For pre-Nier mass spectrometry, see the review by Bleakney (1936):
Friedman and O'Neil (USGS 440-KK) have a brief history of standards and fractionation factors:
Gonfiantini has a nice write up of reference materials (and yes, it was a toilet seat) and early days of CO2 isotopic measurements:
CO2 is used because it is easy to work with--but I don't have a good reference off the top of my head. It can be frozen down using LN2, and cleaned up cyrogenically, i.e. pump away residual air. You do not need a Toepler pump, though mercury pistons were
used for pressure balancing. And since it can be introduced directly as a gas into the mass spectrometer, you can use electron ionization. A number of early papers dealt with ionization in the source and source tuning--especially important in stable isotope
analyses since consistent signal strength was needed to compare amounts.
Dewar flasks were invented in 1892. Commercial scale liquid air (liquid N2) plants were starting to be built in the 1930's. Electronics were well enough developed to build stable stable isotope mass spectrometers, so all the pieces were in place.
CO2 is also readily available from geological samples--just react carbonates with acid (phosphoric). And it can be equilibrated with water, so it can be used to determine the 18O composition of the water.
I've been reading up on the history of mass spectrometry (fascinating!), especially with regards to the technological advancements and scientific discoveries made by Alfred Nier. It seems that many of us stable isotope (geo)chemists consider measurement of CO2 isotopologues and specifically d13C measurements to be the 'easiest' (or perhaps the most common?), new instruments seem to be first developed for CO2 measurements (and then tested for the other systems), and d13C measurements typically have the highest precision. Indeed, Nier and Gulbransen laid the foundation for carbon isotope measurements (published) in 1939. There are lots of great scientific reasons for measuring CO2 isotopologues and/or d13C of some material.
My question is, from a philosophical, scientific, or technological standpoint, where does this (historical) proclivity for d13C and/or CO2 measurements come from?
I look forward to your thoughts!
Bethany Theiling, Ph.D.Research Scientist
Planetary Environments Laboratory, Code 699NASA Goddard Space Flight CenterGreenbelt, MD 20771