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Low Limits (low + limit)
Selected AbstractsA Simple and Innovative Route to Prepare a Novel Carbon Nanotube/Prussian Blue Electrode and its Utilization as a Highly Sensitive H2O2 Amperometric SensorADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Edson Nossol Abstract The utilization of iron-based species (mainly metallic iron, hematite and magnetite) encapsulated into multi-walled carbon nanotubes (CNTs) as reactants in an electrochemical synthesis is reported for the first time in this work. Prussian blue (PB) is electrosynthesized in a heterogeneous reaction between ferricyanide ions in aqueous solution and the iron-species encapsulated into CNTs, resulting in novel CNT/PB paste electrodes. This innovative preparation route produces an intimate contact between the PB and the CNTs, which improves the stability and redox properties of PB. The PB formation and the chemical interaction between the PB and the CNTs are confirmed by Raman spectroscopy. The electrode is employed as a hydrogen peroxide amperometric sensor, resulting in a very low limit of detection (1.94,×,10,8,mol L,1) and very high sensitivity (15.3,A cm,2M,1). [source] Quantification of fudosteine in human plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry employing precolumn derivatization with 9-fluorenylmethyl chloroformateJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2006Fengguo Xu Abstract This paper describes a novel method for the sensitive and selective determination of fudosteine in human plasma. The method involves a derivatization step with 9-fluorenylmethyl chloroformate (FMOC-Cl) in borate buffer and detection based on high-performance liquid chromatography-electrospray ionization mass spectrometry (LC/ESI/MS). After acetonitrile-induced protein precipitation of plasma samples, fudosteine was derivatized with FMOC-Cl, then extracted by ethyl acetate, evaporated, reconstituted and injected using an LC/ESI/MS instrument. Separation was achieved using an ODS column and isocratic elution. Excellent linearity was obtained for the entire calibration range from 0.05 to 20 µg/ml. Validation assays of the lower limit of quantification (LLOQ) as well as for the intra- and inter-batch precision and accuracy met the international acceptance criteria for bioanalytical method validation. Using the developed analytical method, fudosteine could be detected for the first time in human plasma with a low limit of detection (LLOD) of 0.03 µg/ml. The proposed method has been successfully applied to study the pharmacokinetics of fudosteine in healthy Chinese volunteers after single and multiple oral administration. Copyright © 2006 John Wiley & Sons, Ltd. [source] Mixed Aza-Thioether Crowns Containing a 1,10-Phenanthroline Sub-Unit as Neutral Ionophores for Silver IonELECTROANALYSIS, Issue 24 2002Mojtaba Shamsipur Abstract Three different recently synthesized aza-thioether crowns containing a 1,10-phenanthroline sub-unit (L1,L3) and a corresponding acyclic ligand (L4) were studied to characterize their abilities as silver ion ionophores in PVC-membrane electrodes. Novel conventional silver-selective electrodes with internal reference solution (CONISE) and coated graphite-solid contact electrodes (SCISE) were prepared based on one of the 15-membered crowns containing two donating S atoms and two phenanthroline-N atoms (L1). The electrodes reveal a Nernstian behavior over wide Ag+ ion concentration ranges (1.0×10,5,1.0×10,1,M for CONISE and 5.0×10,8,4.0×10,2,M for SCISE) and very low limits of detection (8.0×10,6,M for CONISE and 3.0×10,8,M for SCISE). The potentiometric response is independent from pH of the solution in the pH range 3.0,8.0. The electrodes manifest advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations. The electrodes can be used for at least 2 months (for CONISE) and 4 months for (SCISE) without any appreciable divergence in potentials. The electrodes were used as an indicator electrode in the potentiometric titration of Ag+ ion and in the determination of silver in photographic emulsions and in radiographic and photographic films. [source] Roxarsone and transformation products in chicken manure: Determination by capillary electrophoresis-inductively coupled plasma-mass spectrometryELECTROPHORESIS, Issue 7-8 2005Charlita G. Rosal Abstract The determination of the animal feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid) and six of its possible transformation products (arsenite, arsenate, monomethylarsonate, dimethylarsinate, 3-amino-4-hydroxyphenylarsonic acid, and 4-hydroxyphenylarsonic acid) in chicken manure was investigated using capillary electrophoresis-inductively coupled plasma-mass spectrometry (CE-ICP-MS). Initial method development was conducted using ultraviolet (UV) detection for ruggedness and time efficiency. Separation of these seven arsenic species was effected using a 20,mM phosphate buffer at pH 5.7. The CE-ICP-MS limits of detection in terms of As for each of the species was in the low µg·L,1 range, corresponding to absolute detection limits in the range 20,70,fg As (based on a 23,nL injection). Overall, the method developed in this study provides high selectivity and low limits of detection (1,3,µg·L,1 or low-ppb, based on As), uses small sample volume (low nL), and produces minimal wastes. [source] Fiber introduction mass spectrometry: determination of pesticides in herbal infusions using a novel sol,gel PDMS/PVA fiber for solid-phase microextractionJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2007Rogério Cesar da Silva Abstract An application of the direct coupling of solid-phase microextraction (SPME) with mass spectrometry (MS), a technique known as fiber introduction mass spectrometry (FIMS), is described to determine organochlorine (OCP) and organophosphorus (OPP) pesticides in herbal infusions of Passiflora L. A new fiber coated with a composite of poly(dimethylsiloxane) and poly(vinyl alcohol) (PDMS/PVA) was used. Sensitive, selective, simple and simultaneous quantification of several OCP and OPP was achieved by monitoring diagnostic fragment ions of m/z 266 (chlorothalonil), m/z 195 (,-endosulfan), m/z 278 (fenthion), m/z 263 (methyl parathion) and m/z 173 (malathion). Simple headspace SPME extraction (25 min) and fast FIMS detection (less than 40 s) of OCP and OPP from a highly complex herbal matrix provided good linearity with correlation coefficients of 0.991,0.999 for concentrations ranging from 10 to 140 ng ml,1 of each compound. Good accuracy (80 to 110%), precision (0.6,14.9%) and low limits of detection (0.3,3.9 ng ml,1) were also obtained. Even after 400 desorption cycles inside the ionization source of the mass spectrometer, no visible degradation of the novel PDMS/PVA fiber was detected, confirming its suitability for FIMS. Fast (ca 20 s) pesticide desorption occurs for the PDMS/PVA fiber owing to the small thickness of the film and its reduced water sorption. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||