Here is a similar thread:
https://www.researchgate.net/post/Why_is_reversed_phase_high-performance_liquid_chromatography_HPLC_preferred
RP could be applied to separation of a very wide range of molecules including charged and polar molecules. It also allows precise control of variables such as organic solvent type and concentration, and pH.
RP column is highly stable and efficient. Thus, these advantages explain the most frequent use of RP in HPLC application in these days.
Mainly because it works well, and the columns are relatively inexpensive per use. With care the columns are reusable. People generally try other columns only if the C18 doesn't work. Like Sonika said, it works on a wide variety of compounds and a wide polarity range.
In RP-HPLC the nature of mobile phase is polar and stationary phase (column) is non-polar. it is very efficient to separate the polar compounds due to interaction between polar compounds (most of the pharmaceutical ingredients- polar nature) with polar mobile phase. C18- column indicates more non polar because of high carbon load, hence c18 and RP are more preferred to separate polar compounds.
The solvent system used with RP chromatography (acetonitrile / methanol / water / formic acid) is ideal to promote analyte ionization in electrospray (ESI) and/or APCI ion sources. Ion pairing chromatography can also be achieved using the same column and solvents with addition of a strong ion pairing agent like HFBA. Likewise HILIC is a useful variant of C18 RP that extends the utility of this chromatographic system. Most other LC separation systems, like normal phase, size exclusion or ion exchange, use solvents which aren't sufficiently polar to promote ESI or which contain high concentrations of involatile salts that would contaminate any MS ion source. The 'Hydro' and 'polar' variants of C18 should not be overlooked - they can often retain and separate analytes that would pass straight through conventional C18 columns.
I think that these are not strong solvent and you use these in low percentage, which in phase you would use a much stronger solvent and higher percentage, otherwise you molecule will not be able to bind to your column. As well as RP could be applied to separation of a very wide range of molecules including charged and polar molecules.
And of course and above all others correct remarks, WATER is the greenest and cheapest solvent that you can find!
It is worth noting that 'reversed-phase' chromatography has been around for over 60 years and has been continually evolving in that time. As a result the mechanisms involved in the interactions between stationary phase, analyte and mobile phase are relatively well understood in comparison to other modes of chromatography. This allows for quicker and easier method development. In addition, the variety of chemistries; from polar-embedded to mixed-mode RP allows for this mode to be able to retain and separate a wide variety of compounds with different chemical properties, even within the same run .
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