Page 15 - Customer Needs and Use Assessments (CNUA) of pH Sensors

ACT In Situ pH Sensors Customer Needs and Use Assessment............................................................................ 14
Range/detection limits, Specificity or Interferences (the ability to separate a pH signal from other signals),
Automatic calibration, and I/O Interfaces each received 4 responses. Real-time sensor data display and In-field
maintenance each received 2 responses. Sampling Interval and Flow Sensitivity received no responses for in situ
pH sensors currently in use.
Actual User Responses (edited):
• We’d like to have better accuracy and precision to at least 0.01 as we seldom use our existing pH data due to
the sensor’s poor resolution and accuracy.
• Unsure as to the causes of sensor failure, but we have had sensors that would not calibrate correctly and
had to be replaced by the manufacturer.
• Over 6 months of use: clogging of the intake tubing due to suspended sediment in shallow areas.
• One instrument noisy due to LED quality or low life time (?)
• Poor packaging (replacing the battery is difficult).
• No way in software to adjust the calibration (for example after replacing the dye), no way in software to
post-process the data with salinity given by another instrument.
• We observe an increased difference in pH between probe data and spec measurements with increased
depth. It seems there is a non-linear relationship between pressure and probe pH. Currently trying to
resolve this issue. Furthermore, we have had difficulty keeping our sensors working for more than 2 years
before the housing leaks, the probe fails, etc...
• Calibration techniques and standards.
• We know very little about the uncertainty and reproducibility of these sensors in the real environment. We
know less about responses characteristics in changing temperature, pH and salinity which is the real world.
• Commercially available seawater buffers for calibration have been the biggest issue for use.
• “We have used pH sensors at depth, which were pretty poor. Large pH drift, short (<days) calibration
confidence due to drift. Deployment depth of ~3000 m. There wasn’t anything else available.
• We are now using ISFET pH sensors in the lab - they are fantastic. We have also deployed a coupled on
small benthic moorings at 100 m depth - this is near or over their max depth range. Hope to see great data
when they are recovered!
• Sensor is frustratingly slow to calibrate and VERY slow to stabilize in low ionic strength waters. I recently
was introduced to a new pH probe at a workshop in 9/2011 at University of Michigan Biological Station.
This sensor appears to not have many of the problems associated with traditional ISE pH sensors (e.g.
calibration frequency, life expectancy) and I may use this in the future.
I do not have any sensors yet, but wish to deploy pH sensors at my coral calcification monitoring stations
on the outer reef tract, Florida Keys, USA
• Availability-sensors are being custom built by one lab (not truly commercially available). There are
reliability issues in that as a small production group, not every sensor has proven to work in the field
consistently.
• Been using the glass bulb technology with is very sensitive and needs to be calibrated/cleaned often.
Accuracy is the real issue.
• Our current favored pH system for the ship-of-opportunity measurements that I do would be an ISFET
pH system. However, we pretty much need to collect and measure discrete samples for DIC and TA to
standardize our measurements. This seems to work adequately in bluewater settings, but is definitely an
issue in coastal and estuarine environments in that calculated pH values will be off where dissolved organic
matter changes alkalinity.
• Biofouling