We developed a robust and fast analytical method for the separation and quantification of psilocybin and psilocin in under 2 minutes using inexpensive equipment, consumables, and reversed phase C18 HPLC. The importance of consistent eluent preparation and issues with standard compositions of formic acid were highlighted in our experiments and prudent eluent preparation. We assume the low pKa of formic acid may cause some amount of degradation via hydrolysis or dephosphorylation. Moreover, unbuffered formic acid may not fix the eluent and analyte pH and therefore multiple charge states are detected in-flow. Further investigation is currently underway to determine the nature of formic acid's interference with psilocybin. The simple conditions employed here use only a small concentration of ammonium formate as an eluent additive and pure acetonitrile to achieve good quantitative accuracy and precision (0.32% RSD and 3.5% bias). High purity solvents and the optimized instrument conditions achieved consistent results with excellent peak shape and a method limit of detection of 2.1 ppm.