间接光度法测定水中硫酸根

硫酸根离子的测定是水质分析主要项目之一。常见分析方法包括硫酸钡比浊法和铬酸钡光度法。但前者不稳定，分析条件较为严格，分析结果重现性和准确度不理想；而后者铬酸钡悬浊液配制麻烦，硫酸盐与铬酸钡交换反应缓慢，过滤除去硫酸钡和过量铬酸钡也费时。也有用二甲基磺基偶氮肿Ⅲ光度法，但必须采用阳离子交换树脂消除某些阳离子的干扰。本文利用氯化钡和铬酸钾等摩尔反应生成铬酸钡，加入等摩尔氯化钡和铬酸钾以代替铬酸钡悬浊液，溶液中存在的铬酸根与溴邻苯三酚红反应生成黄色产物，溴邻苯三酚红与反应产物的对比度达90nm，建立了测定硫酸根较为快速且结果可靠的方法。     

火焰原子吸收光谱法间接测定水中硫酸盐

研究利用硫酸根与铬酸钡悬浊液反应释放出铬酸根,以火焰原子吸收光谱法测定溶液中游离的铬酸根,间接测定硫酸根。并研究了试验条件对测定灵敏度的影响,确定了最佳试验条件,该法用于水中可溶性硫酸盐的分析,回收率在88．5～104．8％之间。     

分光光度法测定三氧化铀中的硫酸根

采用TBP-萃淋树脂吸附三氧化铀样品中的铀,硫酸根与铬酸钡进行交换反应后,直接比色法测定硫酸根的含量。实验中研究了三氧化铀样品中硫酸根含量测定的样品制备、分离、反应酸度,煮沸时间,铬酸钡用量等影响因素。优化条件下,采用硝酸(5mol/L)淋洗、1mL HCl溶液(2.5mol/L)调节溶液中酸浓度、使用2mL BaCrO_4进行交换反应、煮沸3min,得到方法相对标准偏差小于10%,加标回收率为92.9%～110%。实验结果表明,直接显色的测定方法灵敏、快速、准确度高。方法测定条件易于获得,适于推广应用。     

光度法及离子色谱法测定驱油剂中硫酸根含量——联合运用盐析法及活性炭吸附法除去其复杂有机物基体干扰

提出了一种简单、快速的盐析与活性炭吸附混合法,用于去除铬酸钡光度法及离子色谱法测定驱油剂中硫酸根时复杂的有机物基体干扰。考察了样品处理方法、盐种类、盐用量、活性炭用量对基体去除效果的影响。发现使用盐析与活性炭吸附混合法且盐、活性炭质量浓度分别为60,40g·L~(-1)时具有最佳的去除基体干扰效果。方法用于5种驱油剂样品的预处理,并与铬酸钡间接光度法及离子色谱结合用于硫酸根的测定,两种方法测定结果吻合良好。     

石墨材料中硫含量的间接原子吸收法测定

１引言 本文采用高温半融法分解石墨材料,并用铬酸钡间接原子吸收法测定硫含量。其特点是方法简单快速,灵敏度好,准确度高,重现性好,适于硫含量大于１００μｇ／ｇ的石墨材料的测定。２实验部分２．１试剂艾氏卡试剂：将碳酸钠（Ａ．Ｒ）和氧化镁（Ａ．Ｒ）按１：２的重量比混合即得。铬酸钡悬浊液：称取０．５巴铬酸钡溶于含浓盐酸０．４２ｍＬ和冰醋酸１４．７ｍＬ的２００ｗＬ混酸中。硫酸根标准溶液（１００ｍｇ／Ｌ　ＳＯ４２－）：准确称取０．０７４ｇ烘干过的无水硫酸钠（Ａ．Ｒ）溶于去离子水中,定容至５００ｍＬ。氯化钙溶…     

用流动注射二甲基偶氮磺-Ⅲ分光光度法测定水中硫酸根

基于硫酸根使Ｂａ２＋－二甲基偶氮磺－Ⅲ络合物的褪色反应，将采样环和离子交换柱安 装在多功能进样阀上消除干扰，建立了流动注射光度测定硫酸根的新方法。该法对硫酸根线 性范围为０～２６ｍｇ／Ｌ。所建立方法在进样时对离子交换柱自动再生处理，有望应用于硫酸根 的自动测定。     

间接光度法测定水和废水中硫酸盐

在稀盐酸介质中定量加入铬酸钡悬浮液使与SO2-4反应生成BaSO4沉淀。经煮沸,并调节溶液的酸度后,将含有沉淀的溶液以1500r·min-1的速率离心1min,在420nm波长处用1cm吸收皿,以水作参比测定上层澄清液中CrO2-4的吸光度。硫酸根浓度在0～6mg/50ml范围内符合比耳定律。检出限为0.48μg·ml-1,RSD(n=8)为5.38%(SO2-40.50mg)和1.03%(SO2-42 00mg)。平均回收率为99.5%,方法已应用于雨水、地面水及废水中硫酸根的测定。     

小型氧化铝交换柱分离—电位滴定法测定氢氧化镍中硫酸根

报道了小型氧化铝交换柱分离－电位滴定法测定氢氧化镍中的硫酸根。采用小型氧化铝交换柱将氢氧化镍中的硫酸根定量地与基体的镍分离，然后用铅离子电化学传感器作指示电极，电位滴定法测定硫酸根，对分离条件和滴定条件进行了研究。     

用流动注射二甲基偶氮磺—Ⅲ分光光度法测定水中硫酸根

基于硫酸根使Ｂａ＾２＋－二甲基偶氮磺－Ⅲ络合物的褪色反应，将采样环和离子交换柱安装在多功能进样阈上消除干扰，建立了流动注射光度测定硫酸根的新方法。该法对硫酸根线性范围为０￣２６ｍｇ／Ｌ。所建立方法在进样时对离子交换柱自动再生处理，有望应用于硫酸根的自动测定。     

等离子体原子发射光谱法（ICP─AES）间接测定水样中的硫酸根

本文报导以Ｂａ２＋将样品溶液中的硫酸根（ＳＯ）以硫酸钡形式分离，用等离子体光谱法测定余量Ｂａ２＋，从而间接测得ＳＯ含量的方法。该法操作简便、快速、灵敏、准确，化学干扰和光谱干扰小，可准确测定低至０．２ｍｇ的硫酸根含量。方法适用于各种水样中硫酸根的测定，获得满意结果。     

Enhanced electrodeposition and separation of metallic Cr from soluble K_2CrO_4 on a liquid Zn cathode

Carbon contamination and the formation of low-valence oxides limit the preparation of refractory metals by molten salt electrolysis.In this paper,a liquid Zn cathode is adopted for the electrochemical reduction of soluble K_2Cr O_4to metallic Cr in Ca Cl_2-KCl molten salt.It is found that Cr O_4~(2-)can be directly electrochemically reduced to Cr via a six-electron-transfer step and low-valence Cr oxides is hardly produced.The reduction rate is obviously increased from 16.7 mg_(Cr)h~(-1)cm~(-2)on the solid Mo cathode to58.7 mg_(Cr)h~(-1)cm~(-2)on liquid Zn cathode.The electrodeposited Cr is distributed in liquid Zn cathode.Carbon contamination is effectively avoided due to the negligible solubility of carbon in the liquid Zn cathode.Furthermore,Cr can be effectively separated and enriched to the bottom of liquid Zn under supergravity field,realizing the efficient acquisition of metallic Cr and recycling of liquid Zn.The method herein provides a promising route for the preparation of refractory metals with high-purity by molten salt electrolysis.     

A solid-state 53Cr NMR study of chromate and dichromate salts

Solid-state (53)Cr NMR spectra of a series of chromate (CrO4(2-)) and dichromate (Cr2O7(2-)) salts have been examined by employing the stepped-frequency quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) experiment and high applied magnetic field strengths, 11.75 and 18.8 T. Cr-53 nuclear quadrupolar coupling constants, CQ(53Cr), ranging from 1.23 to 5.01 MHz for the Cr(4(2-) salts and 7.25 to 8.14 MHz for the Cr2O7(2-) salts have been measured. For the dichromate salts, this corresponds to central transition 53Cr NMR lineshapes of 200-250 kHz at 18.8 T. The use of hyperbolic secant (HS) pulses in combination with the Hahn-echo (HE) or QCPMG experiment results in significant sensitivity enhancements when acquiring 53Cr NMR spectra of magic-angle spinning (MAS) samples, provided the MAS rate is fast with respect to the second-order quadrupolar interaction. For the CrO4(2-) and Cr2O7(2-) salts, the anisotropic chromium magnetic shielding interaction is generally negligible compared to the second-order 53Cr nuclear quadrupolar interaction. No simple correlation between the structure of the CrO4(2-) and Cr2O7(2-) anions and the observed CQ(53Cr) values has been found.     

用原子吸收光谱对痕量铬作价态分析

本文详细研究了鱼腥藻对Ｃｒ＾３＋和Ｃｒ＾６＋离子的选择吸附条件，发现Ｃｒ＾３＋的最佳吸附ＰＨ值为４－５；Ｃｒ＾６＋的最佳ＰＨ为７左右，一定量柠檬酸能抑制Ｃｕ＾２＋，Ｐｂ＾２＋及Ｃｄ＾２＋对Ｃｒ＾６＋的吸附干扰。建立了痕量铬的不同价态原子吸收分析方法；对金属离子与藻之间的吸附机理作了初步探讨。     

Increased reactivity of the *Cr(CO)3(C5Me5) radical with thiones versus thiols: a theoretical and experimental investigation

2-pyridinethione (2-mercaptopyridine, H-2mp) undergoes rapid oxidative addition with 2 mol of the 17-electron organometallic radical *Cr(CO)3Cp (where Cp*=C5Me5), yielding hydride H-Cr(CO)3Cp* and thiolate (eta1-2mp)Cr(CO)3Cp*. In a slower secondary reaction, (eta1-2mp)Cr(CO)3Cp* loses CO generating the N,S-chelate complex (eta2-2mp)Cr(CO)2Cp* for which the crystal structure is reported. The rate of 2-pyridine thione oxidative addition with *Cr(CO)3Cp* (abbreviated *Cr) in toluene best fits rate=kobs[H-2mp][*Cr]; kobs(288 K)=22 +/- 4 M(-1) s(-1); DeltaH++=4 +/- 1 kcal/mol; DeltaS++=- 40 +/- 5 cal/mol K. The rate of reaction is the same under CO or Ar, and the reaction of deuterated 2-pyridine thione (D-2mp) shows a negligible (inverse) kinetic isotope effect (kD/kH=1.06 +/- 0.10). The rate of decarbonylation of (eta1-2mp)Cr(CO)3Cp* forming (eta2-2mp)Cr(CO)2Cp* obeys simple first-order kinetics with kobs (288 K)=3.1x10(-4) s(-1), DeltaH++=23 +/- 1 kcal/mol, and DeltaS++=+ 5.0 +/- 2 cal/mol K. Reaction of 4-pyridine thione (4-mercaptopyridine, H-4mp) with *Cr(CO)3Cp* in THF and CH2Cl2 also follows second-order kinetics and is approximately 2-5 times faster than H-2mp in the same solvents. The relatively rapid nature of the thione versus thiol reactions is attributed to differences in the proposed 19-electron intermediate complexes, [*(S=C5H4N-H)Cr(CO)3Cp*] versus [*(H-S-C6H5)Cr(CO)3Cp*]. In comparison, reactions of pyridyl disulfides occur by a mechanism similar to that followed by aryl disulfides involving direct attack of the sulfur-sulfur bond by the metal radical. Calorimetric data indicate Cr-SR bond strengths for aryl and pyridyl derivatives are similar. The experimental conclusions are supported by B3LYP/6-311+G(3df,2p) calculations, which also provide additional insight into the reaction pathways open to the thione/thiol tautomers. For example, the reaction between H* radical and the 2-pyridine thione S atom yielding a thionyl radical is exothermic by approximately 30 kcal/mol. In contrast, the thiuranyl radical formed from the addition of H* to the 2-pyridine thiol S atom is predicted to be unstable, eliminating either H* or HS* without barrier.     

Colour reaction of chromium (VI) with N,N-diethyl-1,4-phenylenediame in the presence of ethanol and cyclohexyldiamine tetraacetic acid as well as its application in the species analysis of chromium

A simple, rapid and precise spectrophotometric method for the determination of Chromium (III and IV) has been developed. The reaction of Cr(VI) with N,N-diethyl-1,4-phenylenediamine is almost complete in a twinkling, which yields a red product with a wavelength of maximum absorption at 530 nm. Beer's Law is obeyed in the Cr concentration range of 0-2.0 mug ml(-1). The molar absorptivity is 5.0x10(4) l mol(-1) cm(-1), limit of detection 0.002 mug ml(-1) and relative SD=1.13% for 5.04 mug Cr. The colouring rate and absorbance are not noticeably affected by temperature from 2 to 45 degrees C. The amounts of Cr(VI) and Cr(III) were measured by determining Cr(VI) first under the condition of masking Cr(III) by cyclohexyldiamine tetraacetic acid, and then the total amount by oxidation of Cr(III). The method was applied to the analyses of some industrial waste waters containing Cr with satisfactory results.     

Cr_2O_7~(2-)/Cr~(3+)间接氧化环己醇合成己二酸

以Cr2O72-/Cr3+作为间接氧化剂电氧化环己醇制备己二酸.应用正交实验优化工艺条件,得出在原料比n(环己醇)∶n(Cr2O72-)=0.4∶1,t=35℃和CH2SO4=5mol.L-1条件下己二酸的收率可达70.29%.同时研究了Ag2SO4、(NH4)2SO4、H2SO4浓度、电流密度对Cr3+电氧化为Cr2O72-的影响,Cr3+的转化率可达82.52%.     

Synthesis of a pyridinium bis[citrato(2-)]oxochromate(V) complex and its ligand-exchange reactions

The reaction of citric acid (caH(4)) with pyridinium dichromate (PDC) in anhydrous acetone yields pyridinium bis[citrato(2-)]oxochromate(V), pyH[CrO(caH(2))(2)], as a mixed salt with the Cr(III) product. The compound persists in the solid state for months, is highly soluble in water (pH 4.0), and gives a sharp electron paramagnetic resonance (EPR) signal in solution (g(iso) = 1.9781, A(iso)(Cr) = 17.1 x 10(-4) cm(-1)), which is characteristic of d(1) Cr(V). The presence of [Cr(V)O(caH(2))(2)](-) in the solid state was confirmed by electrospray mass spectroscopy, X-ray absorption near-edge structure (XANES), and EPR spectroscopy. Solid-state EPR spectroscopy, XANES, and a spectrophotometric assay showed that the solid is a mixture of [Cr(V)O(caH(2))(2)](-) and a Cr(III)-citrate complex. The structures of the [Cr(V)O(caH(2))(2)](-) and [Cr(III)(caH(2))(2)](-) components of the mixture were established by multiple-scattering MS analysis of the X-ray absorption fine structure data. The structure of [Cr(V)O(caH(2))(2)](-) is similar to that of other 2-hydroxy acid complexes with Cr=O, Cr-O(alcoholato), and Cr-O(carboxylato) bond lengths of 1.59, 1.81, and 1.90 A, respectively. The Cr(III) complex has bond lengths typical for ligands with deprotonated carboxylate and protonated alcohol donors with distances of 1.90 and 1.99 A, respectively, for the Cr-O(carboxylato) and Cr-O(alcohol) bond lengths. In aqueous solution, [CrO(caH(2))(2)](-) is short lived, but it is a convenient starting material for ligand-exchange reactions. It has been used to generate short-lived mixed-ligand Cr(V) complexes with citrate and picolinate, iminodiacetate, 2,2'-bipyridine, or 1,10-phenanthroline, which were characterized by EPR spectroscopy. The g values are between 1.971 and 1.974. For the picolinate, 2,2'-bipyridine, and 1,10-phenanthroline mixed-ligand complexes, there is hyperfine coupling (2.2 x 10(-4) to 2.4 x 10(-4) cm(-1)) to a single proton of the citrate ligand.     

Speciation of chromium by in-capillary reaction and capillary electrophoresis with chemiluminescence detection

A sensitive method for the simultaneous determination of chromium(III) (Cr3+) and chromium(VI) (CrO4(2-)) using in-capillary reaction, capillary electrophoresis (CE) separation and chemiluminescence (CL) detection was developed. The chemiluminescence reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by Cr3+ ion followed by capillary electrophoresis separation. Based on in-capillary reduction, chromium(VI) can be reduced by acidic sodium hydrogensulfite to form chromium(III) while the sample is running through the capillary. Before the electrophoresis procedure, the sample (Cr3+ and CrO4(2-)), buffer and acidic sodium hydrogensulfite solution segments were injected in that order into the capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr3+ ions migrate to the cathode, while CrO4(2-) ions, moving in the opposite direction toward the anode, react with acidic sodium hydrogensulfite which results in the formation of Cr3+ ions. Because of the migration time difference of both Cr3+ ions, Cr(III) and Cr(VI) could be separated. The running buffer was composed of 0.02 mol l(-1) acetate buffer (pH 4.7) with 1 x 10(-3) mol l(-1) EDTA. Parameters affecting CE-CL separation and detection, such as reductant (sodium hydrogensulfite) concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, were optimized. The limits of detection (LODs) of Cr(III) and Cr(VI) were 6 x 10(-13) and 8 x 10(-12) mol l(-1) (S/N=3), respectively. The mass LODs for Cr(III) and Cr(VI) were 1.2 x 10(-20) mol (12 zmol) and 3.8 x 10(-19) mol (380 zmol), respectively.     

Speciation of Cr(III) and Cr(VI) in potable waters by using activated neutral alumina as collector and ET-AAS for determination

The speciation of Cr(III) and Cr(VI) has been performed by using activated neutral alumina as adsorbent. Both species were quantitatively adsorbed on a small column filled with neutral alumina. The adsorbed Cr(III) was eluted with 4 mol L(-1) HNO(3) and Cr(VI) with 1.0 mol L(-1) ammonia solution. Recoveries of Cr(III) and Cr(VI) were 99% and 100%, respectively. Using ET-AAS for Cr determination the limit of detection in the sample was 0.01 microg L(-1). The combined procedure is fast and sensitive. It can be applied for routine analysis of water samples at sub-microg L(-1) levels with a relative standard deviation (RSD) of 2-10% (three determinations).     

Cr(N)Cl4]2-: a simple nitrido complex synthesized by nitrogen-atom transfer

A new general route to nitrido complexes of Cr(V) based on nitrogen-atom transfer from Mn(N)(salen) to labile CrCl3(THF)3 is presented. By this approach, the simplest nitrido complex of a first row transition metal, [Cr(N)Cl4]2-, has been synthesized and isolated. [[N(CH3)4]2[Cr(N)Cl4].H2O crystallizes in the cubic space group Fm-3m with disordered anions. Cr-N is 1.555(19) A, Cr-Cl is 2.2912(16) A, and N-Cr-Cl is 101.24(4) degrees . The orbital splitting scheme of [Cr(N)Cl4]2- is extreme with the dx2-y2 orbital 10 000 cm-1 lower in energy than the degenerate {dzx, dyz} set of orbitals destabilized by pi-bonding with the nitrido ligand. Hydrolysis of [Cr(N)Cl4]2 preserves the {CrN}2+ moiety.