Cation Exchange Characteristics Research Articles

Preparation of Composite Single‐Ion Conductor Membrane and Its Application in Lithium–Oxygen Battery

Redox mediators (RMs) are reported to effectually encourage the inactive decomposition of discharge products in lithium–oxygen batteries (LOBs); however, oxidized RMs and other injurious species still attack the Li anodes. An ionic liquid (IL)‐modified PVDF single‐lithium‐ion conducting composite membrane that can permit Li+ only but blocks anions and other molecules is prepared. The PVDF is combined with the strong‐acid cation styrene exchange resin with cation exchange characteristics to make a heterogeneous composite single‐ionic conductor membrane and the IL modification causes the formation of a more‐dense groove inside the PVDF membrane apparently strengthening the conductivity of the membrane without losing its impermeability to cations and discharge intermediates. The utility of the modified composite PVDF (MCP) separator greatly extends the cycle life of the LOB from 66 to 347 cycles at 1000 mAg−1 and 1000 mAhg−1 compared to cells using glass fiber separators. Rate performance is significantly enhanced at 3000 and 5000 mAg−1, increasing from 33 and 21 cycles to 171 and 137 cycles. The full discharge capacity also expands from 3702 to 51 205 mAhg−1. The MCP separator enables iodide‐assisted cathode processes and improves lithium anode stripping/plating, which is essential to improve the performance of nonelectrolytic LOBs.

Immobilization of Eu3+ Ions in Zeolite Matrices in Order to Develop Solid-State Radioluminescent Light Sources

Immobilization of europium ions in the Rho, Beta, and paulingite zeolites using ion exchange is studied in order to search for the optimal alumosilicate matrix for the development of solid-state radioluminescent light sources. The phase composition, thermal stability, moisture adsorption ability, and spectral characteristics of the specimens are studied. It is determined that Beta zeolite possesses the highest sorption capacity, high chemical and thermal stability, a significant constant capacity by water, and the highest cation-exchange characteristics regarding Eu3+.

Adsorption of rare earth elements by strong acid cation exchange resin thermodynamics, characteristics and kinetics

The equilibrium and kinetic characteristics of rare earths adsorption process using the strong acid macro reticular resin Dowex 50X8 from El-Erediya chloride liqueurs have been determined. The adsorption parameters including pH, contact time, temperature, resin to aqueous ratio and rare earths initial concentration in aqueous have been optimized. The practical adsorption capacity of rare earths upon the resin under the optimum conditions has been found to attain 80 mg/g which matches with Langmuir theoretical capacity. The physical parameters including the adsorption kinetics, the isotherm models and the thermodynamic data have also been determined. The adsorption process has been found to agree with both the pseudo second order reaction, the Langmuir isotherm and confirms with the concept of the matrix diffusion controls. A successful preconcentration process for the rare earths content was done with a preconcentration factor of about 42.33. Considerable rare earths cake was precipitated from the chloride eluate solutions using oxalic acid.

Synthesis and characterization of an enhanced heterogeneous cation exchange membrane via nanoclay

Electrodialysis (ED) is a separation process based on the transport of ions through ion exchange membranes. Ion exchange membranes are the key factor of this system. In this research, PVC/HIPS/ABS blended heterogeneous cation exchange membranes were made by solution casting method using tetrahydrofuran as solvent and cation exchange resin. The blend of various ratios of these polymers was prepared, and the best ratio was selected as the polymeric matrix. Montmorillonite K10 nanoparticles (with cation exchange characteristics) were then added to the appropriate polymeric matrix to enhance the electrochemical properties of the membrane. All the electrochemical properties of the synthesized membranes (with and without additives) were investigated. Montmorillonite K10 particles enhanced the membrane properties due to their cation exchange capacity. The best results were obtained with PVC/ABS binder and 0.03 additive ratio, where the membrane electrical resistance was decreased 37% while the IEC and transport number were improved 75 and 6%, respectively.

Synthesis and characterization of a new anionic zinc-adeninate metal–organic framework, [Zn3(ad)(BTC)2·(Me2NH2), 5.75 DMF, 0.25 H2O

A new anionic zinc-adeninate metal–organic framework, [Zn3(ad)(BTC)2·(Me2NH2), 5.75DMF, 0.25H2O] (ad = adeninate; BTC = benzene tricarboxylate; DMF = dimethylformamide), was synthesized via solvothermal reaction at 403 K for 24 h between adenine, zinc acetate dehydrate, and benzene tricarboxylic acid in DMF. The single-crystal structure of the framework was determined by single-crystal X-ray diffraction techniques in the monoclinic space group P2(1)/n and was refined to the final error indices R1/wR2 = 0.0663/0.1714 for I > 2sigma(I). The coordination of adenine and BTC expands the structure in different directions, resulting in a three dimensional structure. This framework contains a pore with the size ca. 6.6 × 3.9 A. The chemical stability, thermal stability, and cation-exchange characteristics were investigated by powder XRD, TGA, EDX, 1H NMR, and EA.

Highly Selective Enrichment of Multi-Phosphopeptides by Click TE-GSH

Multisite phosphorylation of proteins plays an important role in signal transduction. However, it is difficult to describe precisely the mechanism of these phosphorylation cascades. In order to study the function of phosphorylated proteins in a deep-going way, enrichment protocol with high selectivity and coverage is urgent needed. In the present study Click TE-GSH, a novel HILIC material synthetized in our group, was used to enrich and sequentially elute phosphorylated peptides in different fractions. As a mixed-mode chromatographic material, Click TE-GSH exhibits both hydrophilic interaction and cation-exchange characteristics. To understand the retention mechanism, we firstly carried out investigation to study the influence of acetonitrile (ACN) concentration, solution pH value and salt concentration on the retention of phosphorylated peptides respectively. The results showed that phosphorylated peptides were eluted with low concentration of ACN and non-phosphorylated peptides were eluted with high concentration of ACN, which was in accordance with the hydrophilic retention characteristics of Click TE-GSH material. Meanwhile, pH value and salt concentration affected the retention of phosphorylated peptides, owing to the change of surface charge on the stationary phase. Under the optimized condition, mono-phosphorylated peptide, di-phosphorylated peptides and multiply phosphorylated peptides were enriched selectively. 6 mono-phosphorylated peptides, 2 di-phosphorylated peptides and 15 multiply phosphorylated peptides were effectively enriched and detected. By contrast, immobilized metal ion affinity chromatography (IMAC) was utilized to enrich phosphorylated peptides. 2 mono-phosphorylated peptides and 6 multiply phosphorylated peptides were identified. It is obvious the enrichment efficiency of Click TE-GSH was much higher than that of IMAC. The established method was validated with relatively complex sample, including peptide mixture of a-casein and bovine serum albumin (BSA) at the molar ratio of 1: 1 and 1 : 10. In addition, Click TE-GSH was applied to enrich phosphorylated peptides in milk. 11 multiply phosphorylated peptides were successfully identified. The result proved the excellent selectivity of the method. Therefore, this optimized protocol has great potential for the enrichment of multiply phosphorylated peptides.

Effect of cation exchange on dimethyl methylphosphonate permeation kinetics in a pentablock hydrocarbon ionomer and a perfluorocarbon ionomer

The present work is concerned with the effect of cation exchange, with calcium, aluminum and cupric cations, on the permeation kinetics of dimethyl methylphosphonate (DMMP) in a pentablock ionomer (Nexar™) and a perfluoroionomer (Nafion™). The diffusion constant was determined by matching a Fickian solution to early time data, with a zero-time shift, initially attributed to the effect of immobilization. The diffusion time-lag relation was applied in an expanded form to include contributions of immobilization and relaxation. The primary effect of cation exchange was a marked reduction in diffusion constant and introduction of significant relaxation. The effects were explored in a two step procedure in which the sample was first exposed to DMMP vapor at activity 0.6 and then at activity 0.8. In cation modified Nexar at the lower activity the delay in onset of permeation was due solely to immobilization. The delay was absent at the higher activity, indicating that extent of immobilization was unchanged with increased concentration, but approach to steady state was still relaxation controlled. In cation modified Nafion delay in onset of permeation was dominated by relaxation, but kinetics at the higher activity was essentially Fickian. The strong relaxation effects appear to be a consequence of cation modification, which results in a network of ionic crosslinks formed by multivalent cation–sulfonate interactions. The combined analytical and experimental procedure developed in this study provided a systematic set of values for the effect of cation exchange and ionomer characteristics on parameters controlling DMMP permeation kinetics.

Glutathione-based zwitterionic stationary phase for hydrophilic interaction/cation-exchange mixed-mode chromatography

As a naturally hydrophilic peptide, glutathione was facilely immobilized onto silica surface to obtain a novel hydrophilic interaction/cation-exchange mixed-mode chromatographic stationary phase (Click TE-GSH) via copper-free “thiol-ene” click chemistry. The resulting material was characterized by solid state 13C/CP MAS NMR and elemental analysis. The measurement of ζ-potential indicated the cation-exchange characteristics and adjustable surface charge density of Click TE-GSH material. The influence of acetonitrile content and pH value on the retention of ionic compounds was investigated for understanding the chromatographic behaviors. The results demonstrated that Click TE-GSH column could provide both hydrophilic and cation-exchange interaction. Taking advantage of the good hydrophilicity and inherent cation-exchange characteristics of Click TE-GSH material, the resolution of neutral fructosan with high degree of polymerization (DP), basic chitooligosaccharides and strongly acidic carrageenan oligosaccharides was successfully realized in hydrophilic interaction chromatography (HILIC), hydrophilic interaction/cation-exchange mixed-mode chromatography (HILIC/CEX), cation-exchange chromatography (CEX) and electrostatic repulsion/hydrophilic interaction chromatography (ERLIC). On the other hand, the separation of standard peptides varying in hydrophobicity/hydrophilicity and charge was achieved in both CEX and HILIC/CEX mode with high efficiency and distinct selectivity. To further demonstrate the versatility and applicability of Click TE-GSH stationary phase, the separation of a human serum albumin (HSA) tryptic digest was performed in HILIC/CEX mode. Peptides were adequately resolved and up to 86 HSA peptides were identified with sequence coverage of 85%. The results indicated the good potential of Click TE-GSH material in glycomics and proteomics.

Influence of Locust Bean Waste Ash on Cation Exchange and Plasticity Characteristics of Cement Modified Lateritic Soil

A laboratory testing programme was carried out to investigate the influence of Locust Bean Waste Ash (LBWA) on cation exchange and plasticity characteristics of Ordinary Portland Cement (OPC) modified lateritic soil. Preliminary tests were carried out on the natural soil to determine its properties. Other tests were carried out on soil-cement mixtures with up to 4% OPC admixed with 8% locust bean waste ash content by dry weight. Improvement in the plasticity characteristics of the soil was reflected in the decrease of liquid limit, increase in plastic limit and decrease in plasticity index with increased cement and locust bean waste ash content. The results using analysis of variance showed statistical significance. These results showed that modification with cement and locust bean waste ash blend significantly improved the plasticity characteristics through cation exchange of the lateritic soil.

Preparation of a novel dual-function strong cation exchange/hydrophobic interaction chromatography stationary phase for protein separation

We have explored a novel dual-function stationary phase which combines both strong cation exchange (SCX) and hydrophobic interaction chromatography (HIC) characteristics. The novel dual-function stationary phase is based on porous and spherical silica gel functionalized with ligand containing sulfonic and benzyl groups capable of electrostatic and hydrophobic interaction functionalities, which displays HIC character in a high salt concentration, and IEC character in a low salt concentration in mobile phase employed. As a result, it can be employed to separate proteins with SCX and HIC modes, respectively. The resolution and selectivity of the dual-function stationary phase were evaluated under both HIC and SCX modes with standard proteins and can be comparable to that of conventional IEC and HIC columns. More than 96% of mass and bioactivity recoveries of proteins can be achieved in both HIC and SCX modes, respectively. The results indicated that the novel dual-function column could replace two individual SCX and HIC columns for protein separation. Mixed retention mechanism of proteins on this dual-function column based on stoichiometric displacement theory (SDT) in LC was investigated to find the optimal balance of the magnitude of electrostatic and hydrophobic interactions between protein and the ligand on the silica surface in order to obtain high resolution and selectivity for protein separation. In addition, the effects of the hydrophobicity of the ligand of the dual-function packings and pH of the mobile phase used on protein separation were also investigated in detail. The results show that the ligand with suitable hydrophobicity to match the electrostatic interaction is very important to prepare the dual-function stationary phase, and a better resolution and selectivity can be obtained at pH 6.5 in SCX mode. Therefore, the dual-function column can replace two individual SCX and HIC columns for protein separation and be used to set up two-dimensional liquid chromatography with a single column (2DLC-1C), which can also be employed to separate three kinds of active proteins completely, such as lysozyme, ovotransferrin and ovalbumin from egg white. The result is very important not only to the development of new 2DLC technology with a single column for proteomics, but also to recombinant protein drug production for saving column expense and simplifying the process in biotechnology.

Chromatographic evaluation of reversed-phase/anion-exchange/cation-exchange trimodal stationary phases prepared by electrostatically driven self-assembly process

This work describes chromatographic properties of reversed-phase/cation-exchange/anion-exchange trimodal stationary phases. These stationary phases were based on high-purity porous spherical silica particles coated with nano-polymer beads using an electrostatically driven self-assembly process. The inner-pore area of the material was modified covalently with an organic layer that provided both reversed-phase and anion-exchange properties while the outer surface was coated with nano-sized polymer beads with strong cation-exchange characteristics. This design ensured spatial separation of the anion-exchange and the cation-exchange regions, and allowed reversed-phase, anion-exchange and cation-exchange retention mechanisms to function simultaneously. Chromatographic evaluation of ions and small molecules suggested that retention of ionic analytes was influenced by the ionic strength, pH, and mobile phase organic solvent content, and governed by both ion-exchange and hydrophobic interactions. Meanwhile, neutral analytes were retained by hydrophobic interaction and was mainly affected by mobile phase organic solvent content. Depending on the specific application, selectivity could be optimized by adjusting the anion-exchange/cation-exchange capacity ratio (selectivity), which was achieved experimentally by using porous silica particles with different surface areas.

Acidichromic Spiropyran-Functionalized Mesoporous Silica: Towards Stimuli-Responsive Metal Ion Separations Media

An acidichromic silyl spiropyran was synthesized and covalently immobilized on the surface of mesoporous silica (SBA-15) through either post-modification or a co-condensation route. The integration of the spiropyran into the porous silica was probed by thermogravimetric analysis, nitrogen adsorption/desorption studies and UV-Vis optical spectroscopy. While the co-condensation route provides the higher spiropyran loading levels, it also leads to two different states of attachment. Both synthetic procedures favor the formation of the open, merocyanine form of the spiropyran within the framework, but this form can be readily switched from a protonated to a deprotonated state by treatment with buffered aqueous solutions. Preliminary evaluation of the metal ion sorption capabilities of the spiro-functionalized SBA-15 for selected monovalent, divalent, and trivalent metal ions indicates that the spiropyran-modified materials show modestly improved cation exchange characteristics versus the unfunctionalized mesoporous framework.

Soil characteristics, belowground diversity and rates of simazine mineralisation of a New Zealand Gley Soil in a chronosequence under horticultural use

The chemical, physical and biological conditions of a New Zealand Gley Soil was examined on matched sites under long-term permanent pasture or used to grow blackcurrants (Ribes nigrum) for 2, 8, 10 or 20 years. The chemical and physical conditions of topsoils (0–10 cm) were assessed by soil pH, Olsen P, total C, total N, mineralisable N, cation exchange, bulk density, porosity and moisture release characteristics. The biological conditions were assessed from the microbial biomass, soil respiration, catabolic evenness and numbers and diversity of the soil nematode populations. The ability of the soil populations to degrade the triazine herbicide simazine was tested. The particle size distribution confirmed all the sites were very well matched, within 2%, in terms of percentage clay, silt and sand contents, which were 36.5–40.5% clay and 59.5–62.5% silt. Compared with the soil under pasture, that under horticultural use for 2, 8, 10 and 20 years had lower total C and N, lower mineralisable N, lower cation exchange and lower porosity but higher bulk density and particle density. The differences were greater the longer the plots had been under blackcurrant production. Olsen P content was greatest (58 μg P cm−3) under the 20-year blackcurrant plots. Changes in biological characteristics were greater than in physical or chemical characteristics. Microbial biomass was 1.73 mg C cm−3 under pasture and decreased to 0.87 mg C cm−3 after 20 years of blackcurrants. Total nematode populations deceased from 3.89 million m−2 under pasture to 0.36 million m−2 after 2 years of blackcurrant production and to 108 000 m−2 after 20 years. There were similar proportional decreases in bacterial-feeding, fungal-feeding, plant-feeding and omnivore nematodes; however, there was comparatively little change in nematode diversity (Shannon–Weiner) or in microbial catabolic diversity or soil respiration. Despite the decreased microbial biomass, the microbial community under blackcurrant production had enhanced capacity to degrade simazine, as compared with the pasture soil. That capacity to degrade simazine was similar in soils that had grown blackcurrants for 2, 8, 10 or 20 years. Yield of blackcurrants had been maintained in the longer-term sites, despite the marked changes in soil chemical, physical and biological conditions.

An Evaluation of Cation Exchange Characteristics of Two Soils in South Western Nigeria

An Evaluation of Cation Exchange Characteristics of Two Soils in South Western Nigeria

Analysis of heterocyclic aromatic amines

Heterocyclic aromatic amines are formed in protein and amino acid-rich foods at temperatures above 150 degrees C. Of more than twenty heterocyclic aromatic amines identified ten have been shown to have carcinogenic potential. As nutritional hazards, their reliable determination in prepared food, their uptake and elimination in living organisms, including humans, and assessment of associated risks are important food-safety issues. The concentration in foods is normally in the low ng g(-1) range, which poses a challenge to the analytical chemist. Because of the complex nature of food matrixes, clean-up and enrichment of the extracts are also complex, usually involving both cation-exchange (propylsulfonic acid silica gel, PRS) and reversed-phase purification. The application of novel solid-phase extraction cartridges with a wettable apolar phase combined with cation-exchange characteristics simplified this process--both the polar and apolar heterocyclic aromatic amines were recovered in one fraction. Copper phthalocyanine trisulfonate bonded to cotton ("blue cotton") or rayon, and molecular imprinted polymers have also been successfully used for one-step sample clean-up. For analysis of the heterocyclic aromatic amines, liquid chromatography with base-deactivated reversed-phase columns has been used, and, recently, semi-micro and capillary columns have been introduced. The photometric, fluorimetric, or electrochemical detectors used previously have been replaced by mass spectrometers. Increased specificity and sub-ppb sensitivities have been achieved by the use of the selected-reaction-monitoring mode of detection of advanced MS instrumentation, for example the triple quadrupole and Q-TOF instrument combination. Gas chromatography, also with mass-selective detection, has been used for specific applications; the extra derivatization step needed for volatilization has been balanced by the higher chromatographic resolution.

Efficiency of different methods of extraction and purification of cytokinins

The increasing use of advanced methods, such as mass spectrometry, for the determination of cytokinins has raised special requirements for the extraction and purification of this class of plant hormones. Extraction of Arabidopsis thaliana plants with three different solvents, [80% (v/v) MeOH, Bieleski’s MCF-7, and modified Bieleski’s] provided similar yields of most analyzed cytokinins determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS/MS). However, the extraction with a modified Bieleski’s solvent (MeOH–HCO 2H–H 2O [15:1:4, v/v/v]) gave the highest responses of deuterated cytokinins (used as test compounds) in plant extracts as compared to the responses of pure deuterated standards (relative internal standard response, RISR). Purification of cytokinins using Oasis MCX sorbent with reversed-phase and cation-exchange characteristics, in comparison to the DEAE Sephadex RP-C 18 method, provided higher levels of zeatin riboside monophosphate and similar levels of cytokinin bases, ribosides and glucosides. Using this method the content of UV-absorbing contaminates was decreased by about 90% and the RISR values of all tested cytokinin standards but riboside monophosphates were increased about two-fold. The former method provided preparations more suitable for HPLC/MS/MS analysis with respect to simplicity and sample purity.

Influence of changed management of sugarcane on some soil chemical properties in the humid wet tropics of north Queensland

A study was undertaken to quantify changes in chemical attributes and cation exchange characteristics of soils associated with two forms of changed management in sugar production systems 6–9 years after their implementation. The two production systems included a long-term green cane trash blanketed (GCTB)/burn trial and a rotation experiment established to investigate crop management strategies to reduce the effects of yield decline in long-term sugarcane monocultures. The treatments investigated in the latter trial were (a) long-term continuous GCTB, (b) grass ley, and (c) a bare fallow treatment. Under both the GCTB and grass ley systems, pH significantly declined over 6 years with an associated increase in aluminium saturation and decline in base saturation of the cation exchange complex. Although the decline in base saturation under the GCTB treatment would effectively indicate a degree of degradation, this base diminution is easily reversed through conventional management strategies. Organic carbon levels increased by 4 t/ha under the GCTB treatments compared with the burnt over a 9-year period. In contrast, under a grass ley system, organic carbon increased by 9 t/ha over a 6-year period compared with continuous cane, clearly demonstrating the superior nature of grass leys in sequestering carbon in this tropical environment. The increased net proton addition in the GCTB system relative to the burnt system was estimated to be 0.71�kmol H+/ha.year, and the net proton additions for the continuous cane, grass ley, and fallow systems were 1.38, 3.81, and 0.87 kmol H+/ha.year, respectively. The cation exchange characteristics were derived from bulk samples collected from each of the trials. The divergence between the cation exchange curves due to treatment was greatest in the surface 10 cm, but this diminished with depth, indicating that the influence of trash retention or grass leys on soil charge characteristics was confined to the surface layer. The increases in cation exchange capacity (CEC) at pH 5.5 of the GCTB treatment compared with the burnt, and of the grass ley treatment compared with the continuous cane, were estimated to be 0.67 and 0.75 cmolc/kg over the 0–10 cm depth interval. Plots of effective CEC v. CEC clearly indicated that 9–31% of the cations measured where not associated with the exchange complex and would therefore be subject to leaching loss. Organic C oxidisable by 33 mM KMnO4 (C1) or 333 mM KMnO4 (C3) was highly linearly correlated with total organic C across both sites and all treatments. This suggests that the proportions of different functional organic groups were not greatly affected by burning, trash retention, or pasture.

CHARACTERISTICS OF PYROXENES IN THE MAFIC-ULTRAMAFIC ROCKS OF THE UBO MARBLE AREA

Pyroxene crystals of a dolerite, gabbro and pyroxenite that intruded in the Ubo marble area have been analysed on the basis of 4 cations and 6 oxygen anions using conventional electron microprobe coupled with a scanning electron microscope. The results show that SiO2 in the pyroxenite (51.43–52.52%) was slightly higher than that of the gabbro (48.32-50.83%) and that of the dolerite (47.83-48.95%) due to disilication of dolerite and gabbro liquids. The magnesium content of the pyroxenite (12.29-12.95%) is relatively higher than that of the gabbro (9.95.12.31) and dolerite (4.72-6.33%)because of the more primitive nature of the pyroxenite. ‘Others' in the pyroxenites (Cr. Ni Ba, Zr, Ti, Al) were more abundant in the gabbro (8.38-13.92) and dolerite (5.96-6.98) than that of the pyroxenite (2.45-4.51) which was probably due to crystallization modes of the different rocks. The CaO content of all pyroxenes was (21.99-24.43) which appears to be on the high side when compared to calcic pyroxenes from several diverse bulk compositions. The high abundant CaO enhanced a Wo-content of (41.43-49.36) and Xca=Ca/(Ca+Mg) (0.57-0.78) suggesting an excess of Xca = (0.02-0.23). The intergrowth of amphiboles with the pyroxenes is thought either due to exsolution-hydration process of genetic solid solution or due to both. When cation exchange and site occupation characteristics of the pyroxenes are investigated, high concentration of Alvi,. AI/Si, and Ti/AL implied high pressure/temperature crystallization conditions under bimodal or tholeiitic-alkaline transition magmatism in an island arc environment. Key words: Pyroxenite Ultramafic amphibole Island arcs. [Global Jnl Geol. Sci. Vol.1(1) 2003: 13-28]

Ion chromatographic separation of common mono- and divalent cations on silica gel modified with zirconium using tartaric acid-15-crown-5 as eluent

The Zorbax BP-SIL silica gel acted as a cation exchanger under strongly acidic conditions and was successfully applied to ion chromatography with conductimetric detection (IC-CD) for the simultaneous separation of common mono- and divalent cations (Li +, Na +, NH 4 +, K +, Mg 2+, and Ca 2+). Therefore, the main cause of the cation-exchange characteristics of the Zorbax BP-SIL silica gel was investigated for the preparation of a newly advanced silica-based cation-exchange stationary phase for IC-CD using strongly acidic eluents. As a result, it was found that the main cause could be attributed to zirconium present as an impurity in the silica matrix. The preparation of silica gel modified with zirconium (Zr-silica) was carried out by the reaction of the silanol group on the surface of silica gel with zirconium butoxide (Zr(OCH 2CH 2CH 2CH 3) 4) and the Zr-silica prepared was applied to IC-CD for these mono- and divalent cations. Highly sensitive indirect-conductimetric detection and excellently simultaneous separation for these mono- and divalent cations were achieved in 12 min on the Zr-silica column ( 150 mm×4.6 mm i.d.) using a 5 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as eluent.

Variability in the quality and potential decomposability of Pinus sylvestris litter from sites with different soil characteristics: acid detergent fibre (ADF) and carbohydrate signatures

We investigated variations in the biochemical composition and biodegradation of Scots pine ( Pinus sylvestris) needles and litter on four soils with different cation exchange characteristics, ranging from 7 to 92% base saturation. Trends in cellulose, non-crystalline holocellulose concentrations (as measured by a trifluoracetic acid (TFA) hydrolysis technique) and ratios of lignin-to-cellulose and lignin-to-N in needles and litters varied significantly between sampling sites and reflected trends in soil base status under P. sylvestris stands. Although these relationships need to be tested rigorously on a more extensive sample set, clearly the biochemical quality of needles and litter within the same tree species is not uniform. Detailed analysis of the carbohydrate composition of TFA extracts from plant tissues showed that the ratios of selected hexoses (predominantly of microbial origin) to pentoses (mainly from plant cell wall constituents) were between 1 and 15 times lower in decomposing litter than needles. The hexose-to-pentose ratios also increased from 0.117:1 to 0.136:1 (as rhamnose+fucose-to-arabinose+xylose) and from 1.32:1 to 1.67:1 (as galactose+mannose-to-arabinose+xylose) with increasing base saturation of soils. It is concluded that the former ratio most clearly differentiated between the contrasting sites, whereas the latter ratio was more diagnostic of biotransformations during litter decomposition and associated development of microbial biomass. The study highlights a need to further clarify intraspecific differences in tree leaf and litter biochemistry in relation to soil characteristics and challenges the conventional definition of litter quality in terms of C-to-N or lignin-to-N ratio without consideration for the biochemical quality and spatial patterns of a “holocellulose” fraction. The determination of constituent carbohydrates in TFA extracts may provide a useful diagnostic for the potential decomposition of litter and the depolymerisation of structural carbohydrates.