A closer look at how the dispersive liquid-liquid microextraction method works. Investigation of the effect of solvent mixture composition on the quality and stability of the cloudy state

The dispersive liquid-liquid microextraction (DLLME) is one of the most popular miniaturized extraction procedures. In this paper, the degree of dispersion and dispersion stability were studied with the aim to assess the correlations of these parameters with efficiency for the selected analytical application. The dependence between the degree of dispersion (cloudy state quality) and its stability obtained by various emulsification procedures, such as solvent-assisted emulsification (using various dispersive solvents) and mechanical emulsification (using auxiliary energies), is investigated and discussed. It was found out that the degree of dispersion depends on the type of emulsification procedure and decreases in the series: solvent-assisted (SA-) = ultrasound-assisted (UA-) > air-assisted (AA-) > vortex-assisted (VA-) emulsification. The emulsion stability depends on the degree of dispersion and there were 1810 and 2070 s for the most effective emulsification procedures, such us solvent-assisted and ultrasound-assisted emulsification, respectively. A comparison between the sensitivity of the analytical methods (using spectrophotometric determination of the anionic surfactants) and the degree of dispersion have been made. The sensitivity of the methods was ranked as follows: DLLME > UA-LLME > VA-LLME > AA-LLME.

Ultrasound-assisted liquid–liquid spray extraction for the determination of multi-class trace organic compounds in high-volume water samples

A premier analytical method for the determination of multi-class trace organic compounds in high-volume water matrices.

Ultrasonic energy enhanced the efficiency of advance extraction methodology for enrichment of trace level of copper in serum samples of patients having neurological disorders

An innovative dual dispersive ionic liquid based on ultrasound assisted microextraction (UDIL-μE), for the enrichment of trace levels of copper ion (Cu²⁺), in serum (blood) of patients suffering from different neurological disorders. The enriched metal ions were subjected to flame atomic absorption spectrometry (FAAS). In the UDIL-μE method, the extraction solvent, ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆], was dispersed into the aqueous samples using an ultrasonic bath. The(PAN) 1-(2-pyridylazo)-2-naphthol was used as ligand for the complexation of Cu ion in IL (as extracting solvent). The various variables such as sonication time, pH, concentration of complexing agent, time and rate of centrifugation, IL volume that affect the extraction process were optimized. The enhancement factor (EF) and detection limit (LOD) was found under favorable condition was 31 and 0.36μgL^-1, respectively. Reliability of the proposed method was checked by relative standard deviation (%RSD), which was found to be <5%. The accuracy of developed procedure was assured by using certified reference material (CRM) of blood serum. The developed procedure was applied successfully to the analysis of concentration of Cu ion in blood serum of different neurological disorders subjects and referents of same age group. It was observed that the levels of Cu ion was two folds higher in serum samples of neurological disorders patients as related to normal referents of same age group.

Highly sensitive determination of copper (II) ions using fluorescence and chemiluminescence emissions of modified CdS quantum dots after it’s preconcentration by dispersive liquid–liquid microextraction

Two highly sensitive and selective methods based on fluorescence (FL) and chemiluminescence (CL) emissions of 8-mercaptoquinoline-capped CdS quantum dots (MCQ-CdS QDs) were described for the determination of copper (II) after it’s preconcentration. High fluorescent CdS QDs, synthesized in an aqueous medium, generated a relatively intense CL emission in the presence of potassium permanganate as an oxidant. Furthermore, low quantities of copper (II) ions showed a remarkable quenching effect on both of the CL and FL emissions of MCQ-CdS QDs. Based on this effect, two selective and simple methods were established for Cu2+, and the detection limits of 0.28 and 0.026 ng mL−1 were obtained for the FL and CL methods, respectively. Also, due to the high propensity of MCQ to Cu2+, good selectivity was obtained and no sensible interfering effects from other metal ions were observed. To more sensitize the developed method, an efficient preconcentration process was designed based on the high-yield ultrasound-assisted temperature-controlled ionic liquid dispersive liquid–liquid microextraction (UA-TIL-DLLME) method. Under the optimum conditions, the extracted Cu2+ showed a suppressing effect on the FL and CL emissions of CdS QDs proportional to its initial concentration over the ranges of 0.008–1.4 and 0.001–1.4 ng mL−1, respectively. The limits of detection of 3.7 and 0.37 pg mL−1, respectively, were also achieved. The established methods showed great features and were satisfactorily applied to the monitoring of ultratrace Cu2+ in some different environmental samples.

Lead Quantification in Urine Samples of Athletes by Coupling DLLME with UV-Vis Spectrophotometry

Urine lead level is one of the most employed measures of lead exposure and risk. The urine samples used in this study were obtained from ten healthy male cyclists. Dispersive liquid-liquid microextraction combined with ultraviolet and visible spectrophotometry was utilized for preconcentration, extraction, and determination of lead in urine samples. Optimization of the independent variables was carried out based on chemometric methods in three steps. According to the screening and optimization study, 133 μL of CCl₄ (extracting solvent), 1.34 mL ethanol (dispersing solvent), pH 2.0, 0.00 % of salt, and 0.1 % O,O-diethyl dithiophosphoric (chelating agent) were used as the optimum independent variables for microextraction and determination of lead. Under the optimized conditions, R ² was 0.9991, and linearity range was 0.01-100 μg L^-1. Precision was evaluated in terms of repeatability and intermediate precision, with relative standard deviations being <9.1 and <15.3 %, respectively. The accuracy was estimated using urine samples of cyclists as real samples and it was confirmed. The relative error of ≤5 % was considered significant in the method specificity study. The lead concentration mean for the cyclists was 3.79 μg L^-1 in urine samples. As a result, the proposed method is a robust technique to quantify lead concentrations higher than 11.6 ng L^-1 in urine samples.

Colorimetric sensing of copper(II) based on catalytic etching of gold nanoparticles

Based on the catalytic etching of gold nanoparticles (AuNPs), a label-free colorimetric probe was developed for the detection of Cu(2+) in aqueous solutions. AuNPs were first stabilized by hexadecyltrimethylammonium bromide in NH3-NH4Cl (0.6M/0.1M) solutions. Then thiosulfate (S2O3(2-)) ions were introduced and AuNPs were gradually dissolved by dissolved oxygen. With the further addition of Cu(2+), Cu(NH3)4(2+) oxidized AuNPs to produce Au(S2O3)2(3-) and Cu(S2O3)3(5-), while the later was oxid-ized to Cu(NH3)4(2+) again by dissolved oxygen. The dissolving rate of AuNPs was thereby remarkably promoted and Cu(2+) acted as the catalyst. The process went on due to the sufficient supply of dissolved oxygen and AuNPs were rapidly etched. Meanwhile, a visible color change from red to colorless was observed. Subsequent tests confirmed such a non-aggregation-based method as a sensitive (LOD=5.0 nM or 0.32 ppb) and selective (at least 100-fold over other metal ions except for Pb(2+) and Mn(2+)) way for the detection of Cu(2+) (linear range, 10-80 nM). Moreover, our results show that the color change induced by 40 nM Cu(2+) can be easily observed by naked eyes, which is particularly applicable to fast on-site investigations.

Enantioselective analysis of ranolazine and desmethyl ranolazine in microsomal medium using dispersive liquid–liquid microextraction and LC–MS/MS

Background: An enantioselective bioanalytical method using dispersive liquid–liquid microextraction (DLLME) and LC–MS/MS was developed for the chiral analysis of ranolazine (RNZ) and one of its metabolites (desmethyl ranolazine [DRNZ]). Results: The analytes were extracted from microsomal medium by DLLME, using chloroform as extractor solvent and acetone as dispersive solvent. The enantiomers of RNZ and DRNZ were analyzed simultaneously for the first time using a Chiralcel OD-H®. Method validation showed recoveries in the order of 55 and 45%, and LLOQ of 25 and 10 ng ml-1 for the enantiomers of RNZ and DRNZ, respectively. Linearity was established in the concentration range of 10 to 1000 and 25 to 2500 ng ml-1 for each DRNZ and RNZ enantiomer, respectively. Conclusion: The unprecedented use of DLLME was demonstrated to be very useful for sample preparation of microsomal matrix. Furthermore, the in vitro metabolism of RNZ was enantioselective.

Development, validation, and application of a liquid chromatography-tandem mass spectrometry method for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in human hair

The tobacco-specific nitrosamine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a valuable biomarker for human exposure to the carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in tobacco and tobacco smoke. In this work, an efficient and sensitive method for the analysis of NNAL in human hair was developed and validated. The hair sample was extracted by NaOH solution digestion, purified by C(18) solid-phase extraction (SPE) and molecularly imprinted solid-phase extraction, further enriched by reverse-phase ultrasound-assisted dispersive liquid-liquid microextraction (USA-DLLME) into 1.0 % aqueous formic acid, and finally analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry. Good linearity was obtained in the range of 0.24-10.0 pg/mg hair with a correlation coefficient of 0.9982, when 150 mg hair was analyzed. The limit of detection and lower limit of quantification were 0.08 and 0.24 pg/mg hair, respectively. Accuracies determined from hair samples spiked with three different levels of NNAL ranged between 87.3 and 107.7 %. Intra- and inter-day relative standard deviations varied from 4.1 to 8.5 % and from 6.9 to 11.3 %, respectively. Under the optimized conditions, an enrichment factor of 20 was obtained. Finally, the developed method was applied for the analysis of NNAL in smokers' hair. The proposed sample preparation procedure combining selectivity of two-step SPE and enrichment of DLLME significantly improves the purification and enrichment of the analyte and should be useful to analyze NNAL in hair samples for cancer risk evaluation and cancer prevention in relation to exposure to the tobacco-specific carcinogen NNK.

Automatic determination of copper by in-syringe dispersive liquid-liquid microextraction of its bathocuproine-complex using long path-length spectrophotometric detection

The recently proposed concept of automatic in-syringe dispersive liquid-liquid microextraction was successfully applied to the determination of copper in environmental water samples. Bathocuproine was added to the organic phase as a selective reagent, resulting in the formation of a complex with copper. Dispersion was achieved by aspiration of the organic phase and then the watery phase into the syringe as rapidly as possible. After aggregation of the solvent droplets at the head of the syringe, the organic phase was pushed into a liquid waveguide capillary cell for highly sensitive spectrophotometric detection. The entire analytical procedure was carried out automatically on a multisyringe flow-injection analysis platform and a copper determination was accomplished in less than 220 s. A limit of detection of 5 nmol L(-1) was achieved at an extraction efficiency >90% and a preconcentration factor of 30. A linear working range for concentrations of up to 500 nmol L(-1) and an average standard deviation of 7% in peak height were found. The method proved to be well-suited for the determination of copper in water samples, with an average analyte recovery of 100.6%.