21
CALIBRA
TION
7.4. ENSURE ACCURATE CALIBRATION
The procedure below should be carefully followed during testing and
calibration:
• All glassware that comes into contact with standards should be
maintained clean. Wash with the
HI93703-50
cleaning solution
and rinse with
HI93703-0
or turbidity free water.
• Rinse the vial twice with 5 mL of the liquid to be tested. This
removes the effect of any previous liquid and any dust or foreign
objects that may be present inside. Gently pour the liquid down
the side of the vial to reduce air bubbles (no mixing is required
when
HI93703-0
and
HI93703-10
AMCO-AEPA-1 standards are
used).
• Before inserting the vial into the instrument, wipe it with
HI93703-70
or a soft, lint-free tissue. Handle vials so that no
fingerprints can get on the areas where light passes (approx.
bottom 2cm/1”).
7.5. STANDARD SUSPENSION
Presently, there are only two recognized primary standards: AMCO-
AEPA-1 and formazine.
Hanna Instruments supplies
HI93703-11
with the AMCO-AEPA-1
which has a much longer shelf life at all concentrations (approx. six
months, if free from contamination). In addition, no special handling
or disposal is required and a much higher stability of suspended
particles has been observed.
On the other hand, formazine is a toxic substance, generated by a
known carcinogen, with poor stability (particles flocculate and settle
quickly). Lower concentrations change value within a few days or
hours after dilution. The consistency of
HI93703-11
readings by
using both standards has been separately established by Advanced
Polymer Systems and Hanna Instruments.
Additional documentation about the formazine standard and more
complex calibration procedures is available upon request.
