I am searching for disadvantages of ion-pair chromatography. Why is this technique not more favourable with chromatographers? Is there any other alternative technique available for analyzing ionic compounds except ion-pair chromatography? Kindly enlighten me regarding this. If you have any material kindly upload.
Some of the reputation of ion pairing being problematic is well deserved. The concentration of ion-pair reagent in the stationary phase is controlled by several variables including the organic content of the mobile phase and the column temperature. This means that temperature must be controlled carefully and that gradient elution is difficult, if not impossible. Further compounding the process is the slow equilibration between the mobile phase and the column. Whereas we think 10 column volumes of mobile phase (15–25 mL) is adequate to equilibrate the typical reversed-phase column with a traditional buffer-organic mobile phase, ion-pair reagents can take 20–50 column volumes (50–100 mL) or more to equilibrate. This further discourages gradient elution.
Many ion-pair reagents have substantial UV absorbance, which precludes use with low-UV detection. Also, when the baseline is autozeroed at the beginning of a run, it appears that the baseline is low, but it might be elevated significantly in reality. Whenever anything with lower UV absorbance than the mobile phase enters the column (such as the injection solvent or other reagents in the sample), a negative peak will occur. This means that negative peaks and ghost peaks are common with ion pairing.
Ion-pair reagents can never be washed fully from the column, even with extensive column flushing. This means that you should dedicate a particular column to ion-pair applications. It is alright to switch from one ion-pair reagent to another in a given column, but never use a column for other applications once it has been used for ion pairing. Trace levels of the ion-pair reagent can change selectivity when used for non-ion-pair applications, making column-to-column reproducibility a problem.
Ion pairing has justly earned a bad reputation over the years. However, when ion pairing solves your separation problem, many of its shortcomings can be overlooked. Be careful when using ion pairing to allow sufficient time for the mobile phase to equilibrate with the column and avoid changes in temperature or mobile phase organic that can disrupt the equilibrium. Before you embark on developing an ion pairing method, consider carefully if there are alternatives, such as the mixed-mode, AQ, embedded polar phase, or other speciality columns.
because it takes more time for system stabilisation and column washing.
About the washing: often it is impossible to wash the ion-paring reagent out of the column. It is more like You create a modified column. As a consequence You need a separate column for each ion-paring reagent to have reliable performance.
Some of the reputation of ion pairing being problematic is well deserved. The concentration of ion-pair reagent in the stationary phase is controlled by several variables including the organic content of the mobile phase and the column temperature. This means that temperature must be controlled carefully and that gradient elution is difficult, if not impossible. Further compounding the process is the slow equilibration between the mobile phase and the column. Whereas we think 10 column volumes of mobile phase (15–25 mL) is adequate to equilibrate the typical reversed-phase column with a traditional buffer-organic mobile phase, ion-pair reagents can take 20–50 column volumes (50–100 mL) or more to equilibrate. This further discourages gradient elution.
Many ion-pair reagents have substantial UV absorbance, which precludes use with low-UV detection. Also, when the baseline is autozeroed at the beginning of a run, it appears that the baseline is low, but it might be elevated significantly in reality. Whenever anything with lower UV absorbance than the mobile phase enters the column (such as the injection solvent or other reagents in the sample), a negative peak will occur. This means that negative peaks and ghost peaks are common with ion pairing.
Ion-pair reagents can never be washed fully from the column, even with extensive column flushing. This means that you should dedicate a particular column to ion-pair applications. It is alright to switch from one ion-pair reagent to another in a given column, but never use a column for other applications once it has been used for ion pairing. Trace levels of the ion-pair reagent can change selectivity when used for non-ion-pair applications, making column-to-column reproducibility a problem.
Ion pairing has justly earned a bad reputation over the years. However, when ion pairing solves your separation problem, many of its shortcomings can be overlooked. Be careful when using ion pairing to allow sufficient time for the mobile phase to equilibrate with the column and avoid changes in temperature or mobile phase organic that can disrupt the equilibrium. Before you embark on developing an ion pairing method, consider carefully if there are alternatives, such as the mixed-mode, AQ, embedded polar phase, or other speciality columns.
Thank you very much for your answers. It would be great help if you would provide me with the references or some materials regarding the disadvantages of ion-pairing reagents as mentioned above.
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