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A rapid, simple, and inexpensive spectrofluorimetric sensor has been developed for the simultaneous determination of methotrexate (MTX) and folic acid (FA) based on their interactions with hollow carbon dots (HCDs). Since the use of folic acid to cope with the toxic side effects of MTX in patients is essential, the simultaneous determination of these two compounds has been interesting. The results showed that  MTX could quench the fluorescence of HCDs with a dynamic quenching mechanism. The sensor exhibited a linear concentration range of 1.0 × 10 -6 -1.9 × 10 -4  mol L -1  for MTX and 1.5 × 10 -5 -9.4 × 10 -4  mol L -1  for FA and the obtained detection limits for MTX and FA were 1.6 × 10 -7  and 5.0 × 10 -7  mol L -1 , respectively. The applicability of the method was investigated in the analysis of the urine samples and the partial least squares (PLS) method was used for the simultaneous determination of MTX and FA., (© 2023. The Author(s), under exclusive licence to The Japan Society for Analytical Chemistry.)

This work discusses the application of a silanized fiberglass (SFG) modified by carbon dots (CDs) as an effective adsorbent for up-taking some heavy metal ions including lead (Pb 2+ ), chromium (Cr 3+ ), cadmium (Cd 2+ ), cobalt (Co 2+ ), and nickel (Ni 2+ ) as pollutant in the aqueous solution by batch method. Removal tests were carried out after optimization of pH, contact time, initial concentration of metal ions, and CDs amount. The SFG modified with CDs (CDs-SFG) was applied for the removal of 10 ppm of each metal ion solution after 100 min and the corresponding results showed the removal efficiencies of 100, 93.2, 91.8, 90, and 88.3% for Pb 2+ , Cd 2+ , Cr 3+ , Co 2+ , and Ni 2+ , respectively. The adsorption capacity of CDs-SFG in the metal ion mixed solution was also evaluated, and the results indicated the same trend in the adsorption capacity for metal ions in the mixed solution, though with lower absolute values compared to the single metal solutions. Moreover, the selectivity of this adsorbent for the adsorption of Pb 2+ was almost twice of other tested metal ions. The regeneration of the CDs-SFG showed that its adsorption capacity after five cycles was reduced about 3.9, 6.0, 6.8, 6.7, and 8.0% for Pb 2+ , Cd 2+ , Cr 3+ , Co 2+ , and Ni 2+ , respectively. Finally, the applicability of the CDs-SFG adsorbent was examined with the analysis of the metal ions in water and wastewater samples., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Two chiral stationary phases (CSPs) based on crystalline degradation products (CDPs) of vancomycin by using different synthetic methods were prepared and compared. Crystalline degradation products of vancomycin were produced by hydrolytic loss of ammonia from vancomycin molecules. Performances of two chiral columns prepared with these degradation products were investigated using several acidic and basic drugs as model analytes. Retention and resolution of these analytes on the prepared columns, as two main parameters, in enantioseparation were studied. The results demonstrated that the stationary phase preparation procedure has a significant effect on the column performance. The resolving powers of prepared columns for enantiomers resolution were changed with the variation in vancomycin-CDP coverage on the silica support. Elemental analysis was used to monitor the surface coverage of silica support by vancomycin-CDP. The results showed that both columns can be successfully applied to chiral separation studies.

A simple high-performance liquid chromatographic method for simultaneous determination of ethylenediaminetetraacetic acid (EDTA), sorbic acid, and diclofenac sodium was developed and validated. Separation was achieved on a C(18) column (10 cm×4.6 mm) using gradient elution. The mobile phase consisted of acetonitrile-ammonium dihydrogen phosphate buffer solution (0.01 M, pH=2.5, containing 0.8% tetra-n-butyl ammonium hydroxide). The detector wavelength was set at 254 nm. Under these conditions, separation of three compounds was achieved in less than 10 min. The effect of two metal salts and metal concentration on peak area of EDTA was investigated. The pH effect on retention of EDTA and sorbic acid was studied. The method showed linearity for EDTA, sorbic acid, and diclofenac in the ranges of 2.5-100.0, 5.0-200.0, and 20.0-120.0 μg/mL, respectively. The within- and between-day relative standard deviations ranged from 0.52 to 1.94%, 0.50 to 1.34%, and 0.78 to 1.67% for EDTA, sorbic acid, and diclofenac, respectively. The recovery of EDTA, sorbic acid, and diclofenac from pharmaceutical preparation ranged from 96.0-102.0%, 99.7-101.5%, to 97.0-102.5%, respectively. To the best of our knowledge, this is the first report about simultaneous determination of EDTA, sorbic acid, and diclofenac.

This study reports the feasibility of applying directly suspended liquid-phase microextraction (DSLPME)-gas chromatography detection for the pre-concentration and determination of low levels of eight polychlorinated biphenyls (PCBs) in aqueous samples. The technique requires minimal sample preparation, analysis time and solvent consumption and represents significant advantages over conventional analytical methods. The experimental parameters such as salt content, sample temperature, stirring rate, extraction time, micro-drop volume and breakthrough volume were investigated and found to have significant influences on DSLPME. Under the optimal experimental conditions, the enrichment factor ranged from 578 to 729, and the recovery was above 93 %. Calibration curves possessed good linearity (R(2) > 0.99) over a wide concentration range of 0.1-10.0 μg L(-1) with limits of detection ranging from 0.01 to 0.07 μg L(-1). The relative standard deviations for 1.0 μg L(-1) of PCBs in water by using internal standard were in the range 2-14 % (n = 3). The proposed simple, accurate and sensitive analytical method was applied successfully to the determination of trace amounts of PCBs in water samples.

Investigations on thermal behavior of drug samples such as acyclovir and zidovudine are interesting not only for obtaining stability information for their processing in pharmaceutical industry but also for predicting their shelf lives and suitable storage conditions. The present work describes thermal behaviors and decomposition kinetics of acyclovir and zidovudine in solid state, studied by some thermal analysis techniques including differential scanning calorimetry (DSC) and simultaneous thermogravimetry-differential thermal analysis (TG/DTA). TG analysis revealed that thermal degradation of the acyclovir and zidovudine is started at the temperatures of 400°C and 190°C, respectively. Meanwhile, TG-DTA analysis of acyclovir indicated that this drug melts at about 256°C. However, melting of zidovudine occurred at 142°C, which is 100°C before starting its decomposition (242°C). Different heating rates were applied to study the DSC behavior of drug samples in order to compute their thermokinetic and thermodynamic parameters by non-isothermal kinetic methods. Thermokinetic data showed that both drugs at the room temperature have slow degradation reaction rates and long shelf lives. However, acyclovir is considerably more thermally stable than zidovudine.

A novel on-line flow-injection liquid-phase microextraction (FI-LPME) and spectrophotometric determination of the Cu(2+) ion using trithia-9-crown-3 (TT9C3) as a sensitive and selective charge transfer complexing agent was developed. After phase segmentation by pulsating motions of a peristaltic pump, the phase separation takes place by the aid of gravitation forces. The optimum values of the pH (= 5 of phosphate buffer) and ionic strength (5 mM Na2SO4) of the solution, amount of ligand (2.0 × 10(-3) mol L(-1)), nature of the counter ion (10 mM SDS), volume of the organic solvent (150 μL), coil length (3 m) and extraction time (2 min) for an efficient extraction were determined. The calibration curve was found to be linear over a concentration range of 0.008 - 4.2 μg mL(-1) (R(2) = 0.9985) with a limit of detection of 0.37 ng mL(-1). The enrichment factor and relative standard deviation (n = 7) were 16 and 5.7%, respectively. Finally, the proposed method was applied to the determination of copper(II) as an impurity in the several commercial metallic salts.

A new coated ion-selective electrode for the determination of trace thorium ions by flow-injection potentiometry (FIP) has been developed. A poly(vinyl chloride) (PVC)-based membrane was coated on a graphite electrode. The optimum membrane contained 5 wt% diphosphoryl-dicarboxylicacid-p-tert-butylcalix[4]arene (L) as the ionophore, 59 wt% dioctyl phthalate (DOP), 33 wt% PVC and 3 wt% additive sodium tetraphenylborate. The response was linear from 2.0 × 10(-7) to 1.0 × 10(-2) M with a slope of 13.9 mV decade(-1) and a limit of detection of 9.0 × 10(-8) M. The pH-independent region ranged from 3.15 to 6.5, and the lifetime was longer than 8 weeks when used in the flow injection analysis (FIA) system. Selectivity coefficients for several ions were obtained by the separate solutions method. Results showed that, for all cations used, the selectivity coefficients were in the order of 10(-3), or smaller. The flow cell is simple to construct and free from memory effect problems over long periods of use. The proposed sensor was successfully applied to the direct determination of thorium in both real and synthetic samples.

A graphene-based carbon ionic liquid electrode modified with gold nanoparticles was fabricated. The electrochemical response of the modified electrode toward celecoxib was studied by means of cyclic voltammetry and differential pulse voltammetry. The structural morphology of the modified electrode was characterized by a scanning electron microscopy technique and electrochemical impedance spectroscopy. The prepared electrode showed excellent electrocatalytic activity in the reduction of celecoxib in a phosphate buffer solution, leading to remarkable enhancements in the corresponding peak currents and lowering of the peak potential. The advantages are related to the unique properties of graphene and gold nanoparticles such as a large surface area and increased electron-transfer abilities. Differential pulse voltammetry was applied to the quantitative determination. The calibration curve was linear in the concentration range of 0.5 to 15 μM and the detection limit was about 0.2 μM (Sb/N = 3). The proposed electrochemical sensor was successfully applied to the determination of celecoxib in real samples.

The degradation of some organophosphorus pesticides (OPPs) in the presence of metal ions was studied by (31)P-NMR spectroscopy. Both (31)P-NMR and gas chromatography/mass spectroscopy results were used in order to determine the nature of metabolites formed after degradation. The degraded organophosphorus pesticide were investigated for chlorpyrifos and phoxim in the presence of several metal ions including Hg(2+), Cu(2+), Cd(2+), Ni(2+), Pb(2+), and Ag(+). (31)P-NMR results indicated Ag(+) and Hg(2+) ion promoted degradation of OPPs and other metal ions formed complex with OPPs and cannot degrade OPPs. We found that the degradation of chlorpyrifos and phoxim with Ag(+) or Hg(2+) led to the formation of O,O-diethyl-O-methyl phosphorothionate, (C(2)H(5)O)(2)(CH(3)O)PS, at metal ion/pesticide mole ratios ≤1.0 and completely decomposed at a higher mole ratio of 10. Finally, the method was successfully applied to the degradation study of a number of technical and formulated pesticides in the presence of Ag(+) ion at a metal ion/pesticide mole ratio of 10.

An iodide-miconazole ion-paired complex was used as a suitable ion-exchanger for the preparation of a plasticized-PVC membrane electrode. Among different solvent mediators tested, dioctylsebacate exhibited the proper response characteristics, including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of -59.8 +/- 0.5 mV decade(-1) for I- ion over a concentration range of 1.0 x 10(-5) - 1.0 x 10(-2) M with a limit of detection of 7.0 x 10(-6) M. The electrode displays a good selectivity for I- with respect to a number of inorganic and organic species. It canbe used over a pH range of 2.5 - 8.5. The membrane sensor was successfully applied to the determination of iodide in water samples and blood serum, as well as in pharmaceutical products such as iodoquinol and thyroxin.

A rapid flotation method for separation and enrichment of ultra trace amounts of copper(II), cadmium(II), nickel(II) and cobalt(II) ions from water samples is established. At pH 6.5 and with sodium dodecylsulfate used as a foaming reagent, Cu2+, Cd2+, Ni2+ and Co2+ were separated simultaneously with 2-aminocyclopentene-1-dithiocarboxylic acid (ACDA) added to 1 l of aqueous solution. The proposed procedure of preconcentration is applied prior to the determination of these four analytes using inductivity coupled plasma-atomic emission spectrometry (ICP-AES). The effects of pH, concentration of ACDA, applicability of different surfactants and foreign ions on the separation efficiency were investigated. The preconcentration factor of the method is 1000 and the detection limits of copper(II), cadmium(II), nickel(II) and cobalt(II) ions are 0.078, 0.075, 0.072 and 0.080 ng ml(-1), respectively.

A chloroform membrane system containing a given mixture of ketoconazole and oleic acid was applied for the uphill transport of Cd2+ ions as CdI42-. In an HCl medium the ligand could form a stable ion-pair with CdI4(2-), which was readily extractable in the membrane phase. A weak basic solution (pH 8) was used as a suitable stripping medium for the quantitative transport of cadmium across the liquid membrane after 120 min. The selectivity and efficiency of Cd2+ transport from an aqueous solution containing other cations, such as Co2+, Cr3+, Ni2+, Fe2+, Mn2+, Pd2+ and Zn2+ ions, were investigated. It was found that none of these cations interfered with Cd2+ transport.

[5,10,15,20-Tetrakis(4-N,N-dimethylaminobenzene)porphyrinato]Mn(III) acetate (MnTDPAc) was applied as an ionophore for an iodide-selective PVC membrane electrode. The influences of the membrane composition, pH of the test solution and foreign ions on the electrode performance were investigated. The sensor exhibited not only excellent selectivity to iodide ion compared to Cl- and lipophilic anions such as ClO4- and salicylate, but also a Nernstian response with a slope of -59.4 +/- 1.2 mV per decade for iodide ions over a wide concentration range from 1.0 x 10(-2) to 7.5 x 10(-6) M at 25 degrees C. The potentiometric response was independent of the pH of the solution in the pH range of 2 - 8. The electrode could be used for at least 2 months without any considerable divergence in the potential. Good selectivity for iodide ion, a very short response time, simple preparation and relatively long-term stability were the silent characteristics of this electrode. It was successfully used as an indicator electrode in the potentiometric titration of iodide ions, and also in the determination of iodide from seawater samples and drug formulations.

The complexation of five recently synthesized hydroxy-thioxanthone derivatives with Al3+ ion was studied in a methanol solution spectrophotometrically, and the stepwise formation constants of the resulting 1:1 and 2:1 (ligand-to-metal) complexes were evaluated. The suitability of the thioxanthone derivatives as neutral ionophores for the preparation of a new Al3+ ion-selective PVC-membrane electrode was investigated, and 1-hydroxy-3-methyl-thiocanthone was selected as the best compound for this purpose. The prepared electrode exhibits a Nernstian response for Al3+ ions over a wide concentration range (2.0 x 10(-2) to 2.0 x 10(-6) M), with a limit of detection of 1.0 x 10(-6) M. It has a very fast response time of about 5 s and can be used for at least 3 months without any considerable divergence in the potentials. The proposed membrane sensor revealed very good selectivities for Al3+ over a wide variety of other metal ions, and could be used at a working pH range of 3.4 - 5.0. It was used as an indicator electrode in potentiometric titration of aluminum ions with EDTA, and in the determination of Al3+ in different real samples.

A 1H-NMR procedure based on an analysis of its data by a multivariate calibration method was conducted for the simultaneous determination of theophylline and caffeine in synthetic and real samples. Partial least squares regression (PLS) was chosen as the calibration method. The methyl signals of theophilline at 3.36 and 3.54 ppm that overlapped with those of caffeine were significant characteristics which were employed in this study for their analyses. The proposed method was successfully applied to recovery studies of theophylline and caffeine from real tablet samples.

Poly(vinyl chloride) (PVC) based membranes of zinc-phthalocyanine (ZPC) with hexadecyltrimethylammonium bromide (HTAB) as a cation excluder, and dibutyl phthalate (DBP) and benzyl acetate (BA) as plasticizing solvent mediators were prepared and investigated as a SO4(2-) selective electrode. The best performance was observed with a membrane having a composition of ZPC-PVC-HTAB-BA in a ratio of 5%:32%:3%:60%, which works well over a wide concentration range (1.0 x 10(-2) - 1.0 x 10(-6) M) with a Nemstian slope of -29.2 mV per decade of activity, between the pH values of 2.0 to 7.0. This sensor shows a very fast response time of 10 s, and can be used over a period of 2 months with good reproducibility. The proposed sensor displays excellent selectivity for SO4(2-) over a large number of common inorganic anions. The sensor has been successfully applied for the direct and indirect determination of sulfate and zinc in zinc sulfate tablets, respectively. It was also used as an indicator electrode in the potentiometric titration of sulfate ions with barium ions.

The construction, performance characteristics, and application of a novel polymeric membrane coated on a graphite electrode with unique selectivity towards SCN- are reported. The electrode was prepared by incorporating Ni(II)-2,2,4,9,9,11-hexamethyltetraazacyclotetradecanediene perchlorate into a plasticized poly(vinyl chloride) membrane. The influences of membrane composition, pH and foreign ions were investigated. The electrode displays a near Nernstian slope (-57.8 mV decade-1) over a wide concentration range of 1 x 10(-7)-1 x 10(-1) M of SCN- ion. The electrode has a detection limit of 4.8 x 10(-8) M (2.8 ng/cm3) SCN- and shows response times of about 15 s and 120 s for low to high and high to low concentration sequences, respectively. The proposed sensor shows high selectivity towards SCN- over several common organic and inorganic anions. The electrode revealed a great enhancement in selectivity coefficients and detection limit for SCN-, in comparison with the previously reported electrodes. It was successfully applied to the direct determination of SCN- in milk and biological samples, and as an indicator electrode in titration of Ag+ ions with thiocyanate.

New polymeric membrane (PME) and coated graphite (CGE) copper(II)-selective electrodes based on 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone were prepared. The electrodes reveal linear emf-pCu2+ responses over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M with a slope of 27.3 mV decade-1 for PME and 8.0 x 10(-8)-5.0 x 10(-2) M with a slope of 29.1 mV decade-1 for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 5.0 x 10(-8) M for CGE). The potentiometric response is independent of the pH of the test solution in the pH range 3.0-6.0. The proposed electrodes possess very good selectivities over a wide variety of other cations, including alkali, alkaline earth, transition and heavy metal ions, the selectivity coefficients for the CGE being much improved over those for the PME. The electrodes were used as indicator electrodes in the potentiometric titration of Cu2+ and in the recovery of copper ions from wastewater.

A highly selective PVC membrane electrode based on a cerium-salen complex was prepared. The sensor displays an anti-Hofmeister selectivity sequence with a preference for iodide ion over many common organic and inorganic anions. The proposed electrode exhibits a near-Nernstian behavior over a wide concentration range (5.0 x 10(-2) - 8.0 x 10(-6) M) with a slope of 57.5 mV per decade, and a detection limit of 6.0 x 10(-6) M. The electrode has a very fast response time and can be used in the pH range of 3.0 - 1 1.0. It was applied, as an indicator electrode, in potentiometric titration of Ag+ ions.

A new, simple, sensitive, low cost and rapid potentiometric method for direct determination of ultra trace amounts of sodium dodecyl sulfate (SDS) with a new DS(-)-selective electrode is reported. The electrode was prepared by electropolymerization of aniline in acidified DS- ion on the surface of a Pt electrode. The cyclic voltammetry (CV) was used for electropolymerization of polyaniline (PA) in the potential range of -200 to +1000 mV vs. Ag/AgCl. This sensor showed a Nernstian behavior (59.0 +/- 2.3 mV/decade) over a very wide linear range (1.0 x 10(-9)-3.0 x 10(-6) M) with a detection limit of 1.0 x 10(-9) M. The response time of the electrode was 15 s for 1.0 x 10(-7) M of analyte; the electrode can be used for 4 weeks without any major deviation. This electrode can be used in the pH range of 3.5-9.8. The selectivity of electrode to DS- over some organic, inorganic and anionic surfactants was investigated with the fixed primary ion method. The results show that the electrode is highly selective to DS- ion over other ions. The proposed electrode was applied to the determination of DS- in real samples.

A simple method for the rapid extraction and determination of ultra-trace amounts of Ag+ ions using octadecyl-bonded silica membrane disks modified with a recently synthesized fulvalen (tetramethyltetrathiafulvalen) (TMTTF) and graphite furnace atomic absorption spectrometry is presented. The extraction efficiency and influence of the flow rate, pH, nature of the counter ion and type and the least amount of eluent for the stripping of Ag+ from disks and breakthrough volume were evaluated. The maximum capacity of the membrane disks modified by 5 mg of TMTTF used was found to be 482 +/- 6 micrograms Ag+. The detection limit of the proposed method is 1.0 ng/dm3. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.

A PVC-membrane electrode based on a recently synthesized 18-membered macrocyclic diamide is presented. The electrode reveals a Nernstian potentiometric response for Co2+ over a wide concentration range (2.0 x 10(-6)-1.0 x 10(-2) M). The electrode has a response time of about 10 s and can be used for at least 2 months without any divergence. The proposed sensor revealed very good selectivities for Co2+ over a wide variety of other metal ions, and could be used over a wide pH range (3.0-8.0). The detection limit of the sensor is 6.0 x 10(-7) M. It was successfully applied to the direct determination and potentiometric titration of cobalt ion.

A PVC-based membrane electrode for lead ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lead concentration range from 1.0 x 10(-6) to 8.0 x 10(-3) M at 25 degrees C, and was found to be very selective, precise and usable within the pH range 3.0-6.0. The electrode was successfully used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.

A facile supported liquid membrane (SLM) system for the selective and efficient transport of silver ion is introduced. The SLM used is a thin porous polyvinyldifluoride membrane impregnated with hexathia-18-crown-6 (HT18C6) dissolved in nitrophenyloctyl ether. HT18C6 acts as a specific carrier for the uphill transport of Ag+ ion as its picrate ion paired complex through the SLM. In the presence of thiosulfate ion as a suitable stripping agent in the strip solution, transport of silver occurs almost quantitatively after 4 h. The selectivity and efficiency of silver transport from aqueous solutions containing other Mn+ cations such as Mg2+, Ca2+, Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, Hg2+, Fe3+ and Cr3+ ions were investigated.