Inorganic Nutrient Analysis

Julian Herndon (RTC-SFSU) 

When you think of what a potted plant needs to grow, what do you think of? 

Fertilizer (soil), water, trace metals, carbon dioxide, sunlight... Similarly these are the components of growth in the oceanic primary producers. Yet, ocean water doesn't have soil. It does, however, have the same necessary nutrients for the photosynthetic algae that populates the seas: nitrogen and phosphorus particularly.

Reagents

Julian Herndon through the Romberg Tiburon Center for Environmental Studies at San Francisco University runs the analytical lab in a room just forward of the main lab. For days (and nights), he has been carefully setting up the lab, calibrating the instruments and preparing the reagents that are needed to get a complete profile of the ocean water, those necessary nutrients: phosphate, nitrate and silicate which is used by diatoms, the most common phytoplankton, to make their intricate frustules, their porous cell wall. The amount of care that goes into the programming and plumbing is astounding. The nutrient auto-analyzer is made up of four spectrophotometers, a peristaltic pump and a robotic auto-sampler and pipette that does what any good technician would do: it transfers a constant volume of sample, mixes it with a predetermined volume of reagent, records the results and clears the Teflon tubing with pure water--ready for the next sample. It repeats at a rate that would not be obtainable manually.

Automated nutrient analyzer

Basically, the instrument measures the "disappearance of light" as the light is absorbed by the specific compound. Visible light is actually a mixture of different wavelengths, each a different color that is seen as light. What the "spec" does is control the wavelength of light to transmit a particular ray at a specific wavelength through the sample. The reagents react with the sample to allow the machine to read and record the amount of that wavelength that passes through versus that which is absorbed. As an analogy, think of the compounds as stained glass windows, each one a different shade, absorbing that particular color, wavelength, of light. Light passes through, but we only see the color of the glass because its absorbed.

Julian Herndon, research associate for RTC-SFSU, ensures
proper protocols are followed for sampling.

Robotic autosampler system

Each type of stained glass has an associated wavelength of light, transmitting a different color; therefore, the spectrophotometer shoots a specific type of light through the sample and records the amount of that very specific color that makes its way through the system. If the stained glass represents nitrate (NO3, a pinkish red color), then the number of nitrate molecules is proportional to the number that is absorbed and unable to pass. Each element or compound absorbs a color. The greater the concentration, the less color passes through to be read by the detector. One of Julian's jobs is to change the "stained glass" needed to measure that particular compound in the sample by creating a new product through a chemical reaction so that it reads that very specific lightwave emitted by that one specific element or compound of interest. By doing this, we can determine the amounts of each of those important nutrients for growth and photosynthetic processes present in the ocean water being studied. He has meticulously set up the robotic machine and computer to do this work for him.

Automated spectrophotometer with cadmium column
 that strips the oxygen, turning nitrate (NO3) to nitrite (NO2)

As a man that has traveled the world in the name of science, Julian is man rich with more than just knowledge of his chemical craft, but he is one of the most interesting people that I have met. His expresso maker sits in the corner with classical music one hour and classic rock the next. With his lab assistant (pictured below), Maribel Albarran, I've never seen such careful attention to detail, cleanliness and consideration of contamination and safety--especially in this raw environment and rough seas--but then again, I've never been a part of something so important where every slight variation counts so much.

Maribel Albarran, student researcher (RTC-SFSU)

I have learned a lot and have a lot to learn. Julian has patiently explained his laboratory practices and the science behind his work, and I will be taking his teaching to heart and practicing these same methods in my classroom from now on, for safety and precision. I am honored to work and learn from him and all of the professionals onboard.

This standard spectrophotometer measures
one sample at a time.