Determination of low thiourea concentrations in industrial process water and natural samples using reversed-phase high-performance liquid chromatography.

A rapid LC method was developed to determine thiourea in natural samples and freshly prepared as well as used tin-baths from the galvanic industry, with LC on a C18-bonded silica column and with doubly distilled water as eluent. The retention time of thiourea is 1.35 min +/- 5%. UV detection is at 236 nm. Small sample volumes of 10-50 microl allow detection down to 2 microg/l thiourea without any interference by heavy metals or organic compounds and in the case of marine samples by mineral salts. The presented technique should be highly useful for industrial purposes.     

Regularities in the Sorption Recovery of Osmium in Various Oxidation States (VIII, VI, and IV) on Silica Chemically Modified with Thiourea Derivatives

Regularities in the sorption recovery of osmium(VIII, VI, IV) on silica chemically modified with thiourea derivatives (N-allyl-N"-propylthiourea (ATUS), N-phenyl-N"-propylthiourea (PTUS), and N-benzoyl-N"-propylthiourea (BTUS)) were studied. The equilibrium attainment time for the solid-phase extraction of osmium(VIII) is 15, 30, and 40 min for ATUS, PTUS, and BTUS, respectively. For the solid-phase extraction of osmium(VI), equilibrium attainment time is independent of the type of the sorbent and is no more than 5 min. The recovery of osmium(IV) at 95°C and equilibration time 120 min is no higher than 5%. The quantitative recovery of osmium(IV) with silica chemically modified with thiourea derivatives is attained on long-term heating and in the presence of tin(II) chloride. Based on the regularities in the sorption recovery of osmium in different oxidation states and its interaction with thiourea in aqueous solutions with low mole ratios, it was suggested that osmium(VIII, VI) and osmium(IV) interact with thiourea and its derivatives including those covalently bonded to the silica surface via different mechanisms.     

Influence of the pressure on the properties of chromatographic columns .III. retention volume of thiourea, hold-up volume, and compressibility of the C18-bonded layer

The influence of the average column pressure (ACP) on the elution volume of thiourea was measured on two RPLC columns, packed with Resolve-C18 (surface coverage 2.45 micromol/m2) and Symmetry-C18 (surface coverage 3.18 micromol/m2), and it was compared to that measured under the same conditions on an underivatized silica (Resolve). Five different methanol-water mixtures (20, 40, 60, 80 and 100% methanol, v/v) were used. Once corrected for the compressibility of the mobile phase, the data show that the elution volume of thiourea increases between 3 and 7% on the C18-bonded columns when the ACP increases from 50 to 350 bar, depending on the methanol content of the eluent. No such increase is observed on the underivatized Resolve silica column. This increase is too large to be ascribed to the compressibility of the stationary phase (silica + C18 bonded chains) which accounts for less than 5% of the variation of the retention factor. It is shown that the reason for this effect is of thermodynamic origin, the difference between the partial molar volume of the solute in the stationary and the mobile phase, Delta V, controlling the retention volume of thiourea. While Delta V is nearly constant for all mobile phase compositions on Resolve silica (with Delta V approximately equal to -4 mL/mol), on RPLC phases, it significantly increases with increasing methanol content, particularly above 60% methanol. It varies between -5 mL/mol and -17 mL/mol on Resolve-C18 and between -9 mL/mol and -25 mL/mol on Symmetry-C18. The difference in surface coverage between these two RP-HPLC stationary phases increases the values of Delta V by about 5 mL/mol.     

1-Allyl-3-propylthiourea modified mesoporous silica for mercury removal

1-Allyl-3-propylthiourea modified mesoporous silica has high adsorption capacity for mercury ions and its regeneration can be accomplished by washing with 10% thiourea in aqueous 0.05 M HCl.     

Silica modified with a thiourea derivative as a new stationary phase for hydrophilic interaction liquid chromatography

Nowadays there are limited types of commercially available stationary phases for hydrophilic interaction liquid chromatography and therefore new ones with unique selectivity are urgently in demand to meet the need of separations of various polar and hydrophilic analytes. The present study describes the preparation and evaluation of a new stationary phase based on thiourea derivative modified silica for hydrophilic interaction liquid chromatography. Thiourea derivative was bonded onto the surface of silica particles via a mild addition reaction between –NH₂ and –SCN, and the result of elemental analysis together with infrared analysis and solid‐state NMR spectroscopy proved that the synthesis method was feasible. The new stationary phase succeeded in fast separations of a wide range of polar and hydrophilic analytes and exhibited excellent separation performance, especially unique selectivity. Furthermore, the effects of water content, buffer pH, and salt concentration on retention indicated that a complicated separation mechanism rather than partitioning was involved in the stationary phase and hydrogen bonding interaction between analytes and thiourea functional group could play a very important role in its selectivity. For sure, the new stationary phase is of a great potential as a new type of hydrophilic interaction liquid chromatographic stationary phase.     

毛细管硅胶基质整体柱的制备及其电色谱性能研究

采用热引发一步法制备了毛细管电色谱硅胶基质整体柱。通过使用表面活性剂(十二烷基磺酸钠)增加了反应液中两相之间的相互溶解,使得反应液最终成为均相溶液,实现了硅胶整体柱的均相聚合制备。所制备的均相硅胶整体柱内部结构更加均匀,大大提高了分离度。评价了该整体柱的电色谱性能,深入探讨了有机溶剂比例、pH值、电压以及温度等电色谱操作条件对电渗流、保留机理和柱效的影响。在该均相硅胶基质整体柱上成功地分离了9种中性物质(硫脲、苯、甲苯、乙基苯、正丙苯、萘、正丁基苯、芴和蒽)以及7种中性、酸性和碱性物质(硫脲、邻氨基酚、苯酚、苯、邻甲苯胺、α-萘胺和2,4-二氯苯胺)。该柱对硫脲的柱效超过110000塔板/m。     

Dynamic Adsorption and Desorption Behaviors of Cu(II), Ag(I), and Au(III) on Silica Gel Microspheres Encapsulated by Salicylic Acid–Functionalized Polystyrene

Composite material silica gel microspheres encapsulated by salicylic acid functionalized polystyrene(SG–PS–azo–SA) have been synthesized, and the dynamic adsorption and desorption properties of this silica gel matrix inorganic–organic composite material for Cu(II), Ag(I), and Au(III) have been investigated. The results displayed that SG–PS–azo–SA had excellent adsorption for Cu(II), and the film diffusion dominated the adsorption process of SG–PS–azo–SA for Cu(II), Ag(I), and Au(III). These metal ions could be desorbed with the eluent solution of 2.5 mol/L HCl, 3% thiourea in 0.5 mol/L HCl, and 0.5% thiourea in 1 mol/L HCl, respectively. When the elution was carried out for 30 min, 30 min, and 132 min, the desorption ratio ω could reach 91.1%, 99.4%, and 60.84%, respectively. Thus, silica gel encapsulated by polystyrene coupled with salicylic acid (SG–PS–azo–SA) is favorable and useful for the removal of metal ions Cu(II), Ag(I), and Au(III), and the high adsorption capacity make it a promising candidate material for the metal ions removal.     

Dependence of mechanical and aging properties of chloroprene rubber on silica and ethylene thiourea loadings

The interaction between precipitated silica and chloroprene rubber (CR) was investigated using a nuclear magnetic resonance (NMR) technique. The results reveal that the silanol groups on silica surface could chemically react with CR. Crosslinking of CR is therefore possible in the presence of silica at high temperature. The effects of silica and ethylene thiourea (ETU) loadings on properties of the silica-filled CR were thereafter investigated. With increasing silica loading, the compound viscosity increases considerably due to the dilution effect. As silica could act as a curative for CR, increasing silica loading results in both faster cure rate and increased crosslink density. The optimum tensile strength is found at approximately 30 phr of silica loading. The results also show that silica loading has little effect on most aging properties, except the relative modulus in which it increases rapidly with increasing silica loading due to the post curing effect. Similar to the effect of silica loading, the compound viscosity, cure rate and crosslink density are all increased with increasing ETU loading. The tensile strength is, on the other hand, slightly affected by ETU loading. Exception is found at high loading where the tensile strength drops noticeably. Interestingly, aging resistance of the vulcanizate is found to improve with the addition of ETU. Explanation is given by the hindrance capability of ETU to post curing.     

A Green Protocol for the Easy Synthesis of Thiiranes from Epoxides Using Thiourea/Silica Gel in the Absence of Solvent

The use of thiourea/silica gel provides a green protocol for the easy and high-yielding preparation of thiiranes from different classes of epoxides in the absence of solvent at room temperature. The high stereospecific conversion of (R)(+)-styrene oxide to (S)(+)-styrene sulfide is also reported using this reagent system.     

Influence of the pressure on the properties of chromatographic columns. I. Measurement of the compressibility of methanol-water mixtures on a mesoporous silica adsorbent

The compressibilities of aqueous solutions of methanol or acetonitrile containing 0, 20, 40, 60, 80 and 100% (v/v) organic solvent were measured with a dynamic chromatographic method. The elution volumes of thiourea samples (2 microL) in these solutions were measured at different average column pressures, adjusted by placing suitable capillary restrictors on-line, after the detector. The reproducibility of the measurements was better than 0.2%. In the range of average pressures studied (10-350 bar), the maximum change in elution volume of thiourea is 1.3% (in pure water) and 4.0% (in pure methanol). This difference is due to the different compressibilities of these pure solvents. For mixtures, the plots of the elution volume of thiourea versus the pressure are convex downward, which is inconsistent with the opposite curvature predicted by the classical Tait model of liquid compressibility. This difference is explained by the variation of the amount of thiourea adsorbed with the pressure. The deconvolution of the two effects, adsorption of thiourea and solvent compressibility, allows a fair and consistent determination of the compressibilities of the methanol-water mixtures. A column packed with non-porous silica particles was also used to determine the compressibility of methanol-water and acetonitrile-water mixtures. A negative deviation by respect to ideal behavior was observed.     

An electroosmotic pump for packed capillary liquid chromatography

An electroosmotic pump (EOP) capable of generating pressure above 3 MPa and μl/min flow rate with reverse phase mobile phases of HPLC was constructed and evaluated. The pump consisted of three parallel connected fused silica capillary columns (25 cm×320 μm I.D.) packed with 2 μm silica materials, hollow electrodes, a high voltage DC power supply, and a liquid pressure transducer. The EOP was applied in a capillary liquid chromatographic system for mobile phase delivery instead of a mechanical pump. Standard samples containing thiourea, naphthalene, anthracene, phenanthrene and acetonitrile were separated on a 15 cm×320 μm I.D. 5 μm Chromasil C₁₈ packed capillary column with acetonitrile/water as mobile phase.     

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2-aminoethyl methacrylate unit in the 4,7-positions of the BD core. Concerted charge transfer in this electron donor-acceptor-donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron-rich carboxylate guests at the thiourea receptor leads to further analyte-induced red-shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1–5×10⁵ M⁻¹ in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP-coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.     

Investigation of the novel mixed-mode stationary phase for capillary electrochromatography. I. Preparation and characterization of sulfonated naphthalimido-modified silyl silica gel

A novel packing material, 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP), was prepared for the use as a stationary phase of capillary electrochromatography (CEC). The sulfonic acid groups on SNAIP stationary phase contributed to the generation of electroosmotic flow (EOF) at low pH and served as a strong cation-exchanger. In CEC with SNAIP, a mixed-mode separation was predicted, comprising hydrophobic and electrostatic interactions as well as electrophoretic migration process. In order to understand the retention mechanism on SNAIP, effects of buffer pH, concentration, and mobile phase composition on EOF mobility and the retention factors of barbiturates and benzodiazepines were systematically investigated. Moreover, the retention behavior of barbiturates on SNAIP was investigated and compared with those on octadecyl silica (ODS), phenyl-bonded silica, and 3-(1,8-naphthalimido)propyl-modified silyl silica gel to confirm the presence of pi-pi interaction on its retention mechanism. It was observed that a column efficiency was more than 85,000 N/m for retained compounds and the relative standard deviations for the retention times of EOF marker, thiourea, and five barbiturates were below 2.5% (n = 4). Under an applied voltage of 20 kV and a mobile phase consisted of 5 mM phosphate (pH 3.8) and 40% methanol, the baseline separation of five barbiturates was achieved within 3 min.     

Three Component Reaction: An Efficient Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Thiones Using Heterogeneous Catalyst

Fluoroboric acid supported on silica gel (HBF₄‐SiO₂) catalyzes efficiently the three component condensation of an aldehyde, a 1,3‐dicarbonyl compound and urea or thiourea to afford the corresponding 3,4‐dihydropyrimidin‐ 2(1H)‐ones and thiones in high yields. The ambient conditions, fast reaction rates, and excellent product yields are the important characteristics of this reaction.     

Large-pore mesoporous SBA-15 silica particles with submicrometer size as stationary phases for high-speed CEC separation

A new mesoporous sphere-like SBA-15 silica was synthesized and evaluated in terms of its suitability as stationary phases for CEC. The unique and attractive properties of the silica particle are its submicrometer particle size of 400 nm and highly ordered cylindrical mesopores with uniform pore size of 12 nm running along the same direction. The bare silica particles with submicrometer size have been successfully employed for the normal-phase electrochromatographic separation of polar compounds with high efficiency (e.g., 210,000 for thiourea), which is matched well with its submicrometer particle size. The Van Deemeter plot showed the hindrance to mass transfer because of the existence of pore structure. The lowest plate height of 2.0 microm was obtained at the linear velocity of 1.1 mm/s. On the other hand, because of the relatively high linear velocity (e.g., 4.0 mm/s) can be generated, high-speed separation of neutral compounds, anilines, and basic pharmaceuticals in CEC with C18-modified SBA-15 silica as stationary phases was achieved within 36, 60, and 34 s, respectively.     

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives with H2SO4 Supported on Silica Gel or Alumina

The one-pot condensation of aromatic aldehydes, β-dicarbonyl compounds, and urea or thiourea in the presence of H₂SO₄ supported on silica gel or alumina (80% m/m) in refluxing n-hexane produces 3,4-dihydropyrimidin-2(1H)-ones and their sulfur derivatives in high to excellent yields.     

Solvent‐Free One‐Pot Synthesis of Amidoalkyl Naphthols Catalyzed by Silica Sulfuric Acid

An efficient, inexpensive, and mild method for the synthesis of amidoalkyl naphthols, catalyzed by ‘silica sulfuric acid’ (SSA), was elaborated under solvent‐free conditions at room temperature. Various amidoalkyl naphthols were synthesized in high yields from aromatic or aliphatic aldehydes, α‐ or β‐naphthols, and amides or urea or thiourea.     

Selective solid-phase extraction of trace mercury(II) using a silica gel modified with diethylenetriamine and thiourea

We describe a solid phase extractor for selective separation and preconcentration of Hg(II) ion. It was prepared by immobilizing the adduct of diethylenetriamine and thiourea on silica gel. The effects of solution acidity, preconcentration time, sample flow rate and volume were optimized. The results show that Hg(II) can be selectively extracted from acidic solutions and in presence of common other metal ions. The adsorbent is stable, can be reused more than 10 times, and the maximum adsorption capacity is 23 mg g^?1. Hg(II) was quantified by inductively coupled plasma optical emission spectrometry. The method has a detection limit of 23 ng L^?1, and the relative standard deviation is <2 %. The procedure was validated by analyzing two standard materials (river sediment and hair powder), and was successfully applied to the preconcentration of Hg(II) in real samples.

Extended architectures constructed of thiourea-modified SBA-15 nanoreactor: A versatile new support for the fabrication of palladium pre-catalyst

We designed and synthesized a novel catalyst consisting of ordered mesoporous silica (SBA-15) functionalized with bis(thiourea) (BTU) linker. The regular and unique pore channels of BTU-SBA-15 ensure proper control of the size and homogeneous distribution of palladium nanoparticles. The physiochemical properties of the hybrid Pd@BTU-SBA-15 pre-catalyst were investigated using various techniques. The proposed catalyst is found to be very active, reusable, stable and scalable, and has excellent reactivity and selectivity for Suzuki and Heck coupling reactions under very mild and sustainable reaction conditions.     

Chromatographic analysis of binary mixtures of isomeric complexes

Summary Mixed ligand complexes of Cr(III), Co(II), Cu(II) and Zn(II) with the p-diethylaminoanil of phenylglyoxal and either thiourea or ammonia, isolated as binary mixtures of isomers, were separated on thin layers of alumina or silica gel and on paper strips. Separation of mixtures in bulk was by column chromatography whereas quantitative analysis including determination of isomeric compositions of isolates was by TLC. Resolved isomers were identified using correlations of their R_F with spectral properties.