Spectrofluorimetric flow-injection determination of cyanide

The spectrofluorimetric determination of cyanide (0.1–20 μg ml^?1) with pyridoxal and pyridoxal-5-phosphate by a normal flow-injection method and a stopped-flow procedure is reported. The large number of interfering species in the normal method is significantly decreased by the use of the stopped-flow method. The relative standard deviation is <2%.     

Spectrofluorimetric determination of diquat by manual and flow-injection methods

A reliable, highly sensitive and selective method is described for the determination of the herbicide diquat in different materials. It involves the formation of a stable radical obtained by reduction of diquat with sodium dithionite. The radical is a very fluorescent species (φ_F=0.37), and there is a linear relationship between diquat concentration and fluorescence intensity over the range 3–900 μg l^?1. The limit of detection is 0.4 μg l^?1. The method can be successfully adapted as a flow system using a two-channel manifold, the peak height being proportional to the diquat concentration over the range 18–4000 μg l^?1. Manual and flow-injection methods were successfully applied to the determination of diquat in commercial herbicides, waters, potatoes, flowers and soils. Both procedures were also been applied to the determination of diquat in serum and urine without prior preparation of the samples and with good results.     

Spectrofluorimetric flow-injection determination of cerium in carbon and low alloy steels

Cerium can be determined spectrofluorimetrically (_em 350 nm, _ex 260 nm) based on the relatively intense native fluorescence of the cerium(III) aquo-ion. The main potential interference in the analysis of steel from iron(III), cerium(IV) and chromium(VI) are removed by use of a carrier solution containing 2.5% w/v hydroxylammonium chloride. The slight residual interference from iron(II) can be corrected by a matrix matching factor linearly related to the amount of iron present. The calibration graphs are linear over the range 0–7 g ml^–1 based on 250 l injection volumes. The sampling rate was 30 h^–1. The relative standard deviation was 2.0% (n=5) at 3 g ml^–1 cerium. The system has been applied to the determination of cerium in carbon or low alloy steels.     

Spectrofluorimetric determination of carbaryl and 1-naphthol in micellar media

The interaction of 1-naphthol-N-methyl-carbamate (carbaryl) and its degradation product, 1-naphthol, with the surfactant hexadecyl-trimethylammonium bromide has been studied. The micellar medium allows the direct spectrofluorimetric determination of carbaryl, with 6.2 ng/ml as detection limit in acidic medium, or indirectly, after hydrolysis, as 1-naphthol at pH 11.0 or pH 3.0 with detection limits of 0.4 and 1.6 ng/ml, respectively. The recoveries of carbaryl and 1-naphthol from natural waters are acceptable.     

Flow-injection determination of secondary amines in non-aqueous solution with fluorescence detection

The procedure is based on derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole to form a fluorescent adduct. Interference from primary amines is overcome by on-line chemical masking with an equimolar mixture (58 mM) of o-phthalaldehyde and 2-mercaptoethanol with a tolerance of 20 mM 1-ethylpropylamine for the determination of dibutylamine (0.3 mM). The r.s.d. for dihexylamine (0.34 mM) is 1.3% (n=5) and the limit of detection (unweighted least-squares method) is 0.06 mM.     

The use of microemulsions in flow injection analysis: Spectrofluorimetric determination of primary amines

The use of microemulsion in flow-injection systems is considered, with particular reference to the determination of C₆C₁₀ primary amines by derivatization with o-phthal-aldehyde and 2-mercaptoethanol. Microemulsions provide an ideal interface for reactions between a water-soluble reagent and a non-aqueous sample. The effect of reaction conditions (R value, droplet concentration, pH and flow rate) on the fluorescence signal is discussed and calibration data for three primary alkylamines are given.     

Extraction-spectrofluorimetric determination of cadmium with diethyldithiocarbamate and calcein in non-aqueous media

Cadmium (7–80 ng ml^?1) is extracted with diethyldithiocarbamate into chloroform from aqueous media, at pH 11–12 and the fluorescent complex is developed by addition of a calcein solution in dimethylformamide. The method is applied to the determination of cadmium in waste waters, high-purity metals and zinc ores.     

Cerimetry in non-aqueous media

Summary It was found that ceric oxalate is an intermediate product in the oxidation of oxalic acid by ammonium hexanitrato cerate in solvents such as acetonitrile, and a mixture of acetonitrile and glacial acetic acid. Conditions for the formation of ceric oxalate and its decomposition into carbon dioxide and cerous oxalate have been studied. An analytical method for the estimation of oxalic acid in non-aqueous media has been evolved based on this reaction.

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Zusammenfassung Es wurde festgestellt, daß bei der Oxydation von Oxalsäure mit Ammoniumhexanitratocerat(IV) in Acetonitril oder einem Gemisch von Acetonitril und Essigsäure Cer(IV)-oxalat als Zwischenprodukt auftritt. Die Bedingungen für die Bildung von Cer(IV)-oxalat und seine Zersetzung zu CO₂ und Cer(III)-oxalat wurden untersucht. Ein Verfahren zur Oxalsäurebestimmung in nichtwäßrigem Medium wurde ausgearbeitet.

     

Spectrofluorimetric determination of benzodiazepinooxazoles

Summary A study of fluorescence properties of Cloxazolam and Oxazolam has been carried out. pK_a-values were calculated and a spectrofluorimetric method was developed in acidic hydroalcoholic medium for the determination of the drugs. The fluorescence intensity was linear with the concentration up to at least 6.00×10^–6 mol/l for Cloxazolam and 5.17×10^–6 mol/l for Oxazolam. Detection limits obtained were 2.91×10^–8 mol/l and 4.56×10^–8 mol/l for Cloxazolam and Oxazolam, respectively. Spectrofluorimetric methods were applied to the determination of both drugs in pharmaceuticals and errors lower than 2.5% were obtained. Spectrophotometric determination methods were also developed.     

Electrostatic stabilization in non-aqueous media

This paper discusses electrostatic stabilization of dispersions in non-aqueous media. It begins with the theory of repulsion, with particular attention to the roles of the dielectric constant and ionic strength of the liquid medium. Results for flat plates and spheres are compared. Methods are reviewed to measure the dielectric and electric parameters in non-aqueous media, in conjunction with procedures to determine the mechanical properties of electrostatically stabilized, concentrated suspensions.From theoretical considerations it appears that the extent of the electrostatic stabilization in non-aqueous media is extremely sensitive to the dielectric constant ϵ of the liquid, affecting stability in particular through the degree of dissociation of the stabilizing electrolyte. It is essential that, besides the presence of charge on the particles, there also are certain levels of ions in the solution to ensure a sufficient force of repulsion. It is expedient to distinguish three regimes of ϵ: (a) ϵ ⩾ 11, the (semi-)polar range, where systems can be charge-stabilized more or less as in aqueous systems, (b) the low-polar regime (5 ⩽ ϵ ⩽ 11), where electrostatic stabilization is possible provided some dissociated electrolyte is present and (c) the apolar range (ϵ⩽ 5), where screening is exclusively determined by the polarization of the solvent, and where electrostatic stabilization may be more problematic.Concentrated dispersions of solids in liquid nonionic carriers with dodecyl-benzene sulphonic acid (HDBS) as the stabilizer arc good models for the ‘low polar’ category, as detailed experimental data illustrate. In such media HDBS creates a ζ-potential, and enhances the dielectric constant and the ionic strength of the continuous phase. Especially when attraction between suspended salt particles in liquid nonionics is weak, electrostatic stabilization is easily achieved. This is particularly noticed in the rheology of the concentrated suspensions of some salts.     

Spectrofluorimetric determination of serotonin and 5-hydroxyindoleacetic acid in urine with different cyclodextrin media

Alternative and sensitive spectrofluorimetric methods for the determination of hydroxyindoles, such as serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIA), were developed on the basis of supramolecular interaction with cyclodextrin (CD) nanocavities (βCD and hydroxypropyl-βCD, HPCD) at different pH values. Both substrates and receptors have acidic protons, therefore the interactions produced in different systems were considered. The effects of neutral CD at pH 2.00 and 6.994, and of anionic CD at pH 13.00 on the specific acid-base species of the compounds at each pH were determined. In all the conditions studied, the fluorescence of the substrates in the presence of CD increased. The association constants (K_A, mol⁻¹ L) between the substrates and CD were determined (30-300) and interpreted. A zero-crossing first-derivative spectrofluorimetric method with and without HPCD was developed for the simultaneous determination of 5HT and 5HIA. The limits of detection (L_D, ng mL⁻¹) for the best conditions were 0.37 for 5HT and 0.50 for 5HIA at pH 2.00 with HPCD. These L_D proved to be better than others reported. The applicability of the direct and derivative spectrofluorimetric methods to urine samples was demonstrated with good recoveries 92-110% and R.S.D. 1-10%.     

Spectrofluorimetric determination of triethylenethiophosphoramide in blood

The method is based on a reaction of the ethyleneimine group with sodium sulfide, taurine and o-phthalaldehyde to give a fluorescent product. Triethylenethiophosphoramide (thioTEPA) can be determined in the range 9.4–945 ng in 100 μl of 1-propanol with a relative standard deviation of 2.3–4.7%. The method is applied to the determination of thioTEPA in rabbit blood plasma. The use of Extrelut 3 proved to be efficient for the clean-up of thioTEPA in plasma samples.     

Polymers of tertiary amines

Polymers of tertiary amines and their hydrochlorides of molecular weights in the range 300–2000 have been prepared, starting from trans-1,4-dichlorobutene-2, and primary amines. The polymers present interesting solubility properties. Variation of the reaction conditions leads to crosslinked insoluble polymers. Reaction of the soluble tertiary amine polymers with organic acid dichlorides leads to polymers of tertiary amine–amides, a new type of polymer.     

Generation of bismuthane in non-aqueous media

The generation of BiH₃ in non-aqueous media in an MHS-10 Perkin-Elmer hydride generator is studied. Optimal conditions for generation of BiH₃ inN,N-dimethylformamide, dimethylsulfoxide and formamide (concentration of NaBH₄, acidic medium, optimum volume, characteristic concentration and detection limit) are studied. The results obtained are compared with those corresponding to hydride generation in aqueous medium.     

Spectrofluorimetric determination of 1,4-thienodiazepines

The fluorescence characteristics of four 1,4-thienodiazepines in aqueous and methanolic solutions and the effect of pH on fluorescence intensity are described. The pK_a values are calculated. Fluorimetric methods with limits of detection between 3 and 38 ng ml^?1 were developed, and applied for determinations of one drug in tablets, and the others in serum after extraction with a Sep-Pak C₁₈ cartridge.