29
SECTION 2, continued
2.3.5.2 Adding a surfactant
Surfactants should be limited to severe problems when other degassing
methods are ineffective. Surfactants change the surface tension of the
water, which releases trapped gases. Hach recommends a surfactant
such as Triton X-100 or the equivalent, Hach Cat No. 14096-37. Put one
drop of Triton X-100 in the sample cell before adding sample.
Note: Any turbidity contributed by surfactant addition is negligible.
This technique is very effective when the water is super-saturated with
air. However, changing the surface tension may accelerate settling of
turbidity-causing particles. Mix the sample gently, but thoroughly, and
analyze as soon as possible after adding the surfactant. Avoid vigorous
mixing as the surfactant may foam. Rinse the sample cells thoroughly
between samples to prevent surfactant accumulation.
1. Fill a sample cell to
the mark with sample.
Insert a #2 single-hole
rubber stopper and
syringe into the cell.
If using a pump, insert
a piece of glass tubing
into the stopper.
2. Slowly apply the
vacuum by carefully
pulling the plunger
upward, then holding it.
If using a hand or electric
pump, connect the tubing
to the vacuum pump with
vacuum hose. Apply
vacuum until visible gas
bubbles disappear.
Slowly release the
vacuum. Remove the
vacuum apparatus and
cap the cell.
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