Headspace gas analysis: Comparison of the efficiency of thick film,ultra thick film,and activated charcoal open tubular capillary traps for the concentration of volatile,airborne, organic compounds

Determination of the rate at which volatile organic molecules diffuse through the wall of a polysiloxane rubber tube, shows that the full depth of the rubber lining of ultra-thick film open tubular traps is utilized for the retention of volatile organic compounds in headspace gas analysis. Small apolar molecules migrate rapidly through the rubber, but larger molecules and polar compounds diffuse relatively slowly into the rubber. Neither traps with a thick film of an apolar stationary phase, nor those with an ultra thick polysiloxane rubber lining retain highly volatile compounds very effectively. Traps containing activated charcoal particles fused into their inside glass surface have a much higher capacity than those with activated charcoal particles embedded in a layer of stationary phase.     

卤化银乳剂制备中的新型掺杂剂

本文综述了近年来乳剂制备中常用的新型掺杂剂,较详细地介绍了两种能提高光电子利用效率的掺杂剂,即过渡金属络合物浅电子陷阱掺杂剂和羧酸盐(酯)有机空穴陷阱掺杂剂,总结了掺杂剂的选择原则,并举例说明了掺杂剂对乳剂感光度的影响.     

Radical steps in the reactions of organometallic compounds with 2-methyl-2-nitrosopropane: experimental evaluation of the validity of the nitroxyl method for investigations of homolytic reactions of organometallic compounds

Radical adducts formed in the reactions of organometallic compounds of group II-V elements and of some organochromium and organoiron compounds with 2-methyl-2-nitrosopropane and phenyl(tert-butyl)nitrone were studied by ESR. Nitroso compounds and nitrones can be used as selective spin traps for investigations of homolytic reactions involving organometallic compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 916–920, May, 1994.     

Addition of carbon-centered radicals to C60. Determination of the rate constants by the spin trap method

The rate constants of addition of the^.CMe₃,^.CH₂Me,^.CH₂(CH₂)₃Me,^.CH₂Ph,^.CH₂CH=CH₂, and^.CH(Me)Et radicals to fullerene C₆₀ were determined by the method of competitive addition of free radicals to spin traps. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp 2369–2372, December, 1999.     

On the Most Powerful Chemical Traps for Bis(methoxycarbonyl)carbene (=2‐Methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene)

The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)carbene (=2‐methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene; 1 ) is dependent on the conditions of carbene generation. On conventional photolysis of dimethyldiazomalonate (=2‐diazopropanedioic acid dimethyl ester; 2 ) by long‐wave UV light (through a Pyrex filter, λ>290 nm), the most powerful trap for carbene 1 in the series of substrates Me₂S, MeOH, cyclohexane, and pyridine is Me₂S (with an efficiency ratio of ca. 6 : 4 : 2 : 1, resp.). When short‐wave decomposition of diazomalonate 2 is employed (through a quartz filter, λ>210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene ( 1 ) are pyridine and cyclohexane, whose adducts with 1 are rather stable under short‐wave‐irradiation conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous monitoring of carbene and oxoketene formation during photolysis is necessary.     

Spin-trapping evidence for the formation of alkyl, alkoxyl, and alkylperoxyl radicals in the reactions of dialkylzincs with oxygen

The reactions of dialkylzincs (Me(2)Zn, Et(2)Zn, and nBu(2)Zn) with oxygen have been investigated by EPR spectroscopy using spin-trapping techniques. The use of 5-diethoxyphosphoryl-5-methyl-1-pyrrroline N-oxide (DEPMPO) as a spin-trap has allowed the involvement of alkyl, alkylperoxyl, and alkoxyl radicals in this process to be probed for the first time. The relative ratio of the corresponding spin-adducts depends strongly on the nature of the R group, which controls the C-Zn bond dissociation enthalpy, and on the experimental conditions (excess of spin-trap compared with R(2)Zn and vice versa). The results have demonstrated that Et(2)Zn and, to a lesser extent, nBu(2)Zn are much better traps for oxygen-centered species than Me(2)Zn. When the dialkylzincs were used in excess with respect to the spin-trap, the concentration of the oxygen-centered radical adducts of DEPMPO was much lower for Et(2)Zn and nBu(2)Zn than for Me(2)Zn. A detailed reaction mechanism is discussed and C-Zn, O-Zn, and O-O bond dissociation enthalpies for the proposed reaction intermediates were calculated at the UB3LYP/6-311++G(3df,3pd)//UB3LYP/6-31G(d,p) level of theory to support the rationale.     

Spectroscopic properties of trapped electrons on the surface of MgO nanoparticles.

To characterise electron-trapping sites on the surface of MgO nanoparticles, surface colour centres were generated using UV light in conjunction with selected hydrogen-based electron sources. Four different colour-centre species, including the characteristic (e-)(H+) or F(S)+(H) centre, were identified due to the distinct shape of the respective electron paramagnetic resonance (EPR) signals. The analysis of the EPR saturation behaviour down to microwave powers of 5 x 10(-3) mW reveals an enhanced spin-relaxation probability of the (e-)(H+) centre compared to all other F(S)+ centres that do not exhibit significant magnetic interactions with hydroxylic protons. Beside the dipolar magnetic interaction in the (e-)(H+) centre observed by EPR, the electronic interaction between the unpaired electron and the proton of a closely spaced OH group produces a redshift of the OH stretching band by about 70 to 170 cm(-1), as observed by infrared spectroscopy. EPR and IR spectroscopic data obtained after the selective address of individual reaction channels for surface colour-centre formation point to the fact that (e-)(H+) centres are formed by trapping electrons from H atoms. Consequently, the underlying surface defect does not belong to the sites of the MgO surface, which chemisorb hydrogen via a heterolytic splitting process.     

Evaluation of the working conditions of light adsorbents and their use as sampling material for the GC analysis of organic air pollutants in work areas

Summary The use of traps containing graphitized carbon black for the collection and pre-analysis of atmospheric pollutants in industrial areas is presented. The working conditions, in terms of trapping capability and effectiveness of release by thermal desorption are discussed. Some practical applications are also given.     

Revelation in the cotton plant of chromosomes responsible for the regulation of plant growth

The monosomic nature of the dwarf line L-691 of the cotton plant has been established. The influence of various factors on the growth of the main stem of this line has been studied.Institute of Experimental Plant Biology, Academy of Sciences of the Republic of Uzbekistan, Tashkent, ul. F. Khodzhaeva, 28. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 136–138, January-February, 1995. Original article submitted October 17, 1994.     

An HPLC method forin vivo quantitation of oxygen free radicals using spin and chemical traps in biological systems

Summary We describe here anin vivo method for direct and simultaneous determination and quantitation of the oxygen free radicals (OFR) superoxide (O₂ ^–) and hydroxy (OH) radicals in biological tissue and blood of 2 week-old swine. Our method utilizes OFR trapping techniques, a spin trap 5,5-dimethyl-1-pyrroline-n-oxide (DMPO), 50 mg/kg, for O₂ ^– and a chemical trap, Na salicylate, (SA, 100 mg/kg) for OH, was infused into the right atrium or pulmonary artery of two-week old swine (n=12). The OFR contents of coronary sinus (CS) blood and left ventricular (LV) tissue (quick frozen at 77°K) were measured by an HPLC method developed by us (Waters 590 solvent delivery system, using Waters electrochemical 460 EC detector, and 740 data module) at +0.6V. The DMPO-O₂ ^– (measured as DMPO-OH) adduct assay was performed with a mobile phase consisting of 0.03 M citric acid, 0.05 M NaOH and 8.5% acetonitrile (Ph 5.1) at a flow rate of 1 ml/min through a Waters Resolve 5 C₁₈ column. The salicylate-OH products (2,5 and 2,3 dihydroxy benzoic acids, DHBA) were assayed using mobile phase of 0.03 M Na citrate, 0.03 M Na acetate, with N₂ bubbled (pH 3.6) at a flow rate of 0.8 ml/min through a 5 Resolve C₁₈ column. The detected peak for DMPO-O₂ ^– adduct (9.5 min) was standardized with a hypoxanthine (HX) and xanthine oxidase (XO) mixture and the salicylate-OH products (11.5 min) were standardized with HX, XO and FeCl₃. Forin vitro experiments, the blood/tissue samples were immediately (<30 sec) incubated directly with 100 mM DMPO and/or 200 mM salicylate for 1 min, vortexed and injected for HPLC analysis. Superoxide dismutase (1 M) and DMSO (10 mM) scavenged O₂ ^– and OH adduct peaks by 77 and 80% respectively. The coefficient of variation for DMPO-O₂ ^– adduct was ±12.6% and for salicylate-OH adduct was ±10.9% (n=12). The normal LV tissue levels determined for O₂ ^– and OH were 0.41 and 0.32 nm/g wet weight, respectively. (In blood, the OFR contents were very small: 0.09 and 0.06 nm/ml, respectively.) This method is very specific and sensitive, 50 pm for O₂ ^– and 0.2 pm for OH radicals.Presented at the 39th National Meeting, American Association of Clinical Chemistry, New Orleans, 1988.     

Spin Trapping of Radical Intermediates Generated by the Oxidation of Substituted 4‐Methylphenols

A series of substituted 4‐methylphenols 1 and 2 was oxidized with PbO₂ in the presence of nitroso compounds 3 – 10 . The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H‐atom from the methyl substituent of 1 or 2 . In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky ^tBu groups in ortho‐position (see 2,6‐di(tert‐butyl)‐4‐methylphenol ( 1a )), the stable 2,6‐di(tert‐butyl)‐4R‐phenoxy radicals (R=? CH?N⁺(O^?)? X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO radicals.     

Capturing of volatiles emitted by living plants by means of thick film open tubular traps

Fused silica open tubular traps coated with a 15μm film of methyl silicone have been successfully applied to capture volatiles emitted by living plants. The atmosphere surrounding the plants is sucked through the trap where the volatiles are retained. After sampling, the trap is installed as pre-column in a multidimensional CGC system. The volatiles are thermally desorbed, reconcentrated in a cold trap and analyzed on-line on the analytical capillary column.     

Spatial Taming and Trapping of Molecules

Molecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field-free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser-induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer-gas cooling, an intense infrared laser can typically confine molecules for long-times (-hours) within a small (-picoliter) and cold (?1°K) “pocket of light.”