Metrohm 781 pH/Ion Meter - Manual (Page 84)

6.5 Direct ion measurement (781 only: Conc mode)
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780/781 pH/Ion Meter, Manual
rer has been connected and the settings made under CON-
FIG/peripheral units then the stirring rate can also be selected:
stirring rate 1...5...15
If you want your measurement to be made without stirring but still want
to stir the solution before the measurement then you should select the
control setting. In this way you can trigger a stirring sequence before
the start of each measurement with <MEAS/PRINT>:
prestir pause 0...99999 s
stir time 0...99999 s
poststir pause 0...99999 s
The prestir and poststir pauses represent waiting periods in which stir-
ring does not take place. The measurement itself only starts when the
complete stirring sequence has ended.
Please note that this parameter is binding for the report output and for
storing a measured value. Therefore when you start a measurement
with <MEAS /PRINT> or an addition sequence with <ENTER> the stir-
rer will be switched on and off accordingly. This is why you should pref-
erably carry out drift-controlled measurements for the direct determina-
tion of the concentration (see Section 5.2 and Section 5.3).
6.5.4 Calculation parameters
PARAMETER Conc
:
├
calculation parameters
: ├
smpl.size
├
V total
├
factor
└
smpl.size unit
The calculation parameters can be used for directly including sample
preparation data for the automatic calculation of the analytical result. In
this way the measured value shown will refer to the concentration of the
ion in the original sample and not in the sample solution to be meas-
ured.
smpl.size 0.0001...99999.9 (mL or g), OFF
V total 0.001...100.0...9999.9 mL
factor -1.00E+30...1.0...1.00E+30
smpl.size unit: mL, g
smpl.size describes the volume or weight of the sample under inves-
tigation, depending on the selected smpl.size unit . If you do not
want to use this parameter then set it to ' OFF '.
V total represents the volume of the sample solution at the start of
the measurement, e.g. after the addition of a buffer (TISAB, etc.).
The calculation of the measured value is then carried out according to
the following equation: