Comparison of HPLC and solid phase clean-up methods for identification of PCBs in cod-liver oil by HRGC/MS-SIM technique

Summary A group of non-planar PCBs (IUPAC nos. 28, 52, 101, 118, 138, 153, and 180) was identified in a cod-liver oil product by using high resolution gas chromatography-mass spectrometry (HRGC/MS) in electron impact (EI) and negative chemical ionization (NCI) modes. The cod-liver oil samples were prepared either in a cyano column by high performance liquid chromatography (HPLC) or by a solid phase extraction (SPE) clean-up procedure that included e.g. purified charcoal treatment. The two methods of sample preparation were evaluated on the basis of the detectabilities of the congeners. The GC/MS-SIM method allowed quantitative monitoring of congeners nos. 52, 101, 118, 138, 153, and 180 at low concentration levels. Detection limits were 1.2 pg and 130 fg (m/z 292.00) in EI and NCI modes, respectively. The determination levels in EI and NCI were 1.8 pg and 290 fg in HPLC followed by HRGC/MS and 170 pg and 27 pg in SPE followed by HRGC/MS. The linear range was from 5.0 pg/l to 1.0 ng/l and from 1.0 pg/l to 1.0 ng/l in EI and NCI modes, respectively. In addition, the co-planar PCBs, PCDDs, and PCDFs were also screened and two of the chlorinated furanes were identified by HRGC/MS-NCI after separation from non-planar PCBs by SPE. In this case the only congeners that could be quantified were 2,3,4,7,8-PCDF and 1,2,3,4,6,7,8-HCDF, the detection limit for them being 740 fg (m/z 351.90) with NCI. SPE allows the separation of the planar and non-planar compounds, but LC separation is more effective for separation of the compounds of interest from the matrix. LC clean-up is easier and faster to perform than SPE clean-up.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Solid phase extraction/programmed temperature vaporizer (PTV) injection in GC-analysis of toxaphene and PCBs in aqueous samples

Summary A high-resolution gas-chromatographic (HRGC) method with electron capture detection is described for the sensitive determination of PCBs and toxaphene in water in the lower ng/l range. The required low detection limits are guaranteed by isolation of the target compounds and concentration from the filtered water sample by solid phase extraction with specific C₁₈ silica gel (200–250 m) alone or combined with the injection of larger extract volumes into a programmed temperature vaporizer (PTV) operating in the solvent venting mode. The bonded silica gel was prepared by reaction of the surface silanol groups with octadecyltrichlorosilane. A C₁₈ silica of reproducible coverage was received. Practical aspects of the use of the solid phase extraction in combination with the PTV injection technique are discussed. The recoveries for toxaphene and PCBs were 85 and 78%.     

Attempt to unravel the composition of toxaphene by comprehensive two-dimensional gas chromatography with selective detection

Comprehensive two-dimensional gas chromatography (GC x GC) coupled with micro electron-capture and time-of-flight mass spectrometric (TOF-MS) detection has been used to analyse technical toxaphene. An HP-1 x HT-8 column combination yielded highly structured chromatograms and revealed a complex mixture of over 1000 compounds what is significantly higher number than in any study before. The analysis of a mixture of 23 individual congeners and TOF-MS evaluation of technical toxaphene showed that the chromatogram is structured according to the number of chlorine substituents in a molecule. The nature of the compounds (bornane and camphene) does not appear to have any influence. The sum of the peak areas of all congeners in each group was calculated using laboratory-written software; based on these results, the composition of technical toxaphene as a function of the number of chlorine substituents was provisionally calculated and was found that hepta- and octachlorinated compounds represents 75% of the total toxaphene area.     

Sensitive fluorescence labelling for analysis of organotin compounds with morin

Summary Analytical procedures based on reversed-phase high-performance liquid chromatography combined with post-column derivatization with morin for the determination of organotin compounds in peanut oil, water samples or diet mixtures are described. A mixture of the isooctylesters of monooctyl tin and dioctyl tin thioglycolic acid (ZK 30 434), a mixture of the isooctylesters of monododecyl tin and didodecyl tin thioglycolic acid (ZK 32 283) or dibutyl tin difluoride (ZK 38 068) had to be analysed. The data obtained from validation and during routine analysis show that the post-column derivatization with morin is a powerful tool for the selective and sensitive detection of organotin compounds in complicated matrices. Interferences of peaks related to the organotins and the matrix constituents were not found. The values of the limit of detection were 10 g ZK 30 434 or ZK 32 283/ml peanut oil, 60 ng ZK 38 068/ml water and 2.5 mg ZK 30 434/kg rodent diet mixture. Regarding to the repeatability, the methods described are characterized by values of the relative standard deviation of mostly less than 5%. In case of the determination of ZK 30 434 dissolved in peanut oil atomic absorption spectrometry was used to investigate the accuracy of the HPLC method. A good correlation between the HPLC and AAS data was found. The limits of quantitation were 0.25 mg ZK 30 434/ml peanut oil, 0.22 mg ZK 32 283/ml peanut oil and 1.0 g ZK 38 068/ml water. The analytical procedures were applied within the framework of the analytical service for validation of toxicological studies according to the guidelines of good laboratory practices (G.L.P.). Both the correct preparation of the formulations and the homogeneity or stability could be checked.     

Characterization of citrus and kiwi flavors and their degradation processes by combination of GC/FTIR and GC/MS

Flavor samples are complex mixtures with components of sometimes very similar chemical behavior (e.g. isomeres). As an approach towards their characterization an integrated analytical method on the basis of capillary gas-chromatography (HRGC) was applied consisting of two molecular specific techniques for component-identification in unknown samples: GC-FTIRS (GC-Fourier transform infrared spectrometry) and GC-MS (GC-mass spectrometry).In addition GC-retention indices-from simultaneous GC on two columns (nonpolar/polar) —were stored in a database for routine retrieval and quantitative monitoring. To correlate this information with sensory perception sniffing chromatograms were generated with the human nose as a high performance detector.Because of the high information contents of GC-FTIR spectra in this field a small but specific vapor-phase-FTIR flavor library was accumulated, which dramatically improved the fast identification power of GC-FTIRS alone.     

Physicochemical characterization and stability of microbeads containing cod-liver oil encircled with natural cyclodextrins

The ability of cyclodextrins (CDs) to solubilize cod-liver oil in aqueous solutions was evaluated. Only the natural α-cyclodextrin (αCD) and γ-cyclodextrin (γCD) were able to fully disperse 10 % (v/v) cod-liver oil in aqueous solutions. Confocal imaging revealed that the oil was located in the center of the CD enveloped microbeads (<20 μm in diameter) where it was enclosed within nanocompartments (<1 μm in diameter). The aqueous microbead suspensions were lyophilized to produce dry powder microbeads with rough surfaces. To assess the stability of the cod-liver oil/γCD (3:1 molar ratio) microbead powder, three groups of samples were incubated over a period of 1, 2, 4, 12 and 84 weeks. Group 1 (G1) and group 2 (G2) were incubated at 25 °C and 60 % humidity. G1 was exposed to O₂ for 10 min before sealing off the glass containers while G2 was kept under nitrogen. Group 3 was stored under accelerated conditions at 40 °C and 75 % humidity under nitrogen. The reference was pure cod-liver oil. Results indicated that encapsulating cod-liver oil with γCD delays oxidative degradation when oxygen is present, but does not significantly decrease or increase the long term stability of cod-liver oil under anaerobic conditions. Cod-liver oil/γCD microbeads could be compressed into tablets without decreasing the integrity of encapsulation. The cod-liver oil/γCD microbead powder might be of interest to the pharmaceutical industry as a carrier for lipophilic drugs.     

Comment on the “dielectric properties of LDPE/Ny6 blends”

Data published by La Mantia et al. [1] on dielectric dispersion and loss in polyethylene/nylon 6 blends are analyzed in terms of dielectric mixture formulae. It is shown that an ohmic interfacial polarization process can not be responsible for the unexpected increase of and values observed in these blends at high temperatures. The observed phenomena are tentatively attributed to space charge processes at the electrodes or to other defects dipole mechanisms.     

A comparison of X-ray fluorescence spectrometric (XRF) techniques for the determination of metal traces,especially in plastics

A comparative study of energy-dispersive X-ray fluorescence techniques (without and with polarized radiation) and a wavelength-dispersive technique was carried out in order to investigate their sensitivity for the quantitative determination of 3d transition metal traces in plastic materials. For this purpose, liquid calibration samples in paraffin oil for the elements Cr, Mn, Co, Ni and Cu were prepared. Calibration lines in the concentration range of 1–100 g/g were evaluated for commercially available XRF-instruments and the results were critically compared. Limits of detection (LOD) ranged from 0.1 to 0.7 g/g for wavelength-dispersive XRF and energy-dispersive XRF with polarized radiation. The LOD's for energy-dispersive XRF without polarized radiation ranged from 0.9 to 8.6 g/g for elements in the same atomic number range between 24 and 29. The application of these optimized methods to the quantitation of wear and corrosion phenomena in plastic extruders and in a relevant model test apparatus, the annular slit tribometer, is elucidated.     

Phosphorus determination in biological materials

Summary An analysis scheme for the spectrophotometric determination of phosphorus as phosphate in biological materials has been worked out. The wet digestion of the sample was carried out in Kjeldahl flasks by a mixture of perchloric and nitric acids. The relative standard deviation (RSD) of the obtained results is not more than 1% for amounts up to 30 g. The method was applied to various biological materials.     

Interaction of tri-O-methyl-β-cyclodextrin with drugs

Summary The effect of tri-O-methyl--cyclodextrin(methyl--CD) on the partition coefficients of drugs, such as p-nitrophenol, salicylic acid, benzoic acid, and aspirin, was studied at 25°C. The partition coefficients of these drugs were increased linearly with methyl--CD concentration. The increase of partition coefficients was interpreted by the 11 complex formation between methyl--CD and the drug in CHCl₃ phase.The interaction between p-nitrophenol and methyl--CD in solution was studied by UV and PMR spectroscopies. It was concluded that p-nitrophenol is included in the cavity of methyl--CD in both aqueous solution and CHCl₃ solution.Inclusion compounds of these drugs with methyl--CD in the solid state were studied by X-ray diffractometry, IR spectroscopy, and DSC measurements. 11 crystalline inclusion compounds were obtained from hot water. It is also suggested that amorphous inclusion compound was obtained by the grinding of drug with methyl--CD.The dissolution rate and the bioavailability of ketoprofen were significantly increased in the presence of methyl--CD. The bioavailability of ketoprofen after oral administration with methyl--CD to rats was 3.7 times that of ketoprofen alone.     

Preparation of 16-substituted 3-hydroxyestra-1,3,5(10)-triene-17-ones starting with the bromination of estrone acetate

The bromination of estrone acetate (Ia) leads to a mixture of acetates of 16-bromo-16-bromo-, and 16,16-dibromoestrone (IIa, IIIa, and IVa) in a ratio of 63:28:9. On treatment with an aqueous methanolic solution of potash, depending on the conditions, a mixture of (IIa) and (IIIa) gives 3,16-dihydroxyestra-1,3,5(10)-trien-17-one (V) or 3,17-dihydroxyestra-1,3,5(10)-trien-16-one (VI). When 5 g of (Ia) was brominated with 2.8 g of Br₂ in chloroform and the products were chromatographed on silica gel, 0.36 g of (IVa), C₂₀H₂₂Br₂O₃, mp 165–166°C (from ether) 0.37 g of (IIIa), mp 169–170.5°C, 4.6 g of a mixture of (IIa) and (IIIa), 30 mg of (Ia) and 0.2 g of a mixture of 16- and 16-bromoestrones was obtained. The action of potash on a mixture of (IIa) and (IIIa) in aqueous MeOH at 20°C led to the epimerization of the (IIa) into (IIIa) and then the conversion of the latter into (V) with mp 203.5–206°C; diacetate with mp 172–173°C (acetone-ethanol). Similarly, but with heating (98°C, 3 h), a mixture of (IIa) and (IIIa) was converted into (VI), with mp 234–236°C. Characteristics of the IR and PMR spectra of the compounds obtained are given.S. Ordzhonikidze All-Union Scientific-Research Institute of Pharmaceutical Chemistry, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 465–469, July–August, 1983.     

Examples of the application of cyclodextrin in formulation of oral drug preparations

Fendiline hydrochloride [N-/1-phenylethyl/-3, 3-diphenylpropylamine. HCl] is a sparingly soluble and hardly absorbable coronary vasodilator. The fendiline base forms complex with -cyclodextrin in a molar ratio of 12. The enhanced solubility and dissolution rate of the complex resulted in a better bioavailability of the drug, which is represented by the elevated blood levels in rats. The -cyclodextrin complex of PGI₂Me /3% active ingredient content/ was prepared. The freeze-dried powder can be stored at 0°C for 1.5 years, while the pure substance only for 4 months. The biological effectiveness of the complex agrees well with that of the active ingredient. After oral administration the cytoprotective effect of the free and complexed drug on indomethacin induced ulcers in rats was similar in their order of magnitude, however the prolonged effect of the complex was detected in this case too.     

Offline coupling of high-speed counter-current chromatography and gas chromatography/mass spectrometry generates a two-dimensional plot of toxaphene components

High-speed counter-current chromatography (HSCCC), a separation technique based solely on the partitioning of solutes between two immiscible liquid phases, was applied for the fractionation of technical toxaphene, an organochlorine pesticide which consists of a complex mixture of structurally closely related compounds. A solvent system (n-hexane/methanol/water 34:24:1, v/v/v) was developed which allowed to separate compounds of technical toxaphene (CTTs) with excellent retention of the stationary phase (S_f = 88%). Subsequent analysis of all HSCCC fractions by gas chromatography coupled to electron-capture negative ion mass spectrometry (GC/ECNI-MS) provided a wealth of information regarding separation characteristics of HSCCC and the composition of technical toxaphene. The visualization of the large amount of data obtained from the offline two-dimensional HSCCC–GC/ECNI-MS experiment was facilitated by the creation of a two-dimensional (2D) contour plot. The contour plot not only provided an excellent overview of the HSCCC separation progress, it also illustrated the differences in selectivity between HSCCC and GC. The results of this proof-of-concept study showed that the 2D chromatographic approach involving HSCCC facilitated the separation of CTTs that coelute in unidimensional GC. Furthermore, the creation of 2D contour plots may provide a useful means of enhancing data visualization for other offline two-dimensional separations.     

Asymmetric synthesis of S-5-benzyloxytryptophan,S-α-allylglycine and S-β-(2-naphthyl)alanine

Conclusions The synthesis of optically pure S-5-benzyloxytryptophan, S--(2-naphthyl)alanine, and S--allylglycine was carried out by alkylating glycine in the Ni(II) complex of its Schiff base with S-2-N-(N-benzylpropyl)aminobenzophenone, followed by Chromatographic separation of the mixture of diastereomeric alkylated complexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2818–2821, December, 1988.     

Separation and quantitation of nicergoline and related substances by high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry

Summary This study demonstrated the utility of high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry (HPLC/API-MS) in the investigation of 10-methoxy-1,6-dimethylergoline-8-methanol 5-bromonicotinic acid ester (Nicergoline) and its related substances. The analysis was performed by using an ODS column with ammonium acetate and methanol mixture as the mobile phase. Nicergoline and its related compounds could be characterized by HPLC/API-MS in terms of their molecular weight. The use of multiple ion detection techniques for the quantitation of these compounds was also investigated. The detection limits of nicergoline and its related substances were 5 to 10 ng each at a signal-to-noise ratio of 4. The method was also applied to the study of the decomposition products of nicergoline in simulated gastric and intestinal fluids.     

Effect of bulky ligands on one-dimensional platinum compounds

Summary Diaminedithiocyanatoplatinum(II) complexes react with iodine in ethanolic suspension to yield diamagnetic compounds of empirical formula Pt(diamine)(SCN)₂I, which exhibit properties characteristic of one-dimensional materials. Incorporation of bulky substituents in the diamine ligand does not prevent the extended z-axis interaction responsible for these properties, in contrast to the effect of large ligands upon cooperative phenomena in Magnus' Green Salt analogues.Reprintsof this article are not available.The phase cooperative phenomena refers to magnetic and electronic properties that arise form the interaction between neihbouring metal in the solid state.     

Comments on the approximate calculation of lattice potential

The potential of a charge distribution due to a lattice of point charges may be evaluated by the classical multipole expansion method. The leading terms in the resultant expressions are just those used in some of our previous calculations [1–3]. In addition, for cases where the leading terms vanish because of the effect of orthogonality of the basis functions upon the Mulliken expansion (this being especially serious in the case of a one-centre charge distribution), we have derived the first nonvanishing term, involving |r|. In other cases it may be necessary to proceed to still higher multipole terms before a non-zero contribution is obtained. The entire procedure is formulated in such a way that it can be easily applied to LCAO-MO calculations for polyatomic ions in ionic lattices.     

Characterization of strong metal-support interaction in Pt/TiO2 catalysts by thermal programmed desorption of benzene

The Pt–TiO₂ interaction after HTR was studied by the TPD of benzene. Shifts in desorption temperatures are detected after HTR. They may be ascribed to electronic and morphologic changes.

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Pt/TiO₂ . . .

     

Application of the vapor phase supporting (VPS) method for preparing SnO2/SiO2 catalysts

Supported SnO₂/SiO₂ catalysts have been prepared by the reaction of the surface hydroxy groups of silica gel and gas phase tin chloride (PS method). The catalytic properties have been examined in the reaction of 2-propanol to show the effect of VPS cycles on the amount and nature of the active sites.

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SnO₂/SiO₂ . 2- VPS .

     

Mixed suspensions of semiconductors forming microheterojunctions. A new type of highly efficient photocatalysts: Photocatalytic production of dihydrogen from a water solution of sulfide ions in the presence of platinized ZnyCd1-y/CuxS suspension

A new method is proposed for increasing the quantum efficiency of H₂ production for the photocatalysts based on semiconductor suspensions. The method consists of the formation of suspended particles with microheterojunctions between their components--semiconductor phase.

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H₂ .