Zinc oxide-copper oxide nanoplates composite as coating for solid phase microextraction combined with high performance liquid chromatography-UV detection for trace analysis of chlorophenols in water and tomato juice samples

Electrodeposited histidine-(CuCr)layered double hydroxides/carbon dots for in-tube solid-phase microextraction of chlorophenols from water, juice, and honey samples followed by HPLC-UV

A novel adsorbent consisting of a composition of carbon dots and CuCr-layered double hydroxides intercalated with l-histidine (C-dots@His/LDHs) was introduced. This adsorbent was electrochemically deposited on the inner surface of a capillary copper tube. It was used as an adsorbent for in-tube solid-phase microextraction of chlorophenols (CPs). Separation and measurement of CPs were done by high-performance liquid chromatography-ultraviolet detector. The main parameters which had the most impact on the extraction efficiency and time such as extraction time and flow rate, desorption time and flow rate, ionic strength (salt concentration) and pH were optimized. Calibration curves (0.5-1000 μg L-1) were plotted in real sample (tap water) under optimal conditions which coefficients of determination better than 0.9893 and relative recoveries in the range of 88-120 % were obtained. The limits of detection (S/N = 3) and limits of quantification (S/N = 10) were obtained in the range of 0.1-1.0 μg L-1 and 0.3-3.0 μg L-1, respectively. The intra- and inter-assay precisions (RSD%, n = 3) were better than 5.9 and 8.8 %, respectively.

Dual optical detection approach for capillary electrophoresis following two-step liquid-liquid extraction to determine ten phenols in water samples

In this research, the analytical method was developed and evaluated for determining phenol and its nine derivatives belong to the US EPA priority pollutant list in water samples by using dual-channeled capillary electrophoresis (CE) coupled with two types of optical detectors, namely LED-induced fluorescence (LEDIF) and ultraviolet (UV) detectors. The optimal background electrolytes for the first and second CE channels were 20 mM borate (pH 9.80) with 400 µM fluorescein and 55 mM borate (pH 11.75), respectively. The two-step liquid-liquid extraction (LLE) was used for sample preparation and enrichment, in which phenol and its derivatives were extracted from the aqueous phase using 10 mL of n-hexane/1-octanol (60/40, v/v) and then were back extracted into a 0.1 M NaOH as a final acceptor phase. Under the optimal CE and two-step LLE conditions, the enrichment factors of 10 phenols were 184 - 1120-fold, and the method detection limits were lowered to 0.02-0.60 µg/L. The obtained intra-day and inter-day precisions in terms of relative standard deviations (RSD) were between 4.0 and 7.3 % and 6.7 and 14 %, respectively. This approach was used to determine phenols in water samples, with recoveries ranging from 82.0 to 108.9 %. In combination with sample enrichment by two-step LLE extraction, this is the first CE study conducted to determine phenols in the EPA list using two detector approaches, specifically CE-LEDIF/CE-UV.

Zinc oxide-aluminum oxide nanocomposite solid phase microextraction for diazepam and oxazepam trace determination

A new efficient ZnO-Al2O3 nanocomposite (ZANC) was synthesized to form solid-phase microextraction (SPME) fiber. The prepared fiber was used for trace determination of benzodiazepines by gas chromatography-flame ionization detector in urine samples. The effective parameters on the extraction process including extraction time, salt percentage, desorption time and sample pH were optimized by a factorial design method. The method was evaluated at the optimum conditions and limits of detection (LODs) were calculated 20 µg/L for diazepam and oxazepam. The method repeatability for oxazepam and diazepam (50 µg/L, n = 4) was calculated at 8.8 % and 6.4 %. Also, the method reproducibility was obtained, 7.45 % and 6.61 % for oxazepam and diazepam (50 µg/L, n = 4). Also, fiber-to-fiber relative standard deviation (RSDs%) for the target analytes were less than 15.5 %. The method linearity is within the range of 62-500 µg/L for diazepam and oxazepam. The ZANC-SPME fiber showed a good lifetime (60 times) with high chemical stability. The high thermal stability of ZANC-SPME fiber was attained at 280 °C. The extraction results of poly dimethylsiloxan/divinyl benzene (PDMS/DVB) fiber were compared by ZANC-SPME fiber. Therefore, the method is proposed as a suitable technique for benzodiazepines detection in the urine sample.

Field-amplified sample injection combined with capillary electrophoresis for the simultaneous determination of five chlorophenols in water samples

A sensitive method of CZE-ultraviolet (UV) detection based on the on-line preconcentration strategy of field-amplified sample injection (FASI) was developed for the simultaneous determination of five kinds of chlorophenols (CPs) namely 4-chlorophenol (4-CP), 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and 2,6-dichlorophenol (2,6-DCP) in water samples. Several parameters affecting CZE and FASI conditions were systematically investigated. Under the optimal conditions, sensitivity enhancement factors for 4-CP, 2-CP, 2,4-DCP, 2,4,6-TCP, and 2,6-DCP were 9, 27, 35, 43, and 43 folds, respectively, compared with the direct CZE, and the baseline separation was achieved within 5 min. Then, the developed FASI-CZE-UV method was applied to tap and lake water samples for the five CPs determination. The LODs (S/N = 3) were 0.0018-0.019 µg/mL and 0.0089-0.029 µg/mL in tap water and lake water, respectively. The values of LOQs in tap water (0.006-0.0074 µg/mL) were much lower than the maximum permissible concentrations of 2,4,6-TCP, 2,4-DCP, and 2-CP in drinking water stipulated by World Health Organization (WHO) namely 0.3, 0.04, and 0.01 µg/mL, respectively, and thereby the method was suitable to detect the CPs according to WHO guidelines. Furthermore, the method attained high recoveries in the range of 83.0-119.0% at three spiking levels of five CPs in the two types of water samples, with relative standard deviations of 0.37-8.58%. The developed method was proved to be a simple, sensitive, highly automated, and efficient alternative to CPs determination in real water samples.

Double -shelled hollow ZnO/carbon nanocubes as an efficient solid-phase microextraction coating for the extraction of broad-spectrum pollutants

Efficient extraction of pollutants with different chemical properties from environmental samples has attracted great attention in the development of analytical chemistry. However, it is still a challenge to develop an appropriate and sensitive adsorbent for determining broad-spectrum analytes. Herein, zeolitic imidazole framework-8 (ZIF-8)-derived double-shelled hollow zinc oxide/carbon (ZnO/C) nanocubes were reported as a novel coating for solid-phase microextraction (SPME). The nanocubes with a unique structure and composition were obtained by controlled etching of ZIF-8 with tannic acid (TA) followed by pyrolysis. When a ZnO/C nanocube-coated fiber (ZnO/C-F) was used to extract the complex environmental samples containing both nonpolar (benzene compounds (BTEX)) and polar (chlorophenols (CPs)) pollutants, excellent extraction performance was achieved; we obtained low detection limits (0.14-0.56 ng L-1 for BTEX and 1.10-2.84 ng L-1 for CPs), good repeatability (2.2-5.9% for six replicated extractions) and excellent reproducibility (0.61-7.8%, fiber to fiber). The broad-spectrum SPME performance was ascribed to the synergistic effect between the composition and structure of ZnO/C nanocubes. Compositionally, the uniform dispersion of ZnO and carbon framework could provide abundant adsorption active sites, where Zn-OHs bound CPs by hydrogen bonding and carbon absorbed BTEX through π-π stacking interaction and hydrophobic interaction. Structurally, the double-shelled hollow morphology of the nanocubes was favorable for the sensitive extraction. Finally, the established ZnO/C-F-based headspace-SPME method was used for the preconcentration and determination of abundant analytes from real water samples. These findings open the door for the practical use of double-shelled hollow multicompositional inorganic materials.