The identification of 10 and 11 substituted 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-ones through 1N NOE studies on their methyl p-toluenesulfonate salts

The spectral similarities of 10 and 11 substituted 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-ones hinder the identification of the individual isomers. Preparation of the 13-methyl p-toluenesulfonate salts of these compounds has allowed the assignment by the use of NOE techniques. Saturation of the N-methyl caused an NOE at H-12. The coupling pattern of H-12 then provides identification of the compound.     

Screening for selected toxic elements in urine by sequential-scanning inductively-coupled plasma atomic emission spectrometry

A rapid screening method for nine elements (Se, As, Cr, Zn, Cd, Pb, Ni, Mn, and Cu) in human urine is described. A sequential-scanning inductively-coupled plasma atomic emission spectrometer, incorporating a cross-flow nebulizer, was used. Internal standardization with yttrium compensated for the differences between the aqueous calibration standards and the undiluted urine specimens. Accuracy was evaluated with aqueous (NBS SRM 1643a, EPA 378-13, and EPA 476-3) and urine (NBS SRM 2670 and Fisher Urichem Level II) reference and control materials. Detection limits for the system were evaluated from analyses of normal urine materials found to contain low levels of the elements investigated.     

Determination of paraquat in marijuana by reversed-phase paired-ion high performance liquid chromatography.

A sensitive and selective method is described for the quantitative determination of paraquat in marijuana. Paraquat is extracted from finely ground plant material with hydrochloric acid with sonification, and the resulting acidic solution is extracted with chloroform:isopropanol (9:1) and evaporated to dryness. The residue is reconstituted with aqueous phosphate buffer pH 7.0; the solution is passed through a C-18 SEP-PAK TM and is analyzed with high performance liquid chromatography, using a reversed-phase column and an "ion pairing" reagent in the mobile phase. The recovery of paraquat in laboratory-spiked material varied from 90-97%. Results obtained with confiscated, field-sprayed marijuana by the procedure described were in excellent agreement with those obtained with a well-established ultraviolet procedure. The calculated limit of detection with this method is 2 ng of paraquat.     

Biological monitoring with atomic spectroscopy

Atomic spectroscopy holds a central role in biological monitoring. With this powerful and mature analytical tool, meaningful measurements can be made of a number of important elements in biological specimens. These measurements are useful in two general settings: (1) with toxic elements, by measurement of concentrations in excess of “expected” ranges; and (2) with essential elements, in which deficiencies may be observed. Several considerations are of major importance to effectively apply atomic spectroscopy to these measurements; (1) choice of an appropriate specimen; (2) selection of the most appropriate analytical method; (3) collection and preservation of the specimen; (4) analysis of the specimen; and (5) evaluation of the data generated. The usefulness of the various forms of atomic spectroscopy will be shown with two illustrative examples, and some evaluation will be provided of the future directions of research and upcoming issues in biological monitoring.     

The stereochemical outcome of electrophilic addition reactions on the 5,6-double bond in the spinosyns.

The electrophilic addition of reagents to the 5,6-double bond in spinosyn A and spinosyn D systems occurred with high pi-diastereofacial selectivity. Addition occurred preferentially from the beta face of the molecule with selectivities ranging from 5:1 to better than 30:1. Various NMR properties were investigated in order to distinguish the beta and alpha isomers with the help of theoretical models of the products. These NMR properties include a (13)C gamma effect to C-11 and vicinal coupling between H-4 and H-5. To help rationalize the selectivity, computational studies on the transition states for epoxidation were calculated using density functional theory. The results indicate that beta epoxidation is favored and that the geometries of the transition structures are consistent with torsional steering being the source of the selectivity.     

Determination of pKa values using 15N and 13C nuclear magnetic resonance spectroscopy. The case of apramycin

By comparison of pK^a values derived from ¹⁵N and ¹³C nuclear magnetic resonance (NMR) spectroscopies, the assignment of the ¹⁵N resonances of apramycin is completed. ¹³C NMR spectra appear to provide accurate pK_a determinations with this aminoglycoside. Hydroxylation adjacent to one of the basic nitrogens of apramycin appears to change the pK_a values of all five amines of the molecule.     

13C n.m.r. spectroscopy: Comparison of the spectra of some dimeric Catharanthus alkaloids and their derivatives

The ¹³C n.m.r. spectra of some dimeric Catharanthus alkaloids are reported and assigned. Methods devised to aid in the assignment of resonances in complex molecules are described. The ¹³C n.m.r. spectra of several derivatives of vinblastine are discussed.     

Determination of paraquat in sunflower seeds by reversed-phase high-performance liquid chromatography

The herbicide paraquat was determined with extracts from 1-g samples of sunflower seeds. The liquid chromatography procedure utilized a microparticle (10 micron) C18 reversed-phase column and isocratic elution with 27% acetonitrile in water, 10 mM in the sodium salt of octanesulfonic acid. Eluted paraquat was detected at 254 and 280 nm and quantitated by paraquat internal standard peak height ratios. This procedure provided linear working curves over the concentration range of 0-20 microgram/g of paraquat. Recovery of paraquat varied from 89-101%, with an average recovery of 93%. Good agreement was obtained in the comparison of results of the described procedure with those from a well established UV procedure.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.