Differential pulse polarographic determination of europium in the presence of humic substances

Humic substances (HS) and other substance of similar nature (“building blocks” of HS, such as salicylates or phthalates) influence strongly a polarographic behaviour of europium at a mercury drop electrode. An addition of these substances into the supporting electrolyte causes an enhancement of the differential pulse polarographic (DPP) peak of Eu and an anodic shift of the maximum peak potential. It was deduced from the dependence of the peak height on the pulse time and from other experimental dependencies that an adsorption of the Eu-HS (salicylate, phthalate) complexes on the working electrode is the main mechanism responsible for the peak enhancement. Because no peak distortion or splitting were observed, the DPP determination of Eu can be realised readily in the presence of HS, e.g. in environmental samples. The sensitivity of the measurements increased in the presence of HS, whereas the limit of detection (LOD) decreased (LODs were 255 and 140 nmol/l in the absence and in the presence of HS, respectively). However, the calibration dependencies were non-linear in the presence of HS. It was found that the non-linear calibration dependencies may be approximated by the Langmuir-type equation. Special procedures, such as a method of (at least) two standard additions and numerical iterative calculations, are necessary for an evaluation of measurements.     

A software package for the evaluation of Zeeman AAS data using a Perkin-Elmer model 3600 data station

The Perkin-Elmer Zeeman/5000 Atomic Absorption Spectrometer is only able to perform a calibration with three single standards or a one-point standard addition. The accuracy and precision of these methods are inappropriate in ETA-AAS, a computer-based data management is essential.A software package for calibration and evaluation was developed using curve fitting by linear regression based on a leastsquares fit when absorbances were transformed by the Baule-Mitscherlich function. The total analytical range could be covered by this method whether peak area or peak height values were fitted. The maximum absorbance levels could be calculated, as well.Absorbance signals were collected and stored by the HGA-graphics software (modified by Perkin-Elmer Nederland B. V.). The Pecowriter software was used for identifying data and file manipulations. The results of the calibration and evaluation can be stored on disk and/or printed. Calibration curves can be plotted on hardcopy output. The Limit of Detection and the Characteristic Mass can be calculated.The use of the CALIBRATION program is demonstrated by the calibration curves for the determination of Pb, Cd, As, Se, Cr, Al, Cu and Ni using mostly STPF-conditions. The performance of the method evaluated by the root mean square percent deviation of the fit is equal to the traditional curve-fitting function as well as to rational or quadratic functions.The use of the EVALUATION program is demonstrated by the results of the direct determination of lead in mineral waters.     

Nitrogen Bridgehead Compounds. Part 79. Synthesis and structure elucidation of benzimidazolo[2,1-f][1,6]naphthyridine aza-derivatives

6-Substituted 1,6-naphthyridine-5(6H)-ones were prepared from diethyl 2-[2-(dimethylamino)vinyl]-6-methylpyridine-3,5-dicarboxylate 1 [2] by ring closure with aromatic and heteroaromatic diamines (o-phenylenediamine, 2,3-diaminopyridine, 3,4-diaminopyridine and 4,5-diaminopyrimidine, respectively). 1,6-Naphthyridine-5(6H)-ones were cyclised in phosphoryl chloride to yield nitrogen bridgehead tetracycles 6-9 . The structure of the products was established by nOe difference spectroscopy. A complete ¹H and ¹³C nmr assignment was achieved by different 2D carbon-proton correlation measurements.     

Accuracy of film thickness determination in electron probe microanalysis

The thickness of copper films (100–450 nm) on silicon substrates was determined by electron probe microanalysis (EPMA) applying (z) procedures of Pouchou and Pichoir. Film thickness was calculated from experimental k-ratios analyzed with electron energies between 6 and 30 keV using commercial software (LAYERF distributed by CAMECA). The influence of the incident electron energy and X-ray line chosen for analysis on the results was investigated. Accuracy of film thickness determination was evaluated by comparison with Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS). The difference between layer thicknesses determined with EPMA and RBS is in general less than 2%, if EPMA measurements are performed with various electron energies. Layer thicknesses determined with Cu-L are mostly closer to values obtained by RBS than those derived from Cu-K radiation. Preliminary SIMS measurements yielded inconsistent results and, thus, cannot be used in this case to determine the layer thickness of Cu films on Si accurately.     

Photocyclisierungen von 1, 1'-Polymethylen-di-2-pyridonen. 46. Mitteilung über Photoreaktionen

Photocyclization of 1, 1′-Polymethylene-di-2-pyridones . Benzophenone sensitized irradiation of the four dipyridones 1-4 gave the internal photocyclization products 6 (64%, Scheme 4), 7 (60%, Scheme 5), 8 (Scheme 6), and 11 (26%, Scheme 7), respectively. The decamethylene compound 5 yielded only polymeric material. The primary [2+2] photoproduct 8 from dipyridone 3 (Scheme 6) is relatively unstable. Further irradiation or heating to 65° induced a Cope rearrangement to give compound 9 which, on heating to 137°, was converted into the isomeric compound 10 . This product, as well as the other photoproducts mentioned, are rearranged back to their respective starting materials upon direct irradiation with 254 nm light or by heating to higher temperatures. The various possibilities for cycloadditions of pyridones are discussed as well as the possible factors which are responsible for the highly regioselective photoreactions of the dipyridones 1–4 .     

Eigenschaften und Verwendbarkeit des 10, 11-Dihydro-5H-dibenzo[a,d]cyclohepten-5-yl-Rests (= 5-Dibenzosuberyl-Rests) als neue Schutzgruppe für Amine,Aminosäuren,Alkohole, Thiole und Carbonsäuren

Properties and suitability of the 10,11-dihydro-5 H-dibenzo[a, d]cyclohepten-5-yl group (= 5-dibenzosuberyl group) as a new protecting group for amines, amino-acids, alcohols, thiols and carboxylic acids. The 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-yl group (5-dibenzosuberyl group): has been found useful for protecting amines, alcohols, thiols, and carboxylic acids. Furthermore, the investigated 5-amino compounds are extremely stable in strongly acidic media (e. g. in hydrogen bromide) and still the amino group is easily cleaved under mild conditions, such as those used for N-trityl compounds (e.g. boiling in dilute acetic acid or catalytic hydrogenation). Hence this ring system could be a valuable and adaptable protecting group, especially in peptide chemistry.     

Spectrophotometric study of the complexation and extraction of chromium(VI) with cyanine dyes

Solvent extraction of chromium(VI) ion associates with symmetric cyanine dyes including the heterocyclic radicals of 1,3,3-trimethyl-3N-indoline, benzooxazol, benzothiazol and quinoline has been studied by means of spectrophotometric method. In the acidic medium in the presence of chloride ions, extractable by aromatic hydrocarbons and esters of acetic acids, chromium(VI) ion associates are formed. The molar absorptivities of ion associates are 2.5-3.6x10(5) l mol(-1) cm(-1) in dependence on extractant and dye. The absorbance of the coloured extracts obeys the Beer's law in the range 0.01-2.1 mg l(-1). The extraction of chromium is the highest during extraction from the sulphuric acid medium in the range 0.05-03 M H(2)SO(4). It was found that the Cr(VI):Cl:R molar ratio is 1:1:1. A novel procedure of chromium(VI) extraction and spectrophotometric determination in various types of soils and sewage doped with chromium(VI) was examined.     

The highest water exchange rate ever measured for a Gd(III) chelate

The complex [Gd(L)(H2O)]3- (H(6)L =N,N'-bis(6-carboxy-2-pyridylmethyl)ethylenediamine-N,N'-methylenephosphonic acid) displays the highest water exchange rate ever measured for a Gd(III) chelate (k(298)(ex)= 8.8 x 10(8) s(-1)), which is attributed to the flexibility of the metal coordination environment.