3) Gently stir the buffer cup vertically. At an ambient temperature of 20 ±2° C, the pH reading should
be 4.00 ±0.10 pH. If the reading is outside this range, repeat the calibration at pH7 and then re-check
reading at pH4. If pH4 reading is still not within tolerance, it is necessary to reactivate the pH sensor
using the pH etching solution (supplied with the probe).
Both pH7 and pH4 buffer solutions used in the cup must be thrown away and not placed in the pH7
and pH4 bottles again. The pH7 and pH4 buffer solutions will generally last no longer than one year
after opening the bottles, as the ambient CO
2
and pollutants can deteriorate with them. In case of
doubt or of bad results, use fresh pH7 and pH4 buffer solutions as, in many cases, the pH problems
are simply due to bad pH solutions.
7.3.1 To etch the sensor, perform the following:
❖ Half-fill the transparent cap with the pH SENSOR ETCHING SOLUTION.
Note
Use gloves in order to avoid any direct skin contact with the pH sensor etching solution since the solution
contains hydrofluoric acid and ammonium fluoride and is highly corrosive.
❖ Place the cap on the pH sensor, gently squeezing the sides to limit the inclusion of air bubbles
during insertion. Take care that the etching solution covers the full round end of the sensor. After
no more than 1 minute, remove the cap and carefully rinse both the pH sensor and cap with
plenty of water. The electrode should be left in distilled water before use overnight.
IMPORTANT
A. The etching solution must not be used improperly, for instance to store the electrode as this will
permanently damage its pH glass membrane. The electrodes should always be stored either in
distilled water or in the pH7 buffer solution.
B. The treatment of the pH sensor with the etching solution cannot be performed indefinitely. After
performing this step a few times, the treatment ceases to have any positive effect and the sensor
should be replaced with a new one.
C. Do not use the etching solution with the reference sensor. Permanent damage to the reference
electrode will result.
D. When not in use, the pH sensor must be fitted with the protective cap filled with either pH7 buffer
or distilled water. (Alternatively, a salt solution - normally 3M KCl - can be used).
7.3.2 Important remark on the pH measurement
The ph and reference sensors should never be allowed to completely dry out. For short-term storage of
up to one day, the probe’s sensor head can simply be immersed in clean water. If the probe remains
unused for periods longer than one day, always place the hydrating caps on both sensors. The pH
sensor cap should be filled with the pH7 Buffer Solution (or simply with clean water). The reference
sensor cap should be filled with the Idronaut Reference Sensor Storage Solution (or even with KCl
saturated solution).
7.4 CONDUCTIVITY SENSOR
For accurate determinations of conductivity, it is important that the seven platinum electrodes of the
sensor flow cell be not contaminated with oils, biological growths or other foreign materials, which can
cause a reduction in the conductivity reading. During long-term monitoring, the growth of fouling
within the cell can cause a decrease of performance
7.4.1 Important remarks on conductivity measurement
1) To obtain the best accuracy, the conductivity sensor and therefore the probe sensor head, must be
immersed in clean seawater for at least 15 minutes before measurements.
2) When the conductivity sensor is not in use, it is kept dry. Therefore, when the conductivity sensor is
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