If you use a pH buffer even with moderate ionic strength, at pH 9, the capillaries would not be expected to last very long.
It is hard to predict how many runs you get because it will depend on your run times, your conditioning step, etc. However, these capillaries are not designed for a pH higher than 8. The silica was and the organo-silane bond of the polyacrylamide is susceptible to hydrolysis, degradation and pitting at high ionic strength buffers above pH 8.
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