This study describes the enrichment ability of ZnO-modified methacrylic acid-co-ethylene dimethacrylate polymer monoliths as stationary phases for the simultaneous determination of antibiotics (ofloxacin, ciprofloxacin, enoxacin, and pefloxacin) combined with high-performance liquid chromatography. The prepared monolith was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transformed infrared spectroscopy, and thermogravimetric analysis. The polymer monolith microextraction method has been applied to the enrichment of fluoroquinolone antibiotics and satisfactory results were obtained in the analysis of water samples. Compared with the conventional methacrylic acid based monolith, the developed monolith exhibited a higher enrichment capacity because of the introduction of zinc oxide into the preparation process.

A polymer monolith microextraction method coupled with high-performance liquid chromatography was developed for the determination of adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate. The monolithic column was synthesized inside fused-silica capillaries using thermal initiation free-radical polymerization with glycidyl methacrylate as the monomer, ethylene dimethacrylate as the cross-linker, cyclohexanol, and 1-dodecanol as the porogen. N-Methylolacrylamide, an important hydrophilic monomer, was incorporated into the polymerization mixture to enhance the hydrophilicity of the poly(glycidyl methacrylate-co-ethylene dimethacrylate) column. The obtained poly(glycidyl methacrylate-co-N-methylolacrylamide-co-ethylene dimethacrylate) monolith was characterized by scanning electron microscopy, Fourier-transform infrared spectra, and X-ray photoelectron spectroscopy. Optimum conditions for the preconcentration and separation of the target adenosines were also investigated. Under the optimum conditions, we obtained acceptable linearities, low limits of detection, and good relative standard deviations. The developed polymer monolith microextraction with high-performance liquid chromatography method exhibited a good performance with recovery values in the range of 76.9−104.7% when applied to the determination of the adenosines in five royal jelly samples.

Monolithic materials were synthesized in capillaries by in situ polymerization with N-isopropylacrylamide, glycidyl methacrylate, and ethylene dimethacrylate as the monomers, and methanol and PEG as the porogens. With γ-alumina nanoparticles attached to the surface of the porous monolithic column via epoxide groups, a novel polymer monolith microextraction (PMME) material was prepared with a good mechanical stability and a high extraction capacity. SEM and X-ray photoelectron spectroscopy were employed to characterize the modified monolithic column, demonstrating that γ-alumina nanoparticles were effectively functionalized onto the monolithic column. In addition, a new method was developed for the analysis of Sudan I–IV dyes using PMME coupled with HPLC. In order to obtain the optimum extraction efficiency, the PMME conditions including desorption solvent type, sample pH, sample volume, sample flow rate, and eluent flow rate were investigated. Under the optimum conditions, we obtained acceptable linearities, low LODs, and good intra- and interday RDSs. When applied to the determination of Sudan I–IV dyes in red wine samples, satisfactory recoveries were obtained in the range of 84.0–115.9%.

A method based on ultrasound-assisted cloud point extraction (CPE) was developed for the determination of phenolic compounds in water samples by high-performance liquid chromatography coupled with diode array detection (DAD) (HPLC–DAD). A nonionic surfactant, Tergitol 15-S-7, was chosen as the surfactant. The parameters affecting the CPE efficiency, such as Tergitol 15-S-7 concentration, salt concentration, extraction temperature, incubation time, centrifugation time, ultrasonic time, sample pH, and dilution solvent were systematically evaluated and optimized. Under the optimum experimental conditions, the linear regression coefficients of the standard curves were greater than 0.9986 and the limits of detection were in the range of 1.7–6.0 μg/L. The method was shown to be reproducible and reliable with intraday and interday relative standard deviations lower than 4.0 and 5.8%, respectively. The recoveries for the addition of different concentrations of phenolic compounds to water samples were in the range of 81.1–109.4%.

In this study, a novel method for the determination of nitroanilines in hair dye samples has been developed based on poly(methacrylic acid-co-ethylene glycol dimethacrylate) monolith microextraction (PMME) and high-performance liquid chromatography (HPLC) analysis. Four nitroanilines, p-nitroaniline (PNAL), m-nitroaniline (MNAL), o-nitroaniline (ONAL), and 2,4-dinitroaniline (DNAL), are studied as representatives. To obtain optimum extraction efficiency, several experimental parameters including sample flow rate, sample volume, sample pH, and eluent flow rate have been investigated. Under the optimal experimental conditions, the linear regression coefficients of the standard curves are greater than 0.9990. The limits of detection for p-nitroaniline, m-nitroaniline, o-nitroaniline, and 2,4-dinitroaniline are 0.012, 0.008, 0.018, and 0.005 μg/mL, respectively. The intraday and interday relative standard deviations are less than 3.1 and 5.4%, respectively. The proposed method is simple, rapid, sensitive, and competent when used for the determination of nitroanilines in hair dye samples and the accuracy is assessed through recovery experiments.

BACKGROUND: Synergistic extraction has been proven to enhance extractability and selectivity. Numerous types of synergistic extraction systems have been applied to rare earth elements, among which sec-nonylphenoxyacetic acid (CA100) has proved to be an excellent synergistic extractant. In this study, the synergistic enhancement of the extraction of holmium(III) from nitrate medium by mixtures of CA100 (H₂A₂) with 2,2′-bipyridyl (bipy, B) in n-heptane has been investigated. The extraction of all other lanthanides (except polonium) and yttrium by the mixtures in n-heptane has also been studied.

RESULTS: Mixtures of CA100 and bipy have significant synergistic effects on all rare earth elements, for example holmium(III) is extracted as Ho(NO₃)₂HA₂B with the mixture instead of HoH₂A₅, which is extracted by CA100 alone. The thermodynamic functions, ΔH^o, ΔG^o, and ΔS^o have been calculated as 2.96 kJ mol⁻¹, − 6.23 kJ mol⁻¹, and 31.34 J mol⁻¹ K⁻¹, respectively.

CONCLUSION: Methods of slope analysis and constant molar ratio have been successfully applied to study the synergistic extraction stoichiometries of holmium(III) by mixtures of CA100 and bipy. Mixtures of these extractants have also shown various synergistic effects with other rare earth elements, making it possible to separate them. Thus CA100 + bipy may be used to separate yttrium from other lanthanides at appropriate ratios of the extractants. Copyright © 2011 Society of Chemical Industry

BACKGROUND: Liquid–liquid extraction is widely used for the separation of rare earths, among which synergistic extraction has attracted more and more attention. Numerous types of synergistic extraction systems have been applied to rare earths with high extraction efficiency and selectivities. In the present study, mixtures of sec-octylphenoxyacetic acid (CA12, H₂A₂) and 1,10-phenanthroline (phen, B) have been used for the extraction of rare earths from nitrate medium. The stoichiometry of samarium(III) extraction has been studied using the methods of slope analysis and constant molar ratio. The possibility of using synergistic extraction effects to separate rare earths has also been studied.

RESULTS: Mixtures of CA12 and phen display synergistic effects in the extraction of rare earth elements giving maximum enhancement coefficients of 5.5 (La); 13.7 (Nd); 15.9 (Sm); 24.5 (Tb); 45.4 (Yb) and 12.3 (Y). Samarium(III) is extracted as SmHA₄B₃ with mixtures of CA12 and phen instead of SmHA₄ when extracted with CA12 alone. The calculated logarithm of the equilibrium constant is 6.0 and the thermodynamic functions, ΔH, ΔG, and ΔS, have been calculated as 4.3 kJ mol⁻¹, − 33.7 kJ mol⁻¹ and 129.7 J mol⁻¹ K⁻¹, respectively.

CONCLUSION: Mixtures of CA12 and phen exhibit synergistic effects on rare earth elements. Graphical and numerical methods have been successfully used to determine their stoichiometries. The different synergistic effects may provide the possibility of separating yttrium from heavy lanthanoids at an appropriate ratio of CA12 and phen. Copyright © 2010 Society of Chemical Industry

BACKGROUND: Di-(2-ethylhexyl)phosphoric acid (D2EHPA, H₂A₂) has been used extensively in hydrometallurgy for the extraction of rare earths, but it has some limitations. Synergistic extraction has attracted much attention because of its enhanced extractabilities and selectivities. In the present study, sec-octylphenoxyacetic acid (CA12, H₂B₂) was added into D2EHPA systems for the extraction and separation of rare earths. The extraction mechanism of lanthanum with the mixtures and the separation of lanthanoids and yttrium were investigated.

RESULTS: The synergistic enhancement coefficient for La³⁺ extracted with D2EHPA + CA12 was calculated as 3.63. La³⁺ was extracted as La(NO₃)₂H₂A₂B with the mixture. The logarithm of the equilibrium constant was determined as 0.80. The thermodynamic functions, ΔH, ΔG, and ΔS were calculated to be 4.03 kJ mol⁻¹, − 1.96 kJ mol⁻¹, and 20.46 J mol⁻¹ K⁻¹, respectively. The mixtures have synergistic effects on Ce³⁺, Nd³⁺, and Y³⁺, with an especially strong synergistic effect on Y³⁺. Neither synergistic nor antagonistic effects on Dy³⁺ and weak antagonistic effects on Lu³⁺ were found.

CONCLUSION: Mixtures of D2EHPA and CA12 exhibit evident synergistic effects when used to extract La³⁺ from nitric solution. The stoichiometries of the extracted complexes have been determined by graphical and numerical methods to be La(NO₃)₂H₂A₂B with the mixture. The extraction is an endothermic process. The mixture exhibits different extraction effects on rare earths, which provides possibilities for the separation of Y³⁺ from Ln³⁺ at a proper ratio of D2EHPA and CA12. Copyright © 2008 Society of Chemical Industry

BACKGROUND: 2-ethylhexylphosphonic acid mono-(2-ethylhexyl) ester (HEHEHP, H₂A₂) has been applied extensively to the extraction of rare earths. However, there are some limitations to its further utilization and the synergistic extraction of rare earths with mixtures of HEHEHP and another extractant has attracted much attention. Organic carboxylic acids are also a type of extractant employed for the extraction of rare earths, e.g. naphthenic acid has been widely used to separate yttrium from rare earths. Compared with naphthenic acid, sec-nonylphenoxy acetic acid (CA100, H₂B₂) has many advantages such as stable composition, low solubility, and strong acidity in the aqueous phase. In the present study, the extraction of rare earths with mixtures of HEHEHP and CA100 has been investigated. The separation of the rare earth elements is also studied.

RESULTS: The synergistic enhancement coefficient decreases with increasing atomic number of the lanthanoid. A significant synergistic effect is found for the extraction of La³⁺ as the complex LaH₂ClA₂B₂ with mixtures of HEHEHP and CA100. The equilibrium constant and thermodynamic functions obtained from the experimental results are 10^−0.92 (K_AB), 13.23 kJ mol⁻¹ (ΔH), 5.25 kJ mol⁻¹ (ΔG), and 26.75 J mol⁻¹ K⁻¹ (ΔS), respectively.

CONCLUSION: Graphical and numerical methods have been successfully employed to determine the stoichiometries for the extraction of La³⁺ with mixtures of HEHEHP and CA100. The mixtures have different extraction effects on different rare earths, which provides the possibility for the separation of yttrium from heavy rare earths at an appropriate ratio of HEHEHP and CA100. Copyright © 2009 Society of Chemical Industry