Yes you can. Using only acetonitrile and water with no mobile phase additives is fully compatible with the column and will not damage it.

If you find the peak shape is not as good without formic acid, try using a steeper gradient to sharpen it. Some compounds’ retention and / or peak shape may be significantly affected by the presence of a mobile phase additive and others may not. It depends on various factors pertaining to the analyte, the stationary phase, and so on.

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