An electrodeposited terephthalic acid-layered double hydroxide (Cu-Cr) nanosheet coating for in-tube solid-phase microextraction of phthalate esters

A CuCr-layered double hydroxide nanosheet intercalated with terephthalic acid (TPA/LDH) was introduced as a coating for the in-tube solid phase microextraction (IT-SPME). The coating was placed on the inner surface of a stainless steel tube by using two-electrode electrodeposition. The sorbent was characterized by X-ray diffraction, scanning electronic microscopy, and Fourier transform infrared spectroscopy. The TPA/LDH coating, compared to a nitrate-LDH coating, exhibits enhanced extraction efficiency, long lifetime, good mechanical stability, and a large specific surface. The method was used for the extraction, preconcentration, and subsequent HPLC-based determination of dimethyl phthalate (DMP), dibutyl phthalate (DBP), diallyl phthalate (DAP), and diethylhexyl phthalate (DEHP). The effects of pH value of the solution, salt concentration, extraction and desorption conditions, and the effect of the alcohol content of the solution on the extraction efficiency were optimized. Under optimal conditions, the response is linear in the 0.05 to 1000 μg L−1 ester concentration range, and the limits of detection (at S/N = 3) range between 0.01 to 0.1 μg L−1. The inter- and intra-assay precisions (RSD%, for n = 3) range from 3.8 to 6.8% and from 3.5 to 5.7%, respectively. The method was successfully applied to the determination of four phthalate esters in different beverage samples.