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Digitale Medien

A practitioner's approach to the assessment of the quality of sampling, sample preparation, and subsampling (1998)

van der Veen, Adriaan Marten Heine ; Alink, Anton

Springer

Accreditation and quality assurance 3 (1998), S. 20-26

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ISSN: 1432-0517

Schlagwort(e): Key words Sampling ; Quality assessment ; Statistical modelling ; Uncertainty

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: Abstract The methodology of evaluating the performance of sampling, sample preparation, and subsampling is reviewed. The requirements to be set for a successful experiment are revisited. The central role of the reference method is explained, and so is the choice of the parameters and the measurement methods. Based on the principles of the "Guide to the expression of uncertainty in measurement" (GUM), a statistical model is developed that demonstrates the influence of the experimental design on the outcome of the assessment experiment. This relationship is often overlooked in practice, as it is hardly mentioned in written standards dealing with this kind of quality assessments. The statistical framework thus developed covers the statistical procedures commonly appearing in written standards. Finally, the issue of testing the significance of the bias obtained from the experiment is discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/s007690050177

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Digitale Medien

Rheological study of the pH-dependence of interactions between gelatin and anionic surfactants: flow behaviour and gelation (1996)

Dreja, M. ; Heine, K. ; Tieke, B. ; [weitere]

Springer

Colloid & polymer science 274 (1996), S. 1044-1053

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ISSN: 1435-1536

Schlagwort(e): Rheology ; gelatin ; anionic surfactants ; interactions ; gelation ; surface tension

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie , Maschinenbau

Notizen: Abstract The interactions between gelatin and two anionic surfactants (sodium di-sec-butylnaphthalenesulfonate and sodium dodecylbenzenesulfonate, respectively) were investigated using rheological methods, charge and surface tension measurements. Upon the addition of surfactants, the viscosity of aqueous gelatin solutions increases at pH values higher than the isoelectric point (IEP) of the gelatin, provided that a distinct surfactant concentration is exceeded. The increase in viscosity depends on the structure of the hydrophobic moiety of the surfactant. Surface tension measurements suggest the formation of gelatin-surfactant-complexes. If the surfactant is added in high concentration, the viscosity does not further increase, and free micelles are formed in the solution. Directly at the IEP and at pH values below, the addition of surfactants leads to flocculation because of electrostatic interactions. At all surfactant concentrations, the flow behaviour was strictly Newtonian. As a model of the structure of the complex, a modified ‘bead and necklace’-model is suggested. This model proposes the nucleation of micelles at the hydrophobic gelatin regions (‘micellar surfactant-gelatin complexes’). The number of micelle moieties per gelatin chain could be estimated to be about three. The complex stability is dependent on the extent of hydrophobic interaction. The gelation behaviour of gelatin is strongly affected by the addition of the surfactant. The ratio between the attainable linear storage and loss moduli,G′ andG″, decreases strongly. Gelation is generally hindered, but the effect is stronger at pH values below the IEP than above.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00658369

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Digitale Medien

Literaturkarussell. Biologie (1998)

Wieser, Wolfgang ; Penzlin, Heine ; Welsch, Ulrich ; [weitere]

Weinheim : Wiley-Blackwell

Chemie in unserer Zeit 32 (1998), S. VI

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ISSN: 0009-2851

Schlagwort(e): Chemistry ; Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/ciuz.19980320215

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Digitale Medien

Die 2,6-Diisopropyl-phenylgruppe als sperriger Substituent in Bor-Stickstoff-Verbindungen. II [1] (1995)

Luthin, W. ; Stratmann, J.-G. ; Elter, G. ; [weitere]

Weinheim : Wiley-Blackwell

Zeitschrift für anorganische Chemie 621 (1995), S. 1995-2000

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ISSN: 0044-2313

Schlagwort(e): 2,6-Diisopropylphenyl-, Amino(fluoro)boranes ; Amino-imino-boranes ; Diazadiboretidines ; Diazasilaboretidines ; Chemistry ; Inorganic Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Beschreibung / Inhaltsverzeichnis: The 2,6-Diisopropyl-phenyl Group as a Bulky Substituent in Boron-Nitrogen Compounds. IIFluoro-bis(amino)boranes R′ (Me3Si)N-BF-NHR (R = 2,6-)Me2CH)2C6H3, R′ = Me (Ia), CH2Me (Ib), CHMe2 (Ic), CMe (Id), SiMe3 (Ie), R (If) react with t-butyllithium (molar ratio 1:1) by elimination of HF to give the amino-imino-boranes (IIa - f). The thermal stabilities of the latter depend upon the steric requirement of the substituent R′, IIa - c and IIe dimerize to yield the diazaboretidines IIIa - c and IIIe. IId remains unchanged at 200°C and above, and IIf isomerizes forming the B-Me substituted diazasilaboretidine IVf. If a twofold amount of t-butyllithium is employed, B-CMe3 substituted diazasilaboretidines (Va - f) are the main products. All compounds are characterized by elemental (C, H) analyses and their mass- and n.m.r. (1H, 13C, 15N (in part), 19F, 29Si) spectra. Characteristic i.r.-bands are reported for the amino-imino-boranes (II). An X-ray structure analysis is presented for IVf.

Notizen: Die HF-Eliminierung aus Fluorbis(amino)boranen des Typs R′ (Me3Si)NBFNHR (R = 2,6-)Me2CH)2C6H3, R′ = Me (Ia), CH2Me (Ib), CHMe2 (Ic), CMe3 (Id), SiMe3 (Ie), R (If)) mit t-Butyllithium im Molverhältnis 1:1 führt zu den Amino-imino-boranen (IIa-f), die - abhängig von der Größe des Substituenten R′ - unterschiedliche thermische Stabilität aufweisen. IIa - c und IIe dimerisieren zu den Diazadiboretidinen IIIa - c und IIIe. IId ist bis über 200°C stabil, während sich IIf bei dem Versuch seiner Isolierung zum Bor-Methyl-substituierten Diazasila-boretidin IVf umlagert. Führt man die gleiche Umsetzung mit t-Butyllithium im überschuß (Molverhältnis 1:2) durch, erhält man fast ausschließlich die Bor-t-Butyl-substituierten Diaza-sila-boretidine Va - Vf.Alle Verbindungen sind elementaranalytisch (C, H) und spektroskopisch MS, NMR (1H, 13C, 15N (teilweise), 19F, 29Si) charakterisiert. Charakteristische IR-Banden werden für die Amino-imino-borane (II) angegeben. Eine Röntgenstruktur-analyse wurde von IVf angefertigt.

Zusätzliches Material: 1 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/zaac.19956211204

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