What should we do if mircro syringes is blocked? A four-step guide to unblocking it, explained step by step from the simplest to the most drast

 **Author:Orginal from Ms Xiaoyue Lü | HAMAG

 

The injection needle is the ‘lifeline’ of chromatographic analysis. If it becomes blocked, the consequences range from fluctuating peak areas in mild cases to system errors and shutdowns in severe cases. Today, we’ll get straight to the point and explain how to deal with this, without beating about the bush.

01 Why do blockages occur? Identify the cause before taking action

There are five main causes of blockages:

① Accumulation of sample residues — high-boiling-point compounds, oils and fats, and polymers depositing inside the needle;

② Particle blockage — solid particles entering the needle directly because the sample was not filtered or centrifuged;

③ Salt crystallisation — high-salt samples (such as biological fluids or environmental water samples) crystallise upon drying, blocking the needle tip;

④ Debris from the injection septum — the injection septum has deteriorated or is of poor quality, and debris is drawn into the needle;

⑤ Excessively high sample concentration or prolonged lack of cleaning — residual sample inside the needle orifice has solidified.First determine which cause applies, then select the appropriate remedy; do not proceed blindly.

02. Clearing blockages: a four-step approach from mild to severe

Step 1: Repeated solvent flushing (minor blockage)

Repeatedly flush the needle using a dedicated cleaning solution (methanol, isopropanol, deionised water, etc.). After soaking for 10–15 minutes, repeat the flushing process. Check the pattern of solvent discharge from the needle—under normal circumstances, it should flow out in a straight line.

Step 2: Solvent Soaking (Moderate Blockage)

Soak the injection needle in methanol. For minor blockages, soak for 2–3 hours; for severe blockages, soak for 6–8 hours or longer. After soaking, rinse as described in Step 1.

Step 3: Ultrasonic Cleaning (Stubborn Blockage)

Place the solvent-soaked injection needle into an ultrasonic cleaner and sonicate for 10–15 minutes, maintaining a power setting of 20–40 W.

⚠️ Ultrasonic cleaning is a controversial method that may damage the internal structure of the injection needle; it should only be used as a last resort. Furthermore, do not place the entire needle into the ultrasonic bath—only immerse the needle tip in the solvent for sonication.

Step 4: Mechanical Clearance (Severe Blockage)

If the tip of a 10–100 μL syringe is blocked, carefully pierce through the blockage using a fine steel wire with a diameter of 0.1 mm, taking care not to scratch the inner wall of the syringe whilst doing so.

⚠️ Under no circumstances should the tip of the syringe be heated with a flame—annealing will soften it and render it incapable of penetrating the blockage; nor should the plunger be forced back and forth whilst the syringe is blocked—the high pressure may cause the barrel to crack.

03.Cleaning frequency

Dirty or sticky samples: daily cleaning is recommended; routine samples: thorough cleaning at least once a week.

▍After Each Injection

Whether for standards or samples, the needle must be cleaned with a needle-cleaning solution after every injection.

▍Commonly Used Needle-Cleaning Solvents

Methanol, acetonitrile and acetone are the standard choices; dichloromethane has strong solvent power but may corrode certain materials and should be used with caution; select according to the nature of the contaminants—following the principle that like dissolves like.

▍Daily plunger check

Pull the plunger to the full stop and push it back. If it feels stiff or alternates between tight and loose, cleaning is required: remove the plunger and wipe it with filter paper moistened with acetone.

▍Long-term storage

Clean with needle-cleaning solution at least 10 times, then clean with acetone at least three times; allow to air-dry before storing.

04.Four Taboos to Remember

① Do not interchange push rods—metal push rods and syringes are ground to fit each other; interchanging them may result in a poor seal or jamming;

② Do not fill the entire syringe with solvent—this will damage the bonded joints;

③ Do not pull the push rod when the needle is dry—this will damage the inner wall of the syringe;

④ Do not draw up strong acids or alkalis—these will corrode the glass or metal.

05.How to Tell if the Blockage Has Been Cleared?

Test by pushing solvent through with a syringe — if the flow rate is even and there is no resistance, the blockage has been cleared.

If the blockage persists after trying all the above methods, do not hesitate to replace the needle immediately — the cost of a single needle is far lower than that of a batch of scrapped data.

The septum is sometimes partly to blame for needle blockages.

The debris mentioned in Reason ④ often originates from the cap gasket itself. Hamag pre-assembled sample vial cap gaskets feature a dual-layer structure comprising an upper layer of silicone and a lower layer of PTFE, ensuring the gasket does not fall out and minimising debris shedding, thereby reducing the likelihood of the needle being ‘ambushed’ at source.(A bit of advertising now and then:D)