoretical development of the limit of detection (LOD) concept is exte nded from one separation column or channel used in gas, liquid, and size-ex clusion chromatography, capillary electrophoresis, and held-flow fractionat ion to the case where multiple columns and channels are utilized in the so- called "comprehensive" and "heart cutting" modes of operation. Simple equat ions show that the column dilution factors and the split ratios used to com pute the LOD are multiplicative per dimension. Thus, when more than one sep aration dimension is utilized in a sequential column mode of operation, a l arger overall dilution of the original injected solute concentration will o ccur. The dilution of the initial zone in multidimensional geometrical sepa ration systems such as planar two-dimensional thin-layer chromatography and two-dimensional slab gel electrophoresis is also considered. The practical aspects of this dilution are discussed with respect to the types of separa tion techniques that can be used to implement multidimensional separation s ystems.