The purpose of the Resolution Test Mixture (RTM) is twofold.
- As a sort of “System Suitability” test, if only to make sure you have prepared the mobile phase correctly.
- To be sure that the test column is not completely degraded.
You could use just a caffeine injection for this purpose. However, by using a mixture of several peaks as in the RTM, you can graph the total observed variance, which is comprised of column variance + extra column variance. The intercept of that regression is the extra column variance.
This information can be useful; for example, most of our Agilent 1100/1200 instruments produce a 120uL^2 of extra column volume variance (or 11uL as the standard deviation). This is adequate for most standard size analytical columns, but too large for a short 2.1 mm type column, and that can be a significant finding. Some older instruments have been found to have 800-900 ul^2 of volume variance which would make using a 2.1 mm column for your analysis, not recommended for use with this instrument.
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