oxygen and pH sensors
oxygen sensor
Sensor is used in conjunction with an oxygen electrode. Good for demonstrations where you monitor photosynthesis, fermentation or where you re-breathe the air in plastic bag.
Before you use the electrode for the first in a long time, fill the membrane cap with electrolyte without introducing air bubbles. Connect the electrode to the sensor, switch on and leave it in air for up to twenty minutes to stabilise. It is easier to calibrate the sensor in air, although some prefer to use an aquarium pump to aerate water for an hour and use this as a 100% saturated standard solution. When you have finished, keep the electrode suspended in de-ionised water to prevent the electrolyte from drying out. The usual advice is that the electrode should only be kept like this for a week before taking it apart, washing with soapy water and rinsing in de-ionised water. Some say they’ve kept it in a ready-to-use state for months. But do take great care of the membrane caps – physical damage to the polythene membrane may be a cause of poor readings. I have used dry-cleaner bag polythene to replace this. Other snags are due to a poor connection between the electrode and the adapter, cleanliness of the electrode tip and condition of the electrolyte. Do allow time for the electrode to stabilise and appreciate that movement of the liquid you are testing is highly recommended. A few goldfish will make useful stirrers for an aquarium.
pH sensor
A versatile sensor used in conjunction with a pH electrode. It makes creating acid-base titration curves easy and there are biological applications in monitoring photosynthesis, respiration, fermentation and the activity of lipase. These uses aside, compared to a regular pH meter it can good value as a pH measuring device. The main issue is that in many places, pH electrodes are so rarely used that they suffer during storage. The key piece of advice is to keep them wet and never wipe or dry them. Elsewhere on this site you’ll see photos of the bottles I used to store my twenty electrodes for years with only occasional failures.
I’ve rated these sensors but your assessment will be different. I give a score, out of five, for the sensor’s intrigue, interest, and learning potential. I also give a score for how often a science department might use it.