The oxygen-shielded air-acetylene flame in emission analysis

Flame-emission studies have been made on 18 elements in the inner zone of an oxygen-shielded air-acetylene flame. The shielded flame gave higher emission sensitivity that that of the C(2)H(2)N(2)O flame for Cu and Tl, and comparable sensitivity for a number of other elements, but poorer sensitivity for elements forming stable refractory oxides in flames. The inner zone of the shielded flame has low emission-background and high flame-temperature, permitting good analytical sensitivity to be obtained with relatively low-resolution optical equipment.     

Studies on Excitation and Rotational Temperatures of an Oxygenshielded Argon Microwave Plasma Torch Source

IntroductionPlasma sources have been widely used for traceelemental analysis in atomic emission spectrometry(AES)or mass spectrometry(MS).The microwaveplasma torch(MPT),as a relative new source,wasfirst developed by Jinet al.in1985[1,2]and modifiedby Jin …     

Comparison of the helium/oxygen/acetylene and air/acetylene flames as atom sources for continuum-source atomic fluorescence spectrometry

The helium/oxygen/acetylene flame is compared to the more widely used air/acetylene flame for its utility as an atom cell for atomic fluorescence spectrometry. Nearly identical experimental arrangements were used for both flames in order to make the comparison valid. With a continuum source used for excitation, fluorescence detection limits in the helium/oxygen/acetylene flame were between 13 and 60 times better (lower) than those determined for the same eight elements in the air/acetylene flame. The improved detection limits are attributable mainly to the higher temperature, increased thermal conductivity and lower quenching in the helium flame. Fluorescence background spectra were obtained for both flames over the wavelength range 185–650 nm, and showed the helium flame to have slightly smaller background fluctuations, but a much larger background because of the more favorable fluorescence conditions in the flame.     

Organic fuelled flames in selective ionization detectors for chromatography

Summary The selectivities of two flame-based ionization detectors identified as a Remote FID (RFID) and a Flame Thermionic Ionization Detector (FTID) have been improved by introducing methane as a fuel for the flame. Both the RFID and FTID feature a detector struture in which the ionization polarizer and collector are located several centimeters downstream of an oxygen-rich flame, rather than immediately adjacent to the flame as in a flame ionization detector. The RFID detects long-lived negative ions produced in the flame by the combustion of lead, tin, phosphorus, or silicon compounds. The FTID re-ionizes and detects neutral electronegative products generated by combustion of nitrogen, halogen, or phosphorus compounds. An organic-fuelled RFID can detect 1 pg Pb (Sn, P)/sec with a selectivity of the order of 10⁶ versus hydrocarbons. An organic fuelled FTID is applicable to detection of compounds at nanogram and higher levels. FTID selectivity for PCB compounds in a transformer oil matrix is of the order of 10⁵1. The improved selectivity achieved by using an organic-fuelled flame is also applicable to the detection of phospholipid and other non-volatile N, P, or Cl compounds using an FID/FTID detector accessory for a TLC/FID analyser.     

Studies in atomic-fluorescence spectroscopy-VII Fluorescence and analytical characteristics of arsenic, with a microwave excited electrodeless discharge tube as source

The construction of an electrodeless arsenic discharge tube and its use for atomic-fluorescence studies is described. Cool nitrogen-hydrogen and argon-hydrogen diffusion flames as well as normal premixed flames are considered as atom reservoirs and the atomic-fluorescence emission at 15 different wavelengths is evaluated. The diffusion flames give the largest emission signals at arsenic concentrations below 200 ppm, but show a premature curvature at higher concentrations because of the presence of an abnormally high density of arsenic atoms. Above 200 ppm of arsenic, the premixed air-acetylene flame is superior. The limit of detection at 1890 A is 0.2 ppm of arsenic in the nitrogen-hydrogen diffusion flame and 1.0 ppm in the airacetylene flame. A long path-length diffusion flame is also particularly useful in atomic-absorption measurements because it absorbs very little radiation in the far ultraviolet region and gives an abundance of arsenic atoms.     

Atomization efficiencies in halocarbon-loaded acetylene-air flames—I. Monochlorides of readily volatilized elements

Carbon tetrachloride vapour was introduced with a carrier air stream into the mixing chamber of an acetylene-air flame while nebulizing aqueous solutions of several metal salts. The atomic absorption signal was measured under increasing flow rate of the halocarbon vapour at constant fuel-to-oxidant ratio, and the latter parameter was also varied in separate experiments. By applying the theory developed by Sugden and Bulewicz, the exclusive formation of monochlorides in the gaseous phase (presented here, in Part I) and the additional formation of hydroxychlorides and dichlorides (presented in Part II) could be elucidated. From the decrease of the signal measured for the alkali elements of known monochloride dissociation constants and dissociation energies, the temperature and the chlorine concentration present in the observed flame zone could be calculated. It is inferred that only 19% of the total halogen introduced is converted to HCl and Cl species in a slightly fuel-rich flame. The signal depression is stronger in a fuel-lean flame of higher monoatomic chlorine concentration for those elements which have a relatively efficient atomization under these flame conditions. An increase of the electron concentration resulting from the introduction of the halocarbon in an alkali-containing flame was deduced from the experimental findings, in agreement with earlier observations.     

Atomic fluorescence and atomic emission measurements with an image dissector echelle spectrometer

This paper deals with the investigation of an image dissector echelle spectrometer as an analytical instrument for flame atomic fluorescence spectrometry and for flame atomic emission spectroscopy. The fluorescence was induced by high-pressure xenon arc lamps, which emitted continuum spectra and had higher power ratings, i.e. 1.6 and 2.5 kW, than those normally used for the same purpose. The experimental set-up included two different types of premix burners and one type of total consumption burner. A spherical reflector was applied to improve the utilization of the fluorescence radiation. Two different coatings were tested. None gave the expected enhancement.Detection limits and growth curves were measured for 8 different elements (Ca, Co, Cu, Fe, K, Mg, Na and Ni) in a non-separated air/acetylene flame. The attained detection limits were found to be equally good or somewhat better in flame atomic fluorescence excited with continuum sources than previously reported in the literature, i.e. using similar flames. In flame atomic emission spectroscopy better detection limits have been reported before.     

Effect of ethyl‐bridged diphenylphosphine oxide on flame retardancy and thermal properties of epoxy resin

Three commercialized flame retardants, 1,2‐bis(diphenylphosphinoyl)ethane (EDPO), 6,6‐(1,2‐phenethyl)bis‐6H‐dibenz[c,e][1,2]oxaphosphorin‐6,6‐dioxide (HTP‐6123), and hexa‐phenoxy‐cyclotriphosphazene (HPCTP), were used to prepare the flame retardant diglycidyl ether of bisphenol A (DGEBA) epoxy resin (EP) under the same experimental conditions. The effects of T_g, thermal stability, and water absorption properties of EP caused by the three flame retardants were investigated and compared, together with their flame retardant efficiency. Results showed that the introduction of the three flame retardants improved the flame retardant performance of EP but led to decreases in T_g and decomposition temperature. EDPO showed higher flame retardant efficiency than the other two flame retardants. EP/EDPO showed higher thermal stability, better flame retardant performance, higher T_g value, and lower water absorption than EP/HTP‐6123 and EP/HPCTP. The study discovered that EDPO and HTP‐6123 primarily act through the gas phase flame retardant mechanism, while HPCTP is primarily driven by the condensed phase mechanism.     

The role of oxygen in the ignition of polystyrene by a small flame

The ignition of slabs of high-impact polystyrene by a lean hydrogen–oxygen flat flame was studied. The ignition delays and inital rates of flame development after ignition are reported as functions of gas temperature and the separation between flame and polymer surface. The delays follow an Arrhenius-type expression with an activation energy of 98 ± 18 kJ mol^?1. The rates of flame development drop as the gas temperature increases. During long ignition delays the apparent heat transfer coefficient at the sample surface dropped from about 100 W m^?2 K^?1 to values close to that expected for a hot gas impinging at right angles on a cold surface. For short delays it was higher and more constant at about 100 W m^?2 K^?1. Although the surface temperature reached before ignition exceeded that required for nonoxidative pyrolysis, the polymer surface charred only when oxygen was present. It is concluded that both oxidative and nonoxidative pyrolysis contribute to the ignition of polystyrene.     

Fire retardancy of a reactively extruded intumescent flame retardant polyethylene system enhanced by metal chelates

A reactive extrusion technology was adopted to synthesize a flame retardant (ER), based on the esterification of melamine phosphate and pentaerythritol. The ER imparts good flame retardancy and non-dripping for polyethylene (PE) when combined with ammonium polyphosphate to yield an intumescent polyethylene (PE-IFR). The performance of this intumescent system has been enhanced by the addition of small amounts (0.2%) chelated copper(II)salicylaldehyde (CuSA) and salicylaldoxime, (CuSAO). The thermal stabilization and burning behaviour of the flame retardant PE system have been investigated by TGA, LOI, the UL-94 test and cone calorimetry. All formulations studied provide good flame retardant behaviour, with LOI ≥ 27.4 and UL-94 V-0 rating. The onset of decomposition in TGA for flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) commences at lower temperature than that of PE with release of blowing agent, but continues to a higher temperature, leaving a greater residue. Significant differences have been observed in burning behaviour using cone calorimetry, between flame retarded PE (PE-IFR, PE-IFR-CuSA and PE-IFR-CuSAO) and PE, showing decreases in HRR, PHRR, MLR, FIGRA and CO emission.     

不同囊材聚磷酸铵微胶囊在环氧树脂中的阻燃研究

采用原位聚合法合成制备了以蜜胺树脂(MF)、环氧树脂(EP)以及EP和MF为囊材的微胶囊阻燃剂MFAPP、EPAPP、EMFAPP,用红外光谱(FT-IR)和扫描电镜(SEM)表征微胶囊阻燃剂的核壳结构。采用极限氧指数(LOI)和垂直燃烧等级测试(UL94)对MFAPP、EPAPP、EMFAPP在环氧树脂中的阻燃特性进行了研究。当添加量大于7%时,阻燃复合材料均能通过UL 94 V-0级测试,极限氧指数大于27.0%,表明MFAPP、EPAPP、EMFAPP均为EP的高效阻燃剂,这些阻燃剂在EP阻燃过程中均形成了膨胀炭层,属于膨胀阻燃机理。另外在耐水性实验中发现,添加EPAPP、EMFAPP的EP复合材料具有更好的耐水性,经75℃水浸泡6天后,阻燃性能得到了较好的保持。     

Scale effect of porous mesh on the inhibition mechanism of wheat dust flame

The combustible features of wheat dust easily induce a potential hazard in its processing and application. To clearly reveal the effects of porous mesh parameters on the flame propagation of wheat dust, a vertical combustion pipeline together with the data collecting by the high-speed photography and fine thermocouple was built. Results indicate that with the increase in the mesh scale, the dust combustion and peak temperature are intensified first and then decreased with a darker luminescence. The increasing mesh number shows an inhibition effect on both peak temperature and combustion pressure, but an accelerating first and then weakening effect on flame velocity. A smaller particle size contributes to a more complete combustion, causing a higher peak temperature and flame velocity. At the particle mass of 2.5 g, the maximum value of peak temperature, flame velocity and combustion pressure were obtained during the flame propagation.

     

The determination of gallium by atomic absorption spectrometry

The use of a nitrous oxide-acetylene flame for the determination of gallium by atomic absorption spectrometry was compared with the use of air-acetylene flames. The nitrous oxide method provided higher sensitivity and was much less sensitive to acid and base composition and to diverse added salts. Significant matrix and background effects, which occurred when gallium was determined in ore solutions with the air-acetylene flame, were eliminated with the nitrous oxideacetylene flame.     

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.     

三（2，4，6－三溴苯氧基）锑酸酯的合成及其阻燃性能与阻燃机理

合成了三（２，４，６－三溴苯氧基）锑酸酯，通过元素分析和ＩＲ光谱予以表征，并就其对聚乙烯和聚丙烯的阻燃性能与阻燃机理进行了研究。结果表明：这种分子中同时含有溴、锑的阻燃剂，比相应的仅含溴和仅含锑的阻燃剂混合物具有更高的阻燃性能。     

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.     

Preparation of phosphorus‐containing phenolic resin and its application in epoxy resin as a curing agent and flame retardant

For the sake of improving the flame retardancy of epoxy resin (EP), a novel phosphorus‐containing phenolic resin (PPR) synthesized in our group instead of conventional phenolic resin (PR) was used to cure EP in the present research. The curing processes and the corresponding crosslinking structure and mechanical performance were investigated by differential scanning calorimeter and dynamic mechanical thermal analysis. Because of the introduction of flame‐retarding elements including P and Si, PPR exhibited higher charring capacity in the condensed phase, which is helpful to construct a char layer of higher quality. Correspondingly, PPR‐cured EP displayed remarkably improved flame retardance as compared to conventional PR‐cured EP through the related evaluations including limiting oxygen index, vertical burning test, and microscale combustion colorimeter. As a multifunction agent, it is believable that PPR possesses potential commercial value to prepare flame‐retardant EP with high performance.     

Ternary structure design based on hydrogen bonding for transparent and flame retardant PMMA with good mechanical properties

The synthesis of intrinsic flame retardant copolymer by copolymerization with reactive flame retardants is the most potential method to prepare transparent and flame retardant poly (methyl methacrylate) (PMMA) at present,but the main challenge of this method is that the copolymer usually has poor mechanical properties and heat resistance. In this work, the hydrogen bond enhancement strategy is adopted, and the flame retardant PMMA with excellent comprehensive properties is obtained by ternary copolymerization with methyl methacrylate (MMA) as matrix unit, diethyl (methacryloyloxymethyl) phosphonate (DEP) as flame retardant unit and methacrylamide (MAA) as hydrogen bond unit. Due to the formation of intermolecular hydrogen bond via MAA unit, the storage modulus, flexural strength and impact strength of the terpolymer containing 15 mol% MAA are 48%, 19%, and 24% higher than those of the copolymer of MMA and DEP, and its hardness, glass transition temperature and load thermal deformation temperature (increased by 7°C) are also superior. Moreover, owing to the gas-phase dilution and charring flame retardancy of MAA unit, the terpolymer shows increased limiting oxygen index (24.3%) and UL94 rating (V-1). This work not only provides a promising flame retardant PMMA for practical application, but also offers a new strategy to design flame retardant polymers with good mechanical properties.     

Towards the development of thermally latent novolac-based char formers for ABS resins

Novel novolac-based char formers for ABS resins, [PN-PI], [PN-BPI], [CN-PI] and [CN-BPI], were prepared from phenol formaldehyde novolac (PN), cresol formaldehyde novolac (CN), phenyl isocyanate (PI), and 4-biphenyl isocyanate (BPI) via a simple urethane-forming reaction. The four compounds were used as thermally latent char formers for this study. Thus, a two component system employing novolac-isocyanate adduct as a char former, and tetra-2,6-dimethyl phenyl-resorcinol diphosphate (DMP-RDP) as a phosphorous-based flame retardant was blended with ABS, and the thermal degradation behaviour and flame retardancy were determined by thermogravimetric analysis (TGA) and LOI test. The mixtures show a synergistic effect between DMP-RDP and novolac-isocyanate adduct on the flame retardance enhancement of ABS. Those containing higher molar mass CN-BPI adduct are found to be most flame retardant, and a LOI value as high as 35 is obtained.     

Reduction of spectral interferences in inductively-coupled plasma emission spectrometry by selective spectral-line modulation

Spectral interferences in inductively-coupled plasma (i.c.p.) emission spectrometry can be significantly reduced through the use of selective spectral-line modulation. In this method, a mirrored, rotating chopper directs the emission from an i.e.p. alternately through and past a flame; selective modulation is achieved when the flame contains absorbing atoms identical to emitting atoms in the i.c.p. The ability of selective spectral-line modulation to minimize broadband, narrow line, and scattered light spectral interferences is demonstrated. Signal-to-background ratios for detection with spectral-line modulation are shown to be higher than those obtained by conventional detection. The effect of modulating conditions on working curve slope and linearity is discussed and the limitations of the proposed method are critically evaluated.