Orion Star A325 Protocol

protocol
equipment
Orion Star A325 Protocol
Author

Ariana Huffmyer

Published

June 5, 2026

Overview

This protocol details the calibration and use of the Orion Star A325 probe for measuring temperature, salinity, and pH.

This protocol is based off of the Putnam Lab protocol.

Materials

Set up

  1. Turn instrument on –> button shared between on/off and brightness
  2. You can change screen modes by pressing F3 (channel), which can show one probe (salinity or pH) at a time or both probes at a time.
  3. Connect the probes by plugging in the black conductivity probe to the ATC/COND plug at the top of the probe. Do so carefully to make sure the pins align!
  4. Connect the pH probe with the metal twist connector to the top of the probe (under the protective black cap).
  5. Remove the pH probe gently from the plastic holding solution bottle by unscrewing the plastic bottle and pulling the probe out gently. When finished, always put the pH probe back in the storage solution bottle - NEVER store in DI water or any other liquid than the pH storage solution.
  6. Always keep the instrument clean, away from seawater, and wipe down with DI water when finished.
  7. Replace the pH storage solution regularly and ensure the probe is fully submerged when storing.

Here is the instrument:

You can see the pH probe connected on the left and the conductivity probe connected on the right:

The probes are stored in the back portion of the case (note that the label is peeling off on the pH probe):

This is the conductivity probe:

This is the pH probe:

When the pH probe is removed from the solution it looks like this - do not touch or wipe the glass probe inside the plastic housing.

Take readings

  1. Once the probe is connected and ready, you can take readings.
  2. Submerge the probes in seawater and gently swirl.
  3. Press “measure” on the instrument.
  4. The instrument will blink and then display values. Once you see “ready” the values are stable and can be recorded.
  5. I highly recommend taking one “dummy” measurement before recording actual measurements so the machine is warmed up.

Calibration (pH)

See pictures below of the supplies needed.

  1. pH should be calibrated <24 hours before use and done once every 2-3 weeks with regular use.
  2. Fill a small clean beaker with DI water, and pour the three calibration solutions (pH of 4, 7, and 10) into three clean beakers, and place near your work station.
  3. Turn on the meter and wait for the measurement screen to appear.
  4. Press F1 to select “cal” and go into Calibration settings. You should then select pH by pressing f2. 5. Follow the on screen instructions.
  5. Remove the probe from the storage solution
  6. Rinse the probe in DI water to remove any storage solution, and dry the probe (but not the sensor tip) with a chem wipe.
  7. Place the probe into the pH 4 solution, fully submerging the sensor tip, and agitate the probe tip back and forth briefly.
  8. Press F3 to Start the first calibration and wait for the reading to stabilize.
  9. The probe should read ~4 at the lab’s ambient temperature. If it does not, you can press F3 to override and manually enter pH 4. Press Accept once you are happy with the value.
  10. Then proceed to the next pH 7 and then pH 10 and repeat the steps. Rinse between pH solutions.
  11. If you are satisfied with the three calibration values on the summary screen, you can return to the Measurement screen.

Conductivity calibration

  1. Press the f1 (cal) key to start the calibration.
  2. Rinse the conductivity sensor with DI water and wipe gently with a Kimwipe.
  3. Place sensor into the first conductuctivity standard (12.9 mS/cm) and press the f3 (start) key.
  4. Wait for the value on the meter to stabilize and perform one of the following actions. Press the f2 (accept) key to accept the conductivity value. Or press the f3 (edit) key to access the popup number entry screen and manually enter the conductivity standard value expected at the measured temperature.
  5. Proceed to the next standard and repeat for the second conductivity standard (1413 μS/cm).
  6. Press the f3 (cal done) key to save and end the calibration.

The calibration supplies are on this shelf in 213:

This box has all of the supplies needed:

The salinity standards look like this:

pH buffers are in these pouches in boxes:

This is the pH probe storage solution:

Cleaning and storage

pH meter storage

  • Always store the pH meter submerged in a solution, the special conductive glass coating shouldn’t be left to dry out.
  • After each use store the pH meter in its accompanying sealed tight tube with the pH storage solution.
  • Never use distilled or deionized water, as prolonged submersion in water can encourage diffusion out of the electrode, which will affect its sensitivity. ONLY use the pH storage solution.

Conductivity meter storage

  • The conductivity meter can be stored dry in the Orion Star Meter plastic black case after cleaning with DI water and drying.

User manual

Orion Star User Manual