Separation and Determination of Phenolcarboxylic Acids by Capillary Zone Electrophoresis with Dynamic Preconcentration on Hypercrosslinked Polystyrene

The sorption of phenolcarboxylic acids in the batch and dynamic modes on MN-200 hypercrosslinked polystyrene was studied. Conditions of the separation of phenolcarboxylic acids by capillary zone electrophoresis were optimized. The time of the analysis of a ten-component mixture including salicylic, 4-hydroxybenzoic, -resorcylic, protocatechuic, gallic, syringic, caffeic, ferulic, benzoic, and cinnamic acids is no longer than 15 min. A procedure is described for the dynamic group preconcentration of phenolcarboxylic acids on a microcolumn filled with MN-200 and the subsequent determination of individual compounds in the eluate by capillary zone electrophoresis; performance characteristics are presented.     

Sorption of caffeine and theophylline on hypercrosslinked polystyrene

The sorption of caffeine and theophylline from water solutions on hypercrosslinked polystyrene MN-200 was studied. It is shown that sorption is described by the Langmuir equation. The conditions of the dynamic sorption concentration of caffeine and theophylline on a concentrating column and the conditions of its desorption were found. A procedure for spectrophotometric determination of caffeine and theophylline with a dynamic preconcentration is proposed.     

Synchronous fluorescence for simultaneous determination of hydroquinone and resorcinol in air samples

Several phenolic compounds are present in tobacco smoke. They are formed from the pyrolysis of tobacco during the smoking process and all of them are toxic. Therefore, the determination of these compounds in air samples is important. A rapid, simple, and sensitive method using a synchronous spectrofluorimetry technique was developed to quantify hydroquinone and resorcinol simultaneously. One of the advantages of this method is the simple and rapid sampling technique, which uses water as the absorption solution of the analytes in the air sample. The precision of the method (%RSD) was 1.8% and the detection limits were 0.125 mg m^–3 and 0.292 mg m^–3 for hydroquinone and resorcinol, respectively.     

Determination of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts by electrothermal atomic absorption spectrometry after preconcentration by column solid phase extraction

Methods are described for the determination of trace and ultra trace amounts of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts. Separation and preconcentration of trace metals is achieved by a column solid phase extraction procedure using silica gel modified with derivatives of dithiocarbamates — Na-DDTC (sodium diethyldithio-carbamate and HMDTC (ammonium hexamethylene-dithiocarbamate) as column packing material. The influence of the sorbent preparation procedure on the degree of sorption of the trace analytes is examined for different pH values of the sample solution. Isobutylmethyl ketone (IBMK) is proposed as an effective eluent for quantitative elution of retained metal ions. Optimal instrumental parameters for ETAAS determination of preconcentrated elements in organic eluate are presented. Practical application of sorbents in analysis of natural waters and alkali and alkaline earth salts is demonstrated. Proposed preconcentration procedure combined with ETAAS determination of trace analytes allows the determination of 0.04 g l^–1 Cd, 0.1 g l^–1 Cr, Cu, and Mn and 0.3 g l^–1 Co, Fe, Ni and Pb in natural waters and 1.10^–7% Cd, 3.10^–7% Cr and Mn, 7.10^–7% Co, Ni and Pb and 2.10^–6% Cu and Fe in alkali and alkaline earth salts.     

Comparison of adsorbents for the preconcentration of sulfanilamides from aqueous solutions prior to HPLC determination

We studied the adsorption of sulfanilamide, sulfamethazine, sulfamethoxazole, sulfamethoxypyridazine, and sulfachloropyridazine on hypercrosslinked polystyrene, polymer adsorbents Strata-X and Strata SDB-L, carbon nanomaterial Taunit, and Diasorb-100-C₁₆T depending on the acidity of the solution and the concentration of adsorbates. Conditions were optimized for the preconcentration of sulfanilamides on a microcolumn packed with hypercrosslinked polystyrene. The compounds were desorbed with 1 mL of acetonitrile and determined in the eluate by reversed-phase HPLC with spectrophotometric detection at 255 nm. The preconcentration step decreases the detection limits for sulfanilamides by more than 60 times (to 3 ng/mL). The procedure was used for the analysis of a model mixture in river water.     

On-Line Sorption–Chromatographic Determination of Phenols with Amperometric Detection

Conditions of the preconcentration of phenol on a microcolumn filled with MN-200 hypercrosslinked polystyrene were determined using the linear sorption dynamics model. Conditions of the on-line determination of phenol and its chloro derivatives by reversed-phase high-performance liquid chromatography with amperometric detection were optimized. The detection limit of phenol and chlorophenols for preconcentration from 30 mL of a sample was 3 and 15 ng/L, respectively. The proposed procedure was used for the determination of phenols in tap and river water.     

Flow injection chemiluminescence analysis of phenolic compounds using the NCS-luminol system

A flow injection system coupled with two simple and sensitive chemiluminescence (CL) methods is described for the determination of some phenolic compounds. The methods are based on the inhibition effects of the investigated phenols on the CL signal intensities of N-chlorosuccinimide-KI-luminol (NCS-KI-luminol) and NCS-luminol systems. The influences of the chemical and hydrodynamic parameters on the decrease in CL signal intensities of NCS-KI-luminol and NCS-luminol systems for hydroquinone, catechol, and resorcinol, serving as the model compounds of analyte, were studied in the flow injection mode of analysis. Under the selected conditions, the proposed CL systems were used for the determination of some phenolic compound and analytical characteristics of the systems including calibration equation, correlation coefficient, linear dynamic range, limit of detection, and sample throughput. The limits of detection for hydroquinone, catechol, and resorcinol were 0.002, 0.01, and 0.3 μM using the NCS-KI-luminol system; for the NCS-luminol system these were 0.01, 0.17, and 1.6 μM, respectively. The relative standard deviation for 10 repeated measurements of 0.04, 0.06, and 1 μM of hydroquinone, catechol, and resorcinol were 1.9, 1.4, and 2.0%, respectively, with the NCS-KI-luminol system; for 0.2, 0.5, and 4 μM of hydroquinone, catechol, and resorcinol these were 2.6, 2.2, and 3.7%, respectively, using the NCS-luminol system. The method was applied to the determination of catechol in known environmental water samples with a relative error of less than 6%. A possible reaction mechanism of the proposed CL system is discussed briefly.      

Voltammetric determination of pyrocatechol at a mechanically renewed electrode made of a graphite-epoxy composite

The reversibility of a two-electron pyrocatechol/o-benzoquinone system (ΔE _p = 28 ± 1 mV) is found by cyclic voltammetry at a mechanically renewed electrode from a graphite-epoxy composite. The closeness of the found and theoretical values of ΔE _p indicates the high electrochemical activity of the graphite-epoxy composite electrode renewed in situ by cutting a thin surface layer. The potentials of pyrocatechol anodic and cathodic peaks are proportional to E ₀ ± 0.059pH in the pH range of 1–9. The pyrocatechol anodic and cathodic peak currents remain linear functions of pyrocatechol concentration in the concentration range from 0.01 to 0.08 and from 0.08 to 0.9 g/L, respectively. A procedure for the voltammetric determination of pyrocatechol in its individual solutions and in the presence of hydroquinone is proposed. Good precision and the absence of a systematic error in the determination of pyrocatechol by measuring its cathodic peak are demonstrated.     

Oxidation of organic substances by tervalent manganese compounds : VIII. Determination of benzene polyhydroxy and aminohydroxy derivatives with a standard solution of hexaquomanganese(III) ion in perchloric acid

The reaction of hexaquomanganese(III) ion with hydroquinone, p-aminophenol, metol, pyrocatechol, resorcinol, and phloroglucinol was studied. It has been found that the first three substances are oxidized quantitatively with the exchange of two electrons to the corresponding quinone compounds and that this reaction can be employed for direct or indirect titrimetric determination of these substances. On the other hand, pyrocatechol, resorcinol, and phloroglucinol are oxidized nonstoichiometrically with a deeper destruction of the aromatic system, which prevents analytical use of these reactions.     

Testing and Determination of Iron(II, III) as an Adsorbate of Iron(II) Phenanthrolinate by Chromaticity Measurements

It was demonstrated that cation exchangers of different nature can be used for the sorption preconcentration of iron(II) as phenanthrolinate and its determination in the adsorbent phase by diffuse reflectance spectrometry and chromaticity measurements. A procedure was developed for the determination of iron in solutions with a detection limit of 2.5 g/L. A scale was proposed for the visual determination of iron(II) at concentrations down to 0.4 g/L. The test procedure was verified using water samples from the Severnaya Dvina estuary and Dvinskii Bay taken during the summer and winter periods in 2000–2001.     

Adsorption–Spectrophotometric Determination of Rhenium from Reflectance Spectra of Its Complexes on a PAN–AV-17 Adsorbent

A simple and sensitive procedure for determining rhenium in 500-mL water samples with a detection limit of 0.2 g/L was developed. The analysis took 15–20 min. The procedure was based on the dynamic preconcentration of perrhenate ions from neutral or weakly acidic solutions on disks made of a poly(acrylonitrile) (PAN) fiber and filled with an AV-17 ion exchanger (PAN–AV-17 adsorbent). After preconcentration, rhenium was determined at 420 nm from diffuse reflectance spectra of a colored thiocyanate complex that was obtained on treating the disks with a hydrochloric acid solution of potassium thiocyanate and tin(II). The procedure was tested in analyses of lake water and can be used in field conditions.     

Use of Silica Gel Chemically Modified with Mercapto Groups for the Extraction, Preconcentration, and Spectroscopic Determination of Palladium

Silica gel chemically modified with mercaptopropyl groups is proposed for the extraction and preconcentration of palladium. This silica gel extracts palladium(II) at an acidity from 6M HCl to pH 4 with distribution ratios at a level of n× 10⁴ g/cm³. Hyphenated procedures for the adsorption–photometric determination of palladium with detection limits of 0.1 g/0.1 g of the adsorbent have been developed. The procedure includes the adsorption preconcentration of palladium, elution by hot (50 ± 5°C) 8% thiourea in 1M HCl, and atomic absorption determination of palladium in the eluate (detection limit is 0.05 g/mL). The procedures were applied to the determination of palladium in standard reference samples of copper–nickel ore and copper concentrate.     

Conformational analysis of benzenediols: pyrocatechol,resorcinol and hydroquinone

Molecular orbital calculations are carried out for pyrocatechol, resorcinol and hydroquinone. The structural parameters, stable conformations, potential barrier heights, dipole moments and charges for these molecules are discussed. Only one stable isomer for pyrocatechol, three for resorcinol and two for hydroquinone are established.     

Monodisperse silica nanoparticles coated with gold nanoparticles as a sorbent for the extraction of phenol and dihydroxybenzenes from water samples based on dispersive micro‐solid‐phase extraction: Response surface methodology

A selective and sensitive method was developed based on dispersive micro‐solid‐phase extraction for the extraction of hydroquinone, resorcinol, pyrocatechol and phenol from water samples prior to high‐performance liquid chromatography with UV detection. SiO₂, SiO₂@MPTES, and SiO₂@MPTES@Au nanoparticles (MPTES = 3‐mercaptopropyltriethoxysilane) were synthesized and characterized by scanning electronic microscopy, thermogravimetric analysis, differential thermogravimetric analysis, and infrared spectroscopy. Variables such as the amount of sorbent (mg), pH and ionic strength of sample the solution, the volume of eluent solvent (μL), vortex and ultrasonic times (min) were investigated by Plackett–Burman design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under optimized conditions, the calibration graphs of phenol and dihydroxybenzenes were linear in a concentration range of 1–500 μg/L, and with correlation coefficients more than 0.995. The limits of detection for hydroquinone, resorcinol, pyrocatechol, and phenol were 0.54, 0.58, 0.46, and 1.24 μg/L, and the limits of quantification were 1.81, 1.93, 1.54, and 4.23 μg/L, respectively. This procedure was successfully employed to determine target analytes in spiked water samples; the relative mean recoveries ranged from 93.5 to 98.9%.     

Liquid chromatography of phenolic compounds in natural water using on-line trace enrichment

Summary Two packing materials, C18 and PLRP-S, are studied for on-line trace enrichment of phenolic compounds in water. Various precolumns of different internal diameter are also tested and the addition of an ion-pair reagent to increase retention and thus, breakthrough volumes of phenolic compounds, is studied. Best results are obtained when a PLRP-S precolumn is coupled on-line with a C18 analytical column and DAD detector. Addition of TBA considerably increases breakthrough volumes. In contrast, when a C18 precolumn is used, breakthrough volumes are lower and it is impossible to determine TCP and PCP, under the experimental conditions used, because of interference of other nonpolar compounds in the samples. The performance of the system is evaluated with river and tap water and the preconcentration of 10 ml of sample in a PLRP-S precolumn involves a linear range between 1 g 1^–1 and 20 l^–1 and limits of determination between 0.5 g l^–1 and 1 g l^–1 are obtained.     

Reductive coprecipitation and extraction as separation methods for the determination of gold in copper concentrates by AAS and ICP-AES

Summary Simple methods for the determination of gold in copper concentrates are presented. Two separation procedures for gold are proposed. The first preconcentration procedure is based on the reductive coprecipitation of Au using part of the matrix copper as collector. The second implies selective quantitative extraction of Au using the extraction system 0.2 mol/l HCl/IBMK. Flame AAS or ICP-AES are used as instrumental methods and permit the determination of 0.1–50 g/g gold with a relative standard deviation of 3–12%.     

Ideal gas thermodynamic properties of benzenediols: Pyrocatechol, resorcinol and hydroquinone

The vibrational fundamentals have been selected using the available literature data. −271.96, −274.89 and −261.71 kJ mole⁻¹ are selected for the enthalpies of formation (g, 298.15 K) for pyrocatechol, resorcinol and hydroquinone, respectively. The ideal gas thermodynamic properties are obtained assuming one, three and two rotational isomers for 1,2-, 1,3-, and 1,4-benzenediol, respectively.     

纤维素纤维接枝β-环糊精对苯二酚类分子的包络识别性能

用分光光度滴定法在不同温度、不同pH值条件下测定了纤维素纤维接枝β-环糊精与苯二酚类分子形成超分子包合物的表观热力学参数. 化学计量法表明, 纤维素纤维接枝β-环糊精上环糊精与客体苯二酚类分子形成了1∶1的超分子包合物. 从主-客体间包合物的表观热力学参数、尺寸关系、溶液pH值、包合时间等因素讨论了纤维上环糊精对客体苯二酚类分子的分子识别机制. 结果表明, 纤维素纤维接枝β-环糊精上环糊精对苯二酚类分子不同位置羟基具有分子选择性和识别能力.     

Indirect Kinetic–Spectrophotometric Determination of Resorcinol, Catechol, and Hydroquinone

A rapid, simple, and sensitive method for the determination of trace amounts of resorcinol, catechol, and hydroquinone in aqueous media has been proposed. The method is based on their reaction with nitrite. The excess nitrite is then determined by a kinetic method based on its reaction with Neutral Red. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance at 530 nm by a fixed time method. Resorcinol, catechol, and hydroquinone could be determined by the proposed method in the ranges of 0.1–2.0 mg/mL, 0.25–2.0 mg/mL and 0.1–3.0 mg/mL, respectively. The method was applied to the determination of resorcinol and catechol in pharmaceutical formulations with satisfactory results.     

Gas Chromatographic Determination of Diacetylmorphine with Mass Spectrometric Detection

The possibility of determining diacetylmorphine traces in various matrices by gas chromatography with mass spectrometric detection is demonstrated. Diacetylmorphine can be reliably determined by gas chromatography–mass spectrometry in the range 0.02–7.5 g/mL. A procedure is developed for the quantitative determination of diacetylmorphine and its concomitants, including acetylated opioid derivatives, in forensic samples. The detection limit for diacetylmorphine without preconcentration is 0.01 g/mL. The detection limit in the selective-ion monitoring mode with preconcentration is 1 × 10^–4 g/mL.