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Just don’t do it!! Don’t overtighten your LC direct connect guard.

29 Sep 2023

Overtightening High-Performance Liquid Chromatography (HPLC) guard columns to HPLC columns can cause several issues, leading to suboptimal chromatographic performance and potential damage to the equipment.

We offer three distinct direct-connect guard systems: EXP Holders, ROC Holders, and Trident Holders. It depends on the HPLC phase you are using. For more details, please refer here.

LC Direct Connect Guard column Selector

Guard columns are small, protective columns placed before the main analytical column to protect it from sample debris and HPLC system contaminants. Overtightening the guard column can cause physical damage to the PEEK ferrule. Excessive tightening can cause the PEEK ferrule to partially block the inlet frit of the HPLC column causing elevated backpressure. Overtightening can make it extremely challenging to remove the guard column or the HPLC column during maintenance or when switching columns. This difficulty can result in accidental damage to the column threads or the column itself (unable to remove ferrule).
What are the consequences of overtightening on the PEEK ferrule and guard cartridge? Below are some images illustrating the effects of excessive tightening on the components of the Trident guard holder and cartridge.

PEEK ferrule stuck in the HPLC column

Guard Cartridge inlet side.

Ferrule that has been overtightened

PEEK ferrule immovably embedded within an HPLC column impression on the guard cartridge resulting from excessive tightening PEEK ferrule damaged due to overtightening unused PEEK ferrule (catalog 27476)
Figure 1 Figure 2 Figure 3  Figure 4

Figure 1: displays the PEEK ferrule immovably embedded within an HPLC column (column will need to be discarded).

Figure 2: exhibits the impression on the guard cartridge resulting from excessive tightening. 

Figure 3: showcases a photograph of a PEEK ferrule damaged due to overtightening.

Figure 4: illustrates an unused PEEK ferrule (catalog 27476).

To prevent these problems, it is essential to adhere to our guidelines for attaching the guard column to the HPLC column. Usually, hand-tightening should suffice. A wrench may be necessary to ensure a leak-free connection, but it should only be turned an additional 1/8 to ¼ of a rotation beyond hand-tight. Please see the instruction sheets for the three different holders for more details. 

EXP Direct Connect Holder instruction sheet

ROC LC Guard Column Holder instruction sheet

Trident LC Column Holder instruction sheet

Furthermore, it is equally crucial to routinely inspect and replace the ferrule to maintain effective sealing without the risk of overtightening. You will notice a new ferrule (figure 4) to start to expand and look like figure 3 when it needs to be replaced. Replace ferrule every few times the guard holder is removed or shows signs of wear. 

Replacement ferrules:

EXP Holder replacement ferrule (catalog 25935)

ROC Holder replacement PEEK ferrule (catalog 26391)

Trident Holder replacement PEEK ferrule (catalog 27476)

Further information:

Do I Need an LC Guard Column? (Video)