An improved approach for hydrogen analysis in metal samples using single laser-induced gas plasma and target plasma at helium atmospheric pressure

We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration of the conventional LIBS method. PACS 51-52     

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO2 laser plasma in He gas at 1 atm

A TEA CO₂ laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO₂ laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO₂ laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO₂ laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.     

Chiroptical properties of n-nitrosopyrrolidines and n-nitrosamino acids : Implications for the nitrosamine sector rule

CD data for a variety of N-nitrosamino acids and N-nitrosopyrrolidines are presented. The effects of nitrosamino group conformation, pyrrolidine ring geometry, different perturbing substituents, and especially intramolecular H-bonding upon the n → π^* CD band are discussed. Stereochemical conclusions can be made with confidence in many cases, although no sector diagram, as yet published, successfully correlates all the available chiroptical data in this series of compounds. However, a negative CD band due to the π → π* transition was observed tor all N-nitrosamines having the L-proline configuration at C-2, regardless of nitroso group conformation; it is suggested that this band be used whenever possible for stereochemical correlations.     

Phase transition phenomena induced by the successive appearances of new types of aggregation states of water molecules in the “l-dipalmitoylphosphatidylcholine-water” system

Thermal analysis of the aggregation state of water molecules m the “L-di-palmitoylphosphatidylcholine (DPPC)-water system revealed that in the low-temperature crystal phase below the sub-transition temperature, there are three kinds of interlamellar water, i.e., tightly, loosely, and more loosely bound water, which are incorporated between the bilayers of l-DPCC molecules, while the Lβ' gel phase lacks the third bound water molecule. Furthermore, we found that both the sub- and pre-transitions below the main transition temperature appear, for the first time, at water contents of around 11 and 18 g%, respectively, just at which point the new types of water structure occur. These findings indicate that the condition necessary for the appearance of these two kinds of phase transition is the existence of the characterized aggregation state of water molecules, that is, more loosely bound water for the sub-transition and bulk free water coexisting with the Lβ' gel phase for the pre-transition.     

Progress in planar chromatography II. Chemically bonded phases

Chemically bonded phases are almost indispensable in modern column liquid chromatography. In thin-layer chromatography, plates precoated with non-polar and polar chemically bonded phases also are becoming increasingly important. Wettability problems that were encountered earlier with plates coated with C₈- or C₁₈-modified silicas have now largely been solved, and successful separations can rapidly be achieved using eluents ranging from pure organic solvents to almost pure water. Data transfer from thin-layer to column liquid chromatography is another area of interest. Here, much time and effort can indeed be saved, but pitfalls are not always easily avoided.     

Total synthesis of arteannuin and deoxyarteannuin

Arteannuin 1 is a new sesquiterpene lactone containing a peroxide linkage and is an antimalarial principle isolated from Artemisia annua L. . R(+)-Citronellal 5 as a starting material for the total synthesis was converted into 11R(-)-methyl dihydroarteannuinate 12 in 14 steps. The key intermediate 4 was obtained from compound 12 in 5 steps. The introduction of hydroperoxide in 4 by photooxidation followed by acid treatment gave 1. Hydroxylation of 4 with osmium tetraoxide afforded deoxyarteannuin 2.     

Mise au point d'un procede de preparation catalytique de perfluoroalkyl sulfonamide par addition d'ethylamine a un chlorure d'acide perfluoroalcane sulfonique

Addition of N-ethylamine to a perfluoroalkylsulfonic acid chloride R_FSO₂Cl has been studied, to obtain the corresponding perfluoroalkylsulfonamide R_FSO₂NHC₂H₅. First a two-step synthesis has been considered : transformation of the perfluoroalkylsulfonic acid chloride R_FSO₂Cl to the corresponding fluoride R_FSO₂F, and addition of N-ethylamine; the study of the first step is reported. Then, a sulfonamide one-step synthesis involving a fluoride catalysis, is described.     

Photoreaction of 9-dicyanomethylene-1,2,3,4-tetrahydro-1,4-methanonaphthalene: the 1,3-carbon migrations and the ethylene extrusion to dicyanoisobenzofulvene

Irradiation of 9-dicyanomethylene-1,2,3,4-tetrahydro-1,4-methanonaphthalene gave 3,3-dicyano-1,2,3,8b-tetrahydrocyclopent [a] indene and 2-dicyanomethylene-2H-indene.