A comparison of differential pulse and d.c. amperometric detection modes for the liquid chromatographic determination of oxalic acid

Oxalic acid determinations are made using two modes of electrochemical detection, namely, classical d.c. and differential pulse, after separation by ion-pair, ion exchange high performance liquid chromatography. Peak height ratio plots are constructed and compared for uric acid and oxalic acid mixtures using both electrochemical detection modes. The enhanced selectivity realized by use of the differential pulse electrochemical detection mode is demonstrated.     

Intramolecular interactions between chalcogen atoms: organoseleniums derived from 1-bromo-4-tert-butyl-2,6-di(formyl)benzene

[structure: see text] The synthesis and characterization of a series of low-valent organoselenium compounds derived from 1-bromo-4-tert-butyl-2,6-di(formyl)benzene (22) is described. The synthesis of diselenide 25 was achieved by the lithiation route whereas bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) was synthesized by treating 22 with disodium diselenide. A series of monoselenides (27, 28, and 29) was obtained by facile nucleophilic substitution of bromine in 22, using the corresponding selenolates as nucleophiles. The halogenation reactions of bis(4-tert-butyl-2,6-di(formyl)phenyl) diselenide (26) did not afford the corresponding selenenyl halides but resulted in the isolation of an unexpected cyclic selenenate ester 34 as a product. The selenide 32 was synthesized by the treatment of dimethoxymethyl diselenide with trilithiated 2-bromo-5-tert-butyl-N,N'-di(phenyl)isophthalamide. The existence of potential Se...O intramolecular nonbonding interactions was examined by IR, (1)H, and (77)Se NMR spectroscopy, X-ray crystallography, and computational studies. The X-ray crystal structures of 26 and 27, having two ortho formyl groups, reveal the absence of any Se...O interactions. However, the Se...O interactions were observed in the selenenate ester 34 where one of the formyl groups has been utilized for the selenenate ring formation. The crystal structures of 26 and 27 exhibited intermolecular short-range C-H...Se interactions (hydrogen bonding). Although there are four heteroatoms in carbamoyl moieties ortho to selenium capable of forming a five-membered ring on intramolecular coordination, no such intramolecular Se...X (X = N, O) interaction was observed in the crystal structure of 32. The density functional theory calculations at the B3LYP/6-31G* level predicted that for all the diformyl systems (47a-c, 48a-c), the anti,anti conformer (when both formyl oxygen atoms point away from the selenium) is more stable. This preference was found to be reversed in the monoformyl-substituted systems (50a,b, 51a,b), where the syn conformer (when formyl oxygen is near the selenium) is energetically more favorable than the anti conformer.     

Complexity of intercalation of hydrazine into kaolinite--a controlled rate thermal analysis and DRIFT spectroscopic study

Controlled rate thermal analysis (CRTA) allows the separation of adsorbed and intercalated hydrazine. CRTA displays the presence of three different types of hydrogen-bonded hydrazine in the intercalation complex: (a) The first is adsorbed loosely bonded on the kaolinite structure fully expanded by hydrazine-hydrate and liberated between approx 50 and 70 degrees C (b) The second intercalated hydrazine is lost between approx 70 and 85 degrees C. (c) The third type of intercalated-hydrazine molecule is lost in the 85-130 degrees C range. CRTA at 70 degrees C enables the removal of hydrazine-water and results in the partial collapse of the hydrazine-intercalated kaolinite structure to form a hydrazine-intercalated kaolinite. Removal of the adsorbed hydrazine enables the DRIFT spectra of the hydrazine-intercalated complex without any adsorbed hydrazine to be obtained. A band at 3626 cm(-1) attributed to the inner surface hydroxyls of kaolinite hydrogen bonded to hydrazine is observed. The intercalation of hydrazine-hydrate into kaolinite is complex and results from the different types of surface interactions of the hydrazine with the kaolinite surfaces.     

Vakuumspektrometrische Analyse gepre?ter Stahlsp?ne

Zusammenfassung Die Vakuumspektrometrische Analyse von Stahlspanpreßlingen wird verbessert und ausgedehnt. Es wird das Abfunkverhalten der Preßlinge unter verschiedenen atmosphärischen Bedingungen in der Funkenkammer beschrieben. Der Zusatz von Wasserstoff zum Argon wirkt sich günstig aus, die Reproduzierbarkeit der Abfunkergebnisse ist gut. Unter den angegebenen Bedingungen lassen sich Spanbriketts aus unberuhigten und beruhigten Stählen einwandfrei vakuumspektrometrisch analysieren.Unberuhigte und beruhigte schwefel-bleihaltige Automatenstähle lassen sich ebenfalls analysieren, wenn die Probenvorgeschichte durch starke Warmverformung und Zerspanung, mit anschließender Mischung und Brikettierung der Späne ausgelöscht wird. Neben der Form hat auch die Größe der Mangansulfid-Bleieinschlüsse einen großen Einfluß auf den Zeit-Intensitätsverlauf aller Spektrallinien.

---

Vacuumspectrometric analysis of briquetted steel chips

Improvements on vacuumspectrometric analysis of briquetted steel chips are dealth with. The influence of different atmospheric conditions in the spark chamber on sparking behaviour of briquettes is shown. An addition of hydrogen to the argon gas will give better results, the reproducibility of analysis is very good. A method is given for vacuumspectrometric analysis of briquetted chips, taken from rimming or killed steels.After hot working, milling and briquetting, samples of rimming and killed sulphurized, leaded free-cutting steel can be analysed, too. There is a great influence of the dimension and the shape of the MnS-Pb inclusions on the pre-spark curves.

---

---

Auszug aus der Doktordissertation, Montanistische Hochschule Leoben, 1967.     

Thermal characterization of portland cement-magnesia blends

Summary Due to growing environmental concerns and the need to use less energy-intensive building products, alternatives and improvements to Portland cement (PC) are being actively researched worldwide. Use of supplementary materials is now a common practice where PC is the predominant component of inorganic building products. This study aims to investigate the potential of magnesia (MgO), derived from a naturally occurring raw material magnesite, as a supplementary material. Results from mortar samples prepared with 10 and 20% replacements of ordinary Portland cement (OPC) by MgO are presented. DTA-TG was used to study and characterise the hydration behaviour of MgO in OPC environment after 3, 7, 14, 28, 56 and 90 days of moist curing. Microstructural and compressive strength determinations providing additional information on the influence of hydrated phases are also reported.     

Preparation and X-ray crystal structures of mixed ligand complexes containing the S3N ligand

Reaction of Hg(S₇N)₂ with cis- PtCl₂(PR₃)₂ (PR₃ = PPh₃, PPh₂Me, PPHMe₂, PEt₃) in the presence of Na[PF₆] gives [Pt(S₃N)(PR₃)₂][PF₆] in 32–46% yield. The complexes have been characterized by IR, NMR and microanalyses. The X-ray crystal structures of two examples (PR₃ = PPh₂Me and PEt₃) show that the S₃N⁻ ligand coordinates in a bidentate fashion via two sulphur atoms.     

Nitrogen atom insertion into Ir-S and C-S bonds initiated by photolysis of iridium(III)-azido-dithiocarbamato complexes

Photolysis of acetonitrile solutions of Cp*Ir(R2dtc)(N3) [Cp* = eta5-C5Me5, R2dtc = S2CNR2; R = Me (1) or Et (1')] at temperatures below 0 degrees C afford five-coordinate complexes Cp*Ir{NSC(NR2)S} (2 or 2'), where a nitrogen atom has been inserted into one of the Ir-S bonds. In solution, complex 2 thermally convert to the azaethene-1,2-dithiolate complex, Cp*Ir[SN=C(NMe2)S] (3), which could be crystallized as the corresponding dimer, {Cp*Ir[mu-SN=C(NMe2)S-kappa3S:S,S']}2 (4). As a result, a nitrogen atom that originated in the azide ligand is transferred into a C-S bond of the dithiocarbamate.     

Near-infrared spectroscopy of stitchtite, iowaite, desautelsite and arsenate exchanged takovite and hydrotalcite

The hydrotalcite minerals stitchtite, iowaite and desautelsite together with the arsenate exchanged takovite and arsenate exchanged hydrotalcite have been studied using near-IR reflectance spectroscopy. Each mineral has its own characteristic NIR spectrum enabling recognition of the particular hydrotalcite. As such the technique has application in the field for the analysis and identification of hydrotalcites. Hydrotalcites have proven useful as an anion exchange material. Takovite and hydrotalcite were used to exchange carbonate anions by arsenate. Three Near-IR spectral regions are identified: (a) the high wavenumber region between 6400 and 7400 cm(-1) attributed to the first overtone of the fundamental hydroxyl stretching mode, (b) the 4800-5400 cm(-1) region attributed to water combination modes of the hydroxyl fundamentals of water, and (c) the 4000-4800 cm(-1) region attributed to the combination of the stretching and deformation modes of the MOH units of the hydrotalcites. NIR spectroscopy enables the separation of the hydroxyl bands of the water and M-OH units for the hydrotalcites. Compared with the NIR spectroscopy of the structural units of the hydrotalcites namely gibbsite and brucite, the bands are broad.     

Preparation and characterization of individual peptide-wrapped single-walled carbon nanotubes

Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images.     

Raman microscopy of selected tungstate minerals

A series of tungstate bearing minerals including scheelite, stolzite, ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analyzed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The nu1(Ag) band is observed at 909 cm(-1) and although the corresponding nu1(Bu) vibration should be inactive a minor band is observed around 894 cm(-1). The bands at 790 and 881 cm(-1) are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695 cm(-1) is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The nu4(Eg) band was absent for scheelite. The bands at 353 and 401 cm(-1) are assigned as either deformation modes or as r(Bg) and delta(Ag) modes of terminal WO2. The band at 462 cm(-1) has an equivalent band in the infrared at 455 cm(-1) assigned as delta(as)(Au) of the (W2O4)n chain. The band at 508 cm(-1) is assigned as nu(sym)(Bg) of the (W2O4)n chain.