Introduction
There are many options available for Container Closure Integrity (CCI) testing of glass vials and syringes. From traditional probabilistic methods like Dye Immersion (tracer dye) or Bacterial or Microbial Challenge testing, to a variety of deterministic methods like Vacuum Leak, Headspace Analysis, Mass Extraction, Voltage Leak, and Tracer Gas there should be an option for any need. Each method has pros and cons that should be considered when choosing an appropriate test method for a particular container type. Not all options are suitable for all sample configurations and some methods particularly shine in certain applications, but fall short in others. With the newest edition of USP 1207, the pharmaceutical industry is moving away from traditional dye and bacterial immersion test methods and moving toward deterministic methods for CCI testing.
While there is no “one size fits all” CCI option, Mass Extraction is proving itself a strong contender for many different applications. Like most deterministic CCI methods, Mass Extraction is nondestructive. This allows for 100% in-line testing to be performed in a manufacturing setting. In a laboratory setting, non-destructive testing is a major advantage because failed samples can be investigated for cause of failure. Like other deterministic methods, Mass Extraction is faster, more sensitive, and not prone to contamination as compared to traditional dye or bacterial immersion methods. Some additional advantages of Mass Extraction include leak detection in both the headspace and liquid, testing with ambient air, evaluation of the entire container for leaks, suitability for rigid and some flexible applications, independence of part volume or configuration, and direct leak measurement (vs. indirect) which increases test sensitivity.
How Mass Extraction Works
Mass extraction is similar to Vacuum Decay with respect to the UUT (unit under test) being inserted into a vacuum test chamber. Beyond the use of a vacuum test chamber and testing under vacuum, these two test methods are very different. Mass Extraction directly measures mass leaking (gas flow) from a UUT. Vacuum Decay measures pressure increase which is used in combination with the volume to calculate a leak flow rate. This type of measurement is sometimes referred to as an indirect flow measurement since the actual flow rate is not measured. Another difference is that the calculated flow rate from Vacuum Decay is volumetric flow whereas Mass Extraction uses mass flow to determine the flow rate from leaks in packages. Volumetric flow is the rate of volume change over time (cm3/minute). Mass leak flow is the rate of mass change over time (μg/minute).
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The Mass Extraction test method is based on the Mass Conservation Law, which is simply that the mass flow will not change in a closed system. So if you measure the “make-up flow” required to maintain a constant vacuum, then that flow is equivalent to the leak rate. The Mass Extraction instrument has a detector capable of direct flow measurements and can measure ultra-low leak flow rates. This gives Mass Extraction the ability to detect leaks in some container systems down to 1μm (see ASTM F3287-17E1 – Standard Test Method for Nondestructive Detection of Leaks in Packages by Mass Extraction Method).
The mass extraction instrument is controlled by a microprocessor and is capable of being operated as a stand-alone instrument. A computer can be connected in conjunction with a software program if data collection and 21 CFR Part 11 compliance is desired. The test cycle is divided into steps for pre-evacuation, evacuation, pre-stability, stability, pressure checks, and leak checks. The timing and order for each step and the flow and pressure maximum and minimum set points are contained in a test method. The test method is validated and a pass/fail threshold value is determined. Methods will vary based on test method characteristics. Some sample types will require longer or shorter timing steps and larger or smaller pressure and flow limits.
The test is performed by placing a sample into a specially designed test chamber and applying a vacuum to evacuate the air in the chamber. A series of evacuation cycles are performed, each designed to detect a smaller leak size. Each leak check has a predetermined flow limit. Exceeding the limit will stop the test. The first is the gross leak check. This is a safety step designed to detect a gross leak before any liquid from the defect can contaminate the test system with moisture. Gross leaks would typically be over 20 microns. The next leak check is called the large leak check. This is another safety step to prevent moisture contamination in the test system. The final leak check is done through the IMFS (Intelligent Molecular Flow Sensor) which is capable of detecting leaks down to 1 micron.
Determination of Pass or Fail
A pass/fail threshold value is determined for each method by testing both non-leaking parts and parts with either simulated leaks using the calibrated leak orifice (CLO) or actual defects in the test samples. Both groups are analyzed statistically. The limit is calculated as a safety factor below the average bad part or above the average good part. A common approach to establishing the method limit is by subtracting two times the standard deviation from the average of the defect parts tested in the method validation. The flow limit value will change based on a number of factors, including, the amount of free space in the test chamber, the container type, and the method cycle parameters.
Testing Overview
Prior to testing, we must verify the system is dry and free of residual mass; to do this we test a “master part.” The master part is a solid-metal piece similar in size and shape to the test sample and represents a nonleaking sample.
The void space or free volume in the test chamber is filled using a library of solid metal filler parts. The amount of void space in the test chamber will directly affect the flow values, so it is important to minimize the void space as much as possible.
The positive control for the test is a calibrated leak orifice (CLO) which is a glass microcapillary encased in a special housing attached to the mass extraction instrument. When the CLO is turned “on”, the flow is diverted through the CLO, simulating a defect of known size. The master part for the test is run with the CLO turned on. This CLO flow value is reported for every sample set and represents a 2μm or 5μm defect in the test system used with the sample set.
The test samples are run using a Mass Extraction method that has been validated for that sample type. If the sample fails at the gross leak or large leak check, the sample is reported as a “fail” with no final leak value. If the test goes through the fine leak check, then the sample is reported as a “pass” or “fail” depending on the final flow value, with the final flow value.
Conclusion
With all the CCI test options available, selecting an appropriate CCI method can be overwhelming at times. However, after a very thoughtful review of CCI options, Nelson labs selected Mass Extraction as the optimal test method with the best overall advantages. For more information on Mass Extraction testing at Nelson Labs, visit our website at 
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About the Author
Jennifer Gygi has over 25 years of medical device laboratory experience. She has worked in the Microbiology, Bioburden, IDs, and Packaging sections at Nelson Labs. Jennifer has experience with various microbial tests, including microbial limits, plate counts, Biological Indicator population verifications, organism ID tests and bioburden tests.
Jennifer has spent the last 15 years working in the Packaging group. As one of the original packaging group members at Nelson Labs, Jennifer was heavily involved in validating all the packaging test methods and equipment and writing the test procedures for the packaging tests performed at Nelson Labs. Jennifer is a participating member on the ASTM F02 committee for packaging and is registered as a Specialist Microbiologist with ASM.