Are there any other methods you could use to determine phosphate content in the colas

Concentration of phosphate (phosphoric acid mostly) in soft drinks can be measured with acid-base titration. For titration sodium hydroxide solution is used. Hydrogen ions (H⁺) from the first dissociation of phosphoric acid react with hydroxide ions from sodium hydroxide: 
H₃PO₄(aq) + OH⁻ (aq) → H₂O(l) + H₂PO₄⁻ (aq).
Use pH sensor to monitor pH of titration solution. Determine the equivalence point (the region of most rapid pH change), measure the volume of sodium hydroxide titrant used at the equivalence point and calculate concentration of phosphate with concentration of used titrant.

Dield-Alder Reaction is a type of Cycloaddition reactions. These reactions belongs to Pericyclic Reactions in which a cyclic Trasnsition State is formed during the reaction.

Diels-Alder reaction takes place between a Diene and a Dienophile. The Diene has a Electron Donating group and Dienophile has an Electron Withdrawing group attached to it. Below the reaction shows the reaction between Furan (Diene) and cyclohex-2-ene-1,4-dione (Dienophile).