Electrolytic (Conductance) Testing Method

A. Introduction 

DestructiveTo detect microchannel leaks and pinholes in hermetically sealed packages by measuring electrical discharges between the food product and device electrodes.> 50 μm micro-channels & pinholesOff-line, > 30 mins

B. Operation 

This technique is based on the principle of an electrolytic cell. The package is cut in half, partially filled with an electrolyte solution, and placed in a cell/vessel containing the same electrolyte solution. Voltmeter probes are then introduced into the electrolyte both inside and outside the package, and the resistance to flow of electricity is measured. A leaky package would permit the flow of electrons (low resistance) while a sound package would not (high resistance). The association of Official Analytical Chemist (AOAC) approved a test protocol for electrolytic testing of flexible packages.

Electrolytic testing is applicable only to packages having at least one nonconducting layer. Packages constructed with paper as the outer layers are nonconducting but not readily suited to this technique due to possibility of liquid absorption. The sensitivity of electrolytic testing can be improved by the addition of a surfactant into the electrolyte to increase surface wetting (contact). Overall, electrolytic testing is most appropriate for plastic packages and is not quantitative.

  • 1% NaCl in water (brine solution)
  • Scissors
  • Battery 9V, three 12-inch lengths of wire, 9V light bulb, or a conductivity meter (VOM).
  • Plastic bowl large enough to submerge package.
  1. Obtain sample food package and cut off one end with scissors.
  2. Aseptic paperboard packages and flexible pouches may be cut on all but one edge along package equator and folded 180 on uncut side to form 2 equal halves.
  3. Wash samples to remove all food contents and any dried plugs that may occlude holes. Oven drying at 180oF is recommended but not required before immersion.
  4. Wipe the cut edges with a paper towel if necessary, as wet edges may result in false-positive test results.
  5. Place samples in bowl containing brine solution and partially fill sample with brine so that it stands upright and is almost completely submerged.
  6. Place a VOM or light bulb with one probe inside the package and the other outside the package.
  7. Submerge both probes into their respective brine solutions.
  8. Test the other half of package similarly for current flow.

Positive

Current flow indicates break in hermetic barrier. 

Negative

No current flow indicates hermetic barrier exists.

False positive

Aluminum foil conducts electricity. A pinhole or partial break through inner layers of a package may expose the
foil layer, resulting in false-positive test result. Dye testing will confirm presence or absence of holes. Moisture may form a bridge over cut edge of a package, creating a false positive.

False negative

Dried product may occlude minute microleaks in a package. If plugs do not rehydrate quickly, they will not conduct electricity when packages are immersed.

C. Application 

PACKAGE TYPES AND DEFECTS

 PACKAGE TYPE
DEFECTSFlexible PouchSemi-rigid and
Rigid plastic container
Plastic Can (Double-seam Metal End)Paperboard
Abrasion
Corner Dent   
Crushed 
Cut (Fracture)
Delamination 
Double Seam Defects*   
Flexcracks 
Foreign Matter Inclusion  
Gels  
Hotfold   
Label Foldover   
Leaker   
Leaker (Channel) 
Leaker (Corner)   
Leaker (Notch)   
Leaker (Perforation)   
Leaker (Pulltab)   
Leaker (Seal)   
Loose Flap or Ear   
Malformed  
Puncture (Pinhole)
Seal Defects (Blister)   
Seal Defects (Blocked)   
Seal Defects (Burnt)   
Seal Defects (Compressed)   
Seal Defects (Contaminated)  
Seal Defects (Convolution/Embossing)   
Seal Defects (Creep)   
Seal Defects (Crooked)   
Seal Defects (Incomplete)   
Seal Defects (Misaligned/Deformed)  
Seal Defects (Nonbonding/Weak)   
Seal Defects (Plastic Lumps)   
Seal Defects (Seal-width Variation)   
Seal Defects (Stringy)   
Seal Defects (Uneven Impression)   
Seal Defects (Uneven Juncture)   
Seal Defects (Wrinkle)  
Swell (Swollen Package)
Waffling   

D. Source 

Tetra Pak Inc. 101 Corporate Woods, Parkway, Vernon Hills, IL 60061. TEL (847)-955-6000 (http://www.tetrapak.com/us/Pages/default.aspx)ARNDT., G.W. JR. 1998. Chapter 22C Examination of Flexible and Semirigid Food Containers for Integrity. FDA Bacteriological Analytical Manual (8th Ed)