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LC Column Maintenance: Reverse Flushing

LC Column Maintenance: Reverse Flushing

Maintaining care of items helps preserve the quality and efficiency of its performance.  Cars need frequent oil changes and tire rotations to maintain safe and reliable performance. HVAC systems need air filters to be swapped periodically to avoid clogs and damages to the central air system. Flossing and brushing teeth on a routine basis helps prevent cavities and tooth decay. Similarly, chromatographic columns require periodic maintenance and care to ensure LC instrumentation and analysis longevity and integrity. 

Having chromatographic column maintenance integrated into the routine laboratory workflow is essential for maintaining accurate and reliable qualitative and quantitative analysis. Without proper care, dirty chromatography columns may affect the efficiency, quality, and life span of analytical equipment.  This may lead to inaccurate test results due to poor column performance resulting in longer time spent on projects and higher incurred costs. Some indications of poor performance in columns may include anomalies in peak shape such as tailing, shouldering, splitting, and broadening. Further, poorly maintained columns may lead to high back pressure in your system and inefficiency between analytes. While chromatographic columns are replaceable and easy to purchase, maintaining column care will extend its life and minimize unnecessary costs. 

Reverse flushing, also known as back-flushing, columns helps to remove any contaminants, particulates or analytes that may be trapped and lingering in the column. Below are steps to follow to back-flush your column.

How to Clean a Column Using Back-Flushing

  1. Turn off the instrument's pumps to stop the flow of the mobile phase.
  2. Remove the column and/or column guard from the instrument's flow path. Observe the directional flow of the column.
  3. If applicable, remove the column guard from the column.
  4. Flip the column and reinstall the column in the flow path of the LC instrument. The directional flow of the  column should be pointed in the opposite direction as the flow of the mobile phase. 
  5. Place a waste beaker below the opening of the column to collect a solution that is used to flush the column. Your column should not be attached to the detector. Flushing your column into the detector may cause unwanted contaminants and particulates to enter the 
  6. Begin flushing the column out with a cleaning solution. This is typically methanol, isopropanol, or acetonitrile for the CannID application.
  7. Flush your system out for 15 minutes to 1 hour. Adjust the flow rate of your cleaning solution as needed.
  8. Once flushed, turn the instrument flow off and reassemble your column to its original configuration.
  9. Run a test mix to observe column performance.

If there are still issues with your column after a backflush, it may be necessary to isolate the issue between the column and the column guard. On some occasions, the column guard and/or the column will need to be replaced.

Implementing reverse flushing as a part of preventive maintenance is a good method to prolong the lifespan of your columns and instruments. Maintaining clean and flushed columns improves the accuracy and integrity of your data and test results. To learn more about column flushing, please email


Figure 1. Example of a column orientation in a HPLC instrument. The column flow direction is inline to the mobile phase flow direction.

Figure 2. Example of a column orientation during the back flush of the column. The column flow direction is pointed the opposite direction of the mobile phase flow.

Figure 3. Initial calibration verification prior to reverse flush maintenance for Ionization Labs 14 analyte method

Figure 4. Initial calibration verification after a reverse flush maintenance for Ionization Labs 14 analyte method

Figure 5. Overlay of two analyte peaks. The green peaks are the analytes prior to backflushing the column. The blue peaks are the analytes after flushing the column.

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