Photometrische Bestimmung von Nitrat und Nitrit in Schwefels?ure mit Brucin

Zusammenfassung Bei der Wahl einer geeigneten analytischen Methode für die Nitrat- und Nitritbestimmung in konzentrierter Schwefelsäure sind die bisher bekannten Verfahren [1,3–12] wegen ihrer ungenügenden Empfindlichkeit oder wegen Schwierigkeiten bei der Probeaufbereitung auszuschließen. Wir haben daher für diesen Zweck eine einfache und zuverlässige Modifikation unserer Brucinmethode [2] ausgearbeitet, wobei eine noch größere Empfindlichkeit der Nitratbestimmung erreicht wurde. Bei geeigneter Acidität kann die Brucin-methode auch für die selektive Nitritbestimmung verwendet werden. Das hier beschriebene Verfahren ersetzt eine analoge Modifikation [5], die wegen ihrer methodischen Unrichtigkeit unzureichend ist.

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Photometric determination of nitrate and nitrite in sulphuric acid using brucine

A modified brucine method is recommended as a result of a detailed study of the reaction conditions. By suitable selection of acidity and tempering period two ranges of sensitivity have been obtained for the nitrate determination (0–5 and 0.1 bis 0.5 g NO₃ ^–-N/g H₂SO₄, resp.). At low concentrations of sulphuric acid nitrite may be determined in presence of nitrate by the same brucine method. Maximum errors are ±0.02 resp. ±0.05 g NO₃ ^–-N and ±0.05 NO₂ ^–-N.

     

Encapsulation of porphyrins and chlorins in biodegradable nanoparticles: the effect of dye lipophilicity on the extravasation and the photothrombic activity. A comparative study

In the present work, we performed a preclinical inter-comparison study using several photosensitizers with the goal of optimizing photodynamic therapy (PDT) for the treatment of choroidal neovascularization (CNV) associated with age-related macular degeneration. The tested molecules were the porphyrins meso-tetraphenylporphyrin (TPP) and meso-tetra-(4-carboxyphenyl)-porphyrin (TCPP), and the chlorins pheophorbide-a (Pheo-a) and chlorin e(6) (Ce(6)). Each of these molecules was entrapped in biodegradable nanoparticles (NP) based on poly(d,l-lactic acid). The influence of the degree of lipophilicity on the incorporation efficiency of the drug in the NPs, and on the dye leakage from blood vessels as well as on the photothrombic efficiency was investigated using the chick chorioallantoic membrane (CAM) as in vivo model. NP characterization showed that the dye was more effectively entrapped in the polymeric matrix when its degree of lipophilicity increased. While less lipophilic compounds (TCPP, Ce(6)) extravasate rather easily, the more lipophilic dyes (TPP, Pheo-a) tend to remain inside the blood vessels. After injection of a drug dose of 1 mg/kg body weight and a drug-light application interval of 1 min, irradiation with light doses ranging from 5 to 20 J/cm(2) led to the highest photothrombic efficiency when using the NPs loaded with the most lipophilic molecule (TPP). The latter induced vascular damage, which was significantly higher than that observed with the other molecules tested. Thus, in addition to minimal leakage from blood vessels, the TPP in NP formulation exhibited photothrombic efficiency similar to Visudyne which was also tested in the CAM model.     

Rapid determination of 5-hydroxytryptamine in whole blood by liquid chromatography with fluorimetric detection.

A rapid and simple reversed-phase (using muBondapak C18 as the stationary phase) liquid chromatographic method with fluorimetric detection is described for the quantitation of 5-hydroxytryptamine in whole blood. The rapidity and simplicity of the method are explained by the absence of a pretreatment. 5-Fluoro-dl-tryptophan was used as internal standard. The mobile phase was 0.01 M phosphate buffer (pH 4.5) with 0.0025 M 1-heptanesulfonic acid and 20% methanol. The detection wavelength were 302 nm for excitation and 340 nm for emission. Analysis time was 10 min with retention times for 5-hydroxytryptamine of 9 min and for 5-fluoro-dl-tryptophan of 7 min. This method is proposed for biological exploration of psychiatric disorders involving 5-hydroxytryptamine and would be useful for tryptophan.     

Development and validation of an analytical method for detection of estrogens in water

An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L^–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L^–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004     

Photoinduced electron transfer at liquid|liquid interfaces: dynamics of the heterogeneous photoreduction of quinones by self-assembled porphyrin ion pairs

The initial stages of the heterogeneous photoreduction of quinone species by self-assembled porphyrin ion pairs at the water|1,2-dichloroethane (DCE) interface have been studied by ultrafast time-resolved spectroscopy and dynamic photoelectrochemical measurements. Photoexcitation of the water-soluble ion pair formed by zinc meso-tetrakis(p-sulfonatophenyl)porphyrin (ZnTPPS(4)(-)) and zinc meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP(4+)) leads to a charge-separated state of the form ZnTPPS(3)(-)-ZnTMPyP(3+) within 40 ps. This charge-separated state is involved in the heterogeneous electron injection to acceptors in the organic phase in the microsecond time scale. The heterogeneous electron transfer manifests itself as photocurrent responses under potentiostatic conditions. In the case of electron acceptors such as 1,4-benzoquinone (BQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and tetrachloro-1,4-benzoquinone (TCBQ), the photocurrent responses exhibit a strong decay due to back electron transfer to the oxidized porphyrin ion pair. Interfacial protonation of the radical semiquinone also contributes to the photocurrent relaxation in the millisecond time scale. The photocurrent responses are modeled by a series of linear elementary steps, allowing estimations of the flux of heterogeneous electron injection to the acceptor species. The rate of electron transfer was studied as a function of the thermodynamic driving force, confirming that the activation energy is controlled by the solvent reorganization energy. This analysis also suggests that the effective redox potential of BQ at the liquid|liquid boundary is shifted by 0.6 V toward positive potentials with respect to the value in bulk DCE. The change of the redox potential of BQ is associated with the formation of hydrogen bonds at the liquid|liquid boundary. The relevance of this approach toward modeling the initial processes in natural photosynthetic reaction centers is briefly discussed.     

Speciation of metal complexes with biomolecules by reversed-phase HPLC with ion-spray and inductively coupled plasma mass spectrometric detection

Complementarity of ion-spray MS and ICP-MS as detection techniques in reversed-phase HPLC for the characterization of metals complexed by biomacromolecules is discussed by the example of the speciation of metallothionein-bound cadmium. The commercially purified rabbit liver MT-2 isoform is eluted from a microbore C₈ column with a gradient of up to 50% methanol in acetate buffer (pH 6.0) to give one major and three minor peaks detected at 254 nm. The preparation is further characterized by using an ICP mass spectrometer interfaced with HPLC via a direct injection nebulizer which allows for the specific detection of cadmium down to the 10 ng mL^–1 level. On-line detection by mass spectrometry with an ion-spray (pneumatically-assisted electrospray) ion source further allows the determination of the molecular masses of the eluted compounds. Received: 30 July 1997 / Revised: 7 November 1997 /Accepted: 11 November 1997     

Photodynamic actinometry using microspheres: concept, development and responsivity

Photodynamic therapy (PDT) relies on three main ingredients, oxygen, light and photoactivating compounds, although the PDT response is definitively contingent on the site and level of reactive oxygen species (ROS) generation. This study describes the development of a novel, fluorescent-based actinometer microsphere system as a means of discerning spatially resolved dosimetry of total fluence and ROS production. Providing a high resolution, localized, in situ measurement of fluence and ROS generation is critical for developing in vivo PDT protocols. Alginate-poly-L-lysine-alginate microspheres were produced using ionotropic gelation of sodium alginate droplets, ranging from 80 to 200 microm in diameter, incorporating two dyes, ADS680WS (ADS) and Rhodophyta-phycoerythrin (RPE), attached to the spheres' inside and outside layers, respectively. To test the responsivity and dynamic range of RPE for ROS detection, the production of ROS was initiated either chemically using increasing concentrations of potassium perchromate or photochemically using aluminum tetrasulphonated phthalocyanine. The generation of singlet oxygen was confirmed by phosphorescence at 1270 nm. The resulting photodegradation and decrease in fluorescence of RPE was found to correlate with increased perchromate or PDT treatment fluence, respectively. This effect was independent of pH (6.5-8) and could be inhibited using sodium azide. RPE was not susceptible to photobleaching with light alone (670 nm; 150 Jcm(-2)). ADS, which absorbs light between 600 and 750 nm, showed a direct correlation between radiant exposure (670 nm; 0-100 Jcm(-2)) and diminished fluorescence. Photobleaching was independent of irradiance (10-40 mW cm(-2)). We propose that actinometer microspheres may provide a means for obtaining high spatial resolution information regarding delivered PDT dose within model systems during investigational PDT development and dosimetric information for clinical extracorporeal PDT as in the case of ex vivo bone marrow purging.     

One-step cleanup for PAH residue analysis in plant matrices using size-exclusion chromatography

A new one-step cleanup procedure, based on size-exclusion chromatography (SEC), usable for the extracts from accelerated solvent extraction (ASE), Soxhlet extraction, or ultrasonic extraction (USE), is described. The method is suitable for the determination of polycyclic aromatic hydrocarbons (PAHs), especially from very complicated plant matrices (e.g. pine needles, deciduous leaves, mosses). The main improvement compared with previous conventional procedures is that analyte peaks barely overlap with matrix peaks in the chromatograms and that it is a very rapid and simple one-step procedure with clearly improved analytical performance. Essential advantages of this SEC procedure are the sharper GC-MS chromatograms for the PAH fraction at retention times between 9.2 and 12.0 min, distinctly separated substance peaks resulting in better analysis, shorter running times, and lower solvent consumption.     

Some Tris[(triorganophosphine)gold(I)]-oxonium and -Organoimonium Tetrafluoroborates with Bulky Substituents

Tris{[tri(2-methylphenyl)phosphine]gold(I)}-, tris{[tri(2,4,6-trimethylphenyl)phosphine]gold(I)}- and tris{[tri(cyclohexyl)phosphine]gold(I)}-oxonium tetra-fluoroborate ( 1?3 ) have been prepared from the corresponding (phosphine)gold(I) chlorides, silver oxide, and sodium tetrafluoroborate in acetone. These oxonium salts are excellent aurating agents for primary amines. Thus in the reaction with 1, t -butylamine ^tBuNH₂ and aniline PhNH₂ are readily converted into the tri nuclear imino complexes {[(2-MeC₆H₄)₃P]Au}₃N^tBu⁺BF₄^? ( 4 ) and {[(2-MeC₆H₄)₃P]Au}₃NPh⁺BF ( 5 ) in high yields. With 3 , both aniline and 8-amino-quinoline also give the tri nuclear complexes, i.e. {[(c-C₆H₁₁)₃P]Au}₃ NPh⁺BF ( 6 ) and {[(c-C₆H₁₁)₃P]Au}₃N(C₉H₆N)⁺BF ( 7 ). Auration of aniline with the most sterically hindered reagent 2 yields only the bi nuclear complex {[2,4,6-Me₃C₆H₂)₃P] · Au}₂N(Ph)H⁺BF ( 8 ). The reagents 1?3 and the Products 4 – 8 have been characterized by analytical and NMR spectroscopic data, and the crystal structures of compounds 4 and 6 have been determined by single crystal x-ray diffraction. In the cations of 4 , a triangle of gold atoms with short Au — Au contacts [3.036(1), 3.107(1), and 3.214(1) Å] forms a steep pyramid with the nitrogen atom, in which the angles Au? N? Au are all much smaller than the tetrahedral standard of 109.7°: 94.8(4), 98.1(4), and 103.0(4)°. This triangular Au₃ unit is staggered relative to the three methyl groups of the ^tBu substituent at nitrogen. The results for 6 are similar [Au — Au: 3.037(1), 3.071(1), and 3.222(1) Å; Au? N? Au: 95.3(3), 96.5(3), and 103.6(3)°]. Variable temperature NMR studies of compounds 3 and 8 show hindered rotation of the mesityl groups about the P? C bonds of the ligands originating from the steric congestion within each tertiary phosphine.     

Determination of albendazole and its main metabolites in ovine plasma by liquid chromatography with dialysis as an integrated sample preparation technique

Albendazole is a benzimidazole derivative with a broad-spectrum activity against human and animal helminth parasites. In order to determine the main pharmacokinetic parameters in sheep after oral and intravenous administration of a new formulation of albendazole (an aqueous solution), a fully automated method was developed for the determination of this drug and its main metabolites, albendazole sulfoxide (active metabolite) and sulfone in ovine plasma. This method involves dialysis as purification step, followed by enrichment of the dialysate on a precolumn and liquid chromatography (LC). All sample handling operations were executed automatically by means of an ASTED XL system. After conditioning of the trace enrichment column (TEC) packed with octadecyl silica with pH 6.0 phosphate buffer containing sodium azide, the plasma sample, in which a protein releasing reagent (1 M HCl) containing Triton X-100 was automatically added, was loaded in the donor channel and dialysed on a cellulose acetate membrane in the static-pulsed mode. The dialysis liquid consisted of pH 2.5 phosphate buffer. By rotation of a switching valve, the analytes were eluted from the TEC in the back-flush mode by the LC mobile phase and transferred to the analytical column, packed with octyl silica. The chromatographic separation was performed at 35°C and the analytes were monitored photometrically at 295 nm. Due to the differences in hydrophobic character between albendazole and its metabolites, a gradient elution was applied. The mobile phase consisted of a mixture of acetonitrile and pH 6.0 phosphate buffer. The proportion of organic modifier was increased from 10.0 to 50.1% in 12.30 min, then from 50.1 to 66.9% in 1.70 min. First, the gradient conditions and the temperature were optimised for the LC separation using the DryLab software. Then, the influence of some parameters of the dialysis process on analyte recovery was investigated. Finally, the method developed was validated. The mean recoveries for albendazole and its metabolites were about 70 and 65%, respectively. The limits of quantification for albendazole and its metabolites were 10 and 7.5 ng/ml, respectively.