Microextraction methods for the determination of phthalate esters in liquid samples: A review

1,2‐Benzenedicarboxylic acid esters, commonly referred to as phthalate esters, form a group of compounds that are mainly used as plasticizers in polymers. Because phthalate esters are not chemically bound to the plastics, they can be released easily from products and migrate into the food or water that comes into direct contact. Due to their widespread use, they are considered as ubiquitous environmental pollutants. Phthalate esters are regarded as endocrine disrupting compounds by means of their carcinogenic effect. Phthalate esters can be analyzed by gas chromatography or high‐performance liquid chromatography, however, their sensitivity and selectivity limit their direct use for determination of phthalates at very low level of concentrations exist in environmental samples with complex matrices. Therefore a sample pretreatment prior to their analysis is necessary. In this review, the historical development and overview of sample preparation methodologies have briefly been discussed and a comprehensive application of these methods in combination with different analytical techniques for preconcentration and determination of phthalate esters in various matrices have been summarized. Finally, a critical comparison of the different approaches in terms of enrichment factors achieved, extraction efficiency, precision, selectivity and simplicity of operation is provided.     

Development of a green effervescence-assisted dispersive liquid–liquid microextraction method using a home-made tablet disperser for trace analysis of Cd(II) and Pb(II)

An analytical approach for the determination of trace amounts of Cd(II) and Pb(II) has been developed using a home-made tablet-based effervescence-assisted dispersive liquid–liquid microextraction (DLLME) method which was performed in a narrow-bore tube, followed by flame atomic absorption spectrometry. In this method, a mixture of tartaric acid, sodium bicarbonate and NaCl was used to make the disperser tablet. Then, microlitre level of an extraction solvent was added in the tablet, and then, it was released into a narrow-bore tube containing sample solution and a complexing agent. An acid–base reaction immediately occurred between tartaric acid and sodium bicarbonate, and the produced CO₂ led to the dispersion of the extraction solvent into the solution as tiny droplets and subsequent extraction of the analytes. The method made possible the determination of Cd(II) and Pb(II) in the ranges of 0.1–10 and 1.0–20 µg L^?1, respectively. The limits of detection were obtained 0.43 and 0.05 µg L^?1 for Pb(II) and Cd(II), respectively. The limits of quantifications were 0.80 and 0.09 µg L^?1 for Pb(II) and Cd(II), respectively. Repeatability of the method, which is expressed as relative standard deviation, was obtained 3.1% (n = 6, C = 2 µg L^?1) and 1.3% (n = 6, C = 0.2 µg L^?1) for Pb(II) and Cd(II), respectively. The accuracy of the developed method was verified by analysing a certified reference material, namely SPS-WW2 Batch 108. Relative recoveries (84–107%, obtained at three fortification levels) confirmed the usefulness of the method for analysis of the analytes in the environmental water samples and fruit juices. The method was shown to be fast, reliable and environmentally friendly with low organic solvent consumption.     

Spectrofluorimetric Determination of Cu2＋ Using New Fluorogenic Reagent

A new synthesized fluorogenic reagent,8-[(2-pyridine)methylideneamino] quinoline (PMAQ), was utilized for spectrofluorimetric determination of Cu(II) at trace levels. PMAQ, a good fluorogenic reagent, though insoluble in water, but is soluble in ethanol and 20% ethanol-water. The excitation and the fluorescence wavelengths of PMAQ were 310 and 434 nm respectively. When the reagent was complexed with Cu(II), the fluorescence intensity decreased proportionally with the concentration of Cu(II) at pH 4.5 by a static quenching effect. The highest sensitivity to Cu^2＋ determination was shown to be at PMAQ concentration of 1.0×10^－5mol•L^－1. In order to enhance the quenching effect, the Cu(II)-PMAQ complex solution was kept at 22 ℃ for 20 min. Though the interferences by Co(II) and Fe(III) were very serious, they were however, completely eliminated by being masked with oxalate and ascorbate ions respectively. The linear dynamic range for Cu(II) determination was between 25—441 µg•L^－1 with the detection limit of 18 µg•L^－1 (RSD＝3.7%, n＝6). The proposed method was successfully applied to the determination of Cu(II) in real samples including human blood serum, commercial tea and wheat flour.     

A Simple and Cheap Device for Colorimetric Determination of Serum Iron

A simple and cheap device for colorimetric determination of serum iron and TIBC (total iron‐binding capacity) was devised. The proposed device employs an LED as a light source and a common light dependent resistor (LDR) as a detector. This device functions on the basis of the light intensity received by LDR, connected to a digit multimeter, yielding resistance readings. The serum, standard, and blank solutions were prepared according to the kits instructions and introduced into the colorimeter with a disposable syringe. The iron content of the serum was calculated from the resistance difference of serum and standard solutions. The precision of the method was assessed with two commercially available serum‐based chemistry controls. The values obtained with the proposed device indicated that the serum iron concentrations correlated well with the values obtained with the commercial automated analyzer. The calibration graph was linear for iron concentrations up to 90 μmol/L (500 μg/dL). The proposed fabricated colorimeter is considerable cheaper, requires smaller sample volumes, and is suitable for serum iron assay.     

Chromium speciation by a surfactant-coated alumina microcolumn using electrothermal atomic absorption spectrometry

A simple and convenient method has been developed for the speciation of chromium(III) and chromium(VI) in aqueous solutions using a sodium dodecyl sulphate coated alumina micro-column (1.5 cm x 5 mm i.d.) and graphite furnace-atomic absorption spectrometry (GF-AAS). Under the optimized conditions (pH 0.6, adjusted with hydrochloric acid; flow rate, 1 ml min(-1)) chromium(VI) is retained on the column and chromium(III) is collected and determined by GF-AAS. Total chromium is directly determined by GF-AAS and chromium(VI) is calculated by difference. The relative standard deviations (10 replicate analyses) at the 20 mug l(-1) level for chromium(III) and chromium(VI) and at the 40 mug l(-1) level for total chromium were 1.4%, 3.6% and 1.8%, and the corresponding limits of detection (based on 3sigma) were 0.57 mug ml(-1), 0.61 mug ml(-1) and 0.35 mug l(-1) respectively. No large interference effects have been observed from other investigated species and the method has been successfully applied to a range of water samples.     

Determination of copper in urine and water samples using a simple led-based colorimeter

A cheap and simple colorimetric assay based on the reaction with sodium 8-aminoquinoline-5-azobenzene-4′-sulfonate (SPAQ) is applied to the determination of copper in urine and water samples. The proposed technique employs a light emitting diode (LED) as a light source and a cheap common light dependent resistor (LDR) as a detector. This device functions on the basis of the level of light received by photoresistor (LDR), which is connected to a digit multimeter yielding resistance readings increasing with the increase in light absorption by sample solution. Experimental variables affecting the complex formation were optimized applying the Taguchi method. Under the optimum conditions, calibration plot was linear in the analyte concentration range of 0.1–2 μg/mL. The stoichiometry of metal/ligand ratio, the stability constant, and molar absorptivity (ɛ) of Cu(II)-SPAQ complex were also found. The relative standard deviation for five replicate determinations of 1 μg/mL Cu(II) was 3.64% and the corresponding limit of detection was 35 μg/L.     

Local resolution of two-way data from multicomponent equilibria

A self-modeling curve resolution (SMCR) method is proposed to calculate concentration and spectral profiles for the two-way spectral data from an equilibrium containing several chemical components. The proposed method has three main distinctive steps: (i) fixed size moving window evolving factor analysis (FSMWEFA) is used to identify the selective and zero concentration regions for a desired component, (ii) orthogonal projection resolution (OPR) is used to calculate its concentration profile and (iii) the component striping is done directly to resolve other components. The results of simulated and real polyprotic acid dissociation equilibria showed that the proposed combined method performs well even in situation when the successive stepwise equilibrium constants are close to each other. The applicability of method for resolving the triprotic acid system with rank deficiency due full spectral overlapping of two involved chemical species also is shown.     

A green solventless temperature-assisted homogeneous liquid–liquid microextraction method based on 8-hydroxyquinoline simultaneously as complexing agent and extractant for preconcentration of cobalt and nickel from water and fruit juice samples

A green, simple, rapid and efficient solventless temperature-assisted homogeneous liquid-liquid microextraction based on 8-hydroxyquinoline as complexing agent and extractant, followed by flame atomic absorption spectrometry was developed for the extraction, enrichment, and determination of trace amounts of nickel and cobalt in aqueous samples. For this purpose, first, a specified amount of 8-hydroxyquinoline is added to the analytes solution. Then the temperature of the solution is increased to melt 8-hydroxyquinoline and form a homogeneous solution. Then, it is cooled to room temperature and a cloudy solution is formed due to decreasing 8-hydroxyquinoline solubility. The solution is then centrifuged, and 8-hydroxyquinoline particles containing the produced complexes (8-hydroxyquinoline-cation) are collected at the bottom of the tube. They are removed and dissolved in a suitable solvent and injected to the detection system. The main parameters affecting the extraction efficiency, such as the amount of 8-hydroxyquinoline, solvent nature, pH, extraction temperature and heating time were investigated. Under optimum conditions, linear ranges for Co(II) and Ni(II) were 1–100 and 0.5–75 µg L^?1, respectively. Relative standard deviations for intra- and inter-day precisions calculated from six repeated determinations at three different concentrations of Co(II) and Ni(II) were ≤5.2 %. Moreover, the obtained detection limits of the analytes were 0.35 and 0.20 µg L^?1 for Co(II) and Ni(II), respectively. The accuracy of the developed procedure was checked by analysing SPS-WW2 Batch 108 water as a certified reference material. Finally, the developed method was successfully applied for the determination of the selected cations in water and fruit juice samples.     

Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots,and its application to the sensitive determination of dopamine

We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.