Showing papers in "Analytical and Bioanalytical Chemistry in 2002"

A review of modern sample-preparation techniques for the extraction and analysis of medicinal plants.

Abstract: Sample preparation is the crucial first step in the analysis of herbs. In recent years there has been increasing interest worldwide in the use of alternative/herbal medicine for the prevention and treatment of various illnesses. Currently, however, quality-related problems (lack of consistency, safety, and efficacy) seem to be overshadowing the potential genuine health benefits of various herbal products. Thus, the development of "modern" sample-preparation techniques with significant advantages over conventional methods for the extraction and analysis of medicinal plants is likely to play an important role in the overall effort of ensuring and providing high-quality herbal products to consumers worldwide. In this article, recent developments and applications of modern sample-preparation techniques for the extraction, clean-up, and concentration of analytes from medicinal plants or herbal materials are reviewed. These modern techniques include solid-phase microextraction, supercritical-fluid extraction, pressurized-liquid extraction, microwave-assisted extraction, solid-phase extraction, and surfactant-mediated extraction.

Quick measurement of protein sulfhydryls with Ellman's reagent and with 4,4'-dithiodipyridine

Abstract: Since its introduction in 1959, Ellman's reagent (5,5′-dithio-bis(2-nitrobenzoic acid)) has been the favorite reagent for spectrophotometric measurement of protein sulfhydryls. Meanwhile however, evidence has accumulated that many protein sulfhydryls give an incomplete reaction with Ellman's reagent, even during prolonged assay times. In the present study, the kinetic problem was solved by including cystamine as a "mediator" between the protein sulfhydryl and Ellman's reagent, as previously applied in an enzymatic thiol assay [9]. As an alternative, 4,4′-dithiodipyridine (DTDP) was used in place of Ellman's reagent. Due to its small size, amphiphilic nature, and lack of charge, DTDP quickly reacts with poorly accessible protein sulfhydryls, without any catalysis by cystamine. The DTDP method and the Ellman/cystamine method were both optimized for maximal sensitivity, minimal sample consumption (detection limit 0.2 nmol mL–1, determination limit 0.6 nmol mL–1), and minimal assay time (5 min). In validation experiments, both methods gave identical results and the measured sulfhydryls/protein matched the expected values. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00216-002-1347-2.

Sorptive sample preparation – a review

Abstract: Most sample-enrichment procedures currently available rely on adsorption of the analytes of interest by a suitable adsorbent material. Although good performance can be obtained for many practical problems, in some cases the applicability of adsorptive sample preparation falls short, particularly for the enrichment of polar and/or high-molecular-weight compounds, especially in combination with thermal desorption. Because of the very strong retention of adsorbent materials, undesired effects such as incomplete desorption and artifact formation are observed. Polar solutes are easily adsorbed but readily undergo surface-catalyzed reactions and on desorption yield compounds different than those originally sampled. High-molecular-weight compounds cannot be desorbed because of extremely strong interactions with the adsorbent and their low volatility. To overcome some of these problems sample-preparation techniques based on polydimethylsiloxane sorption have been developed over the past 15 years. In contrast with adsorptive trapping, sorption is based on dissolution of the analytes in a liquid polymeric material. This is a much more inert means of solute retention which overcomes some of the limitations encountered when working with adsorbents. In this contribution, the basic principles of sorption, the different instrumentation used, and applications of the technique will be reviewed. The review covers the sorptive sample-preparation techniques, open-tubular trapping (OTT), solid-phase microextraction (SPME), gum-phase extraction (GPE), equilibrium gum-phase extraction (EGPE), and stir-bar-sorptive extraction (SBSE). Because of the nature of sorptive sample-preparation techniques, which perform particularly well in combination with thermal desorption, this review focuses strongly on gas chromatography as the means of chemical analysis.

Aptasensors – the future of biosensing?

Abstract: Aptamers are artificial nucleic acid ligands that can be generated against amino acids, drugs, proteins and other molecules. They are isolated from combinatorial libraries of synthetic nucleic acid by an iterative process of adsorption, recovery and reamplification. Aptamers, first reported in 1990, are attracting interest in the areas of therapeutics and diagnostics and offer themselves as ideal candidates for use as biocomponents in biosensors (aptasensors), possessing many advantages over state of the art affinity sensors. The properties of aptamers, their applicability to biosensor technology, current research and future prospects are addressed in this short review.

Small molecule analysis by MALDI mass spectrometry.

Abstract: This review focuses on the application of matrix assisted laser desorption/ionization (MALDI) mass spectrometry to the characterization of molecules in the low mass range (<1500 Da). Despite its reputation to the contrary, MALDI is a powerful technique to provide both qualitative and quantitative determination of low molecular weight compounds. Several approaches to minimize interference via sample preparation and matrix selection are discussed, as well as coupling of MALDI to liquid and planar chromatographic techniques to extend its range of applicability.

Fiber-optic biosensors--an overview.

Abstract: This article reviews progress and developments during the past five years in the field of optical fiber biosensors. Because of the expense and time constraints associated with modern laboratory analysis, there is a growing need for real-time, low-cost technology that can be used industrially, environmentally, and clinically, and to monitor food processing. Miniaturization, integrated systems, and multianalyte determination have become key aspects of sensor development and efforts in this direction will also be discussed, with some pointers to likely directions of future research in the area. The review will provide information about the analytical characteristics and applications of fiber-optic biosensors classified depending on the biorecognition element employed – enzymes, whole cells, antibodies, nucleic acids, and biomimetic polymers.

Automated sample preparation using in-tube solid-phase microextraction and its application – a review

Abstract: Sample preparation, such as extraction, concentration, and isolation of analytes, greatly influences their reliable and accurate analysis. In-tube solid-phase microextraction (SPME) is a new effective sample preparation technique using an open tubular fused-silica capillary column as an extraction device. Organic compounds in aqueous samples are directly extracted and concentrated into the stationary phase of capillary columns by repeated draw/eject cycles of sample solution, and they can be directly transferred to the liquid chromatographic column. In-tube SPME is an ideal sample preparation technique because it is fast to operate, easy to automate, solvent-free, and inexpensive. On-line in-tube SPME-performed continuous extraction, concentration, desorption, and injection using an autosampler, is usually used in combination with high performance liquid chromatography and liquid chromatography-mass spectrometry. This technique has successfully been applied to the determination of various compounds such as pesticides, drugs, environmental pollutants, and food contaminants. In this review, an overview of the development of in-tube SPME technique and its applications to environmental, clinical, forensic, and food analyses are described.

MEMS-based sample preparation for molecular diagnostics.

Abstract: Completion of the Human Genome Project is driving the rapid development of molecular diagnostics in the laboratory. To accelerate the penetration of genetic tests and other nucleic acid-based tests into clinical markets, simple, compact, automatic sample-preparation systems for molecular diagnostics must be developed. Microelectromechanical systems (MEMS) is a promising approach for the development of automated sample preparation for the clinical laboratory or point-of-care setting. This review discusses MEMS-based components that could be applied to the different stages of the sample-preparation process such as cell separation, nucleic acid purification, and nucleic acid amplification. Examples of functional component integration are given. Issues discussed include partitioning of functions between the instrument and disposable unit, methods of propulsion of fluids and particles, vapor and liquid barriers, and sample size. Although further evaluation and development are needed to provide practical solutions to some of these issues, we conclude that MEMS-based components might contribute to some components in a sample-preparation system consisting of modular instruments and disposable units, but will not provide a generic or a totally integrated solution.

Adsorbent materials commonly used in air analysis for adsorptive enrichment and thermal desorption of volatile organic compounds.

Abstract: A review is given dealing with commonly used adsorbent materials in ambient air analysis of volatile organic compounds (VOCs). The adsorbents covered in the paper are selected in consideration of their compatibility with thermal desorption. Initially, we discuss the requirements that an adsorbent should fulfill, and useful parameters for the selection and evaluation of an appropriate material. Then, the most important materials are presented considering their properties, advantages, and drawbacks. A few applications are given, but a complete review of sampling techniques and applications dealing with adsorptive enrichment and thermal desorption is beyond the scope of this paper.

Electronic tongues and their analytical application

Abstract: Electronic tongues for liquid analysis, based on the organizational principles of biological sensory systems, developed rapidly during the last decade. A brief historical overview of the research and development in the field of electronic tongue systems is presented. Current achievements of scientific groups working in this field are outlined and critically reviewed. The performance of electronic tongues in quantitative analysis and in classification of multicomponent media is considered. The exciting possibility of establishing a correlation between the output from an electronic tongue and human sensory assessment of food flavour, thereby enabling quantification of taste and flavour, is described. Application areas of electronic tongue systems including foodstuffs, clinical, industrial, and environmental analysis are discussed in depth. Prospective research and development in the field of electronic tongues is discussed.

Speciation of heavy metals in environmental water by ion chromatography coupled to ICP–MS

Abstract: Biogenic (e.g. phytochelatins, porphyrins, DOM) as well as anthropogenic (e.g. NTA, EDTA, phosphonates) chelators affect the mobility and cycling of heavy metals in environmental waters. Since such chelators can form strongly bound anionic heavy metal complexes that are stable and highly mobile, anion-exchange chromatography coupled to ICP–MS was investigated. A narrow bore HPLC system was connected to a micro concentric nebuliser for in-line sample introduction. A new chromatographic procedure based on a synthetic hydrophilic quaternary ammonium anion exchanger in combination with nitrate as a strong eluent anion, and gradient elution, provided high separation selectivity and a large analytical window. Low detection limits (nmol L–1) were achieved by on-column matrix removal and sample preconcentration. This allowed the method to be successfully applied to different environmental research areas. In ecotoxicological studies of heavy metal effects on algae low concentrations of metal EDTA complexes were determined in nutrient solutions without interference from high (buffer) salt concentrations. In groundwater, infiltrated by a polluted river, mobile metal EDTA species were observed. In river water of different pollution levels beside CuEDTA other anionic Cu-complexes were found in nmol L–1 concentrations.

Metabolites from the biodegradation of pharmaceutical residues of ibuprofen in biofilm reactors and batch experiments

Abstract: The three metabolites hydroxyibuprofen (OH-Ibu), carboxyibuprofen (CA-Ibu), and carboxyhydratropic acid (CA-HA), also known from human metabolism of ibuprofen, could be identified in biodegradation experiments. Identification was based on EI mass spectra and comparison with literature data. Detection was performed by selective MS–MS measurements by GC–ion-trap MS and online methylation. Ibuprofen (Ibu), OH-Ibu, and CA-Ibu could be detected with a signal-to-noise ratio of 10:1 at a concentration of 2 nmol L–1, CA-HA at 0.5 nmol L–1. Degradation experiments in both biofilm reactors (BFR) and batch experiments with activated sludge (BAS) reveal OH-Ibu as the major metabolite under oxic conditions, and CA-HA under anoxic conditions. CA-Ibu was found under oxic and anoxic conditions almost only in the BAS. The metabolites together do not account for more than 10% of the initial concentration of Ibu.

Developments in ion mobility spectrometry-mass spectrometry.

Abstract: Ion mobility spectrometry (IMS) has been used for over 30 years as a sensitive detector of organic compounds. The following is a brief review of IMS and its principles with an emphasis on its usage when coupled to mass spectrometry. Since its inception, IMS has been interfaced with quadrupole, time-of-flight, and Fourier-transform ion cyclotron resonance mass spectrometry. These hybrid instruments have been employed for the analysis of a variety of target analytes, including biomolecules, explosives, chemical warfare degradation products, and illicit drugs.

Analytical utility of valence band X-ray photoelectron spectroscopy of iron and its oxides, with spectral interpretation by cluster and band structure calculations

Abstract: The valence band and core-level X-ray photoelectron spectroscopy (XPS) of iron and its oxides are reported, and the valence band spectra interpreted by various calculation models. The paper focuses upon the valence band region, which shows significant differences between the metal and the following oxidized iron species: FeO, Fe3O4, α-Fe2O3, γ-Fe2O3, α-FeOOH and γ-FeOOH. The core region is of little analytical value as a means of distinguishing between these species, but the valence band region shows significant differences. These differences are consistent with spectra predicted by cluster and band structure calculations. Cluster calculations are valuable as a means for interpreting the spectra of iron oxides with multiple iron sites and defect characteristics.

Environmetric modeling and interpretation of river water monitoring data.

Abstract: This environmetric study deals with modeling and interpretation of river water monitoring data from the basin of the Saale river and its tributaries the Ilm and the Unstrut. For a period of one year of observation between September 1993 and August 1994 a data set from twelve campaigns at twenty-nine sampling sites from the Saale river and six campaigns from the river Ilm at seven sampling sites and from river Unstrut at ten sampling sites was collected. Twenty-seven chemical and physicochemical properties were measured to estimate the water quality. The application of cluster analysis, principal components analysis, and apportioning modeling on absolute principal components scores revealed important information about the ecological status of the region of interest:identification of two separate patterns of pollution (upper and lower stream of the rivers);identification of six latent factors responsible for the data structure with different content for the two identified pollution patterns; anddetermination of the contribution of each latent factor (source of emission) to the formation of the total concentration of the chemical burden of the river water. As a result more objective ecological policy and decision making is possible.

Enzyme sensor array for the determination of biogenic amines in food samples.

Abstract: An enzyme sensor array for the simultaneous determination of the three biogenic amines (histamine, tyramine and putrescine) by pattern recognition using an artificial neural network and its application to different food samples is described. A combination of a monoamine oxidase, a tyramine oxidase and a diamine oxidase (with specific activities sufficient for rapid detection) are immobilised each on a separate screen-printed thick-film electrode via transglutaminase and glutaraldehyde to compare these cross-linking reagents with regard to their suitability. To calculate the amount of a specific biogenic amine, the raw data from multichannel software were transferred to a neural network. The sensor array takes 20 min to complete (excluding statistical data analysis) with only one extraction and subsequent neutralisation step required prior to sensor measurement. The lower detection limits with the enzyme sensor were 10 mg/kg for histamine and tyramine, and 5 mg/kg for putrescine with a linear range up to 200 mg/kg for histamine and tyramine and 100 mg/kg for putrescine. The application area of the enzyme sensor array was tested from fish to meat products, sauerkraut, beer, dairy products, wine and further fermented foods and compared with the data of conventional LC analyses (mean correlation coefficient: 0.854).

Stir bar sorptive extraction-thermal desorption-capillary GC-MS applied to biological fluids.

Abstract: A new sample preparation method, stir bar sorptive extraction (SBSE), has been evaluated for the enrichment of organic solutes from biological fluids such as urine and blood. In SBSE, a stir bar coated with a polydimethylsiloxane layer is stirred for a given time in the sample. After sampling the stir bar is placed in a thermal desorption unit coupled on-line to capillary gas chromatography-mass spectrometry (SBSE-TD-CGC-MS). The principle and operation of SBSE are presented. Total profiling and target compound analysis have been selected as applications to illustrate the performance of SBSE-TD-CGC-MS (MSD). It is demonstrated that a variety analytes ranging from biological markers (phenols, hormones, fatty acids) to artificial contaminants (recreational drugs, plasticizers) can be enriched with high sensitivity. For polar solutes, in-situ derivatization can enhance both recovery into the polydimethylsiloxane (PDMS) layer and chromatographic analysis. Two types of derivatization have been applied, derivatization with ethyl chloroformate and with acetic acid anhydride. Linearity, detectability, and repeatability are illustrated by the determination of 1-hydroxypyrene in a urine sample from a smoker.

Method optimization for the determination of carbonyl compounds in disinfected water by DNPH derivatization and LC–ESI–MS–MS

Abstract: A method has been developed for quantitative determination of carbonyl disinfection by-products (DBP) from aqueous samples by derivatization with 2,4-dinitrophenylhydrazine combined with high-performance liquid chromatography (HPLC) and electrospray ionization (ESI) tandem mass spectrometry (MS–MS). The effect of excess of derivatization reagent and derivatization time, the effect of buffer and dry-gas temperature in the ESI process, and the effect of focus potential and collision energy in MS measurement are shown. Major fragment ions for compound identification on the basis of collision-induced dissociation (CID) mass spectra (MS) are given, as are common fragments for screening analyses by MS experiments such as the use of precursor ion scans. Detection limits in the µg L–1 range could be achieved by selected ion monitoring measurements without sample preconcentration. Solid-phase extraction improved the sensitivity by a factor of 25 to 250. The applicability of the method is illustrated by DBP analyses of samples from outdoor swimming pools after chlorination. Several carbonyl compounds, e.g. aldehydes, ketones, hydroxybenzaldehyde, and dicarbonyl compounds were identified.

Capillary electrophoresis mass spectrometry and its application to the analysis of biological mixtures

Abstract: Capillary electrophoresis (CE) mass spectrometry (MS), with its ability to separate compounds present in extremely small volume samples rapidly, with high separation efficiency, and with compound identification capability based on molecular weight, is an extremely valuable analytical technique for the analysis of complex biological mixtures. The highest sensitivities and separation efficiencies are usually achieved by using narrow capillaries (5–50 µm i.d.) and by using sheathless CE-to-MS interfaces. The difficulties in CE-to-MS interfacing and the limited loadability of these narrow columns, however, have prevented CE-MS from becoming a widely used analytical technique. To remedy these limitations, several CE-MS interfacing techniques have recently been introduced. While electrospray ionization is the most commonly used ionization technique for interfacing CE-to-MS, matrix assisted laser desorption ionization has also been used, using both on-line and off-line techniques. Moreover, the high concentration detection limit of CE has been addressed by development of several sample concentration and sample focusing methods. In addition, a wide variety of techniques such as capillary zone electrophoresis, capillary isoelectric focusing, and on-column transient isotachophoresis have now been interfaced to MS. These advances have resulted in a rapid increase in the use of CE-MS in the analysis of complex biological mixtures. CE-MS has now been successfully applied to the analysis of a wide variety of compounds including amino acids, protein digests, protein mixtures, single cells, oligonucleotides, and various small molecules relevant to the pharmaceutical industry.

An international intercomparison exercise for the determination of purified microcystin-LR and microcystins in cyanobacterial field material.

Abstract: The comparability of current microcystin analysis methods has been evaluated in an international intercomparison exercise. The focus was on the analysis of microcystins by high-performance liquid chromatography coupled with ultraviolet or photodiode-array detection (HPLC–PDA/UV), currently the most widespread method for microcystin analysis, but the exercise was open for other methods such as enzyme-linked immunosorbent assay (ELISA), protein phosphatase inhibition assay (PPA) and high-performance liquid chromatography coupled with mass spectrometry (HPLC–MS).

Carbon paste electrodes modified with Bi(2)O(3) as sensors for the determination of Cd and Pb.

Abstract: Carbon paste electrodes bulk-modified with Bi2O3 were used for the determination of Cd(II) and Pb(II). The best composition was 1% (wt%) Bi2O3 in the paste. The measurements were made by differential pulse voltammetry in the potential range from –1.2 V to –0.3 V. The peak potential of the reoxidation of Cd is –0.85 V, and of Pb –0.60 V vs. SCE. The lowest concentration that could be determined was 5 µg L–1 of both metals (preconcentration time 240 s), the relative standard deviation was 3.5%–5.0% (four determinations). The correlation coefficient (r 2) of the calibration curves was 0.9966 (for Cd) and 0.9971 (for Pb). The Bi2O3-modified electrode could be used for the analysis of drinking water, mineral water and urine.

Mercury methylation in macrophytes, periphyton, and water – comparative studies with stable and radio-mercury additions

Abstract: Comparative tests of net mercury methylation potentials, with cultivated and macrophyte-associated periphyton and using stable (200HgCl2 and CH3 199HgCl) and labeled (203HgCl2) mercury, have been conducted in the Everglades nutrient removal area (Florida, USA) and in a tropical coastal Brazilian lake (RJ, Brazil). More methylmercury was formed by macrophyte-associated (up to 17% of added 203Hg(II)) than cultivated (up to 1.6%) periphyton and methylmercury formation was lower in periphyton exposed to light (0.2%). High methylation was also observed for samples incubated with stable mercury isotopes (1.5–7.7% of added 200Hg(II)), confirming the results obtained with labeled mercury. Simultaneous addition of 200HgCl2 and CH3 199HgCl indicated that CH3 199HgCl had no inhibitory effect on Hg methylation. The elevated methylation potentials observed in macrophytes, because of their root-associated periphyton, might contribute significantly to the high levels of methylmercury observed in Everglades biota. Comparative mercury methylation tests were also conducted in the water of a stratified temperate lake (Wisconsin, USA). Similar trends were observed for both stable and radioisotopes, with increasing mercury methylation along the depth profile. The highest levels (0.9% 203Hg(II) and 0.8% 200Hg(II)) were obtained below the oxic/anoxic boundary, where sulfide starts to increase, probably as a result of the intense activity of sulfate-reducing bacteria in the anoxic layer.

Modern trends in the speciation of selenium by hyphenated techniques

Abstract: The complexity of selenium speciation in the environment and in living organisms results in broad analytical challenges. The importance of the selective determination of the particular species of this element, to understand its metabolism and biological significance in clinical chemistry, biology, toxicology, and nutrition, calls for state-of-the-art analytical techniques. In this paper hyphenated techniques are evaluated with particular emphasis on interfaced separation with element-selective detection and identification of the selenium compounds detected.

Determination of xylanase, beta-glucanase, and cellulase activity.

Abstract: A simple, robust and highly reproducible method for the determination of xylanase, β-glucanase, and cellulase in commercial feed enzyme preparations is described. The method is based on measurement of reducing moieties released by the enzymes from arabinoxylan, β-glucan, or carboxymethylcellulose (CMC) and is independent of enzyme standards.

Comparison of reflectometric interference spectroscopy with other instruments for label-free optical detection.

Abstract: On the basis of kinetic measurements of biomolecular interactions, a reflectometric interference spectroscopy (RIfS) setup is compared with two commercial instruments. These instruments are based on evanescent wave techniques, surface plasmon resonance (SPR) (represented by BIAcore 2000) and resonant mirror (RM) technique (using IAsys plus). All methods allow a label-free and time-resolved optical detection of biomolecular interaction. These methods are mainly used in biomolecular interaction analysis (BIA). They provide practical techniques for quantifying equilibrium constants and rate constants over several orders of magnitude. The general parameters of the three detectors, namely baseline noise and drift as well as overall sensitivity and limits of detection were compared. The fluid handling and the related implications on the measurements have also been considered. The interaction between thrombine and thrombine inhibitor (TI) was investigated as a test system with the three different methods and the kinetic rate constants were determined and compared. For this TI was immobilized on the surface and binding of thrombine was monitored time-resolved. Determination of the kinetic rate constants could prove that the RIfS set-up is comparable with SPR using BIAcore 2000 and RM technique represented by IAsys plus.

Hyphenated techniques for the characterization and quantification of metallothionein isoforms

Abstract: Recent developments in the coupling of highly selective separation techniques such as capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) to element-specific and molecule-specific detectors, such as inductively-coupled plasma mass spectrometry (ICP-MS) and electrospray ionization-tandem mass spectrometry (ESI-MS/MS) for the characterization and quantification of metallothioneins (MTs) are critically reviewed and discussed. This review gives an update based on the literature over the last five years. The coupling of CE to ICP-MS is especially highlighted. As a result of progress in new interface technologies for CE-ICP-MS, research topics presented in the literature are changing from "the characterization of interfaces by metallothioneins" to the "characterization of metallothioneins by CE-ICP-MS". New applications of CE-ICP-MS to the analysis of MTs in real samples are summarized. The potential of the on-line isotope dilution technique for the quantification of MTs and for the determination of the stoichiometric composition of metalloprotein complexes is discussed. Furthermore, a selection of relevant papers dealing with HPLC-ICP-MS for MT analysis are summarized and compared to those dealing with CE-ICP-MS. In particular, the use of size-exclusion (SE)-HPLC as a preliminary separation step for metallothioneins in real samples prior to further chromatographic or electrophoretic separations is considered. Additionally, the application of electrospray ionisation-tandem mass spectrometry (ESI-MS/MS) for the identification of metallothionein isoforms following electrophoretic or chromatographic separation is discussed.

Electron transfer of hemoglobin at electrodes modified with colloidal clay nanoparticles.

Abstract: Nanostructured sodium montmorillonite was prepared via a colloidal chemical approach and deposited onto glassy carbon electrodes (GCE). Subsequently, hemoglobin was spontaneously adsorbed onto the clay membrane-modified electrode. The colloidal clay nanoparticles and the adsorbed protein were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical impedance behavior of the system was studied using a microlithographically fabricated interdigitated microsensor electrode (IME). The interaction of the clay nanoparticles with hemoglobin was investigated by UV-VIS spectroscopy and electrochemical methods. The heme protein adsorbed in this way displayed a well-defined electrode process and the electron transfer was confirmed to originate from its heme site. Furthermore, nitric oxide affects the hemoglobin electrochemistry.

Total synchronous fluorescence scan spectra of petroleum products.

Abstract: Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan (TSFS) spectral measurement gives the total synchronous fluorescence characteristics of a multifluorophoric sample at various possible wavelength intervals (Δλ), which could help to characterize multifluorophoric systems better. TSFS spectra of petroleum products such as diesel, kerosene, petrol, engine oil etc., available in the Indian market, are reported. Fluorescence in these samples is due to the presence of polycyclic aromatic hydrocarbons (PAHs) of various ring sizes. The TSFS contour plot profiles of the neat samples measured at right-angle geometry is a result of various energy-degrading photophysical processes such as inner filter effect, light attenuation, resonance energy transfer, collisional quenching etc. TSFS plots make it easy to obtain the optimized Δλ of an unknown sample of analytical interest. TSFS and the excitation-emission matrix (EEM) techniques are similar, but the contour profiles generated are different. The response of the TSFS contour profiles to dilution is different from that in the EEM contour profiles. Thus, TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples.

Monitoring of total antimony and its species by ICP-MS and on-line ion chromatography in biological samples from patients treated for leishmaniasis.

Abstract: Results from a study are reported in which patients with leishmaniasis were monitored by whole blood, blood plasma, urine, and hair analysis, before, during, and after intramuscular administration of N-methyl meglumine antimoniate. Quadrupole ICP-MS was used for the detection of antimony and on-line ion chromatography for the separation of its species. After typically 30 consecutive daily injections of 5 mg antimony per kg of body weight, Sb concentrations of up to 250 µg L–1 in whole blood and plasma, and 60 mg of Sb per gram of creatinine in urine, were measured 24 h after drug administration. Antimony in hair samples of these patients showed concentrations of up to 24 µg g–1. Speciation studies of Sb5+ and Sb3+ in drug, urine, and plasma samples were performed by ion chromatography using a Hamilton PRP-100X anion exchange column and EDTA (2 or 20 mM, pH 4.7) as the mobile phases. Repeatability of elution time and peak area measurements for a 0.125 ng spike were <1.2% and <3.5%, respectively. Method detection limits for both species, using a 1:10 diluted urine or plasma sample, were typically 1.6 µg L–1. The procedure was capable of separating the very intense drug peak from its inorganic species, thus permitting the first studies on the bio-transformation of N-methyl meglumine antimoniate to Sb5+ and Sb3+ in the human body.

HPLC-ICP-MS determination of selenium distribution and speciation in different types of nut.

Abstract: In addition to determination of total selenium in nuts, the element distribution among different fractions (lipid extract, low molecular weight, and protein fractions), and speciation analysis were studied. Improved precision for total selenium determination was observed after elimination of lipids. Because selenium was not detected in any of the lipid extracts obtained from the different types of nuts (ICP–MS), in each determination and/or speciation procedure used in this work lipids were extracted (chloroform–methanol, 2:1) and discarded before analysis. In agreement with previously reported data, high selenium levels were found in Brazil nuts (those purchased without shells contained approximately a quarter the content than those purchased with shells) and significantly lower levels in walnuts, cashews, and pecans nuts. Low-molecular-weight compounds were extracted with perchloric acid (0.4 mol L–1) to furnish a fraction containing 3 to 15% of the total selenium in different types of nuts. The proteins were isolated from nut samples by dissolution in 0.1 mol L–1 sodium hydroxide and subsequent precipitation with acetone. They were then dissolved in phosphate buffer pH 7.5. Analysis of protein fractions focused on selenium in two possible states – weakly and firmly bound to proteins. Results obtained for Brazil nuts by size-exclusion chromatography with on-line ICP–MS detection, in the absence and in the presence of β-mercaptoethanol, showed that approximately 12% of total selenium was weakly bound to proteins. To obtain information about firmly bound selenium, the protein extracts were hydrolyzed enzymatically with proteinase K. Speciation was performed by means of ion-pairing HPLC–ICP–MS. The primary species found in all types of nuts was Se-methionine (19–25% of total selenium for different types of nuts).