Vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction with solidification of floating organic droplet combined with flame atomic absorption spectrometry for the fast determination of cadmium in water samples

Determination of cadmium in bread and biscuit samples using ultrasound-assisted temperature-controlled ionic liquid microextraction

BACKGROUND

In the present work, a simple and rapid method was proposed for the preconcentration of cadmium using ultrasound-assisted temperature-controlled ionic liquid microextraction (TC-IL-LPME). The dispersion of the ionic liquid (1-Hmim[PF₆ ]) in the aqueous phase was performed by heating it in an ultrasonic bath, followed by cooling in an ice bath. After centrifugation, the enriched phase was dissolved in 45% (w/w) nitric acid solution to reduce viscosity, and the cadmium content was measured employing electrothermal atomic absorption spectrometry (ET-AAS). The 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol reagent (Br-PADAP) was used as a complexing agent.

RESULTS

Under optimized conditions, the method had a detection limit of 2.0 ng L^-1 and an enrichment factor of 24. The accuracy of the method was evaluated through the analysis of the certified reference material of brown bread (BCR-191). The method was applied to the determination of cadmium in samples of bread and biscuit. The limit of detection of the solid samples was 0.10 μg kg^-1 . The recovery of cadmium in the samples varied between 93% and 107%.

CONCLUSION

The proposed method is presented as a simple, cheap, ecological and a sensitive alternative for the determination of cadmium in bread and biscuit samples. © 2019 Society of Chemical Industry.

An Ultrasensitive Colorimetric Strategy for Detection of Cadmium Based on the Peroxidase-like Activity of G-Quadruplex-Cd(II) Specific Aptamer

We rationally designed an ultrasensitive and label-free sensing platform for determination of cadmium (Cd). The sensing platform contains G-quadruplex-Cd(II) specific aptamer (GCDSA) constructed by incorporating G-rich sequence at the end of 5' and the critical domain of the Cd-4 aptamer. GCDSA designed act as both a special recognition sequence for Cd²⁺ and a signal DNAzyme. In absence of Cd²⁺, GCDSA may mainly exist in a random coil sequence. Upon addition of Cd²⁺, GCDSA could probably be induced to fold into a G-quadruplex structure. The generation of plentiful active G-quadruplex interacts with hemin to form a peroxidase-like DNAzyme, leading to increased absorbance signal of the sensing system. ΔA was directly proportional to the two segments of concentrations for Cd²⁺, with the detection of limit of 0.15 nM. The proposed method avoids the labeled oligonucleotides and allows directly quantitative analysis of the samples by cheap instruments, with an excellent dynamic range.

Methods of liquid phase microextraction for the determination of cadmium in environmental samples

Liquid phase microextraction (LPME) has been widely used in extraction and preconcentration systems as an excellent alternative to conventional liquid phase extraction. In this work, a critical review is presented on liquid phase microextraction techniques used in the determination of cadmium in environmental samples. LPME techniques are classified into three main groups: single-drop liquid phase microextraction (SDME), hollow fiber liquid phase microextraction (HF-LPME), and dispersive liquid-liquid microextraction (DLLME). Methods involving these liquid phase microextraction techniques are described, addressing advantages and disadvantages, samples, figures of merit, and trends.