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What is the difference between an isocratic and a gradient elution method?
Posted December 16, 2021
Answer
Isocratic and gradient elution methods are two different modes of separation in high-performance liquid chromatography (HPLC).
| Basis of comparison | Isocratic elution method | Gradient elution method |
| Definition | Is an HPLC mode in which the concentration of the mobile phase remains constant over the full analysis time. | Is an HPLC mode in which the concentration of the mobile phase is changed throughout the analysis. |
| Retention of components | Retention of the components is not affected because of the unchanging concentration |
Retention of the components is affected because of the varying concentration |
| Polarity of the mobile phase | Polarity of the mobile phase remains the same throughout | Polarity of the mobile phase may gradually increase or decrease throughout the separation process |
| Effect of column dimensions on selectivity or order of elution | Selectivity or elution order is not dependent on column dimensions. The peaks elute in the same order. | Selectivity or elution order changes with changes in column dimensions. |
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