Potentiometric Titration Curves Research Articles

The adsorption of U(VI) on chlorite: batch, modeling and XPS study

Abstract A mechanistic modelling of the adsorption processes onto individual minerals presenting in the near- and far-fields can greatly enhance the credibility of long-term safety assessments of granite-based geological repositories. In this study, the titration and U(VI) adsorption characteristics of chlorite, one of the major minerals of rock fractures, have been studied. Potentiometric titration curves at two ionic strengths (0.1 and 0.4 mol/L NaCl) are successfully interpreted by considering protonation/deprotonation reactions on generic edge sites (≡SOH) in the framework of a non-electrostatic surface complexation model (SCM). The adsorption of U(VI) on chlorite was reached after 24 h, the adsorption kinetics can be described by a pseudo-second-order model. A non-electrostatic SCM with three surface complexes (≡SOUO2 +, ≡SO(UO2)3(OH)5 and ≡SO(UO2)3(OH)7 2−) was set up based on pH edges of U(VI) at adsorption equilibrium in the absence of CO2. Additional, experimental data measured as a function of U(VI) concentration, solid-to-liquid ratio and carbonate concentration were well reproduced by the proposed model. Finally, parallel experiments were conducted using X-ray photoelectron spectroscopy (XPS) to analyze the variation of U(VI) surface species speciation at different pH values. The good agreement between SCM prediction and XPS analysis demonstrates the reliability of the model in predicting and quantifying the radionuclides retention by chlorite.

DEVELOPMENT OF RECYCLING TECHNOLOGY FOR SPENT CHEMICAL NICKEL PLATING SOLUTION

Currently, the chemical nickel plating process is one of the most popular electroplating methods compared to others due to a number of advantages. However, the production process generates a significant amount of spent chemical nickel plating solutions, which poses a threat of environmental pollution. To solve this problem, the possibility of regenerating the spent solution of chemical nickel plating from one of the industrial enterprises of Udmurtia by the reagent method was studied. Sodium carbonate was chosen as the precipitant for nickel ions, the amount of which was determined from potentiometric titration curves; the most complete precipitation of nickel ions occurs at pH 10. It has been established by IR spectroscopy that nickel hydroxide salts are formed as a result of the interaction of the spent electrolyte with the precipitant. The results of thermogravimetric and differential thermal analysis of the precipitate showed three endothermic effects: at temperatures up to 100 °C, it corresponds to dehydration; at 280±10 °C - to the removal of a part of chemisorbed water and carbonates; at 420 °C - to the final removal of water. As a result of heat treatment of the hydroxocarbonate precipitate, a black fine powder of nickel(II) oxide is obtained, the IR spectrum of which has a set of bands characteristic of this compound. Two variants of the technological scheme for the regeneration of spent electrolytes for the preparation of initial working solutions for chemical nickel plating from nickel(II) hydroxocarbonate and nickel oxide are proposed. The quality of the obtained solutions was checked by applying a nickel coating on brass products. The thickness of the coating was measured by scanning electron microscopy. It has been established that the highest quality coating is obtained using an electrolyte prepared from nickel hydroxocarbonate.

Assessment of the metal exchanged phosphomolybdic acid salt-catalyzed nerol oxidation reactions with hydrogen peroxide

In this work, phosphomolybdate salts were synthesized by exchanging the protons of the phosphomolybdic acid with metal cations (i.e., Co2+, Cu2+, Zn2+, Mn2+, Ni2+, Al3+, and Fe3+ cations) and evaluated as catalysts in oxidation reactions of terpene alcohols with hydrogen peroxide. All the catalysts were characterized by Raman, UV-Vis, and infrared spectroscopies, powder X-rays diffraction, energy dispersive spectroscopy, scanning electronic microscopy, and thermal analyses. The strength of the acid sites was determined by potentiometric titration curves. Among the catalysts tested in nerol oxidation (i.e., model molecule selected), AlPMo12O40 was the most active and selective catalyst toward nerol epoxide, the main product. Main reaction variables such as the H2O2: substrate molar ratio, time, temperature, type, and catalyst load were assessed. The focus was to correlate the physicochemical properties of the catalysts with their performance. The reaction scope was extended to other terpene alcohols. Allylic alcohols (nerol and geraniol) were mainly converted to epoxides, while the oxidation of secondary (borneol) and tertiary (linalool) alcohols gave carbonylic products (camphor), or cyclization products (furane and pyrane rings), respectively.

Study of Cationic Surfactants Raw Materials for COVID-19 Disinfecting Formulations by Potentiometric Surfactant Sensor.

The behavior of a new 1,3-dioctadecyl-1H-imidazol-3-ium tetraphenylborate (DODI-TPB) surfactant sensor was studied in single and complex mixtures of technical grade QACs-benzalkonium chloride (BAC), N,N-didecyl-N,N-dimethylammonium chloride (DDAC), and N,N-dioctyl-N,N-dimethylammonium chloride (DOAC) usually used in COVID-19 disinfecting agents formulations. The results obtained with the new DODI-TPB sensor were in good agreement with data measured by a 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DMI-TPB) surfactant sensor, as well as two-phase titration used as a reference method. The quantitative titrations of a two-component mixture of the cationic homologs (a) DDAC and DOAC; and (b) BAC and DOAC showed that the new DODI-TPB surfactant sensor can clearly distinguish two separate mixture components in a single potentiometric titration curve with two characteristic inflexion points. The consumption of SDS (used as a titrant) in the end-point 1 (EP 1) corresponded to the content of DDAC (or BAC), whereas the consumption in the end-point 2 (EP 2) corresponded to the total content of both cationic surfactants in the mixture. DOAC content in both mixtures can be calculated from the difference of the titrant used to achieve EP1 and EP2. The addition of nonionic surfactants resulted in the signal change decrease from 333.2 mV (1:0; no nonionic surfactant added) to 243.0 mV (1:10, w/w). The sensor was successfully tested in ten two-component COVID-19 disinfecting formulations.

The 1,3-Dioctadecyl-1H-imidazol-3-ium Based Potentiometric Surfactant Sensor for Detecting Cationic Surfactants in Commercial Products

A low-cost and fast potentiometric surfactant sensor for cationic surfactants, based on the new ion-pair 1,3-dioctadecyl-1H-imidazol-3-ium-tetraphenylborate (DODI-TPB), is presented. The new cationic surfactant DODI-Br was synthesized and characterized by NMR, LC-MS, and elemental analysis, and was used for synthesis of the DODI-TPB ionophore. The DODI-TPB surfactant sensor was obtained by implementation of the ionophore in PVC. The sensor showed excellent response characteristics with near-Nernstian slopes to the cationic surfactants DMIC, CPC, CTAB, and Hyamine 1622. The highest voltage responses were obtained for DMIC and CPC (58.7 mV/decade of activity). DMIC had the lowest detection limit (0.9 × 10-6 M) and the broadest useful linear concentration range (1.8 × 10-6 to 1.0 × 10-4 M). An interference study showed remarkable stability. Potentiometric titration curves for the titration of cationic surfactants (DMIC, CPC, CTAB, and Hyamine 1622), with DDS and TPB used as titrants, showed sigmoidal curves with well-defined inflexion points and a broad signal change. The standard addition method was successfully applied with recovery rates from 98.9 to 101.2 at two concentrations. The amount of cationic surfactant found in disinfectants and antiseptics was in good agreement with the referent two-phase titration method and the surfactant sensor on the market. This new surfactant sensor represents a low-cost alternative to existing methods for cationic surfactant detection.

Absolute and Relative Positioning of Natural Organic Matter Acid-Base Potentiometric Titration Curves: Implications for the Evaluation of the Density of Charged Reactive Sites.

Potentiometric acid-base titration curves collected on humic (nano)particles as a function of pH and salt concentration reflect the electrostatics of the particles and the amount of chemical charges (Q) they carry. In turn, the interpretation of titration data helps quantify their reactivity toward metals provided that both intrinsic chemical and nonspecific electrostatic contributions to proton binding are correctly unraveled. Establishing a titration curve requires several steps, i.e., blank subtraction, relative curve positioning with respect to the electrolyte concentration, and absolute curve positioning achieved by the estimation of particle charge Q0 at low pH. Failure to properly establish each step may lead to the misevaluation of nanoparticle charging behavior. Here, we report (i) a simple procedure to measure and position titration curves for humic substances (HS) versus salt concentration and (ii) an original approach for absolute curve positioning upon the exploitation of proton affinity spectra. The latter do not depend on Q0 and they thus constrain the titration data analysis using the soft Poisson-Boltzmann-based titration (SPBT) formalism for nanoparticles in the thick electric double-layer regime. We illustrate the benefits of our approach by analyzing titration measurements for a large range of humic nanoparticles and by comparing the outcome with results from the literature.

Ophthalmic drug delivery system based on the complex of gellan and ofloxacin

Complex formation between a natural polysaccharide – gellan and an antimicrobial drug – ofloxacin was studied in aqueous solution. Conductimetric and potentiometric titration curves revealed that gellan and ofloxacin forms a water-soluble complex of composition 2:1 mol/mol stabilized by ionic and hydrogen bonds. The formation of the gellan-ofloxacin complex was confirmed by FTIR spectroscopy, dynamic light scattering, zeta-potential and thermogravimetric analysis. The average hydrodynamic size of the complex was found 307±5 nm and its zeta-potential was negative and equal to -15 mV. Thin films of the gellan-ofloxacin complex, gelled in 0.3 wt.% of CaCl2, were used to study the release kinetics of ofloxacin in distilled water and phosphate buffer. The drug release kinetics evaluated by UV-Vis spectroscopy at λmax = 289 nm and calculated by the Ritger-Peppas model correspond to non-Fickian diffusion in distilled water and Case II transport (zero-order kinetics) in phosphate buffer. The cumulative release of ofloxacin from the gellan-ofloxacin films was equal to 96±2% and 36±2% in phosphate buffer and distilled water, respectively. It is expected that the gellan-ofloxacin complex is able to form in situ gel on the surface of the eye and to prolong the drug residence time in the tear fluid.

The Measurement of Mixed Potentials Using Platinum Decorated Nanoporous Gold Electrodes

Potentiometric redox sensing in solutions containing multiple redox molecules was evaluated using in-house constructed nanoporous gold (NPG)-platinum (Pt) and unmodified NPG electrodes. The NPG-Pt electrode was fabricated by electrodepositing Pt into the nanoporous framework of a chemically dealloyed NPG electrode. By varying the concentration of the Pt salt and the electrodeposition time, different amounts of Pt were introduced. Characterization by SEM shows the pore morphology doesn’t change with the addition of Pt and XPS indicates the electrodes contain ∼2.5–24 wt% Pt. Open-circuit potential (OCP) measurements in buffer and solutions containing ascorbic acid, cysteine, and/or uric acid show that the OCP shifts positive with the addition of Pt. These results are explained by an increase in the rate of the oxygen reduction reaction with the addition of Pt. The overall shape of the potentiometric titration curves generated from solutions containing one or more bioreagents is also highly dependent on the amount of Pt in the nanoporous electrode. Furthermore, the generation of OCP vs Log [bioreagent] from the results of the potentiometric experiments shows an ∼2-fold increase in sensitivity can result with the addition of Pt. These results indicate the promise that these electrodes have in potentiometric redox sensing.

Titration of weak base fibrous anion exchangers in the presence of complex-forming divalent cations

Curves of potentiometric titration of fully protonized fibrous ion exchangers with potassium hydroxide against the background of 1 M KCl in the presence of chlorides of Ni2+, Со2+, Сu2+ and Ca2+ were obtained. The ion exchangers were synthesized by modifying of industrial polyacrylonitrile fiber with diethylenetriamine and triethylenetetraamine and predominantly contained functional groups R-CO-NH- (CH2CH2NH)nH (n = 2 or 3) and a small amount of carboxyl groups. The sorption of Ni2+, Со2+, Сu2+ и Ca2+by ion exchangers was calculated from the data obtained depending on the pH of the medium. It was found that the investigated ion exchangers with high selectivity sorb heavy metal ions in a wide range of acidity of solutions (pH 2–9) due to the formation of metal-polymer complexes with polyamine functional groups. The maximum sorption capacity is 1.5–2.7 and 4–5 meq/g for ion exchangers with n = 2 and 3, respectively.

The Influence of Plasticizers on the Response Characteristics of the Surfactant Sensor for Cationic Surfactant Determination in Disinfectants and Antiseptics.

Surfactant liquid-membrane type sensors are usually made of a PVC, ionophore and a plasticizer. Plasticizers soften the PVC. Due to their lipophilicity, they influence the ion exchange across the membrane, ionophore solubility, membrane resistance and, consequently, the analytical signal. We used the DMI-TPB as an ionophore, six different plasticizers [2-nitrophenyl-octyl-ether (P1), bis(2-ethylhexyl) phthalate (P2), bis(2-ethylhexyl) sebacate (P3), 2-nitrophenyl phenyl ether (P4), dibutyl phthalate (P5) and dibutyl sebacate (P6)] and a PVC to produce ionic surfactant sensors. Sensor formulation with P1 showed the best potentiometric response to four usually used cationic surfactant, with the lowest LOD, 7 × 10−7 M; and potentiometric titration curves with well-defined and sharp inflexion points. The sensor with P6 showed the lowest analytical performances. Surfactant sensor with P1 was selected for quantification of cationic surfactant in model solutions and commercial samples of disinfectants and antiseptics. It showed high accuracy and precision in all determinations, with recovery from 98.2 to 99.6, and good agreement with the results obtained with surfactant sensor used as a referent one, and a standard two-phase titration method. RDS values were lower than 0.5% for all determinations.

Stabilization of the Computation of Stability Constants and Species Distributions from Titration Curves

Thermodynamic equilibria and concentrations in thermodynamic equilibria are of major importance in chemistry, chemical engineering, physical chemistry, medicine etc. due to a vast spectrum of applications. E.g., concentrations in thermodynamic equilibria play a central role for the estimation of drug delivery, the estimation of produced mass of products of chemical reactions, the estimation of deposited metal during electro plating and many more. Species concentrations in thermodynamic equilibrium are determined by the system of reactions and to the reactions’ associated stability constants. In many applications the stability constants and the system of reactions need to be determined. The usual way to determine the stability constants is to evaluate titration curves. In this context, many numerical methods exist. One major task in this context is that the corresponding inverse problems tend to be unstable, i.e., the output is strongly affected by measurement errors, and can output negative stability constants or negative species concentrations. In this work an alternative model for the species distributions in thermodynamic equilibrium, based on the models used for HySS or Hyperquad, and titration curves is presented, which includes the positivity of species concentrations and stability constants intrinsically. Additionally, in this paper a stabilized numerical methodology is presented to treat the corresponding model guaranteeing the convergence of the algorithm. The numerical scheme is validated with clinical numerical examples and the model is validated with a Citric acid–Nickel electrolyte. This paper finds a stable, convergent and efficient methodology to compute stability constants from potentiometric titration curves.

Characterization and stabilization of nano-metakaolin colloidal suspensions

Nanometric powders bear significant problems in the efficiency of dispersion. The ideal situation would be to ensure full nanoparticle separation in suspensions or composites matrix, which is hard to achieve due to the high reactivity and aggregation. This study evaluates the conditions to stabilize nano-metakaolin (NMK) in water suspension by analyzing the influence of solute concentration, pH, type and content of dispersants. Potentiometric titration curves, zeta potential and average particle size measurements were performed, along with rheological measurements, at different times: 0 h, 3 h, 6 h and 24 h. NMK particles showed the same tendency of surface charge distribution, regardless of solute concentration. The dispersed NMK particles presented two isoelectric points, attributed to the multiple arrangements they form when in suspension. Polycarboxylate (PC) was the dispersant that provided greater dispersion stability. Regarding the rheological and zeta potential measurements, the suspensions presented stability up to 24 h.

Metal silicotungstate salts as catalysts in furfural oxidation reactions with hydrogen peroxide

In this work, metal cations exchanged silicotungstic acid salts were synthesized and evaluated as catalysts in furfural oxidative esterification reactions with hydrogen peroxide in alkyl alcohols solution. The protons of silicotungstic acid were totally exchanged with Co2+, Cu2+, Ni2+, Al3+, and Fe3+ cations, generating catalysts that were characterized by infrared spectroscopy, X-rays diffraction patterns, energy dispersive spectroscopy, scan electronic microscopy images, and thermal analyses. Isotherms of adsorption/ desorption of nitrogen provided the surface area, distribution, volume, and pores diameter. The strength and amount of the acid sites were determined by potentiometric titration curves. Noticeably, the oxidation of furfural proceeded without opening the furan ring. Furoic acid and alkyl furoate were the main reaction products, with the formation of the furfural acetal as a secondary product. The effect of main reaction parameters such as the H2O2: furfural molar ratio, the catalyst amount, and the temperature were studied. The reactivity of the furfural with other alkyl alcohols was also assessed. The solid, active, and easily synthesizable catalyst, and the use of an inexpensive and environmentally benign oxidant are positive aspects of this selective process for oxidative esterification of furfural.

A Simplified Method of Synthesis to Obtain Zwitterionic Cellulose under Mild Conditions with Active Ionic Moieties.

A simplified procedure to synthesize zwitterionic cellulose by means of N-protected aspartic anhydride under mild conditions was developed. The preparation of modified cellulose samples was carried out under heterogeneous, aqueous conditions by reacting NH4OH-activated cellulose with aspartic anhydrides N-protected with trifluoroacetyl (TFAc) and carbobenzyloxy (Cbz). Modified cellulose samples Cel-Asp-N-TFAc and Cel-Asp-N-Cbz were characterized by Fourier Transform Infrared (FTIR) and 13C solid state Nuclear Magnetic Resonance (NMR) spectroscopy. The functionalization degree of each cellulose sample was determined by the 13C NMR signal integration values corresponding to the cellulose C1 vs. the Cα of the aspartate residue and corroborated by elemental analysis. In agreement, both analytical methods averaged a grafting degree of 20% for Cel-Asp-N-TFAc and 16% for Cel-Asp-N-Cbz. Conveniently, Cel-Asp-N-TFAc was concomitantly partially N-deprotected (65%) as determined by the ninhydrin method. The zwitterion character of this sample was confirmed by a potentiometric titration curve and the availability of these amino acid residues on the cellulose was inspected by adsorption kinetics method with a 100 mg L−1 cotton blue dye solution. In addition, the synthesis reported in the present work involves environmentally related advantages over previous methodologies developed in our group concerning to zwitterionic cellulose preparation.

Investigation of the cobalt (II) hydroxide preciptaition process

Hydroxides of transition metals are widely used as pigments, adsorbents, catalysts. A special place is occupied by cobalt (II) and cobalt (III) hydroxides. Very often they are used as raw materials to obtain compounds of complex structure. Cobalt oxides, hydroxides, oxyhydroxides is a promising raw material for the production of magnetocarriers, chemisorbents, catalysts, current sources, special ceramics, IR detectors, magnetoresistors, and laser materials. The main task is to study a cobalt (II) hydroxide deposition mechanism based on a set of analysis methods such as potentiometric titration, residual concentrations, conductivity measurements, apparent volume of precipitation, cyclic voltammetry, and numerical differentiation. Potentiometric titration curves for the Co2+-NaOH-H2O system show that with a ratio of [OH-/Cо2 +] = 1.8 a small plateau is observed that corresponds to the formation of the basic salt, with a stoichiometric ratio of [OH-/Cо2 +] = 2 complete deposition in the form of cobalt hydroxide Co(OH)2 occurs. The apparent volume dependence curve in the CoSO4-NaOH-H2O system consists of two parts corresponding to a potentiometric titration curve. Conductivity curves have a clear kink at the point corresponding to the formation of the base salt and hydroxide. CVA for cobalt-containing solutions have characteristic peaks on the cathode wave, corresponding to the reduction of cobalt (III) to cobalt (II) and cobalt (II) to cobalt (0), the anode wave has an additional peak in the range of potentials +0.19 - +0.20 V. The gradual release of cations from cycle 1 to cycle 5 indicates the formation of stable cobalt polyhydroxocomplexes, which are gradually destroyed. Thus, it was found that the reaction between CoSO4 and NaOH proceeds in several stages with the formation of first the basic salt and then polyhydroxocomplexes. In solutions with a concentration of ССoSO4 = 0.4-0.5 mol/L, a basic salt of the composition Co(OH)1.8(SO4)0.1 is formed. In more dilute solutions a basic salt of the composition Cо(OH)1.9(SO4)0.05 is formed.

Establishment and In Vitro Evaluation of Porous Ion-Responsive Targeted Drug Delivery System

Protein drugs have disadvantages, such as short half-lives, unstable biological activities, and low utilization efficiency. In this paper, a porous ion-responsive targeted drug delivery system was designed, combining biodegradable carriers with ion exchange technology to overcome problems for protein drug delivery systems. Carboxymethyl Chitosan Porous Microspheres (CCPM) were prepared using an emulsification- chemical crosslinking method. Chitosan-bovine serum albumin-carboxymethyl chitosan porous microspheres (CBCCPM) were prepared using a dynamic ion exchange method and static self-assembly technology. CCPM were round in appearance mostly with a particle size distribution of 5-15 μm, which facilitates passive targeting to the lungs. CCPM had a total ion exchange capacity of 9.97 ± 0.07 mmol/g and showed a strong ability to attract and contain positively charged drugs. A potentiometric titration curve was used to identify the dissociation behavior of exchangeable groups on the microspheres; the optimal pH for ion exchange of microspheres was ≥ 4.3. CCPM had ion responsiveness, in vitro degradation ability, thermal stability and biocompatibility. In vitro release results confirmed that BSA and CCPM were mainly bound together by ionic bonds and the drug release mechanism of the self-assembled microspheres changed from particle diffusion to membrane diffusion under pH 7.4 PBS solution containing 0.02% Tween 80. Circular dichroism and sodium dodecyl-sulfate polyacrylamide gel electrophoresis results showed no significant change in the secondary structure and purity of BSA after binding to CCPM. The cumulative in vitro release rate of microspheres after 24 h was 86.78%. In this paper, CBCCPM, a porous ion-responsive targeted drug delivery system, was designed.

Synthesis and Characterization of Homo and Mixed Ligand Complexes of Fe(III) with Hydroxypyridinone and Hydroxypyranone Type Ligands


 Hydroxypyridinone and hydroxypyranone are known to be used for the treatment of iron overload by chelation therapy for a long time. Both the ligands have their own side effects when used as medicines. In the present study homo and mixed ligand complexes of both the ligands with iron were prepared and characterized by UV-visible spectrophotometry, Potentiometric study, IR spectroscopy, SEM/EDX and XRD. Overlay spectra obtained from UV-visible spectroscopy of our studied system show the formation of different types of species and confirm that mixed ligand complex is different from the other two systems. Potentiometric titration curves of homo and mixed ligand complexes show the formation of different types of species at different pH and confirm the formation of mixed ligand complex. The comparative results of SEM images of these systems show different surface topologies and hence conform to the formation of mixed ligand complex.

Multyfunctional device for electrochemical analytical methods

The simple version of multyfunctional potentiostat-galvanostat MTech PG-410 based on microcontroller C8051F410 has been designed. The C8051F410 chip is fully integrated, low power, mixed-signal system-on-a-chip microconroller unit. It includes high-speed 8051-compatible core, precision programmable 24.5 MHz internal oscillator, 32 kbytes of on-chip flash memory, 12-bit 200 ksps analog to digital converter with analog multiplexer, two 12-bit current output digital to analog converters and 2.2 V voltage reference. The potentiostat-galvanostat controls the potential between the working electrode and the reference electrode in range ±2 V. The potentiostat-galvanostat has three ranges of measured current with manual selecting: ±0.5, ±2 and ±10 mA. The device can measure voltammograms under high sweep rate up to 4 000 mV/s. The device is equipped with RS232-USB converter based on PL2303 chip for power supply and communication with the computer through USB port. Computer program on Visual Basic 5.0 language for operating with potentiostat has been developed. This software allow to measure and visualize voltamperograms, chronopotentiograms, chronoamperograms, potentiometric and coulometric titration curves. For reduction of influence of electromagnetic noise and improvement signal/noise ratio the program makes digital processing of measured polarograms by Savitzky-Golay filter. Potentiostat-galvanostat MTech PG-410 has been successfully tested on model systems using resistive electrochemical equivalents. Also, the main measuring techniques embedded in the device were tested using well-known analysis methods: potentiometric titration of dichromate with Mohr's salt, coulometric titration of thiosulfate with electro-generated iodine and cyclic voltammetry of ferrocyanide/ferricyanide redox couple. Keywords : potentiostat, galvanostat, microcontroller C8051F410, voltammetry, potentiometry.

Initial growth and root surface properties of dicotyledonous plants in structurally intact field soil and compacted headland soil

The root surface physicochemical properties affect the ratio and uptake of cations by plants and are influenced by environmental threats. In this study, we examine the effect of soil compaction on the root surface properties and growth of dicotyledonous plants including Fabaceae: lupine, pea, soybean and Brassicaceae: mustard and rape. Undisturbed samples from a Haplic Luvisol derived from loess were taken in cores at 5–15 cm depth from a structurally intact area in the centre of a field (reference R) vs. repeatedly and intensively compacted headland area of the same field (compacted C). The soil dry bulk densities were 1.29 and 1.61 Mg m−3, respectively. Plants were grown in these soil cores for 11 days in a controlled environment chamber. Based on the curves of potentiometric titration, the cation exchange capacity (CEC), the total negative charge (Qtot) and the acid strength of the surface groups responsible for surface charging were determined. The apparent surface area (S) was calculated using the adsorption of water vapour method. Soil compaction resulted in a reduced fraction of strongly acidic groups (pKapp<5.5) in rape and mustard and increased in soybean and pea. The CEC of roots response to soil compaction increased in pea and soybean (by 6.1 and 22.8%, respectively) and decreased in mustard and rape (by 10.5 and 22.9%, respectively). In lupine roots, the number of the surface groups and CEC were not significantly influenced by soil compaction. The S decreased from R to C in lupine and pea (by 32.8 and 20.8%, respectively) and increased in soybean, mustard, and rape (by 10.3, 44.1, and 38.3%, respectively). Fourier-transform infrared (FTIR) spectroscopy was used to describe the chemical composition and structure of plant roots. Soil compaction caused an increase and a decrease of the pectin carboxylic groups in the Fabaceae and Brassicaceae species, respectively. The peaks of lignin and cellulose decreased mostly in the lupine grown under C. Cluster analysis grouped the obtained FTIR spectra in two clusters for the Fabaceae and Brassicaceae species with a higher heterogeneity between the roots from R and C for the former. Among the five dicotyledonous plants used in this study, the lowest relative reduction in root length was recorded for lupine with the thickest roots. Based on results of the surface physicochemical properties and root and shoot growth, incorporating lupine in crop rotation seems to be most reasonable to improve plant growth conditions in compacted headland soil.

STUDY THE CHARACTERISTIES Of VARIABLE CHARGES OF SOME SELECTED SOILS FROM NORTHERN IRAQ

This study was carried out in three selected areas from North Iraq included (Makhmour, Shikhan and Zakho).these location Varied in annual temperature and rainfall .Nine soil samples were collected from three soil profiles (one soil profile from each location). Clay was separated without using any corrosive acid or base, except sodium acetate in order to remove calcium carbonate. Variable charge (pH-dependent charge) was measured using potentiometric titration. Results from titration curves showed a clear variations in positions of (ZPC) and the amounts of negative and positive charges from different samples. The extent of (ZPC) varies from (pH 4.4-5.8).However the amount of negative varies between(100-180) Cmole/kg. and the positive charge between(150-350) C.mole/kg. These variations in potentiometric titration curves are partially related to the presence of varying amounts of iron oxides and also the variations in type of minerals dominant in clay samples .In addition to that, there is a possibility of the presence of some calcium carbonate in clay that not completely removed by treatments with sodium-acetate.