This study proposes a simple sample preparation procedure using tetramethylammonium hydroxide (TMAH) and nitric acid (HNO3) to determine Cr, Cu, Fe, K, Mg, Mn, and Zn concentrations in shrimp (Macrobrachium amazonicum) and crab (Ucides cordatus) samples from the Amazon region by microwave-induced plasma optical emission spectrometry (MIP OES). The sample solubilization was carried out employing TMAH and HNO3 using an ultrasound bath and a thermostatic water bath. The accuracy of the proposed procedure was performed using microwave-assisted digestion as comparative method. Certified fish protein reference material (DORM-4) and also addition recovery experiments were used to assess the accuracy of the proposed procedure and recoveries obtained were adequate, ranging from 91 to 106%. In this study, the use of TMAH and HNO3 simplified sample preparation, maintaining the identity of analytes and ensuring efficiency in determinations.