The liquid chromatography column is the core component of any LC analysis system. Whether the experimental results are accurate often depends on correct usage and proper maintenance. Only by using and maintaining the column correctly can you ensure reliable analytical data every time.
I. Instructions for Column Use
Precautions Before Use
The storage solvent in a new column is generally the mobile phase specified in its performance test report. Before using the column, confirm that this storage solvent is miscible with the mobile phase you intend to use for your samples. Do not mix them directly without verification. For reversed‑phase chromatography, if your eluent contains a high concentration of salt or a buffer, it is recommended to first flush the column with a low‑concentration (10%) organic solvent eluent to avoid salt precipitation and column blockage.
Mobile Phase Requirements
It is recommended to use HPLC‑grade organic solvents and ultrapure water when preparing the mobile phase. If the mobile phase contains salt, it should be filtered through a 0.45 μm membrane. Mobile phase containers and in‑line filters should also be cleaned regularly to prevent accumulation of particulate impurities.
Conventional silica‑based bonded phases are suitable for use in the pH range 2.0‑8.0. When analysing basic compounds, a BDS C18 packing is more appropriate as it tolerates a pH range of 2.0‑10.0. However, if the column is used near the pH limit, it should be cleaned promptly with a suitable solvent after use.
Sample Preparation
Samples must be pre‑treated, for example using a sample filter or a solid‑phase extraction (SPE) column. For difficult samples, adding a guard column can save a lot of trouble. Additionally, for normal‑phase chromatography, all solvents and samples must be strictly dehydrated, otherwise the analytical results may be affected.
II. Column Storage Methods
Daily Maintenance
After each use of a buffer or a salt‑containing mobile phase, first flush the column with 10% methanol/water for 30 minutes to remove salt, then flush with pure methanol for 30 minutes. Note: Do not flush with pure water alone, as this may cause the packing to collapse and damage the column.
Long‑Term Storage
Different column types require different storage conditions:
Reversed‑phase columns: store in pure methanol or acetonitrile.
Normal‑phase columns: store in dehydrated pure hexane.
Ion‑exchange columns: store in an aqueous solution containing sodium azide.
When storing, always replace the original end‑fittings (plugs) and keep the column at room temperature.
III. Column Regeneration
Reversed‑Phase Column Regeneration
Flush the column with 20‑30 column volumes of the following solvents in sequence:
First: methanol/water (10/90, V/V) → then acetonitrile → then isopropanol.
After that, flush in reverse order: isopropanol → acetonitrile → methanol/water (10/90).
Normal‑Phase Column Regeneration
Flush the column with 20‑30 column volumes of the following solvents in sequence:
First: hexane → then isopropanol → then dichloromethane → then methanol.
Then flush in reverse order: methanol → dichloromethane → isopropanol → hexane.
Special reminder: All solvents used must be strictly dehydrated – no water content is allowed.
IV. Common Problems and Solutions
Abnormally High Column Backpressure
If the column pressure rises unexpectedly, the causes and corresponding actions are generally as follows:
Blocked frit: Back‑flush the column, or remove the column end‑fitting and sonicate the frit in 10% dilute nitric acid for 10 minutes, then sonicate in pure water for another 10 minutes.
Contaminated packing: Replace the contaminated packing at the column inlet.
Salt precipitation: Flush the column with 10% methanol/water to dissolve the crystallised salt, then continue flushing with a higher concentration of methanol.
Unsuitable pH: If the stationary phase structure has been damaged due to improper pH, recovery is usually impossible. The best practice is to always pay attention to the column’s pH range.
In fact, with correct usage and proper maintenance, you can not only extend the service life of your column but also ensure stable and accurate results every time, saving you from many experimental detours.
