Flow-injection chemiluminescence determination of fluoroquinolones by enhancement of weak chemiluminescence from peroxynitrous acid

A flow-injection chemiluminescence (CL) method is described for the determination of fluoroquinolones including ciprofloxacin, norfloxacin and ofloxacin. The method is based on the enhancement by these compounds of the weak CL from peroxynitrous acid. The linear ranges are 1.0×10⁻⁷ to 1.0×10⁻⁵ mol l⁻¹ for ciprofloxacin and norfloxacin, and 3.0×10⁻⁷ to 3.0×10⁻⁵ mol l⁻¹ for ofloxacin, respectively. The detection limits (S/N=3) are 4.5×10⁻⁸ mol l⁻¹ ciprofloxacin, 5.9×10⁻⁸ mol l⁻¹ norfloxacin and 1.1×10⁻⁷ mol l⁻¹ ofloxacin, respectively. The proposed method was applied to the determination of fluoroquinolones in pharmaceutical preparations.     

Explorative data analysis of two-dimensional electrophoresis gels

Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots on the gels for further investigation. The explorative approach in analysis of 2-D gels makes it possible, in a fast and convenient way, to screen many gels in order to determine the protein patterns that form clusters and could be selected for further examination.     

Evaluation of different mediator-modified screen-printed electrodes used in a flow system as amperometric sensors for NADH

This work presents a comparative study between two different methods for the preparation of mediator-modified screen-printed electrodes, to be used as detectors in a reliable flow injection system for the determination of the nicotinamide adenine dinucleotide (NADH) coenzyme. The best strategy was selected for the final development of compact biosensors based on dehydrogenase enzymes. For the first immobilisation strategy, different redox mediators were electropolymerised onto the SPE surface. The second immobilisation strategy was carried out using polysulfone–graphite composites, which were deposited by screen-printing technology onto the screen-printed electrode (SPE) surface. Both methods achieved an effective and reliable incorporation of redox mediators to the SPE configuration. Finally, a flow system for ammonium determination was developed using a glutamate dehydrogenase (GlDH)-Meldola's Blue (MB)-polysulfone-composite film-based biosensor.

The stability of the redox mediators inside the composite films as well as the negligible fouling effect observed on the electrode surface improve the repeatability and reproducibility of the sensors, important features for continuous analysis in flow systems. Furthermore, the optimised bio/sensors, incorporated in a flow injection system, showed good sensitivities and short response times. Such a good analytical performance together with the simple and fast sensor construction are interesting characteristics to consider the polysulfone-composite films as attractive electrochemical transducer materials for the development of new dehydrogenase-based SPEs.     

Non-destructive in situ determination of pigments in 15th century wall paintings by Raman microscopy

Raman microscopy has been applied to the study of 15th century wall paintings in a chapel of St. Orso Priory palace (Aosta, Italy) in view of their restoration. The use of a transportable instrument has made it possible to work non-destructively in situ without sampling. The main inorganic pigments used by the unknown artist, namely mercury sulphide, azurite, white lead, red and yellow ochre, carbon black and lead tin yellow type I have been identified, and the presence of organic substances and of some decay products (calcium sulphate and oxalate) has been observed.     

Flow analysis-hydride generation-Fourier transform infrared spectrometric determination of antimony in pharmaceuticals

In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K₂S₂O₈ and KI, respectively; prior to the stibine generation. The gaseous SbH₃ is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm⁻¹ band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l⁻¹, limit of detection (3σ)=0.9 mg l⁻¹, limit of quantification (10σ)=3 mg Sb l⁻¹, precision (R.S.D.) less than 1% and sample frequency=28 h⁻¹), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis.     

Synthesis of new macrocyclic aminomethylphosphines based on 4,4"-diaminodiphenylmethane and its derivatives

The reaction of bis(hydroxymethyl)phenylphosphine with 4,4"-diaminodiphenylmethane in DMF afforded 1,1",5,5"-bis[methylenedi(p-phenylene)]di(3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) (1) whose structure was established by X-ray diffraction analysis. Sulfurization and oxidation of macrocyclic tetraphosphine 1 gave rise to products 2 and 3, respectively, compound 3 being obtained as a stable hexahydrate. The reaction of bis(hydroxymethyl)phenylphosphine with bis(4-N-methylaminophenyl)methane in DMF followed by sulfurization yielded monocyclic bis{methylenedi[p-phenylene(N-methyl)aminomethyl]}di(P-phenyl)phosphine sulfide (4).     

Evaluation of epifluorescence image analysis of biofilm growth on stainless steel surfaces

Biofilm growth of Bacillus subtilis, Pseudomonas fragi, Pediococcus inopinatus and Listeria monocytogenes was studied on stainless steel surfaces at room and low temperatures to evaluate the results of traditional hygiene measures. The results were compared with those of image analysis of stainless steel surfaces in an epifluorescence microscope. Statistical analyses were carried out to determine the variations between the conventional cultivation swab method, the glycocalyx amount obtained using swabbing, and the values of the areas of the biofilm, slime and cells. As a general rule, old biofilms showed total counts at approximately the same levels as the young biofilm. The results showed that temperature affected the results for all strains except B. subtilis. The strains of Pe. inopinatus and Ps. fragi showed increased attachment at 6°C and L. monocytogenes at 25°C. The biofilm slime was more easily detached than the cells. The results indicated that the traditional swab method is not reliable for the measurement of biofilm formation on surfaces.     

New heteroorganic betaines containing the (+)E15—C—E14—X(–) and (+)E15—C—E14(–) structural fragments (E15 = P,As; E14 = Si,Ge, Sn; X = C,S, O,NR)

The review surveys the data on the reactions of phosphorus and arsenic ylides with compounds containing E=X bonds (E = C, Si, Ge, or Sn; X = C or S), cyclic oligomers (R₂ES)_n (n = 2 or 3), and heavier analogs of carbenes. These reactions give rise to two new classes of heteroorganic betaines containing the ⁽⁺⁾E¹⁵—C—E¹⁴—X^(–) (I) and ⁽⁺⁾E¹⁵—C—E^14(–) (II) (E¹⁵ = P or As; E¹⁴ = Si, Ge, or Sn; X = C or S) structural fragments. Procedures for the synthesis of these compounds, their reactivities, the X-ray diffraction structures, and the electronic structures established by high-level quantum-chemical calculations are considered in detail. The carbon analogs of betaines of type I, viz., compounds bearing the ⁽⁺⁾P—C—C—X^(–) fragment (III), are also discussed. The latter were long considered as possible intermediates in the reactions of compounds containing the polar C=X bond (X = C, O, S, NR, etc.) with phosphorus ylides (classical Wittig and Corey—Chaykovsky reactions and related processes).     

Microdialysis sampling and high-performance liquid chromatography with chemiluminescence detection for in-vivo on-line determination and study of the pharmacokinetics of levodopa in blood

A simple, reliable, and reproducible method for in-vivo on-line separation and determination of levodopa has been based on microdialysis then high-performance liquid chromatography with chemiluminescence detection. The perfusate is perfused at a flow rate of 5 L min^–1. The concentration of levodopa in the dialysate is determined on line with a chemiluminescence system. The dialysate sample volume is approximately 20 L. The response of the system is linearly related to the concentration of levodopa in the range 1×10^–8 to 1×10^–6 g mL^–1 (r²=0.9995) with a detection limit (3) of 3×10^–9 g mL^–1 and sample throughput of 12 h^–1; RSD is 2.8% (n=11). The method has been successfully used to study the pharmacokinetics of levodopa in vivo; the values of the pharmacokinetics parameters C_max, AUC_0–t and T_max were 16.60, 20.92 ng mL^–1, and 90 min, respectively.