For interlaboratory comparison and cost-effectiveness, methods involving expensive or time-consuming steps, such as high-resolution mass spectrometric detection or timeconsuming chemical derivatization strategies, were not considered. For similar reasons, and because many laboratories use C18 octadecyl silica HPLC columns, more expensive column chemistries including ion-exchange resins were not considered. As an alternative, we used a conventional (Poroshell 120 EC-C18 2.7µm 3.0x50 mm) 2.7 µm particle C18 column which is best for (U)HPLC performance at lower operational pressures (Agilent Poroshell 120 EC-C18 Threaded Column Data Sheet, 2009). This particular particle size and column chemistry are known to significantly improve reversed-phase chromatography peak resolution and feature high separation efficiency. C18 columns are preferable to C8 (arguably the next most common HPLC column material) columns for polar organic compound separation. This column chemistry and effects on retention are like that of traditional, fully porous, ZORBAX Eclipse-type C18 columns. The choice of column ensured this method is applicable in many laboratories.