The current compendial method for the assay of monomer impurities in Basic Butylated Methacrylate copolymer is performed as per the European Pharmacopia monograph. It consists of a RP-HPLC assay of the Butyl and Methyl methacrylate monomer impurities and a normal phase HPLC assay of the polar 2-Dimethylaminoethyl methacrylate impurity. The normal phase HPLC assay method has issues regarding the use of stabilized and unstabilized tetrahydrofuran as well as the use of a non-commercial Dimethylaminoethylsilyl silica column for the 2-Dimethylaminoethyl methacrylate impurity. There is no current USP monograph.
The method under investigation aims to improve the current method by combining the two compendial methods into a single HILIC assay for all three methacrylate monomer impurities. This will eradicate the issues mentioned above by eliminating the use of the normal phase HPLC in its entirety. This will also reduce analysis time and increase throughput.
The proposed method for the quantitation of methacrylate monomer impurities utilizes a HILIC method using an Alltech Platinum-C18 column with an isocratic elution consisting of 25:75 [25 mM phosphate buffer, pH 2.5]:acetonitrile (v/v). The flow rate is 0.5 mL/min, the injection volume is 10 �L and the column temperature is ambient. Detection is by UV at 220 nm.
The method has been demonstrated to be robust with respect to pH,column temperature, flow rate and column to column variation. Specificity, linearity and accuracy were demonstrated with individual methacrylate monomer concentrations at 12% to 120% range of the target compendial specification limit of 1000PPM. The correlation coefficients of the Butyl, Methyl and 2-Dimethylaminoethyl methacrylate impurities were greater than 0.9999 and the mean recoveries were 97 � 102%.
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