One of the deterministic leak test methods outlined in USP <1207>, vacuum decay has a long history of implementation relative to some of the more modern container closure integrity test technologies. An ASTM standard is available for reference, ASTM F2338-09: “Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method”. However, as with all CCI technologies, a vacuum decay method must be developed and validated for its intended use, influenced by the package, the product, and the study goals at hand.
Principle of Operation USP <1207> | Vacuum Decay
This nondestructive test operates on the principal of vacuum decay and relies on a series of time-dependent steps with measurements at key timepoints in the test cycle. A test package is placed into a chamber, and vacuum is pulled down to a defined setpoint. Sensitive pressure transducers measure change in chamber pressure to ensure the setpoint is reached within the acceptable range. Inability to reach the intended vacuum setpoint may be an indication of gross package leakage, such as a deformed stopper.
Once at the predefined pressure setpoint, additional pressure transducers monitor chamber pressure over time. In a set of negative controls, or otherwise good, non-leaking samples, a certain baseline level of pressure rise over the test period is expected and characterized in method development. This rise in pressure is largely a result of material outgassing, a phenomenon in which gas and water vapor molecules adsorbed onto and absorbed into packaging materials is released under vacuum. Naturally, the more porous a material, the more outgassing is expected to occur. A glass vial will have substantially less outgassing than a plastic vial with the same dimensions, for example.
In a positive control, or otherwise leaking sample, the observed pressure rise over the test period will be larger, as the resulting pressure rise includes the effect of outgassing, but also includes the resultant pressure rise from gas or liquid migrating from the inside of the package system, through a defect, and into the vacuum chamber. Using acceptance criteria established through method development, quantitative test results are qualitatively judged as pass or fail.
Applications and Limitations USP <1207> | Vacuum Decay
Method development and validation is critical to ensure optimization of test parameters to maximize test sensitivity. The applicability to a given package system as well as method parameters and limit of detection, must be considered on a product-package to product-package basis. Factors such as outgassing can impact sensitivity and mask small leaks, a challenge exacerbated by certain package configurations including plastic and elastomeric materials. Additionally, as leak response is directly related to flow through a defect, defect clogging as a result of product formulation, storage time, or conditions can further complicate vacuum decay tests. For this reason, vacuum decay is often not able to test to the maximum allowable leakage limit (MALL) for a given product-package system. However, it remains a fantastic tool for assessment of complete, product-filled package systems and is often incorporated as part of a broader CCI testing strategy, making it one of the more common and well-documented deterministic CCI test technologies.
The team at CS Analytical consists of founding members of the world’s first cGMP, FDA-registered contract CCI laboratory housing all deterministic technologies as listed in USP <1207>. The resulting laboratory set standards and best practices for industry still used today, many of which are directly incorporated into USP <1207>. CS Analytical is the most trusted source for advisory services on CCI method selection, and developing and validating methods using state-of-the-art PTI VeriPac 465 Vacuum Decay Leak Test Systems that represent the cutting edge of best practices with respect to CCI testing.