Thermo Scientific Orion 320, User Manual

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5-3 Thermo Scientific Orion 320, 350 and 370 PerpHecT
®
LogR
®
Meter User Guide
A one, two or three buffer calibration should be performed using fresh
buffers before pH is measured . Always use a fresh aliquot of buffer
whenever calibrating . It is recommended that a two buffer calibration,
using buffers that bracket the expected sample range, be performed at the
beginning of each day to determine the slope of the electrode . This serves
the dual purpose of determining if the electrode is working properly and
storing the slope value in memory . For maximum accuracy, perform a one
buffer calibration every two hours to compensate for electrode drift, using a
fresh aliquot of pH 7 buffer .
The instrument uses a point to point calibration scheme, i .e . the meter
stores in memory the different electrode slopes for each portion of the
calibration curve . When measuring in a particular region of the curve, the
electrode slope for that region is employed in the calculation of sample pH .
After calibration, the average electrode slope for all the segments of the
entire calibration curve is displayed . Use of this scheme increases accuracy
in the different regions of the calibration curve . However, the electrode
slope may appear lower than normal, especially if buffers from the pH
extremes (pH less than 2 .00 or pH greater than 12 .00) are used .
When operating in the LogR mode, the meter does not require the use of
a separate ATC probe . The PerpHecT meters measure the resistance of the
pH sensing glass and converts the value to temperature-compensated pH
measurements . For optimum results, PerpHecT electrodes or PerpHecT
ROSS electrodes should be used .
For best results, it is recommended that the unit be calibrated for
temperature in the LogR mode . Alternately, an ATC probe may be used .
If LogR or an ATC probe is not used, all samples and standards should be
at the same temperature or manual temperature compensation should be
used .
Stir all buffers and samples with a magnetic stirrer while a measurement
is being made . Some magnetic stirrers generate enough heat to change
solution temperature . To avoid this, place a piece of cardboard, foam
rubber, or other insulating material between the stir plate and beaker .
Note:
When making measurements in the LogR mode, you must calibrate
for temperature before attempting a pH calibration .
pH Calibration