A ring oven method for the determination of sulfate at nanogram levels

Summary A ring oven method for the determination of sulfate at ng levels is described. Sulfate is bound as 2-perimidinyl ammonium sulfate by spotting the sample solution on a glass fiber filter impregnated with 2-perimidinyl ammonium bromide. The excess reagent is removed by frontal elution chromatography with methanol and the sample spot cut out and then exposed to nitric acid vapor where upon the organic amine, bound as sulfate, is converted to the highly colored 2-amino 4,6,9-trinitro perimidine. The excess acid is neutralized by exposure to ammonia vapor. The sample spot is finally placed on a filter paper positioned on a ring oven and the color is eluted to the ring zone by successive aliquots of acetone. The sensitivity of the method is 5 ng sulfate and the working range is 20 ng to 1 g. The method is free of significant interferences.

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Zusammenfassung Für die Bestimmung von Nanogramm-Mengen Sulfat wurde eine Ringofenmethode angegeben. Das Sulfat wird auf einem mit 2-Perimidinammoniumbromid imprägnierten Glasfaser-Filter durch Auftropfen der Probe als Salz der genannten Base gebunden. Der Reagensüberschuß wird elutionschromatographisch mit Methanol entfernt, der Probefleck ausgeschnitten und Salpetersäure-Dämpfen ausgesetzt, wobei die organische Base, die als Sulfat gebunden war, in das stark gefärbte 2-Amino-4,6,9-trinitroperimidin übergeht. Die überschüssige Säure wird mit Ammoniakdämpfen gebunden. Schließlich wird der Probefleck auf einen Ringofen gebracht und mit Aceton in den Ring gewaschen. Die Empfindlichkeit der Methode beträgt 5 ng Sulfat, der geeignete Arbeitsbereich erstreckt sich von 20 ng bis 1 g. Die Methode unterliegt keinen Störungen.

     

Time resolved photofragmentation of Au n + and Ag n + clusters (n = 9, 21)

Gold and silver cluster ions were produced by laser vaporization and stored in a Penning trap. After mass selection the cluster sizes of interest were illuminated by a laser pulse and electronically excited. Photoabsorption cross sections and fragmentation patterns were measured for photon energies of 2.3 eV to 5.2 eV. Unimolecular dissociation was observed time resolved on a microsecond to millisecond scale. Dissociation energies were deduced from the measured life times.     

Microtitration of Sulfate with Beryllon II as indicator: Determination of sulfate in environmental samples

Summary A new indicator, 2-(8-hydroxy-3,6-disulfo-1-naphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid (Beryllon II, DSNADNS) is proposed for microtitrimetric determination of sulfate with barium. This method is an order of magnitude more sensitive (LOD 0.25 ppm) and has less interference than the existing indicators. The color change is sharper and faster compared to Thorin. Titration is carried out in 80% 2-propanol at an apparent pH of 3.5. The superiority of the indicator is attributed to the lower solubility of the bariumdye salt. Results are presented for environmental samples and compared with values obtained by ion chromatography.

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Mikrotitration von Sulfat mit Beryllon II als Indikator: Bestimmung von Sulfat in Umweltproben

Zusammenfassung Als neuer Indikator für die Bestimmung von Sulfat mit Barium wurde 2-(8-Hydroxy-3,6-disulfo-l-naphthylazo)-1,8-dihydroxynaphthalin-3,6-disulfonsäure (Beryllon II, DSNADNS) vorgeschlagen. Das Verfahren ist um eine Größenordnung empfindlicher und wird weniger gestört als bei Verwendung üblicher Indikatoren. Der Farbwechsel ist schärfer und rascher als mit Thorin. Die Titration erfolgt in 80% 2-Propanol bei pH 3,5. Die Überlegenheit des vorgeschlagenen Indikators dürfte der geringeren Löslichkeit seines Bariumsalzes zuzuschreiben sein. Ergebnisse für Umweltproben wurdenmit den Werten der Ionenchromatographie verglichen.

     

Automated determination of total phosphorus in aqueous samples

The determination of total phosphorus in an automated microbatch analyzer system is described. The procedure combines persulfate digestion of the sample and colorimetric detection of orthophosphate by the ascorbic acid reduction of phosphomolybdate in a single processing chamber. Approximately 9 min are required per sample; approximately 1.7 ml of sample and 0.17 ml of total reagent are consumed. The limit of detection is < or =10 microg/1. phosphorus. The method is tolerant of variations in salinity of the sample. Good agreements with ASTM procedures are shown for a variety of test compounds, lake water, wastewater and urine samples.     

Transversely illuminated liquid core waveguide based fluorescence detection Fluorometric flow injection determination of aqueous ammonium/ammonia

The analytical performance of a new type of fluorescence detector, based on a transversely illuminated liquid core waveguide (LCW), has been investigated using the determination of NH(3)/NH(4)(+) as the 1-sulfonatoisoindole. With a very inexpensive combination of a miniature Hg blacklight as an excitation source, a colored plastic sheet as the emission filter, and an integrated blue sensitized photodiode-operational amplifier as the detector (totaling <$100 in hardware cost), we were able to achieve a limit of detection (LOD) of 35 nM (1.6 pmol) NH(3) with a linear dynamic range up to 60 muM NH(3). Details of detector construction and performance are given.     

Rate equation simulation of temporal characteristics of a pulsed dye laser oscillator

A time-dependent, two-dimensional (in space) rate equation model of a transversely-pumped pulsed dye laser oscillator, which incorporates transverse pump intensity variation in the presence of intracavity dye laser radiation, is proposed to understand and predict its temporal behaviour. The model yields output pulses which agree well with experimental results using rhodamine 6G and kiton red dyes. The shape, amplitude and temporal position of the simulated pulse within the pump pulse vary dramatically across the tuning range of each dye depending on the relative gain and loss values.     

N-Aryl Modification in γ-Lactam: Design and Synthesis of Novel Monocyclic γ-Lactam Derivatives as Inhibitor for Bacterial Propagation

In search of novel γ-lactam antibacterial agents as non-β-lactam mimics of some γ-lactam antibiotics, N-aryl modification in the γ-lactam ring has been made to synthesize compounds 4–8 in two to six steps. Compound 4 was synthesized using the intermolecular Michael addition of diethyl N-(6-coumarinyl)-2-aminomalonate and 3-aryl/(2-heteroaryl)acryloyl chloride followed by intramolecular amidification. Hydrolysis and stereoselective decarboxylation of 4 resulted in the formation of trans- γ-lactam carboxylic acids (5), which on side chain homologation followed by saponification of the intermediate γ-lactam monoester (7) afforded γ-lactam carboxylic derivatives 8. Moderate to good bacterial growth inhibition was observed for some of the synthesized compounds against E. coli and S. aureus.     

Evaluation of 1st and 2nd generation of poly(amidoamine) dendrimer functionalized carbon nanotubes for the efficient removal of neptunium

Journal of Radioanalytical and Nuclear Chemistry - Herein, sorption of pentavalent neptunium from aqueous acidic solution was carried out onto 1st and 2nd generation of poly(amidoamine) dendrimer...     

A highly contorted push–pull naphthalenediimide dimer and evidence of intramolecular singlet exciton fission

Singlet fission is a process by which two molecular triplet excitons are generated subsequent to the absorption of one photon. Molecules that enable singlet fission have triplet state energy at least half of the bright singlet state energy. This stringent energy criteria have challenged chemists to device new molecular and supramolecular design principles to modulate the singlet–triplet energy gap and build singlet fission systems from a wide range of organic chromophores. Herein, we report for the first time intramolecular singlet fission in the seminal naphthalenediimide (NDI) scaffold constrained in a push–pull cyclophane architecture, while individually the NDI chromophore does not satisfy the energy criterion. The challenging synthesis of this highly contorted push–pull cyclophane is possible from the preorganized pincer-like precursor. The special architecture establishes the shortest co-facial NDI⋯NDI contacts (3.084 Å) realized to date. Using broadband femtosecond transient absorption, we find that the correlated T–T pair forms rapidly within 380 fs of photoexcitation. Electronic structure calculations at the level of state-averaged CASSCF (ne,mo)/XMCQDPT2 support the existence of the multi-excitonic T–T pair state, thereby confirming the first example of singlet exciton fission in a NDI scaffold.

We report for the first-time intramolecular singlet fission (SF) in the naphthalenediimide (NDI) scaffold constrained in a cyclophane architecture, while individually the NDI units does not satisfy the requisite energy criterion for SF.