We developed a voltammetric method using hanging mercury drop electrode (HMDE) for the determination of copper, zinc, lead, and cadmium, and an atomic absorption spectrometry method with flame and electrothermical atomisation for the determination of cobalt, copper, cadmium, lead, zinc, ferrum, manganese, and nickel. These methods were applied for the determination of elements in bottom sediment and animal tissue samples – candidates for certificate reference materials. The mineralisation procedure using a closed microwave-assisted system, which allowed for total decomposition of samples, was applied. For accurate testing of developed methods for elemental determination, Buffalo River sediment (NIST) and fish muscle (ERM) certified reference materials were used. Limits of detection (LOD) and limits of quantification (LOQ) varied depending on technique used. For F-AAS, LOD values were between 2.2-12 mg·kg^-1, for ET-AAS 0.10-0.35 mg·kg^-1, and 0.014-0.021 mg·kg^-1 for HMDE. LOQ values varied between 6.5-30 mg·kg^-1, 0.31-1.1 mg·kg^-1, and 0.042-0.063 mg·kg^-1, for F-AAS, ET-AAS, and HMDE, respectively. Linearity ranges also varied for each technique: 0.005-1.0 mg·kg^-1 for HMDE, 0.35-50 mg·kg^-1 for ET-AAS, and 6.5-500 mg·kg^-1 for F-AAS technique. Homogeneity within and between bottles was calculated for each element. Variances did not differ in a statistically significant way, which is why materials can be considered homogenous.