Extraction and thin layer chromatographic confirmation of urine residues: new plate development

AOAC method 44.146--44.148 (12th ed.) yielded incomplete separation of compounds recovered from urine residues. Problems with decomposition of standard compounds, loss of sample during extraction/concentration, and development of excessive background color during plate spraying were encountered. Modifications were made to deal with these problems as follows: Allantoin standard is now stored in 90% acetone, 30ml beakers are used instead of conical tubes during extraction, and smaller amounts of pDMAB are used during plate spraying. A collaborative study was conducted to compare sandwich chamber spot separation to larger tank separation. The study showed that total separation of all spots among all analysts was obtained with the sandwich chamber, whereas incomplete separation of spots was obtained with the tank. Also, standard deviation of spot Rf values was smaller with the sandwich chamber. The modified method has been adopted as official first action.