The S2 emission characteristics of several organic sulfur compounds obtained by molecular emission cavity analysis and pyrolysis

Emission profiles of several organic sulfur compounds are investigated by modified molecular emission cavity analysis (MECA). Thiourea, 1,3-diethylthiourea, S-methyl- cysteine and taurine are pyrolyzed in a hydrogen stream and the pyrolytic products are determined by gas chromatography. The S₂ emission mechanism is discussed on the basis of emission profiles and the composition of the pyrolytic products. Although some compounds give multipeaked responses, the splitting disappears when a worn surface cavity is used or oxalic acid is added to the sulfur compound in the cavity. When the emission profile from thiourea is compared with that from 1,3-diethylthiourea, it is clear that the multipeaked response is due to quenching by degradation products of the latter compound. The main product of pyrolysis is hydrogen sulfide. The emission intensity is related to the yield of hydrogen sulfide in pyrolysis. As methylmercaptan was not detected in the pyrolysis products, it is suggested that the quenching by the organic fragments results from their hydrogen consumption rather than their reaction with sulfur species. The S₂ emission from sulfur-containing compounds is rapidly complete in the presence of oxalic acid, and it is suggested that such compounds are subject to reductive breakdown in the cavity.     

Magnetic quenching of the emission intensities of HPO and SnH in hydrogen—oxygen flames

The effects of a magnetic field on the emission intensities of some excited species in hydrogen—oxygen flames have been studied. The emission intensities of HPO and SnH were partially quenched by an external magnetic field below 1.8 T, while those of CuH, CuCl, S₂, Se₂ and Te₂ were not changed by the field.     

Determination of chlorpromazine hydrochloride in tablets by molecular emission cavity analysis

Sulphur in chlorpromazine hydrochloride (2–50 mg) is oxidized by dichromate in condensed phosphoric acid (CPA) to sulphate, which in turn is reduced to hydrogen sulphide by heating with tin dissolved in CPA. The gas is carried by nitrogen to a steel cavity situated in a hydrogen/nitrogen flame and the S₂ emission is measured at 384 nm. The method is applied to determine the drug in powdered tablets. No sample pretreatment is needed; the procedure takes 10 min.     

Molecular emission cavity analysis: Part 20. Indirect determination of amines by their reaction with the formaldehyde—sulphite addition compound

Aromatic and aliphatic amines and hydrazine in the range 1–30 × lO^-5 M are determined by measuring the S₂ emission in a carbon cavity held in a hydrogen—nitrogen flame arising from the formation of an addition compound between the amine, formaldehyde and sulphite. As little as 1.8 ng of aniline in 5 μl (4 × 10^-6 M) can be detected.     

Molecular emission cavity analysis : Part XI. The determination of carbonyl compounds

Formaldehyde (2–750 μg), acetaldehyde (0.05–1.0 μg) and acetone (0.4–3.5 smg) can be determined in aqueous solution (? 17.5 ml) by MECA. Sodium sulphite solution (5 ml, 500 p.p.m. S) and 1.5 ml of l M phosphoric acid are added and the delayed S₂ emission from the sulphite addition compound in 5 ml of the solution is measured in a MECA cavity; a hydrogen-nitrogen flame is used. Mixtures of formaldehyde and acetone can be determined simultaneously on the basis of the resolved MECA peaks of their sulphite addition compounds, after evaporation of the excess of sulphite from the cavity.     

The determination of inorganic sulphate in urine by molecular emission cavity analysis

Summary Urinary sulphate is determined by 100-fold dilution with 0.1M phosphoric acid, and measurement of the S₂ emission at 384 nm generated in a MECA cavity placed in hydrogen-nitrogen-air flame.

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Zusammenfassung Im Harn enthaltenes Sulfat wird bestimmt, indem man mit 0,1M Phosphorsäure hundertfach verdünnt und die S₂-Emission bei 384 nm bestimmt, die sich nach Anbringung der Probe in einer MECA-Vertiefung² in einer Wasserstoff-Stickstoff-Luft-Flamme einstellt.

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Dedicated to Prof. Hans Lieb on the occasion of his 90th birthday.     

Continuous-flow molecular emission cavity analysis for sulphide

Sulphide (1–10 μg ml^?1) is determined by mixing the sample with an excess of orthophosphoric acid in a segmented continuous-flow system. The hydrogen sulphide evolved is swept into the cavity for generation of S₂ emission. The analysis is completely automated, requires no sample pretreatment and samples can be analyzed at 24 h^?1.     

The accurate determination of total sulphur and disulphide and polysulphide compounds in petroleum products by metal reduction and flame emission spectrometry

Conditions for the determination of total sulphur and disulphide/polysulphide in petroleum products are described. The sulphur is reduced by heating with sodium or Devarda's alloy under reflux with subsequent liberation of H₂S and measurement of the chemiluminescent S₂ emission intensity in a hydrogen—argon diffusion flame. The precision and accuracy are good. Applications to light distillates and waxy residues are discussed.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Determination of sulphur anions by flow injection with a molecular emission cavity detector

A molecular emission cavity detector is attached to a flow injection system for the determination of sulphide, sulphite and sulphate in the ranges 2–130, 3–150 and 5–250 ng S, respectively, in 3-μ1 samples. The sample throughput is abort 100 h^?1. Resolution of mixtures of these anions is also possible, based on the sequential appearance of their S₂ emission peaks. The use of a hydrogen peroxide carrier stream allows the determination of total sulphur.     

The determination of sulphur and phosphorus by cool-flame chemiluminescence emission spectrometry with an electrothermal atomiser for sample introduction

The technique described allows simple and rapid determination of sulphur and phosphorus in solutions of samples and sample digests. A graphite-tube atomisation device is employed for the introduction of microlitre volumes of liquid samples, after desolvation, into a cool argon—hydrogen entrained air flame in which the chemiluminescent emission from S₂ and HPO species is monitored by using a wide band-pass monochromator system.     

Fundamental studies of mixed-gas inductively coupled plasmas

The effects of adding foreign gases to the central-gas flow or the intermediate-gas flow of an argon inductively coupled plasma are presented. In particular, the influence of up to 16.7% added helium, nitrogen or hydrogen on radially-resolved electron number density, electron temperature, gas-kinetic temperature and calcium ion emission profiles is examined. It is shown that these gases affect not only the fundamental parameters and bulk properties of the plasma, but also how energy is coupled and transported through the discharge and how that energy interacts with the sample. For example, added helium causes an increase in the gas-kinetic temperature, most likely due to the higher thermal conductivity of helium compared to argon but, in general, does not appear to affect significantly either the electron temperature or electron concentration. The shift in the calcium ion emission profile towards lower regions in the discharge with added helium may be attributable to higher droplet desolvation and particle vaporization rates. In contrast, the addition of nitrogen or hydrogen to an Inductively Coupled Argon Plasma (Ar ICP) results in dramatic changes in all three fundamental plasma parameters: electron number density, electron temperature, and gas-kinetic temperature. The net effect of these molecular gases (N₂ or H₂) on calcium ion emission and on the fundamental plasma parameters is shown to be dependent on the amount of gas added to the plasma and whether the gas is introduced as part of the central- or intermediate-gas flow. In general, nitrogen added to the central-gas flow causes a significant reduction in the number of electrons throughout most of the discharge (over an order of magnitude in certain regions), mainly in the central and upper zones of the ICP. A drop of 3000–5000 K in the central channel electron temperature and a smaller drop in the gas-kinetic temperature are also observed when N₂ is added to the central-gas flow. In contrast, the introduction of nitrogen in the intermediate flow causes about a 1 × 10¹⁵ electrons cm⁻³ increase in the electron concentration in the low, toroidal regions of the plasma and an increase in the gas-kinetic temperature of around 1000 K throughout most of the discharge. As seen with the addition of nitrogen to the central-gas flow, the electron temperature is found to increase in the toroidal zones of the plasma when N₂ is added to the intermediate flow. These combined effects cause a 20-fold depression in the calcium ion emission intensity only a 1.7-fold depression when N₂ is added to the central- or intermediate-gas flows, respectively. On the other hand, hydrogen causes a depression in the electron concentration in the upper areas of the plasma when this gas is added to the central flow but increases the number of electrons in the same region when added to the intermediate flow. Hydrogen also causes a dramatic effect on the electron and gas-kinetic temperatures, significantly increasing both of these parameters throughout the discharge. An increase in the calcium ion emission intensity, accompanied by a downward shift, elongation and broadening of the calcium ion emission profile is also observed with H₂ addition.     

Electronic emission and absorption spectra and the effect of hydrogen bonding on the ground and excited electronic states of some anilines

From electronic absorption and emission spectra in solutions it appears that intramolecular hydrogen bonding, strong enough to resist rupture by dioxane, exists in o-chloroaniline in the excited state only. Fluorescence quenching behaviour in the presence of dioxane indicates that intermolecular hydrogen bonding significantly increases intersystem crossing rate in m-chloroaniline only. This and other emission spectral characteristics in this hydrogen bonding solvent at 77 K show that the first excited singlet electronic state S₁ of m-chloroaniline is ππ*, whereas the states S₁ of aniline, toluidines and p-chloroanilines have some nπ* character. On formation of intermolecular hydrogen bond in dioxane, the corresponding triplet states of the molecules acquire pronounced nπ* character. An examination of phosphorescence decay curves reveals triplet complex formation in m- and p-chloroaniline but there is no evidence of triplet complex in the other aromatic amines studied.     

Photoluminescent copolymer-pendant Ru(BPY)32+ grafted onto non-woven silk fabric and its application to oxygen sensor

Copolymer-pendant Ru(bpy)₃²⁺ grafted onto silk fibroin was prepared by at first grafting copoly(4-methyl-4′-vinyl-2,2′-bipyridine - methylmethacrylate) onto non-woven silk fabric, and then by reacting the grafted sample with cis-Ru(bpy)₂Cl₂. Photoluminescence of this silk-poly Ru complex and its quenching by oxygen were studied in gas, methanol and water phases. The relative emission intensity and the emission lifetime of the silk-poly Ru showed that there are two kinds of sites for the Ru complex. The major, longer lifetime component (1070 ns, 77.1%, under Ar gas) is considered to be surrounded by polymer matrices, and the minor, shorter one (288 ns, 22.9%) seems to be exposed and is subjected to concentration quenching. The shorter lifetime species are quenched by oxygen more effectively than the longer ones. The mechanism of the quenching by oxygen and its application to oxygen sensor were discussed.     

Oxciplex emission of naphthalenes in polymer matrices

In this communication we report the observation of oxciplex emission, (T₁ + O₂(¹Δ)) → (S₀ + O₂(³Σ)) + hν from naphthalene and octafluoronaphthalene in polystyrene fluffs. We detect this emission as an oxygen induced luminescence burst upon admission of oxygen to a phosphorescing sample. The assignment is based on a mirror image relationship of the emission to the absorption, and energetic, kinetic, and intensity considerations.     

Quenching of dual fluorescences of pyrene vapor by high-pressure oxygen or nitric oxide

Quenching of dual fluorescence emissions (S₁ - and S₂-fluorescence) of pyrene-h₁₀ and pyrene-d₁₀ by oxygen or nitric oxide in the vapor phase at 170°C has been investigated over a wide range of the quencher pressure up to 1000 torr. In addition to slow emission, the S₂-fluorescence contains a small amount of fast emission which is not quenched even at the highest pressure of quenching gas. From the change of the ratio between the S₁ - and S₂-fluorescence quantum yields with the pressure of the quenching gas, the rate constant of the forward internal conversion S₂

S₁ is found to be ≈ 3 × 10¹³ s^?1 regardless of excitation energy, while that of the reverse internal conversion S₂

S₁ is found to change from 1 × 10⁹ to 3 × 10¹⁰ s^?1 on increasing the excitation energy from 33.6 × 10³ to 42.7 × 10³ cm^?1. The quantum yield of the fast S₂-fluorescence is evaluated to be about 5 × 10^?6 irrespective of excitation energy.     

Timing gases for picosecond chemical timing of molecular fluorescence spectra

The generality of the chemical timing or collisional timing technique for imposing picosecond time resolution on fluorescence from molecular gases is demonstrated by comparing S₁ → S₀p-difluorobenzene fluorescence spectra quenched by NO, CS₂, CF₃NO, and CO₂ with spectra quenched by O₂, the timing gas used in all previous studies. Additions of NO, CS₂ and CF₃NO reproduce the spectral changes previously observed with added O₂. Thus the changes in fluorescence spectra at high gas additions truly appear to be the consequence of fluorescence timing. All of these gases can be used to impose time resolution on molecular fluorescence spectra, and the desirability of each as a timing gas is discussed. CO₂ is not effective because collision-induced vibrational relaxation dominates the collisional interaction. The rate constant for quenching of the S₁ state of naphthalene (zero-point level) is reported for each of fourteen gases.     

Absorption and emission spectroscopic characterization of Ir(ppy)3

The absorption and emission spectroscopic behaviour of cyclometalated fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)₃] is studied at room temperature. Liquid solutions, doped films, and neat films are investigated. The absorption cross-section spectra including singlet–triplet absorption, the triplet–singlet stimulated emission cross-section spectra, the phosphorescence quantum distributions, the phosphorescence quantum yields and the phosphorescence signal decays are determined. In neat films fluorescence self-quenching occurs, in diluted solid solution (polystyrene and dicarbazole-biphenyl films) as well as deaerated liquid solution (toluene) high phosphorescence quantum yields are obtained, and in air-saturated liquid solutions (chloroform, toluene, tetrahydrofuran) the phosphorescence efficiency is reduced by triplet oxygen quenching. At intense short-pulse laser excitation the phosphorescence lifetime is shortened by triplet–triplet annihilation. No amplification of spontaneous emission in the phosphorescence spectral region was observed indicating higher excited-state absorption than stimulated emission.     

Emission characteristics of high-powered microwave induced plasma optical emission spectrometry by using nitrogen–oxygen mixture gas

A high-powered, microwave-induced nitrogen–oxygen plasma (N₂–O₂–MIP) generated by using an Okamoto cavity at atmospheric pressure was investigated when the observation height, the flow rate of carrier gas, and the oxygen content were varied as the experimental parameters. The emission characteristics of the plasma were evaluated with regard to the excitation temperature and the intensity ratio of atomic line to ionic line. The excitation temperature of the N₂–O₂–MIP was in the range of 5100–5700 K when the oxygen content was varied from 0 to 30% at the observation height of 7 mm and the carrier gas flow rate of 0.6 l/min. The intensity ratio of atomic line to ionic line was elevated with an increase in the oxygen content.     

Recombination emission in hydrogen-fluorine systems

Visible emission which is generated when H₂ is added to partially dissociated F₂ is found to be due to Δυ = 4, 5, and 6 transitions of HF(X). The temporal and stoichiometric dependence of this emission strongly suggests that it results from direct combination of hydrogen and fluorine atoms and/or from recombination of hydrogen atoms with subsequent transfer of vibrational energy from H₂ to HF.