Concentration limit of detection, CLOD

The limit of detection (LOD) of a system can be defined in two ways the concentration limit of detection (CLOD) and the mass limit of detection (MLOD). The CLOD of a typical peptide is about 1 jLg/mL using absorbance detection at 200 nm. If 10 nL are injected, this translates to an MLOD of 10 pg at three times the baseline noise. The MLOD illustrates the measuring capability of the instrument. The more important parameter is the CLOD, which relates to the sample itself. The CLOD for HPCE is relatively poor, whereas the MLOD is quite good, especially when compared to HPLC. In HPLC, the injection size can be 1000 times greater compared to HPCE. 

Although CE technology has many advantages as an analytical tool, it has some disadvantages which are currently under investigation for improvements. For example, two major CE drawbacks frequently discussed by investigators are (a) the low concentration limits of detection (CLOD) and (b) the lack of detectors which provide structural information. Recent advances have addressed both of these issues. Enhancements in CLOD have been achieved by the advent of a number of preconcentration methods, in particular the use of on-line solid-phase microextractors or analyte concentrator-microreactors (see Refs. 50,51,58,68,... 

It was shown in Section 2.3.7.1 that the absolute detection limit is a strict function of the volume and efficiency of the separation column, as well as the response factor and basehne noise of the detector. To calculate the LOD in concentration units (clod)> it was shown in Eq. 2.24 that the injected analyte mass must be taken into account. At a given analyte concentration in the sample, and in this case this relates to Clod> inj varied, by changing the injection volume... 

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