pH testing is carried out on unfiltered stream water samples collected in small bottles with
black caps, using an electronic pH meter with an electrode.
The first task is to take the take the sample bottles and place them in numerical order.
Check that each site number label is legible, that the cap is tightly secured, and that
there are no air bubbles.
Count the number of bottles and note this against the number of pairs of ‘F/A’
and ‘F/UA’ samples.
All field based chemical testing must be recorded in a water chemistry data book.
First, write out the site numbers in numerical order.
Using the wooden blocks, carefully arrange the samples in numerical order. The convention
is to place the lowest number on the bottom left and the highest number on the top right.
Cross check each site number against the water chemistry data book as you place the bottles
in the block.
Leave the samples and three colour coded buffer solutions for at least one to two hours in
order to equilibrate them to room temperature.
Once equilibrated, the pH meter must be set up and calibrated using the three colour coded
buffer solutions.
Before pH testing commences, record the temperature of a buffer solution and the first sample.
Place the thermometer into the pink coloured buffer solution for pH 4. Record the temperature
in the water chemistry data book.
Clean the thermometer by rinsing with deionized water and dry with a Kimwipe™. To test the
sample temperature, pour a little of the stream water sample over the thermometer, before
placing it into the bottle. Record the temperature, and be satisfied that the recorded temperatures
are the same before proceeding.
Wipe down the thermometer, return it to its case and replace the lid on the sample bottle.
Before testing, the pH meter must be calibrated using the three colour coded buffer solutions.
Turn on the pH meter and remove the electrode from its protective case and electrode storage
solution. As storage solution may have evaporated salt crystals may be found in and around the
protective cap or on the pH bulb. This is normal. Inspect the electrode for any scratches
or cracks on the bulb or stem. If any are present, replace the electrode.
The electrode should always be rinsed with deionized water before and after placing it
in any buffer solution.
Begin the calibration mode on the meter. Insert the electrode into the pink coloured pH 4
buffer solution. The meter should recognise the solution and give a reading. Once happy
that the pH reading on the meter closely matches that of the buffer solution, record it in
the water chemistry data book.
Remove the electrode from the buffer solution, rinse and wipe clean.
Replace the cap on the pink coloured pH 4 buffer solution.
The next calibration point is the yellow coloured pH 7 buffer solution. Repeat the calibration
process and record the reading.
Remove the electrode from the buffer solution and rinse and wipe clean. Insert the electrode
into the blue coloured pH 10 buffer solution. Repeat the calibration process and record
the reading. This is the final calibration point.
Exit calibration mode on the meter.
You are now ready to test and measure. The first test is to measure the yellow coloured
pH 7 buffer solution. Record the result in the water chemistry data book, taking care
to clean the electrode and replace the cap between all measurements.
pH testing of the stream water samples can now begin. Remove the cap from the first sample.
Pour a little of the stream water sample over the electrode, before placing it into the
bottle. Take care to minimise disturbance of any suspended solids or sediment in the
bottle. Do not let the electrode rest at the bottom of the bottle.
Wait until the meter reading stabilises and then write this reading into the water chemistry
data book, double checking that the site number on the bottle matches
the one written in the book.
Remove the cap from the next sample bottle before taking the electrode out of the sample
just tested. As before, pour a little of the stream water sample over the electrode, before
placing it into the next sample bottle. Ensure you replace the cap on the previous sample.
Await the reading on the pH meter—it may take its time to settle on a result. Record
the measurement immediately.
Repeat this process for every stream water sample, carefully recording each pH reading
into the water chemistry data book.
When all pH measurements have been taken, always repeat the process
for the first three samples.
As always, rinse the electrode with a small amount of the sample
before placing it into the bottle.
Record the repeat measurements in the water chemistry data book in brackets after the
original ones.
Also take repeat measurements for any readings that you feel are atypical.
Finally, the three coloured pH buffer solutions must be re-measured. As before, clean the
electrode with deionised water and wipe before placing it into each solution. Measure pH
buffers 4, 7 and 10 in that order, and record each reading in the water chemistry data book.
This repeat measuring is done to find out if the calibration of the meter
has remained consistent.
Each day, record the weather conditions, monitor site details and your initials in the water
chemistry data book.
When finished, return the electrode to its protective case and electrode storage solution.
Check the level of the electrode storage solution and that it is above the electrode junction,
the small hole on the electrode stem. Switch off the pH meter
and keep the electrode stored upright.