It is incorrect to rinse the ion chromatography column with pure water. Because in general, if pure water is directly used to rinse the ion chromatography column, it is easy to cause the loss of stationary phase and phase collapse in the ion chromatography column. Therefore, it is not recommended to directly rinse the ion chromatography column with pure water.

Usually, when rinsing an ion chromatography column, it is recommended to add substances such as methanol or acetonitrile to pure water and then rinse the column. This flushing of the ion chromatography column generally does not affect the column. The reasons why ion chromatography columns cannot be directly rinsed with pure water are as follows:

1. Generally, the material of ion chromatography columns should not be washed with pure water for a long time. Due to the fact that most ion chromatography columns nowadays use silica gel as the matrix, and the nature of silica gel is that its solubility is much higher in pure water than in general organic solvents, rinsing the ion chromatography column with pure water will cause the silica gel material in the column to dissolve. Long term rinsing with pure water will cause the loss of the stationary phase in the ion chromatography column, thereby reducing the column efficiency.

For a typical C18 column, because the C18 long chains themselves are dissolved in water and the interaction force between C18 long chains is greater than that between C18 and water molecules, washing the ion chromatography column with pure water for a long time will bring the C18 long chains closer to each other and cause the connected C18 long chains to collapse on the surface of the silica gel matrix, resulting in a decrease in the retention ability of hydrophobic substances, i.e. phase collapse.

In order to provide analytical conditions for samples that can only be dissolved in pure water, some companies have introduced pure water columns suitable for ion chromatography column washing. This pure water column will not cause phase collapse, so it can analyze samples that are only dissolved in pure water.

If a mobile phase containing buffer salts has been used in an ion chromatography column, rinsing with pure water cannot remove the buffer salts. This is because the buffer salt itself is insoluble in organic solvents, and the filler used in the C18 reverse phase column is a C18 long chain connected to the surface of the silica gel, which is equivalent to a hydrophobic organic phase. Moreover, because the silica gel matrix is surrounded by organic substances, the buffer salt may not easily reach the silica gel matrix when using a buffer salt aqueous solution as the mobile phase during operation, which may not damage the matrix. However, the mobile phase used usually contains some organic solvents, and these organic solvents and C18 long chains are mutually soluble. Therefore, the addition of organic solvents enhances the ability of the mobile phase to penetrate the silicone matrix, allowing some buffer salts to come into contact with the silicone matrix.

So directly rinsing the ion chromatography column with pure water can only flush the buffer salt on its surface, but the buffer salt that seeps deep into the ion chromatography column will still remain there. So it is recommended to add a portion of organic solvent to pure water when washing the ion chromatography column. The ratio of water to organic solvent depends on the situation, so that water containing organic solvent can wash the ion chromatography column.

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