Sources of impurities - Investigation of 4-(2-chlorophenyl)-3-ethoxycarbonyl-5-methoxycarbonyl-6-methyl-2-[(2-phthalimidoethoxy) methyl]-1,4-dihydropyridine traces formation during the synthesis of amlodipine besylate

General consideration of possible sources of impurities in organic synthesis products is presented, distinguishing between primary and secondary impurities. By an investigation of impurity 3 in amlodipine besylate 1 it is shown that packaging and process equipment materials, involved in a synthesis, can be additional source of impurities. It was found that impurity 3 can be formed by reaction between amlodipine besylate 1 and bis(2-ethylhexyl) phtalate (2) eluted from plastic materials used for storage of solvents for the amlodipine besylate synthesis. A selective and sensitive HPLC-MS/MS method was developed for this investigation.