Microdetermination of arsenic in water,spectrophotometrically, by arsine-silver diethyldithiocarbamate-morpholine-chloroform system

An improved spectrophotometric method for microdetermination of arsenic in water using arsine-silver diethyldithiocarbamate-morpholine-chloroform system is described. Sensitivity and molar extinction coefficient are 0.0055 μg As/ml and 1.35 × 10⁴ M⁻¹ cm⁻¹ at 510 nm. The color is stable for 3 days. Six other systems are also studied and compared including the silver diethyldithiocarbamate-pyridine system. Interference due to 19 diverse ions has been studied. Antimony interference is removed by excess stannous chloride solution. The method replaces the commonly employed less stable arsine-silver diethyldithiocarbamate-pyridine method.     

Variations of thermal-lens spectrophotoetry with helium-cadmium laser excitation for the determination of traces of phosphorus

Single-beam, differential single-beam and dual-beam thermal-lens measurements are compared for the determination of phosphorus traces by means of a helium-cadmium laser. Phosphate is determined as the molybdophosphate/auramine ion-pair which is extracted into 1:2 isobutanol/hexane; acetone is added to dissolve any ion-pair precipitate. In dual-beam thermal lens experiments a low-power HeNe laser is uded as the probe laser. The detection limit, restricted by variable blank measurement, is 0.6 ng cm^?3 phosphorus in all cases. The advantages and drawbacks of each measurement technique are discussed. The dual-beam system of measurement is more sensitive than the single-beam system and is appropriate for measurements on samples of small volume. The dual-beam system is applied for layer-by-layer determination of phosphorus in semiconductor silicon over the concentratin range 5 × 10^?8 ?5 × 10^?4%. The data obtained by the dual-beam method compare well with those obtained by a neutron activation method.     

Simplified determination of bacterial contamination by Escherichia coli using a flow injection system with piezoelectric detection

A rapid and automated method was developed for the determination of bacterial contamination and using Escherichia coli as a model microorganism. The method involves the use of a sensor connected to a flow injection (FI) system. The sample is introduced through a flow injection system into a piezoelectric quartz crystal (PQC) flow-cell. The resulting change of the resonance frequency is related to the bacterial contamination in the sample. The parameters associated with the flow system and the conditions for introducing the sample culture were optimized. Calibration curves are linear in the range from 3.2?×?10⁷ to 3.2?×?10⁹ cfu per mL^-1, with a correlation coefficient of 0.997. The reproducibility was between 3.1 and 7.6%, and the detection limit is 1.1?×?10⁷ cfu per mL^-1. The method allowed the determination of bacterial contamination in residual water and in samples of milk and chicken stock within 5 h, while the conventional plate count method requires 24 to 48 h. The results obtained by these two methods are in good agreement.

A quantitative method for the analysis of ternary systems

The rapid determination is reported of the concentrations of K⁺, Co²⁺ and Pb²⁺ in a ternary system. The method used is based on the measurement of the activity of the solution containing a labelled component, and on the determination of the intensity of β-rays back-scattered in the system. Standard curves are drawn, by means of which the unknown concentrations of the components in the ternary system can be established. The precision of the method is between 0.5 and 2%.     

Automatic HPLC-UV determination of domoic acid in mussels and algae

Summary A rapid and sensitive automatic method is presented for the determination of domoic acid (DA) using HPLC with a column-switching system and UV-detection. Interfering peaks resulting from matrix protein components are excluded by use of an especially designed reversed-phase HPLC column for pre-separation. The method is suitable for extracts both from mussels and from algae. Sample material is extracted with pure water and the crude extract is injected directly. Application of a column-switching system eliminates the need for any further sample clean-up after extraction. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

An α-γ coincidence technique for measuring226Ra concentrations in water

The application of an α-γ coincidence method for measuring²²⁶Ra concentrations in water is investigated. the experimental system, sample preparation, and results of several measurements are discussed. In addition, the lower limit of detection for the coincidence system is calculated.     

Determination of Potassium Ferrocyanide in Foods by Resonance Rayleigh Scattering Method with Double-Charged Triaminotriphenylmethane Dyes

In pH 1.0 acidic medium, double-charged triaminotriphenylmethane dyes such as methyl green （MEG） and iodine green （IG） react with potassium ferrocyanide to form 2 ： 1 ion-association complexes by virtue of electrostatic forces and hydrophobic interaction. It results in the change of absorption and the great enhancement of resonance Rayleigh scattering （RRS） and the appearance of new RRS spectra. Two systems have similar spectral characteristics and their maximum RRS wavelengths are all located at 276 nm and smaller peaks are located at 332 and 457 nm, respectively. The intensity of RRS is directly proportional to the concentration of [Fe（CN）6]^4- in the range of 0.03-5.7 μg·mL^-1 （MeG system） or 0.04-5.9 μg·mL^-1 （IG system）. The RRS method has high sensitivity and the detection limit （3σ） for potassium ferrocyanide is 9.3 ng·mL^-1 （MeG system） or 11.2 ng·mL^-1 （IG system）. The optimum conditions, influencing factors and effects of foreign substances are investigated. The method also has a good selectivity. A sensitive, rapid and simple RRS method for the determination of potassium ferrocyanide in salinized food and table salt has been developed.     

Spectrophotometric determination of titanium with Chrome Azurol S (or Eriochrome Cyanine R) in the presence of some cationic surfactants

A new sensitive spectrophotometric method for titanium determination, based on the ternary Ti-Chrome Azurol S (CAS)-cetyltrimethylammonium (CTA) system, was developed. The molar absorptivity is 7.3 × 10⁴ liters mol^?1 cm^?1 at λ_max = 565 nm. The maximum absorbance is attained in 5 min at pH 1.3 ± 0.1 and at CAS and CTA concentrations of 1.5 × 10^?4 and 5 × 10^?4M, respectively. Zirconium and hafnium in the presence of ascorbic acid are the only interfering metals. Hydrogen peroxide and EDTA interfere with the titanium determination as well. The proposed method was applied to the determination of titanium (about 1 × 10^?2%) in aluminum metal. The method, based on the Ti-Eriochrome Cyanine R-CTA system, is similar to the above method. Among other cationic surfactants, cetylpyridinium chloride (CP) and zephiramine were examined. The color effects when using CP, and especially zephiramine, are worse than in the presence of CTA.     

Flow-injection spectrophotometric determination of aluminium in water with pyrocatechol violet

Optimum conditions for the adaptation of the spectrophotometric pyrocatechol violet method for aluminium to a flow-injection system are described. The detection limit is 3 μg Al l^?1 and calibration graphs are linear up to 3 or 10 mg l^?1 (with 200-μl or 10-μl injection loops, respectively). The relative standard deviation is 〈 2% at 0.1 mg Al l^?1. Potential interferences of 40 common inorganic ions and of 20 organic substances, including fulvic acid, are reported. With the use of conventional masking agents and predigestion of samples with high organic content, the method is suitable for determining total aluminium in natural waters.     

Rapid <Superscript>224</Superscript>Ra measurements in water via multiple radon detectors

We introduce an improved on-site rapid analysis system for measuring ²²⁴Ra in natural waters. Radium isotopes are pre-concentrated on “Mn-fibers” before measurement of ²²⁰Rn. A Nafion drying system is used to lower the humidity in the detectors while maintaining a relatively constant moisture level in the Mn fiber in order to maintain a high and reproducible radon emanation. River water samples measured by this method agreed well with an analysis via RaDeCC, a very sensitive technique for measuring ²²⁴Ra. This method is recommended for fieldwork in remote areas when electricity and helium gas, required by traditional techniques, are not available.     

Thermodynamic representation of ternary liquid–liquid equilibria near-to and far-from the plait point

Common classical expressions for the molar excess Gibbs energy of mixing g^E do not contain a contribution from composition fluctuations that are significant in the vicinity of the plait point for a ternary system. We propose a correction to g^E based on reasonable phenomenological assumptions. This correction requires three ternary constants, but two are obtained from stability relations provided that we know the composition of the plait point. While the method proposed here is not predictive, it provides a consistent thermodynamic procedure for calculating the liquid–liquid phase diagram of a ternary system with a plait point. The proposed method is illustrated for three ternaries. When calculations are based on the classical expressions for g^E alone, calculated results are in serious disagreement with experiment near critical conditions. Inclusion of the proposed correction for g^E provides dramatic improvement.     

A method for the determination of additive elements in sintered tungsten metal rods by fast neutron activation analysis

A non-destructive activation analytical method developed for the determination of the axial concentration distributions of Al, Si and K residual additives in sintered tungsten rods is briefly described. A 14 MeV neutron generator is used to produce the reactions²⁷Al(n, p)²⁷Mg,²⁸Si(n, p)²⁸Al and³⁹K(n, 2n)³⁸K and the activities are compared with standards. A weighted least-squares fitting program is used for peak area determination of the scintillation spectra. A scheme of the irradiating and measuring arrangement with a pneumatic sample-transfer system is presented. The system is applicable to large-scale routine analysis and lends itself well to automation. The results of preliminary measurements with this arrangement are given.     

Direct Determination of Zinc Using Dithizone in Micellar Solution

Abstract

A simple method for direct determination of Zn²⁺ by spectrophotometry using dithizone in micellar solutions is possible. Surfactants are used to overcome the solubility problems of dithizone in aqueous medium. The proposed method saves time and chemicals and is of extremely high sensitivity. Zn²⁺ concentrations of about 2×10^-7 M can be determined. The important analytical parameters and their effects on the reported system are investigated.     

Asymmetric Anion‐selective Membrane Electrode for Determining Nitric Oxide Release Rates from Ppolymeric Films/Electrochemical Devices

A novel potentiometric method for the determination of nitric oxide (NO) is presented. The assessment of NO levels is based on the rapid reaction of NO with oxyhemoglobin, during which nitrate is formed and then detected potentiometrically using a polymeric membrane anion‐selective electrode. The composition of the anion‐selective membrane is optimized to eliminate the response to high levels of oxyhemoglobin reagent used to react with NO to form NO₃^?. The practical utility of the method is demonstrated by determining the NO release rates from NO donor‐doped polymeric films, as well as from a new electrochemical NO generation system within the range of 10 to 55×10^?10 mol ? min^?1. The values measured with the new assay system are shown to correlate well with a chemiluminescence reference method after accounting for the trapping efficiency of NO by the oxyhemoglobin solution.     

The potentiometric determination of insecticides: Part I. Organophosphorus insecticides inhibiting cholinesterase

A potentiometric method for the determination of organophosphorus insecticides based on the inhibition of cholinesterase is presented. The acetic acid formed by hydrolysis of acetylcholine is sensed by a glass electrode in a weakly buffered system. The insecticide is incubated with cholinesterase for 1 h at 25°C or 37°C before addition to the substrate. The effects of incubation time and temperature are discussed. The method is applied to the insecticides bromophos and dichlorvos. The detection limits are 2 × 10^-5 M (7 ppb) for bromophos and 1 × 10^-7 M (22 ppb) for dichlorvos. The initial rates of hydrolysis decrease linearly up to 2 × 10^-7 M and 1 × 10^-6 M, respectively.     

A new method of Fourier-transform smoothing with ratio spectra derivative spectrophotometry

A new method which combines Fourier-transform smoothing with ratio spectra derivative spectrophotometry has been developed for analysis of binary and ternary mixtures. The method proposed has been applied to the simultaneous determination of a binary mixture of 0.974–2.026 × 10^–2?g?L^–1 nitrate and nitrite and to a ternary mixture of 1.840–3.888 × 10^–3 g L^–1 histidine, phenylalanine, and tryptophan. The relative standard derivations are between 0.07 and 5.3% for the former system, and between 0.5 and 7.3% for the latter. The results show that the method proposed is more accurate than multiple linear regression.     

The electrochemical determination of ammonium based on the selective inhibition of the low-spin iron(II)/(III) system of Prussian blue

A new method is described for the determination of ammonium in aqueous solutions with electrodes modified by Prussian blue (PB). The specific voltammetric response of PB-modified electrodes to ammonium ions is used for their analytical determination. In the presence of ammonium ions, a concentration-dependent inhibition of the low-spin iron(II/III) system of PB occurs. Only thallium and rubidium ions cause similar inhibition. A useful electrochemical determination method is thus available for detecting ammonium ions in the presence of frequently interfering potassium and sodium ions. Paraffin-impregnated graphite electrodes modified with a mechanically transferred PB layer and bulk-modified PB-composite electrodes are studied. The method is applicable within a concentration range which extends from 4 × 10⁻⁵ mol/l to 10⁻² mol/l NH₄ ⁺. The composite electrode is used in an electrochemical flow-through system in conjunction with the Kjeldahl method. Received: 21 April 1997 / Accepted: 28 May 1997     

Kinetic Determination of GA by the BZ Oscillating Chemical System

A new analytic method for the determination of gibberellic acid (GA) by perturbation causing different amounts of GA on the BZ oscillating chemical system involving the Mn(II)‐catalyzed reaction between L‐alanine, potassium bromate, and malonic acid in the acidic medium is proposed. The method relies on the linear relationship between the change in the oscillating period of the chemical system and the concentration of GA, which is in this work exposed for the first time. The calibration curve is linearly proportional to the concentration of GA over the range 1.0 × 10⁸ ?1.0 × 10^?6M, where the regression coefficient is 0.9998, and the detection limit is 5.0 × 10^?9 M of GA. Some aspects of the potential mechanism of action of GA on the BZ oscillating chemical system are discussed in detail.     

Vapour-liquid equilibria. X. The ternary system cyclohexane-methanol-acetone at 293.15 and 303.15 K

Total vapour pressure measurements made by the modified static method for the ternary system cyclohexanemethanolacetone and all the constituent binary systems at 293.15 and 303.15 K are presented. The alcohol high-dilution region of the cyclohexanemethanol system has been thoroughly studied. Different exprerssions for G^E suitable for correlation of these data are tested. The prediction of ternary VLE from the constituent binaries is studied. The accuracy of the prediction of H^E from two (P, x) isotherms is studied for the binary systems. The possibility of predicting the ternary H^E from VLE isotherms is also. Our results are compared with literature data.     

Direct spectrophotometric determination of ruthenium in aqueous streams of nuclear reprocessing

A fiber optic aided spectrophotometric technique has been developed for determination of ruthenium in nitric acid medium. The developed method is simple, accurate and applicable to aqueous streams of nuclear reprocessing. The system obeys Lambert–Beer’s law at 468 nm in the concentration range of 30–360 μg/mL of ruthenium. The molar absorption coefficient, detection limit and Sandell’s sensitivity are 68.477 L Mol^?1 cm^?1, 31 μg/mL and 0.0124 μg/cm² respectively. Relative standard deviation was less than 2 % and correlation coefficient was 0.9998. The results obtained by the developed procedure are in good agreement with those obtained by the standard ICP-OES method. Fission products like zirconium and strontium are not interfering. Uranium is interfering and needs prior separation by solvent extraction method. The developed method is adaptable for remote operation and on-line monitoring.