Influence of ionic strength and organic modifier concentrations on characterization of aquatic fulvic and humic acids by high-performance size-exclusion chromatography

Aquatic fulvic acid (FA) and humic acid (HA) were characterized by an aqueous high-performance size-exclusion chromatography (HPSEC) using a hydrophilic polymeric stationary phase and an aqueous eluent at neutral pH and low-ionic strength (5 mM Na2HPO4; final ionic strength, 13 mM). Employed HPSEC showed low sensitivity of FA to variations in ionic strength (13 and 100 mM) and contents of organic modifier (0.1 or 40% methanol) in aqueous eluent. Under these analytical conditions, peak maxima of relative UV signals versus molecular mass (Mr) defined as M'p and peak maxima of relative mass concentrations versus Mr defined as Mp of FA were shown to be located at 548-690 and 500, respectively. Organic modifier concentrations of 40% methanol in aqueous eluent enabled not only analysis of FA, but also analysis of some aquatic HA by HPSEC. Analysis showed M'p and Mp values of aquatic HAs around 1000 and 600, respectively. Measured molecular mass data of FA were found to be consistent with the recently published data describing low molecular masses of FA. Results recommend the use of the described HPSEC as a simple, rapid, reproducible, low-cost method giving consistent molecular sizes/masses of FA and some aquatic HAs.     

硝酸氧解法提高泥炭中黄腐酸的产率

硝酸氧解法提高泥炭中黄腐酸的产率;腐植酸;硝酸氧化降解     

离子液体萃取阿魏酸和咖啡酸的性能研究

以1-甲基-3-丁基咪唑六氟磷酸盐([C4mim][PF6])和1-甲基-3-己基咪唑六氟磷酸盐([C6mim][PF6])离子液体为萃取剂,采用紫外分光光度法研究了溶液pH值、温度、相比率及盐的种类和浓度对其萃取阿魏酸和咖啡酸效率的影响,考察了被萃取物的回收及离子液体的循环使用,探讨了两种离子液体替代传统有机溶剂阿魏酸和咖啡酸的可能性。实验结果表明:萃取温度和无机盐的种类及浓度对FA和CA萃取效率的影响较小;水相pH值对萃取效率有较大的影响,萃取FA适宜pH应小于3.67,萃取CA适宜pH应小于3.71;被萃取物浓度增大,萃取效率降低,而相体积比增大其萃取效率升高;两种离子液体对FA和CA的萃取效率[C4mim][PF6]大于[C6mim][PF6],同种离子液体对FA的萃取效率大于CA;在萃取相中的FA和CA可定量回收,且被萃取物中离子液体的残留[C6mim][PF6]小于[C4mim][PF6],离子液体可循环使用。     

Determination of molecular parameters of hydroxyethyl and hydroxypropyl celluloses by chromatography with dual detection

Hydroxyethylcellulose (HEC) and hydroxypropylcellulose (HPC) were studied by means of size exclusion chromatography with dual detection, i.e. employing simultaneously a refractive index (concentration sensitive) and a multiangle light scattering (molecular weight sensitive) detectors. The eluent was water and water solutions containing different concentrations of ionic salts. Molecular weight distributions and averages, coefficients of the scaling law of molecular dimensions and unperturbed dimensions were thus obtained from a single polydisperse sample of each polymer. Measurements were performed at 25 degrees C and the anomalous chromatographic behaviour, due to a combination of ion and size exclusion mechanisms, found when using pure water as eluent is transformed into a size exclusion mechanism by the addition of ionic salts. However, the two polymers behave on a different way in presence of salts. Thus, HEC, which is of low degree of substitution (DS), is close to theta conditions in the aqueous salt solutions (i.e. the q exponent of the scaling law has a value close to 0.5), whereas in the case of HPC the addition of salt improves the quality of the solvent up to a value of q around 0.6. Unperturbed dimensions are also calculated for both celluloses.     

Studies on the Ion Exchange Separation of Aspirin,Salicylic Acid and Acetic Acid

The liquid chromatography of aspirin, salicylic acid and acetic acid using cation exchange resins with aqueous alcohol and water as eluent was described. The results indicated that acetic acid could be separated from aspirin and salicylic acid by hydrogen form cation exchange resin with 25% ethanol or water as eluent. The possibility of using this method to determine the degree of hydrolysis of aspirin was discussed.     

基于L-半胱氨酸修饰的锰掺杂ZnS量子点应用于叶酸测定

以L-半胱氨酸为表面修饰剂制备了稳定性和水溶性均优的ZnS∶Mn2+纳米晶,并应用于叶酸的检测。在pH 7.4的KH2PO4-Na2HPO4 缓冲溶液中,叶酸的加入使ZnS∶Mn2+体系的荧光发生猝灭,荧光强度的变化与叶酸浓度呈良好的线性关系,其线性范围为1.0×10-6~7.0×10-5 mol?L-1 （4.4×10-4~3.1×10-2 g?L-1）,方法检出限为9.6×10-7 mol?L-1 （4.2×10-4 g?L-1）。该方法用于叶酸片剂和健康人尿液中叶酸的测定,结果满意。采用荧光光谱、紫外可见吸收光谱及X-ray光谱等研究了ZnS∶Mn2+纳米晶及其水溶液的特性,通过热力学参数对叶酸测定的可能机理进行了探讨。     

Preparation and characterization of cross-linked hyaluronan nanoparticles

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on hyaluronic acid (HA). The diamine, 2,2′(ethylenedioxy)bis(ethylamine) was used for cross-linking of the HA linear chains. The condensation reaction of amino groups and pendant carboxyl groups of HA was performed in aqueous media at room temperature using water-soluble carbodiimide. The prepared nanosystems, aqueous solutions, or dispersions of nanoparticles were stable, transparent, or mildly opalescent systems depending on the ratio of cross-linking, findings consistent with values of transmittance above 77%. The structure of products was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. Particle size measured by TEM varied less than 130 nm; in the swollen state, the average size of the particles measured by DLS was in the range of 30–140 nm depending on the ratio of cross-linking and the molecular weight of HA. Formation of cross-linked nanoparticles results in a viscosity drop compared to the viscosity of the corresponding solution of the HA, and this trend becomes decreasingly appreciable as the molecular weight of HA decreases.     

Liquid Chromatographic Determination of Meclofenamic Acid In Equine Plasma

Abstract

Meclofenamic acid is extracted to dichloromethane together with the internal standard diclofenac sodium. After evaporation of the organic solvent the residue is dissolved in the chromatographic eluent and analyzed by liquid chromatography. The acids are separated on a column packed with Spherisorb ODS with methanol - phosphate buffer as the eluent and detected at 280 nm. A possible metabolite of meclofenamic acid was also detected in the chromatograms. The detection limit for meclofenamic acid in plasma was 0.361 μmol/L (0.107 μg/ml) for 1.5 ml sample size. The conditions of quantitative extraction of meclofenamic acid and diclofenac to dichloromethane are given.     

Properties of different natural organic matter influence the adsorption and aggregation behavior of TiO2 nanoparticles

Natural organic matter (NOM) has considerable influence on the aggregation and stability of titanium dioxide nanoparticles (TiO₂ NPs). However, the effect of chemical properties of NOM on the interface interaction and the aggregation process is still not clear. In this study, we investigated the effects of two typical types of NOM (fulvic acid (FA) and humic acid (HA)) on its adsorption onto TiO₂ nanoparticles and their aggregation behavior in aqueous phase. Nuclear Magnetic Resonance (NMR) was used to study their functional groups, indicating that HA has a stronger hydrophobicity than FA. The presence of HA or FA lowered the critical coagulation concentration (CCC) of TiO₂ NPs, while FA showed a more significant effect. HA promotes the aggregation of TiO₂ NPs when ionic strength (IS) > CCC, which was likely due to the bridging effect. Contact angle measurements indicate that HA has higher hydrophobic properties than FA, and it is easier to transfer from water to the surface of TiO₂ NPs. Transmission Electron Microscopy (TEM) was applied to investigate the aggregate formation and colloid interface morphology of NOM-coated-TiO₂ NPs and NOM entanglement. Different structures of HA and FA result in various behavior and their interface interaction mechanisms including IS-induced entanglement and NOM/IS bridging.     

Ion-exchange chromatography of anions with tiron as eluent

The characteristics of Tiron (1,2-dihydroxybenzene-3,5-disulfonic acid and its sodium salt) solution as an eluent for anions in ion-exchange chromatography was investigated with conductivity and UV absorbance detectors. Tiron (acid and sodium salt) has such a strong affinity for the anion exchanger that the concentration in the eluent can be made lower than that of benzene carboxylates, such as phthalate, which have been used similarly. Tiron acid exhibited an unusual effect which increased the sensitivity with a conductivity detector. The water dip was not observed, and a big ghost peak appeared near the sulfate peak. Tiron salt did not produce a ghost peak, and was better for highly sensitive detection in indirect photometric chromatography than phthalate, because of a better balance between UV absorptivity and elution ability. Because Tiron forms stable chelates with many metal ions, pretreatment with a cation-exchange resin is necessary for real samples such as tap water.