Examination of the modified monostandard method in neutron activation analysis

The reproducibility, the small scale as well as the large scale variability of¹³⁷Cs extracted sequentially from the soil by using a modified Tessier procedure was investigated at several grassland sites in Bavaria/Germany and in the Chemobyl area. Because undisturbed grassland soils are never homogeneous with respect to their soil properties, all sequential extractions at the German sites were carried out at each plot separately for different soil layers (e.g., 0–2, 2–5, 5–10, 10–15, 15–20 and 20–30 cm). The results show that the coefficients of variation (CV) for the reproducibility of the extraction procedure for¹³⁷Cs was (with some exceptions) around 10–20% for all fractions. For the small scale variability of¹³⁷Cs (samples within an area of 10×10m²) the values for theCV were (again with a few exceptions) in the same range. Compared to that, the large scale variability of extractable¹³⁷Cs (random soil samples within an area of 100×200 km²) was higher for all fractions, even though only moderately. The implications of these results with respect to a sampling design are discussed.     

Zur emissionsspektralanalytischen Bestimmung von Cu-, Fe- und Pb-Spuren in ZnS-Leuchtstoffen

Zusammenfassung Eine emissionsspektralanalytische Methode wird beschrieben, mit deren Hilfe 3 · 10^–7 bis 3 · 10^–5 g Fe, 2 · 10^–6 bis 3,2 · 10^–6 g Pb und 3 · 10^–8 bis 1 · 10^–5 g Cu pro g ZnS bestimmt werden können.

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Summary An emission spectral analytical method is described by which 3 · 10^–7 to 3 · 10^–5 g iron, 2 · 10^–6 3.2 · 10^–5 g lead, and 3 · 10^–8–1 · 10^–5 g copper per g ZnS can be determined.

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Résumé On décrit une méthode d'analyse spectrale par émission permettant de doser 3 · 10^–7–3 · 10^–5 g Fe, 2 · 10^–6–3,2 · 10^–5 g Pb et 3 · 10^–8–1 · 10^–5g Cu par g ZnS.

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Herrn Prof. Dr.A. A. Benedetti-Pichler zum 70. Geburtstag gewidmet. Vorgetragen am XI. Colloquium Spectroacopicum Internationale, Beograd, 1963.

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Wir danken auch an dieser Stelle HerrnP. Endröi für die Zubereitung der Standards mit Cu- und Fe-Zusatz und Herrn DirektorF. Kömüves für die Erlaubnis zur Publikation dieser Arbeit.     

Qualitative and quantitative analyses of three bioactive compounds in different parts of Forsythia suspensa by high-performance liquid chromatography-electrospray ionization-mass spectrometry

A high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) analytical method was developed to simultaneously detect and quantify three main distinctive compounds (forsythiaside, rutin and forsythin) in different parts of Forsythia suspensa (F. suspensa), an herbal medicine. This was the first report on the quantification of bioactive constituents in different parts of F. suspensa by HPLC-ESI-MS analytical method. The calibration curves of the three compounds showed good linearity (R² > 0.9994). The method was reproducible with intra- and inter-day variation less than 1.35% and 2.00%, respectively. The recovery of the assay was in the range of 98.27–101.07%. The results indicated that the developed assay could be considered as a suitable quality control method for this commonly used herbal medicine.     

Micro-pumping flow system for spectrophotometric determination of anionic surfactants in water

A novel procedure has been developed for spectrophotometric determination of anionic surfactants in water using a solenoid micro-pump as fluid-propulsion device. The proposed method is based on substitution of methyl orange (MO) by anionic surfactants in the formation of an ion-pair with the cetyl pyridine ion (CPC⁺) at pH 5.0. The flow network comprised four solenoid micro-pumps which, under microcomputer control, enabled sample and reagent introduction, and homogenisation in the reaction zone. The system is flexible and simple to operate and control, and sensitive and precise. The analytical plot for the anionic surfactant was linear between 1.43×10^–6 and 1.43×10^–5 mol L^–1 (0.5 to 5.0 mg L^–1; R=0.997, n=5). The relative standard deviation was 0.8% (n=11) for a sample containing 5.74×10^–6 mol L^–1 (2 mg L^–1) surfactant. The limit of detection was 9.76×10^–8 mol L^–1 (0.034 mg L^–1) and the sampling throughput was 60 determinations per hour. The results obtained for washing-water samples were comparable with those obtained by use of the reference method, and no significant differences at the 95% confidence level were observed.     

Spectrophotometric determination of cationic and anionic surfactants with anionic dyes in the presence of nonionic surfactants,part II: Development of batch and flow injection methods

On the basis of the changes in absorption spectra of azo dyes on the addition of an organic onium ion, spectrophotometric methods for the determination of organic onium salts and anionic surfactants were developed, and applied to flow injection method. Propyl orange (PO^–) was used for the determination of organic onium ions. Pairs of PO^– and Zeph⁺ (tetradecyldimethyl-benzylammonium ion) or PO^– and nC₁₈TMA⁺ (n-octadecyltrimethylammonium ion) were used for the determination of anionic surfactants. The determination range of organic onium ions were (0–3) × 10^–5 M by a batch method and were (0–2) × 10^–5 M by a flow injection method. The determination ranges of anionic surfactants were (0–2) × 10^–5 M by the batch method, and were (0–5) × 10^–5 M by the flow injection method, and the detection limit corresponding toS/N = 3 was 3 × 10^–7 M by the flow injection method. By the proposed flow injection method, anionic surfactants in water samples were determined.     

Amperometric and spectrophotometric determination of carbaryl in natural waters and commercial formulations

The work presented describes the development and evaluation of two flow-injection analysis (FIA) systems for the automated determination of carbaryl in spiked natural waters and commercial formulations. Samples are injected directly into the system where they are subjected to alkaline hydrolysis thus forming 1-naphthol. This product is readily oxidised at a glassy carbon electrode. The electrochemical behaviour of 1-naphthol allows the development of an FIA system with an amperometric detector in which 1-naphthol determination, and thus measurement of carbaryl concentration, can be performed. Linear response over the range 1.0×10^–7 to 1.0×10^–5 mol L^–1, with a sampling rate of 80 samples h^–1, was recorded. The detection limit was 1.0×10^–8 mol L^–1. Another FIA manifold was constructed but this used a colorimetric detector. The methodology was based on the coupling of 1-naphthol with phenylhydrazine hydrochloride to produce a red complex which has maximum absorbance at 495 nm. The response was linear from 1.0×10^–5 to 1.5×10^–3 mol L^–1 with a detection limit of 1.0×10^–6 mol L^–1. Sample-throughput was about 60 samples h^–1. Validation of the results provided by the two FIA methodologies was performed by comparing them with results from a standard HPLC–UV technique. The relative deviation was <5%. Recovery trials were also carried out and the values obtained ranged from 97.0 to 102.0% for both methods. The repeatability (RSD, %) of 12 consecutive injections of one sample was 0.8% and 1.6% for the amperometric and colorimetric systems, respectively.     

Mutual diffusion coefficients of aqueous ZnSO4 at 25°C

Diffusion coefficients of the system ZnSO₄–H₂O at 25°C have been measured using Rayleigh optics from 0.004 to 3.33m. The results appear to extrapolate with reasonable agreement to the data of Harned and Hudson at very low concentration. The diffusion coefficients decrease from 0.8486×10^–5 at 0m to 0.2813×10^–5 cm²-sec^–1 at 3.33m. Densities were measured over the concentration range 0.10 to 3.60m and combined with the data of Geffcken and of Gibson to obtain an analytical expression for density over the concentration range 0m3.6.     

Effects of cationic micelles on fluorescence of indole and indolecarboxylic acids. Analytical determinations

The effect of cationic micelles of benzyldimethylhexadecylammonium chloride and hexadecyltrimethylammonium bromide on the fluorescence spectra of indole and its carboxylic derivatives were determined. The larger solute-micelle binding constants were provided by benzyldimethylhexadecylammonium chloride, ranging from 0.10·10⁵ and 2.15·10⁵ M ^–1 for indole-5-carboxylic and indole-2-carboxylic acid, respectively. The determination of indole-4-carboxylic acid with a detection limit of 1.0 ng ml^–1, in the presence of the 3-and 5-substituted derivatives, shows the analytical potential of the synchronous spectrofluorimetry combined with the enhancement effects caused by micellar media.     

The multivariate coefficient of variation for comparing serum protein electrophoresis techniques in external quality assessment schemes

External quality assessment (EQA) schemes are national or transnational programmes designed to control the analytical performance of clinical laboratories and to maintain inter-laboratory variability within acceptable limits. In such EQA programmes, participants are usually grouped by the type of assay technique/equipment they use. The coefficient of variation (CV) is a simple tool for comparing the inter-laboratory reproducibility of such techniques: the lower the CV, the better the analytical performance. Serum protein electrophoresis, a laboratory test profile consisting of five fractions (albumin, α ₁, α ₂, β and γ globulins) summing up to 100% of total proteins, can also be assayed in different ways depending on the media or the analytical principle. We propose a multivariate CV for comparing the performance of electrophoretic techniques in EQA, thus extending the univariate CV concept. First, the compositional nature of electrophoretic data requires a one-to-one transformation from the five-dimensional to the four-dimensional space. Next, robust estimations of the mean and the covariance matrix are needed to avoid the effect of outliers. The new approach is illustrated on electrophoretic datasets from the French and Belgian national EQA programmes.     

Determination of organotin compounds in biological samples using accelerated solvent extraction,sodium tetraethylborate ethylation,and multicapillary gas chromatography–flame photometric detection

A method has been developed for species-selective analysis of organotin compounds in solid, biological samples. The procedure is based on accelerated solvent extraction (ASE) of analytes and includes extraction of the tin species with a methanol–water (90% methanol) solution of acetic acid/sodium acetate containing tropolone (0.03% w/v), their ethylation with NaBEt₄, and separation and detection by GC–FPD. The analytical procedure was optimized with an unspiked sample of harbor porpoise (Phocoena phocoena) liver. Effects of ASE operational variables (extraction temperature and pressure, solvent composition, number of static extraction steps) are discussed. Method detection limits (MDL) were in the range 6–10 ng(Sn) g^–1 dry weight and 7–17 ng(Sn) g^–1 dry weight for butyl- and phenyltin compounds, respectively. Recoveries were comparable with or better than those obtained by use of other procedures reported in the literature. The analytical procedure was validated by analysis of NIES No. 11 (fish tissue) certified reference material.     

Comparative study on the determination of cephalexin in its dosage forms by spectrophotometry and HPLC with UV-vis detection

This paper discusses the spectrophotometric determination of cephalexin as the intact cephalexin or as its acid-induced degradation product. Cephalexin can be determined in the range 1 × 10^–5–18 × 10^–5 M with relative standard deviations of 5-1%. The limits of quantitation and detection were 10^–5 and 0.3 × 10^–5 M, respectively. These procedures were compared with reversed-phase HPLC determination. No interference was observed in the presence of common pharmaceutical adjuvants. The H-point standard additions method was applied in order to correct for the possible presence of the cephalexin precursor, 7-aminocephalosporanic acid; this improves the selectivity of the UV-vis spectrophotometric method.     

Der Einfluß großer Salzkonzentrationen auf die Oxydationsreaktion von Fe(phen) 3 2+ mit Ce(IV) in Schwefelsäure

The influence of NaClO₄, NaCl and Na₂SO₄ on the oxidation of Fe(phen) ₃ ²⁺ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO₄ and NaCl 0.1–1.0M the rate constant values decrease from 1.03·10⁵ to 0.56·10⁵M^–1s^–1 and from 1.08·10⁵ to 0.81·10⁵M^–1s^–1 respectively.In varying concentrations of Na₂SO₄ solutions (0.05–0.35M) the rate constant values decrease from 1.05·10⁵M^–1s^–1 to 0.45·10⁵M^–1s^–1.Taking into account the negative salt effect the mechanism of the reaction progress is proposed.

     

Analysis of High-Purity Volatile Compounds

The current status of the analysis of high-purity volatile substances is considered. Two types of impurities in high-purity volatile substances were distinguished: molecularly dissolved substances and suspended particles. The main factors that restrict the limiting capabilities of analytical techniques were revealed. The attained detection limits were 10^–8–10^–10% for metal impurities, 10^–4–10^–8% for organic substances, 10^–5–10^–9% for water, and 10^–5–10^–7 for permanent gases. Suspended particles of 0.04–0.003 m in size were determined by light scattering.     

Sensitive flow-injection chemiluminescence determination of terbutaline sulfate based on enhancement of the luminol–permanganate reaction

A novel and highly sensitive chemiluminescence (CL) method for the determination of terbutaline sulfate, coupled with flow-injection analysis (FIA), is described in this paper. The method is based on enhancement by terbutaline sulfate of the chemiluminescence emission of the luminol–permanganate system under alkaline conditions. Under the conditions selected the concentration of terbutaline sulfate is proportional to CL intensity in the range 5×10^–10–5×10^–7 g mL^–1, with a detection limit of 1.7×10^–10 g mL^–1 (3). The relative standard deviation is 2.8% for 1×10^–8 g mL^–1 terbutaline sulfate (n=11). Ninety samples can be determined per hour. The proposed method has been used to determine terbutaline sulfate in pharmaceutical preparations and in plasma and urine samples with satisfactory results. The possible mechanism of the chemiluminescence reaction is discussed briefly.     

Use of High-Performance Liquid Chromatography–UV and Gas Chromatography–Mass Spectrometry for Determination of the Imidacloprid Content of Honeybees, Pollen, Paper Filters, Grass, and Flowers

Imidacloprid is a new insecticide with a wide range of action. Because honeybees are very sensitive to this substance, two techniques (HPLC–UV and GC–MS) which enable its detection in several matrices of both animal and vegetable origin were used to monitor its possible presence in cultivated land. In the first method quantification of imidacloprid in honeybees was achieved by use of the external standard method; the detection limit was 50 mg kg^–1, the linear range 0.05–1 mg mL^–1, recovery 60–83%, and the imprecision (coefficient of variation) 8.6% for repeatability and 11.8% for reproducibility. Recovery from pollen was 71–98% in the range 0.05–0.5 mg kg^–1. The repeatability was 9.2–13.9%. Imidacloprid can often be found in the environment, not as a simple molecule but as a group of degradation products. The GC–MS method could be used to quantify all these species as oxidation products and to determine the initial quantity of imidacloprid by use of a conversion factor. The liquid chromatographic analysis could be used to detect, in a standard solution, 10 ng mL^–1 derivatized 6-chloronicotinic acid. The linearity was good (R=0.999) over a wide concentration range (10 g mL^–1–10 ng mL^–1). Several samples with different matrices (filter paper placed on an pneumatic corn seed drill, grass, flowers, honeybees, etc.) obtained during the sowing period for imidacloprid-treated corn were analyzed. The quantification limit (LOQ) was 0.005 mg kg^–1 for grass and flowers, 0.002 mg kg^–1 for honeybees, and 0.024 mg kg^–1 for paper filters.     

Transference numbers for ultra concentrated solutions of aqueous hydrochloric acid at 25°C

Transference numbers of HCl(aq) solutions at 25°C, from 0.01 to 13.6 mol-kg^–1(m) have been obtained by measuring the emf of cells with transference using hydrogen gas/platinum electrodes. Good agreement is obtained at concentrations up to 1 m with all previous data, and our results strongly corroborate those of King and Spiro over the 2–8m concentration range. The transference numbers of the hydronium ion fit the empirical equation, _H ^HCl = 0.821 + 0.0457m ^1/2 – 2.476×10^–2m – 1.90×10^–4 m ² – 1.45×10^–5 m ³ the maximum deviation in T _H ^HCl being 0.003.     

Schnelle coulometrische Mikrobestimmung einzelner Polythionate

Zusammenfassung Das neue Mikrobestimmungsverfahren beruht auf der coulometrischen Titration von S₂O₃ ^2– nach vorheriger Abbaureaktion der Polythionate mit Sulfit bzw. Cyanid. Es werden 10 ml Probelösung (S₄O₆ ^2–: 5 · 10^–5 bis 1 · 10^–3 M; S₅O₆ ^2–; 2,5 · 10^–5 bis 1· 10^–3 M; S₆O₆ ^2–: 1,66 · 10^–5 bis 1 · 10^–3 M) benötigt. Die Titrationskurve wird von einem Schreiber registriert. Die Reproduzierbarkeit der jeweiligen Einzelbestimmung liegt bei VK _p±0,1 bis ± 1,6%.

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Rapid coulometric microdetermination of individual polythionates

The method described is based on the coulometric titration of S₂O₃ ^2– after a preceding degradation of the polythionates with sulphite or cyanide. 10 ml of sample solution are required (S₄O₆ ^2–: 5× 10^–5 to 1×10^–3 M; S₅O₆ ^2– : 2.5×10^–5 to 1×10^–3 M; S₆O₆ ^2–: 1.66×10^–5 to 1×10^–3 M). The titration curve is recorded. The reproducibility of a single determination is VK _p±0.1 to ± 1.6%.

     

Effect of using mixed ion-pairs on PVC-membrane electrodes for ephedrine

Mixed ion-pairs based on the use of ephedrinium (EPH)-TPB plus EPH-reineckate (II) and phenylephrine-TPB plus EPH-reineckate (III) were tried for use in plastic membranes. The results were compared to those of an EPH-reineckate (I) single ion-pair electrode. The Nernstian slopes were 50, 49 and 55 mV decade^–1 for membranes I, II and III, respectively. The linear concentration ranges were 10^–5–10^–1, 4.0 × 10^–5–10^–1 and 6.3 ×^–5–10^–1 M ephedrine. The detection limits were 4 ×^–6,10^–5 and 1.2 × 10^–5 M ephedrine for membranes I, II and III, respectively. The pH ranges were 4–9, 3–9 and 2–8 for I, II and III-membranes, respectively. Selectivity coefficient values for membrane II were better than those for membranes I and III. The effects of increasing KC1 concentration and temperature changes were explained for the three electrodes. The isothermal temperature coefficients were 0.00145, 0.0007 and 0.00055 V/ °C for electrodes I, II and III. Electrode III was applied for the determination of ephedrine in its pharmeaceutical preparations with an overall relative standard deviation range of 1.3–2.4% and an overall mean recovery value of 98.1%.     

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite–polyurethane composite electrode

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L^–1; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s^–1, E_a=50 mV, E_I=2 mV) and detection and quantification limits of 6.4×10^–8 mol L^–1 (12.1 g L^–1) and 5.2×10^–6 mol L^–1 (0.9 mg L^–1), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10^–6 mol L^–1 dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.     

Sorption–Desorption Photometric Determination of Trace Iron in Sodium, Potassium, and Ammonium Thiocyanates Using Polyurethane Foams

A reagent-free sorption photometric method for determining trace iron(III) in alkali-metal and ammonium thiocyanates was developed. The method consists in the adsorption of iron(III) thiocyanate complexes on polyurethane foams at pH 2–3 followed by the desorption of complexes with acetone and a measurement of the absorbance of solutions. The analytical range for iron was 0.5–20 g in a 0.2–2.5-g portion of salt. The determination limit and relative standard deviation were 2 × 10^–5% and 20–30%, respectively (n= 3; P= 0.95). The specific feature of the determination is that an additional photometric reagent is not introduced in the solution of the salt to be analyzed, because thiocyanate, that is, the matrix component of the test sample, acts as such a reagent.