Selection of an analytical line for determining lithium in aluminum alloys by laser induced breakdown spectrometry

Possibilities for determining lithium in aluminum alloys by laser spark spectrometry are studied. The optimum conditions for registering the emission signal of lithium at which the effect of the continuous background radiation of the laser plasma attains a minimum are found. The possibility of determining lithium by laser spark spectrometry using the spectral line at 610 nm is studied for the first time. A comparison of the detection limits and sensitivities of determining lithium by emission its lines at 610 and 671 nm has indicated the advisability of using the line 610 nm for the studied alloys. The detection limit calculated using the 3σ test was found to be 230 ppm (610 nm) and 870 ppm (671 nm).     

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Critique and Bibliography

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A New Enzyme Preparation for Reducing the Viscosity of Whole-Grain Rye Extracts

New recombinant strains based on the lower fungus Penicillium canescens are engineered to produce an extracellular enzyme complex that contains a homologous endo-1,4-β-xylanase E (XylE, EC 3.2.1.8). Expression of the gene encoding XylE is controlled by the promoter of the xylA gene, which encodes endo- 1,4-β-xylanase A. Comparative analysis of enzyme preparations (EPs) isolated from the culture liquid of the host strain (Penicillium canescens RN3-11-7) and the new recombinant P. canescens strains of the XylE series is performed. The specific activity of the EPs against a specific substrate (birch glucuronoxylan) is studied, and the qualitative and quantitative composition of the new EPs XylE-B5 and XylE-C1, as well as the RN3 EP from the host strain, is determined. The decrease in the reduced viscosity of native (not subjected to thermal inactivation) aqueous extracts of rye treated with XylE-B5 EP was double that in the case of treatment with RN3 EP, due to high content of inhibition-resistant XylE in the new EPs.     

Determination of alkali metals by laser-induced atomic-ionization in flames

The technique of laser-induced atomic-ionization (AI) in flames has been used for direct determination of Na, K, Rb, and Cs in samples such as water, high-purity alkali metals and their salts and polymeric organosilicon compounds. Different procedures for sample introduction into the flame were studied: (a) the sample was placed onto the cathode of the detector (this gave limits of detection for Na and Cs of 4 x 10(-16) and 2 x 10(-15) g, respectively), (b) electrothermal vaporization and (c) aspiration of the sample into the flame. To reduce the interference of SiO(2) in the AI determination of K in polymeric organosilicon compounds (at the level of 10(-3)-10(-5)%), a procedure involved additional electrical heating of the FID cathode was developed. The efficiency of certain schemes for the laser stepwise and two-photon excitation of atoms was compared for determination of Na.     

Fluorimetric determination of amino acids and photochemical stability of their reaction products with ortho-phthalic aldehyde under irradiation by high-power pulsed laser

The opportunity of the highly sensitive determination of amino acids using the fluorescence of their derivatives that form in the reaction with aqueous solutions of ortho-phthalic aldehyde and nucleophilic agents, potassium cyanide, sodium sulfite, and N-acetyl-L-cysteine was studied as an example. The chemical stability of forming fluorescent compounds (substituted isoindoles) and their photochemical stability under the action of power pulsed laser radiation is higher, and the analytic characteristics of reagents are highly competive with a standard applied reagent for determining amino acids and a mixture ortho-phthalic aldehyde with 2-mercaptoethanol.