Diazolidinyl urea

ANT, FLU, NAP, PHE, and PYR standards were purchased with the purity of 98.0 to 99.0% (Sigma-Aldrich). Analytical or HPLC grade solvent hexane (Scharlau), acetone (Scharlau), dichloromethane (Scharlau), and methanol (Scharlau) were used to carry out all the experiments. Purified deionized water (D.I. water) which does not contain any measurable quantities of any target analytes or interfering compounds was used.
Sample preservation reagents L-ascorbic acid (Sigma-Aldrich), ethylenediaminetetraacetic acid trisodium salt (Sigma-Aldrich), diazolidinyl urea (Sigma-Aldrich), and premixed crystals of tris(hydroxymethyl)aminomethane (Merck) and tris(hydroxymethyl)aminomethane hydrochloride (Merck) were all analytical reagent grades. Pure anhydrous sodium sulfate (Merck) was freed from interfering organic substances and moisture by heating at 400°C for 4 hours in a muffle furnace.
All required glass apparatuses were cleaned with water using detergent, rinsed about six times with water and then twice with D.I. water, and finally dried in oven. Polytetrafluoroethylene (PTFE) lined screw caps of vials were cleaned by ethanol and heated at 105°C for 4 hours before use.

Formaldehyde solution (36.8–38%), Diazolidinyl urea (N-hydroxymethyl-N-(1,3-di(hydroxymethyl)-2,5-dioxoimidazolidin-4-yl)-N’-hydroxy-methylurea [DAU]), chromotropic acid disodium salt dehydrate (technical grade), sulfuric acid (99.99%), 1N hydrochloric acid, and sodium bicarbonate were purchased from Sigma–Aldrich Corp. (St. Louis, MO, U.S.A.). SMG was obtained from Tyger Scientific Inc. (Ewing, NJ, U.S.A.). DMDM hydantoin (DMDM) was obtained from Oakwood Products Inc. (West Columbia, SC, U.S.A.). All chemical solutions and buffers were prepared fresh using Millipore water (double distilled, deionized water, ρ = 18.2 MΩcm at 25°C) on the day of the experiment.