Mechanical feed burner with total consumption for flame photometry and atomic absorption spectroscopy

A mechanical feed burner has been developed for use in flame photometry and atomic absorption spectroscopy. The optimum flame conditions for cinisaion and absorption are very different. These conditions are also modified when organic instead of aqueous solvents are used. When different organic solvents are used, the interference is eliminated with atomic absorption but not emission. Flame profiles of a.tomic absorption and emission signals indicate that the processes are independent; the best signal for each is obtained at different parts of the flame. With emission, it appears that line spectra and background emission originate from the same process e.g. chemiluminescence     

Construction and performance of a time-multiplex multiple-slit flame atomic fluorescence spectrometer for multi-element analysis

The design and performance characteristics of a new multi-element flame atomic fluorescence spectrometer are presented. Radiation from four hollow-cathode tubes is directed onto an unsheathed air—hydrogen flame. The resulting atomic fluorescence is viewed by a special monochromator with a separate exit slit for each element. The light exiting from all slits is directed to a single photomultiplier tube. The fluorescence signals from different elements are distinguished by a time multiplex approach. Single-element detection limits for ten elements and multi-element detection limits for four elements are presented. The degradation of detection limits by flame background emission noise and effect of flame composition on performance are discussed. Better than 1% precision is obtained for moderate analyte concentrations.     

Solubilities,thermostabilities and flame retardance behaviour of phosphorus-containing flame retardants and copolymers

Thirteen phosphorus-containing flame retardants were synthesized in this work. The solubilities of flame retardant [(6-oxide-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)-methyl]-butanedioic acid (DDP) in selected solvents are measured. TGA measurements of the 13 phosphorus-containing flame retardants were carried out and thermal stabilities of three flame-resistant PET (FRPET) resins were investigated. A FRPET incorporated by DDP with terephthalic acid and ethylene glycol reported in literature was also discussed and compared. The thermal stability of the FRPET is improved by the incorporation of phosphorus-containing flame retardants. The LOI values of all phosphorus-containing polyesters are higher than 27%. The improvement of the flame-resistant ability is due to the formation of the char that is not only caused by the existence of phosphorus elements in the resin but also by the relative large number of carbon atoms of the phenyl group in the flame retardants.     

Evaluation of the analytical capabilities of frequency modulated sources in multielement non-dispersive flame atomic fluorescence spectrometry

Frequency modulated sources of Cd and Zn are used to produce modulated atomic fluorescence signals (at two different frequencies) in a non-dispersive flame atomic fluorescence spectrometer. To reduce the flame background level, a chlorine filter, a separated air—acetylene flame, and a solar blind photomultiplier are used. Even so, there is shown experimentally and theoretically to be a multiplex disadvantage, as compared to the conventional single slit scanning dispersive spectrometer, as a result of the flame background photon noise and an additional multiplex disadvantage at high concentrations of an interference, e.g. in the measurement of Zn (213.9 nm), Cd (228.8nm) results in a reduced S/N for Zn when the Cd signal level becomes comparable with the flame background signal level. Little future for multiplexed techniques in atomic flame spectrometry in the u.v.- Visible is predicted.     

Some optical studies with the air-acetylene flame

The application of Schlieren and shadow techniques for the study of flame processes is discussed in relation to analytically useful premixed flames. The information obtained, particularly with shadowgraphs, may be correlated with the measured signals and signal noise in atomic-absorption and flame-emission spectrometry.     

Noise power spectra of flame atomic absorption spectrometric measurements

Experimental noise power spectra in the frequency range 0 to 5 Hz are reported for 100% T, analyte, and 0% T signals in atomic absorption spectrometry. These spectra are calibrated such that the r.m.s. noise observed in normal measurements can be predicted for a given integration time. A 1/? noise component is observed in lamp flicker noise, flame transmission flicker noise, and analyte absorption flicker noise.     

Effects of organo-clay and sodium dodecyl sulfonate intercalated layered double hydroxide on thermal and flame behaviour of intumescent flame retarded polypropylene

The thermal and flame performances of intumescent flame retarded polypropylene (PP/IFR) composites with organically modified clay or sodium dodecyl sulfonate intercalated layered double hydroxide (SDS-LDH) were studied. The organo-clay particles were partially exfoliated in the PP matrix, while intercalation and aggregation was obtained for SDS-LDH. Incorporation of SDS-LDH improved the thermal stability and flame retardancy of the intumescent flame retarded PP composite in the early stage of heating and combustion; while the effects of organo-clay came into play in the middle-later stage. Differences in degradation pathway of clay and LDH were responsible for the above phenomenon which bore important implication for the barrier mechanism. The introduction of organo-clay into PP/IFR not only increased the char residue, but also formed compact and folded morphology of char residue which provided more effective protect for underlying materials against heat and oxygen relative to LDH, thus improved the flame retardancy of intumescent flame retarded PP samples more efficiently.     

Multichannel integrating flame photometer

A new high-speed optical chopping and demodulation system is described for use in flame photometry. Methods are described which allow integration of signal and noise over many optical pulses of flame energy. The method has been used to develop a direct-reading instrument for sodium, potassium and calcium. With this method, 4 signal channels are integrated simultaneously. With the integration technique, ordinary flame noise is significantly reduced. By using an internal standard, all signal channels are referenced to known energy levels regardless of flame variations.     

Preparation and properties of surface-active organocobalt complexes having long-chain alkyl groups

New types of surface-active organocobaltocenium(I) complexes, η-C_nH_2n+1X-C₅H₄(ηC₅H₅)₂Co⁺Y^? and(η-C_nH_2n+1X-C₅H₄)Co⁺Y^? (n = 6–16; X not present, NHCO or OCO; Y = Cl or PF₆) were prepared and their surface character studied. (1) The critical micelle concentrations of the cobaltocenium chlorides were much lower than those of corresponding trimethylammonium-type cationic surfactants. (2) The surface-active character of the cobaltocenium chlorides in aqueous solution (and the redox potentials of the hexafluorophosphates in acetonitrile) were affected by the substituents (X) in the cyclopentadienyl groups. (3) The surface activities of the cobaltocenium salts were lost on reduction with NaBH₄ to afford (alkyl-substituted cyclopentadiene) cyclopentadienylcobalt (0) complexes which were surface-inactive but could be re-oxidized to afford the surface-active cobaltoceium(I) salts. The cobalt complexes mentioned above may be the first examples of redoxresponsive surfactants.     

Use of a continuous source of excitation,an argon-hydrogen-air flame. and an extended flame cell for atomic absorption flame spectrophotometry

A continuous source of excitation in conjunction with an argon-hydrogen-entrained air flame, an extended flame cell, a medium-dispersion monochromator and a typical detection system is shown to give good sensitivities for the atomic absorption flame spectrophotometric measurement of 21 elements. Useful working curves over a 100-fold concentration range are obtained for each of the 21 elements using the simple experimental system. The advantages gained with this system are discussed.     

Novel flame photometric detector for gas chromatography based on counter-current gas flows

A novel analytical device has been developed for gas chromatography. It is based on optical emission from a counter-current (i.e. counter-flowing) air or oxygen flame, which burns in an opposing stream of hydrogen and column effluent. The flame is typically positioned "upside down" on the upper (air) jet, which faces the lower (hydrogen + effluent) jet. It can also be positioned on the lower jet, be connected to both jets, or be suspended in the gap between them. Excellent stability can be obtained in any of these modes. Overall, this new "counter-current flame photometric detector" (ccFPD) responds to analytes in the manner of a conventional flame photometric detector (FPD); however, it can be operated over a much wider range of gas flows. For instance, the same physical ccFPD burner easily supports stable flames of air flows between 5 and 200 ml/min and corresponding hydrogen flows between 5 and 10,000 ml/min. Visual observation of the counter-current flame, in the presence of sulfur and phosphorus as test analytes, reveals intense, steady luminescence under a wide variety of conditions. Additionally, and in contrast to the commercial FPD, flame conductivity signals can be obtained that are similar in quality to those produced by a conventional flame ionization detector (FID). Thus the ccFPD is a flexible, easily optimized photometric detector. The exceptional flow stability of the ccFPD was used to explore the earlier reported phenomenon of strong signal/noise (S/N) ratios, which had been obtained for hetero-elements of the iron group from a conventional FPD with a small, stoichiometric flame. Results using the ccFPD, which also exhibits this unusual response, indicate that these high S/N ratios are only partly due to the predictable decrease in flame noise with decreasing flame size. Contrary to expectations, the absolute analyte signal often increases as the flame size decreases to the point of extinction. The signal intensity and the magnitude of the observed changes depend to some degree on the flame composition (H2/O2 ratio).     

Control parameters of flame spreading in a fuel container

The processes involved in flame spreading over liquid fuels are subject of this work. A heat and momentum transfer analysis has been undertaken for fuel temperatures below the flash-point that confirms (within this range of temperatures studied in this work) that flame spreading is assisted by a convection pattern ahead of the flame. This assistance mechanism, which is not observed for solid fuels, is the origin (for lower temperatures) of a pulsating behaviour of the flame. A first experimental determination of the characteristic horizontal length of this assistance zone will be given. The analysis of our data lead us to conclude that flame spreading can be reduced by simultaneously preventing the formation of the convection zone and reducing the fuel surface temperature.     

Atomic-fluorescence characteristics and analytical determination of manganese in an air-acetylene flame

The atomic-fluorescence characteristics of manganese atoms in a premixed nitrogen-shielded air-acetylene flame are described. Excitation is obtained at 280 nm from a microwave-excited electrodeless discharge tube. A detection limit of 0-001 ppm for the determination of manganese by atomic-fluorescence spectroscopy is obtained by measurement of the resonance fluorescence observed at this wavelength. In addition to several other weaker atomic-fluorescence signals observed from manganese atoms in the flame, weak resonance fluorescence at 258 and 260 nm from manganese ions stimulated by ion line-emission from the source has been recorded. Linear calibration graphs for atomic-fluorescence measurement at 280 nm are obtained over the range 0.0025-10 ppm of manganese in aqueous solution. Of 26 foreign anions and cations examined for interference at the 1000-fold weight excess level only four produced interference. Large amounts of Si, Th and V interfere by scattering of the incident radiation, while Mg causes depression of the atomic fluorescence by a chemical effect.     

Direct flame solid sampling for atomic absorption spectrometry: determination of copper in bovine liver

In this work a new device for the direct introduction of solid samples into flame atomizers is proposed. The determination of copper in bovine liver reference material by flame atomic absorption spectrometry (FAAS) using a conventional air–acetylene flame was chosen as an example. Between 0.05 and 0.50 mg of the test sample was weighed directly into a small polyethylene vial connected to a glass chamber. A flow of air carries the test sample as a dry aerosol to a T-shaped quartz cell positioned above the burner in the optical path. The atomic vapor generated produces a transient signal of less than 3-s duration; integrated absorbance is used for signal evaluation. Optimized conditions for air flow rate, flame stoichiometry, etc., were evaluated. There was no statistical difference between the results from the proposed system, compared with those obtained by prior sample digestion and determination by conventional FAAS. No excessive grinding of the samples was required and samples with particle size less than 80 μm were used throughout. Background signals were always low and a characteristic mass of 1.5 ng was found for Cu. The proposed system allows the determination of 60 test samples in 1 h and it can be easily adapted to conventional atomic absorption spectrometers.     

Indirect method for the determination of aluminium by atomic-absorption spectrometry using an air-acetylene flame

The enhancement of the atomic-absorption signals of iron, cobalt, nickel and chromium in a fuel-rich air-acetylene flame by small amounts of aluminium makes possible the indirect determination of aluminium in the concentration range 0.01-10 ppm. The optimization of working conditions and the occurrence of interferences are reported.     

Effect of droplet size on the phosphine depression of calcium atomic emission signals in flame spectrometry

The effect of the droplet size on the magnitude of the phosphine depression of calcium signals is discussed. The droplet size governs the time required for droplet desolvation in the flame. It is during the desolvation process that the combustion products of phosphine, PO_x, diffuse into the droplet and form a refractory compound with the analyte. The longer the desolvating droplet resides in the PO_x-contaminated flame, the more severe the depression. A uniform droplet generator, a pneumatic nebulizer spray chamber system, and a glass-frit nebulizer spray chamber system were the sample introduction systems studied. Droplet sizes of (55 μm, 0.5–10 μm (2 μm mean), and <0.1–2 μm (0.1 μm mean) were produced by these systems, respectively, and depressions of the calcium signals of 57%, 55%, and 4% were noted. These results suggest that the phosphine depression on calcium signals may be alleviated by using a glass-frit nebulizer (or modifying a commercial nebulizer) to remove droplets greater than 2 μm in diameter.     

The role of various flame constituents in the production of atoms in the air—acetylene flame

Atom-formation processes in the premixed air—acetylene flame used in atomic absorption spectrometry are examined. Flame profiles of copper, indium and calcium atoms for five flames of differing acetylene: air ratios are compared with the flame profiles of temperature and the natural flame species C₂, CH and H. The flame profiles of the metals bear little resemblance to the temperature profile. C₂ and CH radicals are shown to be confined to the lower region of the flame (approximately to the region of the reaction zone), whereas H radicals persist far beyond the reaction zone. The strong resemblance of the profile of indium atoms to that of H radicals suggests the participation of H radicals in indium atom formation. Experiments on the action of the flame on solid calcium oxide similarly suggest the involvement of H radicals in the reduction of calcium oxide.     

Ignition of low-density polyethylene slabs by a small flame

Slabs of low-density polyethylene (LDPE) were exposed to the wake of a lean hydrogen-oxygen flat flame. The ignition delay and initial flame velocity after the ignition were measured at several gas-air equivalence ratios and distances from the igniting flame. When ignition occurred, the surface temperature was far lower than that required for pyrolysis in the absence of oxygen. Small amounts of char formed on the polymer surface during the delay, consistent with the involvement of oxygen in solid-phase preignition processes. Plots of In(delay) versus 1/(absolute temperature) were linear and the activation energy was derived from the Arrhenius equation, 64 ± 10 kJ/mol. Initial rates of flame development decreased with increased separation between the polymer and the igniting flame, but unlike those reported for poly(methyl methacrylate), they were independent of the duration of the preceding delay except when the polymer was very close to the flame. The results are explained by a model in which both the ignition delay and the subsequent rate of flame development depend on the concentration of species associated with the chain-propagation steps of the combustion process.     

A review on flame retardant technology in China. Part I: development of flame retardants

This paper provides an insight into some developments in flame retardants for different polymeric materials in China, primarily based on the publications that have appeared in the last 15 years. It focuses on the following aspects: halogen‐containing flame retardants, inorganic flame retardants (e.g. metal oxides and hydroxides, silicon‐containing materials, ammonium polyphosphate, red phosphorus, and expandable graphite), and organic flame retardants (e.g. aliphatic and aromatic phosphonates, nitrogen‐containing organics, and multi‐element organics). The inherently flame‐retardant polymer systems are also reviewed. The exploration of the novel flame retardants and flame‐retardant systems provides a powerful basis for the construction of flame‐retardant technologies and industrial applications in China. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal degradation of wood treated with flame retardants

Wood, one of the most flammable materials, was treated with various compounds containing nitrogen, phosphorus, halogens, and boron. For a study of flame retardance from the standpoint of thermal degradation, the samples were subjected to thermogravimetry (TG), differential thermal analysis (DTA) and differential thermogravimetry (DTG) in nitrogen to determine if there were any characteristic correlations between thermal degradation behaviors and the level of flame retardance. From the resulting data, kinetic parameters for different stages of thermal degradation are obtained using the method of Broido. The energies of activation for the decomposition of samples are found to be from 72 to 109 kJ mol^–1. For wood and modified wood, the char yields are found to increase from 10.2 to 30.2%, LOI from 18 to 36.5, which indicates that the flame retardance of wood treated with compounds is improved. The flame retardant mechanism of different compounds has also been proposed.