Spectrophotometric determination of nitrate and nitrite in water and some fruit samples using column preconcentration

A sensitive analytical method for the simultaneous assay of nitrate and nitrite in water and some fruit samples is presented. The method is based on nitrite determination using the diazotization-coupling reaction by column preconcentration and on the reduction of nitrate to nitrite using the Cd-Cu reductor column. Nitrite is diazotized with sulfanilamide (SAM) in the pH range 2.0-5.0, sulfamethizole (SM) in pH 1.8-5.6 and sulfadimidine (SD) in pH 1.8-4.0 in a hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were coupled with sodium 1-naphthol-4-sulfonate (NS) in the pH range 9.0-12.0 for the SAM-NS system, pH 8.6-12.0 for the SM-NS system and pH 9.4-12.0 for the SD-NS system to be retained on naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent packed in a column. The solid mass is dissolved out from the column with 5 ml of dimethylformamide (DMF) and the absorbance is measured by a spectrophotometer at 543 nm for SAM-NS, 537 nm for SM-NS and 530 nm for SD-NS. The calibration graph was linear over 30-600 ng NO(2)-N and 22-450 ng NO(3)-N in 15 ml of final aqueous solution (i.e. 2-40 ng NO(2)-N ml(-1) and 1.5-30 ng NO(3)-N ml(-1) in aqueous sample) for three systems. The detection limits were 1.4 ng NO(2)-N ml(-1) and 1.1 ng NO(3)-N ml(-1) for SAM-NS, 1.2 ng NO(2)-N ml(-1) and 0.89 ng NO(3)-N ml(-1) for SM-NS, 1.0 ng NO(2)-N ml(-1) and 0.75 ng NO(3)-N ml(-1) for SD-NS, respectively. The concentration factor is eight for SAM-NS and SM-NS, and 12 for SD-NS. Interferences from various foreign ions have been examined and the method was successfully applied to the determination of low levels of nitrate and nitrite in water and some fruit samples.     

Active Chemical Constituents from Sauropus androgynus

This paper describes the chemical investigation on BuOH-soluble EtOH extract from the aerial part of Sauropus androgynus. This study led to the characterization of six bioactive ingredients including three nucleosides—adenosine (1), 5′-deoxy-5′-methylsulphinyl-adenosine ( 2 ), and uridine ( 3 ), two flavonol dioside — 3-O-β-D-glucosyl-7-O-α-L-rhamnosyl-kaempferol ( 4 ), 3-O-β-D-glucosyl-(1→6)-β-D-glucosyl-kaempferol ( 5 ), and one rare flavonol trioside — 3-O-β-D-glucosyl-(1→6)-β-D-glucosyl-7-O-α-L-rhamno-syl-kaempferol ( 6 ). Their structures were determined on the basis of spectral analysis.     

利用跟踪TPR—GC和XRD技术考察LaNiO3的还原机理

钙钛矿型复合氧化物对许多反应具有较高的催化活性,它们被广泛地用作CO氧化的催化剂.陈水华等对SmMeO_3(Me:V、Cr、Mn、Fe、Co)和Tascon等对LaMeO_3(Me:V、Cr、Mn、Fe、Co、Ni)上CO催化活性评价说明,LnMnO_3和LnCoO_3(Ln=La、Sm)活性最好,而LaNiO_3则表现和LaCoO_3相似活性,由此可推断这些氧化物具有相似的催化性能.本文用TPR-GC和XRD考察了在还原气氛下,LaNiO_3的还原机理,这对研究其电、磁特性具有一定的指导意义.     

钒、铬、锰磷桥络合物中31P NMR化学位移的研究

ISSIe山和W6flSChllh山子1960年首次用pdCI。和二苯基磷合成出黄色的二聚络合物，后被H。yieY＊确认为具有pRZ的桥式结构．此后一系列该类结构的化合物被合成并引起了广泛的兴趣．磷可以和两个甚至多个金属原子络合构成多核金属络合物，在催化反应中有重要应用．磷原子存在多种电子态，其3d空轨道也能参与成键．P乃1的NMR谱是研究含磷化合物立体结构的有力工具．P－31与其它核素之间的耦合常数以及P－31的化学位移对阐明化合物的立体构象以及电子结构具有重要作用．近年来，West饲用计算机神经网络技术预测P－：if的化学位移，但仅…     

用手性高效液相色谱对β—羟基酯化合物进行对映体分离

本文利用手性ＯＤ柱在高效液相色谱上对光活性β－羟基酯类化合物进行了对映体分离，达到了较好的分离效果，并通过讨论手性ＯＤ涂附物的结构与该类化合物的作用方式，解释了不同的该类化合物的色谱分离效果。     

RE（Ⅲ）—ADP,RE（Ⅲ）—AMP配合物的合成及物性研究

首次合成了具有生物活性的系列配合物RE(Ⅲ)-ADP(稀土-腺苷二磷酸)和RE(Ⅲ)-AMP(稀土-腺苷-磷酸)(RE=Y,La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu),根据红外、紫外、荧光、X射线衍射、元素分析、络合滴定等分析结果,研究了[RE(Ⅲ)(ADP)(H_2O)_3]和[RE(Ⅲ)(AMP)_2(H_2O)_4]H两个系列配合物的化学组成和性质。     

Bis(crown-6)calix[4]arene/Cs+ Coordination Chemistry in NPME Solution

NMR spectroscopy was used to show that the symmetry of the crown ether bis(C6) is increased by an increase of the alkali metal cation radius. The EXAFS spectrum demonstrates that a seven oxygen atom coordinated configuration is present in the bis(C6)/Cs⁺/NPME system, where NPME denotes o-nitrophenylmethyl ether. The seventh oxygen in this complex, besides the six crown ether oxygens of bis(C6), may come either from a H₂O molecule or an NO₃⁻ ion.     

Characterization and separation of Al13 species using gel-filtration chromatography

A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic strength and pH on separation of Al₁₃ were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of Al₁₃ but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible to produce pure Al₁₃ species using a gel column chromatographic technique.     

Characterization and separation of Al13 species using gel-filtration chromatography

A polyaluminum chloride (PAC) sample was prepared using a slow alkaline titration method. The Bio-Gel P-100 gel column chromatographic technique was used to separate and characterize the various forms of aluminum present in the prepared PAC solution. The effluents from a gel column were monitored using online chemical method: Al-Ferron timed complexation spectrophotometry and by ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. Effects of different experimental conditions such as eluent flow rate, ionic strength and pH on separation of Al₁₃ were investigated. Experimental results indicated that molecule size exclusion was not the only parameter affecting the column chromatographic separation efficiency of Al₁₃ but molecule charge as well. Reducing the eluent flow rate, increasing the ionic strength and suitable pH resulted in increase in the separation efficiency. Experimental results clearly indicated that by varying the experimental conditions, it is possible to produce pure Al₁₃ species using a gel column chromatographic technique.     

Synthesis and Mesogenic Properties of Liquid Crystals Containing Terminal Cyclohexylmethanol,Cyclopentylmethanol, Cyclobutylmethanol and Cyclopropylmethanol Moiety

Four series of compounds 11?50 containing terminal alicyclic rings such as cyclohexylmethyl, cyclopentylmethyl, cyclobutylmethyl, and cyclopropylmethyl rings were synthesized and their liquid crystal behavior studied. The ring size and the length of flexible alkoxy chain influence the phase formation in different ways. While the smaller ring and the shorter alkoxy chain tend to favor the formation of the N phase, the larger ring and the longer alkoxy chain tend to favor the formation of the SmC phase. All the compounds except 11 and 21 exhibit SmA phases. The widest temperature range of the N, SmA, and SmC phases are found in the compounds 41 , 46 , and 20 , respectively, which are 75 °C for 41 , 115 °C for 46 , and 100 °C for 20 .