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A possibility of determining antibacterial preparations of the tetracycline series (tetracycline, doxycycline, oxytetracycline, demeclocycline, methacycline and chlortetracycline) in waste water, natural waters, and milk by the sensitized fluorescence of europium on its hydroxide using digital colorimetry (smartphone) is studied. It is found that europium(III) forms complexes with tetracyclines in an alkaline medium, and the formation of the europium hydroxide precipitate does not change its fluorescence properties. The colorimetric parameters of the precipitate after centrifugation are measured using a smartphone. The limits of detection and determination are 0.001–0.004 and 0.005–0.01 µg/mL, respectively, for all analytes. The analytical ranges are 0.005 (0.08)–0.1 (1) µg/mL. The calibration curves are linear, R2 ≥ 0.98. A procedure for determining the total concentration of tetracyclines in waste water, natural waters, and milk is proposed. The duration of analysis is 20–30 min; the relative standard deviation of the results of analysis does not exceed 20%.

The application of sulfur and nitrogen co-doped carbon quantum dot−potassium permanganate chemiluminescence (CL) system for the determination of trace amounts of deltamethrin insecticide was investigated. The results showed that traces of deltamethrin significantly increased the CL of this system in the optimized conditions. This increase was proportional to the concentration of deltamethrin and was used for its determination. We prepared sulfur and nitrogen co-doped carbon quantum dots by hydrothermal method and characterized by fluorescence, X-ray and infrared spectra and transmission electron microscopy. In the optimum analytical conditions, the calibration graph was linear in the range of 1.8 to 20.0 µg/L with a detection limit of 0.3 µg/L. The new tested method has simple set up, high sensitivity and has been successfully applied to the determination of deltamethrin in water samples.

Dispersive liquid−liquid microextraction solidified floating organic drop (SFOD−DLLME) technique was used for sample treatment and extraction of hexavalent chromium from spiked and real samples of workplace ambient air and urine of chromium electroplating workers. Validation of the SFOD−DLLME technique with three solvents, namely, 1-undecanol, 2-dodecanol and n-hexadecane, showed that pH 4, stirring rates of 600 rpm for 1-undecanol and 2-dodecanol and 800 rpm for n-hexadecane, extraction times of 10 min for 1-undecanol and 2-dodecanol and 15 min for n-hexadecane were the conditions allowing to reach the highest extraction efficiency. The maximum acquired enrichment factor was 211 and LODs were in the range of 0.015–0.05 µg/L, and the calibration curves were linear in the range of 0.5–30 µg/L. The results showed that SFOD−DLLME coupled with atomic absorption spectroscopy is a precise and sensitive technique for the determination of hexavalent chromium for biological monitoring of occupational/environmental samples.

A supramolecular dispersive liquid−liquid microextraction method based on the solidification of the floating organic drop (SM-DLLME-SFOD) combined with spectrophotometry was developed for the separation, preconcentration, and determination of trace amounts of nickel from aqueous samples. The method is based on the extraction of the hydrophobic complex of nickel with α-furildioxime in the coacervates made up of undecanol reverse micelles in a water-tetrahydrofuran mixture. The parameters affecting the extraction of nickel were screened by fractional factorial design with central points. Effective experimental parameters were optimized using central composite design. Under the optimized conditions, the calibration graph was linear for nickel in the concentration range of 3–85 µg/L with a determination coefficient of 0.9992. The limit of detection and the enhancement factor of the method were 0.4 µg/L and 147, respectively. The method was successfully applied to the determination of nickel in water and vegetable samples.

A flow injection method for the determination of cysteine (CySH) and glutathione (GSH) amino acids is reported based on lucigenin−diperiodatocuprate(III) complex chemiluminescence (CL) reaction in basic medium. Under optimum conditions, linear calibration curves were obtained in the range of 0.001–30 (R2 = 0.9998, n = 6) and 0.005–30 mg/L (R2 = 0.9989, n = 6) with detection limits (S/N = 3) of 2.5 × 10–4 and 8 × 10–4 mg/L for CySH and GSH, respectively. The relative standard deviation was 4.1% (n = 11) with injection throughput of 160 per hour. We have applied the developed method to determine CySH and GSH in pharmaceutical samples and compared the results with a spectrophotometric method. Statistical tests such as Student’s t- and F-tests were applied for both results with no significant difference observed at a 95% confidence level. The CL reaction of lucigenin−copper(III) complex is also presented.

A new reagent, 1,4-dihydroxyanthraquinone (1,4-DHA), is described for the spectrophotometric determination of thorium(IV). Optimization of the formed thorium−1,4-DHA complex was performed by studying several parameters such as methanol concentration, suitable pH, dye concentration, temporal stability of the formed complex and thorium concentration (calibration curve). The optimized method was applied to different rock types bearing thorium with good accuracy results. This reagent is highly sensitive toward thorium; thorium complex has a molar absorptivity of 1.82 × 104 L/(mol cm) at 600 nm and pH 3.25. Beer’s law was obeyed in the range from 0.9 to 20 µg/mL for Th(IV). The tolerance limits for several metal ions were calculated and gave high tolerance limit especially for uranium. Details are given for the estimation of thorium in standard reference and natural rocks.

In this study, MIL-53(Fe) nano-sized crystals were synthesized under microwave irradiation with various powers (80, 100 W) and ‎times (5, 10 min). Then, the crystals that had the best porous ‎structure were selected to prepare the MIL-53(Fe)/Ag/CNT ternary nanocomposite. Nano-sized crystals were characterized by scanning electron microscopy, Fourier transform infrared ‎spectroscopy, X-ray diffraction, and specific surface area analysis. Prepared nanocomposite was used to fabricate a resistive gas sensor device for detecting volatile organic compounds in environmental conditions (10% relative humidity and 25°C). The resistive gas sensor showed higher response to volatile organic compounds with higher polarity such as methanol. The lowest detectable concentration of methanol was 1.2 ppm. Linearity of the calibration curve was obtained in a wide range from 0 to 30 mg/L.

Magnetic solid phase microextraction (m-SPME) is a well-defined strategy for the preconcentration and separation of hydrophobic species from aqueous samples without the use of toxic organic solvents. This work identifies a new analytical procedure for trace level vanadium(V) by inductively coupled plasma mass spectrometry coupled to magnetic solid phase microextraction. The procedure is based on the preconcentration of the V(V)–H2O2–4-(2-pyridylazo)resorcinol complex. Magnetic Fe3O4 nanoparticles decorated multi-walled carbon nanotubes as an adsorbent were investigated systematically. The calibration curve obtained by using m-SPME for vanadium(V) was linear from 0.011 to 10 µg/L. The method detection limit was found to be 1.5 ng/L. The m-SPME method was applied to the assay of vanadium in a certified reference water sample and the result was in total balance with the declared value. Finally, the proposed method was applied to the determination of vanadium in real water samples.

There is always a need to develop new, fast and non-complicated microextraction methods that consume small amounts of organic solvents. In this study, a new mode of liquid phase microextraction method, termed as continuous sample drop flow-based microextraction (CSDF−ME), was developed for the enrichment and determination of cobalt in water samples. To attain the appropriate conditions for the CSDF−ME, experimental parameters such as pH, type and volume of extraction solvent, concentration of chelating agent, salting effect, sample flow rate and sample volume, needle diameter were examined. The enrichment factor was 167 for 20 mL sample solution. The calibration graph was linear in the concentration range of 5–200 μg/L with the correlation coefficient of 0.999. The limit of detection was 1.3 μg/L. The reliability of the recommended procedure was verified by analysis of real water samples (including tap, mineral and river water) and synthetic sample spiked with known amount of cobalt, and the obtained recoveries of spiked samples have demonstrated accuracy and applicability of the proposed method.

Biodiesel from four different renewable resources was produced. An optimization of the reference methodology by gas chromatography was conducted based on the construction of calibration curves for each biodiesel during fatty acid methyl esters (FAME) quantification. Therefore, in the proposed optimized methodology, pure commercial standards are not necessary. Consequently, a reduction in the research expenses is achieved, making this methodology a cost-effective alternative for FAME quantification. The calibration curves obtained for each biodiesel presented slope values between 0.5–0.7 and regression coefficients (R2) > 0.98 in all cases. These results were compared to those obtained by the conventional methodology. With respect to the validation of the optimized methodology, a comparison of the results obtained by this proposed methodology and the reference one is presented. Finally, a robust and promising technique to quantify FAME present in biodiesel was successfully developed in this study.

Azo dyes constitute about 66% of all colorants and they are widely used in industries such as textiles, plastics, ceramics, cosmetics and food. However, due to the reductive cleavage of some azo dyes into carcinogenic aromatic amines, many countries have set concentration limits or have banned the use of these azo dyes. Selected aromatic amines that pose health risk to consumers were simultaneously determined by gas chromatography mass spectrometry. A good linearity in calibration plot was obtained for the analytes and the low relative standard deviations indicated high instrumental precision. A recovery test was performed to validate the extraction method and the results obtained were between 92–114%. The method was applied to the analysis of real samples and the concentrations of aromatic amines detected were below the 30 mg/kg limit set by regulatory authorities.

In this paper, we evaluated the use of a silylation reagent N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide in the microwave-assisted derivatization method to replace a traditional prolonged heating method for the determination of 12 amino acids. Several parameters, including the kind of extraction solvent, extraction time, microwave power and microwave time, were optimized. The experiment showed that the optimal derivatization time was 3 min with a microwave power of 240 W. The calibration curves were linear with the correlation coefficients ranging from 0.995 to 1.000 in the concentration levels between 0.1–20 μg/mL and the relative standard deviations were between 4.4 and 18%. The limits of detection were 0.1–2.4 μg/mL and the recoveries of those compounds were 62–115%. A comparison of this method to other methods has demonstrated that the proposed method is a rapid and reliable sample-treatment procedure for amino acids determination in real tobacco samples.

Electrochemical properties of regorafenib (REG) were studied in 0.1 M Britton−Robinson buffer-methanol solutions (3 : 2, v/v) with pH between 3 and 8 at carbon paste electrode by cyclic and differential pulse voltammetry. The results exhibited irreversible anodic peak at about 0.90 V vs. Ag/AgCl, NaCl (3 M). The anodic peak was found to be diffusion–adsorption controlled. Mechanism of REG electrochemical reaction was studied by performing density functional theory computations and mass spectrometric analysis. A validated differential pulse voltammetry (DPV) technique for REG determination was performed. The calibration curve of REG on carbon paste electrode was linear in the concentration range of 0.5–13 μg/mL and limit of detection was 0.10 µg/mL. The recommended DPV method was used to detect REG in spiked plasma and urine specimens and average recoveries were 94%.

A glassy carbon electrode modified with a nanocomposite consisting of carbon dots, hexadecyltrimethyl ammonium bromide and chitosan showed excellent electrocatalytic activity toward oxidation of mesalazine (MSA). Under optimal experimental conditions, hydrodynamic amperometry was used for sensitive determination of MSA. Calibration curve was obtained in the range of 0.1–10 μM with a detection limit of 0.05 μM. The repeatability of the method was studied for 5 replicate measurements of MSA (50 μM) and the calculated relative standard deviation (RSD %) was 0.74%. The reproducibility for 5 different electrodes (expressed as RSD %) was 1.96% for MSA (50 μM). The amperometric determination of the drug was successfully performed in spiked blood serum samples with recoveries ranging from 96 to 99%.

The new Russian drug Triazid® is a highly effective antiviral agent. The active substance of the drug (5-methyl-6-nitro-7-oxo-4,7-dihydro-1,2,4-triazolo[1,5-a] pyrimidinide l-arginine monohydrate, triazid) belongs to azoloazine series compounds. Using cyclic voltammetry, it was found that the electrochemical activity of triazid (TD) in Britton–Robinson aqueous buffer solutions (BRB) on a glassy carbon electrode is due to the electroreduction of the nitro group bound with the conjugated aromatic system. The maximum current of triazid reduction in the potential range 0.0‒(‒1.25) V was used as an analytical signal. A method was developed for the quantitative determination of triazid by direct cathodic square-wave voltammetry. The linearity range of the calibration graph using the developed method in a BRB solution (pH 4) is 10–500 mg/L (R2 = 0.9998) with the limit of detection for TD 1.9 mg/L. The developed method was used to analyze the Triazid pharmaceutical substance for the concentration of TD. The results obtained satisfy the stated requirements of the draft pharmacopoeial article of the company “TRIAZID substance” for the content of TD found by HPLC.

A simple, sensitive and efficient method based on hollow fiber liquid phase microextraction followed by high performance liquid chromatography has been developed for preconcentration and determination of trace carbamazepine, an antiepileptic drug, in aqueous and biological solutions.The main parameters affecting the extraction efficiency were studied using response surface methodology. Central composite design was performed at five levels of extraction time, pH and ionic strength. The final model showed good linearity and performance. The optimal conditions were observed at 48.5 min, 8.9 and 0.29 M for extraction time, pH and ionic strength, respectively. The calibration curve was linear in the range of 5–500 µg/L with correlation coefficient of 0.9999 and limit of detection of 2.8 µg/L. Finally, the applicability of the proposed method was evaluated by extraction and determination of the drug in aqueous and plasma samples. The intra- and inter-day coefficients of variation were less than 4.7 for all real samples.

This article describes the effects of microstructures in an analysis of lead-free solders, namely SnAg, SnBi and SnIn, using X-ray fluorescence spectrometry (XRF). The size of the microstructures in the samples and calibration materials has a strong impact on the calibration accuracy and results. A comparison of the microstructure size and critical thickness values demonstrated the importance of the former parameter in terms of the analyzed volume of the specimen. The re-melting and casting in an induction furnace at developed conditions were determined to be a way to obtain samples with fine-grained microstructures. Calibration with re-melted reference materials yielded more accurate calibration curves than calibration using the materials in their original state. Re-melting of the samples resulted in improvements in the XRF results in comparison to the reference values. This improvement is especially important in case of alloying elements with concentrations that determine the recognition of a specific solder grade.

In this research, a fast, simple and highly efficient sample pretreatment technique based on air-assisted liquid–liquid microextraction (AALLME) followed by UV−Vis spectrophotometric detection has been applied for the preconcentration and determination of palladium in water samples. 1-(2-Pyridylazo)-2-naphthol (PAN) and chloroform were used as a chelating agent and extraction solvent, respectively. Parameters affecting AALLME, including pH of sample solution, concentration of PAN, volume of extraction solvent and number of extraction cycles were studied and optimized using Box–Behnken design. Under the optimum conditions, the calibration curve was linear in the concentration range of 5–700 ng/mL with the correlation coefficient (r2) of 0.996. Detection limit, enrichment factor, intra- and inter-day precision were 0.7 ng/mL, 193, 1.3 and 1.8%, respectively. Finally, the developed method was successfully applied for the determination of trace amounts of palladium in environmental water samples.

A novel switchable-hydrophilicity solvent based liquid phase microextraction coupled with flame atomic absorption spectrometry has been applied for preconcentration and determination of Ni(II). Triethylamine (TEA) was selected as an inexpensive switchable solvent in the present work. Ni(II)-1-(2-pyridylazo)-2-naphthol complex was extracted into the TEA phase by converting the protonated carbonate to TEA. The experimental conditions were optimized using Plackett–Burman and Box–Behnken design methods. Such analytical parameters as the limit of detection, relative standard deviation and enhancement factor were 3 μg/L, 1.1% and 70, respectively. The calibration graph was linear over the range of 10 to 800 μg/L with the correlation coefficient of 0.998. The proposed method was successfully applied to the quantification of trace nickel in water and vegetable samples.

A procedure for the determination of AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, Acadesine), an AMP-activated protein kinase agonist prohibited by the World Anti-Doping Agency since 2009, in urine has been proposed including sample clean-up from matrix components by means of solid-phase extraction and detection of the analyte by ultra-high performance liquid chromatography–tandem mass-spectrometry with heated electrospray ionization ion source. Due to the endogenous nature of AICAR, standard additions approach was applied to quantify AICAR and evaluate matrix effects. The limit of detection was 5 ng/mL, calibration curves were linear in the concentration range of 50–5000 ng/mL. The proposed procedure was applied to the analysis of real samples.

A method is considered for determining concentrations of components in solutions of two electrolytes with one common ion. We used optical micrometry by measuring the degree of swelling of granules of crosslinked polyvinyl alcohol in a test solution. To determine the concentration, the test solution was successively diluted, and a set of polymer swelling values was obtained. The data were used to build a total calibration curve for this mixture. Concentrations of the components of the solution were found by the least squares method, the software implementation of which is based on the coordinate descent.

Based on cloud point extraction, a HPLC method was developed for the determination of verapamil in urine. Non-ionic surfactant Triton X-100, an environmentally friendly solvent, was used for the micelle-mediated extraction. Some parameters that influence the extraction, such as the concentration of Triton X-100, effect of pH, incubation time, equilibration temperature and centrifugation parameters, were studied and optimised. The method suggested for the HPLC‒tandem mass spectrometry determination of verapamil in urine after cloud point extraction was validated. The calibration curve was linear in the range of 0.2–50 ng/mL. The limits of detection (3σ) and quantification (10σ) were 0.06 and 0.2 ng/mL, respectively. The matrix effect (96.5%), recovery of the extraction procedure (96%) and overall “process efficiency” (92.6%) were also estimated. All data validation is consistent with international acceptance criteria and no significant matrix effect was observed. The results show that the sensitivity, metrological characteristics, ecological safety, simplicity and convenience of the suggested procedure exceed its analogues based on extraction using organic solvents.

A simple, sensitive, precise, accurate, highly reproducible and economical, visible spectrophotometric method for the determination lurasidone in bulk form was developed and validated. The method is based on the formation of an oxidative coupling product by the reaction of lurasidone with 3-methylbenzothiazolin-2-one hydrazone as a chromogenic reagent in presence of ferric chloride. The linear regression analysis data for the calibration plot showed good linear relationship within the concentration range of 0–100 μg/mL with a correlation coefficient (r) value of 0.9997. The limits of detection and quantitation are 0.6 and 1.7 µg/mL, respectively. The method was tested and validated according to ICH guidelines. The results demonstrated that the procedure is accurate, precise and reproducible (RSD < 2%).

In this study, nickel ferrite magnetic nanoparticles adsorbent was synthesized and developed for solid phase extraction and spectrophotometric determination of trace amounts of lead ions in aqueous media. The adsorbent was characterized by X-ray diffraction, transmission electron microscopy and vibrating sample magnetometry. The magnetic separated lead ions were eluted and quantified based on the complex formation of lead ions with 1,5-diphenylthiocarbazone at pH 8.5. The influence of variables affecting the efficiency of the extraction system, such as sample pH, amount of adsorbent, type and volume of desorption solvent and contact time, was evaluated and optimized. Under the optimal conditions, a linear calibration curve in the range from 0.004 to 0.6 μg/mL was obtained with a preconcentration factor of 80. The limit of detection for lead was found to be 0.27 ng/mL. The developed method was successfully applied for the determination of trace amounts of lead ions in various water samples with satisfactory results.

The presented study focuses on the optimum conditions for chemical activation of pencil graphite electrodes (PGE) used in the determination of bisphenol A (BPA). The prepared ethanol–HCl mixture for chemical activation of pencil graphite electrode exhibits better activation factor compared with traditional activation methods like anodizing. The obtained porous and highly conductive surface of PGE can be used as a sensing device. The electrochemical behavior of BPA at the modified sensor was investigated. The effects of pH, accumulation time and sensor activation were examined. In the optimum experimental conditions, adsorptive differential pulse voltammetry was used for determination of BPA, which exhibits a linear calibration graph of Ip versus BPA concentration in the range 1.25 × 10–8 to 1.34 × 10–4 M. The calculated detection limit for S/N = 3 was 1.0 nM. The presented sensor is reusable. The activated PGE was applied for the determination of BPA leached from baby bottles as a real sample using spike method.

A simple and effective miniaturized homogenous liquid–liquid extraction technique coupled with a gradient HPLC method for the determination of lamivudine and zidovudine in the human plasma samples was developed. Separation of these drugs was performed on a C18 stationary phase by using a mixture of acetonitrile and water as mobile phase. Extraction of drugs was achieved based on salting-out phenomenon. Variables affecting the extraction efficiency, such as solvent type and its volume, type of salt and its concentration and sample pH have been fully evaluated and optimized. These drugs were successfully extracted by acetonitrile as extracting solvent with sodium sulfate as salting-out agent. Under the optimized experimental conditions calibration curves showed good linearity (r 2 > 0.9938) and precision (RSD < 6.7%) in the working concentration ranges. The limits of detection for lamivudine and zidovudine were 0.006 and 0.003 µg/mL, respectively. The limits of quantification for lamivudine and zidovudine were 0.02 and 0.01 µg/mL, respectively. The recoveries were in the range of 88.0–100.0% with RSD values less than 7.5%. The method was successfully applied to extract and determine lamivudine and zidovudine in human plasma.

In this study, a simple and rapid method for N-acetylcysteine (NAC) determination was proposed using positive corona discharge ion mobility spectrometry. To optimize cell and injection temperature, central composite design was used. Other parameters such as corona and drift voltage, carrier and drift gas flow rate, and pulse width were adjusted. The calibration curve was linear under optimum conditions in the range of 3–100 ng with a correlation coefficient (R2) of 0.99. The relative standard deviations were 8.1 and 6.1%, for 20 and 50 ng of analyte (n = 9), respectively. Limits of detection and quantification were 1 and 3 ng, respectively. The developed method was successfully applied for the determination of NAC in pharmaceutical and human plasma samples.

Optimum conditions for the formation and extraction of a slightly soluble ion associate of diphenhydramine with the anionic complex molibydenum–gallein were determined. The ternary complex was extracted with butanol at pH 4–7. In the presence of diphenhydramine, the color strength became stronger, which was manifested in the absorption spectra as hypsochromic and bathochromic shifts. Some physicochemical characteristics of the complex were determined, the specificity of the reaction with respect to diphenhydramine was studied, and the probable complexation scheme was proposed. It was found that the molybdenum–gallein–diphenhydramine complex forms at a component ratio of 1: 2: 2. A procedure for the extraction–photometric determination of diphenhydramine in injection solutions and tablets was developed (RSD = 15–20%). The linearity range of the calibration graph was 0.02–0.20 mg/mL.

The uncertainty of measurement for well-known neurotransmitters like serotonin, noradrenalin and gamma-aminobutyric acid (GABA), glutamate and melatonin hormone with high performance liquid chromatography-fluorescence detection was calculated after the method validation. Two methods were developed for the determination of the neurotransmitters. A derivatization step was performed for the determination of GABA and glutamate. Sensitivity, method detection limit, limit of quantification, linearity, recovery, interday and intraday precision values were calculated. Low detection limit values were obtained especially for the determination of GABA and glutamate. Then, bottom-up approach was used to calculate measurement uncertainty. The critical stages of the method were evaluated. The major sources of the uncertainty budget were calibration curves, stock solution and recovery. The calculated percentage relative uncertainty values for the compounds changed between 10.1 and 16.7.

Sorbents based on inorganic oxides sequentially modified with polyhexamethylene guanidine, ferrozine, and ferene S are proposed for the preconcentration and determination of iron(II). Upon sorption from solutions with pH 2.5–7.0, colored iron(II) complexes with ferrozine and ferene S, having broad bands with maxima at 560 and 600 nm in the diffuse reflectance spectrum, respectively, formed on the sorbent surface. Procedures for the sorption–photometric determination of iron(II) using diffuse reflectance spectroscopy were developed. The limits of detection for iron(II), calculated by the 3s criterion were 0.005 and 0.006 μg per 0.1 g for sorbents based on silica with immobilized ferrozine and ferene S, respectively. The linearity of calibration curves remains up to 5 and 10 μg per 0.1 g for sorbents based on silicon and aluminum oxides, respectively. The procedures were tested in the determination of the total iron concentration in bottled drinking waters and alcoholic drinks.

A rapid screening and determination of 59 pesticides from various classes in natural water without sample preparation by high-resolution ultra HPLC–quadrupole time-of-flight mass spectrometry is proposed. The matrix effect is considered on an example of waters with a high (mineral) and low (artesian) salt concentration. It is demonstrated that pesticides can be determined in water using the calibration curve method with an insignificant matrix effect (neonicotinoids, carbamates, and derivatives of uracil, pyridine, and benzoic and aryloxycarboxylic acids) and the standard addition method with a significant matrix effect (triazines, triazinones, triazoles, imidazoles, pyridazinones, organophosphorus compounds, and urea derivatives). The limits of detection were 0.01–10 ng/mL; the analytical ranges for pesticides were 0.04–50 (100) ng/mL. The relative standard deviation of the results does not exceed 15%; the analysis time is 10–15 min.

A simple and green reversed-phase ultrasonic assisted liquid−liquid microextraction method for determination of Cu, Cd, Ni, Pb and Zn in edible oils was developed. Detection was carried out by flame atomic absorption spectrometry. The influence of main parameters including ultrasonic time and temperature, disperser solvent, volume of extracting solvent and centrifuging time on the extraction efficiency of target analytes were investigated and optimized. In the proposed method, a few microliters of water (containing 3%, v/v, nitric acid) as extracting solvent was injected into the oil sample and mixture transferred to ultrasonic bath. Then, the mixture was centrifuged in order to accelerate in phase separation. Finally, the aqueous phase was removed and delivered to flame atomic absorption spectrometer. Calibration curves for all metals were linear in the range of 5‒100 ng/mL. The limit of detections for Cu, Cd, Ni, Pb and Zn were 0.8, 0.3, 0.5, 1.5 and 0.5 ng/mL, respectively. Relative standard deviation (RSD) values were in the range of 0.6‒1.9%. The recoveries were in the range of 95.2–101.2% with RSD values ranging from 0.8 to 1.9%. The proposed method was applied successfully for the determination of interested metals in commercial edible oils.

A serial analyzer of dissolved oxygen, Expert-009, based on the optical detection method is created. The sensitive element of the sensor is a polymer film with a dye—a metal complex of fluorine-substituted porphyrin—distributed in it. The method is based on the quenching of the phosphorescence of the dye by molecular oxygen, which the analyzer recounts to the concentration value by the calibration curve method. The metrological characteristics of the analyzer are determined.

Magnetite nanoparticles coated with silica and hydrophobic octadecyl layers were successfully synthesized and used in magnetic solid phase extraction of tetracyclines from water samples. The magnetite nanoparticles facilitated a convenient magnetic separation of sorbent from an aqueous sample, the octadecyl layer helped to enhance the adsorption ability and the silica layer helped to prevent the aggregation of the magnetite nanoparticles. The effect of various parameters on the extraction efficiency were optimized including the amount of sorbent, sample pH, stirring rate, extraction time and desorption conditions. Under the optimum conditions, the recoveries were in the range of 82 to 88%, the calibration curves were linear over the concentration range of 0.002 to 1.0 μg/mL for oxytetracycline and 0.01 to 1.0 μg/mL for tetracycline and chlortetracycline, respectively. The developed method had several advantages such as simplicity, convenience, cost-effectiveness and high extraction efficiency.

A new version of the chronoamperometric method, adapted to the determination of the oxidative (oxidant) activity of a medium on an example of chlorinated water, was proposed. The supporting solution contained K4Fe(CN)6. By its oxidation with oxidants present in the sample, K3Fe(CN)6 formed; its reduction current served as an analytical signal. The current of K3Fe(CN)6 reduction was recorded at a potential of 0 V, selected from the cyclic voltammogram of the K3Fe(CN)6/K4Fe(CN)6 system in the range where the oxidized form of the reagent was reduced and the reduced form was stable. A gold electrode was the measuring electrode. The possibility of using a stable solution of K3Fe(CN)6 as a component of a standard addition and as a solution for plotting a calibration curve was demonstrated. The limit of detection of the amount of dissolved chlorine and products of its interaction with water is 8 × 10–6 M. The data obtained by the proposed procedure and by the iodometric methods correlate well with each other (r = 0.93–0.95). The proposed version of the chronoamperometric method can be used to monitor the amount of dissolved chlorine and products of its interaction with water in water supply systems, pools, and disinfecting solutions and to determine other water-soluble oxidants.

A novel method based on the coupling of membrane-supported headspace single-drop microextraction with gas chromatography‒mass spectrometry (GC–MS) is developed for the determination of chlorobenzenes in water samples. For the determination of five chlorobenzenes, a 15 μL toluene microdrop was placed inside the plastic membrane and exposed for 10 min for headspace extraction while stirring at 1000 rpm. The microdrop was then picked up by a microsyringe and directly injected into the injector block of the GC–MS instrument. Under the optimized operation conditions, the calculated calibration curves gave a high level of linearity for all targets with correlation coefficients range from 0.9945 to 0.9987. The limits of detection range from 0.01 to 0.05 μg/L and the RSDs for most of chlorobenzenes were below 7%. The method is simple, sensitive, and stable for single drop microextraction. Its applicability is demonstrated by the determination of chlorobenzenes in tap water samples.

An ultrasonic assisted supramolecular solvent based dispersion solidification liquid–liquid microexraction method was used for the separation and preconcenteration of erythrosine prior to its determination by microspectrophotometry. Under the optimal conditions, the enrichment and preconcentration factors obtained 142 and 33.33 respectively. The calibration curve was linear in the range of 1.0–100 ng/mL of erythrosine with R 2 = 0.9949. Detection limit was 0.6 ng/mL and the RSD for 7 replicate determination of 40.0 ng/mL erythrosine was ±1.4%. The applicability of the methods was examined by determining erythrosine in water and beverage samples.

A procedure is developed for the identification and determination of tetrodotoxin in pharmaceuticals by liquid chromatography coupled with high resolution mass spectrometry (HPLC−HRMS). The components of a pharmaceutical sample were separated in the gradient elution mode on a HILIC hydrophilic sorbent and detected by HRMS with electrospray ionization in the mode of registration of selected ion transitions. The calibration curve is linear in the range 0.75−1.25 μg/mL with the correlation coefficient > 0.9995.

A simple, rapid and inexpensive dispersive liquid–liquid microextraction based on solidification of organic drop combined with HPLC was developed for the extraction and determination of trace levels of 5-hydroxymethyl-2-furfural in fruit juice. Effect of variables such as extracting and dispersive solvent volume and pH were investigated simultaneously using experimental design. Under the optimum conditions, the calibration graph was linear in the range of 1−200 μg/L with the detection limit of 0.3 μg/L. The optimized method revealed a good precision with relative standard deviation of 2.2%.The performance of the method was evaluated for extraction and determination of 5-hydroxymethyl-2-furfural in orange juice sample.

A simple portable spectrophotometer was constructed and used to perform analytical experiments. The developed model uses available tools and materials such as light emitting diode lamps, compact discs, plastic and cardboard boxes and a cell phone camera to build a design that illustrates the major components of spectrophotometers. The spectra of serial concentrations of KMnO4 (50‒600 μM) were recorded and the values of absorbance were extracted at λmax to build the calibration curve. A linear relationship between the concentration and absorbance was obtained with the coefficient of determination 0.994. The model was also utilized to study the spectra of KMnO4, phenolphthalein and bromothymol blue in comparison with a Shimadzu UV-1800 spectrophotometer as a reference instrument. In spite of the differences in the observed spectra, the recorded λmax were almost identical to those measured by the developed model. The model was successfully used to determine the concentration of sodium alendronate through ligand-exchange complexation with ferric salicylate.

An efficient and inexpensive spectrophotometric method has been developed for the determination of lactic acid in the individual state and in food and biological and cultural liquids. The method is based on the spectrophotometric determination of the colored product of the reaction of lactate ions with iron(III) chloride at 390 nm. The optimum conditions of the reaction have been found, and a calibration curve in the range from 0.3 to 10 g/L of lactic acid with the correlation coefficient 0.9999 has been constructed. The method does not require complex sample preparation.

We proposed a procedure for the IR spectrometric determination of lipid hydroperoxides in biological systems. The main bands in the IR absorption spectra of linoleic acid and its hydroperoxide were identified, and analytical bands suitable for the determination of both compounds in their mixtures were selected. It was demonstrated that tert-butyl hydroperoxide can be used as an external standard for determining fatty acid hydroperoxides. Using the external standard method (calibration curve) for tert-butyl hydroperoxides, we calculated the concentration of linoleic acid hydroperoxide in its mixture with linoleic acid; it agreed with the specified values. Using the developed procedure, we estimated the concentration of hydroperoxide groups in natural cardiolipin. The results were compared to those obtained by an independent method (activated chemiluminescence).

A rapid, effective method through an orthogonal design was developed, and four lignanoids were determined by HPLC and confirmed by HPLC coupled with electrospray ionization and quadrupole timeof-flight mass spectrometry (HPLC-ESI–QTOF-MS). The roots, stems and leaves of Zanthoxylum armatum DC were extracted by methanol for 15 min under reflux. Separation was performed using an UPLC system to quantify four bioactive compounds, namely fargesin, asarinin, planispine A and planispine B, in 12 batches of samples of different origin from China. Furthermore, the samples were analyzed using HPLC-ESI–QTOF-MS to confirm the results. The calibration curves of all four analytes showed good linearity (R > 0.998). Accuracy, precision and repeatability were all within required limits. The mean recoveries measured at the three concentrations were higher than 99% with RSDs lower than 4.1%. The established HPLC-DAD method could serve as a rapid and effective method for quality evaluation of Zanthoxylum armatum DC.

A simple sample pre-treatment method for rare earth elements enrichment from environmental water samples prior to optical emission spectrometry determination with inductively coupled plasma (ICP OES) is proposed based on solid phase extraction with octadecyl silica gel modified with 1,2,5,8-tetrahydroxyanthraquinone. Optimal experimental conditions including pH of sample solution, sample volume, type, concentration and volume of eluent were investigated and established. Rare earth elements ions were quantitatively adsorbed from aqueous solution onto octadecyl silica gel modified with Quinalizarin at pH 7.0. The adsorbed ions were eluted with 1.0 mL of 2 M HNO3 and simultaneously determined by ICP OES. Under obtained optimum conditions the calibration curves were linear with the coefficient of variation better than 0.99. The limit of detection of the method for the studied elements was in the range of 0.0004–0.01 ng/mL. The proposed method has a pre-concentration factor of 320–450 in water samples, which results in high sensitivity detection of trace ions. The developed method gave recoveries better than 80% and RSDs less than 15%.

Highly sensitive procedures are proposed for the chromatographic (high-performance liquid chromatography, HPLC) and luminescence determination of trace amounts of Rosuvastatin Calcium in washings after the cleanup of pharmaceutical equipment. The developed procedures are validated for the following parameters: specificity, linearity, accuracy, detection limit, and quantification limit. The calibration curves are presented in the concentration range 0.01–1.0 µg/mL (HPLC) and 0.1–10.0 µg/mL (luminescence); the detection limits are 0.005 and 0.032 µg/mL, respectively. The efficiency of the sampling method is over 90%. It is found that the difference in the results of analysis of samples by two procedures is statistically insignificant. The luminescence procedure compared to HPLC has several advantages, i.e., lesser labor intensity, rapidity, and lesser reagent consumption; but the HPLC procedure is an order of magnitude more sensitive.

A semi-automated microextraction by packed sorbent (MEPS) method was developed for the HPLC determination of ellagic acid (EA) in juice samples. The procedure includes enrichment of the analyte on a nanoporous silica sorbent by the MEPS method using a laboratory-made programmable apparatus. Three functionalized SBA-15 nanoporous sorbents were evaluated for this purpose and 3-[bis(2-hydroxyethyl)amino]propyl-triethoxysilane (HPTES)-SBA-15 showed superior efficiency. Only 2 mg of the adsorbent packed in a syringe’s hub was sufficient for a quantitative recovery of EA. Different factors influencing the performance of the MEPS method such as the nature of desorption solvent, elution volume, pH, number of extraction cycles (draw–eject) and sample volume were carefully studied and optimized. Under the optimized conditions, a detection limit of 0.8 mg/L and a linear calibration curve with an R2 of 0.9995 were obtained for EA. The average recovery of the analyte for juice samples was 97.6% with a relative standard deviation of 4.4% for six replicates. The method was successfully applied to the HPLC determination of EA in pomegranate and grape juice samples.

A new calibration curve equation containing no empirical constants is proposed for calculating the concentration dependence of partial current in local voltammetry of heterogeneous alloys. A good agreement between the calculated and experimental data is found on an example of eutectic alloys Cd−Bi and Sn–Bi.

A sensitive and selective micelle-mediated speciation and preconcentration method has been developed for trace amount of inorganic and organic selenium prior to UV-Vis spectrophotometry determination. The method is based on cloud point extraction of Se(IV) ions with polyethylene glycol tert-octylphenyl ether (Triton X-114) in presence of 2,3-diaminonaphthalene (DAN) as a chelating agent. Se(IV) ions react with DAN in a surfactant solution yielding a hydrophobic complex at pH 3. The phase separation was accelerated by a 20 min centrifugation at 3500 rpm. The calibration graph obtained from Se(IV)-DAN complexes was linear in the concentration range of 5.0–400.0 ng/mL and detection limit was 9 ng/mL. The relative standard deviation was 1.6% in the determination of 80 ng/mL Se(IV). The proposed method was successfully applied to the speciation and determination of selenium species-Se(IV), Se(VI), selenomethionine—in walnut samples with satisfactory results.

A simple, efficient and selective sample preparation technique using low density based dispersive liquid-liquid microextraction has been developed for the analysis of nine multiresidue pesticides inculding six sulfonylurea and three organophosphorus pesticides in environmental waters by HPLC-diod array detector. Various experimental parameters affecting the extraction efficiency were investigated. Under the optimum experimental conditions, matrix-matched calibration curves were established in groundwater and good linearities were obtained with coefficient of determination (r 2) of 0.990 or better. The limits of detection and quantification were in the ranges 0.8–3.3 and 2.5–11.0 µg/L, at a signal-to-noise ratio of 3 and 10, respectively. The relative standard deviations of the precision studies were varied over the range of 0.2–13%. The proposed method was successfully applied to selective extraction of the target pesticide residues in different environmental waters and acceptable recoveries, in the range 81–121%, were obtained.