Abstract
ASTM F2338-09 Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method is applicable for leak-testing rigid and semi-rigid non-lidded trays; trays or cups sealed with porous barrier lidding materials; rigid, nonporous packages; and flexible, nonporous packages. Part 1 of this series describes the precision and bias studies performed in 2008 to expand this method's scope to include rigid, nonporous packages completely or partially filled with liquid. Round robin tests using three VeriPac 325/LV vacuum decay leak testers (Packaging Technologies & Inspection, LLC, Tuckahoe, NY) were performed at three test sites. Test packages were 1-mL glass syringes. Positive controls had laser-drilled holes in the barrel ranging from about 5 to 15 μm in nominal diameter. Two different leak tests methods were performed at each site: a “gas leak test” performed at 250 mbar (absolute) and a “liquid leak test” performed at about 1 mbar (absolute). The gas leak test was used to test empty, air-filled syringes. All defects with holes ≥5.0 μm and all no-defect controls were correctly identified. The only false negative result was attributed to a single syringe with a <5.0-μm hole. Tests performed using a calibrated air leak supported a 0.10-cm3 · min−1 (ccm) sensitivity limit (99/99 lower tolerance limit). The liquid leak test was used to test both empty, air-filled syringes and water-filled syringes. Test results were 100% accurate for all empty and water-filled syringes, both without holes and with holes (5, 10, and 15 μm). Tests performed using calibrated air flow leaks of 0, 0.05, and 0.10 ccm were also 100% accurate; data supported a 0.10-ccm sensitivity limit (99/99 lower tolerance limit). Quantitative differential pressure results strongly correlated to hole size using either liquid or gas vacuum decay leak tests. The higher vacuum liquid leak test gave noticeably higher pressure readings when water was present in the defect. Both the ASTM F2338-09 test method and the precision and bias study report are available by contacting ASTM International in West Conshohocken, PA, USA (www.astm.org).
- Leak detection
- Leak test
- Container/closure integrity test
- Package integrity test
- Syringes
- Nonporous package
- Vacuum decay
Introduction
Vacuum decay leak testing is a variation of pressure/vacuum change leak tests. Vacuum decay and pressure/vacuum change leak testing has been widely used by many industries over several decades (1, 2). Simply put, the vacuum decay leak test method consists of placing the test container in a chamber, sealing and then evacuating the chamber to a predetermined vacuum level, isolating the vacuum source, and then monitoring the rise in pressure (vacuum decay) inside the chamber resulting from container leakage. Vacuum decay's usefulness as a nondestructive leak test method for testing pharmaceutical packages has been recognized in published literature (3, 4) as well as in compendium (5) and a recent U.S. Food and Drug Administration (FDA) regulatory guidance (6).
Improvements in vacuum decay technology have enabled more sensitive and reliable testing. A vacuum decay leak test's capabilities are dependent on several factors, including, for example, test chamber design, pressure transducer sensitivity and design, test vacuum level, test system dead space volume, test time, and test package surface and volume. Thus any given vacuum decay leak test method is specific to both the leak test instrument and its manufacturer.
Two vacuum decay leak test research studies are reported in the literature using Wilco AG (Wohlen, Switzerland; www.wilco.com) leak test systems. In the first study (7), parenteral vials were leak tested using a Wilco WFX100 tester as well as by helium mass spectrometry, a trace gas leak test method previously compared to liquid-borne microbial challenge tests (8). Leaks were simulated by affixing micropipettes into glass vials. The vacuum decay leak test was performed by first reducing the chamber pressure by 999 mbar (gauge), allowing 5 s for system stabilization, and then monitoring the rise in test chamber pressure at the end of various predetermined test times. At a vacuum decay test time of 10 s, the detection limit in terms of gas leak rate was about 0.05 standard cm3 · min−1 (sccm). Standard cm3 · min−1 (sccm) and standard cm3 · s−1 (sccs) are leak rate units based on the flow rate of air at standard SI conditions, namely, air at 0 °C with a vacuum differential of about 100 kPa (9).
The second study utilized the currently marketed Wilco LFC method, which measures the loss of vacuum inside the testing chamber resulting from either headspace gas leakage or liquid vaporization from a leak (10). This technique is based on the concept that partial pressures from solvents adds to the true pressure of gases to produce the total pressure of contained fluid measured by the pressure sensors used in any pressure change leakage rate test (11). The Wilco LFC study used test vials identical in design to those used in the first reported study, but in this case study vials were filled with various solvent systems prior to capping and sealing. The leak test method included an initial evacuation cycle to outgas surface-adsorbed substances, then a second evacuation to a predetermined reference vacuum. Upon reaching the reference vacuum, the vacuum pumps were disengaged and test chamber pressure change was recorded at 5 or 10 s. The LFC method was reportedly more sensitive than the earlier Wilco vacuum decay leak test method.
Wilco AG also reported that the software for their LFC method incorporates a floating reference feature. In other words, the baseline is calculated and continually readjusted based on the most recent leak test values of so-called nonleaking packages in the test sample population. The pass/fail reject criterion also adjusts with the floating baseline according to a proprietary algorithm that calculates the allowable pass/fail pressure rise in “pressure units”. The millibar value assigned to a pressure unit varies with the baseline set point. Therefore, while the allowable pressure rise in number of pressure units remains constant, the actual pressure rise limit itself varies in magnitude as the baseline shifts higher or lower. This adjustment is performed to accommodate baseline drift due to environmental factors (e.g., relative humidity, temperature and atmospheric pressure), system leaks and outgassing effects, and variations among test units. Another separate, unchanging leak rate cut-off limit is used to prevent the floating baseline from excessive deviation (12).
Over the last several years vacuum decay leak test instruments made by Packaging Technologies & Inspection, LLC (PTI; Tuckahoe, NY) have been used to support the creation of ASTM F2338 Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method for testing various pharmaceutical, food, and medical device package systems (13). ASTM F2338 is a Recognized Consensus Standard by the FDA, Center for Devices and Radiological Health (CDRH), effective March 31, 2006 (14). According to the FDA Consensus Standard Recognition Notice, devices that are affected include any devices that are sterilized and packaged. Packages that can be nondestructively evaluated by this method include rigid and semi-rigid non-lidded trays; trays or cups sealed with porous barrier lidding materials; rigid, nonporous packages; and flexible, nonporous packages.
The 2009 revision, ASTM F2338-09, incorporates precision and bias (P&B) study results generated using the newly designed PTI VeriPac 325/LV vacuum decay leak tester. These P&B studies, described in this current report, investigated two different leak test methods: a “gas leak test method” which tests for leakage of package headspace gases, and a “liquid leak test method” which tests for leaks either fully or partially filled with liquid product. The liquid leak test method was also investigated for its ability to test for gas headspace leaks, void of any liquid presence. Part 1 of this research series details these ASTM P&B studies, describes the leak test instrument used, and discusses the advances in vacuum decay leak test technology this work represents. A copy of ASTM F2338-09 and the complete P&B report can be obtained by contacting ASTM International in West Conshohocken, PA 19428 (www.astm.org).
Materials and Methods
Materials and Equipment
Test Packages:
The test packages were 1-mL glass syringes with staked needles and elastomeric, nonrigid needle shields manufactured by Becton Dickinson (Franklin Lakes, NJ) and purchased by Amgen, Inc. (Thousand Oaks, CA).
Negative control (no-defect) syringes included a population filled with water, and a population that remained empty (air-filled). All negative control syringes were shared across all test sites. Each negative control syringe was assigned a unique identifying number by the interlaboratory study coordinator.
Each positive control (with defect) syringe contained a single laser-drilled hole in the glass barrel wall. Positive control syringes were tested both empty (air-filled) and water-filled, according to the protocol described under Methods. Each of the three test sites was provided with 15 positive control syringes consisting of 5 syringes per each hole size subset (5, 10, and 15 μm). The same holed syringes were not tested across sites to lessen their exposure to vacuum decay tests and handling, thereby minimizing hole clogging risks. Each positive control was assigned a unique identifying number by the interlaboratory study coordinator.
The laser-drilled holes were generated by Lenox Laser, (Glen Arm, MD; www.lenoxlaser.com). Although these defects are called “holes”, the photographs in Figure 1illustrate that their actual geometry is really a complex series of irregular holes, channels, and fissures, making direct dimensional sizing impossible. Lenox Laser certified defect sizes by measuring the outlet flow rate of compressed air applied to the defect at 15 psig. Each defect was assigned an equivalent hole diameter to the nearest 0.10 μm by comparing the defect outlet flow rate to calibrated traceable primary transfer standards. Test samples were grouped into target hole diameter subsets of 5, 10, and 15 μm, each sample falling within ±2 μm of the target diameter. The shape and construction of the syringe barrels, along with laser technology limitations, prevented the creation of nominal holes smaller than about 5 μm. All costs for generating these defects were underwritten by PTI.
Photomicrographs of laser-drilled holes in syringe barrel walls. Photographs by Amgen, Inc. Holes were generated by Lenox Laser of Glen Arm, MD (www.lenoxlaser.com). Key: 5-μm holes: Photos 106, 107, E5; 10-μm holes: Photo 124; 15-μm holes: Photo 136.
Vacuum Decay Leak Testers:
Three PTI VeriPac 325/LV model vacuum decay leak testers were used for all tests, one per each test site. The model 325/LV leak tester is a dual transducer system instrument consisting of a 1000-Torr absolute transducer and a 10-Torr differential transducer. The 1000-Torr transducer monitors the initial target vacuum and any subsequent vacuum decay throughout the test cycle; pressure is reported in millibar units. By incorporating an absolute rather than a gauge pressure transducer, readings are not subject to environmental pressure variations due to weather or altitude. The 10-Torr differential transducer measures the smallest pressure changes during the final stages of the test in Pascal units. Readings from both transducers are displayed “live” during the test cycle. Pressure readings are based solely on the transducers' output signals, without mathematical manipulation or algorithms to compensate for drift, thus making for easier data analysis and test method validation. End-of-test pressure readings appear on the instrument display along with a test “pass” or “fail” message. Both transducers are calibrated and certified by their original manufacturer.
A single cavity test chamber connected to the instrument contains the test syringe. This chamber was designed by PTI with a low void volume and a mechanism for restricting the movement of the stopper during the vacuum decay test.
The required test chamber vacuum conditions are generated using an external vacuum pump provided with each instrument.
A National Institute of Standards and Technology (NIST)-calibrated flow meter manufactured by Furness Controls, Ltd. (East Sussex, England; www.furness-controls.com) was used for challenging the test system with calibrated air leaks. Air flow rate is measured in volumetric flow units of cubic centimeters per minute (cm3 · min−1 or ccm) as air moves from atmospheric pressure into the test system at target vacuum.
Methods
Test Site Locations:
The test locations included Amgen, Inc. in Thousand Oaks, CA; Bristol-Myers Squibb Co. in New Brunswick, NJ; and Packaging Technologies & Inspection, LLC in Tuckahoe, NY.
ASTM Precision & Bias Study Requirements:
ASTM International requires all published test methods to reference peer reviewed P&B studies supporting the method's capability claims. Such studies must include multiple test instruments, test sites, and operators. Replicate sample testing is required at each test site, preferably over multiple days. Testing order should be randomized. An independent interlaboratory coordinator (ILC) is responsible for ensuring the right test samples are used at each test site, for generating the randomization plans, and for ensuring the integrity of the raw data. All work is performed under the jurisdiction of an appropriate ASTM subcommittee.
ASTM Subcommittee F02 on Flexible Barrier Packaging supervised and approved all ASTM F2338-09 P&B work. Dana Morton Guazzo, Ph.D., of RxPax, LLC served as the ILC for the current work. Phillip Godorov of ASTM International and Tom Murphy of T.D. Murphy Statistical Consulting, LLC (Morristown, NJ) performed raw data statistical analyses for the final ASTM F2338-09 P&B report. The original test protocols and raw data are maintained on file at ASTM International headquarters in West Conshohocken, PA. Copies of the ASTM P&B report along with the ASTM F2338-09 test method can be obtained by contacting ASTM International (www.astm.org).
Vacuum Decay Gas Leak Tests:
Each test site was responsible for performing five different studies using two different leak test methods and the package population subsets outlined in Table I. Each study was repeated three times at each test site over the course of 2 days. The tests within each replicate study were performed in random order.
Vacuum Decay Leak Test Studies Performed in Triplicate at Each Test Site
Studies 1 and 2 used a “gas leak test” performed at a target vacuum of 250 mbar (absolute) on empty, air-filled test packages. The gas leak test is intended to test packages that contain gas (e.g., air) with little to no risk of liquid filling the leak path. In the first study, the gas test was performed using a population of negative control syringes (no-defect), with and without a calibrated air leak of 0.05 and 0.10 ccm. In Study 2, the gas test was performed using a population of empty negative and positive control syringes. Between replicate tests, the stoppers of the holed syringes were removed and reinserted to prevent the build-up of vacuum within each syringe.
Studies 3, 4, and 5 used a “liquid leak test” performed at a target vacuum of about 1 mbar (absolute). This test's higher vacuum is intended to volatilize any liquid partially or fully blocking a leak pathway, thus yielding a measurable spike in pressure. The capability of the test to identify such leaks was determined using water-filled syringes with and without hole defects (Study 5). In addition, the liquid leak test method was challenged with calibrated air leaks (Study 3), as well as with empty defective syringes (Study 4). Studies 3 and 4 were performed to test the liquid leak test method's ability to identify gas leaks void of liquid occlusion. As in earlier studies, empty holed syringes were disassembled and reassembled after each leak test to prevent vacuum build-up inside the syringe.
Both the gas leak test and the liquid leak test followed the same sequence of events described in Table II. A package fails (leaks) or passes according to the criteria outlined. The test parameter settings used for the gas and liquid leak tests are included in Table III. The same parameter settings were used at all test sites. These settings were chosen based on preliminary test method development studies performed by PTI. Test method parameters are selected by comparing the vacuum decay pressure–time relationship of no-leak packages to known-leaking packages. Parameter settings are unique to each package type/size, test chamber design, and the desired leak test limit of sensitivity. ASTM F2338-09 includes an Annex in which test method parameter setting selection is discussed in greater detail.
VeriPac 325/LV Leak Test Sequence of Events
VeriPac 325/LV Leak Test Parameters
Results and Discussion
Tables IV through VIII include ASTM P&B calculations of repeatability and reproducibility. Refer to the Appendix for definitions of these terms.
Study 1. Vacuum Decay Gas Leak Test at 250 mbar—Calibrated Air Flow Leak Challenge
Vacuum Decay Gas Leak Tests—Study 1, Air Flow Leaks
Study 1 utilized a calibrated air leak challenge with the vacuum decay gas leak test. The test results are summarized in Table IV, and raw data are graphically presented in Figure 2.The test was found to be 100% accurate for all no-defect controls; all results were well below the differential pressure pass/fail limit (dP Ref) of no more than 25 Pa. At the 0.05-ccm leak rate, two readings fell at or near dP Ref (readings = 24 and 25 Pa). All 0.10-ccm leaks yielded “fail” results, demonstrating a differential pressure (dP) range of 30 to 62 Pa. These 0.10-ccm gas leak test data yielded a lower tolerance limit of 31.9 Pa, significantly greater than dP Ref, for 99% of the population at a 99% confidence level.
Study 1 gas leak test at 250 mbar—calibrated airflow leak challenge. Note: 95% confidence intervals indicated. The 0.10-ccm data indicate a lower tolerance limit of 31.9 Pa for 99% of the test sample population at a 99% confidence level (99/99 LTL).
Vacuum Decay Gas Leak Tests—Study 2, Holed Syringes
The vacuum decay gas leak test results using no-defect versus defective syringes are included in Table V. The baseline dP of 11 Pa (mean) was essentially identical to the negative control baseline of Study 1 (Table IV). All negative control, 10- and 15-μm hole syringe results were 100% accurate.
Study 2. Vacuum Decay Gas Leak Test at 250 mbar—Empty, Holed Syringe Challenge
The 5-μm syringe results yielded one false negative result (22 Pa); the other two replicate results for this same test syringe were also near the acceptance limit (28 and 29 Pa). A plot of Lenox Laser certified hole sizes versus VeriPac 325/LV gas leak test results was generated for the 5-μm hole subset (Figure 3),as well as the 10- and 15-μm hole subsets (Figure 4). The results showed a strong correlation between hole size and dP. Excellent reproducibility was demonstrated within the three replicate leak test readings obtained for each test sample. Upon closer examination of Figure 3, hole sizes ≥5.0 μm yielded dP results well above the pass/fail limit. However, dP results for holes <5.0 μm approached the pass/fail cut-off point. Most notably, the one false positive test result was attributed to the smallest hole size syringe. Considering only those syringes with holes ≥5.0 μm, the gas leak test results repeatedly identified all holes 5.0 μm and larger.
Study 2 vacuum decay gas leak test at 250 mbar—nominal hole size 5 μm.
Study 2 vacuum decay gas leak test at 250 mbar—nominal hole sizes 10 and 15 μm.
Vacuum Decay Liquid Leak Tests, Gas Leaks—Study 3, Air Flow Leaks
Study 3 used the higher vacuum liquid leak test, challenged with calibrated air leaks. The test results are illustrated in Figure 5 and are summarized in Table VI. The baseline, negative control tests yielded no false positive results. The test results for both 0.05- and 0.10-ccm calibrated air leaks were also 100% accurate. Statistically, the 0.10-ccm data yielded a lower tolerance limit of 33.1 Pa, significantly greater than dP Ref, for 99% of the population at a 99% confidence level.
Study 3. Vacuum Decay Liquid Leak Test at 1 mbar—Calibrated Air Flow Leak Challenge
Study 3 liquid leak test at 1 mbar—calibrated airflow leak challenge. Note: 95% confidence intervals indicated. The 0.10-ccm data indicate a lower tolerance limit of 33.1 Pa for 99% of the test sample population at a 99% confidence level (99/99 LTL).
Vacuum Decay Liquid Leak Tests, Gas Leaks—Study 4, Holed Syringes
Study 4 again used the higher vacuum liquid leak test, but with holed, empty syringes. The data demonstrated 100% accuracy for all no-hole and with-hole packages (Table VII). The results for the 5-μm and 10–15-μm test sample subsets are illustrated in Figures 6 and 7, respectively. The vacuum decay liquid leak test reliably detected defects ≥5.0 μm in size. Similar to Study 2, the smallest holes <5.0 μm yielded dP results approaching the pass/fail limit. Therefore, the results from Studies 2 and 4 illustrate that gas leaks can be successfully measured using moderate to high vacuum settings. At any given target vacuum, vacuum decay gas leak test sensitivity can be optimized via test times, equipment design, and pressure transducer selection.
Study 4. Vacuum Decay Liquid Leak Test at 1 mbar—Empty, Holed Syringe Challenge
Vacuum decay liquid leak test at 1 mbar, gas leaks (Study 4) versus liquid leaks (Study 5)—nominal hole size 5 νm. Note: In Study 5, the 5.7-μm holed, water-filled syringe gave an ABORT test result for one of three replicate readings (data point not graphed).
Vacuum decay liquid leak test at 1 mbar, gas leaks (Study 4) versus liquid leaks (Study 5)—nominal hole sizes 10 and 15 μm. Note: ABORT test results were assigned a dP value of 599 Pa.
Vacuum Decay Liquid Leak Tests, Liquid Leaks—Study 5, Holed Syringes
Study 5 repeated the higher vacuum liquid leak test using the holed syringes filled with water. All results were accurate with no false positive or false negative results (Table VIII). The data from Study 5 are included in Figures 6 and 7. As expected, the liquid leak test dP results for the water-filled syringes were markedly greater than for the empty syringes. In fact, all the 15-μm holed syringe readings, a majority of the 10-μm holed syringe readings, and even one 5.7-μm hole syringe reading exceeded the Vacuum 2 Reference point (Vac 2 Ref) before the end of the test cycle, causing the test cycle to abort prior to completion. The abort feature is used to prevent larger leaks from flooding the test system. For data analysis and graphing purposes, all abort results were assigned dP readings of 599 Pa.
Study 5. Vacuum Decay Liquid Leak Test at 1 mbar—Water-Filled, Holed Syringe Challenge
Negative Control Liquid and Gas Leak Test Results
Study 2 (gas leak tests) and Studies 4 and 5 (liquid leak tests) all included no-leak syringes as negative controls. These syringes were either empty (Study 2) or water-filled (Studies 4 and 5). The resultant leak test data in Figures 8 and 9 illustrate the steady, consistent baseline readings for both gas and liquid vacuum decay leak test methods, respectively, using three VeriPac 325/LV instruments, located at three test sites, for a total of 6 days of operation. No false positive results occurred; all results fell below the dP reference limits at the 95% confidence level.
Negative control test results—gas leak tests at 250 mbar.
Negative control test results—liquid leak tests at 1 mbar. Note: For Study 4, no-defect negative control syringes were water-filled, although the holed, positive control syringes were air-filled.
Gas versus Liquid Vacuum Decay Leak Test Methods
The test method parameters for the gas and liquid vacuum decay leak tests differ in several respects (Table III). One key difference between the two methods is the target vacuum. As discussed previously, packages that only risk gas leakage can be tested under less extreme vacuum conditions. Lessening the vacuum level puts less stress on the package and the test system, and shortens the time to reach target vacuum. But packages in danger of liquid leaks need to be tested at higher vacuum in order to volatilize any liquid potentially blocking the leak pathway. For both methods the rate of vacuum pumpdown is monitored in order to identify the presence of larger leaks. If target vacuum cannot be reached within a given time frame, the test will abort to minimize test chamber flooding risks.
The selected equalization time is noticeably longer for the gas leak test than for the liquid leak test. Lengthening equalization time in a gas leak test helps minimize background noise due to gas fluctuations within the test system and outgassing from test system and test package surfaces. With less noise, the smallest changes in dP can be more precisely measured. Liquid leak tests, on the other hand, require a very short equalization time. Once target vacuum is reached, liquid vaporization occurs very rapidly, causing a rapid rise in dP, which rather quickly levels off or even drops once saturation partial pressure is reached in the minimal test system void volume.
In light of this, one might reasonably ask how to test packages containing both liquid and gas. For example, a liquid-filled vial, a liquid-filled plastic ampoule or bottle, or even a prefilled syringe may have leaks at gas headspace or liquid product levels. To address this concern the VeriPac 325/LV test system and the liquid leak test method parameters used in the current investigation were optimized in order to detect both gas and liquid leaks using a single test cycle. The liquid leak test data in Study 5 indicate greater differentiation between baseline (no-leak) and hole defect dP results when liquid is present than in Study 4 where gas alone is present. Nevertheless, it is evident that the liquid test method is able to reliably distinguish leaks ≥5.0 μm in either case.
Test Method Qualification and Validation
Studies 1 and 3 utilized a NIST-calibrated air flow introduced into the test chamber to verify test method sensitivity. These studies demonstrate the usefulness of calibrated air flow leaks for verifying instrument functionality and sensitivity. Air flow can be introduced into the test system in a way that is very reproducible, thus ensuring consistent, less variable test results. However, a true understanding of leak test methods and instrumentation can only be obtained by randomly testing large numbers of actual product packages, with and without defects, over several days of operation. Benefits of such research are described below.
A no leak baseline quantitative limit can be established using multiple package component lots, assembled under varying conditions, and tested over multiple days. Gases or liquid trapped between package components or present on component surfaces may vary with package component lots and assembly processes, thus shifting the baseline or increasing background noise level.
The impact of grossly leaking product on the test system can be assessed. Time required for cleaning, cleaning method effectiveness, and trace contaminant impact on test system performance are factors worth considering.
Leaks at various package locations and of various types can be used to challenge the test method. The dP response reading may be affected by leak location, package wall thickness at the leak, gas or liquid presence at the leak, package gas headspace volume, and leak geometry (e.g., hole or channel).
The ability of the tester to return to baseline after a leak test failure can be assessed. In some cases test method cycling or vacuum flushing may be required.
The impact of atmospheric pressure or humidity on leak tester performance can be investigated.
Vacuum Decay versus Microbial Ingress Test Sensitivity
Liquid-borne microbial ingress challenge tests have traditionally been the standard for container/closure integrity tests. In order to compare the current vacuum decay leak tests to microbial ingress tests, the landmark research by Kirsch et al. (8) was utilized. In this work, the leak rate through glass vials with micropipette channel defects was measured by helium mass spectrometry and subsequently compared to the probability of microbial ingress through these same leaks. An aggressive microbial challenge test was used, including 24-h immersion in a bath containing 108 to 1010 viable P. diminuta and E. coli organisms/mL. This was preceded by manipulations designed to eliminate airlocks in the leaks and allow a fluid pathway from the challenge media to the test vial contents. Moreover, the presence of a fluid pathway was confirmed by chemical tracers, and test units that failed to demonstrate such a pathway were eliminated from the analysis.
Kirsch et al.'s results showed the probability of microbial ingress was near 100% at leak rate log −1.5 sccs, which was equivalent to about an 8-μm nominal diameter leak. An 80% probability of ingress corresponded to a leak rate of about log −2.5 (about 5 μm), and a 50% probability of ingress corresponded to a leak rate of log −3.7 (about 0.7 μm). Below this leak rate, the likelihood of microbial failure rapidly dropped off. The likelihood of microbial failure at leak rates ≤log −5 was remote; of the 66 test units with leak rates less than log −4.5 sccs, only three failed the microbial ingress challenge.
In the current Studies 1 and 3, the 0.10-ccm (log −2.8 ccs) calibrated air flow tests yielded a lower tolerance limit for 99% of the test population with differential pressure readings significantly greater than the pass/fail reference limit at a 99% confidence level. By comparison, Kirsch et al. determined a critical leak rate of log −5.2 sccs associated with a low probability of microbial ingress under specified challenge conditions. Although the VeriPac method is unable to detect this smallest critical leak, it was shown to be capable of detecting a leak rate of log −2.8 ccs with a high degree of reliability, within a 17-s test time. At about this same leak rate, the 24-h microbial challenge test was able to identify 70% of the defects (23 out of 33 units). Therefore, while the VeriPac leak test methods described in the present work cannot find the very smallest leaks possible with an aggressive microbial ingress test, it can more reliably, repeatably, and rapidly find leaks ≥log −2.8 ccs measured by calibrated air flow leaks, or about 5 μm and larger using actual defective packages such as prefilled syringes.
Conclusions
P&B studies were performed to expand the scope of ASTM F2338-09 to include rigid, nonporous packages completely or partially filled with liquid. Such packages include, for example, prefilled syringes, liquid filled plastic ampoules or bottles, and liquid-filled vials. Round robin tests were conducted at three test sites utilizing three VeriPac 325/LV vacuum decay leak testers manufactured by PTI. Test packages were 1-mL glass syringes. Positive controls had holes laser-drilled into the barrel ranging from about 5 to 15 μm in nominal diameter. Two different leak tests methods were performed at each site: a gas leak test performed at 250 mbar (absolute) and a liquid leak test performed at about 1 mbar (absolute).
The following key results were obtained and conclusions were reached.
The gas leak test was used to test empty, air-filled syringes. Results for the 5-μm hole subset were 98% accurate; the one false negative result was attributed to a single syringe with a 4.7-μm hole. All 10- and 15-μm defects and all no-defect controls were correctly identified. Calibrated air leaks at 0, 0.05, and 0.10 ccm were 100%, 96%, and 100% accurate, respectively; data supported a 0.10-ccm limit of sensitivity at a 99/99 lower tolerance limit.
The liquid leak test was used to test both empty, air-filled syringes and water-filled syringes. Test results were 100% accurate for all syringes, empty and water-filled, for all no-hole and with-hole syringes (5, 10, and 15 μm). The calibrated air flow leak tests at 0, 0.05, and 0.10 ccm were all 100% accurate; data supported a sensitivity limit of 0.10 ccm at a 99/99 lower tolerance limit.
A strong correlation between hole sizes and leak test dP readings was demonstrated for both liquid and gas leak test methods. Liquid leak tests performed with water in defective test packages yielded much greater dP test results than when testing empty, air-filled test packages.
All three instruments at the three test sites used the same leak test method parameters and acceptance criterion. dP readings are reported in Pascal units with quantitative, verifiable pass/fail acceptance criterion. Baseline data were consistently below the test acceptance limit.
The reliability of the VeriPac 325/LV liquid and gas vacuum decay leak tests was better than research-reported microbial ingress methods down to a leak rate of log −2.8 ccs using a calibrated air flow leak, or down to 5.0 μm using actual defective packages.
These data support the P&B statement requirements for ASTM F2338-09 Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method. Thus the scope of this method is expanded to include rigid, nonporous package leak detection resulting from leakage of test package headspace gases and/or volatilization of test package liquid contents located in or near the leak path.
Appendix
ASTM precision and bias (P&B) statements are based on an evaluation of repeatability, reproducibility, and bias as they are specified in ASTM E 177 Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods. The following definitions are offered as they are used in the current study. Practice E 177 should be consulted for further information regarding precision and bias terminology and concepts.
Repeatability limit (r)—Two test results obtained within one laboratory shall be judged not equivalent if they differ by more than the “r” value for that material; “r” is the interval representing the critical difference between two test results for the same material, obtained by the same operator using the same equipment on the same day in the same laboratory.
Reproducibility limit (R)—Two test results shall be judged not equivalent if they differ by more than the “R” value for that material; “R” is the interval representing the critical difference between two test results for the same material, obtained by different operators using different equipment in different laboratories.
Acknowledgements
The authors gratefully acknowledge the support of Tom Murphy, President of T.D. Murphy Statistical Consulting, LLC of Morristown, NJ.
- © PDA, Inc. 2009
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