32
SECTION 2,
continued
2.10 Condensation (Fogging)
Note: Warming may alter the
sample turbidity. Measure the
sample without warming
whenever possible.
Condensation may occur on the outside surface of a sample cell when a cold
sample is being measured in a warm, humid environment. This condensation or
fogging of the sample cell interferes with turbidity measurement. Make sure all
moisture is thoroughly wiped from the outside of the sample cell prior to placing
the cell in the instrument for measurement. Use the air purge feature when
condensation is probable. Refer to SECTION 4 for instructions on connecting and
using air purge. If condensation persists even with air purging, it may be necessary
to warm the sample slightly by letting it stand at room temperature or by partially
immersing it in a warm water bath for a short period of time. Make sure samples
are well mixed before measurement.
2.11 Calibration Check
Note: Store Gelex Standards at
room temperature. Do not allow to
freeze or exceed 50 °C.
Use Gelex Secondary Turbidity Standards for periodic calibration checks. Please
note that Gelex Secondary Turbidity Standards must be assigned values after each
Formazin calibration.
Gelex Secondary Turbidity Standards are stable suspensions of a metal oxide in a
gel. The standards are labeled with the measurement range for which they are
intended. Due to minor variations in glass and instrument optical systems, the true
value of the Gelex standards must be determined against formazin in the same
instrument they will be used with for later calibration checks.
Note: Calibrated values for
secondary standards are valid only
with the specific instrument on
which they were determined. Do not
use these values for standardization
checks on other instruments.
Gelex standards remain stable when cared for properly. Handle with care, and
store them in their protective box at room temperature. The Gelex suspension can
separate internally if subjected to low or high temperatures. The turbidity values
of scratched, chipped or pitted Gelex standards change; replace these standards
when they become damaged. Wiping the vial surfaces with silicone oil (supplied
with the instrument) minimizes the effects of minor scratches on the vials.
Turbidimeters must be properly calibrated with a primary standard. Hach
Company recommends use of Formazin Primary Standard for turbidimeter
calibration. Quarterly calibration (every 3 months) is required for U.S.
Environmental Protection Agency reporting under NPDES or NPDWR permits. If
data is not for regulatory reporting purposes, calibrate as experience dictates.
2.12 Representative Sampling
A representative sample accurately reflects the true conditions of the source from
which the sample was taken. To ensure a representative sample, gently but
thoroughly mix every sample before collecting aliquots (sample portions). Do not
allow particles to settle before making measurements.
Note: Mix by gentle inversion only.
DO NOT SHAKE.
Run water for at least five minutes before sampling from a water tap in a
distribution system or treatment plant. When sampling from a body of water (e.g.,
a stream, reservoir, clarifier or storage tank), collect at least one liter (1 quart), and
thoroughly mix before taking an aliquot for measurement.
If the sample source is not uniform, it may be necessary to sample several
locations at varying depths, and combine the samples into a single, well mixed
composite sample before measurement.
Tài liệu sưu tầm của Trung Sơn - www.tschem.com.vn - 028.3811.9991 - [email protected]
Tài liệu sưu tầm của Trung Sơn - www.tschem.com.vn - 028.3811.9991 - [email protected]
