Separation and sensitive determination of quercetin in <Emphasis Type="Italic">Rosa canina</Emphasis> L. using solidified floating organic drop microextraction followed by high-performance liquid chromatography determination

Quercetin is a polyphenolic flavonoid found in many plants and is used as a nutritional supplement. It has been reported to have biological properties that may play an important role in the prevention of human diseases, such as cancer, cardiovascular diseases, diabetes, ulcer, cataract and allergies. In this research, solidified floating organic drop microextraction coupled to high-performance liquid chromatography was used to extract and determine quercetin in Rosa canina L., growing in different areas of Lorestan Province in Iran. The effect of important experimental variables such as type and volume of extracting organic solvent, extraction temperature and time, pH and effect of ionic strength on the extraction recovery was investigated and optimized. Under the optimum extraction conditions, a linear response was obtained over the range of 0.5–40 µg mL^?1. Relative standard deviation (RSD%) and enrichment factor were found to be 3.4% and 230, respectively. The proposed method was applied successfully for the determination of quercetin in calycles and fruit of R. canina L. samples. The results showed good agreement compared with those obtained by a validated standard method.     

Cooling/heating-assisted headspace solid-phase microextraction of polycyclic aromatic hydrocarbons from contaminated soils

A simple, low-cost, and effective cooling/heating-assisted headspace solid-phase microextraction (CHA–HS–SPME) device, capable of direct cooling the fiber to low temperatures and simultaneous heating the sample matrix to high temperatures, was fabricated and evaluated. It was able to cool down the commercial and handmade fibers for the effective tapping of volatile and semi-volatile species in the headspace of complex solid matrices, with minimal manipulation compared with conventional SPME. The CHA–HS–SPME system can create large temperature gaps (up to 200 °C) between the fiber and the sample matrix, because the cooling process is directly applied onto the fiber.     

Application of graphene nanoplatelets silica composite,prepared by sol–gel technology,as a novel sorbent in two microextraction techniques

In this study, the application of a novel nanomaterial composite was investigated in two microextraction techniques of solid‐phase microextraction and a needle trap device in a variety of sampling conditions. The optimum sampling temperature and relative humidity were 10°C and 20%, respectively, for both techniques with two sorbents of graphene/silica composite and polydimethyl siloxane. The two microextraction techniques with the proposed sorbent showed recoveries of 95.2 and 94.6% after 7 days. For the needle trap device the optimums desorption time and temperature were 3 min at 290°C and for SPME these measures were 1 and 1.5 min at 240–250°C for the graphene/silica composite and polydimethyl siloxane, respectively. The relative standard division obtained in inter‐ and intra‐day comparative studies were 3.3–14.3 and 5.1–25.4, respectively. For four sample the limit of detection was 0.021–0.25 ng/mL, and the limit of quantitation was 0.08–0.75 ng/mL. The results show that the graphene/silica composite is an appropriate extraction media for both techniques. Combining an appropriate sorbent with microextraction techniques, and using these in conjunction with a sensitive analytical instrument can introduce a strong method for sampling and analysis of occupational and environmental pollutants in air.     

Reversed-phase dispersive liquid-liquid microextraction with multivariate optimization for sensitive HPLC determination of tyrosol and hydroxytyrosol in olive oil

A reversed-phase dispersive liquid-liquid microextraction (RP-DLLME) method coupled to HPLC was developed for the extraction of hydroxytyrosol (HTy) and tyrosol (Ty) from virgin olive oil. In this first application of the RP-DLLME method to non-polar samples, the phenolic compounds were directly extracted into an aqueous micro-drop, which could be injected into a chromatography column without any further pretreatment. A glass test tube with lengthened conical bottom was fitted inside a centrifuge tube in this work for more efficient withdrawal of the sedimented phase with a microsyringe. The volumes of water and ethyl acetate, the pH of water and the centrifuge time as four effective parameters on the extraction were optimized by a central composite design (response surface) method. Five replicated analyses under the optimized conditions (i.e., 0.2 mL ethyl acetate as disperser and 100 μL water at pH 11 as the extraction solvent) resulted in recoveries of 104.3 and 97.6%, and relative standard deviations of 5.75 and 4.57 for HTy and Ty, respectively. The detection limit of the method (3σ) was 0.043 mg L(-1) for HTy and 0.032 mg L(-1) for Ty. The method was successfully applied to the determination of HTy and Ty in five olive oil samples.     

Recent advances in miniaturization of portable liquid chromatography with emphasis on detection

Liquid chromatography is a prominent analytical technique in separation science and chemical analysis, applied across numerous fields of research and within industrial applications. Over the past few decades, there has been a growing interest in the miniaturization of this technique, which has been particularly enabled through new miniature and portable detection technologies for in-field, at-site, and point-of-need (collectively ‘out-of-lab’) analyses. Accordingly, significant advances have been made in recent years in the development of miniaturized liquid chromatography with photometric, electrochemical, and mass spectrometric detection, enabling the development of field-deployable and portable instruments for various applications. Herein, recent developments in the miniaturization of detection systems for inclusion within, and/or coupling with, portable liquid chromatographic systems, are reviewed in detail together with critical comments and expected future trends in this area.     

Preparation of a New Solid‐Phase Microextraction Fiber by Coating Silylated Nanoporous Silica on a Copper Wire

LUS‐1 typed nanoporous silica particles were synthesized and silylated with hexamethyldisilazane and investigated as a highly porous fiber coating for solid‐phase microextraction (SPME). The pore size distribution of the prepared Sil‐LUS‐1 was still typical of MCM‐41 and centered at 3 nm with a specific surface area of 720 m²g^?1. The SPME fiber was prepared by liming the material on a copper wire. The extraction efficiency of the new fiber was compared with a commercial PDMS fiber for headspace extraction and GC‐MS analysis of phenol, 4‐nitrophenol, 2,4‐dichlorophenol and 4‐chlorophenol in water samples. Due to the high porosity of the prepared fiber it showed a higher sensitivity and better selectivity for the extraction of the target compounds. For optimization of different factors affecting the extraction efficiency, a simplex optimization method was used. The relative standard deviation for the measurements by one fiber was better than 7% for five replicates and the fiber‐to‐fiber reproducibility was about 10% for five fabricated fibers. Detection limits in the range of 0.002 to 0.026 μg mL^?1 were obtained for the phenolic compounds. The fiber was successfully applied for the determination of phenolic compounds in natural water samples.     

Determination of BTEX in urine samples using cooling/heating-assisted headspace solid-phase microextraction

Excessive and uncontrolled exposures of the workers to benzene, toluene, ethylbenzene and xylene (BTEX) have currently raised great concerns among industrial hygienist all over the world. Therefore, the effective monitoring of such exposures is assumed to be of prime importance. A cold fiber solid-phase microextraction device based on a cooling capsule as a cooling unit and CO₂ as a coolant was applied to quantitatively analyze BTEX in aqueous samples. A gas chromatography with flame ionization detection was recruited to analyze the target analytes, which had been identified according to their retention times. Several factors such as coating temperature, extraction time and temperature, sample volume and sodium content were optimized. Two modes of extraction, i.e., headspace (HS) and headspace cold fiber (HS-CF) in SPME, were investigated and compared under optimized conditions. The results revealed that HS-CF-SPME has the most appropriate outcome for the extraction of BTEX from aqueous samples. Under the optimized conditions, the calibration curves were linear within the range of 0.2–500 ng ml^?1 and the detection limits were between 0.02 and 0.07 ng ml^?1.The intraday relative standard deviations was lower than about 10%. The method was successfully applied to the determination of BTEX in urine samples with good recovery.     

Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV–Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative pK_a values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated pK_a values provides solid support for the acid–base reactions proposed in this work.     

Determination of silver(I) by electrothermal-AAS in a microdroplet formed from a homogeneous liquid-liquid extraction system using tetraspirocyclohexylcalix[4]pyrroles.

A simple and efficient method for the selective separation and preconcentration of Ag+ using homogeneous liquid-liquid extraction was developed. Tetraspirocyclohexylcalix[4]pyrrole (TSCC4P) was synthesized and investigated as a suitable selective complexing ligand for Ag+. Zonyl FSA (FSA) was applied as a phase-separator agent under mild pH conditions. Under the optimal conditions ([TSCC4P] = 3.4 x 10(-4) M, [THF] = 25.0% v/v, [FSA] = 1.25% w/v, and pH = 4.5), 5 microg of Ag+ in 6.0 ml aqueous phase could be extracted quantitatively into 20 microl of the sedimented phase. The maximum concentration factor was 300-fold. The limit of detection of the proposed method was 0.005 ng/ml. The reproducibility of the proposed method was at most 3.5%. The influence of the pH, type and volume of the water-miscible organic solvent, concentration of FSA, concentration of the complexing ligand and the effect of different diverse ions on the extraction and determination of Ag+ were investigated. The proposed method was applied to the extraction and determination of Ag+ in different water samples.     

A Comparative Study of Hydrodistillation and Hydrodistillation–Solvent Microextraction Methods for Identification of Volatile Components of Echinophora cinerea

A recently developed hydrodistillation–solvent microextraction (HD–SME) method coupled to gas chromatography–mass spectrometry (GC–MS) was applied to the analysis of volatile components of aerial parts of Echinophora cinerea (Boiss). By the use of a simplex optimization method, the effects of extraction time, sample weight and microdrop volume on the extraction efficiency of the method were optimized. In the optimized conditions, 3 µL of n-heptadecane was suspended in the headspace of 6 g of hydrodistillating sample, using a microsyringe. After 7 min, the solvent was retracted back into the syringe and directly injected into the GC–MS injection port. The HD–SME method was compared to a conventional hydrodistillation technique. In general, the extraction with HD–SME was relatively faster and required smaller amounts of sample. The microextraction method also showed some selectivity towards α-phellandrene and Z-β-ocimene monoterpenes. A precision better than 6.5% (expressed as relative standard deviation) was obtained for the method.