Determination of the Rb atomic number density in dense rubidium vapors by absorption measurements of Rb2 triplet bands

A simple and accurate way of determining atom number densities in dense rubidium vapors is presented. The method relies on the experimental finding that the reduced absorption coefficients of the Rb triplet satellite bands between 740 nm and 750 nm and the triplet diffuse band between 600 nm and 610 nm are not temperature dependent in the range between 600 K and 800 K. Therefore, the absolute values of the reduced absorption coefficients of these molecular bands can provide accurate information about atomic number density of the vapor. The rubidium absorption spectrum was measured by spatially resolved white-light absorption in overheated rubidium vapor generated in a heat pipe oven. The absolute values for the reduced absorption coefficients of the triplet bands were determined at lower vapor densities, by using an accurate expression for the reduced absorption coefficient in the quasistatic wing of the Rb D1 line, and measured triplet satellite bands to the resonance wing optical depth ratio. These triplet satellite band data were used to calibrate in absolute scale the reduced absorption coefficients of the triplet diffuse band at higher temperatures. The obtained values for the reduced absorption coefficient of these Rb molecular features can be used for accurate determination of rubidium atomic number densities in the range from about 5 × 10¹⁶ cm^− 3 to 1 × 10¹⁸ cm^− 3.     

Synthesis and application of some novel fluorescent heterocyclic disperse dyestuffs based on phenothiazine on polyester

A series of novel heterocyclic disperse dyestuffs derived from phenothiazine were prepared by standard reactions from phenothiazine as the starting material. Phenothiazine was nitrated and oxidized then reduced to obtain synthesized disperse dyestuffs. The reaction conditions were varied in order to obtain optimal yields for each stage of the preparation to obtain the corresponding derivative and final disperse dyestuffs. All intermediates and disperse dyestuffs were purified and characterized by DSC, FTIR, ¹H NMR, ¹³C NMR, elemental analysis and UV–Visible spectroscopic techniques. The molar extinction coefficients (ε), wavelengths of maximum absorption (λ_max) and solvatochromism effects were studied in solvents as toluene, acetone and N,N-dimethylformamide (DMF). Results represented that the dyestuffs had extinction coefficients of 2011–28189 L mol⁻¹ cm⁻¹, wavelengths of maximum absorption of 448–475 nm in acetone and positive solvatochromism by changing solvent from toluene to DMF. The disperse dyestuffs were applied to locally manufactured polyester fibers and their dyeing properties were investigated. Results showed that the buildup of dyestuffs was acceptable and dyed fibers had very good heat and wash fastness and medium light fastness on polyester fibers.     

Foreign gas broadening and shift of the strongly “forbidden” lead line at 1278.9 nm

The collisional broadening and shift rate coefficients of the “forbidden“ 6p^{2 3}P₀ → 6p^{2 3}P₁ transition in lead were determined by diode laser absorption measurements performed simultaneously in two resistively heated hot-pipes. One hot-pipe contained Pb vapor and noble gas (Ar or He) at low pressure, while the other was filled with Pb and noble gas at variable pressure. The measurements were performed at temperatures of 1220 K and 1290 K, i.e., lead number densities of 4.8 × 10¹⁵ cm^− 3 and 1.2 × 10¹⁶ cm^− 3. The broadening rates were obtained by fitting the experimental collisionally broadened absorption line shapes to theoretical Voigt profiles. The shift rates were determined by measuring the difference between the peak absorption positions in the spectra measured simultaneously in the heat pipe filled with noble gas at reference pressure and the one with noble gas at variable pressure. The following data for the broadening and shift rate coefficients due to collisions with Ar and He were obtained: γ_B^Ar = (3.4 ± 0.1) × 10^− 10 cm³ s^− 1, γ_B^He = (3.8 ± 0.1) × 10^− 10 cm³ s^− 1, γ_S^Ar = (− 7.3 ± 0.8) × 10^− 11 cm³ s^− 1, γ_S^He = (− 6.5 ± 0.7) × 10^− 11 cm³ s^− 1.     

Quantitative analysis of synthetic calcium carbonate polymorphs using FT-IR spectroscopy

Fourier Transform Infrared Spectroscopy (FT-IR) was used successfully for the simultaneous quantitative analysis of calcium carbonate phases (calcite, aragonite, vaterite) in ternary mixtures. From the FT-IR spectra of pure calcite, aragonite and vaterite powders with KBr, the absorptivities, α, of the absorption bands at 713 cm⁻¹ for calcite, 745 cm⁻¹ for vaterite, 713 and 700 cm⁻¹ for aragonite, were determined. In order to overcome the absorption band overlapping a set of equations based on Beer's law was developed. The detection limits were also established and found to be 1.1×10⁻⁴ mg calcite per mm² of pellet at 713 cm⁻¹, 3.6×10⁻⁴ mg aragonite per mm² of pellet at 700 cm⁻¹, 1.8×10⁻⁴ mg aragonite per mm² of pellet at 713 cm⁻¹ and 3.1×10⁻⁴ mg vaterite per mm² of pellet at 745 cm⁻¹. Analysis of a known ternary mixture of calcium carbonate polymorphs tested the validity of the method.     

New methodology for capillary electrophoresis with ESI-MS detection: Electrophoretic focusing on inverse electromigration dispersion gradient. High-sensitivity analysis of sulfonamides in waters

This article describes for the first time the combination of electrophoretic focusing on inverse electromigration dispersion (EMD) gradient, a new separation principle described in 2010, with electrospray-ionization (ESI) mass spectrometric detection. The separation of analytes along the electromigrating EMD profile proceeds so that each analyte is focused and concentrated within the profile at a particular position given by its pK_a and ionic mobility. The proposed methodology combines this principle with the transport of the focused zones to the capillary end by superimposed electromigration, electroosmotic flow and ESI suction, and their detection by the MS detector. The designed electrolyte system based on maleic acid and 2,6-lutidine is suitable to create an inverse EMD gradient of required properties and its components are volatile enough to be compatible with the ESI interface. The characteristic properties of the proposed electrolyte system and of the formed inverse gradient are discussed in detail using calculated diagrams and computer simulations. It is shown that the system is surprisingly robust and allows sensitive analyses of trace amounts of weak acids in the pK_a range between approx. 6 and 9. As a first practical application of electrophoretic focusing on inverse EMD gradient, the analysis of several sulfonamides in waters is reported. It demonstrates the potential of the developed methodology for fast and high-sensitivity analyses of ionic trace analytes, with reached LODs around 3 × 10⁻⁹ M (0.8 ng mL⁻¹) of sulfonamides in spiked drinking water without any sample pretreatment.     

Covalent functionalization of single-walled carbon nanotubes with polytyrosine: Characterization and analytical applications for the sensitive quantification of polyphenols

This work reports the synthesis and characterization of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr); the critical analysis of the experimental conditions to obtain the efficient dispersion of the modified carbon nanotubes; and the analytical performance of glassy carbon electrodes (GCE) modified with the dispersion (GCE/SWCNT-Polytyr) for the highly sensitive quantification of polyphenols. Under the optimal conditions, the calibration plot for the amperometric response of gallic acid (GA) shows a linear range between 5.0 × 10⁻⁷ and 1.7 × 10⁻⁴ M, with a sensitivity of (518 ± 5) m AM⁻¹ cm⁻², and a detection limit of 8.8 nM. The proposed sensor was successfully used for the determination of total polyphenolic content in tea extracts.     

Synthesis of a novel electrode material containing phytic acid-polyaniline nanofibers for simultaneous determination of cadmium and lead ions

The development of nanostructured conducting polymers based materials for electrochemical applications has attracted intense attention due to their environmental stability, unique reversible redox properties, abundant electron active sites, rapid electron transfer and tunable conductivity. Here, a phytic acid doped polyaniline nanofibers based nanocomposite was synthesized using a simple and green method, the properties of the resulting nanomaterial was characterized by electrochemical impedance spectroscopy (EIS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). A glassy carbon electrode modified by the nanocomposite was evaluated as a new platform for the simultaneous detection of trace amounts of Cd²⁺ and Pb²⁺ using differential pulse anodic stripping voltammetry (DPASV). The synergistic contribution from PANI nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the DPASV analysis. Under the optimal conditions, good linear relationships were obtained for Cd²⁺ in a range of 0.05–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.02 μg L⁻¹, and for Pb²⁺ in a range of 0.1–60 μg L⁻¹, with the detection limit (S/N = 3) of 0.05 μg L⁻¹. The new electrode was successfully applied to real water samples for simultaneous detection of Cd²⁺ and Pb²⁺ with good recovery rates. Therefore, the new electrode material may be a capable candidate for the detection of trace levels of heavy metal ions.     

Investigation of multiple-component diffusion through LLDPE film using an FTIR-ATR technique

An FTIR-ATR technique was developed to investigate the multiple-component diffusion properties of 2-octanone, hexyl acetate, octanal, limonene and linalool (equal volume mixture) in a linear low density polyethylene film. Diffusion coefficient (D) values determined for these compounds in the mixture were 7.02 × 10⁻¹⁰, 2.86 × 10⁻⁹, 1.09 × 10⁻⁹, 7.49 × 10⁻⁹ and 5.81 × 10⁻⁹ cm²/s, respectively. Compared with the diffusion of the individual permeants (1:4 permeant:ethanol, v/v), the D values of 2-octanone, hexyl acetate and limonene were lower in the mixture solution, while those of octanal and linalool were higher. Hansen solubility parameters (HSP) were used to elucidate the solubility properties of the permeants. Two-dimensional FTIR data analysis showed that diffusion of the test permeants in LLDPE occurred in the following sequence: limonene (first) → linalool → hexyl acetate → octanal → 2-octanone (last).     

Infrared spectrum and absorption coefficient of the cofactor flavin in water

Flavins play a key role as redox cofactors of enzymes involved in important metabolic processes. Moreover, they undergo photochemical reactions as chromophores in sensors of blue light or magnetic field in many organisms. The reaction mechanisms of flavoproteins have been investigated by infrared spectroscopy and theoretical studies. However, basic information on flavins in the infrared spectral range has been missing, such as absorption spectra in water and absorption coefficients. Here, the cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) were investigated in aqueous medium by Fourier transform infrared spectroscopy. Transmission and attenuated total reflection (ATR) configuration were employed in direct comparison. Absorption spectra in the range of 920–1800 cm⁻¹ were determined after accurate subtraction of the contributions from the water vibrations. The important carbonyl vibrations were resolved at 1661 and 1712 cm⁻¹. The absorption spectra may serve as a reference for theoretical and experimental studies on the effect of the microenvironment on the flavin cofactor. Furthermore, the molar absorption coefficient of FAD at 1547 cm⁻¹ was determined to 2200 L mol⁻¹ cm⁻¹ with an integral absorption coefficient of ∼50,000 L mol⁻¹ cm⁻². These values are prerequisite for the determination of reaction yields in flavoproteins from reaction-induced difference spectra.     

Photo-stable substituted dihydroindolo[2,3-b]carbazole-based organic dyes: tuning the photovoltaic properties by optimizing the π structure for panchromatic DSSCs

Three dihydroindolo[2,3-b]carbazole (DDC) donor based organic dyes (DDC6–DDC8) with long conjugated systems were successfully synthesized and characterized by optical, electrochemical, computational analysis, and photovoltaic methods. It was found that the elongated π system as well as the high molar extinction coefficients (4.2–5.3 M⁻¹ cm⁻¹) sufficiently reinforced the light harvesting ability with the IPCE response of one dye DDC8 extended to 850 nm, which resulted in large J_sc of these dyes based devices (high as 16.41 mA cm⁻²). The attached alkyl chains suppress the dark current to some extent, resulting the DDC6 and DDC7 devices in high V_oc, while DDC8 displayed low V_oc because BTD in DDC8 could attract the iodine ion, which could accelerate the charge recombination. Among the three dyes, DDC7 displayed the best performance with an η value 6.53% under 4 μm thick scattering layer (condition 1+1), which was boosted to 7.49% under 8 μm thick scattering layer (condition 1+2). The photo-stability measurements indicated that all the three dyes are fairly photo-stable.     

Cavity Ring-Down Spectroscopy coupled with helium microwave-induced plasma for fluorine detection

Cavity Ring-Down Spectroscopy with a tunable diode laser has been used for the detection of fluorine at trace levels. A homemade experimental setup was constructed to accommodate the microwave-induced plasma glow discharge inside the optical cavity. The energy delivered by helium plasma discharge was successfully used not only for the dissociation of fluorine molecules but, more importantly, also for the excitation of fluorine atoms into their metastable level 3s⁴P_5/2. The absorption observed at the 3s⁴P_5/2–3p⁴D^o_7/2 transition (corresponding to a 685.603-nm atomic line) was used for fluorine atom detection. Good agreement between theoretical and measured absorption line shapes confirmed the selectivity of fluorine atomic absorption. We observed an absorption coefficient of 4 ? 10⁻⁶ cm⁻¹, corresponding to a detection of F(3s⁴P_5/2) atoms at about 1.5 ? 10⁶ atoms cm⁻³. These data demonstrate that we achieved a detection limit of 100 ng g⁻¹ under the conditions of our initial homemade experimental setup. However, the optimization of the system may lead to the improvement of the detection limit by approximately two orders of magnitude.     

Vibrational spectroscopy standoff detection of explosives

Standoff infrared and Raman spectroscopy (SIRS and SRS) detection systems were designed from commercial instrumentation and successfully tested in remote detection of high explosives (HE). The SIRS system was configured by coupling a Fourier-transform infrared interferometer to a gold mirror and detector. The SRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HE samples were detected on stainless steel surfaces as thin films (2–30 μg/cm²) for SIRS experiments and as particles (3–85 mg) for SRS measurements. Nitroaromatic HEs: TNT, DNT, RDX, C4, and Semtex-H and TATP cyclic peroxide homemade explosive were used as targets. For the SIRS experiments, samples were placed at increasing distances and an infrared beam was reflected from the stainless steel surfaces coated with the target chemicals at an angle of ∼180° from surface normal. Stainless steel plates containing TNT and RDX were first characterized for coverage distribution and surface concentration by reflection–absorption infrared spectroscopy. Targets were then placed at the standoff distance and SIRS spectra were collected in active reflectance mode. Limits of detection (LOD) were determined for all distances measured for the target HE. LOD values of 18 and 20 μg/cm² were obtained for TNT and RDX, respectively, for the SIR longest standoff distance measured. For SRS experiments, as low as 3 mg of TNT and RDX were detected at 7 m source–target distance employing 488 and 514.5 nm excitation wavelengths. The first detection and quantification study of the important formulation C4 is reported. Detection limits as function of laser powers and acquisition times and at a standoff distance of 7 m were obtained.     

A multicommuted flow-system for spectrophotometric determination of tannin exploiting the Cu(I)/BCA complex formation

A flow system exploiting the multicommutation approach is proposed for spectrophotometric determination of tannin in beverages. The procedure is based on the reduction of Cu(II) in the presence of 4,4′-dicarboxy-2,2′-biquinoline, yielding a complex with maximum absorption at 558 nm. Calibration graph was linear (r = 0.999) for tannic acid concentrations up to 5.00 μmol L^− 1. The detection limit and coefficient of variation were estimated as 10 nmol L^− 1 (99.7% confidence level) and 1% (1.78 μmol L^− 1 tannic acid, n = 10), respectively. The sampling rate was 50 determinations per hour. The proposed procedure is more sensitive and selective than the official Folin-Denis method, also minimizing drastically waste generation. Recoveries within 91.8 and 115% were estimated for total tannin determination in tea and wine samples.     

Determination of isoniazid among pharmaceutical samples and the patients’ saliva samples by using potassium ferricyanide as spectroscopic probe reagent

A novel method to determine isoniazid with high sensitivity and good selectivity has been established by using potassium ferricyanide as spectroscopic probe reagent. In the presence of potassium ferricyanide, it has been demonstrated that iron(III) is reduced to iron(II) by isoniazid at pH 4.0. In addition, the in situ formed iron(II) reacts with potassium ferricyanide to give soluble prussian blue. The absorbance of soluble prussian blue is measured at the absorption maximum of 735 nm, and the amount of isoniazid can be calculated based on this absorbance. A good linear relationship of the concentration of isoniazid versus absorbance is observed with a linear range of 0.040-8.00 μg mL⁻¹. The linear regression equation is A = −0.00286 + 0.28588C (μg mL⁻¹) with a correlation coefficient of 0.9992. The detection limit (3σ/k) is 0.037 μg mL⁻¹, and its relative standard deviation (R.S.D.) is 0.35% (n = 11). Moreover, the apparent molar absorption coefficient of indirect determination of isoniazid is 3.92 × 10⁴ L mol⁻¹ cm⁻¹. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to the determination of isoniazid in pharmaceutical samples and saliva samples of patients.     

Phonon spectra and phonon-dependent properties of AgSO4, an unusual sulfate of divalent silver

Phonon spectra of recently synthesized Ag(II)SO₄ have been measured using infrared absorption and Raman scattering spectroscopy, and theoretically predicted using density functional theory calculations. Excellent agreement between experimental and theoretical results with correlation coefficient of 1.05 allowed for full assignment of the experimentally observed vibrational bands, as well as calculation of standard vibrational entropy of AgSO₄ (118.2 J mol⁻¹ K⁻¹), vibrational heat capacity at constant volume (99.1 J mol⁻¹ K⁻¹), zero-point energy (48.3 kJ mol⁻¹). The experimental cut-off frequency of the phonon spectrum equals 1116 cm⁻¹ which translates to the Debye temperature of 1606 K. High frequencies of S–O stretching modes render sulfate connections of Ag(II) attractive precursors of high-T_C superconductors.     

Poly(methylene blue) functionalized graphene modified carbon ionic liquid electrode for the electrochemical detection of dopamine

An ionic liquid 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was used as the substrate electrode and a poly(methylene blue) (PMB) functionalized graphene (GR) composite film was co-electrodeposited on CILE surface by cyclic voltammetry. The PMB–GR/CILE exhibited better electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behavior of dopamine (DA) was further investigated by cyclic voltammetry and a pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔE_p) as 0.058 V in 0.1 mol L⁻¹ pH 6.0 phosphate buffer solution, which proved a fast quasi-reversible electron transfer process on the modified electrode. Electrochemical parameters of DA on PMB–GR/CILE were calculated with the electron transfer number as 1.83, the charge transfer coefficients as 0.70, the apparent heterogeneous electron transfer rate constant as 1.72 s⁻¹ and the diffusional coefficient (D) as 3.45 × 10⁻⁴ cm² s⁻¹, respectively. Under the optimal conditions with differential pulse voltammetric measurement, the linear relationship between the oxidation peak current of DA and its concentration was obtained in the range from 0.02 to 800.0 μmol L⁻¹ with the detection limit as 5.6 nmol L⁻¹ (3σ). The coexisting substances exhibited no interference and PMB–GR/CILE was applied to the detection of DA injection samples and human urine samples with satisfactory results.     

In situ selective determination of methylmercury in river water by diffusive gradient in thin films technique (DGT) using baker's yeast (Saccharomyces cerevisiae) immobilized in agarose gel as binding phase

Saccharomyces cerevisiae immobilized in agarose gel as binding phase and polyacrylamide as diffusive layer in the diffusive gradient in thin films technique (DGT) was used for selective determination of methylmercury (MeHg). Deployment tests showed good linearity in mass uptake up to 48 h (3276 ng). When coupling the DGT technique with Cold Vapor Atomic Fluorescence Spectrometry, the method has a limit of detection of 0.44 ng L⁻¹ (pre concentration factor of 11 for 48 h deployment). Diffusion coefficient of 7.03 ± 0.77 × 10⁻⁶ cm² s⁻¹ at 23 °C in polyacrylamide gel (pH = 5.5 and ionic strength = 0.05 mol L⁻¹ NaCl) was obtained. Influence of ionic strength (from 0.0005 mol L⁻¹ to 0.1 mol L⁻¹ NaCl) and pH (from 3.5 to 8.5) on MeHg uptake were evaluated. For these range, recoveries of 84–105% and 84–98% were obtained for ionic strength and pH respectively. Potential interference due to presence of Cu, Fe, Mn, Zn was also assessed showing good recoveries (70–87%). The selectivity of the proposed approach was tested by deployments in solutions containing MeHg and Hg(II). Results obtained showed recoveries of 102–115 % for MeHg, while the uptake of Hg(II) was insignificant. The proposed approach was successfully employed for in situ measurements in the Negro River (Manaus-AM, Brazil).     

Spectrophotometric determination of trace lead in water after preconcentration using mercaptosephadex

A highly sensitive and selective spectrophotometric method for determination of trace lead in water after pre-concentration using mercaptosephadex (MS-50) has been developed, the method based on the color reaction of lead(II) with dibromohydroxylphenylporphyrin. Under optimal condition, lead(II) reacts with the reagent to form a 1:2 yellow complex in presence of TritonX-100, which has a maximum absorption peak at 479 nm. The color reaction can complete rapidly and remain stable for 24 h in room temperature. The molar absorption coefficient of the lead complex, the limit of quantification, the limit of detection and relative standard deviations were found to be 2.35×10⁵ l mol⁻¹ cm⁻¹, 4.3, 1.4 ng ml⁻¹ and 1.0%, respectively. The absorbance of the lead complex at 479 nm is linear up to 0.48 μg ml⁻¹ of lead(II). The effect of various co-existing ions in water were examined seriously. No interference was observed. Moreover, a simple pre-concentration method for trace lead in water was also studied using MS-50. It was found that trace lead in water can be adsorbed in 1.0 mol l⁻¹ HCl and dissociated from MS-50 with 4.0 mol l⁻¹ HCl quantitatively, that improves the selectivity and the sensitivity of method (its detection limit (3 s) changed into 0.2 ng ml⁻¹ of lead) obviously. The proposed method has been applied to determine trace lead in water samples with satisfactory results.     

Demonstration of cavity enhanced FTIR spectroscopy using a femtosecond laser absorption source

A proof of principle experiment was performed by recording the cavity enhanced absorption spectrum of the weak b–X transition of molecular oxygen in the atmosphere using a Ti:Sa femtosecond laser as an absorption source and a high resolution continuous scan Fourier transform interferometer. The cavity was mode matched and either continuously scanned or stabilized at the so-called magic point. An optimal rms noise equivalent absorption of 3 × 10^?7 cm^?1 Hz^?1/2 was reached in the latter case, corresponding to α_min = 3 × 10^?7 cm^?1.