Quo Vadis total reflection X-ray fluorescence?

The multielement trace analytical method ‘total reflection X-ray fluorescence’ (TXRF) has become a successfully established method in the semiconductor industry, particularly, in the ultra trace element analysis of silicon wafer surfaces. TXRF applications can fulfill general industrial requirements on daily routine of monitoring wafer cleanliness up to 300 mm diameter under cleanroom conditions. Nowadays, TXRF and hyphenated TXRF methods such as ‘vapor phase decomposition (VPD)-TXRF’, i.e. TXRF with a preceding surface and acid digestion and preconcentration procedure, are automated routine techniques (‘wafer surface preparation system’, WSPS). A linear range from 10⁸ to 10¹⁴ [atoms/cm²] for some elements is regularly controlled. Instrument uptime is higher than 90%. The method is not tedious and can automatically be operated for 24 h/7 days. Elements such as S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Sn, Sb, Ba and Pb are included in the software for standard peak search. The detection limits of recovered elements are between 1×10¹¹ and 1×10⁷ [atoms/cm²] depending upon X-ray excitation energy and the element of interest. For the determination of low Z elements, i.e. Na, Al and Mg, TXRF has also been extended but its implementation for routine analysis needs further research. At present, VPD-TXRF determination of light elements is viable in a range of 10⁹ [atoms/cm²]. Novel detectors such as silicon drift detectors (SDD) with an active area of 5 mm², 10 mm² or 20 mm², respectively, and multi-array detectors forming up to 70 mm² are commercially available. The first SDD with 100 mm² (!) area and integrated backside FET is working under laboratory conditions. Applications of and comparison with ICP-MS, HR-ICP-MS and SR-TXRF, an extension of TXRF capabilities with an extremely powerful energy source, are also reported.     

Brodie's or Hummers’ Method: Oxidation Conditions Determine the Structure of Graphene Oxide

Synthesis and studies of graphite oxide started more than 150 years ago and turned into a boom by the measurements of the outstanding physical properties of graphene. A series of preparation protocols emanated trying to optimize the synthesis of graphene oxide in order to obtain a less defective material, as source for graphene. However, over-oxidation of the carbon framework hampered establishing structure-property relationships. Here, the fact that two different synthetic methods for graphene oxide preparation lead to very similar types of graphene oxide with a preserved graphene lattice is demonstrated. Either sodium chlorate in nitric acid (similar to Brodie's method) or potassium permanganate in sulfuric acid (similar to Hummers’ method) treatment are possible; however, reaction conditions must be controlled. With a preserved carbon lattice analytical differences between the samples relate to the altered on-plane functionality. Consequently, terming preparation protocols “according to Brodie's/Hummers’ method” is not sufficient.     

Azobridges from azines, XVII. Intra- and intermolecular [3+2] cycloaddition between nonstabilized azomethineimines and alkenes

Azo compounds 1 and 3 containing a CC-double bond in a parallel but distant position are quatemized by Me₃OBF₄ to 1,MeBF₄ and 3,MeBF₄, whereas MeI produces the cage compounds 2,HX and 4,HX. These [3+2] cycloadducts also are quantitatively formed from 1,MeBF₄ and 3,MeBF₄ with catalytic amounts of azo compounds. Intermolecular [3+2] cycloadditions occur with a mixture of DBH (5) or DBO (8), MeI and a variety of alkenes (→ HI) salts of (6, 7, 9 — 12). The intermediate azomethineimines, if stabilized by a fluorenylidene group, can be isolated (20, 22,24), but not, however, in the presence of a close parallel CC-bond (25 → 26).     

Dual-label autoradiographic analysis of human skin fibroblast and myoblast proteins by two-dimensional polyacrylamide gel electrophoresis using immobilised pH gradients in the first dimension

Horizontal two-dimensional polyacrylamide gel electrophoresis with immobilised pH gradients in the first dimension has been applied to the analysis of human skin fibroblast and muscle myoblast total cell proteins. Excellent two-dimensional separations of skin fibroblast proteins were obtained using pH 4-10 immobilised pH gradient gels with a long interelectrode distance (16 cm), but resolution was degraded, particularly of the more acidic proteins, by the use of shorter (10 cm) gels. Improved resolution of acidic and basic proteins was obtained using separate pH 4-7 and pH 7-10 immobilised pH gradient gels respectively in the first dimension. Two-dimensional protein maps of skin fibroblast proteins were visualised both by silver staining and by autoradiography of samples labelled synthetically with [35S]methionine. Horizontal two-dimensional electrophoresis, using pH 4-7 and pH 7-10 immobilised pH gradient gels in the first dimension, was applied to the analysis of protein samples from skin fibroblasts and muscle myoblasts dual-labelled synthetically with [35S]methionine and [75Se]selenomethionine in an attempt to identify sets of proteins specific to each cell type. In addition, two-dimensional maps or protein samples derived from normal individuals and patients with Duchenne muscular dystrophy were compared to search for protein changes associated with the disease state. Although sets of qualitative protein spot differences were observed by visual inspection of the two-dimensional gels, more rigorous qualitative and quantitative analysis of the patterns using a computerised analysis system will be required to obtain the maximum amount of information from these data.     

The Radical Anions of N,N′-Dicyanoquinone Diimines,a New Class of Electron Acceptors

The radical anions of 12 N,N′-dicyanoquinone diimines, a new class of electron acceptors, hace been characterized by their hyperfine data with the use of ESR and ENDOR spectroscopy. The largest coupling constant (0.30–0.45 mT), due to the two ¹⁴N nuclei in the exocyclic positions, gives rise to a conspicuous broadening of the peripheral ESR lines by an incomplete averaging of the hyperfine anisotropy. The most plausible interpretation of the experimental results for the radical anions of N,N′-dicyano- 1,4-benzoquinone diimine ( 1 ) and N,N′-Dicyano-9,10-anthraquinone diimine ( 9 ) is in terms of both ‘syn’- and ‘anti’-configurations contributing to the ESR and ENDOR spectra and having equal proton- and ¹⁴N-coupling constants. The π-spin distribution in the radical anions of N,N′-dicyanoquinone diimines is compared with those in the analogous ions of tetracyanoquinodimethanes and quinones.     

Intramolecular Baylis-Hillman Reaction: A Pathway to Substituted Coumarins

The acrylate ester of salicylaldehyde, in the presence of DABCO, affords a crystalline coumarin salt. Formation of this derivative confirms a vital intermediate in the mechanism of the reaction. Salicylaldehyde, suitably protected, reacts with methyl acrylate to afford a novel coumarin not unlike the vasodilator chromonar.