Test fixture for Determining the Residual Seal Force (RSF) on Pharmaceutical Vials


Definition of Residual Seal Force (RSF)

The residual seal force (RSF) is the force with which the rubber stopper between the flanged cap and the neck of the vial is braced. This force measurement indicates the security of the vial closure. However, these measurements must be correlated with established tests that examine the seal integrity of the stopper.

    There are two diverse tests for determining the integrity of primary packaging (container-closure integrity tests) (from PDA technical report number 27, pharmaceutical package integrity (2)):

    • Microbial immersion test
    • Microbial aerosol challenge
    • Bubble test
    • Liquid tracer test
    • Dye leak test
    • Helium leak detection
    • High voltage leak detection
    • Corona discharge test
    • Pressure/vacuum decay
    • Vacuum retention
    • Headspace gas analysis

    The following methods should be prioritized over the highly popular dye test:

    • Vacuum decay
    • High voltage leak detection
    • Laser-based Headspace Detection

    a) The safety cap must be removed from the closure before testing

    b) The flanged cap holds the stopper under pre-load

    c) When a suitable compression load is applied to the rim of the flanged cap, it lifts from the neck of the vial. This is displayed as the reduction in force in the force-travel diagram. The inflection point indicates the RSF value.

    Guidelines (USP <1207>, International Standard ISO 8362-2 Anhang C, ISO 3826-1 Anhang C, ISO 15747 Anhang C, PDA Technical Report Nr. 27, FDA Guidance for Industry: Container and Closure System Integrity Testing in Lieu of Sterility Testing as a Component of the Stability Protocol for Sterile Products


    Determining the Residual Seal Force 

    For testing the residual seal force of flanged caps, ZwickRoell recommends a device with inserts and compression dies of various sizes. The preload force of the rubber stopper on an aluminum flanged cap indicates the seal integrity of the vial closure. A modular design allows the various inserts to be changed quickly and easily. The test kit consists of a lower mounting plate for supporting the vial. An integrated prism centering aid with scale is used to read the vial diameter (15 mm to 70 mm) and an upper compression test kit with locking nut for pre-positioning the die holds the compression die. Load is applied via a ball joint to compensate for deviations from parallel up to approximately 1°. All of the components are made of rust-free high-grade steel. 


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