Rapid separation of humic acid in fresh waters by coprecipitation and flotation

After removal of suspended matter in 1 liter of water by flotation with a cationic surfactant, humic acid at theg/l level is separated from fulvic acid by coprecipitation with milligram quantities of iron(III) hydroxide at pH 7 followed by flotation with anionic surfactants. The iron(III) hydroxide is dissolved in 2M hydrochloric acid, and the acid-insoluble humic acid is filtered off on an ultrafilter and then dissolved in 10 ml of 0.1M potassium hydroxide solution for measurements of absorption spectra, molecular weight distribution and complexing ability. The time required for the separation is ca. 1 h.     

Determination of Molybdenum and Vanadium in Seawater by Ion-Exchange Preconcentration-Inductively Coupled Plasma Atomic Emission Spectrometry

A simple and rapid method has been developed for the determination of molybdenum and vanadium in seawater using ion-exchange preconcentration and inductively coupled plasma atomic emission spectrometry (ICP-AES). One hundred milliliters of seawater prepared as 0.05 M hydrochloric acid solution is passed through a cellulose phosphate column, and molybdenum and vanadium adsorbed on the cellulose are eluted simultaneously with dilute ammonia solution. The effluent collected is evaporated to a small volume, in which molybdenum and vanadium can be determined by ICP-AES. The overall recoveries of molybdenum and vanadium are 93.6 and 80.4%, respectively, at the level of 1 μgMo/100 ml and 0.1 μgV/100 ml. The proposed method has been successfully applied to the determination of the two elements in several seawater samples. Relative standard deviations (n = 3) are 2.0-2.9 and 0.3-4.3% for molybdenum and vanadium, respectively.     

Extraction and spectrophotometric determination of titanium(iv) with 3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone

Titanium(IV) in sulphuric, perchloric and hydrochloric acid media reacts with 3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone (HY) to give a complex which is extractable into chloroform. The composition of the extractable complex depends on the acidity of the aqueous phase and on which mineral acid is used. The mixed titanium-perchlorate-HY complex which is formed in the presence of excess of perchlorate is the most suitable for the spectrophotometric determination of titanium. The molar absorptivity of the complex is 1.6×10⁴1·mole^–1·cm^–1 at 355 nm. The optimum titanium concentration range is 0.5–6,g/ml. The method has been successfully applied to the determination of titanium in samples of bauxite and alumina refractory.     

Quantitative separation of the alkali metals by cation-exchange chkomatography with bio-rex 40 resin : Application to silicate analysis

The application of BIO-REX 40, a phenolformaldehyde resin, to the quantitative separation of Li, Na, K, Rb and Cs is described. All five elements can be separated in a single procedure by using a 25-g (62-ml) resin column and eluting lithium with 500 ml of 1.00 M hydrochloric acid in 80% ethanol, sodium with 500 ml of 0.20 M hydrochloric acid, potassium with 250 ml of 0.70 M hydrochloric acid, rubidium with another 450 ml of 0.70 M hydrochloric acid and cesium with 500 ml of 4.0 M hydrochloric acid. Procedures are described for the accurate determination of alkali metals in silicate minerals, plant material and water. Al, Fe, Ti, Zr, V, Mo and some other elements are first separated by absorption as oxalato complexes on a column of AG1-X8 resin. The alkali metals are finally determined by gravimetry or atomic absorption spectrometry. Tables of distribution coefficients and quantitative results of analyses of synthetic mixture and standard silicate samples are presented together with typical elution curves.     

Use of Catecholoxygenase for Determination of Catechol

Abstract

A cell extract from Trichosporon cutaneum containing catechol 1,2-oxygenase catalyzes the oxidation of catechol to cis,cis-muconic acid. The absorbance of the cis,cis-muconic acid at 260 nm can be correlated with the initial catechol concentration in the range 5 × 10^?6 M to 5 × 10^?5 M in aqueous solutions. This enzymatic assay has been applied to the determination of catechol in aqueous samples derived from coal processing.     

Chemiluminescence in model membrane structures chemiluminescence of lucigenin in the presence of estrogens

The chemiluminescence quantum yields of the lucigenin light reaction in 10^–2 M didodecyldimethylammonium bromide (DDAB) lamelar aggregates are affected by the presence of estrone and 17 -ethynylestradiol. A rise in quantum yields is observed at ca. 1·10^–4 M estrogen concentration as compared with the homogeneous (aqueous) medium, followed by a dramatic drop as the estrogen concentration increases. Unexpectedly, the smecticity of the lamelar aggregate is destroyed by estrone concentration as low as 10^–3 M and 17 -ethynylestradiol concentrations as low as 2·10^–4 M.

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Chemilumineszenz in Modell-Membranstrukturen Die Chemilumineszenz von Lucigenin in Gegenwart von Estrogenen

Zusammenfassung Die Chemilumineszenzquantenausbeuten der Lucigenin-Lichtreaktion in 10^–2 M Didodecyldimethylammoniumbromid (DDAB)-Lamellaraggregaten wird bei Gegenwart von Estron und 17 -Ethinylestradiol beeinflußt. Es wird eine Erhöhung der Quantenausbeuten bei ca. 1·10^–4 M Estrogengehalt gegenüber einem homogenen (wäßrigen) Medium beobachtet, bei Erhöhung der Estrogenkonzentration erfolgt jedoch eine drastische Erniedrigung der Quantenausbeuten. Die Smektizität der Lamellaraggregate wird bei Estronkonzentrationen von etwa 10^–3 M und 17 -Ethinylestradiolkonzentrationen von etwa 2·10^–4 M unerwarteterweise zerstört.

     

Simultaneous Determination of the Concentration of Elements and Their Speciation in Solid Samples Using X-ray Fluorescence Spectrometry

A method is proposed for the X-ray emission analysis of solid samples in which two analytical signals are used in one experiment. The first signal depends on the structure and type of the chemical compound in the test sample, and the second one is used for determining the concentration of elements entering into the composition of the test sample. The relative integral intensity of the last emission line in the characteristic X-ray spectrum is used as the first analytical signal. This line is due to an electron transition from the valence band to an inner atomic level (for example, the K ₂ line for elements from Cu to Br). The spectral intensity of the brightest (K , L and, less frequently, M or M ) lines of the characteristic X-ray spectrum serves as the second analytical signal, which is conventionally used in X-ray fluorescence analysis.     

Fibre optic fluorometric enzyme sensors for hydrogen peroxide and lactate,based on horseradish peroxidase and lactate oxidase

An optical biosensor for the determination of hydrogen peroxide based on immobilized horseradish peroxidase is described. The fluorescence of the dimeric product of the enzyme catalysed oxidation of homovanillic acid is utilized to determine the concentration of H₂O₂. The membrane-bound enzyme is attached to a bifurcated fibre bundle permitting excitation and detection of the fluorescence by a fluorometer. The response of the sensor is linear from 1 to 130 M hydrogen peroxide; the coefficient of variation is 3%. The sensor is stable for more than 10 weeks. The operating pH for maximal sensor response is 8.15. This allows the sensor to be used in combination with oxidase reactions producing hydrogen peroxide, as is demonstrated with a co-immobilized lactate oxidase-horseradish peroxidase optode for the determination of L-lactate. The fluorescence intensity of this sensor depends linearly on the concentration of lactate between 3 and 200 M and a throughput of 10 samples per hour is possible. The precision is in the same range as that of the monoenzyme optode. The lifetime of the bienzyme sensor for lactate is considerably shorter than that of the peroxidase sensor; it is limited by the stability of the immobilized lactate oxidase enzyme. The sensor has been applied to the determination of lactate in control serum.     

Column separation and preconcentration of copper(II), lead(II) and zinc(II) from seawater

Summary The sample of seawater (51) is freed from solid particles, buffered at pH 5.6 and percolated through a column filled with ED₃A. After sample passage 15 ml 1 M hydrochloric acid solution are pumped through the column to dissolve the concentrated ions. The final measurement using flame atomic absorption is carried out in the hydrochloric acid solution. The total labour time is less than 15 min. The standard deviations (4 analyses) for the determination of Cu, Pb and Zn (in the normal concentration range of 2–6 g · l^–1) were 2–5%, 5% and 1–10%, the recoveries 100%, 102% and 104%, respectively. A concentration coefficient of 300–500 was obtained.On leave from Lisbon University, Portugal     

Spectrophotometric determination of plutonium with chlorophosphonazo III

Summary Plutonium(IV) forms a Chlorophosphonazo III complex in 0.5–2M hydrochloric acid. Maximum absorbance occurs at 620 and 685 nm. Beer's law is obeyed over the range of 0–50g per 10 ml and the molar absorptivity is 3.7×10⁴ mol^–1 cm^–1 at 690 nm. Plutonium can be determined in the presence of fluoride, sulfate and phosphate. However, lanthanides, thorium, uranium and zirconium interfere seriously.

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Zusammenfassung Plutonium(IV) bildet in 0,5-bis 2-m Salzsäure mit Chlorphosphonazo III eine Komplexverbindung, deren Absorptionsmaxima bei 630 und 685 nm liegen. Bis 50 g/10 ml entspricht die Farbe dem Beer'schen Gesetz; die molare Extinktion bei 690 nm beträgt 3,7·10⁴l·Mol^–1·cm^–1. Plutonium kann damit in Gegenwart von F^–, SO₄ ^2– und PO₄ ^3– bestimmt werden. Lanthanide, Th, U und Zr stören jedoch ernstlich.

     

The Separation and Determination of Molybdenum by Electron Paramagnetic Resonance

Abstract

A procedure is described for the separation and quantitative determination of molybdenum by means of EPR. Molybdenum(VI) was precipitated from a hydrochloric acid solution (1.5 Molar) with α-benzoinoxime. The precipitate was separated by centrifugation and then the sample was dried in an oven at 105°C. Nitrogen was passed over the sample to complete the drying procedure. The precipitate was dissolved in acetonitrile which was 0.5 M in lithium perchlorate. Electrochemical reduction of the sample produced the molybdenum(V) species. The concentration of molybdenum(V) was determined directly from the intensity of the first derivative EPR signal. The range of linearity of the analytical curve was 1.00 × 10^?2 M to 1.00 × 10^?4 M, and a routine accuracy of less than 6% was obtained.     

Extraction-spectrophotometric determination of iron with 1,2,4,6-tetraphenylpyridinium perchlorate

Summary In 7M hydrochloric acid medium, iron(III) forms an ion-association compound with 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) which is extractable into isoamyl acetate. The extracted ionpair, which has an Fe: TPPP mole ratio of 11, is used for the spectrophotometric determination of iron (=3.10×10⁴l·mole^–1· cm^–1) in the concentration range 0.1–1.5g/ml in the organic phase. The interference of a number of foreign ions has been investigated. The method is applicable to the determination of iron in various materials.     

The reaction of Se(IV) with 2-aminodiphenylamine and its application to spectrophotometric determination of selenium in a strongly acidic medium

Se(IV) reacts with 2-aminodiphenylamine in perchloric, sulphuric or hydrochloric acid media to give the phenylbenzoselen-adiazolium cation. The optimum hydrogen-ion concentration ranges from about 0.1 to 5M. The molar absorptivity at =352 nm is 1.81×10⁴ 1 · mole^–1 · cm^–1. The product is extracted as an ion-association complex with perchlorate into a mixture of hexanol and chlorobenzene. The kinetics of the reaction was investigated.     

A Simple and Mild Procedure for the Preparation of Bile Acid Methyl Esters

Bile acid ester are useful intermediates in reaction schemes yielding bile alcohols^2–5 and other acid derivatives. Reported methods for the preparation of bi le acid methyl or ethyl esters consist of dissolving the bile acid in a large excess of absolute alcohol (ei ther methanol or ethanol) containing a catalytic amount of concentrated mineral acid (either hydrochloric or sul furic). Alternately bile acid methyl esters have been prepared using diazomethane thus avoid the use of strong mineral acids. This very simple methods, presented howe ver several drawbacks. In the former method, the use of strong mineral acids, expecially hydrochloric acid, on polyhydroxy steroids, such as bile acids, can often cau se the formation of undesirable side products.     

Multielement characterization of silicon carbide powders by instrumental neutron activation analysis and ICP-atomic emission spectrometry

Summary Instrumental neutron activation analysis (INAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES) have been optimized for application to a comprehensive analysis of silicon carbide powders. Via medium- and long-lived indicator radionuclides with half lives between 2.3 h (¹⁶⁵Dy) and 12.4 a (¹⁵²Eu), INAA can detect 55 elements. Analytical parameters and experimental modes are given with limits of detection obtained for a silicon carbide powder of typical purity grade. For the performance of ICP-AES, a wet-chemical decomposition procedure was optimized for sample portions of about 1 g using a mixture of high-purity conc. HF, HNO₃ and H₂SO₄ for digestion in autoclaves with a PTFE-liner. For all investigated elements, recoveries 98% were obtained. By scanning wavelength profiles, interference-free emission lines were found for 56 elements. By the combined performance of INAA and ICP-AES, 66 elements were assayed in the analysed silicon carbide powder. The limits of detection were below 0.01 g/g for 24 elements, they were between 0.01 and 0.1 g/g for 17 and between 0.1 and 1 g/g for 15 elements. The remaining 10 elements were detectable at levels >1 g/g. The comparison of results of these two methods as well as of results obtained by other laboratories shows that, for the most common impurities, a satisfactory degree of accuracy could be achieved.     

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L^–1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L^–1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 g g^–1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 g g^–1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 g g^–1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.     

Simultaneous determination of iron(III) and cobalt(II) withN-phenylcinnamohydroxamic acid and thiocyanate by extraction and spectrophotometry

Simple, precise, sensitive, and highly selective methods for the separate determination of iron(III) and cobalt(II) and for the simultaneous determination of both metal ions are described. Iron(III) and cobalt(II) react with thiocyanate in the presence ofN-phenylcinnamohydroxamic acid (PCHA) to form pinkish red and blue coloured complexes, respectively. Both the iron(III) and cobalt(II) complexes having stoichiometric composition of 122 (FeSCN^–PCHA) and 14 (CoSCN^–), respectively, are quantitatively extractable into ethylacetate from 0.5–1.5 M hydrochloric acid solutions. The spectra of iron(III) and cobalt(II) complexes in the visible region exhibit absorption maxima at 495 and 625 nm, respectively. The coloured systems obey Beer's law in the concentration range of 0.2–4.0g/ml of iron and 2–40g/ml of cobalt. The effects of foreign ions and of various experimental parameters were studied to establish the optimum conditions for the extraction and determination of iron and cobalt. The methods have been applied successfully to the analysis of blood, vitamin B₁₂, and standard steels for iron and cobalt.     

Universal method for the anion exchange separation of uranium and its application to the determination of uranium in sea water, marine sediments and other geological samples

Summary Before the fluorimetric determination of uranium in sea water, marine sediments and other geological samples an ion exchange procedure is used to separate uranium from interfering elements. This separation is best performed on Dowex 1 in a medium consisting of 90% methyl glycol and 10% 6 N hydrochloric acid. By means of this method easily reproducible and accurate results of determinations of uranium in as little as 250 ml of sea water or in about 0.1 g amounts of solid samples can be obtained. Because of its universal applicability this technique is to be recommended whenever g but also mg quantities of uranium have to be determined.

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Zusammenfassung Vor der fluorimetrischen Bestimmung von Uran in Meerwasser, Meeressedimenten und anderen geologischen Proben wird das Uran durch ein Ionenaustauschverfahren von störenden Elementen getrennt. Diese Trennung wird am besten auf Dowex l in einem Medium aus 90% Methylglykol und 10% 6 n Salzsäure ausgeführt. Mit dieser Methode lassen sich leicht reproduzierbare und genaue Uranbestimmungen im Meerwasser und in festen Proben durchführen, selbst wenn deren Mengen 250ml bzw. 0,1 g nicht überschreiten. Infolge ihrer allgemeinen Anwendbarkeit wird die Methode zur Bestimmung von g- und mg-Mengen Uran empfohlen.

     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

Sodium Coumarin 6-Sulfonate,A Fluorometric Ion-Pairing Reagent for Tertiary Amines. Application to the Determination of Chlorpheniramine Maleate

Abstract

A study of sodium coumarin 6-sulfonate as a fluorescent ionpair reagent indicated that it could be useful in the analysis of tertiary amines such as chlorpheniramine maleate. The physical properties of the coumarin sulfonate that make it suitable as a fluorescent ion-pair reagent for basic drugs are its high relative quantum yield (0.76) and its acidity (pKa of ?7.66). Methylene chloride containing 5% n?pentanol was used to extract the coumarinchlorpheniramine ion-pair from aqueous solution. It was found that a 10^?2 M coumarin concentration yielded a 92% recovery of chlorpheniramine at pH 5. Following phase separation, the coumarin species was completely ionized by the addition of tetrabuty1 ammonium hydroxide to the organic phase. After irradiation for 30 min using long wavelength ultraviolet light (365 nm), the fluorescence intensity of the sample was measured using excitation and emission wavelengths of 400 and 540 nm, respectively. Comparison of fluorescence data of spiked aqueous samples to that of a chlorpheniramine maleate standard curve performed concurrently gave drug concentration in the samples. The calibration curve was linear in the 50–1000 ng/ml range (0.13 ? 2.6 × 10 ^?6 M). The procedure allowed the determination of chlorpheniramine maleate with an accuracy of 4–6% and a precision of 2–6% RSD (relative standard deviation). The minimum detectable concentration of drug (S/N = 2) that can be assayed by this method is 50 ng/ml of the maleate salt (35.3 ng/ml of chlorpheniramine free base).