It’s just a silica support with a C18 bonded on – surely there can’t be much difference between them? Wrong. There are huge differences between standard C18 phases and simply swapping one C18 for another, without accounting for these differences, will produce differences in retention time, resolution and peak elution order. Most of us are aware of the difference between endcapped / non-endcapped columns or the idea of carbon loading. Although this is a start, differences in selectivity are caused by many complex factors and none of the manufacturers have established a standardized system of quantifying the effects of these differences.
The following is an overlay of 4 modern standard C18 columns by popular manufacturers:
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