An automated in-syringe switchable hydrophilicity solvent-based microextraction.

A fully automated in-syringe switchable hydrophilicity solvent-based microextraction approach was suggested for the first time. Di-(2-ethylhexyl)phosphoric acid was investigated as a novel switchable hydrophilicity solvent. The microextraction procedure implemented into a syringe pump included dissociation of the extractant in alkaline sample solution resulting in homogeneous solution formation followed by in situ organic phase generation by acidification and its separation. The microextraction procedure was applied to the HPLC-UV determination of antimicrobial drugs (sulfamethoxazole and sulfamethazine) in human urine samples as a proof-of-concept example. The calibration graphs were linear over the concentration ranges of 0.06-50 mg L-1 for sulfamethoxazole and 0.13-50 mg L-1 for sulfamethazine. The LODs calculated from the blank tests based on 3σ were 0.02 and 0.04 mg L-1 for sulfamethoxazole and sulfamethazine, respectively. The sample throughput was 12 samples h-1. The possibility of using the proposed procedure for assessing sulfamethoxazole/sulfamethazine acetylation in metabolic processes by individual human phenotypes was shown.

Stir membrane liquid phase microextraction of tetracyclines using switchable hydrophilicity solvents followed by high-performance liquid chromatography.

A novel approach for stir membrane liquid phase microextraction of tetracyclines from biological fluids was developed. The microextraction procedure assumed in situ formation of microdroplets of a hydrophobic medium-chain fatty acid (extraction solvent) from homogeneous sample solution containing water-soluble medium-chain fatty acid salt by acidification and simultaneous analytes extraction and organic phase separation into pores of stir membrane disk. Obtained large surface area between the extraction solvent and aqueous phase and high porosity of the membrane provided fast extraction and phase separation (extraction time - 5 min) and reducing extraction solvent volume to the order of several µL. The developed approach was applied for the HPLC-UV determination of tetracycline, oxytetracycline and chlortetracycline in biological fluids samples. The calibration graphs were linear over the concentration ranges of 0.1-100 mg L-1 for oxytetracycline, tetracycline and chlortetracycline. Regression coefficients were in the range from 0.994 to 0.998. The LOD values, calculated from the blank tests based on 3σ, were 30 µg L-1 for tetracycline, oxytetracycline and chlortetracycline. The RSD values expressing intra-day and inter-day repeatability were lower than 5% and 8%, respectively.

Department of Analytical Chemistry of Saint Petersburg State University Celebrates One Hundred and Fifty Years Anniversary: International Year of the Periodic Table of Chemical Elements.

The year 2019 marks the 150th year of the founding of analytical chemistry department at St. Petersburg State University and of the founding of the periodic table of chemical elements as proposed by Professor Dmitry Mendeleev. 2019 has been decreed by chemists as the "International Year of the Periodic Table" in celebration of these historical events. A celebration marking this anniversary was held at the university on March 1. This historical account will recount the early days of the department and Mendeleev's development of the periodic table, and then highlight some of the major analytical contributions of the department.

In-syringe dispersive liquid-liquid microextraction using deep eutectic solvent as disperser: Determination of chromium (VI) in beverages.

A novel approach for dispersive liquid-liquid microextraction based on the use of deep eutectic solvent as a disperser was presented for the first time. The procedure was automated based on an in-syringe flow system coupled with UV-Vis detection and demonstrated by the determination of chromium (VI) in beverages. This analytical task was used as a proof-of-concept example. The automated extraction procedure involved the aspiration of aqueous sample into a syringe pump with homogeneous mixture of extraction solvent (1-oсtanol) and deep eutectic solvent (tetrabutylammonium bromide - formic acid) containing color-forming reagent (1,5-diphenylcarbazide). This led to decomposition of deep eutectic solvent in aqueous phase resulting in dispersion of extraction solvent, oxidation of 1,5-diphenylcarbazide to 1,5- diphenylcarbazone in the presence of chromium (VI), and formation of colored chromium (III) complex with 1,5-diphenylcarbazone and its fast extraction. In this case composition of deep eutectic solvent played a key role for analyte extraction. Tetrabutylammonium bromide promoted mass transfer between aqueous phase and the extraction solvent droplets as a salting out agent, bromide ion acted as an ion-pare agent for analyte complex extraction, formic acid provided required pH value for analyte complex formation. Under the optimal conditions the limit of detection, calculated from a blank test based on 3s, was 0.2 µg L-1. The automated dispersive liquid-liquid microextraction using deep eutectic solvent as disperser can be considered as an available, efficient, rapid and environmentally friendly sample pretreatment approach.

Reversed-phase chromatomembrane extraction as a novel approach for automated sample pretreatment: Anions determination in biodiesel by ion chromatography with conductivity detection.

In this study, a reversed-phase chromatomembrane extraction (RP-CME) method as a novel approach for automated sample pretreatment was suggested for the first time. The RP-CME was applied to automated separation of anions (formate, chloride, nitrate, phosphate and sulfate) from biodiesel samples as a proof-of-concept example. The novel design of chromatomembrane cell was developed for on-line RP-CME. The RP-CME procedure assumed mass-transfer of water-soluble analytes from organic sample phase (biodiesel sample) to aqueous phase supported in a porous composite mass-transfer block. The composite mass-transfer block based on microporous hydrophobic poly (tetrafluoroethylene) and hydrophilic glass fiber was developed for the RP-CME implementation. The block provided the effective retention of aqueous phase into the cell and simultaneous penetration of organic phase. The hydrophilic membrane-based sheet was used for the on-line separation of hydrophilic emulsion (biodiesel in water) containing target analytes obtained during analytes elution by aqueous phase from the mass-transfer block. The RP-CME was successfully coupled with an ion chromatography with conductivity detection. The limits of detection, calculated from a blank test based on 3σ, were 5 µg kg-1 for sulfate, 6 µg kg-1 for nitrate, 3 µg kg-1 for chloride, 5 µg kg-1 for phosphate and 1 µg kg-1 for formate.

Fe3O4-based composite magnetic nanoparticles for volatile compound sorption in the gas phase: determination of selenium(iv).

In this study, Fe3O4-based composite magnetic nanoparticles were found to separate volatile compounds directly in the gas phase for the first time. The phenomenon of H2Se sorption on the magnetic nanoparticles was studied in detail and applied for separation and preconcentration. The developed approach was applied for the determination of selenium in dietary supplement samples after microwave digestion by ETA-AAS as a proof-of-concept example.

An automated salting-out assisted liquid-liquid microextraction approach using 1-octylamine: On-line separation of tetracycline in urine samples followed by HPLC-UV determination.

An automated salting-out assisted liquid-liquid microextraction (SALLME) procedure based on a flow system was developed as new approach for pretreatment of complex sample matrix. In this procedure 1-octylamine was investigated as novel extractant for the SALLME. The procedure involved aspiration of the 1-octylamine and sample solution into a mixing chamber of a flow system followed by their air-bubble mixing resulting to isotropic solution formation. To provide phase separation a salting-out agent solution was added into the mixing chamber. After phase separation, the micellar 1-octylamine phase containing analyte was mixed with methanol and transported to a HPLC-UV system. To demonstrate the efficiency of the suggested approach, the automated procedure was applied for the HPLC-UV determination of tetracycline as a proof-of-concept analyte in human urine samples. Under the optimal conditions, the detector response of the analytes was linear in the concentration ranges of 0.5-20 mg L-1. The limit of detection, calculated from a blank test based on 3σ, was 0.17 mg L-1. The results demonstrate that the developed approach is highly cost-effective, simple and rapid.

An automated continuous homogeneous microextraction for the determination of selenium and arsenic by hydride generation atomic fluorescence spectrometry.

An automated continuous homogeneous microextraction approach based on a flow system has been developed and coupled with a hydride generation atomic fluorescence spectrometry system (HG-AFS). The developed approach was applied for the determination of trace arsenic and selenium in environmental water and liver samples. The nonanoic acid was investigated as a switchable hydrophilicity solvent (SHS) for homogeneous microextraction of As(III) and Se(IV) complexes with pyrrolidinedithiocarbamate (PDC). The procedure involved on-line mixing ammonium PDC (aqueous phase), sodium nonanoate (aqueous phase) and acid sample solution resulting in the formation of SHS (nonanoic acid) dispersed into the acid aqueous phase. By this continuous process, analytes complexes with PDC were formed and extracted into the fine SHS droplets followed by retention into a monolithic column packed with block of porous PTFE. Finally, the retained complexes were eluted with NaOH solution and delivered to the HG-AFS system. The limits of detection, calculated from a blank test based on 3σ, were 0.01µgL-1 for both analytes.

An automated magnetic dispersive micro-solid phase extraction in a fluidized reactor for the determination of fluoroquinolones in baby food samples.

An automated magnetic dispersive micro-solid phase extraction procedure in a fluidized reactor was developed for the determination of fluoroquinolone antimicrobial drugs (fleroxacin, norfloxacin and ofloxacin) in meat-based baby food samples. A stepwise injection system was successfully combined with afluidized reactorand applied for the magnetic dispersive micro-solid phase extraction procedure automation. The developed automated procedure involved injection of the sample solution into the fluidized reactor followed by the on-line separation of the analytes from the sample matrix based on fluidized beds strategy using magnetic nanoparticles, elution and determination of the analytes using a high performance liquid chromatography system with fluorescence detection. The floating of the magnetic nanoparticles in a liquid sample phase was accomplished by air-bubbling. In the developed method Zr-Fe-C magnetic nanoparticles were used as an efficient sorbent for the determination of fleroxacin, norfloxacin and ofloxacin. Under the optimal conditions, the calibration graphs were linear over the concentration ranges of 10-1000 µg L-1 for fleroxacin (R2 = 0.996), 5-1000 µg L-1for norfloxacin (R2 = 0.998) and ofloxacin (R2 = 0.998). The limits of detection, calculated from the blank tests based on 3σ, were 3.0 µg L-1forfleroxacin, 1.5 µg L-1for norfloxacin and ofloxacin. The limits of quantification, calculated from the blank tests based on 10σ, were 10 µg L-1 forfleroxacin, 5 µg L-1for norfloxacin and ofloxacin. The method was applied for the determination of fluoroquinolonesin meat-based baby food samples and the results were compared with those obtained by the reference method. The recovery values for all analytes were within of 86-122% range.

A novel flow injection chemiluminescence method for automated and miniaturized determination of phenols in smoked food samples.

An easily performed fully automated and miniaturized flow injection chemiluminescence (CL) method for determination of phenols in smoked food samples has been proposed. This method includes the ultrasound assisted solid-liquid extraction coupled with gas-diffusion separation of phenols from smoked food sample and analytes absorption into a NaOH solution in a specially designed gas-diffusion cell. The flow system was designed to focus on automation and miniaturization with minimal sample and reagent consumption by inexpensive instrumentation. The luminol - N-bromosuccinimide system in an alkaline medium was used for the CL determination of phenols. The limit of detection of the proposed procedure was 3·10-8·molL-1 (0.01mgkg-1) in terms of phenol. The presented method demonstrated to be a good tool for easy, rapid and cost-effective point-of-need screening phenols in smoked food samples.

An evaporation-assisted dispersive liquid-liquid microextraction technique as a simple tool for high performance liquid chromatography tandem-mass spectrometry determination of insecticides in wine.

A sample pre-treatment technique based on evaporation-assisted dispersive liquid-liquid microextraction (EVA-DLLME), followed by HPLC-MS/MS has been developed for the determination of organophosphate insecticides (malathion, diazinon, phosalone) in wine samples. The procedure includes the addition of mixture of organic solvents (with density higher than water), consisting of the extraction (low density) and volatile (high density) solvents, to aqueous sample followed by heating of the mixture obtained, what promotes the volatile solvent evaporation and moving extraction solvent droplets from down to top of the aqueous sample and, as a consequence, microextraction of target analytes. To initiate the evaporation process an initiator is required. It was established that hexanol (extraction solvent) and dichloromethane (volatile solvent) mixture (1:1, v/v) provides effective microextraction of the insecticides from wine samples with recovery from 92 to 103%. The conditions of insecticides' microextraction such as selection of extraction solvent, ratio of hexanol/dichloromethane and hexanol/sample, type and concentration of initiator, and effect of ethanol as one of the main components of wine have been studied. Under optimal experimental conditions the linear detection ranges were found to be 10-7-10-3gL-1 for malathion, 10-9-10-4gL-1 for diazinon, and 10-6-10-2gL-1 for phosalone. The LODs, calculated from a blank test, based on 3σ, found to be 3×10-8gL-1 for malathion, 3×10-10gL-1 for diazinon and 3×10-7gL-1 for phosalone. The advantages of EVA-DLLME are the rapidity, simplicity, high sample throughput and low cost. As an outcome, the analytical results agreed fairly well with the results obtained by a reference GC-MS method.

Flow method based on liquid-liquid extraction using deep eutectic solvent for the spectrofluorimetric determination of procainamide in human saliva.

In the current study, liquid-liquid extraction, using deep eutectic solvent (DES) as a "green" extraction solvent, was coupled with a stepwise injection system for the first time. The suggested approach was applied for the development of spectrofluorimetric method for procainamide determination. The method is based on aspiration of saliva sample and DES (choline chloride with glycerol at a 1:2M ratio) solution into the mixing chamber of a flow system, followed by injection of acetonitrile into the mixed DES-sample solution. The extraction process and final phase separation were then promoted by air-bubbling. After phase separation, the DES phase, containing the extracted procainamide, was transported to a spectrofluorimetric detector. The excitation and emission wavelengths were set at 280nm and 347nm, respectively. The calibration plot was linear in the range of 5×10-6 to 5×10-5molL-1. The limit of detection, calculated as 3σ of a blank test (n=10), was found to be 1.5×10-6molL-1. The developed method was successfully applied for the determination of procainamide in human saliva samples, and the analytical results agreed rather well with the results obtained by the reference HPLC-UV method.

Automated alkaline-induced salting-out homogeneous liquid-liquid extraction coupled with in-line organic-phase detection by an optical probe for the determination of diclofenac.

A fully automated alkaline-induced salting-out homogeneous liquid-liquid extraction (AI-SHLLE) procedure coupled with in-line organic-phase detection by an optical probe has been suggested. Diclofenac was used as a proof-of-concept analyte. The method is based on the oxidation of diclofenac with potassium ferricyanide in an alkaline medium followed by separation of the acetonitrile phase from the homogeneous sample solution and simultaneous extraction of the derivative. Sodium hydroxide serves as both the alkaline agent for the derivatization of diclofenac and as the salting-out agent for the acetonitrile-rich phase formation. Absorbance of the derivative in the acetonitrile-rich phase was measured in-line using an optical probe. The calibration graph was linear over the range of 2.5-60µmolL-1 with the regression coefficient equal to 0.9997. The LOD calculated from the calibration plot based on 3σ was 0.8µmolL-1. The sample throughput was 7 samplesh-1. The method was applied for the determination of diclofenac in spiked saliva samples and pharmaceutical preparations and the results were compared with those obtained by the reference method.

Automated sugaring-out liquid-liquid extraction based on flow system coupled with HPLC-UV for the determination of procainamide in urine.

A fully automated sugaring-out assisted liquid-liquid extraction procedure was suggested. The procedure was based on the separation of the acetonitrile phase, containing a target analyte from the homogeneous sample solution after injection of sugaring-out reagent (glucose) into a mixing chamber of the flow system. Air bubbling was used to promote the extraction process and phase separation. After the fast phase separation in the mixing chamber, the acetonitrile phase containing the target analyte was transferred to an HPLC-UV system. Under the optimal conditions, the detector response of procainamide was linear in the concentration range of 6×10-7-4×10-5molL-1. The limit of detection, calculated from a blank test based on 3σ, was 2×10-7molL-1. The proposed method was successfully applied for the determination of procainamide in human urine samples and the analytical results agreed fairly well with the results obtained by reference CE method.

An automatic chemiluminescence method based on the multi-pumping flow system coupled with the fluidized reactor and direct-injection detector: Determination of uric acid in saliva samples.

A novel approach for the automatic chemiluminescence (CL) analysis of the complex samples is proposed. A multi-pumping flow system was successfully combined with fluidized reactor and direct-injection CL detector. The possibility of the approach was demonstrated on the determination of uric acid in saliva samples. Uric acid is clinically important analyte and its determination in biological fluids is related to human organism dysfunctions, such as gout. For the first time, the fast luminol - N-bromosuccinimide (NBS) reaction in an alkaline medium was used for the CL determination of uric acid in saliva samples. The CL intensity is greatly quenched in the presence of the analyte. The method includes on-line separation of uric acid from the saliva samples based on fluidized beds strategy using anion-exchange resin Dowex® 2×8 followed by the elution and CL determination using a direct-injection CL detector. The stroke pulsations of the solenoid micro-pumps provided the floating of the anion exchange resin in a sample phase and uric acid separation from the sample matrix into a sample pre-treatment block of flow system. To obtain efficient elution of analyte an eluent circulation was applied. Under the optimal conditions, the detector response for uric acid was linear in the logarithmic concentration ranges from 6·10-6 to 1·10-3molL-1. The limit of detection, calculated from a blank test based on 3σ, was 2·10-6molL-1. Fluidized bed strategy allows us to exclude saliva matrices influence on the luminol-NBS CL reaction, which results in improved selectivity. The applicability of the method developed is demonstrated with the help of real sample analysis. The obtained results are confirmed by reference HPLC-UV method.

A dispersive liquid-liquid microextraction using a switchable polarity dispersive solvent. Automated HPLC-FLD determination of ofloxacin in chicken meat.

In this article, dispersive liquid-liquid microextraction (DLLME), based on the use of so-called switchable polarity dispersive solvent (SPDS) for microextraction, is presented for the first time. The new extraction technique makes use of a mixture of extraction solvent (dichloromethane) and the SPDS (acrylic acid). This mixture is injected into the aqueous sample solution, which was previously fortified with the alkaline agent (NaOH). The SPDS is dissolved in aqueous phase and a cloudy solution consisting of fine droplets of extraction solvent fully dispersed in the aqueous phase is observed. Simultaneously, as a consequence of the fast neutralization reaction, the SPDS investigated is converted into water-soluble salt and phase separation is achieved because the SPDS switches its polarity. Conversion of the SPDS excludes the negative influence of the conventional dispersive solvents used in DLLME on the solubility of target analytes in aqueous phase and, as a result, increases the DLLME efficiency. The proposed extraction technique was automated based on a flow system and coupled with high performance liquid chromatography system with fluorescence detection (HPLC-FLD) and demonstrated by the determination of ofloxacin (OFLX) in chicken meat samples. This analytical task was used as a proof-of-concept example. The automated method includes on-line ultrasound assisted solid-liquid extraction of OFLX from chicken meat samples followed by DLLME using SPDS, solvent exchange and the determination by HPLC-FLD. Under the optimal conditions, the detector response for OFLX was linear in concentration range of 6·10-9 - 5·10-7 mol L-1. The limit of detection, calculated from a blank test based on 3σ, was 2·10-9 mol L-1.

Fast isotopic separation of 10 B and 11 B boric acid by capillary zone electrophoresis.

Fast isotopic separation of 10 B and 11 B boric acid by CZE was demonstrated. The BGE contained 25 mM phenylalanine and 5 mM putrescine (рН 8.95). The running conditions were +25 kV at 20°C with indirect photometric detection at 210 nm. Baseline separation was achieved in less than 9 min. RSD of migration times and corrected peak areas were less than 0.5 and 3%, respectively (n = 5). Linearity was demonstrated in the range 0.2-2 mM for 11 B and 0.2-0.5 mM for 10 B.

Determination of curcumin in biologically active supplements and food spices using a mesofluidic platform with fluorescence detection.

A mesofluidic platform (MP) with fluorescence detection based on a stepwise injection analysis (SWIA) was used for the determination of curcumin in biologically active supplements and food spices. The main units of the MP are a mixing chamber (MC) and an optical channel with a quartz capillary inside. The MC provides rapid and complete mixing solutions by gas bubbling. The proposed method is based on the new rapid and sensitive reaction of curcumin with a fluorescence reagent - 4-(2,3,3-trimethyl-3H-indolium-1-yl)butane-1-sulfonate (TIBS). The fluorescence intensity of TIBS is greatly quenched in the presence of curcumin in an alkaline medium. The linear range was from 1 to 10µM of curcumin, and the limit of detection, calculated as 3σ of a blank test (n=5), was found to be 0.3µM. The sample throughput was 24h(-1). The proposed method was successfully applied for the determination of curcumin in biologically active supplements and samples of food spices. The obtained data were in good agreement with those measured by a HPLC-UV method.

Interfacial reaction using particle-immobilized reagents in a fluidized reactor. Determination of glycerol in biodiesel.

A novel fluidized beads strategy for utilization of particle-immobilized reagents in flow analysis was developed in this study. The performance of the suggested strategy was demonstrated by the determination of glycerol in biodiesel. This analytical task was used as a proof-of-concept example. The method is based on on-line extraction of glycerol from biodiesel into aqueous stationary phase of extraction-chromatographic column, followed by elution and spectrophotometric determination in the form of copper glycerate formed in a fluidized reactor of stepwise injection system. The floating of cation exchange resin Dowex(®) 50WX4, saturated with Cu(II) ions in liquid phase, was accomplished by air-bubbling. The linear range was from 100 to 1000 mg kg(-1), and the limit of detection, calculated as 3s of a blank test (n = 5), was found to be 30 mg kg(-1). The method was successfully applied to the analysis of biodiesel and biodiesel-blend (B 20) samples.

Flow method based on cloud point extraction for fluorometric determination of epinephrine in human urine.

A novel stepwise injection fluorometric method for the determination of epinephrine in human urine has been developed. In the current study, the stepwise injection analysis (SWIA) was successfully combined with on-line in-syringe cloud point extraction (CPE) and fluorometric detection. The procedure was based on the epinephrine derivatization in the presence of o-phenylenediamine followed by the preconcentration stage based on the CPE with the nonionic surfactant Triton X-114. After the phase separation into a syringe of the flow system, the micellar phase containing the epinephrine derivative was transported to a fluorometric detector. The excitation and emission wavelengths were set at 447 nm and 550 nm, respectively. The conditions of epinephrine derivatization and CPE have been studied. The calibration plot constructed using the developed procedure was linear in the range of 1·10(-11)-5·10(-7) mol L(-1). The limit of detection, calculated as 3 σ of a blank test (n = 10), was found to be 3·10(-12) mol L(-1). The proposed method was successfully applied for the determination of epinephrine in human urine samples.