Eine Lösungsmethode Für Eigenwertprobleme

Analytical eigenvalue-problems are usually replaced by finite-dimensional algebraic eigenvalue-problems. An iteration scheme related to Sturm sequences for solving such problems is presented. It is also indicated how the method may reduce the labor for obtaining solutions of the analytical eigenvalue problem.

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Gekürzt erstmals am 14.4. 1964 in Zürich vorgetragen.     

Multiresidue method for determination of algal toxins in shellfish: single-laboratory validation and interlaboratory study

A method that uses liquid chromatography with tandem mass spectrometry (LC/MS/MS) has been developed for the highly sensitive and specific determination of amnesic shellfish poisoning toxins, diarrhetic shellfish poisoning toxins, and other lipophilic algal toxins and metabolites in shellfish. The method was subjected to a full single-laboratory validation and a limited interlaboratory study. Tissue homogenates are blended with methanol-water (9 + 1), and the centrifuged extract is cleaned up with a hexane wash. LC/MS/MS (triple quadrupole) is used for quantitative analysis with reversed-phase gradient elution (acidic buffer), electrospray ionization (positive and negative ion switching), and multiple-reaction monitoring. Ester forms of dinophysis toxins are detected as the parent toxins after hydrolysis of the methanolic extract. The method is quantitative for 6 key toxins when reference standards are available: azaspiracid-1 (AZA1), domoic acid (DA), gymnodimine (GYM), okadaic acid (OA), pectenotoxin-2 (PTX2), and yessotoxin (YTX). Relative response factors are used to estimate the concentrations of other toxins: azaspiracid-2 and -3 (AZA2 and AZA3), dinophysis toxin-1 and -2 (DTX1 and DTX2), other pectenotoxins (PTX1, PTX6, and PTX11), pectenotoxin secoacid metabolites (PTX2-SA and PTX11-SA) and their 7-epimers, spirolides, and homoYTX and YTX metabolites (45-OHYTX and carboxyYTX). Validation data have been gathered for Greenshell mussel, Pacific oyster, cockle, and scallop roe via fortification and natural contamination. For the 6 key toxins at fortification levels of 0.05-0.20 mg/kg, recoveries were 71-99% and single laboratory reproducibilities, relative standard deviations (RSDs), were 10-24%. Limits of detection were <0.02 mg/kg. Extractability data were also obtained for several toxins by using successive extractions of naturally contaminated mussel samples. A preliminary interlaboratory study was conducted with a set of toxin standards and 4 mussel extracts. The data sets from 8 laboratories for the 6 key toxins plus DTX1 and DTX2 gave within-laboratories repeatability (RSD(R)) of 8-12%, except for PTX-2. Between-laboratories reproducibility (RSDR) values were compared with the Horwitz criterion and ranged from good to adequate for 7 key toxins (HorRat values of 0.8-2.0).     

Crystal and molecular structure of cannabispiran and its correlation to dehydrocannabispiran : Two novel cannabis constituents

Full details are provided on the isolation, spectral data and X-ray crystallographic analysis of cannabispiran (1) [7' - hydroxy - 5' - methoxyspiro(cyclohexane - 1,1' - indan) - 4 - one] and its correlation to Δ² -cannabispiran (dehydrocannabispiran) (2); both of which are novel spiro-compounds isolated from the leaves of Cannabis sativa L. Cannabispiran (1) crystallizes in the space group Pbca, cell dimensions: a = 10.388(5) Å, b = 14.754(7)Å, c = 16.950(8)Å, with eight molecules in the unit cell. The structure model was refined, using 852 observed reflections collected by counter methods, to an R-factor of 0.074 and a weighted R_w of 0.054.     

Tobacco chemistry. 27. The structures of four stereoisomeric 8, 12x1-epoxylabd-14-en-13xl-ols isolated from Greek Nicotiana tabacum L.

The structures of four stereoisomeric 8,12x1-expoxylabd-14-en-13x1-ols** obtained from Greek tobacco were determinedby spectroscopic means and by conversion to 12-norambreinolide. Plausible routes for the formation of the new labdanols and related tobacco constituents from a common precursor, abienol, are discussed.     

Identification and analysis of a degradation product of the glucocorticoid desonide in ointment

The major degradation product of desonide in a pharmaceutical ointment formulation has been shown to be identical with the C-17-carboxylic acid obtained on oxidative cleavage of the alpha-ketol group of desonide with alkaline hydrogen peroxide. The pKa value of this acid has been estimated from chromatographic data.