Potentiometric determination of d(+)glucose, d(+)mannose or d(-)fructose in a mixture of hexoses and pentoses, by using streptococcus mutans fermentation

A potentiometric sensor has been developed, based on selective fermentation of carbohydrates by Streptococcus mutans. This combination of bacterial action and a glass electrode responds to beta-d(+)glucose, d(+)mannose and beta-d(-)fructose over a narrow concentration range, with a response time of 4 min, and has negligible response to other hexoses and pentoses.     

Determination of stability constant of copper(II) with thiosemicarbazide by use of a cupric ion-selective electrode

The stability constant of copper(II)—thiosemicarbazide complex has been determined potentiometrically by means of a cupric ion-selective electrode. Value of logK_CuL2 obtained in 0. 1 M KNO₃ at 25 °C corresponded well with the values given in the literature measured spectrophotometrically.     

Determination of (-)-epigallocatechin gallate in rat blood by microdialysis coupled with liquid chromatography

A liquid chromatographic method coupled with microdialysis was used to determine the protein-unbound (-)-epigallocatechin-3-gallate (EGCG) in rat blood. EGCG and dialysates were separated using a Merck RP-18e column maintained at ambient temperature, and a mobile phase comprised of acetonitrile-10 mM monopotassium phosphate (pH 3.82) (20:80, v/v) with a flow rate of 1.0 ml/min. The UV detector wavelength was set at 206 nm. The detection limit for EGCG was 10 ng/ml. The concentration-response relationship was linear (r2 > 0.995) over a concentration range of 0.05-10 microg/ml; intra- and inter-assay precision and accuracy of EGCG fell within predefined limits. Pharmacokinetic parameters of EGCG were assessed using compartmental models. The disposition of EGCG in the rat blood suggests that EGCG was fitted by two-compartmental model. The distribution and elimination half-lives were 6 and 72 min respectively, after the dosage of 30 mg/kg.     

Determination of stability constants of cadmium(II) with some amino-acids by use of an ion-selective electrode

Three different methods were used to obtain the stability constants of the complexes of cadmium with several mino-acids. Two made use of an ion-selective electrode; the third was based on pH-measurement only. Values of beta(ml) and beta(ml)(2) obtained in 0.1M KNO(3) at 25 degrees corresponded reasonably for most amino-acids examined and accorded with the values given in the literature, as far as comparison was possible.     

Reactions of metal(II) ions with sugar α-amino acids: nickel(II) complexes containing an α-amino acid derived from galactose or mannose

Summary The reaction of Ni^II ions with 2-(benzylamino)-2-deoxy-d-glycero-l-gluco. heptonic acid (BnGa:C₁₄H₂₁NO₇) or 2-(benzylamino)-2-deoxy-d-glycero-d-talo heptonic acid (BnMa:C₁₄H₂₁NO₇) in water yields complexes of formulae [Ni(BnGa)₂(H₂O)₂] and [Ni(BnMa)₂]·2H₂O, respectively, which were characterized by elemental analysis, spectral techniques (u.v.-vis.-n.i.r. and i.r.), magnetic susceptibility measurements, thermal measurements (t.g. and d.s.c.) and X-ray powder diffraction. Both complexes are octahedral with two positions of the coordination sphere occupied by nitrogen atoms. Moreover, in [Ni(BnMa)₂]·2H₂O four oxygen atoms of bridging carboxylate groups are coordinated to the metal ion, while in [Ni(BnGa)₂(H₂O)₂] only an oxygen atom of each carboxylate group is bound to Ni^II. In this case, the coordination is completed via two water molecules.     

聚L-白氨酸修饰电极伏安法测定痕量多巴胺的研究

用循环伏安法制备了聚L-白氨酸修饰玻碳电极,研究了多巴胺在聚L-白氨酸修饰玻碳电极上的电化学行为,建立了循环伏安法测定痕量多巴胺的新方法。实验结果表明,在pH 6.0的磷酸盐缓冲溶液中,多巴胺在聚L-白氨酸修饰玻碳电极上产生一对灵敏的氧化还原峰,峰电位分别为Epa=0.281V,Epc=0.170 V(相对Ag/AgCl电极)。峰电流与多巴胺的浓度在5.0×10-8~5.0×10-4mol/L的范围内有线性关系,检出限为5.0×10-9mol/L。对1.0×10-5mol/L多巴胺溶液平行测定9次,其相对标准偏差为4.0%。已用于针剂中多巴胺的测定。     

Determination of nitrite in animal feed by spectrophotometry or potentiometry with a nitrite-selective electrode

A method is presented for the extraction and quantitation of nitrite in animal feed. The extracting solution consists of ammonium sulfate at pH 8.5. The recovery of nitrite usually exceeds 90%. Nitrite is quantified with a nitrite-selective electrode or by a modified Griess reaction. The effects of extraction time on recovery are compared for acidic and alkaline extracting solutions.     

Determination of the hydrothermal degradation products of D-(U-14C) glucose and D-(U-14C) fructose by TLC

The hydrothermal degradation was examined using D-(U-¹⁴C) glucose and D-(U-¹⁴C) fructose. By thin layer chromatography with methylene chloride, tetrahydrofuran (THF), acetic acid −60∶20∶20 as a mobile phase it was, possible to separate and identify the carbohydrates and their reaction products, glyceraldehyde, dihydroxyacetone, methylglyoxal, glycolaldehyde, 5-hydroxymethylfurfural and furfural. Up to 99% of the initial activity was determined by scintillation counting of the TL-chromatograms. A reaction scheme for the hydrothermal degradation of glucose and fructose was obtained from these results.     

Analysis of solids by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS)—I. matching with a glass matrix

The possibility of quantitative elemental analysis of solids by laser ablation - inductively coupled plasma - mass spectrometry (LA-ICP-MS) has been investigated. The solids were mixed with a flux and fused to a glass bead so that a similar matrix composition would be obtained for the different samples (matrix matching), and an internal standard could be added. Strontium, present in the flux materials, was found to be suitable as the internal standard. Two major problems were experienced in the analysis: memory effects and interference from polyatomic ions. The memory effects were probably due to deposits of particles in the transfer tubes between the laser ablation cell and the ICP torch. At masses below 80 m/z, strong interferences from polyatomic ions caused serious problems in the quantification and, for elements studied in that mass region, detection limits were poor. The technique was further applied more specifically to the determination of rare earth elements in geological materials, for which detection limits varied from 0.02 to 3 mg/kg. Quantitative analysis, independent of the kind of sample material, proved possible.     

Titration of thiosemicarbazones with Cu(II) and vice versa by use of a copper selective electrode in acetone-water mixture: Determination of the conditional formation constants of the cupric thiosemicarbazonates

The titration technique of seven thiosemicarbazones by complexation with cupric ion and with the help of a copper selective electrode has been carried out. The conditional formation constants for these chelates are determined by the Ringbom and Harju method.     

Determination of mercury(II) using a modified electrode with zeolite

Summary Chemically modified carbon paste electrodes are prepared by incorporating appropriate quantities of a zeolite directly into the paste mixture. Trace levels of mercury(II) can be preconcentrated on these electrodes. Cyclic voltammetry is used to quantify the accumulated ions. The response is characterized with respect to preconcentration, pH, and other variables. The procedure exhibits good linearity for 0.11 g/ml–2.2 g/ml mercury(II) ions and the peak current varies linearly with preconcentration time between 1 and 6 min for the conditions used.

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Bestimmung von Quecksilber(II) mit einer Zeolith-modifizierten Elektrode

     

Simultaneous determination of l(+)- and d(−)-lactic acid by use of immobilized enzymes in a flow-injection system

The system comprises l(+)- and d(?)-lactate dehydrogenase reactors in parallel and a diaphorase electrode. Separate peaks are obtained for l(+)- and d(?)-lactic acid. The peak current is linearly related to the concentration of both isomers in the range 1 × 10^?5?2 × 10^?3 M.     

Determination of the (+)- and (-)-enantiomers of pirprofen in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed to determine the (+)- and (-)-enantiomers of pirprofen, an anti-inflammatory drug. After addition of an internal standard, the plasma sample was brought onto a glass column pre-packed with silica and eluted with dichloromethane. The extracts were derivatized with 1,1'-carbonyldiimidazole and R (+)-1-methylbenzylamine to form the two diastereomeric amides. The diastereoisomers were separated on a chiral column by HPLC with ultraviolet detection at 272 nm using n-hexane-dichloromethane (64:36, v/v) as the mobile phase. The limit of quantitation was 0.992 mumol/l (0.25 microgram/ml) for each enantiomer.     

Determination of absolute configuration of a metabolite (−)-hydroxyhexamide from acetohexamide, syntheses of (−)- and (+)-hydroxyhexamides and (−)- and (+)-acetoxyhexamides

Enantioselective acetylation of (±)-4-(1-hydroxyethyl)benzenesulfonamide 6 with ‘Acylase I’ (No. A 2156) from Aspergillus melleus in the presence of vinyl acetate gave (R)-4-(1-acetoxyethyl)benzenesulfonamide 7 (98% ee) and (S)-6 (98% ee). Both (S)-6 and (R)-7 were individually converted to the (S)-hydroxyhexamide 2 (>99% ee) and (R)-hydroxyhexamide 2 (>99% ee), respectively. The absolute configuration of a metabolite (−)-hydroxyhexamide 2 from acetohexamide 1 was found to be S based on unequivocal chemical methods including X-ray analysis.     

General approach for the synthesis of 12-methoxy-substituted sarpagine indole alkaloids including (-)-12-methoxy-N(b)-methylvoachalotine, (+)-12-methoxy-N(a)-methylvellosimine, (+)-12-methoxyaffinisine, and (-)-fuchsiaefoline

[structures: see text] The enantiospecific synthesis of 7-methoxy-D-tryptophan ethyl ester was completed by combination of the Larock heteroannulation process with a Sch?llkopf-based chiral auxiliary in good yield. This ester was then employed in the first regiospecific, stereospecific total synthesis of (+)-12-methoxy-N(a)-methylvellosimine, (+)-12-methoxyaffinisine, (-)-fuchsiaefoline, and 12-methoxy-N(b)-methylvoachalotine in excellent overall yield. The asymmetric Pictet-Spengler reaction and enolate-driven palladium-catalyzed cross-coupling processes served as key steps. The quaternary center at C16 of 12-methoxy-N(b)-methylvoachalotine was established via the Tollens reaction between (+)-12-methoxy-N(a)-methylvellosimine and formaldehyde to form diol 17. The two prochiral primary alcohols in diol 17 were differentiated by the oxidative cyclization(DDQ) of the hydroxyl group at the axial position of 17 with the benzylic postion at [C6] to form a cyclic ether [C6-O17]. After oxidative formation of the alpha-ester at C16, the ether bond was reductively cleaved with TFA/Et3SiH in high yield. The DDQ-mediated oxidative cyclization and TFA/Et3SiH reductive cleavage served as protection/deprotection steps in order to provide a versatile entry into the voachalotine alkaloids.     

Total syntheses of (Sp)-(+)- and (Rp)-(-)-spiniferin-1, a pair of unusual natural products with planar chirality

(S(p))-(+)-Spiniferin-1 and (R(p))-(-)-spiniferin-1, a pair of unusual marine natural products with planar chirality, were firstly synthesized via a polyfluoroalkanosulfonyl fluoride induced homoallylic carbocation rearrangement reaction. The chiral resolution and palladium-catalyzed β-H elimination of allylic alcohol derivatives were considered as the key steps of these divergent syntheses.     

Determination of Rh(III) by stripping voltammetry on a graphite electrode modified with lead

Journal of Solid State Electrochemistry - The process of electrooxidation of a lead-rhodium binary deposit on a graphite electrode has been studied. The anodic voltammetric curves show the peak of...     

Determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with sepiolite

Summary A method is described for the determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with 10% (w/w) sepiolite. Preconcentration was carried out under open circuit conditions in 0.01 mol/l acetic acid/potassium acetate medium at pH 5.3 over 10 min, recording the voltammogram in 0.01 mol/l of KH₂PO₄/K₃PO₄ at pH 12. This led to the appearance of a peak at –1.32 V against SCE at 40 mVs^–1 and a pulse amplitude of 100 mV. Under these conditions determination limits of 45 ng ml^–1 were achieved. The method was applied to the determination of tetramethrin in soil and water samples.

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Bestimmung von Tetramethrin (Neo-Pynamin) durch Differential-Puls-Voltammetrie unter Verwendung einer mit Sepiolit modifizierten Kohlepaste-Elektrode