. 1999 Jul;65(7):2807–2812. doi: 10.1128/aem.65.7.2807-2812.1999

TABLE 3.

Calculation of the proportions of acetate species formed from CO₂^a

CO₂ isotopes	Acetate species	% of species
¹²CO₂, ¹²CO₂	¹²CH₃¹²COOH	(% ¹²CO₂/100) × (% ¹²CO₂/100)
¹³CO₂, ¹³CO₂	¹³CH₃¹³COOH	(% ¹³CO₂/100) × (% ¹³CO₂/100)
¹²CO₂, ¹³CO₂	¹²CH₃¹³COOH	(% ¹²CO₂/100) × (% ¹³CO₂/100)
¹³CO₂, ¹²CO₂	¹³CH₃¹²COOH	(% ¹²CO₂/100) × (% ¹³CO₂/100)

For example, with 75% ¹²CO₂ and 25% ¹³CO₂, ¹²CH₃ ¹²COOH = 0.75 × 0.75 = 0.56 and ¹³CH₃ ¹³COOH = 0.25 × 0.25 = 0.06. ¹²CH₃ ¹³COOH and ¹³CH₃ ¹²COOH each accounted for 0.75 × 0.25 or 0.19 of the total acetate with methyl and carboxyl carbons from CO₂. The total number of micromoles obtained with methyl and carboxyl C from ¹²CO₂ ¹³CO₂ was calculated from the concentration of the ¹³C methyl group of acetate and was equal to 1/[(% ¹²CO₂/100) × (% ¹³CO₂/100) × (mM ¹³CH₃)].