Current Analytical Chemistry - Volume 6, Issue 4, 2010

Thermal oxidative degradation of fresh and aged cellulose samples of wood or paper were studied using thermogravimetry (TG), first-order derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) under a forced air flow up to 800°C. TG and DTG data were processed according to three non isothermal kinetic methods - the Arrhenius differential, Satava's integral and lastly Wyden-Widmann's method - to calculate the activation energy Ea of the oxidative degradation process of the cellulose samples investigated. The trends of the Ea values, measured as a function of sample age (whether natural or artificially induced) were discussed, also taking into account what was reported in literature concerning the degradation process of paper using different instrumental techniques, in order to assess their potential for obtaining archaeometric curves. Although the trend shows an inversion in the direction among non aged cellulose sample and samples artificially aged the results obtained may be deemed encouraging.

A stability-indicating liquid chromatographic (LC) method was developed and validated for quantitative determination of gemifloxacin mesylate (GFM) in coated tablets. The procedure was validated by specificity, linearity, accuracy, precision and robustness. Experimental design was used during validation to determinate method robustness and system suitability limits. The chromatographic method employed the Agilent Eclipse® XDB RP-18 (150 x 4.6 mm; 5 μm) with a mobile phase consisting of 0.3%triethylamine (pH 3.0) and acetonitrile (80:20, v/v). GFM (drug and drug product) solutions were exposed to direct UV-A and UV-C radiation, alkaline and acid hydrolysis, thermal stress and an oxidation effect by hydrogen peroxide to evaluate method stability-indication, and peak purity tools were utilized to verify peak purity. There was no interference of the excipients and degradation products in the determination of the active pharmaceutical ingredient. The method showed good recovery and precision (intra- and inter-day), and the response was linear over a range from 5.0 to 40.0 μg mL-1. The GFM photodegradation kinetics in methanol showed a first order process, with a degradation rate constant (k) of 0.0352 min-1 and a t90%of 3.01 min. The results confirm that the proposed stabilityindicating method can be used for routine analysis for quantitative determination of GFM in coated tablets. The results demonstrated the robustness of the analytical method and the worst robustness results were utilized for the determination of system suitability limits.

Bread is consumed worldwide by man, thus contributing to the regular ingestion of certain inorganic species such as chloride. It controls the blood pressure if associated to a sodium intake and may increase the incidence of stomach ulcer. Its routine control should thus be established by means of quick and low cost procedures. This work reports a double- channel flow injection analysis (FIA) system with a new chloride sensor for the analysis of bread. All solutions are prepared in water and necessary ionic strength adjustments are made on-line. The body of the indicating electrode is made from a silver needle of 0.8 mm i.d. with an external layer of silver chloride. These devices were constructed with different lengths. Electrodes of 1.0 to 3.0 cm presented better analytical performance. The calibration curves under optimum conditions displayed Nernstian behaviour, with average slopes of 56 mV decade-1, with sampling rates of 60 samples h-1. The method was applied to analyze several kinds of bread, namely pao de trigo, pao integral, pao de centeio, pao de mistura, broa de milho, pao sem sal, pao meio sal, pao-de-leite, and pao de agua. The accuracy and precision of the potentiometric method were ascertained by comparison to a spectrophotometric method of continuous segmented flow. These methods were validated against ion-chromatography procedures.

This paper reports the sequential voltammetric determination of Hg(II) and Cu(II) at the gold electrode (GE), and of Cu(II), Pb(II), Cd(II), Zn(II) at the hanging mercury drop electrode (HMDE) by differential pulse anodic stripping voltammetry (DPASV). Determination was performed in algae, potential environmental bio-monitor matrices, using 0.1 M HClO4 as supporting electrolyte. The sample digestion was also performed using a concentrated HCl-HNO3-H2SO4 acidic attack mixture. The analytical procedure was validated by the analysis of standard reference materials: Lagarosiphon Major (Aquatic Plant) BCR-CRM 060, Ulva Lactuca BCR-CRM 279 and Platihypnidium Riparioides BCR-CRM 061. For all elements in the certified matrices, in terms of repeatability, expressed as relative standard deviation (sr), precision was on order of 3-5%. In all cases, accuracy, expressed as relative error (e) was less than 6%, while the detection limits expressed in μg/g, dry weight, were in the 0.031-0.085 range. The analytical procedure was transferred and applied to algae, species Ulva Rigida and Gracilaria Rhodophita, sampled in two lagoon ecosystems connected to the Adriatic Sea (Italy): the Goro Bay, located at the mouth of the Po River, and the lagoon ecosystem located in proximity to Ravenna. To better validate the proposed method, a critical comparison with spectroscopic measurements is also discussed.

Ceftazidime (CFT) is a third-generation cephalosporin antibiotic. Like other third-generation cephalosporins, it has broad spectrum activity against Gram-positive and Gram-negative bacteria. In this study, the copper(II) complex of CFT has been synthesized. This prepeared complex was characterized by physicochemical and spectroscopic methods. Its UV-Vis, IR and mass spectra suggest that CFT potentially acts as a bi-dentate ligand. The electrochemical behavior of this synthesized complex was studied over glassy carbon electrode in various buffer solutions using cyclic, linear sweep, differential pulse (DP) and square wave (SW) voltammetric techniques. CFT enrichment is observed over Cu(II) complex. The peak current and peak potential of the complex depend on pH, initial potential, and scan rate. DP and SW voltammetric techniques were used for the determination of CFT-Cu(II) complex. For solid synthesis complex, the linear response was within 1x10-6 - 1x10-4 M with a detection limit on one decimal point: 2.36x10-7 for DPV and 1.60x10-7 M for SWV techniques in Britton Robinson (BR) buffer at pH 8. All necessary validation parameters were investigated as detailed in all media. The complex and CFT have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Pseudomonas aeruginosa, Kluvyeromyces fragilis, Saccharomyces cerevisiae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Bacillus megaterium, Candida albicans, Mycobacterium smegmatis, Bacillus cereus, Enterococcus cloacae and Micrococcus leteus. The complex was found to be more potent against two bacterial species than the uncomplexed CFT.

A new, rapid and simple procedure based on dispersive liquid-liquid microextraction (DLLME) of the Cr(VI) chelate with ammonium pyrrolidine dithiocarbamate (APDC) and subsequent ICP-MS analysis of the extracts by using dried-droplet laser ablation (LA) sample introduction was developed for the determination of ultratrace amounts of Cr(VI). DLLME was performed using 1 mL of methanol containing 50 μL of CCl4 as extraction mixture. Several factors influencing the DLLME performance of Cr(VI), such as sample pH, concentration of APDC and effect of potential interferents were established. Dried microdroplets (7 μL) of the obtained extracts were ablated from a polystyrene substrate and quantitated by ICP-MS. External calibration was used in combination with platinum (195Pt) as an internal standard. No matrix-matched standards are required to perform quantitative analysis. Proposed methodology yields sufficiently low detection limits (0.11 and 0.31 μg L-1 for 52Cr and 53Cr, respectively) with precision between 4 and 8%. The method was applied to determine Cr(VI) in tap and river samples. The spike recoveries showed acceptable performance of the method, with all of the recoveries within 7% of the nominal spike values.

Cefaclor (CEF), a second generation cephalosporin antibiotic, possesses various donor sites for interaction with transition metal (II) ions such as Cu(II), Co(II) and Ni(II) to form complexes of the type [M(CEF)(H2O)Cl], with a molar ratio of metal:ligand (M:L) of 1:1. These complexes were prepared and characterized by physicochemical and spectroscopic methods. Their UV-Vis, IR and mass spectra suggest that CEF potentially acts as a bi-dentate ligand. The electrochemical behavior of these synthesized and in solution complexes is studied over glassy carbon electrode in various buffer solutions using cyclic, linear sweep, differential pulse (DP) and square wave (SW) voltammetric techniques. CEF enrichment is observed over Cu(II) complex. The peak current and peak potential of the complex depend on pH, initial potential, and scan rate. DP and SW voltammetric techniques were used for the determination of CEF-Cu(II) complex. For solid synthesis complex, the linear response was within 1x10-6-3x10-5 M with a detection limit on one decimal point: 2.26x10-7 for DPV and 2.30x10-7 M for SWV techniques in acetate buffer at pH 4.70. The repeatability of the methods was within 0.82-0.78% for peak potentials and 1.16-0.71% for peak currents. All necessary validation parameters were investigated as detailed in all media. The complexes have been screened for antibacterial activity and results were compared with the activity of the uncomplexed antibiotic against Pseudomonas aeruginosa, Kluvyeromyces fragilis, Saccharomyces cerevisiae, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Bacillus megaterium, Candida albicans, Mycobacterium smegmatis, Bacillus cereus, Enterococcus cloacae and Micrococcus leteus. The copper complex was found to be more potent against two bacterial species than the uncomplexed CEF.

A sensitive and simple Gas Chromatographic-Mass Spectrometric method was developed and validated for the determination of captopril in human plasma. Thiosalicylic acid was used as an internal standard, and plasma extraction was performed by solid phase extraction. The limit of quantification was 0.5 ng/mL with signal to noise ratio greater than 5. The calibration curve was linear from 1 to 160 ng/mL with r2 greater than 0.99. The coefficient of variation for within and between assay imprecision of the standards and for the limit of quantification were ≤ 10 % and ≤ 7 %, respectively. The percentage of inaccuracy for within- and between-assay including lower and upper limits of quantitation were ≤ 8 % and ≤ 6 %, respectively. The absolute recovery of captopril and thiosalicylic acid in plasma were greater than 98 % and 99 %, respectively. The high sensitivity and accuracy of this method allowed us to measure low concentrations of captopril in plasma for bioequivalence studies in healthy subjects.

In the present study, we reported the syntheses and investigation of the modes of binding to DNA and serum albumins of the two ethidium derivatives containing ethyl and methyl chloroformate of both amines at 3-and 8- positions. The interactions of calf thymus DNA (ct-DNA) and serum albumins (BSA and HSA) with the two derivatives, E4 and E5, were investigated using fluorescence quenching method and UV-visible absorption spectra. The obtained data suggest that used derivatives can interact strongly with DNA and serum albumins; there are the formation of derivative-DNA and serum albumin complexes and hydrophobic interactions as the predominant intermolecular forces in stabilizing for each complex. The Stern-Volmer quenching constants, binding constants, binding sites and the corresponding thermodynamic parameters ΔH, ΔS and ΔG were calculated at different temperatures. The results of absorption, ionic strength and iodide ion quenching suggested that the interaction mode of E4 and E5 with DNA was groove binding.