Determination of Arsenic and Phosphorus in Doped Polysilicon Layers

Abstract

The method is based on polysilicon dissolution with a water-hydrofluoric-nitric acid etchant mixture followed by matrix volatilization as hexafluorosilicic acid. Losses of arsenic through volatilization are avoided by its oxidation with permanganate. Phosphorus is determined by the molybdenum blue method with direct addition of a mixed reagent to the residue. Spectrophotometric evaluation at 882 nm provides a detection limit of 10 ng P ml^?1 with a precision better than 3%. Arsenic is determined by reducing As(V) to electroactive As(III) on addition of sulphite in 2 M hydrochloric acid. Differential-pulse polarography of this solution provides a precision of 2% and a detection limit of 20 ng As ml^?1.     

Automated on-Line Dialysis and Column-Switching HPLC Determination of Flumequine and Oxolinic Acid in Fish Liver

Abstract

An automated method for residue analysis of oxolinic acid and flumequine in liver of Atlantic salmon is described. Oxolinic acid and flumequine are extracted from liver with 0.4 M phosphate buffer pH 10 and the extracts are automatically analysed by on-line dialysis and column-switching in an HPLC system. The limit of detection was 4 μg/kg for oxolinic acid and 7 μg/kg for flumequine with fluorescence detection. The on-line combination of dialysis and column-switching HPLC was shown to be a reliable technique for residue control of these drugs in fish liver.     

Superoxide Dismutase Mimetic Activity of the Metal (II) Complexes of a Dithiocarbamate Derivative of β-Cyclodextrin1

Abstract

The synthesis of a new β-cyclodextrin derivative containing a dithiocarbamate group (3) by condensation of mono-2-methylamino-2-deoxy-β-CD (2) with CS₂ in the presence of NEt₃ is reported. SOD-mimetic activity was found for the Mn(II) and Cu(II) complexes of 2 and 3 (IC₅₀ = 0.76-7.4 μ). To study the influence of the cyclodextrin residue on the catalytic activity of these complexes, a comparison was made with diethylamine and diethyldithiocarbamate complexes. Complexes of 2 and 3 resulted in 1.3 to 11 fold higher activities. An explanation for this observation, in terms of a possible cooperation of the cyclodextrin residue with the catalytic center of the complex, is given.     

Ion Trap Detection for Development of a Multiresidue/Multi Matrix Method for Pesticide Residues in Agricultural Products

Abstract

In the Netherlands for the determination of more than 400 pesticides thirteen multi residue methods and about 170 single residue methods are in use. A literature search learns that about 200 pesticides are gaschromatography (GC) amenable, that quantitative extraction procedures exist and these pesticides also give good recovery when gelpermeation (GPC) is used for cleanup of extracts. A strategy is discussed to develop a universal multi pesticide method, especially paying attention to plant material, using a universal very sensitive detection system, e.g. the ion trap detector.

Experimental data obtained with diverging matrices are presented together with some thoughts on on-line GPC-GC combinations, using a temperature programmable injector in the GC system.     

HPLC Assay for Trimethoprim in Plasma and Urine

Abstract

A sensitive HPLC method for the quantitation of trimethoprim in plasma and urine was developed using fluorescence detection. Plasma (or urine) samples were made basic by the addition of 3.8N sodium hydroxide and extracted with chloroform:2-propanol (95:5). After evaporation of the organic layer, a portion of the residue was analyzed by HPLC with fluorescence detection. The minimum detectable quantity is 0.1 μg/ml for this method. This method has been applied to the analysis of plasma and urine obtained from subjects after a single 160 mg dose of trimethoprim.     

Liquid Chromatographic Residue Analysis of Carbaryl Based on a Post-Column Catalytic Reactor Principle and Fluorigenic Labelling

Abstract

A method is described for the residue analysis of carbaryl in polluted water samples. The technique is based on catalytic hydrolysis of the carbaryl on anion exchangers followed by fluorescence detection of the α-naphthol or the OPA derivative of the methyl amine. A low cost 200 mesh Amberlite strong anion exchanger can be used for this purpose when coupled to the OPA reaction detector. Combining this approach with on-line preconcentration and clean-up on an 3P-18 loaded precolumn can provide a powerful tool for automated residue analysis of carbaryl (and other N-methyl carbamates) in polluted water sources. Recoveries in the order of 100% are reported. The reproducibility of the technique is better than 2% rel. st. dev. Detection limits are 0.4–2 ng per injection for carbaryl depending on the system and linearity of response is more than two orders of magnitude with r = 0.9998. The selectivity and sensitivity of this method permits residue analysis at the sub ppb concentration level in heavily polluted water samples. Data on hydrolysis yields and band broadening as a function of residence time and temperature in the reactor are given.     

Binaphthyl-Substituted Chiral Phosphines and Oxides from Binaphthophooles and Nucleophiles

Binaphthophospholes 1 are the starting compounds for the synthesis of chiral phosphine oxides 3 or phosphines 4 via reaction of phospholium salts 2 with nucleophiles. The binaphthyl residue acts as a stereochemical probe for monitoring the integrity of the phosphorus stereocenter.     

Quantitation of Serotonin in Human Plasma,Serum and Cerebrospinal Fluid Samples by HPLC-EC Using 6-Hydroxytryptamine as an Internal Standard

Abstract

A simple method for sample clean up and concentration of serotonin (5-HT) in biological samples, such as human cerebro-spinal fluid and serum, is described. To the sample 6-hydroxy-tryptamine (6-HT) is added as an internal standard and it is then absorbed either on C₁₈ SEP-PAK cartridge or Biorex-70 short column. 5-HT and 6-HT are then eluted from the column with methanolic formic acid. After evaporation, the residue is dissolved in the mobile phase and an aliquot is used for LC-EC quantitation.     

Synthesis of Uridine Derivatives Containing Amino Acid Residues

Abstract

Convenient synthesis of uridine derivatives containing amino acid residues were carried out successfully by reacting triazolated uridine with the hydrochloride salts of some amino acid esters, which provides a general method for the direct introduction of amino acid group onto nucleoside residue.     

Spectrophotometic Determination of Pyrene,Fluoranthrene and Phenanthrene in Anthracene Oil

Abstract

A method for the determination of pyrene, fluoranthrene and phenanthrene in the “anthracene oil” residue, after removal of anthracene, is described utilizing measurements of absorbance at three wavelengths in the ultraviolet and solution of the three simultaneous equations produced. Molar absorptivities for the three hydrocarbons are given and the accuracy of the determination is discussed.     

An HPLC Method for Measuring 5-Fluorouracil in Plasma

Abstract

5-Fluorouracil in plasma was determined by extraction with methyl isobutyl ketone, evaporation of the ketone, and reverse phase high performance liquid chromatography of the evaporation residue. With UV detection at 280 nm the lower limit of detection is 10.0 ng/ml and interfering peaks eliminated. The method is highly reproducible.     

Determination of Chlorpyrifos Residue by Near-Infrared Spectroscopy in White Radish Based on Interval Partial Least Square (iPLS) Model

Abstract

This article presents a multivariate method of rapidly determining chlopyrifos residue in white radish, based on near-infrared spectroscopy and partial least squares (PLS) regression. Interval PLS (iPLS) was utilized to select the optimum wave number range. The number of PLS components and the number of intervals were optimized according to root mean square error of prediction (RMSEP) and correlation coefficient (R) in prediction set. The result showed that the iPLS model was more reliable than the full model and that near-infrared spectroscopy with iPLS algorithm could be used successfully to analyze chlorpyrifos residue in white radish.     

Studies of the Synthesis of Rubranitrose and Crystal Structure of Methyl 2,3,6-Trideoxy-3-C-Methyl-3-Nitro-α-D-Ribo-Hexopyranoside

Abstract

The branched-chain nitro sugar methyl 2,3,6-trideoxy-3-C-methyl-3-nitro-α-D-ribo-hexopyranoside 4 was investigated as a precursor to D-rubranitrose, a nitro sugar found in the antibiotic rubradirin. X-ray cyrstallographic analysis of 4 shows that the pyranose ring adopts the ⁴ C ₁ conformation with the methoxy group at C-1 and the nitro group at C-3 in a 1,3-diaxial relationship. There is an intermolecular hydrogen bond involving a nitro group oxygen of one monosaccharide residue and the C-4 hydroxyl group of the adjacent residue in the crystal lattice. This interaction results in a helical crystal packing. A series of nucleophilic displacement reactions was carried out on the triflate derivative of 4 in an attempt to introduce an axial carbon-oxygen bond at C-4 required for rubranitrose. Displacements with acetate and propionate gave as products the monosaccharide esters with the desired D-xylo configuration.     

Determination of Thallium In Solid Environmental Samples By Electrothermal Atomic Absorption Spectrometry

Abstract

A method for the determination of thallium in solid environmental samples is developed. After destruction of the sample, TI(III) is extracted from 0.5 M hydrobromic acid solution into diisopropyl-ether. the organic phase is evaporated and the residue taken up in a mixture of sulfuric and nitric acids. Measurements are carried out with an atomic absorption spectrometer with Zeeman background corrector. the accuracy of the method is tested by analysis of certified reference materials and the method is applied to fly ash and emitted particulate matter from a municipal refuse incinerator and to soil samples.     

Isclation of Lecithin and Sphingomyelin from Lipid Mixtures for Quantitation by Infrared Spectroscopy

Abstract

A new procedure for the determination of lecithin and sphingomyelin in amniotic fluid is described. rapid column chromatography in the sample preparation steps with computer-assisted infrared spectroscopy in the final determination. Lipids are extracted from amniotic fluid with a chloroform/methanol solvent. The organic layer is separated and evaporated to dryness. The residue is The new method couples the use of simple, redissolved i n chloroforn and Fassed through a hydroxyapatite column to remove interfering constituents. The complete isolation cflecithin and sphingomyelin fror other li Fidsis confimec by both infrared spectroscopy and thin layer chronatcgrayhy.     

HPLC Determination of Methylphenidate in Human Plasma

Abstract

A simple, rapid and sensitive method for measuring methylphenidate in human plasma by HPLC has been developed. After the addition of the internal standard, ethylphenidate, the two compounds are extracted under basic conditions. The residue obtained is resuspended in acetonitrile and analysed on an ODS reversed phase column with detection by UV absorbance at 192 nm. The limit of sensitivity is 5 ng/ml and the procedure is linear over the 5–50 ng/ml concentration range.     

A Mössbauer,Chemical Extraction,and X-ray Diffraction Study of a Sediment from the Baie de Villefranche (France)

Abstract

A marine sediment from the Baie de Villefranche (France) has been studied by sequential chemical extraction, X-ray powder diffraction and Mossbauer spectroscopy. The Mossbauer spectra of the solid fractions after each step of the extraction show changes in general agreement with those expected. The exception is siderite which is only partially extracted with other carbonates, the residue being extracted with the Iron(III) oxides. The selective extraction method allows the differentiation of species whose Mossbauer spectra are very similar.     

Synthesis of a Tri- and Tetrasaccharide Fragment Specific for the Shigella flexneri Serotype 5a O-Antigen. A Reinvestigation

ABSTRACT

Stereocontrolled, stepwise synthesis of methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (A(E)B, 1) and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (DA(E)B, 2) is described; these constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Two routes to trisaccharide 1 were considered. Route 1 involved the coupling of a precursor to residue A and a disaccharide EB, whereas route 2 was based on the condensation of a precursor to residue E and a disaccharide AB. Rather surprisingly, the latter afforded the β-anomer of 1, namely methyl α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside as the major product. Route 1 was preferred. Overall, several observations made during this study suggested that, for the construction of higher fragments, a suitable precursor to rhamnose A would require protecting groups of low bulkiness at position 3 and 4. Therefore, the 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate (35) was the precursor of choice to residue A in the synthesis of the tetrasaccharide 2. The condensation product of 35 and methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-4-O-benzyl-α-L-rhamnopyranoside was selectively deacylated and condensed to 2-trichloroacetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl trichloroacetimidate to afford the corresponding fully protected tetrasaccharide 45. Controlled stepwise deprotection of the latter proceeded smoothly to afford the target 2. It should be emphasised that the preparation of 45 was not straightforward, several donors and coupling conditions that were tested resulted only in the complete recovery of the acceptor. Distortion of several signals in the ¹³C NMR spectra of the fully or partially protected tetrasaccharide intermediates suggested that steric hindrance, added to the known low reactivity of HO-2 of rhamnosyl acceptors, probably played a major role in the outcome of the glycosidation attempts.     

Simultaneous Determination of Caffeine and Antipyrine in Plasma and Saliva using High-Performance Liquid Chromatography

Abstract

A rapid and sensitive method of quantitation of caffeine and antipyrine in plasma and saliva is described. Caffeine, antipyrine and phenacetin, the internal standard, are readily extracted from alkalinized plasma and saliva into dichloromethane. After evaporation of the organic solvent, the residue is analyzed by HPLC using a mobile phase of 25% acetonitrile in 0.02 M phosphate buffer at a flow rate of 1.5 ml/min. and a C18 reverse phase column. Baseline separation of all peaks is achieved with retention times for all compounds of less than 10 minutes. There is no interference from endogenous compounds or metabolites of caffeine or antipyrine.     

Synthesis of the Methyl Glycosides of a Di- and Two Trisaccharide Fragments Specific for the Shigella flexneri Serotype 2a O-Antigen

ABSTRACT

The stereocontrolled synthesis of methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (EC, 1), methyl α-L-rhamnopyranosyl-(1→3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (B(E)C, 3) and methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside (ECD, 4) is described; these constitute the methyl glycosides of branched and linear fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a. Emphasis was put on the construction of the 1,2-cis EC glycosidic linkage resulting in the selection of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (8) as the donor. Condensation of methyl 2,3-O-isopropylidene-4-O-trimethylsilyl-α-L-rhamnopyranoside (11) and 8 afforded the fully protected αE-disaccharide 20, as a common intermediate in the synthesis of 1 and 3, together with the corresponding βE-anomer 21. Deacetalation and regioselective benzoylation of 20, followed by glycosylation with 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (15) afforded the branched trisaccharide 25. Full deprotection of 20 and 25 afforded the targets 1 and 3, respectively. The corresponding βE-disaccharide, namely, methyl β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (βEC, 2) was prepared analogously from 21. Two routes to trisaccharide 4 were considered. Route 1 involved the coupling of a precursor to residue E and a disaccharide CD. Route 2 was based on the condensation of an appropriate EC donor and a precursor to residue D. The former route afforded a 1:2 mixture of the αE and βE condensation products which could not be separated, neither at this stage, nor after deacetalation. In route 2, the required αE-anomer was isolated at the disaccharide stage and transformed into 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2,3-di-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (48) as the EC donor. Methyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-β-D-glucopyran-oside (19) was preferred to its benzylidene analogue as the precursor to residue D. Condensation of 19 and 48 and stepwise deprotection of the glycosylation product afforded the target 4.