Semiquantitative estimation of the mycotoxins citrinin, Ochratoxin A, Aflatoxin M1 and penicillic acid on thin-layer chromatograms with a grey scale

Summary Spots of citrinin, ochratoxin A, aflatoxin M₁ and penicillic acid on thin-layer chromatograms can be semi-quantitatively estimated by using a grey scale, commonly used in photo laboratories. The detection limits are 0.01 g for citrinin, 0.006 g for ochratoxin A, 0.002 g for aflatoxin M₁ and 0.01 g for penicillic acid. Standard curves for these mycotoxins are given.

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Halbquantitative Bestimmung der Mycotoxine Citrinin, Ochratoxin A, Aflatoxin M₁ und Penicillinsäure auf Dünnschicht-Chromatogrammen mit Hilfe eines Graukeils

Zusammenfassung Mit Hilfe eines in Photolabors gebräuchlichen Graukeils können dünnschicht-chromatographische Flecke der obengenannten Mycotoxine halbquantitativ bestimmt werden. Die Nachweisgrenzen betragen 0,01 g für Citrinin, 0,006 g für Ochratoxin A, 0,002 g für Aflatoxin M₁ und 0,01 g für Penicillinsäure. Eichkurven werden angegeben.

     

HPLC preparation of nitrate from ice cores for mass spectrometric 15N/14N measurements

Summary A method for the analysis of ¹⁵N-data of nitrate at ultratrace levels in ice cores is described. Samples are pre-concentrated using a HPLC-system. Nitrate is then reduced using the Dumas method to molecular nitrogen, which is analysed by mass spectrometry. The overall analytical precision of the method is ±0.4¹⁵N at a sample size of 35 bar l N₂. First results of deep ice-core analyses from Dome Summit, Greenland, are given.     

Triiron and Triruthenium Carbonyl Clusters Bearing Bridging Long Chain Diphosphine and Capping Chalcogenido Ligands

Treatment of Ru₃(CO)₁₂ with dpphSe₂ (dpph = 1,6-bis(diphenylphosphino)hexane) in refluxing toluene in the presence of Me₃NO afforded two new compounds, Ru₃(CO)₇(-CO)(₃-Se)(-dpph) (1) and Ru₃(CO)₇(₃-Se)₂(-dpph) (2). A similar reaction of Ru₃(CO)₁₂ with dpppeSe₂ (dpppe = 1,5-bis(diphenylphosphino)pentane) gave exclusively Ru₃(CO)₇(₃-Se)₂(-dpppe) (3). Treatment of Ru₃(CO)₁₂ with dpphS₂ and dpppeS₂ at 110°C in the presence of Me₃NO afforded Ru₃(CO)₇(₃-S)₂(-dpph) (4) and Ru₃(CO)₇(₃-S)₂(-dpppe) (5), respectively. Reactions of Fe₃(CO)₁₂ with dpphSe₂ and dpppeSe₂, under identical conditions, afforded Fe₃(CO)₇(₃-Se)₂(-dpph) (6) and Fe₃(CO)₇(₃-Se)₂(-dpppe) (7), respectively. Compounds 1–7 were characterized spectroscopically and the molecular structures of compounds 1–4 were determined by single crystal X-ray crystallography. The core of 1 contains an equilateral triangle of ruthenium atoms with one capping selenium, one bridging dpph, one doubly bridging carbonyl and seven terminal carbonyl ligands. Complexes 2–4 have a square-pyramidal structure with two metal and two chalcogenide atoms alternating in the basal plane and the third metal atom at the apex of the pyramid, and belong to the family of well-known nido clusters with seven skeletal electron pairs.     

Decomposition of isopropanol on V2O5 of different grain morphology and its relation to o-xylene oxidation catalysts

Decompositon of isopropanol has been studied on V₂O₅ samples of different morphology. It has been shown that the selectivity to acetone increases with the increase in the fraction of (010) plane of V₂O₅ on the sample surface, whereas the selectivity to propene decreases. The results are compared with previous data of o-xylene oxidation on the same samples and discussed in terms of the model of V₂O₅ surface [7].

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V₂O₅ . , (010) V₂O₅ , . - V₂O₅.

     

On the nature of surface sites for heterolytic dissociation of hydrogen on Al2O3

A quantum-chemical analysis of the models for geminal OH groups of Al₂O₃ and of the processes of their dehydroxylation with further dissociative chemisorption of hydrogen has been carried out. Calculations were performed by the SCF MO LCAO method using STO-3G basis set in terms of the cluster approach.

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OH- Al₂O₃ . , STO-3G .

     

Trace analysis of cationic surfactants in water using HPLC with conductometric detection

Summary A simple and fast determination of trace amounts of commercially used cationic surfactants is described. After extraction from water cationic surfactants are separated by HPLC and detected by conductometry. The detection limit is 3 g/l for distearyldimethylammonium chloride, 16 g/l for ditallowimidazolinium methosulphate, and 6 g/l for dodecylpyridinium chloride.     

Effect of Rh/Al2O3 on the reduction of ZnO in a mechanical mixture of these components

The effect of reoxidation temperature on TPR of 5% Rh/Al₂O₃ catalyst and its mechanical mixture with ZnO has been investigated. The results suggest bimodal character of supported rhodium and surprisingly high effect of this metal on ZnO reduction in the mixture.

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5% Rh/Al₂O₃ ZnO. , ZnO .

     

Catchment region partitioning of energy hypersurfaces,I

The space of internal coordinates of a molecular system is partitioned into catchment regions of various critical points of the energy hypersurface. The partitioning is based on an ordering of steepest descent paths into equivalence classes. The properties of these catchment regions and their boundaries are analyzed and the concepts of chemical structure, reaction path and reaction mechanism are discussed within the framework of the Born-Oppenheimer and energy hypersurface approximations. Relations between catchment regions and the chemically important reactive domains of energy hypersurfaces, as well as models for branching of reaction mechanisms, caused by instability domainsD , 1, are investigated.     

New cobalt trimethylacetate complexes with pyridine

The reaction of the tetranuclear trimethylacetate complex Co₄(₃-OH)₂(-OOCCMe₃)₄(²-OOCCMe₃)₂(EtOH)₆ with pyridine in acetonitrile was studied. Two new compounds, viz., the hexanuclear cobalt(ii) complex Co₆py₄(₃-OH)₂(-OOCCMe₃)₁₀ (25% yield) and the unusual ionic compound [Co₃py₃(₃-O)(-OOCCMe₃)₆]⁺[Co₄py(₄-O)(-OOCCMe₃)₇]^– (5% yield), were prepared. The structures of the new compounds were established by X-ray diffraction analysis.     

The Synthesis and Reactivity of New μ 2- and μ 3-Aminophosphinidene Cobalt Complexes

The reaction of K[Co(CO)₄] and PCl₂(TMP) at –5°C leads to the unstable and reactive -phosphinidene complex [Co₂(CO)₆{-P(TMP)}] (1), while the same reaction carried out at 35°C gives the chlorophosphido and phosphinidene bridged cluster [Co₃(CO)₇{-P(Cl)TMP}{ ₃-P(TMP)}] (2) (TMP=2,2,6,6-tetramethylpiperidyl). Compound 1 reacts with dppm (dppm=bis(diphenyl- phosphino)methane) and [Co₂(CO)₈] to form the more stable substitution product [Co₂(CO)₄{-P(TMP)}(-dppm)] (3) and [Co₄(CO)₇(-CO)₃{ ₃-P(TMP)}] (4) respectively. The first example of a cationic ₃-phosphinidene cluster compound [Co₃(CO)₉{ ₃-P(TMP)}][AlCl₄] (5) is obtained from reaction of 3 with AlCl₃. The X-ray structures of clusters 2 and 5 are discussed.     

Influence of the crystallite size of platinum of the course of hydrogenolysis of ethane and propane over Pt/Al2O3 catalysts

The effect of the degree of platinum crystallite size on the reaction rate, selectivity and activation energy of ethane and propane hydrogenolysis has been studied in the range of platinum crystallite size of 1.7–4.0 nm. In the same range of Pt crystallite size, the activation energy of both processes shows a clear minimum. The decrease in Pt crystallite size bellow 3.0 nm brings about rapid changes in the selectivity of propane hydrogenolysis.

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( ) , -. 1,7–4,0 , .

     

Addition of HCl to a Cluster-Bound Vinylidene Ligand: Preparation and Structure of Ru5(μ3-SMe)(μ3-CMe)(μ-Cl)(μ-SMe)(μ-PPh2)2(CO)9·PhMe

Addition of aqueous HCl to Ru₅( ₃-C=CH₂)(-SMe)₂(-PPh₂)₂(CO)₁₀ afforded the structurally characterized carbyne complex Ru₅( ₃-SMe)( ₃-CMe)(-Cl)(-SMe)(-PPh₂)₂(CO)₉, formed by addition of H to the vinylidene ligand; a Cl atom bridges an Ru–Ru bond.     

Controlled-potential coulometric studies on fluoride and sulphate complexes of neptunium (VI)

Fluoride and sulphate complexing of Np(VI) has been studied by controlled-potential coulometry at a constant ionic strength. The values of ₁ ^* and ₂ ^* for fluoride complexes were found to be 9.4 and 8.9, respectively, at an ionic strength =0.5. At an ionic strength =1.0, ₁ ^* and ₂ ^* obtained were 6.6 and 10.5, respectively. Sulphate complexing of Np(VI) was studied only at an ionic strength =0.5. The value of ₁ ^* obtained was 5.6.     

Catalysts for metathesis of olefins obtained through [Mo3O4(C2O4)3 (H2O)3]2? coordinated to γ-Al2O3

New highly active catalysts for the metathesis of olefins have been obtained through the interaction of [Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– anion with Al₂O₃ surface and further activation in H₂ or CO atmosphere.

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[Mo₃O₄ (C₂O₄)₃ (H₂O)₃]^2– Al₂O₃ H₂ CO .

     

Studies on catalytically active surface compounds, VIII. On the reaction of VCl4 with aerosil

The preparation and hydrolysis of silica supported vanadium catalysts have been investigated using VCl₄ as a paramagnetic probe. Chemical analysis shows the possibility of the VCl₄ molecule to react one, two, or three hydroxy groups of the surface. The type of reaction is influenced by the temperature of pretreatment of aerosil (TPA). ESR measurements show distortions of the tetrahedral coordination of the (SiO)_nVCl_4–n surface complex, which is strongest for the threefold attachment (n=3) of VCl₄ to the surface. Hydrolysis is accompanied by an increase of the coordination number and leads to highly mobile vanadium species.

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, VCl₄ . , VCl₄ , . . (SiO)_nVCl_4–n, VCl₄ (n=3). .

     

Effect of dispersity on some catalytic reactions on Pt/SiO2

The effect of the dispersity of a Pt/SiO₂ catalyst has been investigated in the hydrogenolysis of ethane, n-butane and in cyclohexane exchange. Turnover number, N_T, for ethane hydrogenolysis increases with decreasing particle size, which may be interpreted by the formation of a surface intermediate in which both carbon atoms are bonded to one platinum atom. Cyclohexane exchange is not influenced by the change in particle size.

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Pt/SiO₂ , - . N_T, , , . .

     

The Aggregation of Cyclodextrins as Studied by Photon Correlation Spectroscopy

Photon correlation spectroscopy has been used to study theaggregation processes of natural and some modified cyclodextrins (CDs) in diluted aqueoussolutions. -, -, and -CD form large, polydisperse aggregatesin water, although the aggregation capability is different depending on the macrocycle considered. -CD solutions filtered through 0.2~m give a single-modaldistribution of aggregates of 224 nm in size. The monomeric -CD can be isolated by filtering through 0.1 m. -CD displays a bimodaldistribution (monomer + aggregates) with both pore sizes. At the concentrations studied (0.012 M) the contribution in mass of the aggregates with both CDs isnegligible. -CD is much more persistent in its aggregation, even after sievingits solutions through 0.02 m filters, and time dependent. The aggregation displayed byCDs with partial substitution of the OH groups (Methyl--CD and Hydroxypropyl--CD) is much weaker, indicating the implication of the hydrophilic rims ofthe CDs in the process. High temperatures, addition of urea or electrolytes andionisation of the OH groups by raising the pH, prevent the aggregation.     

Absorption spectra of hexachlorobenzene adsorbed on SiO2 powders

Summary Photoacoustic spectra of hexachlorobenzene adsorbed on SiO₂ powders of different particle sizes were investigated. A comparison of the measured PA spectra with the calculated optical absorption lengths led to the conclusion that only absorption bands for which is much larger than the particle size, i.e. in the case of carrier transparency, appear in the PA spectrum. This indicates that the particle diameter determines the thickness of the sample. Compared to their solution spectra the PA spectra of HCB on the silica carriers do not show a red shift of the various absorption bands as was claimed in the literature. Permanent address: Institute of Public Health, B. Kidria, 52a, YU-51000 Rijeka, Yugoslavia     

HCN synthesis from NH3 and CH4 on Rh and Ir

The synthesis of hydrocyanic acid from methane and ammonia on Rh and Ir wires was studied at temperatures varying between 1200 and 1500 K at one atmosphere. Activation energies and preexponential factors are reported.

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1200–1500K . .

     

Catalytic decomposition of N2O on La2Cu0.5M0.5O4 (M=Co, Ni, Cu and Zn)

Decomposition of N₂O has been studied over La₂Cu_0.5M_0.5O₄ (M=Co, Ni, Cu and Zn) between 380 and 485°C at 50 torr initial pressure of N₂O to understand the mutual interaction of two different active metal ions of the same concentration and valence in deciding the physico-chemical and catalytic properties. A multicenter type of adsorption of N₂O has been visualized and it is found that the rate is governed by the electronic factor.

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N₂O La₂Cu_0,5M_0,5O₄ (M=Co, Ni, Cu Zn) 380–485°C N₂O, 50 . , - . N₂O. .