Effect of K(+) on the Stoichiometry of Carbonated Hydroxyapatite Obtained by the Hydrolysis of Monetite

This study investigates the stoichiometry and the thermal stability of K(+)- and CO(3)(2)(-)-containing apatites (KCAp's) obtained by the hydrolysis of monetite. The analysis results of the samples after drying reveal that the KCAp's start to lose carbonate at temperatures V(Ca) + CO(3)(2)(-) + V(OH)] and [Ca(2+) + PO(4)(3)(-) <--> K(+) + CO(3)(2)(-)], where V(X) stands for a vacancy in the X-sublattice. Moreover, a small part of the CO(3)(2)(-) ions are presumably incorporated according to [Ca(2+) + 2PO(4)(3)(-) <--> V(Ca) + 2CO(3)(2)(-)]. A comparison of the contributions of these fundamental mechanisms with the results for precipitated Na(+)- and CO(3)(2)(-)-containing apatites shows that no intrinsic coupling whatsoever exists between these mechanisms.     

NMR determination of pKa values of indoloquinoline alkaloids

Malaria is one of the most serious global health problems. Isolating new therapeutic agents with potential antimalarial activity from natural sources or preparing such agents either semisynthetically or synthetically is one strategy for solving the problem of resistance constantly evolving to the drugs currently in use. For alkaloids, the acid–base dissociation constant, pK_a, is an important characteristic, thought to be associated with biological activity. In this contribution, pK_a values for several indoloquinoline alkaloids were determined by using ¹H NMR spectroscopy in a mixture of solvents. The data were recalculated for water solutions using the correction factors reported previously. The structural dependence of the pK_a values for cryptolepine and its isomers neocryptolepine, isocryptolepine and isoneocryptolepine as well as some substituted neocryptolepine derivatives is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparison of inductively coupled argon plasma atomic emission spectrometry and electrothermal atomization atomic absorption spectrometry in the determination of copper and zinc in serum

Summary A comparison of performance characteristics of ICAP-AES and ETA-AAS experienced in analyzing Cu and Zn in blood serum is described. Accuracy and precision were evaluated by a statistical procedure permitting graphical representation of the results. It was concluded that ETA-AAS is very suitable for monitoring and screening purposes in toxicology and clinical chemistry whereas ICAP-AES is to be preferred when more precise determinations are required.

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Vergleich von AES mit induktiv gekuppeltem Argonplasma und AAS mit elektrothermischer Atomisierung für den Fall der Kupfer- und Zinkbestimmung im Serum

Zusammenfassung Die Leistungsfähigkeit der beiden Methoden wurde verglichen, wobei Richtigkeit und Reproduzierbarkeit statistisch mit graphischer Darstellung der Ergebnisse ausgewertet wurden. Als Schlußfolgerung ergab sich, daß sich die ETA-AAS als Überwachungs- und Screeningverfahren in der Toxikologie und klinischen Chemie eignet, während für höhere Präzision die ICAP-AES vorzuziehen ist.

     

Bestimmung von Kohlenoxyd

Ohne Zusammenfassung     

Untersuchung von Wasser und Abwasser

Ohne Zusammenfassung     

Steady Flows in Unsaturated Soils Are Stable

The stability of steady, vertically upward and downward flow of water in a homogeneous layer of soil is analyzed. Three equivalent dimensionless forms of the Richards equation are introduced, namely the pressure head, saturation, and matric flux potential forms. To illustrate general results and derive special results, use is made of several representative classes of soils. For all classes of soils with a Lipschitz continuous relationship between the hydraulic conductivity and the matric flux potential, steady flows are shown to be unique. In addition, linear stability of these steady flows is proved. To this end, use is made of the energy method, in which one considers (weighted) L ²-norms of the perturbations of the steady flows. This gives a general restriction of the dependence of the hydraulic conductivity upon the matric flux potential, yielding linear stability and exponential decay with time of a specific weighted L ²-norm. It is shown that for other norms the ultimate decay towards the steady-solution is preceded by transient growth. An extension of the Richards equation to take into account dynamic memory effects is also considered. It is shown that the stability condition for the standard Richards equation implies linear stability of the steady solution of the extended model.     

Development and validation of an HPLC-method for the determination of alkaloids in the stem bark extract of Nauclea pobeguinii

A new method was developed and validated for the quantification of strictosamide in the extract of the stem bark of Nauclea pobeguinii. This plant belongs to the Rubiaceae family and is widely used in the African traditional medicine against malaria and malaria-like symptoms. Alkaloids are suspected to be responsible for the antimalarial activity. One of these alkaloids is strictosamide, already reported to be the major constituent in the root bark of this plant. Because strictosamide was not commercially available another alkaloid, ajmalicine HCl, with comparable properties was used as a secondary standard. The samples of the dried 80% ethanol extract from the stem bark of N. pobeguinii were purified on C(18) solid phase extraction cartridges and analysed using HPLC-UV. The strictosamide used for the validation of the correction factor for response was isolated and purified by means of preparative HPLC and TLC. Although the relative standard deviation (R.S.D.) of 2.6% was still acceptable, the response factor was determined for every analysis based on the ratio of the peak area of strictosamide compared to the peak area of ajmalicine HCl in a concentration of 0.01 mg/ml. The precision of the method according to the time and the concentration, had a R.S.D. value of 2.2% and 2.6%, respectively. The recovery of the method was 92.2% (R.S.D. of 9.4%) which was acceptable. The method has been proven to be suitable for the determination of alkaloids in the extract of the stem bark of N. pobeguinii, according to the ICH guidelines on the validation of analytical methods.