Preliminary Studies On Melamine Determination By HPTLC In Milk

Three instrumental methods for detection of melamine (MA) contamination in milk were recommended as national standards. However the methods demand expensive equipments, high equipped laboratory and highly qualified operators, high in maintenance and determination cost, expensive supplies and consumables, time consuming and inefficient. Thus, developing a low cost, easy operating and efficient MA detection method is required.This study based on"concentrating the target substance while developing it on thin-layer plate", a innovative design to overcome the insufficient sensitivity of TLC for MA determination, attempts to establish HPTLC analysis for MA pollution in milk. TLC plate, coloring, sample preparation and developing solvent were chosen and optimized in preliminary study. HPTLC silica gel G plate, chlorine-starch/iodine coloring and HCl precipitating-concentrating to remove cream and casein were applied for latter experiments. It was found that the insufficient sensitivity of HPTLC for very low MA determination mainly contributes to diffusion of MA spot while developing and this fade the chrominance of MA. Naturally the thinking of concentrating MA while developing was created and the study focused on developing a"concentrating developing-solvent"to significantly improve the sensitivity of HPTLC for MA detection, and the effort resulted as will. MA qualitative and quantitative determination preliminarily established.The orthogonal optimized concentrating developing-solvent was: Tetrahydrofuran, glacial acetic acid and T reagent (9.5:0.22:0.06, v/v); the MA spot can be remarkably compressed and forms ellipse or crescent. Detection limit was about 1.0mg/L~0.5 mg/L, reaches the level of HPLC. Total operating time is about 40 min or 30min in simplified preparation, each 100×100mm plate test 9 samples and easy to batch processing. Cost for one sample is no more than RMB 1 Yuan.The maximum absorption wavelength of the coloring was 400nm, MA Quantitative range of HPTLC standard curve is large (0.5mg / L ~ 80mg / L), r2 were all above 0.999 in three plates, polynomial or linear regression can be applied according to detection range; RSD of the same and different plate was 3.35% and 12.76% respectively. The method is suitable for melamine screening in milk.