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.     

Ultraviolet derivative absorption spectra of nylon 6,6: Effect of photolysis versus photo-induced oxidation

The irradiation of nylon 6,6 film with light of wavelengths greater than 250 nm and 300 nm has been studied using uv derivative absorption spectroscopy. Initially, the polymer showed a strong absorption at 290 nm which is associated with an α,β-unsaturated carbonyl species. Changes in the absorption band were found to be dependent on the atmosphere and are discussed in terms of a reversible photolysis versus a photo-induced oxidation process.     

Quantitative analysis of X-ray absorption spectra using a 2D map representation

A promising possibility for the quantitative analysis of X-ray absorption near edge structure (XANES) spectra of nanosized electrode materials is demonstrated. We used a 2D map representation technique, which utilizes the values of the first derivatives of the absorbance with respect to the inserted Li(+) content plotted over the two-dimensional space defined by the inserted Li(+) content (mole) versus photon energy (eV) as a single map. The technique was applied to XANES spectra of the Li(y)CoO system in the first Li(+) insertion reaction for determining the structural and electronic variations associated with the change in Li(+) content. The obtained show that the intensities of two peaks at 7725 and 7711 eV increased with the Li(+) content and the difference of intensity change of these two peaks carried out for successive couples of spectra yielded the largest changes at 1.05 and 1.98 mol of Li content. This approach for quantitative analysis of XANES without using conventional simulation techniques enable us to interpret X-ray absorption spectroscopy (XAS) as a quantitative analytical technique with greater confidence.     

铁氰化钾氧化分光光度法测定左旋多巴含量

研究了铁氰化钾与左旋多巴之间的氧化反应所引起的吸收光谱的变化.实验发现,碱性溶液中铁氰化钾氧化左旋多巴生成红色化合物,其最大吸收波长为475nm,铁氰化钾与左旋多巴的物质的量之比为2∶1.体系的吸光度与左旋多巴的浓度在3.2~54.4mg/L范围内呈良好的线性关系,线性回归方程A=-0.038 88+0.020 8c(mg/L),相关系数r=0.999 2,表观摩尔吸光系数ε=5.1×103 L·mol-1cm-1.该方法的检出限为2.32mg/L,对浓度为16.0mg/L的左旋多巴进行平行11次测定,其相对标准偏差为0.3%.据此建立了测定左旋多巴的新方法,能够直接用于市售的左旋多巴片中左旋多巴含量的测定,回收率为96.7%~104.4%.     

High accuracy measurements of OH reaction rate constants and IR absorption spectra: substituted 2-propanols

Rate constants for the gas phase reactions of OH radicals with 2-propanol and three fluorine substituted 2-propanols, (CH(3))(2)CHOH (k(0)), (CF(3))(2)CHOH (k(1)), (CF(3))(2)C(OH)CH(3) (k(2)), and (CF(3))(3)COH (k(3)), were measured using a flash photolysis resonance-fluorescence technique over the temperature range 220-370 K. The Arrhenius plots were found to exhibit noticeable curvature for all four reactions. The temperature dependences of the rate constants can be represented by the following expressions: k(0)(T) = 1.46 × 10(-11) exp{-883/T} + 1.30 × 10(-12) exp{+371/T} cm(3) molecule(-1) s(-1); k(1)(T) = 1.19 × 10(-12) exp{-1207/T} + 7.85 × 10(-16) exp{+502/T } cm(3) molecule(-1) s(-1); k(2)(T) = 1.68 × 10(-12) exp{-1718/T} + 7.32 × 10(-16) exp{+371/T} cm(3) molecule(-1) s(-1); k(3)(T) = 3.0 × 10(-20) × (T/298)(11.3) exp{+3060/T} cm(3) molecule(-1) s(-1). The atmospheric lifetimes due to reactions with tropospheric OH were estimated to be 2.4 days and 1.9, 6.3, and 46 years, respectively. UV absorption cross sections were measured between 160 and 200 nm. The IR absorption cross sections of the three fluorinated compounds were measured between 450 and 1900 cm(-1), and their global warming potentials were estimated.     

Charge-transfer interactions with ferrocyanide ion: electronic absorption spectra

The interaction of ferrocyanide ion with a series of heterocyclic cations in aqueous medium has been investigated by electronic absorption spectroscopy. New electronic transitions due to charge-transfer have been identified. The equilibrium constants and enthalpies indicate that the interaction is appreciable.     

The oxidation of thallium(I) by alkaline ferricyanide

A simple method for the potentiometnc determination of thallium is described. Thus is based essentially on the precipitation of thallic hydroxide by alkaline ferricyanide and the back titration of excess K₃[FeCN)₆] by standard sodium arsemte according to Kolthoff's method Under thc specified experimental conditions. the reduction of trivalent thallium is not effected by As₂O₃ and the procedure offers therefore a unique advantage of simplicity and accuracy.     

Quantitative measurements of inorganic and organic arsenic by flameless atomic absorption spectrometry

Procedures are described for the determination of arsenicals in water and urine by flameless atomic absorption spectrometry ; these avoid the isolation and transfer of arsine(s) and permit some differentiation between the inorganic and organic (methyl) arsenic content of a sample. Samples of water or urine are heated with hydrochloric acid, and treated with iodide ion. Arsenic species, as the iodides, are extracted into chloroform and then either reextracted into deionized water for measurement of inorganic arsenic, or reextracted into dilute dichromate solution for total arsenic determination; the difference furnishes levels of organic arsenic. Aliquots of the final aqueous extracts are analyzed by graphite-furnace atomic absorption spectrometry, with an arsenic electrodeless discharge lamp. The lower detection limit for water and urine was 10 p.p.b. The recoveries (and Sg values) were: 87.0% (3.0) and 93.0 % (7.9), for inorganic arsenic in water and urine, respectively; 92.3 % (5.3) for mixtures of inorganic and methylated arsenic (total arsenic) in water and urine; and 98.7 % (3.9) and 88.4% (3.6) for dimethylarsenic in water and urine, respectively.     

A mild oxidative aryl radical addition into alkenes by aerobic oxidation of arylhydrazines

A mild and practical oxyarylation of alkenes by oxidative radical addition has been developed by using aerobic oxidation of hydrazine compounds. The use of a catalytic amount of potassium ferrocyanide trihydrate (K₄[Fe(CN)₆]?3 H₂O) and water accelerated this radical reaction to give peroxides or alcohols from simple alkenes in good yields. The environmentally friendly and economical radical reactions were achieved at room temperature in the presence of iron catalyst, oxygen gas, and water. A method involving aniline as a radical precursor is also described.     

Sedimentation measurements with the analytical ultracentrifuge with absorption optics: influence of Mie scattering and absorption of the particles

Analytical ultracentrifugation is one of the most powerful methods for the characterization of nanoparticles since the days of its invention due to its high resolution and statistical significance. Latexes with different sizes and their mixtures have been measured by sedimentation with the analytical ultracentrifuge (AUC) OPTIMA XL-I (Beckman Coulter, Palo Alto, CA, USA) with interference optics at λ ₀ = 675 nm and absorption optics at λ ₀ = 546 and 263 nm. Additionally, a blue pigment with high absorption characteristic at visible light has been investigated. A large influence of Mie scattering and Mie absorption on the particle size distribution with respect to absorption optics and samples with moderate or broad size distribution is observed. Therefore, the consideration of the Mie scattering effect is compulsory for most AUC measurements of nanoparticles with absorption optics.     

Laser absorption spectra: Influence of collisions

Laser excitation of HF molecules is studied with and without collisions. It is found that the collisions mainly affect the line intensity rather than the width in intense laser fields. Multiphoton processes are found to be significantly more affected by collisions than one-photon processes.     

Reaction of arylhydrazines with α-formylbutyrolactam derivatives

The Vilsmeier formylation of butyrolactam and of N-phenylbutyrolactam has given their -dimethylaminomethylene derivatives. The reaction of the latter with -substituted arylhydrazines leads to the formation of 1-oxo-1,2,3,4-tetrahydro--carbolines. When unsubstituted phenylhydrazine is used, the occurrence of a competing reaction leading to -aminoethyl derivatives of 5-pyrazolone is also possible. It has been established that the direction of the reaction and the ratio of the products are affected by the substituent at the lactam nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 56–60, January 1984.     

Air-promoted direct radical arylation of anilines with arylhydrazines

Air-promoted coupling reaction of arylhydrazines and arylamines is developed for the selective synthesis of 2-aminobiaryls. This protocol provides a green, cost-effective, and scale-up method for preparation of 2-aminobiaryls.     

Simulations of X-ray absorption spectra: the effect of the solvent

We perform quantum mechanics/molecular mechanics molecular dynamics simulations on the [Pt(2)(P(2)O(5)H(2))(4)](4-) (abbreviated PtPOP) complex; in water, dimethylformamide and ethanol. These are used to calculate the ground state X-ray absorption spectrum of the complex. The structural parameters from X-ray spectra are usually extracted using a fit of the experimental data. In such simulations the solvent is neglected meaning that any effect of the local environment will be compensated for by structural changes of the solute, leading to possible discrepancies in the extracted structural parameters. Our simulations show a significant solvent effect on the spectra, which has important implications for the structural analysis of molecules in solution.