Simultaneous mixture analysis by using non-linear spectrophotometric data and linear iterative target transformation factor analysis

Non-linear absorption spectral data obtained from ternary mixtures of analytes are analyzed by using a linear model, iterative target transformation factor analysis (ITTFA). The use of transformed original variables is used to correct non-linearities in the original data. Absorbance below a certain limit (k) is described as linear and above this limit as non-linear. The extension of the regressor variables is the squared absorbances above the linear range. The variation of the prediction error as a function of the number of the factors and the k-values were considered and the minimum prediction error was evaluated for reaching to optimum. Except the natural non-negativity constraint the correlation constraint also is used on concentration vector in each iteration of ITTFA algorithm. The reliability of the method is evaluated using model data for ternary mixtures by spectral overlapping and different degrees of non-linearity. Simultaneous spectrophotometric determination of Eu³⁺, UO₂²⁺ and Th⁴⁺ with arsenazo III as chromogenic reagent is used as experimental model systems with non-linearity behavior of Eu³⁺and UO₂²⁺ components. The application to both synthetic and real data sets with different degrees of non-linearity demonstrate the ability of the proposed methodology to obtain better results than original data and ITTFA. The relative standard errors of prediction for proposed method in comparison with using the PLS calibration on original and extended data are nearly smaller.     

The identification of non-prescription internal analgesics by thermal analysis

The mechanism of the electrochemical reduction of dithizone to the corresponding hydrazo compound, diphenylthiocarbazide, has been examined in detail by polarographic and voltammetric techniques over a wide pH range. The reaction is reversible and dithizone can be determined polarographically in the range 10^-3–10^-5M. This polarographic behaviour suggests new applications of dithizone as an electroanalytical reagent.     

Determination of pseudouridine at submicromolar concentrations by cathodic stripping voltammetry at a mercury electrode

Pseudouridine (5-ribosyluracil), uridine (N,1-ribosyluracil), deoxyuridine (N,1-deoxyribosyluracil) and uracil are investigated by means of d.c. polarography and by differential and normal pulse polarography. Pseudouridine, which is known to be a cancer marker, yields anodic polarographic currents in the pH range 7–11, whereas uridine and deoxyuridine are inactive under the same conditions. The polarographic response of pseudouridine obtained is due to the formation of a sparingly soluble mercury compound. Pseudouridine can be determined by differential pulse polarography in the concentration range 2–6 × 10^?6 M and by differential-pulse cathodic stripping voltammetry at concentrations two orders of magnitude lower. Small excesses of uridine, deoxyuridine or proteins do not interfere with the determination.     

Direct determination of Cu,Mn, Pb,and Zn in beer by thermospray flame furnace atomic absorption spectrometry

In this work, thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was employed for Cu, Mn, Pb, and Zn determination in beer without any sample digestion. The system was optimized and calibration was based on the analyte addition technique. A sample volume of 300 μl was introduced into the hot Ni tube at a flow-rate of 0.4 ml min⁻¹ using 0.14 mol l⁻¹ nitric acid solution or air as carrier. Different Brazilian beers were directly analyzed after ultrasonic degasification. Results were compared with those obtained by graphite furnace atomic absorption spectrometry (GFAAS). The detection limits obtained for Cu, Mn, Pb, and Zn in aqueous solution were 2.2, 18, 1.6, and 0.9 μg l⁻¹, respectively. The relative standard deviations varied from 2.7% to 7.3% (n=8) for solutions containing the analytes in the 25–50 μg l⁻¹ range. The concentration ranges obtained for analytes in beer samples were: Cu: 38.0–155 μg l⁻¹; Mn: 110–348 μg l⁻¹, Pb: 13.0–32.9 μg l⁻¹, and Zn: 52.7–226 μg l⁻¹. Results obtained by TS-FF-AAS and GFAAS were in agreement at a 95% confidence level. The proposed method is fast and simple, since sample digestion is not required and sensitivity can be improved without using expensive devices. The TS-FF-AAS presented suitable sensitivity for determination of Cu, Mn, Pb, and Zn in the quality control of a brewery.     

Preconcentration procedure using cloud point extraction in the presence of electrolyte for cadmium determination by flame atomic absorption spectrometry

This paper describes a micelle-mediated phase separation in the presence of electrolyte as a preconcentration method for cadmium determination by flame atomic absorption spectrometry (FAAS). Cadmium was complexed with ammonium O,O-diethyldithiophosphate (DDTP) in an acidic medium (0.32 mol l^− 1 HCl) using Triton X-114 as surfactant and quantitatively extracted into a small volume (about 20 μl) of the surfactant-rich phase after centrifugation. The chemical variables that affect the cloud point extraction, such as complexing time (0–20 min), Triton X114 concentration (0.043–0.87% w/v) and complexing agent concentration (0.01–0.1 mol l^− 1), were investigated. The cloud point is formed in the presence of NaCl at room temperature (25 °C), and the electrolyte concentration (0.5–5% w/v) was also investigated. Under optimized conditions, only 8 ml of sample was used in the presence of 0.043% w/v Triton X-114 and 1% (w/v) NaCl. This method permitted limits of detection and quantification of 0.9 μg l^− 1 and 2.9 μg l^− 1 Cd, respectively, and a linear calibration range from 3 to 400 μg l^− 1 Cd. The proposed method was applied to Cd determination in physiological solutions (containing 0.9% (w/v) of NaCl), mineral water, lake water and cigarette samples (tobacco).     

Spurenanalyse von huminstoffen im trinkwasser: The d.c. polarographic determination of traces of humic substances in potable waters

(The d.c. polarographic determination of traces of humic substances in potable waters) The inhibiting effect of a tri-n-butylphosphate layer adsorbed at the mercury drop on the polarographic wave of copper(II) is reduced by humic substances. This effect can be utilized to determine humic substances in the range 0.05–1 mg l^-1. The standard substance used was isolated from peaty water. Humic and fulvic acids are not differentiated but amino acids, peptides and polyhydroxy compounds do not interfere.     

Thermal unimolecular decomposition of formyl fluoride in Ar

The thermal decomposition of formyl fluoride in Ar has been studied behind shock waves over the temperature range 1160–1480 K and the total density range (7.18–18.6) × 10⁻⁶ mol cm⁻³. The decomposition was monitored by means of IR emission from the CH stretching of the reactant and the fundamental band of the CO produced. The decomposition was found to be molecular elimination producing HF and CO and the process proceeded in the low-pressure region under the present conditions. The second-order rate constant was expressed as k/Ar = 10^14,74 exp(−35.2 kcal mol⁻¹/RT) cm³ mol⁻¹ s⁻¹. Applying the RRKM strong collision theory, the value of the threshold energy and the collision efficiency were discussed.     

Electrothermal vaporization coupled with inductively coupled plasma array–detector mass spectrometry for the multielement analysis of Al2O3 ceramic powders

An electrothermal vaporization (ETV) system useful for the analysis of solutions and slurries has been coupled with a sector-field inductively coupled plasma mass spectrometer (ICP–MS) equipped with an array detector. The ability of this instrument to record the transient signals produced for a number of analytes in ETV–ICP–MS is demonstrated. Detection limits for Mn, Fe, Co, Ni, Cu, Zn and Ga are in the range of 4–60 pg μL^− 1 for aqueous solutions and in the low μg g^− 1 range for the analysis of 10 mg mL^− 1 slurries of Al₂O₃ powders. The dynamic ranges measured for Fe, Cu and Ga spanned 3–5 orders of magnitude when the detector was operated in the low-gain mode and appear to be limited by the ETV system. Trace amounts of Fe, Cu and Ga could be directly determined in Al₂O₃ powders at the 2–270 μg g^− 1 level without the use of thermochemical reagents. The results well agree with literature values for Fe and Cu, whereas deviations of 50% at the 90 μg g^− 1 level for Ga were found.     

Sine-wave polarographic determination of zirconium or niobium in aqueous media

The sine-wave polarographic determination of zirconium in aqueous media was investigated using solutions which were 0.55 – 5.5·10^-3M in zirconyl chloride and 1 M in potassium chloride and had been adjusted to pH 2.0 with hydrochloric acid. It was possible to determine zirconium in the concentration range of 0.05 to 0.4 mg per ml. The sine-wave polarographic behavior of zirconium in aqueous solutions in the pH range 2–3 is discussed. The sine-wave polarographic determination of niobium in aqueous media was investigated using concentrated sulfuric acid containing 5 to 0.1 mg of niobium per ml in a supporting electrolyte of citric acid; the determination of niobium was possible down to 0.1 mg of niobium per ml of concentrated sulfuric acid although the D.C. polarographic method was impractical for the determination of less than 0.5 mg of niobium per ml.     

Temperature dependence of the reaction NO + NO3 → 2NO2

The flash photolysis-visible absorption technique has been used to measure rate constants for the reaction NO + NO₃ → 2NO₂ (1) over the temperature range 224–328 K. The temperature dependence of the rate constant is given by the expression k₁(T) = (1.59 ± 0.32) × 10⁻¹¹exp(122/T) cm³ molecule⁻¹ s⁻¹ where the stated uncertainties refer to the ± 2σ limits from both random and systematic errors.     

New technique for the determination of trace noble metal content in geological and process materials

A new two-step sample preparation technique is proposed for the instrumental determination of trace quantities of noble metals (NM) in refractory geological and process materials. The decomposition procedure is based on the oxidizing fluorination of samples with subsequent sulfatization (OFS) of the sample melt or cake. Fluorination of samples is accomplished using a mixture of KHF₂+KBrF₄ or KHF₂+BrF₃ depending on the ratio of sample mass to oxidizing mixture. Both cakes and melts can result using this procedure. Sulfatization of resulting fluorides is completed using concentrated sulfuric acid heated to 550 °C. Validation studies using certified geostandard reference materials (GSO VP-2, ZH-3, Matte RTP, HO-1, SARM-7) have shown that the proposed method is fast, convenient and most often produces non-hygroscopic homogeneous residues suitable for analysis by atomic absorption spectrometry (AAS) and atomic emission spectrometry (AES). Results obtained for NM concentrations in reference materials agreed with certified concentration ranges and results obtained using other methods of analysis. The OFS procedure combined with direct current plasma d.c. plasma AES achieved the following limits of detection (LOD) for the noble metals: Ag, Au, Pd, 1–2×10⁻⁶; Pt, 5×10⁻⁶; and Ru, Rh, Ir, Os, 1–3×10⁻⁷ wt.%. Using graphite furnace AAS (GFAAS) combined extraction pre-concentration the following LODs for NMs were achieved: Pt, Ru, 1×10⁻⁶; Pd, Rh, 1×10⁻⁷; and Au, Ag, 1−2×10⁻⁸ wt.%. The relative standard deviation for NM determinations (S_r) was dependent on NM concentration and sample type, but commonly was in the range of 3–15% for d.c. plasma AES and 5–30% for GFAAS.     

High-resolution Fourier transform infrared spectroscopy and analysis of the ν12 fundamental band of ethylene-d4

The Fourier transform infrared (IR) spectrum of the ν₁₂ fundamental band of ethylene-d₄ (C₂D₄) has been measured with an unapodized resolution of 0.004 cm⁻¹ in the frequency range of 1030–1130 cm⁻¹. A total of 1340 assigned transitions have been analyzed and fitted using a Watson's A-reduced Hamiltonian in the I^r representation to derive rovibrational constants for the upper state (v₁₂=1) up to five quartic terms with a standard deviation of 0.00042 cm⁻¹. They represent the most accurate constants for the band thus far. The ground state rovibrational constants were also further improved by a fit of combination–differences from the IR measurements. The relatively unperturbed band was found to be basically A-type with a band centre at 1076.98492±0.00003 cm⁻¹.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

Polarographic determination of nitrate in concentrated sulphuric acid solutions

The possibility of the polarographic determination of nitrates in the presence of hydroquinone in 65–95% sulphuric acid solutions was investigated. It has been found that nitrates in 95% acid have one polarographic wave without inflection point the height of which is proportional to nitrate concentration. In 85% sulphuric acid and in other acids investigated with lower concentrations, nitrates are not polarographically active. If both nitrate and hydroquinone are present in H₂SO₄, two waves are observed on the polarogram. The more negative wave is completely defined. The height of this wave is proportional to nitrate concentration in the range 5×10^?5?5×10^?3M.     

HPLC-MS/MS multiclass determination of steroid hormones in environmental waters after preconcentration on the carbonaceous sorbent HA-C@silica

In this study, a sensitive and multiclass method has been developed for analysis of three families of steroid hormones, i.e. progestins, oestrogens, androgens, by SPE-HPLC-ESI-MS/MS. The extraction efficiency of thermally condensed humic acids onto silica sorbent (HA-C@silica), here for the first time studied for multiclass enrichment of these sex hormones, was tested in different environmental waters (tap and river water, urban wastewater treatment plant effluent) spiked at the nanograms per litre levels (5–1000 ng L⁻¹). Quantitative adsorption was achieved using 200 mg sorbent for preconcentration of 250–1000 mL sample, at the native pH (pH = 6.5–7.7). Elution was performed by two sequential fractions (methanol followed by acetonitrile), obtaining in all the matrices investigated satisfactory recoveries (71% to 124% for river waters and 71–113% for urban wastewater treatment plant effluent) and RSDs below 15% (n = 3). The high enrichment factors (up to 4000) coupled with high-performance liquid chromatography tandem mass spectrometry quantification (MRM mode) provided low limits of detection and quantification (a few ng L⁻¹), that are suitable for environmental monitoring. Most of the analytes were detected in river water and in wastewater effluent samples (in the ng L⁻¹ concentration range), attesting their environmental diffusion. The proposed method was extended to a fourth class, Glucocorticoids, achieving good results in river samples, by the same SPE cartridge and chromatographic run.     

Photoisomerization dynamics of alkyl-substituted stilbenes in supersonic jets

We report time-resolved fluorescence decay lifetimes from photoselected states of jet-cooled 4-ethyl-trans-stilbene (4ETS) and 4-n-propyl-trans-stilbene (4PTS) in the energy range E_v = 0–2800 cm⁻¹ above the S₁ origin. Alkyl substitution enhances the non-radiative decay rates. These data can be fitted by the statistical RRKM theory in conjunction with the reduction of the photoisomerization threshold from E_t = 1300±50 cm⁻¹ for trans-stilbene to E_t = 1100±100cm⁻¹ for 4ETS, and E_t = 1000±100 cm⁻¹ for 4PTS.     

Electrochemical properties of violuric acid and oxidase biosensor preparation

The electrochemical properties of violuric acid (VA) have been investigated at pH 4.0–10.0 by using cyclic voltammetry on a glassy carbon electrode. The peak current was proportional to the square root of the potential scan rate. The calculated diffusion coefficient was 2.0±0.7×10⁻⁶ cm² s⁻¹. The formal oxidation–reduction potential of VA was 0.63 V versus SCE at pH 7.0. The kinetics of VA interaction with reduced glucose oxidase (GO) was explored in the electrocatalytical system. A typical electrocatalytical wave was generated in the presence of the VA and glucose. An apparent k_ox calculated by using the Nicholson–Shain function was 1.85×10⁶ M⁻¹ s⁻¹ at pH 7.0 and 25 °C. Glucose and l-lactate bioelectrodes were prepared by adsorbing the GO and l-lactate oxidase (LO) onto the VA-modified graphite electrode. The electrode was poised at 0.6 V versus SCE and linear response was obtained over the range of 4–20 mM glucose and 2–12 mM l-lactate, respectively.     

Differential-pulse polarography of amino acids in acetaldehyde-borax medium

A differential-pulse polarographic method for the determination of amino acids is reported, based on the formation of Schiff's base compounds in borax buffer solution (pH 10.10) containing acetaldehyde. The compounds are reduced at a mercury electrode with peak potentials of about ?1.5 V (vs. SCE) and well defined polarographic waves are obtained which can be used to determine amino acids in borax medium. The differential-pulse polarographic method was found to be the most sensitive and suitable for the determination of amino acids in the concentration range 1 × 10^?6–8 × 10^?4 M (lysine) and 2.8 × 10^?6–1 × 10^?3 M (arginine). The polarographic characteristics of these waves were studied by differential-pulse polarographic and cyclic voltammetric methods. The waves are ascribed to the reduction of the imido group in the Schiff's base compounds. The procedure was applied to the determination of lysine and arginine in foodstuffs and the total proteins in serum samples.     

Colorimetric technique for the detection of carbofuran and its application in various environmental samples

A large variety of pesticides have been used in the agriculture area to raise the quality, extend and yield storage life of crops. The nonstop uses of these pesticides have resulted in pollution of the environment and also caused risk to human health. For the rapid detection of selective CBFpesticide, we developed a simple and sensitive colorimetric detection method based on azo-coupling reaction. After a simple pre-treatment of carbofuran (2, 2-dimethyl-2, 3-dihydro-7-benzofuranyl N-methyl carbamate) (CBF) (1000 ​μg ​mL⁻¹) with a diazotized solution, the resulting is rapidly undergoing azo-coupling reaction with p-aminoantipyrine (1% alcoholic) with a dramatic color change only in few minutes. Finally, we successfully applied the concentrations of CBF pesticide on vegetable, fruit, soil, and water samples in the presence of natural interferences using UV–Vis spectrophotometer and FTIR with limits of detection at 0.004μgmL⁻¹. CBF had recoveries in the range of 93–98%, with relative standard deviation values less than 2% and good linearity was achieved with r ​≥ ​0.98. The inhibition rate was linear with CBF concentration in the range of 1μgmL⁻¹ to 10μgmL⁻¹. The proposed method applies to analyze CBF pesticide in real samples. FTIR technique was used to consider and gain structural information about the existing intermolecular interactions for vegetable samples.     

The evolution of inner-shell multielectronic X-ray spectra from threshold to saturation for low- to high-Z atoms

Inter- and intra-shell electronic correlations in an atom are manifested in, and can be studied through, the X-ray emission spectra of multielectronic transitions. We have measured the spectra of K^hα_1,2 hypersatellites (HS), Kα_3,4 satellites (S), and the 3d electron shake-up satellites (D) accompanying the Kα_1,2 diagram lines, and their evolution from the double-ionization threshold, for selected 4- and 5-row elements of the periodic table. These spectra originate in the [1 s]⁻¹, [2p]⁻¹, and [3d]⁻¹ spectator two-electron transitions [1 s]⁻²→[1s2p]⁻¹, [1s2p]⁻¹→[2p]⁻², and [1s3d]⁻¹→[2p3d]⁻¹ respectively. Photoexcitation by monochromatized synchrotron radiation together with high-resolution crystal spectrometers were employed. Ab initio relativistic multiconfigurational Dirac–Fock (RMCDF) calculations reproduce the spectra very well for all transitions, with the HS spectra showing a strong dependence on QED effects. The excitation thresholds were determined accurately. The threshold-to-saturation energy range of the intensity was found to depend strongly on the principal quantum number n of the spectator hole. For example, for Cu, ranges of 2%, 10%, and 60% of the threshold energy are found for the D, S and HS spectra, respectively. Only the D spectrum's evolution conforms to the Thomas model, indicating a dominant shake up/off process. The S and HS spectra seem to be dominated by the knockout (“two-step-one”) process near threshold. The S spectra show a two-regime behavior. Near threshold both shape and intensity vary with excitation energy, and above that only intensity changes are observed. The lower-than-expected K^hα₁/K^hα₂ intensity ratio found for Z=23–30 and 39–46 indicates that the angular momenta coupling scheme at the regime intermediate between the LS coupling at low-Z and the jj coupling at high-Z may not be fully accounted for by the prevailing theory.