Flow-Injection Catalytic Spectrophotometric Determination of Trace Amounts of Nitrite

ABSTRACT

A flow-injection catalytic spectrophotometric method is proposed for the determination of nitrite based on its catalytic effect on potassium bromate oxidation of acridine orange in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of acridine orange at 491.5 nm coupling with the stopped-flow technique. The calibration curve was linear between 3.4 and 65 ng/mL, and the detection limit was 2.2 ng/mL. Up to 30 samples can be analyzed per hour with a relative precision of ca. 1.9%. The proposed method was successfully applied to the determination of nitrite in waters and food samples with satisfactory results.     

Analysis of octopamine in human doping control samples

The biogenic amine octopamine [4‐(2‐amino‐1‐hydroxyethyl)phenol] is prohibited in sports owing to its stimulating and performance‐enhancing properties. Adverse analytical findings in athletes' doping control samples commonly result from surreptitious applications; however, the occurrence of octopamine in nutritional supplements and in selected invertebrates as well as the assumption that its N‐methylated analog synephrine [4‐(1‐hydroxyethyl‐2‐methylamino)phenol, not banned by anti‐doping authorities but currently monitored in prevalence studies) might be converted in‐vivo into octopamine have necessitated a study to investigate the elimination of synephrine and octopamine present in over‐the‐counter products. Urine samples collected after administration of nutritional supplements containing octopamine and/or synephrine as well as urine samples collected after therapeutic application of octopamine‐ or synephrine‐containing drugs were analyzed using a validated solid‐phase extraction‐based procedure employing a weak cation exchange resin and liquid chromatographic/tandem mass spectrometric detection with electrospray ionization and multiple reaction monitoring. In the case of therapeutic octopamine application, the urinary concentration of the target compound increased from baseline levels below the lower limit of detection to 142 µg/mL, while urine samples collected after synephrine as well as dietary supplement administration did not yield any evidence for elevated renal excretion of octopamine. Copyright © 2011 John Wiley & Sons, Ltd.     

A fluorescent molecular switch for room temperature operation based on oligonucleotide hybridization without labeling of probes or targets

A molecular switch was prepared by self-assembly. Neutravidin served as a template that allowed for a biotinylated probe oligonucleotide to be placed adjacent to a biotinylated long-chain linker that was terminated with thiazole orange (TO). Hybridization of probe oligonucleotide with target to form double-stranded DNA resulted in intercalation of the adjacent TO probe. This was a reversible process that could be tracked by fluorescence intensity changes. Formamide was used as a denaturant for double-stranded DNA, and could be used to depress thermal denaturation temperatures. In this work formamide had a dual function, providing for control of hybridization selectivity at room temperature, while concurrently ameliorating non-specific adsorption to improve signal-to-noise when using thiazole orange as a fluorescence signalling agent to determine oligonucleotide hybridization. Room temperature single nucleotide polymorphism (SNP) discrimination for oligonucleotide targets was achieved both in solution and for molecular switches that were immobilized onto optical fibers. In solution, a concentration of 18.5% formamide provided greater than 40-fold signal difference between single-stranded DNA and double-stranded DNA, in contrast to only a 2-fold difference in the absence of formamide. Selectivity for SNP determination in solution was demonstrated using targets of varying lengths including a 141-base PCR amplicon. The improved signal-to-noise achieved by use of formamide is likely due to preferential displacement of dye molecules that are otherwise electrostatically bound to the polyanionic nucleic acid backbone.     

三波长-光谱法测定沙棘果汁中黄酮的含量

以沙棘果汁为对象,对其主要有效化学成分黄酮类化合物总含量进行了测定分析。一般常用的分光光度法存在一定的缺陷,加入铝盐使黄酮类化合物与铝离子形成稳定的配合物,则吸收带Ⅰ会明显产生红移,同时吸光度也大大增加,但由于干扰成分使吸收峰不对称给定量分析造成一定的影响。文章采用三波长-光谱法测定沙棘果汁中黄酮的含量,有效地消除了随浓度不同产生的本底漂移及吸收峰不对称给定量分析造成的影响,并校正了基于干扰组分的吸收光谱具有线性吸收产生的基线倾斜,实验结果,回归方程为: ΔA=-0.007 03＋0.000 48ｃ,相关系数r=0.999 1,黄酮的浓度在0～800 (μg·mL-1)范围内,分别在波长为λ₁=495 nm, λ₂=415 nm, λ₃=368 nm处测吸光度时,则ΔA与浓度ｃ之间呈良好的线性关系,可按标准曲线法进行定量分析。本法的回收率为97.0%～101.0%, 变异系数小于0.058%(n=9)。方法的准确度与精密度均令人满意,而且操作简便易行。     

Adsorptive removal of anionic dyes by modified nanoporous silica SBA-3

Batch sorption experiments were carried out to remove dyes, methyl orange (MO), orange G (OG) and brilliant red X-3B (X-3B), from their aqueous solutions using a mesoporous silica SBA-3 as an adsorbent. The effect of surfactant template in SBA-3 on the removal of OG, MO and X-3B was investigated. Experiments were carried out to investigate the influence of contact time, initial concentration, pH, and adsorbent dosage on the adsorption performance. The adsorption results of anionic dyes on the uncalcined SBA-3 (noted as SBA-3) were compared with those of the calcined SBA-3 (noted as C-SBA-3). The uncalcined SBA-3 adsorbent has a large adsorption capacity and a strong affinity for the anionic dyes. Langmuir, Freundlich and Temkin isotherms were employed to model the experimental results, from which the Freundlich isotherm exhibited the most appropriate to predict the same. Freundlich isotherm exhibited the most appropriate to predict the experimental results. The kinetic data were also analyzed through pseudo-first-order and pseudo-second-order models. The pseudo-second-order kinetic model well depicted the kinetics of dyes adsorption on mesoporous SBA-3.     

Fast degradation of dyes in water using manganese-oxide-coated diatomite for environmental remediation

By a simple wet-chemical procedure using a permanganate in the acidic medium, diatomite coated with amorphous manganese oxide nanoparticles was synthesized. The structural, microstructural and morphological characterizations of the as-synthesized catalysts confirmed the nanostructure of MnO₂ and its stabilization on the support - diatomite. The highly efficient and rapid degradation of methylene blue and methyl orange over synthesized MnO₂ coated Diatomite has been carried out. The results revealed considerably faster degradation of the dyes against the previously reported data. The proposed mechanism of the dye-degradation is considered to be a combinatorial effect of chemical, physicochemical and physical processes. Therefore, the fabricated catalysts have potential application in waste water treatment, and pollution degradation for environmental remediation.     

高效液相色谱法测定浓缩苹果汁中的多菌灵残留量

建立了测定浓缩苹果汁中多菌灵残留量的高效液相色谱法。色谱柱为ZOBAX Extend-C_(18)柱(150mm×4.6mmi.d., 5μm),流动相为甲醇-水(体积比为60:40),流速为1.0mL、min,检测波长为285nm。多菌灵的浓度在0.05～5.00mg/L范围内与峰面积之间具有良好的线性关系,线性回归方程为A=185162c 3432.2,相关系数r=0.9998,回收率为91.8％～104.2％,相对标准偏差为7.59％～8.78％,检出限为1.0μg/L。方法简便、快速、灵敏,可满足农药残留的检测要求。     

固相萃取-离子交换色谱法测定浓缩苹果汁中残留的苯菌灵、多菌灵、噻菌灵

建立固相萃取-离子交换色谱法测定浓缩苹果汁中苯菌灵、多菌灵和噻菌灵的残留量。样品直接用水稀释后,于80 ℃下将苯菌灵完全转化为多菌灵,再经SCX固相萃取柱富集,采用LC-SCX离子交换色谱柱(25 cm×4.6 mm,5 μm)分离,二极管阵列检测器检测,以0.1 mol/L KH2PO4溶液(pH 2.5)-乙腈(体积比为70 ∶30)为流动相,在1.0 mL/min下等度洗脱,于282 nm波长下检测。在0.02～2.0 mg/L范围内,多菌灵和噻菌灵的峰面积与其浓度呈良好的线性关系,最低检出限均可达到0.004 mg/kg,回收率为94.2%～100.4%,相对标准偏差低于4.2%。该方法简便、快速、灵敏、准确,可用于浓缩苹果汁中苯菌灵、多菌灵和噻菌灵残留量的检测。     

p-n异质结BiPO_4/Ag_3PO_4的制备及其增强的模拟太阳光活性

采用一步水热合成法制备了BiPO_4、Ag_3PO_4和BiPO_4/Ag_3PO_4复合光催化剂,通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、紫外-可见漫反射(UV-Vis DRS)等表征手段对其组成结构、形貌及光吸收性质进行了表征,结果表明Ag_3PO_4呈块状结构,BiPO_4则分布在其表面,形成的BiPO_4/Ag_3PO_4复合光催化剂具有单斜相和立方晶相结构,带边吸收拓宽至571 nm。以甲基橙和加替沙星为目标污染物,考察了BiPO_4/Ag_3PO_4复合光催化剂在模拟太阳光照射下的降解矿化能力,结果表明复合催化剂比单一催化剂的降解矿化能力更强,稳定性更好。此外,自由基捕获实验表明空穴是该光催化过程中的主要活性物种,·O2-次之。p-n异质结的形成使BiPO_4/Ag_3PO_4复合光催化剂具有较强的电子空穴分离能力是光催化活性提高的主要原因,这与光电流和电化学阻抗谱测试结果相一致。基于以上结果,文中对BiPO_4/Ag_3PO_4光催化降解有机污染物的机理进行了推测。