EurOCEAN 2000 - Vlaams Instituut voor de Zee

All electrodes had very short adjustment times in 0,0001 M NH4 + even after 5 days of dry
storage. Contrary to former measurements with Nitrate selective electrodes very little
adjustment problems were found for all Ammonium (NH4 + ) selective electrodes even in the
presence of interfering ions like Sodium (Na + ) or Potassium (K + ) at concentrations similar to
those to be expected in seawater.
RESULTS FOR TESTING THE NITRITE ION SELECTIVE
ELECTRODES:
The drifting behaviour observed during the adjustment time measurements also influences the
measurements of the concentration series.
Period of dry storage pH Electrode Adjustment time/ minutes
706
1 day 6.2
4 days 6.0
REAGECON 09 12
REAGECON 10 12
ORION 55
REAGECON 09 14
REAGECON 10 15
ORION 50
The interference of the chloride ion is significant in the whole concentration range but much
smaller than in the case of the nitrate and ammonium electrodes. The chloride interference of
the Reagecon electrodes is smaller than the influence on the Orion electrode.
In the concentration range to be expected in seawater the interference of Bromide (Br - ) and
Nitrate (NO3 - ) is negligible at both temperatures. At 20 o C the interference of Sulphate (SO4 2- )
is moderate, at 10 o C the influence of Sulphate (SO4 2- ) is small.
At 10 o C interfering ions had less of an impact than at 20 o C.
At pH 4.5 the slope of the Reagecon and the Orion electrode are satisfactory. The slopes of the
REAGECON electrodes are somewhat closer to the theoretical value (Nernst value). At pH 8.5
the curves differ significantly from the values measured at pH 4.5. Slope and linearity of the
Orion electrode were very poor in the whole concentration range. In the range −
NO2
m < 0.001
mol/kg the slope of the REAGECON electrodes differs significantly from the theoretical value
(Nernst value).
RESULTS FOR TESTING THE REFERENCE ELECTRODES
CONSTRUCTION AND COMOPSITION:
Reference electrodes of a large variety of construction and composition reflecting the current
state of the art and proprietary knowledge have been prepared and challenged for speedy
response, reproducibility and particularly long term stability in marine matrices and capable of
withstanding bio-fouling. Depending on the outcome of subsequent specialised biological and
physical testing there are 2 prototype reference electrode designs which can be proceed with.