text: # Extract  from carbonates by reaction with anhydrous phosphoric acid. (there is no direct way to measure the abundance of COs in with high enough precision). The phosphoric acid temperature is often held between 25° and 90 °C and can be as high as 110 °C.
  # Purify the  that has been extracted. This step removes contaminant gases like hydrocarbons and halocarbons which can be removed by gas chromatography.
  # Mass spectrometric analyses of purified , to obtain δC, δO, and Δ47 (abundance of mass-47 ) values. (Precision needs to be as high as ≈10, for the isotope signals of interest are often less than ≈10)