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...3 SETTING UP
g) Fit the pressure plate platen on the peristaltic pump (see
Section 8.2.6) and switch the pump on with the switch on
the side of the monitor. Note that the peristaltic pump
rotates, and check that sample and reagent is being drawn
into the monitor by observing the progress of any small
bubbles present in the inlet tubes.
h) Run the monitor for at least one hour to allow the solutions
to be pumped into the system and to purge the air from the
pipework. Check for any leaks around the pipe connections
and rectify as necessary.
j) Set the following parameters to YES using Programming
Page 2.1:
Five-Weekly System Flush
Five-Weekly Solution Replacement
Default Calibration Parameters
For single stream instruments only, set the color
compensation frequency to 'OFF' using Programming
Page 3.3.
Information. If the monitor has not been in use for
a long period, the 're-wetting' process of the system can
be speeded up by introducing the chemical rinse solution
for a period of 30 to 60 minutes (see Section 8.2.4).
Note. Before proceeding to the next step, multi-
stream users must select single stream mode as
described in Section 4.3.
k) If having not already done so energize the secondary CAL
valve (see Programming Page 2.3) and leave for
15 minutes. Adjust the reading on scale with the
switches and run the monitor for 30 to 60 minutes to
purge the old solution and assess stability.
l) If the monitor exhibits good stability, i.e. <5% of reading,
carry out a two-point BASELINE calibration – see
Programming Page 2.3.
For single stream instruments only:
m) If color compensation is required, switch to 'Enable' for
manual compensation only, or to automatic timed
compensation by selecting a frequency between 1 to
24 hours using Programming Page 3.3. For general
information regarding the setting up of the color
compensation see Section 7.2.
4 LIQUID HANDLING SECTION
4.1 Principle of Operation – Fig. 4.1
The chemical method used in the monitor utilizes the reaction
between orthophosphate, molybdate and metavanadate
which in the presence of acid react to form a yellow phospho-
vanado-molybdate complex. The absorbance of the complex,
which is directly related to the phosphate concentration in the
sample, is measured colorimetrically in the optical system.
The sequence of events is:
a) A combined reagent comprising ammonium molybdate,
ammonium metavanadate and nitric acid is added to the
sample and mixed.
b) The solution then enters the reaction coil in the
temperature-controlled block (providing a three minute
delay) where the yellow phospho-vanado-molybdate
complex is developed.
c) The fully developed solution passes to the measuring
cuvette in the optical system where the absorbance of the
complex is measured.
d) Calibration of the monitor is achieved by replacing the
sample with de-ionized water (for the ZERO solution) and
then a phosphate standard for the secondary upscale
calibration solution.
Silica in the sample is prevented from interfering by choosing
sufficiently strong acid conditions to inhibit the silica-
molybdate reaction.
In the chemical method used, the reactive phosphate species
is orthophosphate, PO
phosphate species which are converted to orthophosphate
under the chemical conditions of the monitor, they will also be
and
measured.
For single stream instruments only:
If the sample is colored, the phosphate reading may show a
positive error. Compensation for color is obtained by
measuring the absorbance by the sample without addition of
reagent. This reading is then automatically subtracted from the
phosphate reading to give the color compensated value.
Ammonium molybdate/
ammonium metavanadate/
nitric acid reagent
Sample
Fig. 4.1 Chemical Schematic
3-
. If the sample contains other
4
pH less than 1 to prevent
silica interference
and provide conditions for
production of
yellow phospho-
vanado-molybdate complex
Reacted Sample
To Cuvette
Three Minute
Delay
Mixing Stage
9
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