Gradient capabilities elution

Figure 5.4-6. Online MDLC with gradient elution. This type of MDLC system is similar to the setup with salt-plug elution, but in this case, the elution is performed with a step- or linear-gradient that requires a second gradient capable HPLC-pump.

Fluorescence detectors can also be used and while their sensitivity may be greater, they are less widely applicable owing to the smaller number of fluorescent compounds. Differential refractometers will detect changes in the refractive index of the solvent due to the presence of solutes and, while they are less sensitive than the other detectors and often cannot be used effectively with gradient elution techniques, they are capable of detecting the presence of any solute. 

The Micromeritics 7000 liquid chromatograph (Fig.3.30) also uses a reciprocating pumping system. The pump has several unique features. It delivers pulseless flow without a pulse damper, it can operate from an unlimited reservoir, it requires only a single pump for gradient elution and it is capable of operating at constant pressure or constant flow-rate. 

Fig. 8.2. Schematic illustration of a CEC instrument capable of isocratic and gradient elution and ESI-MS detection.

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