Filtration - LaMotte 1200 Instruction Manual

For dissolved oxygen studies, or for tests requiring small sample sizes, a Water
Sample Bottle (LaMotte Code 1060) will serve as a subsurface or in-depth
sampler. This weighted device is lowered to the sampling depth and allowed to
rest at this depth for a few minutes. The water percolates into the sample
chamber displacing the air which bubbles to the surface. When the bubbles cease
to rise, the device has flushed itself approximately five times and it may be raised
to the surface for examination. The inner chamber of the sampling device is lifted
out and portions of the water sample are carefully dispensed for subsequent
chemical analysis.
A Snap-Plunger Water Sampler (LaMotte Code 1077) is another "in-depth"
sampling device which is designed to collect large samples which can be used for
a multitude of tests. Basically, this collection apparatus is a hollow cylinder with a
spring loaded plunger attached to each end. The device is cocked above the
surface of the water and lowered to the desired depth. A weighted messenger is
sent down the calibrated line to trip the closing mechanism and the plungers seal
the sample from mixing with intermediate layers as it is brought to the surface. A
special drain outlet is provided to draw off samples for chemical analysis.
Sampling of Closed System
To obtain representative samples from confined water systems, such as pipe lines,
tanks, vats, filters, water softeners, evaporators and condensers, different
considerations are required because of chemical changes which occur between
the inlet and outlet water. One must have a basic understanding of the type of
chemical changes which occur for the type of equipment used. Also,
consideration should be given to the rate of passage and retaining time for the
process water.
Temperature changes play an important part in deciding exactly what test should
be performed. Process water should be allowed to come to room temperature,
20–25°C, before conducting any tests.
When drawing off samples from an outlet pipe such as a tap, allow sample to run
for several minutes, rinsing the container several times before taking the final
sample. Avoid splashing and introduction of any contaminating material.

FILTRATION

When testing natural waters that contain significant turbidity due to suspended
solids and algae, filtration is an option. Reagent systems, whether EPA, Standard
Methods, LaMotte or any others, will generally only determine dissolved
constituents. Both EPA and Standard Methods suggest filtration through a 0.45
micron filter membrane, to remove turbidity, for the determination of dissolved
constituents.** To test for total constituents, organically bound and suspended or
colloidal materials, a rigorous high temperature acid digestion is necessary.
**LaMotte offers a filtering apparatus: Syringe Assembly (Code 1050) and
Membrane Filters, 0.45 micron (Code 1103).
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