The Building Blocks

Elements are themselves composed of more elementary particles. The charged particles that give the element its chemical properties and determine what sort of bonds it can make with other atoms are the protons. Carbon has 6,oxygen has 8, hydrogen has one. Uncharged particles, or neutrons, can also exist in an atom and in fact are usually present in about the same number as the protons. Usually. A couple of neutrons above or below the number of protons doesn't upset the atomic applecart. But too many or two few and suddenly you've got glow-in-the-dark watches and Three Mile Island. Carbon usually has 6 protons and 6 neutrons (mass=12). Carbon with 6 protons and 7 neutrons (carbon-13) is still stable. Put in one more extra neutron and you have carbon-14 - a ticking timer of a radioactive atom that can be used to date the Shroud of Turin or measure the growth rate of antarctic phytoplankton.

Where we come in...

At CSL, we make sensitive measurements of the stable atoms (or isotopes when you're talking about atoms that have the same number of protons) of carbon, oxygen and others. We are in effect measuring how much of the oddball stable isotopes like carbon-13 or oxygen-18 there are compared to their more normal counterparts, carbon-12 or oxygen-16 in a sample. The methods we use give the ratios of the atoms which we compare to the ratios in materials that others are familiar with. There is an internationally accepted standard for each element. The data we produce for a carbon sample (for example, a politician) may look like "-26.3 per mille relative to PDB" which simply means that the sample had 2.63 percent less carbon-13 than the standard which is called "PDB". The ratio for a swamp gas sample, however, might look more like -65 per mille. So politicians and swamp gas aren't really closely related, no matter how persuasive the argument.

This is where the fun starts. If the carbon-13 to carbon-12 ratio (¹³C/¹²C) were the same everywhere, we'd be out of business. It turns out that the two isotopes of carbon (and all the others) behave the same except that they react at slightly different rates with slight differences in the strength of their bonds. So the world is full of carbon reservoirs (politicians, swamp gas, honey, oil, great white sharks, etc.) that have variable stable isotope ratios. The ratios differ because of the reactions that produce each reservoir. And since the ratios are different because of the processes that produce them, then we ought to be able to use the ratios as clues to the nature of those processes. Geologists, biologists and chemists are doing just that as we speak (or as you read). Figuring out if a salt marsh is a source of organic matter for a bay or a sink of organic matter from its river. Finding out if a redhead duck depletes its stored energy from Canadian rice before it reaches its winter buffet of Texas coastal seagrass beds. Finding out if the rocks deep below the surface are old enough, compressed enough and heated enough to have produced oil or gas in a reservoir nearby. Finding out how closely coupled the carbon dioxide in the atmosphere is to the carbon dioxide dissolved in the oceans. Finding out how much of the atmospheric methane comes from cow farts... You get the idea.

A lot of practical, day to day questions can be answered by stable isotope ratios too. Check out our application notes for some prime examples. Like,

• 'How much corn syrup did that joker cut this expensive honey (or maple syrup) with?'
• Or 'Is this really fresh squeezed orange juice I paid top dollar for?'
• And 'Is the flaming gas bubbling out my kitchen faucet coming from a broken gas main or is a natural formation injecting it into the aquifer?'.
• How about 'Who's responsible for the eutrophication (sliming) of this creek? The country club with the over fertilized golf course or the old houses with the leaking septic systems?'.
  

Stable isotope ratio analysis (SIRA) to the rescue...