Foreign material between the plunger and barrel in syringes

Pre-filled syringes are common drug delivery systems and liquid observed between the plunger and barrel poses a concern to patient safety. Here's how we investigated a batch of suspected 'leaky syringes'.

The challenge

Pharmachem RD 4915 HR


The syringes were inspected and compared to a reference sterile syringe. Liquid observed between the plunger and barrel of the test syringes was photographed, syringes were disassembled and subsamples of the unknown liquid was isolated from the plunger, barrel and plunger rod.


These subsamples were analysed by Fourier Transform Infrared (FT-IR) spectroscopy (figure 2) and X-ray microanalysis (figure 1). Lubricant from the reference syringe and the parenteral solution were similarly analysed.


Figure 1 - micrograph of the sample, showing the liquid inside the barrel above the syringe plunger.


Figure 2 - FT-IR spectrum of the liquid isolated from the syringe barrel (red) compared with a library silicone lubricant reference spectrum (blue).




No deformations were noted in the gaskets of the syringes on initial inspection. The liquid between the plunger and barrel was consistently identified as silicone, which was also the plunger lubricant identified in the reference syringe.


This liquid was considered to have originated from the silicone-coated plunger stopper. The client then identified an excess of silicone lubricant around the plunger of a particular batch of syringes and was therefore able to eliminate the root cause of the problem.

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