How to Effectively Leak Test Reagent Cartridges

June 28, 2022 | By Dave Kralovetz – Global Medical Device Testing Specialist

Reagent cassettes are commonly used in larger bio labs or point-of-care facilities for infection verification or genetic determination by automated and semi-automated diagnostic (IVD) testing, gene sequencing, and micro-array scanning instrumentation/analyzers. 


Leak testing can be performed on 100% of these components in production before or after filling the container with reagent. The test process is different for each scenario and we cover the requirements for both in this post.

The steps described are based on our experience using either a single-channel Sentinel Blackbelt or multi-channel Blackbelt Pro instrument and CTS Connects for sealing.

The Process to Leak Test Empty Reagent Cartridges

Start by Sealing the Empty Cartridge for the Test
Correct sealing is essential to ensure test accuracy. All openings of the cartridge are sealed with standard CTS Connects designed to seal radially either around the outside (CO30/31) or inside diameter (CI30/31) port(s) of the cartridge.

The Empty Reagent Cartridge is Then Pressurized
The leak test instrument pressurizes the cartridge with regulated compressed air/nitrogen through one or more CTS Connects. The approach to pressurizing depends upon the design of the cartridge: for example, some have separate but adjacent internal chambers within them. If chamber-to-chamber leaks are a concern, each should be pressurized separately. Chambers not under test should remain vented to atmosphere.

At the end of pressurization, the instrument can detect improper pressure supply or gross leaks on the cartridge.

Testing to Find Gross and Fine Leaks in the Reagent Cartridge Chamber
The next step is stabilization, where pressure is trapped inside the pathway to minimize the natural pressure loss of even non-leaking parts due to expansion or creep, adiabatic thermal effect and potentially absorption, increasing the separation of the final measured pressure loss/decay between good parts and rejects. At this stage, slightly smaller but still gross leaks on the cartridge chamber are detected.

Once stabilization is complete, the instrument records the pressure loss/decay over a set test time and compares it to min/max pressure limits to determine whether fine leaks are present.

Final Step: Exhausting the Cassette Chambers
Following the end of the test, the pressure inside the cartridge or chamber is vented for a defined exhaust time.

If the cartridge has multiple internal chambers, the full test cycle is then repeated for each untested chamber mated to a different test port until all have been individually tested. These sequential tests inspect for both chamber-to-exterior and chamber-to-chamber leakage.

The Sentinel Blackbelt enables multi-port sequential testing so that you can test multiple chambers as part of a programmed test. Learn more about the Blackbelt.

Leak Test Process for Cassettes Filled with Reagent

Unlike empty cartridges, ones filled with reagent are sealed, making it impossible to pressurize or evacuate the interior of non-leaking units. These sealed cartridges require a somewhat consistent internal air headspace volume inside the cartridge or internal chamber at the foil seal to allow accurate dry leak testing.  

Instead of the positive pressure testing used for empty cartridges, these tests are usually performed with negative pressure (vacuum), which challenges each foil seal by attempting to pull the internal air inside the cartridge out through a leaking foil seal.

Sealing the Filled Reagent Cartridge for Test
For an effective test, all foil sealed openings of the cartridge must be sealed using custom fixturing with sealing heads surrounding each of the foil sealed openings. If sealing around only the foil-sealed areas is impossible due to either the part’s physical geometry or small cartridge size, the entire cartridge is placed within a custom-made vacuum chamber designed to minimize the external volume surrounding the cartridge exterior to maintain maximum sensitivity during both gross and fine leak tests.

In either case, the cartridge must be oriented in a manner that allows the entire foil seal to be exposed to the internal trapped air headspace, with no reagent contacting the foil seal—otherwise leaks may be masked.

Evacuation of the Sealing Heads or Vacuum Chamber and Gross Leak Test
As there is only a finite amount of air inside the cartridge above the reagent fill, a gross leak test must first be performed; otherwise, the foil leakage may be so severe that all air headspace is evacuated during a conventional Fill step and no air would later remain to decay during the final test.

Within the instrument, a fixed reference volume is evacuated and its vacuum level compared to set min and max limits. The tester then releases this vacuum into the sealing heads or test chamber and verifies the final delivered vacuum level compared to another set of limits. If this value is below that minimum vacuum limit, the cartridge is immediately rejected, assuming that a gross leak is present on the cartridge, as the vacant headspace inside the test head or chamber is greater than it should be.

For test efficiency, the gross leak testing sequence can be adjusted so the final delivered vacuum to the seal heads or vacuum chamber matches the specified fine leak testing vacuum level. Then the test may immediately proceed to fine leak detection.

Detecting Fine Leaks in Reagent-filled Cartridges
The isolation valve inside the test instrument closes, removing the reference volume from the fine leak test volume and trapping vacuum inside the seal heads or vacuum chamber for a defined stabilization time. Like in the empty cartridge, this is intended to minimize the natural vacuum loss of even non-leaking parts due various factors. The vacuum level is measured to detect smaller but still gross leaks.

Following stabilization, the vacuum loss/decay is recorded over a set test time and compared to min/max decay limits to determine whether fine leaks are present. At the end of the test, the vacuum trapped is vented to atmosphere and the user may release the seals or open the vacuum chamber to remove the tested cartridge.

CTS Provides Reliable Solutions for Reagent Cartridge and Cassette Leak Testing

Contact us to talk about your reagent cartridge design and the most effective leak test to meet your requirements.

You can also access the full application bulletin on how to leak test both empty and reagent-filled cartridges for more information and tips on how to conduct the test.

Access the Reagent Cartridges Application Bulletin  >>

Need a multi-channel leak test instrument? The Sentinel Blackbelt Pro delivers and has 21 CFR Part 11 / Euro Annex II friendly features. Learn more about the Blackbelt Pro.