A revision of General Chapter <621> on Chromatography is proposed in the Pharmacopeial Forum (volume 38, edition 2). This new chapter has a major impact on system suitability tests (SST).
In the current USP 35, adjustments in the mobile phase in gradient conditions are not recommended. Now, adjustments should be possible but as they may cause changes in selectivity, they should be made with caution.
The revised USP chapter now defines for each variable of the SST whether this variable applies for isocratic separations only or for gradient separations, too. In the future, the following parameters of the SST will be possible for gradient separations:
pH of the mobile phase (± 0.2)
Concentration of salts in buffer (± 10 %)
Column temperature (± 10%)
Different length, internal diameter, and/or particle size in the stationary phase in gradient separations are not allowed.
Also the formula for calculating the flow rate will be modified. A new table will also be created to show the interaction between the variables length, internal diameter, particle size, and flow rates for a few significant column configurations. The objective of this is to maintain the performance of the separation system when modifying the SST parameter.
On the contrary, changes in the chemical characteristics of the stationary phase will be considered a modification to the method and will require full validation.
Comments to the draft of the new USP chapter on Chromatography can be sent until 31 May 2012.