LaMotte TC-3000 Tri-Meter - Manual (Page 7)

TAKING TURBIDITY WATER SAMPLES
Clean plastic or glass containers may be used for turbidity samples. Ideally, samples
should be tested soon after collection and at the same temperature as when collected.
CHLORINE
What is Chlorine?
Chlorine is added to water systems to sanitize the water. There are various forms of
chlorine that are added to water. These can be gas, liquid (commonly called bleach or
sodium hypochlorite), calcium hypochlorite mixtures, stabilized chlorine products and
as chlorine generated using salt. When these forms of chlorine are added, they react
with water to form free chlorine, hypochlorous acid. If free chlorine reacts with
ammonia, it will form various types of combined chlorine (chloramines). Depending on
the chlorine to ammonia ratio, these can be mono, di or tri chloramines.
Because free chlorine can react with precursors in the water to form carcinogenic
trihalomethanes (THMs), many water systems have switched to chloramines. In these
systems, free chlorine and ammonia are added together and controlled to form
monochloramine. Although not as active a sanitizer as free chlorine, chloramine is less
likely to form THMs. Since it is a slower sanitizer, the concentration of chloramine in
water is higher than the concentration of free chlorine in water distribution systems.
The present EPA limit of chlorine in water systems is 4.0 ppm. The amount of chlorine
used to process waste may be higher than this.
Many states also establish limits on the amount of chlorine that can be discharged into
a body of water after waste processing. These usually are less than 0.1 ppm. The low
detection limit of the TC-3000 makes it ideal for such measurements. Because of its
wide range, the TC-3000 can be used to measure the water used in the wastewater
process, in a distribution system and for many low level discharge requirements.
How is Chlorine Measured?
The most common methods for measuring chlorine are colorimetric methods. In
colorimetric methods, chlorine reacts with reagents added to a water sample. The
reaction of the chlorine with the reagents produces a color. The intensity of the color
produced is proportional to the concentration of chlorine in the sample. The intensity
of the color can be measured by visual comparison with a calibrated color chart or
othere types of visual color comparators. Visual methods suffer due to the subjective
observations of the person judging the colors.
The TC-3000 uses EPA approved DPD reagents to react with chlorine. In the absence
of iodide, free available chlorine reacts instantly with DPD to produce a pink color.
Subsequent addition of potassium iodide (DPD 3) causes a reaction with combined
form of chlorine. The TC-3000 electronically measures the color produced in these
reactions in comparison to a colorless water sample. First it measures the intensity of a
light beam passing through a clear colorless sample, the blank. Then it measures the
intensity of light passing through the pink reacted sample. The TC-3000 uses the ratio
of these two measurements to calculate the concentration of chlorine and displays the
result. The TC-3000 uses the EPA approved wavelength of 525 nm, to make these
measurements.
CHLORINE 7