Post #17 - One doesn't use litmus paper anymore....

In science labs in school when growing up, we used colorful litmus paper to measure pH. When dipped in a solution, the paper turned a color based on the solution's pH.  Things are a LOT different these days.  In order to publish work on ocean acidification, you need to use techniques that give you both the pH and what is called the pCO2 (basically the amount of CO2 dissolved in the water) with great precision.  The techniques can be very time consuming, and thus I have spent a great deal of my time here doing the water chemistry necessary to support both Emily's and my research.

The pH is measured with a spectrophotometer.  Here, the sliding top door is open so that you can see the white cap of a quartz glass cuvette.   The cuvette is filled with 3 mL of the water we are testing.  With the door shut, the machine shines light of very specific wavelengths through the cuvette and measures how much makes it through the solution.  Then I add a special dye and the process is  repeated.  A computer (out of view to the right) records the before-dye and after-dye numbers.  We put these numbers into our laptop where they are fed into calculations that give us a tentative pH.

The water bath on the floor does two things.  It is set at 25oC and sends water through the hoses to the cuvette holder, because this process is very temperature sensitive so we try to keep the sample as close to 25oC as possible.  This is why we place the samples in the water bath reservoir prior to measuring their pH.  On top of the spectrophotometer is a digital thermometer that has a thermocouple on the end of a thin wire.  The last thing we do after the sample is read by the spec is to take the temperature of the sample as it sits in the cuvette inside the spec.  This temperature is used in the calculation of the pH.

This is the prep area for our samples.  In the dish at right are white-capped glass vials in which we collect our water samples.  During Emily's experiments, I was collecting two vials of water from each of eight aquaria.  When the samples are collected, we must make sure there are no air bubbles, because that could change the CO2 levels in the water and hence the pH.  The dye takes a full morning to prepare if everything goes right, and is stored in an aluminum foil-wrapped bottle (at left) because it is light sensitive.  The dye can go bad, as ours did about several days ago.  The new batches were not checking out with the standards we were using, and we spent a good two and a half days figuring out how to adjust things to get it to work.  It disrupted my fertilization experiment schedule in a big way, so now I'm running two experiments per day for the next several days.

When the dye is working well, even your naked eye can see the color difference between normal sea water in the cuvette to the left (it is more purplish) and the water acidified by CO2 at right.

Using the spectrophotometer is only one part of the process.  A titrator is used to determine what is called the "total alkalinity" or TA of each water sample.  This is what the $50k machine looks like:

The red cylinder on top has a piston that sucks an acid from the bottle to the left of the titrator and pumps it through the red hoses into the sample cup suspended at the right.  Here's a closeup of the sample cup:

The cup holds a very carefully weighed sample of sea water.  Projecting down into the sample are a pH probe, a tube for delivering the acid, a temperature probe, a white stirrer, and for our samples an air bubbler.  Over a period of about 20 minutes, very precise volumes of acid are periodically pumped into the sample as it is being stirred, and the pH and temperature are measured.   All the data are fed into a computer program that  calculates the TA.  The TA numbers are then added to another program along with the pH measurements from the spectrophotometer to calculate the pCO2 levels in the samples.

All this is necessary in order to do OA research, and with eight different experimental aquaria running, you can see why, when I was running samples during Emily's experiments, it could take from 7 in the morning (when the samples are carefully collected) to early- to mid-afternoon (if there are no major interruptions) to complete that day's water chemistry.  And this went on day after day as long as Emily's corals were producing larvae...

Now with Emily's coral experiments over and our COT fertilization experiments going full speed, she's doing most of the water chemistry while I'm focussing on the rest of the experiments.  It's a lot of lab work for both of us, but worth it.  Still, getting out in the late afternoon to snorkel, even if it is a quick trip to check the SeaFET, is a wonderful break when you can see so many colorful fish hovering around the coral........