Separation and detection of common mono- and divalent cations by ion chromatography with an ODS column and conductivity/UV detection

The retention and detection behavior of common mono- and divalent cations (M⁺, alkali metal (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) and ammonium ions (NH₄⁺); M²⁺, alkaline earth metal ions (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) was examined using an ODS column (150×4.6 mm I.D.) and conductivity (CD)/UV detection. The results obtained were as follows: (1) for M⁺, the mobile phase, 0.1 mM sodium dodecyl sulphate (SDS)+10 mM HNO₃ and indirect CD detection were effective. (2) Addition of Ce(III) in the mobile phase accelerated the elution of both M⁺ and M²⁺. The separation of above 10 cations on an ODS column was achieved for the first time without any coelution of cations and disturbance by system peak. Addition of higher SDS resulted in good separation of M⁺ and M²⁺ with longer retention times. CD detection was possible for M⁺ and M²⁺ and UV detection for M²⁺. (3) For M²⁺, the mobile phase, 0.8 mM Ce(III)+0.1 mM SDS+1 mM HNO₃ and indirect UV detection were effective. The IC methods were applied to real samples.     

Retention behavior of transition metals on a bifunctional ion-exchange column with oxalic acid as eluent

The common eluents used with a bifunctional ion-exchange column (IonPac CS5A) for separating transition metals are pyridine-2,6-dicarboxylic acid and oxalic acid (Ox). When Ox is used, cadmium and manganese co-elute. Although much research has been done to overcome the Cd²⁺–Mn²⁺ co-elution problem, the role of lithium hydroxide in separating the transition metals has received little attention. In this study, it is found that when the Ox concentration is higher than 35 mM, Cu²⁺ elutes after Pb²⁺ and Ox plays a predominant role in the retention behavior of the seven metals. When Ox concentration is lower than 35 mM especially when its concentration (25 mM) is half of the usually used standard concentration (50 mM), Cu²⁺ elutes before Pb²⁺, and at the same time, Mn²⁺and Cd²⁺ can also be baseline separated. Lithium hydroxide plays a predominant role in the separation of the metals separated by cation exchange. So, lithium hydroxide is used to adjust the pH of the eluent. The use of an isocratic elution (25 mM Ox/LiOH/2 mM Na₂SO₄, pH 3.88) allows the separation of seven metals (Cu²⁺, Pb²⁺, Co²⁺, Mn²⁺, Cd²⁺, Zn²⁺ and Ni²⁺) in a single run. The effects of inorganic modifiers such as NaNO₃, Na₂SO₄ and Na₄P₂O₇ on retention behavior of the metals are also investigated.     

Analysis of water extracts from airborne dust samples by capillary isotachophoresis

Application of capillary isotachophoresis (CITP) for the analysis of water extracts of the dust samples collected in different periods in air-filtration devices in Prague car traffic tunnels and in Parisian metro station is presented. The extracts were analyzed in cationic mode with a leading electrolyte (LE) of 10 mM KOH, 25 mM acetic acid, pH 4.4, and a terminating electrolyte (TE) of 10 mM β-alanine, adjusted to pH 4.4 with acetic acid, and in anionic mode with LE 10 mM HCl, 20 mM histidine, pH 5.8 and TE 10 mM 2-(N-morpholino)ethanesulphonic acid, pH 3.7. Extracted amounts of UV-absorbing substances, including pollen allergens and organic pollutants, the number of the found components and concentrations of some inorganic ions (e.g. Cl⁻, K⁺, Na⁺, Ca²⁺) in the dust samples were determined. It was found that the extracted amounts of anionic components and their number were much higher than those of cationic components. Significant differences have been found in the analyses of the extracts of different origin. Much more material and more components were present in the extracts of samples from the pollen-rich period than from the pollen-free period, especially in anionic CITP mode.     

Simultaneous separation of common mono- and divalent cations on a zirconium-modified silica gel column by ion chromatography with non-suppressed conductimetric detection and tartaric acid–15-crown-5 as eluent

The application of laboratory-made zirconium-modified silica gels (Zr-silicas) as cation-exchange stationary phases to ion chromatography with conductimetric detection (IC–CD) for common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) was carried out. Zr-silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide (Zr(OCH₂CH₂CH₂CH₃)₄) in ethanol. Zr-silica adsorbed on 10 mg zirconium g⁻¹ silica gel was a suitable cation-exchange stationary phase in IC–CD for the separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection for these cations were achieved in 10 min by IC–CD using a Zr-silica column (150×4.6 mm I.D.) and 10 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as the eluent. The proposed IC–CD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.     

Separation and indirect detection by capillary zone electrophoresis of ppb (w/w) levels of aluminum ions in solutions of multiple cations

Solutions of multiple cations in aqueous solutions at concentrations as low as 200 ppb were analyzed by capillary zone electrophoresis. Aluminum ions were cleanly separated from Li⁺, K⁺, Ca²⁺, Cr³⁺, Zn²⁺, CU²⁺, and other ions less than 6 min after injection of the solution on a 50 cm × 50 μm I.D. uncoated fused-silica capillary column at 15 kV. Indirect detection at 204 nm was carried out using a pH 2.8 background electrolyte containing 5.2 mM ephedrine as a UV-absorbing co-ion and 4.7 mM -hydroxyisobutyric acid as a completing counter ion. Mobilities for Al³⁺ and 14 other complexed cations were determined for this electrolyte.     

一种新的镧系金属有机骨架材料的合成、 结构及荧光检测性质

利用溶剂热方法合成了一种以Tb³⁺离子为中心的金属有机骨架材料［Tb₂(bpt)₂(H₂O)₂］·(DMA)_4.5, 并通过单晶X射线衍射(SXRD)、 粉末X射线衍射(PXRD)、 元素分析(EA)、 热重分析(TGA)、 傅里叶变换红外光谱 (FTIR)以及荧光光谱技术(FS)表征了该材料的结构与基本物理化学性质. 单晶衍射分析结果显示该材料具有包含一维直孔道的三维结构, 结构中孔道窗口尺寸约为1.23 nm×1.10 nm. 荧光分析测试结果表明该材料对Cr³⁺离子有荧光响应, 离子检测限低至0.22 mg/L, 同时具有良好的选择性, 在Cr³⁺离子的荧光检测领域具有重要的应用潜力.     

Single-column method of chelation ion chromatography for the analysis of trace metals in complex samples

A single-column chelation ion chromatographic system for the preconcentration and separation of trace transition metals is described. The system includes standard chromatographic equipment with a post-column reagent system based on the reaction with 4-(2-pyridylazo)resorcinol followed by photometric detection at 495 nm. Iminodiacetic acid bonded to 5 μm silica (Diasorb IDA) was used as a chelating stationary phase. The strong complexing ability in combination with good kinetics of complexation and ion-exchange selectivity of iminodiacetic functional groups allow both preconcentration of Mn, Co, Cd, Zn, Ni and Cu from waters of high salinity and efficient separation with the same column. The retention characteristics of alkaline-earth and transition metal ions on Diasorb IDA silica (250×4 mm I.D.) column was investigated for a variety of eluents including nitric acid, maleic, malonic, citric, dipicolinic, picolinic, tartaric and oxalic acids. The influence of ionic strength on retention of metal ions involving high nitrate and chloride concentrations was also evaluated. The baseline separation of preconcentrated metals was achieved using a three-step gradient elution scheme which involved first, flushing of the column loaded with the sample with 0.5 M KCl−0.5mMHNO₃ for 10 min, followed by 80 mM tartaric acid for 20 min and finally 10 mM picolinic acid for 20 min.     

Construction of a nano-rectangular Zn-Nd complex with near-infrared luminescent response towards metal ions

One 6-metal Zn-Nd complex[Zn₂Nd₄L₂(OAc)₁₀(OH)₂(CH₃OH)₂](1)with Schiff base ligand bis(3-methoxysalicylidene)ethylene-1,2-phenylenediamine(H₂L)was constructed,and it has nanoscale rectangular structure(8×11×28 A).Excited by ligand-centered absorption bands,1 shows NIRemission of Nd³⁺ion.Interestingly,1 exhibits lanthanide luminescent response towards metal ions,especially to alkali metal ions(Li⁺,Na⁺ and K⁺)at ppm level.     

Ion chromatography of organic-rich natural waters from peatlands II. Na, NH4, K, Mg and Ca

Organic rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) environments were analysed for Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ using ion chromatography. These cations were determined simultaneously in surface and pore water samples from the continental bogs using a 250-μl injection loop in an isocratic separation. Using this loop, detection limits of the order of 1 ng/g were achieved. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. Analyses of deionized water filtered through these cartridges showed acceptably low blank values (e.g., ca. 5 ng/g) and appeared to have no significant effect on the measured cation concentration. For the maritime bog waters, the low concentrations of NH₄⁺ (ca. 1 μg/g) compared with Na⁺ (ca. 100 μg/g) required improved peak separation. This was accomplished using a gradient separation beginning with 40 mM HCl—1 mM , -2,3-diaminopropionic acid monochloride (DAP) and switching to 40 mM HCl-12 mM DAP after 2 min. Using a 25 μl injection loop, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ were determined simultaneously in less than 25 min. In this instance, even with Na⁺/NH₄⁺ > 100, there was no interference from Na⁺ in the determination of NH₄⁺ (baseline separated).     

[(Me3Sn)2(Me3Sb)M(CN)6]∞ (M = Fe, Ru): Neuartige Organo-Sn/Sb-Polymere von besonderer chemischer und thermischer stabilität

The thermally (decomp. temp. 300°C) and completely air stable, novel coordination polymers [(Me₃Sn^IV)₂(Me₃Sb^V)M^II(CN)₆]_∞ with M = Fe and Ru can be prepared by co-precipitation from aqueous solutions of Me₃SnCl, Me₃SbBr₂ and K₄[(M(CN)₆], or, alternatively, by the ion-exchange-like reaction of the polymers [A(Me₃Sn)₃M(CN)₆]_∞ (A⁺ = Et₄N⁺, Cp₂Co⁺, Me₃Sn⁺ etc.) with Me₃SbBr₂. IR-spectroscopic findings suggest a statistical distribution of quasi-octahedral M(CN-Sn··)_6-x(CNSb ··)_x building blocks (with x = 0–6) within a three-dimensional network.     

Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic–zwitterionic micelles as the column coating solution

This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C₁₈ column (250×4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO₃ or Na₂CO₃ aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F⁻4²⁻−4²⁻2⁻−3⁻. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F⁻4²⁻4²⁻−2⁻−3⁻. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F⁻, HPO₄²⁻, Cl⁻, SO₄²⁻, NO₂⁻, Br⁻ and NO₃⁻ (S/N=3, sample injection volume 100 μl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 μM, respectively.     

钒硼双原子阳离子活化甲烷研究

Methane activation by transition metal species has been extensively investigated over the past few decades. It is observed that ground-state monocations of bare 3d transition metals are inert toward CH₄ at room temperature because of unfavorable thermodynamics. In contrast, many mono-ligated 3d transition metal cations, such as MO⁺ (M = Mn, Fe, Co, Cu, Zn), MH⁺ (M = Fe, Co), and NiX⁺ (X = H, CH₃, F), as well as several bis-ligated 3d transition metal cations including OCrO⁺, Ni(H)(OH)⁺, and Fe(O)(OH)⁺ activate the C―H bond of methane under thermal collision conditions because of the pronounced ligand effects. In most of the above-mentioned examples, the 3d metal atoms are observed to cooperate with the attached ligands to activate the C―H bond. Compared to the extensive studies on active species comprising of middle and late 3d transition metals, the knowledge about the reactivity of early 3d transition metal species toward methane and the related C―H activation mechanisms are still very limited. Only two early 3d transition metal species HMO⁺ (M = Ti and V) are discovered so far to activate the C―H bond of methane via participation of their metal atoms. In this study, by performing mass spectrometric experiments and density functional theory calculations, we have identified that the diatomic vanadium boride cation (VB⁺) can activate methane to produce a dihydrogen molecule and carbon-boron species under thermal collision conditions. The strong electrostatic interaction makes the reaction preferentially proceed the V side. To generate experimentally observed product ions, a two-state reactivity scenario involving spin conversion from high-spin sextet to low-spin quartet is necessary at the entrance of the reaction. This result is consistent with the reported reactions of 3d transition metal species with CH₄, in which the C―H bond cleavage generally occurs in the low-spin states, even if the ground states of the related active species are in the high-spin states. For VB⁺ + CH₄, the insertion of the synergetic V―B unit (rather than a single V or B atom) into the H₃C―H bond causes the initial C―H bond activation driven by the strong bond strengths of V―CH₃ and B―H. The mechanisms of methane activation by VB⁺ discussed in this study may provide useful guidance to the future studies on methane activation by early transition metal systems.     

Second sphere interaction in fluoroanion binding: Synthesis, spectroscopic and X-ray structural study of trans-dichlorobis(ethylenediamine) cobalt(III) terafluoroborate

Trans-dichlorobis(ethylenediamine) cobalt(III) terafluoroborate was synthesised and detailed packing analysis was undertaken to delineate the topological complimentarity of [trans-Co(en)₂Cl₂]⁺ and BF₄⁻ ions by second sphere coordination. The complex was completely characterised by elemental analyses, solubility product measurement and spectroscopic studies (IR, UV–Vis, multinuclear NMR). In the crystal lattice, discrete ions [trans-Co(en)₂Cl₂]⁺ and BF₄⁻ are arranged in A–B–A–B pattern (in both a and c directions of the lattice) forming columns of anions and cations. Crystal lattice is stabilized by electrostatic forces of attraction and hydrogen bonding interactions, i.e. N–HF⁻ and N–HCl involving second sphere coordination. It appears that the topological features of [trans-Co(en)₂Cl₂]⁺ are conducive for generating second sphere interactions. This strategy may be used as a viable method for the capture of other fluoroanions.     

Quadruple-stranded Eu-helicate Assembled from Bis-β-diketonate: Its Stability Towards Metal Ions

Herein, we reported the synthesis and investigation of highly luminescent quadruple-stranded helicate (C₆H₁₆N)₄[Eu₂(MBDA)₄]₂^.3C₄H₁₀O·4C₂H₃N(1-Eu)[H₂MBDA=N-methyl-4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)di- phenylamine] for its stability toward metal ions in the solution. The material was characterized via X-ray crystallographic technique, Fourier transform infrared(FTIR) spectroscopy and electrospray ionization quadrupole time-of- flight(ESI-TOF) mass spectrometry. The results on the luminescence quantum yields clearly demonstrate that the ligand can effectively sensitize the luminescence of the Eu³⁺ ions(Φ_overall=15%). Upon the addition of different metal ions(i. e., Ag⁺, Cd²⁺, Zn²⁺, Fe³⁺, Al³⁺ and Ni²⁺) to the CH₃CN solution of compound 1-Eu, the emission intensities of Eu³⁺ ions at 612 nm were affected to some extent, which could be attributed to the presence of ion exchanges between Eu³⁺ ions and the metals ions, and the result was confirmed by ESI-TOF mass spectrometry.     

Histidine as a dipolar eluent component in cation chromatography: II. Prediction of retention data for alkaline and alkaline-earth ions

The utility of cation chromatography has been developed by the application of -histidine as a multiprotic and dipolar (zwitterionic) eluent component. The method simplifies the cation analysis. The chromatographic characteristics of this system were studied in detail with a view to determining the selectivity and the mechanism by which the cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) are retained. Complete separations were observed in the isocratic run over the eluent concentration range 3.0–6.0 mM at pH below 2.0. Sensitive detection was achieved using suppressed conductivity at the pH of isoelectric point of the histidine. Retention equations are derived for mono- and divalent cations eluted from ion-exchange separation column with multiple ionic eluents. The theory is based on the extension of ion-exchange equilibrium by protonation equilibria. The selectivity data for analyte and eluent species are determined using the model from the experimental retention data by computer-assisted iterative calculations. The model was utilized to predict retention data. The results in three-dimensional retention surfaces together with species distribution graphs are presented.     

X-ray diffraction, Raman study and electrical properties of the new mixed compound [Rb0.44(NH4)0.56]2HgCl4 · H2O

Differential scanning calorimetry of [Rb_0.44(NH₄)_0.56]₂HgCl₄ · H₂O material showed three anomalies at 340, 355 and 424 K, respectively. The room temperature phase has space group Pcma (a=8.433(1) Å, b=9.1817(9) Å and c=11.954(1)). Phase II (T=350 K) is disordered and exhibits orthorhombic symmetry (a=8.456(13), b=9.202(9) and c=12.011(10) Å). Hydrogen bonding, the nature and the degree of structure (dis)order and the mechanisms of the transitions are discussed. The dielectric constant ^′ at different frequencies and temperature revealed a phase transition at T=340 K related to NH₄⁺ reorientation and H⁺ diffusion, and a characteristic increase above 355 K, which might be due to loss of water of crystallization. Transport properties in this compound appear to be due to an Rb⁺/NH₄⁺ and H⁺ ions hopping mechanism.     

Ion chromatographic separation of alkali metal and ammonium cations on a C18 reversed-phase column

The separation of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and ammonium cations on a C₁₈ reversed-phase column using three anionic surfactants [sodium 1-eicosyl sulphate, sodium dodecyl benzenesulphonate and sodium dodecyl sulphate (SDS)] is described. Two methods were examined: (a) “permanent” coating, with the use of a C₁₈ reversed-phase column previously coated with the surfactants; and (b) dynamic coating, with addition of the surfactants to the mobile phase. With method (a) the separation of the six cations was achieved with SDS. However, the retention times gradually decreased owing to dissolution of the SDS coating. Good separation was obtained with method (b), where 10 mM HNO₃ containing 0.1 mM SDS was used as the mobile phase with conductivity detection, and it was applied satisfactorily to real samples. The effect of system peaks on determination is also discussed.     

Structural and spectroscopic properties of Hexamethylenetetramine cobalt(II) complex: [Co(NCS)2(hmt)2(H2O)2][Co(NCS)2(H2O)4] (H2O)

Synthesis, structure, spectroscopy and thermal properties of complex [Co(NCS)₂(hmt)₂(H₂O)₂][Co(NCS)₂(H₂O)₄] (H₂O) (I), assembled by hexamethylenetetramine and octahedral Co(II) metal ions, are reported. Crystal data for I: F_w 387.34, a=9.020(8), b=12.887(9), c=7.95(1) Å, =96.73(4), β=115.36(5), γ=94.16(4)°, V=820(1) Å³, Z=2, space group=P−1, T=173 K, λ(Mo-K)=0.71070 Å, ρ_calc=1.718567 g cm⁻³, μ=17.44 cm⁻¹, R=0.088, R_w=0.148. An interesting two-dimensional network is assembled via hydrogen bonds through coordinated and free water molecules. The d–d transition energy levels of Co(II) ion are determined by UV–vis spectroscopy and calculated by ligand field theory. The calculated results agree well with experiment ones.     

Interaction of titanium and tin chlorides in tetrahydrofuran. The X-ray crystal structure of [trans-TiCl2(THF)4][SnCl5(THF)]

The direct reaction between [TiCl₄(THF)₂] and SnCl₂ in tetrahydrofuran (THF) yields the green paramagnetic salt [trans-TiCl₂(THF)₄][SnCl₅(THF)]. The same compound is also formed in the reaction between [TiCl₃(THF)₃] and SnCl₄ in THF. Crystals of the title compound are monoclinic with a = 8.442(4), b = 21.589(9), c = 9.262(5) Å, β = 107.91(5)°, Z = 2, space group P2₁/m. Both metal ions are in an octahedral environment. The titanium atom in the cation [TiCl₂(THF)₄]⁺ lies on the symmetry centre. The tin atom in [SnCl₅(THF)]⁻ is located on the mirror plane.     

Structural Analysis of ZnⅡ and CdⅡ Complexes with Bis(1,1,3,3-tetramethylbutyl)dithiophosphinic Acid by FT-IR and 1H NMR

Bis(l,l,3,3-tetramethylbutyl)phosphinic acid (HMBP) as an extractant is of selectivity to many kinds of metal ions.¹Bis(1,1,3,3-tetramethylbu1yl)dithiophosphinic acid (HDTP), which has a similar structure to HMBP, is stronger acid than HMBP; moreover, its extractive behavior is very different from HMBP to some metal ions as a result of S atom replacing of O in HMBP.²In order to understand its extraction mechanism and regularity, we selected metal ions such as Zn^Ⅱ and Cd^Ⅱ for preparing extracted complexes and analyzing their structure. The composition of the complexes, M(DTP)₂ (M=Zn, Cd), were supposed by elementary analysis, and confirmed by FT-IR and ¹HNMR spectra.