To ensure package integrity, standard operating procedures typically include a testing protocol. Traditionally, leak testing has relied on blue-dye, water-bath, drop, or burst tests. Unfortunately, these tests destroy the package and the product inside, which then must be disposed of in an audited process. For an expensive drug, the cost of product lost to testing quickly mounts to hundreds of dollars per hour. Water-bath and dye tests are relatively time-consuming and exacerbate this cost problem.
Many bad packages often are produced before a problem is identified. As a result, faster, nondestructive testing is replacing destructive methods in many situations. Nondestructive leak testing relies on various technologies, including high-voltage, pressure, vacuum, and imaging.High-voltage testing
High-voltage electrical testing ensures incoming blister-packaging materials (i.e., formable bottom webs and lidstock material) are free of pinholes. In this test, the company that produces the blister material or lidstock mounts a tester near the end of its production line so the material passes between high-voltage and grounded electrodes before it is wound into rolls. Blister material or lidstock should insulate electrodes from each other. If a pinhole is present, an arc will discharge through the flaw to the ground. With sufficient voltage, the system can detect pinholes smaller than 1 μm ("PDC20" pinhole tester, Clinton Instrument Co., Villa Rica, GA, http://www.clintoninstrument.com/). This level of resolution is more than adequate, because the threshold for detectable pinholes typically is greater than 50 μm.
Pressure and vacuum testing
Quality-control systems for finished blister packs rely on pressure or vacuum conditions. Most units are operated off-line and allow operators or quality-control personnel to check a periodic sampling of a run such as 8 or 10 packs every 30 min.
One vacuum method relies on the detection of a tracer gas that is present naturally or added by flushing the blister package just before it's sealed. Under vacuum conditions, the gas escapes through any pinholes or cracks that are present and is detected by an infrared sensor ("Pac Guard Model 400," leak tester, Mocon, Minneapolis, MN, http://www.mocon.com/).
Some leak detectors look for pressure or vacuum decay to identify leaks. One dual-mode unit detects defects as small as 5 μm in a pressue or vacuum test cycle that lasts less than 30 s. An audible and visual reject alarm alerts the operator if the blister card fails. The system can store 100 different tests and record 5000 results. A two-way RS232 connection links the unit to a host system or network and enables uploading of test data and downloading of test parameters. Interchangeable test chambers accommodate various card sizes and shapes ("TME Solution-C Blister Card Chamber Test System," TMElectronics, Inc. , Boylston, MA, http://www.tmelectronics.com/).