Μg Cm-3 Research Articles

Complexation equilibrium between iron(III) and N,N'-bis(2-hydroxyphenylmethyl)-N,N'-bis(2-pyridylmethyl)-1,2-ethanediamine

Complexation equilibrium between iron(III) and N,N' -bis(2-hydroxyphenylmethyl)-N,N' -bis(2-pyridylmethyl)-1,2- ethanediamine (H2bbpen), a colorless hydrophobic divalent hexadentate ligand, and potential use of the ligand for the spec- trophotometric determination of iron(III) in aqueous solution was investigated. In the pH range 2.0 - 3.0, Fe(III) forms stable 1:1 complex with H2bbpen, and Fe(III) can be determined selectively as the purple Fe(bbpen) + complex (λmax = 560 nm, e = 4.3 〈 103 dm3 mol-1 cm-1, log β1 = 32.6 ∠ 0.1). In this system, linear calibration range of Fe(III) was 5 〈 10-6 - 2 〈 10-4 mol dm-3 (0.3 - 12 µg cm-3) and detection limit was 3 〈 10-6 mol dm-3 (0.2 µg cm-3). Furthermore, most of foreign metal cations did not influence largely the determination of Fe(III).

Accumulation of cadmium, lead and strontium, and a role of calcium oxalate in water hyacinth tolerance

Eichhornia crassipes plants brought from the River Nile were cultured in jars containing river water supplemented with various concentrations of Cd, Pb, and Sr (0 to 100 μg cm-3), added simultaneously. Treatment continued for 20 d during which each cultivation solution was being replaced with fresh one every 3 d. The growth of Eichhornia was drastically retarded at heavy metal concentrations higher than 15 μg cm-3. At concentrations 15 or 25 μg cm-3, the accumulation of Cd and Pb to levels several times higher than those in control plants was found. More than 50 % of the uptaken metals were retained by roots alone. Leaves and leaf petiols received around 30 and 20 % of the accumulated metals, respectively. X-ray microanalysis indicated the presence of the three heavy metals in Ca oxalate crystals. Content of metals in the crystals increased progressively over time of exposure in a way similar to those in whole plant tissues. These results suggest a possible role for Ca oxalate crystalization in toxic heavy metal deposition and thus tolerance by Eichhornia.

Silicon and copper interaction in the growth of spring wheat seedlings

Shoot and root fresh and dry matters and their Cu content were determined in 7-d-old seedlings of Triticum aestivum L. cv. Alkora treated with Cu (10,20, 40 µg cm-3) and Si (500 µg cm-3). Si significantly reduced the toxic effect of Cu on fresh and dry matter production of wheat seedlings. Moreover, plants treated with Cu and Si absorbed less Cu from the solution and had higher water content in shoots and roots than that treated with Cu only.

Determination of the Total Inorganic and Ammoniacal Nitrogens in Water by Gas-Phase Molecular-Absorption Spectrometry.

Based on a vapor-liquid equiribrium of ammonia, a simplified and rapid technique was developed for the determination of the total inorganic and ammoniacal nitrogens in aqueous solution. Ammonium ion was converted into gaseous ammonia by adding a sodium hydroxide solution to a sample solution. The generated ammonia was directly introduced into a quartz cell in order to measure the molecular absorption. As for the determination of the total inorganic nitrogen, the sample solution was pretreated with titanium(III) chloride solution in order to reduce nitrate and nitrite ions to ammonium ion. The ammonia was then evolved and determined in the same manner as mentioned above. The detection limit (3S/N) of 0.01μg cm-3 for both ammonia and the total inorganic nitrogen was obtained. The calibrationgraph was linear up to 0.8μgN cm-3 for each nitrogen species. The relative standard deviations for five replicate measurements were 3.9, 4.5 and 4.7% for 0.40μg cm-3 of nitrogen present in the form of ammonium, nitrate and nitrite ions, respectively. The analytical results for some environmental and industrial water samples are presented.

External hyphal production of vesicular-arbuscular mycorrhizal fungi in pasture and tallgrass prairie communities.

External hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi were quantified over a growing season in a reconstructed tallgrass prairie and an ungrazed cool-season pasture. In both sites, hyphal lengths increased throughout the growing season. Peak external hyphal lengths were 111 m cm-3 of soil in the prairie and 81 m cm-3 of soil in the pasture. These hyphal lengths calculate to external hyphal dry weights of 457 μg cm-3 and 339 μg cm-3 of soil for prairie and pasture communities, respectively. The relationships among external hyphal length, root characteristics, soil P and soil moisture were also determined. Measures of gross root morphology [e.g., specific root length (SRL) and root mass] have a strong association with external hyphal length. Over the course of the study, both grassland communities experienced a major drought event in late spring. During this period a reduction in SRL occurred in both the pasture and prairie without a measured reduction in external hyphal length. Recovery for both the pasture and prairie occurred not by increasing SRL, but rather by increasing external hyphal length. This study suggests that growth is coordinated between VAM hyphae and root morphology, which in turn, are constrained by plant community composition and soil nutrient and moisture conditions.

Extraction-Spectrophotometric Determination of Cadmium with N-Hydroxy-N,N’-diphenylbenzamidine and 4-(2-Pyridylazo)resorcinol

A simple, sensitive and selective spectrophotometric method for the determination of cadmium at trace levels in various environmental samples is reported. The binary complex formed between cadmium(II) and N-hydroxy-N, N′-diphenylbenzamidine (HDPBA) is extracted with chloroform at pH 9.0±0.2 and shows a maximum absorbance at 400nm with a molar absorptivity of 1.96×104l mol-1 cm-1. The sensitivity of the binary complex was enhanced by adding 4-(2-pyridylazo)resorcinol (PAR) after extracting cadmium(II) with HDPBA at pH 9.0±0.2. The reddish-orange complex shows a maximum absorbance at 520nm with a molar absorptivity of 5.9×104l mol-1 cm-1. This method follows Beer′s law up to 1.6μg cm-3 Cd. Various experimental parameters such as the effect of solvents, pH, time, temperature, concentration of the reagent and order of addition of reagents have been studied for establishing the optimum conditions for the determination of cadmium. The effect of diverse ions was examined; the results indicated that most of the common ions like Fe(III), Co(II), Ni(II), Cu(II), Mn(II), AI(III), V(V), Cr(III), Mg(II), Mo(VI), Sn(IV) and Bi(III) do not interfere. The detection limit of cadmium in this method is 0.05μg cm-3. The relative standard deviation of the method for ten replicate measurements is ±1.4%. This method has been successfully employed for the determination of cadmium in various environmental samples.

Soil humic substances affect transport properties of tonoplast vesicles isolated from oat roots

The effect of a low molecular size (<5 KDa) humic fraction, essentially fulvic acids, on microsomal and tonoplast ion-stimulated ATPase activity was studied. After 20 min of pre-incubation with microsomal vesicles from oat roots, humic substances at organic C concentration of up to 0.5 μg cm-3 increased KCl-stimulated ATPase activity, while they inhibited enzyme activity at higher concentrations. Cl--stimulated ATPase activity of tightly sealed tonoplast-enriched vesicles was similarly affected by <5 KDa humic substances. This behaviour was not observed when gramicidin D was added to the assay medium. Proton transport by vesicles incubated up to 5 min with <5 KDa humic molecules was affected in a concentration-dependent manner, strongly resembling that observed for ATP hydrolysis, whereas it was severely reduced when the assay conditions were close to those used for measuring ATP hydrolysis (20 min pre-incubation of vesicles with humic substances). The transmembrane electrical potential was negatively affected, irrespective of the concentration of humic molecules. Furthermore, a 15-min pre-incubation strongly reduced the formation of a potential gradient. The size and concentrations of humic substances employed make an interaction with the vacuolar membrane of root cells plausible. The results show that the main target of humic molecules is the electrical membrane potential and suggest a possible way of interference of these naturally occurring substances with the biochemical mechanisms involved in plant mineral nutrition.

Spectrophotometric determination of ammonium ion after solvent extraction with Cryptand(2.2.2)-dithizone system.

Ammonium ion reacts with 4, 7, 13, 16, 21, 24-hexaoxa-1, 10-diazobicyclo[8.8.8]hexacosane, Cryptand(2.2.2), to form ammonium cryptate which is quantitatively extracted into chloroform as vermilion complex with dithizone. In this work the resulting vermilion complex was utilized for the spectrophotometric determination of ammonium ion. Twenty five milliliters of an aqueous solution containing ammonium ion was shaken with 25 cm3 of chloroform containing 1.0×10-3 mol dm -3 Cryptand(2.2.2) and 4×10-5 mol dm-3 dithizone in a separatory funnel. The mixture was shaken for 10 min by a mechanical shaker. After phase separation, the absorbance of the chloroform phase at 496 nm and the pH value of the aqueous phase were measured. The extracted species had a molar absorptivity of 1.0×104 dm3 mol-1 cm-1 at the absorption maximum of 496 nm. As Na+, K+ and several heavy metals were expected to interfere with the extraction process, a distillation step was introduced to remove these metal ions. A linear calibration curve was obtained up to 1 μg cm-3, the detection limit of the present method being 0.13 μg cm-3 of ammonium ion. The relative standard deviation of the measurements was 1.4% for 0.60 μg cm-3 ammonium ion standard solution. The present method was successfully applied to the analysis of several river water samples.

Fluorometric determination of aluminium with 2,2'-dihydroxy-4,4'-dimethylazobenzene.

Aluminium readily reacts with DDAB (the title compound) in the presence of ethylenediamine (en) to form a stable fluorescent complex, which showed a maximum fluorescence intensity at pH values from 6.9 to 7.6. The fluorescence intensity of the complex increased remarkably with the addition of dioxane to its aqueous solution. The analytical procedure was as follows: Take 0?9 cm3 of a sample solution containing less than 3 μg of aluminium, and add 15 cm3 of a buffer solution described below and 1 cm3 of a 0.02% DDAB solution in dioxane. Dilute the mixture to 25 cm3 with water. After standing for 15 min, measure the fluorescence intensity at 575 nm with excitation wavelength of 485 nm by using 0.01?0.5 μg cm-3 of a Rhodamine B solution as the reference standard. When analysis of samples solution containing 0.005?0.05 μg of aluminium were required, 1 cm3 of a 0.004% DDAB solution was used. The buffer solution (pH 7.4) was prepared by adding 20 cm3 of en and 65 cm3 of (1+1) acetic acid to 200 cm3 of methanol and then diluting it to 500 cm3 with dioxane. The composition of the complex formed under the analytical conditions was Al:DDAB:en:acetate=1:1:2:1. En also acted as a masking agent of interfering ions. The proposed procedure was applied to the determination of aluminium in copper alloys.

Extraction-Spectrophotometric Determination of Pilocarpine in Ophthalmic Solution

Extraction-spectrophotometric determination of pilocarpine with copper(II) and tetrabromophenolphthalein ethyl ester(TBPE) has been developed. Pilocarpine reacts with copper(II) to form a 1:1 stable cationic complex that can be extracted with TBPE dye anion in an aqueous layer buffered at pH 9 into 1, 2-dichloroethane. Molar absorptivity of the ion associate is 1.8×104mol-1 cm-1 dm3 at 528nm and concentrations of copper(II) and TBPE for 1×10-5 mol dm-3 (2.4μg cm-3) pilocarpine are 2×10-4mol dm-3 and 3.2×10-4mol dm-3, respectively. This method can be applied to the determination of trace amounts of pilocarpine in an ophthalmic solution.

Atomic absorption method for the determination of trace amount of iron with ion-pair extraction of dimercaptomaleonitrile complex.

Dimercaptomaleonitrile (rant, H2L) forms a 1:3 complex with iron, FeL3-3.The complex forms an ion-pair with tetrabutylammonium ion (tba+), which can then be extracted into methyl isobuthyl ketone (MIBK). The sensitivity of this method was 0.039 μg cm-3 in MIBK for 1 % absorption. Moderate amounts of most of the ions did not interfere with the determination. This method was also successfully applied to the determination of trace amounts of iron in underground water and tap water.

Phosphate release from synthetic glasses and inhibition of phosphate fixation on ferric hydroxide

Abstract Release of phosphate from glasses in the systems basalt-K3PO4 granite-K2SiO3 Na2SiO3-apatite has been studied. Equilibrium leachate concentrations in water are attained in 3-5 hr (K+, 5-60 μg cm-3; PO4 3-, 2-15 μg cm-3). Glass composition, pH, and grain size influence solubility. Phosphate fixation on freshly precipitated Fe(OH)3 and on iron-rich laterites appear to be inhibited when glasses are rich in Na-K silicates. This may be due to surface modification of Fe(OH)3 by the formation of sodium ferric silicates which are known to be stable at low temperatures.

Direct Determination of Air Density in a Balance Through Artifacts Characterized in an Evacuated Weighing Chamber.

This paper describes a simple device which permits mass comparisons in air without appeal to the correction for air buoyancy. The device consists of a canister which is evacuated and weighed on a laboratory balance with a mass inside. A second weighing of another mass in the evacuated canister provides the desired mass comparison. The method was used to determine the mass difference between two stainless steel weights of widely differing densities. With knowledge of this mass difference and of the volume difference one may, by a simple air weighing of the two objects, determine directly the density of the air in the balance case. Densities of air determined by this method were compared with those calculated from the barometric pressure, the temperature, and the relative humidity of the laboratory air. The experimental and calculated values agree throughout to within 1.0 μg cm-3 (where the normal air density is about 1.2 mg cm-3). The calculated and experimental values of day-to-day fluctuations in air density agree to within 0.5 μg cm-3.

New vibrating sample magnetometers for use between 4 and 1000 K

A vibrating sample magnetometer is described using a compressed air turbine as a vibration mechanism. This device has the advantage of imparting a vibration of fixed stroke (1.2 cm) to the sample and has no inherent sources of electrical noise. A mechanical governor constrains the frequency to 70 c/s and small frequency variations are compensated for by suitable electronic circuits. Hysteresis loops can be measured in fields up to 50 kOe between 4.2 and 1000°K. The limit of sensitivity corresponds to a sample dipole moment of 1 μG cm3, in the absence of an applied field. Ripple in the field reduces the useful sensitivity to about 1 mG cm3.