Cobb Tester – Operation and Cleaning SOP

Standard Operating Procedure (SOP) for Operation and Cleaning of COBB TESTER used for the analysis of packing/packaging material in the Quality Control Laboratory.

SOP for Cobb Tester

1.0   Purpose :

    • The purpose of this SOP is to describe the procedure for the operation and cleaning of Cobb tester.

2.0   Scope :

    • This SOP is applicable for the operation and cleaning of Cobb tester at the Quality control Department
Make Model
Ubique CT

3.0   References – SOP for Cobb Tester:

    • Manual supplied by the manufacturer for Cobb Tester

4.0   Responsibilities: SOP for Cobb Tester:

    • Analyst:

    • To operate and follow the procedure as per SOP.Cobb Tester
    • To maintain the equipment history card.
    • QC Head or Designee:

    • Review of the SOP.
    • To give training to all concerned persons before the implementation of SOP for Cobb Tester.
    • To ensure that the Cobb Tester equipment is operated as per SOP.
    • Quality Assurance:

    • To check the SOP.
    • To ensure the implementation of the system as per SOP.
    • Quality Head:

    • To review and approve the SOP.
    • To ensure that system is implemented.
    • Definition of terms:
    • Cobb value: Cobb value of paper or paper board is defined as the water absorption property by paper or paper board in a specific time by specific area. The unit of measurement is gm/m2.   

5.0   Procedure for Operation and Cleaning of Cobb Tester:

    • General :

    • For the entry of usage of equipment, follow the SOP on “Instrument/equipment usage logbook”.
    • In case of any maintenance of equipment, follow SOP on “Maintenance of laboratory instrument/equipment”.
    • Precautions during handling of Cobb Tester:

    • Keep the outer surface of the sample to be tested uppermost in the cobb clamping plate.
    • Before taking final weight, dry excess water if any from the sample with the help of tissue paper.
    • Perform the activities without loss of time i.e. in as minimum time as possible.
    • Samples should be free from folds, blisters, and other surface defects.
    • Operation of Cobb Tester:

    • Select and cut the sample in circular shape with area more than 100 cm2 in such a way that it can easily fit in the clamp of the equipment.
    • Take the initial weight of the sample W1
    • After weighing the sample, clamp it properly in the Cobb tester ring.
    • Rotate the assembly to the assembling position, by bringing the clamping plate on top and engage the assembly to the lock groove.
    • Lift up rubber backed clamping plate.
    • Place the sample below rubber face between the clamping plate and water chamber, and clamp down clamping plate by means of turning grip.
    • Release the position lock and rotate the assembly in 180° to lock it in the test position.
    • Measure about 100ml of water in a measuring cylinder and pour it into the water chamber carefully, start the stopwatch simultaneously.
    • After 45 seconds, start to pour out water from the chamber carefully, so that at the end of 1 minute, there is no water in contact with the sample.
    • Quickly rotate the assembly to the assembling position, by bringing the clamping plate on top and engage the assembly to the lock groove.
    • Disengage and remove the clamping plate to remove the sample.
    • Remove the surplus water by pressing the sample on blotting paper and roll the 10kg steel roller on the sample 2-3 times.
    • Take the weight of the sample again W2 gm
    • The increase in weight is the amount of water penetrated/absorbed by the board through the surface during the test.
    • Calculate the cobb value of sample (one-minute cobb value) by the given formula:

           Cobb Value = (W2 – W1)  x 100   gm/m2



                        W2  =  Final weight, gm

                        W1 =  Initial weight, gm

                         A =  Area of the circular plate, m2

    • If the cobb value of the sample is high, means the sample is going to absorb more water, more ink, and more adhesive and if the cobb value of the sample is low, means it is less adhesive less water absorbent.
    • Place the roller in a safe place.
    • Cleaning of Cobb Tester:
    • Clean the equipment after use with tissue paper.
    • Clean and dry the water chamber after completion of testing.



Janki Singh is experienced in Pharmaceuticals, author and founder of Pharma Beginners, an ultimate pharmaceutical blogging platform. Email: [email protected]

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