Reference method for measuring the surface tension of chromium electroplating: chapter 5

5. Sampling

  • 5.1 Samples for surface tension analysis must be taken from solutions at the representative operating temperature of the facility. The solutions should also be agitated for at least 10 minutes before the sample is collected. Agitation of the solution can be done either by conventional mechanical or physical means. Allow any foam (which may be present on the surface of the solution) to dissipate, such that a clear area of solution is present. This allows for collection of a sample without any surface foam being collected in the bottle or pipette. During the sampling process and as the sample is being collected, foam may be created in the bottle or in the pipette, which is acceptable. Note: foam collected from the surface of the solution can interfere with the true surface tension reading of the solution.
  • 5.2 Plating solution samples must be collected from at least 30 cm (12 inches) below the surface of the solution.
    • 5.2.1 One method to do this is to place a 100 mL or 200 mL pipette below the surface of the solution (to avoid collecting any foam) and collect the sample into the pipette with a bulb. If the sample is collected from below the surface of the solution, then foam is not likely to be present.
    • 5.2.2 Once the sample is collected from the tank, do not allow any sample to escape from the pipette and immediately transfer the sample from the pipette to a 200 ml or larger volume beaker.
    • 5.2.3 As an alternative to collecting a sample with a pipette, a sample container may be used. With this sampling method, use safety gloves (of sufficient length to protect the wearer) and dip the sampling container under the surface, with the opening of the sample container facing down. Slowly turn the sampling container right side up and pull the container straight up once filled with sample.
  • 5.3 Samples for surface tension must not be preserved chemically or physically. If samples are to be sent off-site for surface tension analysis, do not pack them in ice. Ambient cooling of the samples during transit is allowable as long as the samples are not cooled to below 10°C for more than 24 hours. Do not allow the samples to freeze.
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