Application of constrained mixture design and Doehlert matrix in the optimization of dispersive liquid-liquid microextraction assisted by ultrasound for preconcentration and determination of cadmium in sediment and water samples by FAAS

• A new analytical method for determination of cadmium was developed;
• The detection limit (LD) of 0.23 mg L− 1;
• The preconcentration factor of 15 for a sample volume of 3.0 mL.
• The reagent is new for cadmium complexation 5-(4-Dimethylaminobenzylidene) Rhodanine)

A dispersive liquid-liquid microextraction assisted by ultrasound (USADLLME) with 5-(4-Dimethylaminobenzylidene)Rhodanine procedure has been developed for preconcentration of cadmium in water and sediment samples by flame atomic absorption spectrometry (FAAS). The proportions of mixture composed of disperser, extractor solvents and complexing reagent was optimized using a constrained mixture design. The variables pH, concentration of NaCl and sonication time were optimized using a Doehlert matrix. The precision of method expressed as relative standard deviation (RSD) of 2.92 and 3.38% for 50 and 20 μg L− 1, respectively, the detection limit was 0.23 μg L− 1 and the limit of quantification of 0.76 μg L− 1. The accuracy was confirmed by the analysis of certified reference materials (Drinking Water Standard APS 1071, Fresh Water Sediment 3 RTC 016, Oyster Tissue NIST 1566b, Tomato Leaves NIST 1773a), the Spike test showed recoveries between 90 and 110%. The method was applied to river water, drinking water and sediment, the concentration of cadmium ranged from 1.46–4.60 μg L− 1 for water samples and from 0.90 to 1.23 μg g− 1 for sediment samples.