TPS smartCHEM-Titro - Calibration Buffer Sequence

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4.3 Calibration Buffer Sequence
Before proceeding to pH Calibration (section 4.4), please consider the sequence in which the
buffers should be used. This will vary depending on whether a 1, 2 or 3 point pH calibration is
required.
4.3.1 1 Point Calibration
A 1 point pH calibration can be performed in any buffer and will only adjust for the asymmetry of
the pH sensor. See section 18.1.1 for a detailed explanation of asymmetry. A 1 point calibration will
not remove the " ∗
∗∗
∗ ", which is shown in place of the decimal point when pH is un-calibrated or has
failed calibration.
4.3.2 2 Point Calibration
A 2 point calibration is performed automatically after a successful 1 point calibration, when the pH
sensor is calibrated in a buffer that is at least 1.50pH higher or lower than the buffer that was used
for the first point.
A 2 point calibration can be performed in any two pH buffers, and in any order, as long as they are
at least 1.50pH apart.
4.3.3 3 Point Calibration
A 3 point calibration must be performed in the correct order.
For the pre-programmed buffers (see section 4.2), this order can be any one of the following…
First Point Second Point Third Point
pH6.88 or pH7.00 pH4.00 pH9.23 or pH10.06
pH4.00
pH6.88 or pH7.00 pH9.23 or pH10.06
When using buffers other than the pre-programmed buffers, please use the following guidelines to
determine the correct order in which to perform a 3 point calibration…
1. Definitions
a) A neutral buffer must be between pH6.50 and pH7.50, inclusive.
b) An acidic buffer must be 1.50pH or more lower than the neutral buffer that is being used.
c) A basic buffer must be 8.50pH or higher.
2. Buffer Order
a) Neutral → Acid → Base
b) Acid → Neutral → Base
3. Notes
a) When using buffers other than the pre-programmed buffers, ensure that the pH versus
Temperature characteristics are known. The buffer value corresponding to the calibration
temperature must be keyed in correctly.
b) pH sensors offer an extremely linear response over a wide range. A 2 point calibration
would normally be sufficient for most measurements between pH2.00 and pH10.00.
c) When a 3 point calibration has been successfully performed, an extra line appears in the
GLP Recall (section 10.1) and the GLP print-out (section 10.3) labelled “ SlopeB ”.