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How long can a chromatographic column last? One month, half a year, or a year? Some may experience column splitting, fronting or tailing, and reduced column efficiency within days, while others might use it for one or two years. Why such a big difference? Usage habits play a significant role. Let’s explore with Sister Xiaoxi.

Common Issues with Chromatographic Column Usage

Increased Column Pressure

Cause: Improper use of buffer salts leading to salt precipitation, blocking the pores between the frit and bonded phase particles, hindering mobile phase mass transfer, and causing increased column pressure.

Changes in Retention Time of the Same Compound Cause: If the column is not thoroughly rinsed before injection, salts remaining in the column can alter the retention time of compounds.

Decreased Column Efficiency Causes:

1. Some buffer salts penetrate deep into the bonded phase, damaging the silica matrix, leading to loss of bonded phase, loosening of the column bed, and reduced column efficiency; 2. Condensation on the bonded phase surface, making it difficult for C18 carbon chains to extend, reducing retention capacity for substances, and resulting in decreased column efficiency. Therefore, after using buffer salts, the column must be rinsed. Special attention is needed when the buffer salt concentration in water is high.

Correct Usage of Buffer Salts in the Mobile Phase 1. Pre-treatment: Before using buffer salts as the mobile phase, rinse the column with a mobile phase without buffer salts until the baseline stabilizes. In principle, the aqueous proportion of the rinsing mobile phase should be the same as that used in analysis (or higher), except that the rinsing mobile phase contains no buffer salts. Reason: Buffer salts are usually soluble in water but difficult to dissolve in organic solvents. When analyzing with a mobile phase containing buffer salts (especially when the water in the mobile phase is a saturated buffer salt solution), if the aqueous proportion in the mobile phase used to preserve the column before analysis is relatively low and not rinsed off, and the organic solvent content in the subsequent sample analysis mobile phase is high with insufficient water to dissolve the buffer salts, the buffer salts may precipitate and deposit on the column, potentially causing the aforementioned damage.

2. Post-treatment: Rinse with a mobile phase having the same aqueous proportion as the analysis mobile phase (the difference is that the rinsing mobile phase contains no buffer salts) for about 30 minutes until the baseline stabilizes. If the column will not be used for a long time and needs long-term storage, add an additional step: rinse with pure organic solvent until the baseline stabilizes.

Points to Note When Using Buffer Solutions 1. Avoid using hydrochloride salts as they corrode steel.

2. Prepare buffer solutions fresh for each use, as they are often good culture media for bacteria. Strange phenomena may occur if used after a day or stored for a long time.

3. Do not directly transition to organic solvents after experiments, as organic solvents can cause salt precipitation, clogging the fluid path or column. Use a 95:5 water-methanol mixture for rinsing.

4. Monitor the pH range of the buffer solution promptly and keep it in mind.

5. When cleaning the fluid path and column, heating to 30°C with temperature control can facilitate rinsing.

6. When using buffer solutions for extended periods, check for precipitation at connections. If white salt deposits are observed, consider periodically rinsing the fluid path with 10% nitric acid (remove the column, flush with 30ml, then rinse with 5 times the volume of water) to prevent clogging.

7. Use reliable reagents for buffer solutions to avoid impurities causing unnecessary issues.

If the organic solvent proportion in the mobile phase is high, it cannot be used to rinse buffer salts, as it won’t wash them out. Typically, for C18 columns, rinsing with 5%~10% methanol can remove buffer salts, followed by pure organic solvent to protect the column. The method involves using the same concentration of mobile phase without salts for cleaning, though it is slower. Using water allows for quick replacement, usually within 15 minutes, with a flow rate of 0.8 being preferable. Using pure water may cause loss of bonded carbon chains; use a 5%~10% methanol-water solution instead. Replacing the buffer in the mobile phase with pure water while keeping the organic phase unchanged is a safer way to rinse the column.

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