Determination of carboxylic acids in non-alcoholic beer samples by an ultrasonic-assisted dispersive micro-solid phase extraction based on Ni/Cu-Al layered double hydroxide nanocomposites followed by gas chromatography

Magnetically separable layered double hydroxide Ni/CuAl-LDH nanocomposites were synthesized and employed as ultrasonic-assisted dispersive micro-solid phase extraction (UA-D-μSPE) sorbent to extract several carboxylic acids (namely propionic, butyric, pentanoic, hexanoic, heptanoic, octanoic, and decanoic) from non-alcoholic beer samples. Ni/CuAl-LDH sorbent was characterized by Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Effective variables such as amount of sorbent (mg), pH and ionic strength of sample solution, volume of eluent solvent (μL), vortex, and ultrasonic times (min) were investigated via fractional factorial design (FFD). The significant variables were optimized by a Box-Behnken design and combined by a desirability function (DF). Under optimized conditions, the calibration graphs of analytes were linear in a concentration range of 0.05-100 μg/mL and had correlation coefficients more than 0.997. The limits of detection and quantification were in the ranges of 16-40 μg/L and 53-133 μg/L, respectively. This procedure was successfully employed in the determination of target analytes in spiked beer samples, and the relative mean recoveries ranged from 87 to 110%.