19
PHO
TOMETER
7.2. CUVETTE PREPARATION
Proper mixing is very important for reproducibility of the measurements. The proper
mixing technique is listed in the method procedure.
Invert the cuvette a couple of times or for a specified time: hold the cuvette in the
vertical position. Turn the cuvette upside-down and wait for all of the solution to flow
to the cap end, then return the cuvette to the upright vertical position and wait for all
of the solution to flow to the cuvette bottom. This is one inversion. The correct speed
for this mixing technique is 10-15 complete inversions in 30 seconds. This mixing
technique is indicated with “invert to mix” and the following icon:
In order to avoid reagent leaking and to obtain more
accurate measurements, close the cuvette first with the
supplied HDPE plastic stopper
and then the black
cap.
Whenever the cuvette is placed into the measurement
holder, it must be dry outside and free of fingerprints,
oil or dirt. Wipe it thoroughly with
HI731318
microfiber
cleaning cloth prior to insertion.
Shaking the cuvette can generate bubbles in the sample,
causing higher readings. To obtain accurate measurements,
remove such bubbles by swirling or by gently tapping the
cuvette.
Do not let the reacted sample stand too long after reagent
has been added. For best accuracy, respect the timings
described in the method.
It is possible to take multiple readings in a row, but it is recommended to take a new
zero reading for each sample and to use the same cuvette for zeroing and measurement
when possible.
Discard the sample immediately after the reading has been taken, or the glass might
become permanently stained.
All the reaction times reported in this manual are at 25 °C (77 °F). In general, the
reaction time should be increased for temperatures lower than 20 °C (68 °F), and
decreased for temperatures higher than 25 °C (77 °F).
