LaMotte 1964-EPA, Manual

Page: 21 / 80

measurement. The light source for nephelometric measurements can be one of two
types to meet EPA or ISO specifications. The EPA specifies a tungsten lamp with a
color temperature of 2,200–3,000 K. The units of measurement for the EPA method
are nephelometric turbidity units (NTU). The ISO specifies a light emitting diode (LED)
with a wavelength of 860 nm and a spectral bandwidth less than or equal to 60 nm.
The units of measurement for the ISO method are formazin nephelometric units
(FNU). The TC-3000e meets the EPA specification and the TC-3000i meets the ISO
specification. The nephelometric method is most useful for low turbidity.
The TC-3000 is a nephelometer that is capable of measuring turbidity by both the
attenuation method and the nephelometric method. It uses a detector placed at 180°
to the light source for the attenuation method. It uses a detector placed at 90° to the
light source for the Nephelometric method. The TC-3000 also has a third detector that
monitors the intensity of the light source. It uses this detector to improve instrumental
stability and minimize calibration drift. The TC-3000 also has a signal averaging
option to improve the stability of readings on low turbidity samples.
The TC-3000 has two different turbidity calibrations, formazin and Japanese
polystyrene. The formazin calibration is the EPA and ISO approved method of
calibrating nephelometers. This calibration can be used with user prepared formazin
standards or commercially purchased formazin standards. LaMotte Company
approved AMCO
TM standards labeled for use with the TC-3000 can also be used with
the formazin calibration. Stablcal
â
standards below 50 NTU should not be used to
calibrate the TC-3000.
The polystyrene calibration is a calibration for a Japanese Water Works standard. It is
based on Japanese formulated polystyrene turbidity standards. This calibration should
only be use to meet Japanese Water Works requirements. The Japanese polystyrene
standards can only be purchased in Japan. Formazin, AMCO and Stablcal
â
standards
cannot be used with this calibration.
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
INTRODUCTION 21