Low-Temperature Adsorption–Luminescence Determination of Gold Using Silica Gel Chemically Modified with Mercapto Groups

Silica gel with mercaptopropyl groups covalently bonded to the surface extracts gold(III) from its hydrochloric solutions in a wide acidity range (from 6 M HCl to pH 8). An adsorption equilibrium is attained in no more than 5 min. The distribution ratio is 1.65 × 10⁴–1 × 10⁵ cm³/g. The intense yellow–orange luminescence (_max = 575 nm) appearing in the adsorbent phase under UV irradiation of wet liquid-nitrogen cooled adsorbates (77 K) is used for the low-temperature adsorption–luminescence determination of gold. The calibration plot is linear in the range of 1–100 g of gold per 0.1 g of adsorbent. The detection limit is 0.05 g/0.1 g of adsorbent. The relative standard deviation for the determination of more than 10 g of gold is no more than 5%.     

Sorption–Photometric Determination of Osmium after Its Extraction from the Gas Phase with Silica Gel Chemically Modified with Mercapto Groups

The sorption of osmium(VIII) from H₂SO₄ solutions and from the gas phase with silica gels chemically modified with mercapto or disulfide groups was studied. A procedure is proposed for the sorption–photometric determination of osmium including the oxidation of osmium, the sorption of OsO₄ from the gas phase with silica gel chemically modified with mercapto groups, and the determination of osmium in the sorbent phase by diffuse reflectance spectrometry. The detection limit is 0.5 g of Os per 0.2 g of the sorbent. The calibration plot is linear up to 700 g Os/0.2 g. The relative standard deviation in the determination of more than 15 g is no larger than 6%. The procedure was used for the determination of osmium in standard reference samples of platinum concentrates.     

Low-Temperature Sorption–Luminescence Determination of Platinum Using Silica Chemically Modified with N-Allyl-N"-Propylthiourea and N-Phenyl-N"-Propylthiourea

Silicas chemically modified with N-allyl-N"-propylthiourea and N-phenyl-N"-propylthiourea were proposed for the low-temperature sorption–luminescence determination of platinum. The sorption of platinum(II) and platinum(IV) at the surface of sorbents yields coordination compounds luminescing at 77 K under UV irradiation. Luminescence spectra of platinum(II) complexes of thiourea derivatives covalently bonded to the silica surface exhibit a broad structureless band with a maximum at 585 nm. For the sorbent with N-allyl-N"-propylthiourea groups, the detection limit of platinum is 0.1 g per 0.1 g of the sorbent. The calibration plot is linear up to 50 g/0.1 g. The detection limit and the linearity range of calibration plots depend on the mass of the sorbent. The proposed procedure was used for the analysis of aluminoplatinum catalysts.     

Thermodynamics of the Sorption of Benzimidazoles on Octadecyl Silica Gel from Water–Methanol Eluents

The standard enthalpy and entropy component of transferring benzimidazoles from water-methanol solutions to surfaces of octadecyl silica gel are determined using reversed-phase high-performance liquid chromatography (RP HPLC). The dependences between the enthalpy and polarizability of the molecules of the studied benzimidazoles, the enthalpy and the entropy factor are studied, and the influence of the quantitative composition of the water-methanol solution on the enthalpy are studied.     

Study of the Nano-Size Silica Sol–Gel Film as the Matrix of Chemically Modified Electrode

This paper reports a new method to make the sol–gel film from silicate. It provided more profitable conditions than hydrolysis of alkoxyl silane to prepare the high-quality nanometers thin film. The thin film could be applied as the matrix to directly modify the molecules of methylene blue on electrode surface and kept their electrochemical activity excellently. It exhibited the remarkable catalytic activity for the oxidation of NADH or reduction of hemoglobin while severally embedding them in the sol–gel film together with methylene blue.     

Spectrophotometric Determination of Copper in Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of copper in waste water is described. The procedure is based on the formation of an ion-pair between tetrabutylammonium and the tetrathiocyanatocuprate(II) anion. This ion-pair is extracted with chloroform, and the absorbance of the organic phase is measured at 485nm. Concentrations of copper 0.4mg L^–1 can be detected with a linear application range of between 0.5 and 25mg L^–1, a relative standard deviation of 2.3% (0.8mg L^–1, n=10) and a sampling frequency of 30h^–1. Under the proposed working conditions, only Ni(II) and Pd(II) interfere at molar ratios Ni(II)/Cu(II) 50 and Pd(II)/Cu(II) 100.     

Sorption Properties of α-Aluminum Oxide Modified with Decationized Silica Sol

The method of sorption of tetrachloromethane vapor at the solid/gas interface was applied to study the sorption and structural properties of a mesoporous aluminum oxide material obtained by deposition of amorphous hydrated silicon(IV) oxide onto -aluminum oxide particles submerged in decationized silica sol.     

Rapid—In—situ Determination of Chromium （VI） in Water Using Modified Diphenylcarbazine with Citrate

In recent years, the determination of Cr (VI) has attracted great attention because of its toxicity to human, plants and animals1-5. Usually, in the industrial waste water, the concentration of Cr (VI) is relatively high and should be determined frequently. So, an accurate, quick, and convenient method for the measurement of Cr (VI) in environmental water, as well as in river, lake, sea and tap water, is of great importance. The method for determination of Cr (VI) by diphenylcarbazine …     

Effect of Synthesis Parameters on Sol–Gel Silica Modified by Zirconia

An experimental strategy was developed to obtain mesoporous SiO₂-ZrO₂ mixed oxides via a sol–gel process, which involved the use of tetraethylorthosilicate (TEOS) and an inorganic Zr-containing salt. The effects of key process parameters on the properties of the materials were investigated, including the choice of Zr(IV) source (zirconium oxychloride or nitrate), the ZrO₂ content and the synthesis pressure (i.e. ambient pressure or hydrothermal conditions). The resulting solids were dried, calcined at 500 °C, and characterized by nitrogen physisorption, pyridine chemisorption, ²⁹Si Nuclear Magnetic Resonance and X-ray diffraction. The data revealed that mesoporous materials with very narrow pore diameter distribution were obtained when using the autoclave procedure from both zirconium nitrate and oxychloride salts. The surface areas and pore size distributions were a function of ZrO₂ content. Differences in acidity, as determined by pyridine adsorption, were observed depending on the synthesis parameters.     

Sorption–Atomic Absorption Determination of Trace Elements in Natural Waters Using Simultaneous Atomization of a Solid Concentrate and Suspended Matter

A sorption–atomic absorption technique with dynamic preconcentration on DETATA adsorbents in a microcolumn crucible followed by the direct atomization of a solid matrix (concentrate + suspended matter) was used to determine the total dissolved and suspended Cd, Pb, and Tl (El_dis+ El_susp) in natural waters. The detection limits were 1–3 ng/L for Cd and 5–30 ng/L for Pb and Tl. The results of the sorption–filtration atomic absorption determination of the total dissolved and suspended elements can provide extra information for the speciation analysis of waters.     

Sorption–Spectrometric Determination of Palladium in Chloride Solutions

A sorption–spectrometric method was developed for the determination of palladium in solutions of complex composition using cellulose filters impregnated with trioctylamine with the subsequent formation of the colored compound of palladium with 4-(2-pyridylazo)resorcinol on the filter. It was demonstrated that conditions for the preconcentration of palladium coincide with conditions for the formation of colored compounds (green and red forms of palladium complexes) in the sorbent phase. The highest selectivity is observed for the formation of the green form; in this case, the determination of palladium is not affected by the interference from large amounts of concomitant elements (macrocomponents of ores). Palladium was determined on filters by diffuse reflectance spectrometry with the calculation of chromaticity characteristics and by a test scale. The detection limits were 0.5 (green form) and 0.3 (red form) g of palladium on the filter. High precision of results of the determination of palladium (RSD < 5%) is attained in a wide range of its concentrations.     

Determination of Volatiles in Water Lily Flowers Using Gas Chromatography–Mass Spectrometry

Volatile organic compounds in the stamens, petals, and pistils of 56 water lily cultivars were determined by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. The stamens released a majority of the volatiles. A total of 117 volatile organic compounds were determined. Alkanes and alkenes were the most abundant, followed by aldehydes and ketones. Cluster analysis was used to divide the cultivars into three subsets characterized by specific aromatic compounds and associated aromas. Discriminant analysis confirmed the results of the cluster analysis. Three tropical water lily cultivars Colorata, 34, and Ai Ji Bai and one hardy water lily cultivar Somptuosa had particularly high aromatic compound concentrations and are recommended to produce fragrant, colorful, and hardy specimens.     

Anodic Stripping Voltammetric Determination of Mercury in Water Using a Chitosan‐Modified Carbon Paste Electrode

Abstract

This paper describes the preparation and electrochemical application of a modified carbon paste electrode with chitosan for the determination of Hg(II) ions in water using anodic stripping voltammetry. Experimental parameters, including the pH of the supporting electrolyte, time and potential of accumulation and scan rate were investigated. The best voltammetric response was observed for a paste composition of 60% (m/m) of graphite powder, 20% (m/m) of chitosan and 20% (m/m) of mineral oil, with 0.1 mol/l NaNO₃ solution at pH 6.3 as supporting electrolyte, a preconcentration potential of ?0.2 V, preconcentration time of 270 s and a scan rate of 25 mV/s. Under these optimal experimental conditions, the voltammetric signals were linearly dependent on the Hg(II) concentration in the range of 9.99×10^?7 to 3.85×10^?5 mol/l with a detection limit of 6.28×10^?7 mol/l. Three “spiked” samples of water were evaluated using the proposed sensor, and results agreed with those obtained by a reference method at the 95% confidence level.     

Preconcentration and Determination of Copper（Ⅱ） Using Octadecyl Silica Membrane Disks Modified by 1,5-Diphenylcarhazide and Flame Atomic Absorption Spectrometry

A simple and reproducible method for the rapid extraction and determination of trace amounts of copper（Ⅱ） ions using octadecyl-bonded silica membrane disks modified by 1,5-diphenylcarbazide （DPC） and atomic absorption spectrometry was presented, which was based on complex formation on the surface of the ENVI-18 DISK^TM disks followed by stripping of the retained species by minimum amounts of appropriate organic solvents. The elution was efficient and quantitative. The effect of potential interfering ions, pH, ligand amount, stripping solvent, and sample flow rate were also investigated. Under the optimal experimental conditions, the break-through volume was found to be about 1000 mL providing a preconcentration factor of 400. The maximum capacity of the disks was found to be （255±5） lag for Cu^2＋, and the limit of detection of the proposed method was 5 ng per 1000 mL. The method was applied to the extraction and recovery of copper in different water samples.     

Flow-Injection Determination of Trace Antimony in Natural Waters with Extraction–Chromatographic Preconcentration

A procedure was developed for the flow-injection spectrophotometric determination of trace antimony in natural waters. The flow extraction preconcentration step involved the extraction of antimony(V) complex associates with basic dyes in an extraction–chromatographic column and the chromatomembrane separation of the extract from the aqueous phase. The detection limit was 1 g/L for a 20-mL sample using a (1 : 5) methyl isobutyl ketone–carbon tetrachloride mixture as an extractant.     

A Gas Chromatographic Analysis of Light Hydrocarbons on a Column Packed with Modified Silica Gel

IntroductionAnalysis of light hydrocarbons achieved by gas-solid chromatography is important in petrochemical industry, environmental protection and some other areas. A variety of columns have been used, including conventional packed column1, Al2O3 and graphitized carbon black PLOT column2, 3 and silica gel SCOT column4. Al2O3 PLOT column is excellent for the analysis of light hydrocarbons. Conventional packed column also has its own advantages, such as easy column preparation, resistanc…     

Determination of Chromate Ion in Water Using High Performance Capillary Electrophoresis

ThereisarapidIyincreasingdemandforfastandreliableanalyticaImethodsforthedeterminationofchemicaIformsofelementSinenvironmentalsamples.IthaslongbeenknownthatCrfIII)isessentialformammals,however,CrfVI)isconsideredtobeatoxicagent[l].Theanalysisofchromateion(Vl)inenvironmentwaterisusuallyperformedbyusingspephotometryandatomicabsorption,p..tr...ny[2].TheformerneedsfairIylargeamountofsample,pretreatmenLandlonganalysistime.Thelaterequipmentismuchmoreexpensive.InpreviousreportS,chromateisnormaI1…     

Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503nm (for Ph₄As⁺) or 475nm (for But₄N⁺). Iron concentrations higher than 0.9×10^–6molL^–1 (50µgL^–1) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application rangeof between 1.34 and 54.0×10^–6molL^–1 (75–3015µgL^–1), and a sampling frequency of 30h^–1. For the ion pair with But₄N⁺, the detection limit is 0.52×10^–6molL^–1 (29µgL^–1), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10^–6molL^–1. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.     

Determination of Nicotine in Dried Mushrooms by Using a Modified QuEChERS Approach and GC–MS–MS

Levels of nicotine higher than the maximum residue level were detected in edible mushrooms. Analyses of self-collected and purchased dried mushrooms were performed with a QuEChERS approach. A small amount (2.5 g) of dried sample matrix was mixed with 5 mL sodium hydroxide solution, 2.5 g of sodium sulfate/sodium chloride mixture (4:1) and 5 mL ethyl acetate. The organic phase was cleaned by using dispersive solid-phase extraction and analysed by GC–MS–MS. The linear range of the method was 0.01–10.00 mg kg^?1 and the limit of detection 0.006 mg kg^?1 on dry weight basis by using EURACHEM method.