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Analytical and Bioanalytical Chemistry (v.378, #2)

Precise isotope ratio measurements as a unique tool in modern analytical chemistry by Frank Vanhaecke; Klaus G. Heumann (pp. 227-228).

TIMS versus multicollector-ICP-MS: coexistence or struggle for survival? by Thomas Walczyk (pp. 229-231).

Overcoming spectral overlap in isotopic analysis via single- and multi-collector ICP–mass spectrometry by Frank Vanhaecke; Luc Moens (pp. 232-240).

For isotope ratio applications where an internal isotope ratio precision >0.05–0.1% relative standard deviation suffices, single-collector inductively coupled plasma mass spectrometry (ICPMS) is fit-for-purpose, but for detecting more subtle variations in the natural isotopic composition of a target element, only multi-collector ICPMS (MC-ICPMS) can compete with thermal ionization mass spectrometry (TIMS). While as a result of the extensive sample preparation (analyte isolation) preceding TIMS and the "softer" ionization in vacuum, spectral interferences only seldom occur with this technique, their occurrence is recognized to be the most important drawback of ICPMS. This paper discusses high mass resolution and chemical resolution in a collision or dynamic reaction cell as powerful and versatile means to overcome spectral overlap and illustrates how their introduction has led to a substantial extension of the application range of ICPMS for isotope ratio applications. High mass resolution is the most elegant and straightforward way to overcome the problem of spectral overlap. Offering the possibility to operate the mass analyzer at a higher mass resolution, while at the same time preserving the flat-topped or trapezoidal peak shape required for highly precise isotope ratio measurements, was a challenge for the manufacturers of MC-ICPMS instrumentation. It will be discussed how these apparently contradicting requirements could be fulfilled simultaneously and an overview of the current situation will be given. Chemical resolution in a collision or dynamic reaction cell is an alternative to high mass resolution for overcoming spectral overlap. Real-life examples will be given to illustrate how also this approach can be used to advantage in isotope ratio work. Despite the greater flexibility and straightforwardness of high mass resolution, some situations will be discussed where chemical resolution is to be preferred. Finally, some desires as to future instrumentation are formulated.

Measurement of isotope ratios on transient signals by MC-ICP–MS by Ines Günther-Leopold; Beat Wernli; Zlatko Kopajtic; Detlef Günther (pp. 241-249).

Precise and accurate isotope ratio measurements are an important task in many applications such as isotope-dilution mass spectrometry, bioavailability studies, or the determination of isotope variations in geological or nuclear samples. The technique of MC-ICP–MS has attracted much attention because it permits the precise measurement of isotope compositions for a wide range of elements combined with excellent detection limits due to high ionisation efficiencies. However, the results are based mainly on measurements using continuous sample introduction. In the present study the determination of isotope ratios on various transient signals with a time duration of 30 to 60 s has been achieved by coupling high-performance liquid chromatography to a multicollector inductively coupled plasma mass spectrometer. In order to investigate the origin of ratio drifts across the transient signals for this hyphenated technique, measurements with the same standard solutions were also carried out using a flow-injection device for sample introduction. As a result of this application it could be concluded that the main source of the bias in the measured isotope ratios is within the ICP–MS instead of fractionation effects on the chromatographic column material. Preliminary studies on short transient signals of gaseous samples (dry plasma) showed a reverse fractionation effect compared with wet plasma conditions (flow injection and HPLC).

Keywords: Multicollector ICP–MS; Transient signals; Isotope ratios; Hyphenated techniques

Precise isotope-ratio determination by CGC hyphenated to ICP– MCMS for speciation of trace amounts of gaseous sulfur, with SF₆ as example compound by Eva M. Krupp; Christophe Pécheyran; Simon Meffan-Main; Olivier F. X. Donard (pp. 250-255).

Capillary gas chromatography coupled to an inductively coupled plasma mass spectrometer with multiple-collector detection (GC–ICP–MCMS) has been used to assess the precision and instrumental mass bias in sulfur isotope-ratio determination for the gaseous sulfur species SF₆. The isotopic composition of the compound was certified by the institute for reference materials and measurements (IRMM, Belgium) and is available as PIGS 2010. Integration of the peaks (peak half-width 1.4 s) was performed using a special peak-integration method based on definition of the integration area by assessment of a uniform isotope-ratio area within the chromatographic peak. Instrumental mass bias was determined to be approximately 12% per mass unit and proved to be stable in the concentration range measured. Replicate injections of 2, 10, 20, and 30 ng (as S) SF₆ diluted in argon gave precision for the ³²S/³⁴S ratio from 0.6% RSD for 2-ng injections to 0.03% RSD for 30-ng injections. The ³²S/³³S and ³³S/³⁴S isotope-ratio precision was better than 0.4% RSD for injections of 10 ng (as S) and higher. Detection limits were in the absolute pg range for all measured sulfur isotopes.

Keywords: Sulfur; Isotope ratio; Speciation; GC coupling; ICP–MCMS; Precision

Mass spectrometric method for the absolute calibration of the intramolecular nitrogen isotope distribution in nitrous oxide by Jan Kaiser; Sunyoung Park; Kristie A. Boering; Carl A. M. Brenninkmeijer; Andreas Hilkert; Thomas Röckmann (pp. 256-269).

A mass spectrometric method to determine the absolute intramolecular (position-dependent) nitrogen isotope ratios of nitrous oxide (N₂O) has been developed. It is based on the addition of different amounts of doubly labeled ¹⁵N₂O to an N₂O sample of the isotope ratio mass spectrometer reference gas, and subsequent measurement of the relative ion current ratios of species with mass 30, 31, 44, 45, and 46. All relevant quantities are measured by isotope ratio mass spectrometers, which means that the machines’ inherent high precision of the order of 10⁻⁵ can be fully exploited. External determination of dilution factors with generally lower precision is avoided. The method itself can be implemented within a day, but a calibration of the oxygen and average nitrogen isotope ratios relative to a primary isotopic reference material of known absolute isotopic composition has to be performed separately. The underlying theoretical framework is explored in depth. The effect of interferences due to ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O in the ¹⁵N₂O sample and due to ¹⁵N ₂ ⁺ formation are fully accounted for in the calculation of the final position-dependent nitrogen isotope ratios. Considering all known statistical uncertainties of measured quantities and absolute isotope ratios of primary isotopic reference materials, we achieve an overall uncertainty of 0.9‰ (1σ). Using tropospheric N₂O as common reference point for intercomparison purposes, we find a substantially higher relative enrichment of ¹⁵N at the central nitrogen atom over ¹⁵N at the terminal nitrogen atom than measured previously for tropospheric N₂O based on a chemical conversion method: 46.3±1.4‰ as opposed to 18.7±2.2‰. However, our method depends critically on the absolute isotope ratios of the primary isotopic reference materials air–N₂ and VSMOW. If they are systematically wrong, our estimates will also necessarily be incorrect.

Keywords: Nitrous oxide; Isotopic composition; Absolute position-dependent calibration; Intramolecular nitrogen isotope ratios; Isotope ratio mass spectrometry

Isotope-abundance ratios of light (bio) and heavy (geo) elements in biogenic tissues: methods and applications by Stefan Hölzl; Peter Horn; Andreas Rossmann; Susanne Rummel (pp. 270-272).

The use of ICPMS for stable isotope tracer studies in humans: a review by Stefan Stürup (pp. 273-282).

The use of stable isotope tracers in human studies is a rapidly growing research field that benefits from the many new developments in inorganic mass spectrometric instrumentation and from the better availability of mass spectrometric techniques to nutritional scientists during the last three decades. Traditionally, thermal ionization mass spectrometry (TIMS) has been the preferred technique for these studies, but the development of new inductively coupled plasma mass spectrometric (ICPMS) techniques with better isotope-ratio measurement and interference-removal capabilities (e.g. single and multi-detector ICPMS and reaction/collision cell ICPMS) has enabled broader use of ICPMS for determination of stable isotope tracers in nutritional research. This review discusses the current and future use of ICPMS in stable isotope tracer studies in humans.

Keywords: Stable isotope tracers; ICPMS; Human nutrition; Isotope ratio

Compound-specific stable isotope analysis of organic contaminants in natural environments: a critical review of the state of the art, prospects, and future challenges by Torsten C. Schmidt; Luc Zwank; Martin Elsner; Michael Berg; Rainer U. Meckenstock; Stefan B. Haderlein (pp. 283-300).

Compound-specific stable isotope analysis (CSIA) using gas chromatography-isotope ratio mass spectrometry (GC/IRMS) has developed into a mature analytical method in many application areas over the last decade. This is in particular true for carbon isotope analysis, whereas measurements of the other elements amenable to CSIA (hydrogen, nitrogen, oxygen) are much less routine. In environmental sciences, successful applications to date include (i) the allocation of contaminant sources on a local, regional, and global scale, (ii) the identification and quantification of (bio)transformation reactions on scales ranging from batch experiments to contaminated field sites, and (iii) the characterization of elementary reaction mechanisms that govern product formation. These three application areas are discussed in detail. The investigated spectrum of compounds comprises mainly n-alkanes, monoaromatics such as benzene and toluene, methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons such as tetrachloromethane, trichloroethylene, and polychlorinated biphenyls (PCBs). Future research directions are primarily set by the state of the art in analytical instrumentation and method development. Approaches to utilize HPLC separation in CSIA, the enhancement of sensitivity of CSIA to allow field investigations in the µg L⁻¹ range, and the development of methods for CSIA of other elements are reviewed. Furthermore, an alternative scheme to evaluate isotope data is outlined that would enable estimates of position-specific kinetic isotope effects and, thus, allow one to extract mechanistic chemical and biochemical information.

Keywords: CSIA; IRMS; Isotope fractionation; Isotope ratio; Isotopic shift; Fingerprinting; Source allocation; Biodegradation; Degradation; Transformation; Weathering; Environmental forensics; Geomicrobiology; Contaminant hydrology; SPME; Purge and trap; ¹³C; D/H; Primary isotope effect; Secondary isotope effect; Kinetic isotope effect; Rayleigh equation; Chloromethane; Tetrachloromethane; Trichloroethylene; Tetrachloroethylene; Methane; Perylene; Creosote; Sulfate; Chlorinated solvents; PAH; PCB; Aromatic hydrocarbon; Biogenic; Petrogenic; BTEX; VOC

Stable isotope variation as a tool to trace the authenticity of beef by M. Boner; H. Förstel (pp. 301-310).

Organic beef coming principally from Germany was analysed for the hydrogen, carbon, oxygen, nitrogen and sulfur stable isotopic composition to test the possibility of tracing back the geographical origin. Since there is a well-known pattern of D/H and ¹⁸O/¹⁶O in meteoric water and in ground water, there is an existing link to tissue water in the beef. By including the stable isotope ratios of the other elements of life further information is available: soils show different isotope ratios of ¹⁵N/¹⁴N and ³⁴S/³²S depending on the geological composition, cultivation and atmospheric sulfur deposition. As organic farming is mainly obliged to use only their produced fodder, that ratio is reflected in the beef as well.Different organic beef samples from various German farms have been collected and analysed over nearly two years. To check the differentiation of foreign beef, samples from Argentina and Chile were also included in the study. The analyses of meat samples indicate that it is possible to trace back the region (e.g. Argentina and Germany) by using isotopes of oxygen and hydrogen. A local geographical differentiation can be done by using the stable isotopes of nitrogen and sulfur, as was demonstrated for three farms in Colonia Bay. An optimal differentiation also depends on the quality of further information (e.g. the season, kind of cattle breeding or the declaration of the local geographical origin). Certainly authenticity of beef is not only linked with the geographical origin but can also reflect the differentiation of organic and conventional farming. The fodder of organic cattle farming consists mainly of C₃ plants and the use of C₄ plants is more usual in conventional cattle farming. A ¹³C/¹²C ratio above −20‰ appears as a limit for organic farming. Increased values have to be controlled based on their authenticity.

Keywords: Stable isotope; Beef; Authenticity; Organic farming; Origin; Traceability

ICP-MS measurements of lead isotopic ratios in soils heavily contaminated by lead smelting: tracing the sources of pollution by Vojtěch Ettler; Martin Mihaljevič; Michael Komárek (pp. 311-317).

The Pb isotopic composition (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) in smelter-impacted soils was measured using a quadrupole-based ICP-MS. Four forest/tilled soil profiles were sampled according to the distance from the lead smelter in Příbram (Czech Republic), prevailing wind direction, geological background and soil type. The results were compared with the Pb isotopic composition of bedrocks and waste materials from Pb metallurgy (smelting slags, air-pollution-control residues). The isotopic composition of soils confirms the predominant role of metallurgy on the general pollution in the area. The highly contaminated soils from the vicinity of the smelter contain up to 35,300 mg Pb kg⁻¹ and exhibit an isotopic composition close to that of car battery processing (²⁰⁶Pb/²⁰⁷Pb up to 1.177). A coupled concentration/isotopic study of soil profiles showed that the smelter-induced pollution had penetrated even to the mineral soil horizons, indicating an important vertical mobility of Pb contaminant within the soil profile. The calculated downward penetration rate of Pb in soils ranges from 0.3 to 0.36 cm year⁻¹.

Keywords: Pb isotopes; ²⁰⁶Pb/²⁰⁷Pb; ICP-MS; Soil; Pollution; Metallurgy; Penetration rate

Isotope-dilution ICP–MS for trace element determination and speciation: from a reference method to a routine method? by Klaus G. Heumann (pp. 318-329).

This critical review discusses the conditions under which inductively coupled plasma–isotope dilution mass spectrometry (ICP–IDMS) is suitable as a routine method for trace element and element-speciation analysis. It can, in general, be concluded that ICP–IDMS has high potential for routine analysis of trace elements if the accuracy of results is of predominant analytical importance. Hyphenated techniques with ICP–IDMS suffer both from lack of commercially available isotope-labeled spike compounds for species-specific isotope dilution and from the more complicated system set-up required for species-unspecific ICP–IDMS analysis. Coupling of gas or liquid chromatography with species-specific ICP–IDMS, however, enables validation of analytical methods involving species transformations which cannot easily be performed by other methods. The potential and limitations of ICP–IDMS are demonstrated by recently published results and by some unpublished investigations by our group. It has been shown that possible loss of silicon as volatile SiF₄ during decomposition of a sample by use of hydrofluoric acid has no effect on trace silicon determination if the isotope-dilution step occurs during digestion in a closed system. For powder samples, laser ablation ICP–IDMS can be applied with an accuracy comparable with that only available from matrix-matched standardization, whereas the accuracy of electrothermal vaporization ICP–IDMS was strongly dependent on the element determined. The significance of easy synthesis of isotope-labeled spike compounds for species-specific ICP–IDMS is demonstrated for monomethylmercury and Cr(VI). Isotope-exchange reactions between different element species can prevent the successful application of ICP–IDMS, as is shown for iodinated hydrocarbons. It is also shown for monomethylmercury that species transformations during sample-pretreatment steps can be followed by species-specific ICP–IDMS without loss of accuracy. A relatively simple and time-efficient procedure for determination of monomethylmercury in environmental and biological samples is discussed. The method, which entails a rapid microwave-assisted isotope dilution step and in-situ extraction of the derivatized species, has good potential for routine application in the future.

Keywords: Inductively coupled plasma isotope dilution mass spectrometry; Trace elements; Element species; Species-specific and species-unspecific spiking; Routine method; Validation

New mathematical models with associated equations for isotope dilution mass spectrometry (IDMS) by Heinrich Kipphardt; Paul De Bièvre; Philip D. P. Taylor (pp. 330-341).

Vector models which progressively lead to a general model for isotope dilution mass spectrometry (IDMS) are presented for the case of two ‘monitor isotopes’ and one blend involved. They enable one to find the boundary conditions for performing IDMS, and cover the cases of highly enriched isotopes, radioactive isotopes and ratios that are given with different denominator. The models identify the key measurements in their simplest form as well as the conditions which minimise the measurement effort and in some cases the propagated measurement uncertainties. The equations are discussed and compared with other published IDMS equations. Combined with discussion on fundamental aspects of IDMS, this results in an even more ‘general’ but also more complex IDMS equation.

Keywords: Isotope dilution mass spectrometry; IDMS; Measurement equation

Application of isotope-dilution laser ablation ICP–MS for direct determination of Pu concentrations in soils at pg g⁻¹ levels by Sergei F. Boulyga; Markus Tibi; Klaus G. Heumann (pp. 342-347).

The methods available for determination of environmental contamination by plutonium at ultra-trace levels require labor-consuming sample preparation including matrix removal and plutonium extraction in both nuclear spectroscopy and mass spectrometry. In this work, laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) was applied for direct analysis of Pu in soil and sediment samples. Application of a LINA-Spark-Atomizer system (a modified laser ablation system providing high ablation rates) coupled with a sector-field ICP–MS resulted in detection limits as low as 3×10⁻¹³ g g⁻¹ for Pu isotopes in soil samples containing uranium at a concentration of a few μg g⁻¹. The isotope dilution (ID) technique was used for quantification, which compensated for matrix effects in LA–ICP–MS. Interferences by UH⁺ and PbO₂ ⁺ ions and by the peak tail of ²³⁸U⁺ ions were reduced or separated by use of dry plasma conditions and a mass resolution of 4000, respectively. No other effects affecting measurement accuracy, except sample inhomogeneity, were revealed. Comparison of results obtained for three contaminated soil samples by use of α-spectrometry, ICP–MS with sample decomposition, and LA–ICP–IDMS showed, in general, satisfactory agreement of the different methods. The specific activity of ^239+240Pu (9.8±3.0 mBq g⁻¹) calculated from LA–ICP–IDMS analysis of SRM NIST 4357 coincided well with the certified value of 10.4±0.2 mBq g⁻¹. However, the precision of LA–ICP–MS for determination of plutonium in inhomogeneous samples, i.e. if "hot" particles are present, is limited. As far as we are aware this paper reports the lowest detection limits and element concentrations yet measured in direct LA–ICP–MS analysis of environmental samples.

Keywords: Plutonium; Soil; Isotope dilution; Laser ablation; Inductively coupled plasma mass spectrometry

Ultratrace analysis and isotope ratio measurements of long-lived radioisotopes by resonance ionization mass spectrometry (RIMS) by N. Trautmann; G. Passler; K. D. A. Wendt (pp. 348-355).

Resonance Ionization Mass Spectrometry (RIMS) is a sensitive and selective method for ultratrace analysis of long-lived radioisotopes and isotope ratio measurements. It provides extremely high isobaric suppression and good overall efficiency. The experimental limits of detection are as low as 10⁶ atoms per sample and isotopic selectivities of 5×10¹² have been obtained. The widespread potential of RIMS, using different experimental arrangements, is demonstrated for the determination of the radiotoxic isotopes Pu-238 to Pu-244 and Sr-89/Sr-90 in various environmental samples as well as for Ca-41 in nuclear reactor components and biomedical samples.

Keywords: Resonance ionization spectroscopy; Mass spectrometry; Ultratrace detection; Isotope ratio measurements; Long-lived radionuclides

Current perspectives of ¹⁴C-isotope measurement in biomedical accelerator mass spectrometry by Graham Lappin; R. Colin Garner (pp. 356-364).

Accelerator mass spectrometry (AMS) is an extremely sensitive nuclear physics technique developed in the mid-70’s for radiocarbon dating of historical artefacts. The technique centres round the use of a tandem Van de Graaff accelerator to generate the potential energy to permit separation of elemental isotopes at the single atom level. AMS was first used in the early 90’s for the analysis of biological samples containing enriched ¹⁴C for toxicology and cancer research. Since that time biomedical AMS has been used in the study of (1) metabolism of xenobiotics in animals and humans (2) pathways of drug metabolism (3) biomarkers (4) metabolism of endogenous molecules including vitamins (5) DNA and protein binding studies and (6) clinical diagnosis. A new drug development concept which relies on the ultrasensitivity of AMS known as human microdosing (Phase 0) is being used to obtain early human metabolism information of candidate drugs arising out of discovery. These various aspects of AMS are reviewed in this article and a perspective on future applications of AMS provided.

Keywords: Accelerator mass spectrometry; Microdosing; Ultrasensitive drug analysis; Biomarkers; Phase 0

Chemometric studies of polycyclic aromatic hydrocarbon shape selectivity in reversed-phase liquid chromatography by Katrice A. Lippa; Lane C. Sander; Stephen A. Wise (pp. 365-377).

The molecular shape recognition differences between monomeric and polymeric C₁₈ stationary phases in the reversed-phase liquid chromatography (RPLC) separation of unsubstituted polycyclic aromatic hydrocarbons (PAHs) and methyl-substituted polycyclic aromatic hydrocarbons (MPAHs) are examined through the use of partial least squares (PLS) analysis techniques. The resulting PLS models are able to describe the enhanced shape selectivity of the polymeric phase for recognizing subtle structural differences among planar and nonplanar isomers. PLS component analyses of these models reveal that spatial and topological descriptors are primarily used to rank structural differences among the PAHs (i.e., fused-ring patterns, molecular length and breadth) that control such shape-selective chromatographic processes. This is consistent with the view that polymeric alkyl chain stationary phases contain size- and shape-specific “slots” that promote the separation of structurally-related solutes. In contrast, the monomeric phase model is limited in resolving both the isomer classes and the nonplanarity shape differences among the PAHs. However, an improvement of shape recognition on the monomeric phase was elucidated by the PLS model for two PAHs (phenanthro[3,4-c]phenanthrene and dibenzo[g,p]chrysene) exhibiting the most extreme nonplanarity. These results suggest that a limited amount of space between alkyl chains may exist within the higher-density polymeric phase to recognize shape differences among the bulkier and nonplanar solutes.

Keywords: Partial least squares (PLS); Polycyclic aromatic hydrocarbons (PAHs); Shape selectivity; Polymeric C₁₈columns; Monomeric C₁₈columns; Quantitative structure–retention relationship (QSRR)

Rapid speciation of Se(IV) and Se(VI) by flow injection–capillary electrophoresis system with contactless conductivity detection by Pavel Kubáň; Petr Kubáň; Vlastimil Kubáň (pp. 378-382).

A flow injection–capillary electrophoresis system with contactless conductivity detection and hydrostatic-pressure-generated flow was used for the fast and sensitive speciation of Se(IV) and Se(VI). The sample throughput was 25 samples per hour using a background electrolyte solution containing 8.75 mM l-histidine (His) adjusted to pH 4.00 with acetic acid. The repeatability of peak areas (n=8) was better than 1.41% and the limits of detection were 190 μg L⁻¹ and 7.5 μg L⁻¹ for Se(IV) and Se(VI), respectively. The interference from carbonate, typically present in water samples, was eliminated by using a low-pH electrolyte in which carbonate is uncharged and migrates at the EOF front. The method was applied to the analysis of Se(IV) and Se(VI) in soil samples that were spiked with both selenium species and the results for recovery of both selenium species were in good agreement with their introduced concentrations.

Keywords: Flow injection analysis; Capillary electrophoresis; Contactless conductivity detection; Selenium; Inorganic anions; Speciation

Study of the feasibility of using a pellicular anion-exchange column for separation of transferrin isoforms in human serum by HPLC with UV detection by M. B. de la Calle Guntiñas; G. Bordin; A. R. Rodriguez (pp. 383-387).

A method has been optimised for the separation of glycoforms of human serum transferrin, using a high-performance pellicular anion-exchange chromatographic column. The effect of the eluent pH and of the column temperature on the separation of transferrin glycoforms was studied using a standard solution of commercially available human serum transferrin. An HPLC system equipped with an ultraviolet detector was used for the analysis. No immunoassay was used after the anion-exchange chromatographic separation of the glycoforms, in contrast with most currently used methods. The method was applied to the separation and quantification of transferrin glycoforms in serum from a healthy, non-pregnant woman, after saturation of transferrin with iron and further precipitation of lipoproteins. The whole chromatographic run, including re-equilibration of the column, took 35 min.

Keywords: HPLC–UV; Pellicular anion-exchange column; Transferrin isoforms; Human serum

An easy and rapid method to determine aristolochic acids I and II with high sensitivity by Ziyi Sun; Lifang Liu; Xiaofeng Zheng; Chunhai Fan; Qiang Wang; Genxi Li (pp. 388-390).

Aristolochic acid (AA), a natural component in some Chinese medicinal plants, is nephrotoxic and carcinogenic, and is involved in a specific type of renal fibrosis, called Chinese herbs nephropathy (CHN). In this paper, we report the electrochemistry of AA and a novel method to detect the species based on the electrochemical studies. The detection limit is estimated to be 1.0×10^-8 M with a linear range from 5.0×10^-8 M to 1.3×10^-6 M. Meanwhile, this method is applicable in detection in real samples, such as Caulis Aristolochiae Manshuriensis (CAM), Radix Aristolochiae (RA), Fructus Aristolochiae (FA) and Radix Stephaniae Tetrandrae (RST). The concentration of AA in the CAM sample was 3.50±0.12×10^-4 M. Consistent results have been obtained from both the electrochemical approach described here and the previously reported HPLC method.

Keywords: Aristolochic acid; Determination; Cyclic voltammetry; Caulis Aristolochiae Manshuriensis

Fermentation monitoring using multisensor systems: feasibility study of the electronic tongue by Kim Esbensen; Dmitry Kirsanov; Andrey Legin; Alisa Rudnitskaya; John Mortensen; Joan Pedersen; Lene Vognsen; Sergey Makarychev-Mikhailov; Yuri Vlasov (pp. 391-395).

The electronic tongue based on an array of 30 non-specific potentiometric chemical sensors has been applied to qualitative and quantitative monitoring of a batch fermentation process of starting culture for light cheese production. Process control charts were built by using PLS regression and data from fermentations run under “normal” operating conditions. Control charts allow discrimination of samples from fermentation batches run under “abnormal” operating conditions from “normal” ones at as early as 30–50% of fully evolved fermentations. The capability of the electronic tongue to quantify concentrations of important organic acids (citric, lactic and orotic) in the present type of fermentation media was demonstrated. Average prediction errors were assessed in the range 5–13% based on test set validation. Correlation between peptide profiles determined using HPLC and the electronic tongue output was also established. The electronic tongue was demonstrated to be a promising tool for fermentation process monitoring and quantitative analysis of growth media.

Keywords: Electronic tongue; Fermentation monitoring; Process control; Determination of organic acids

Water sorption properties of carbonized layers produced by controlled B⁺ bombardment of thin polyimide and polysulfone films by Karin Sahre; Klaus-J. Eichhorn; Margarita Günther; Gunnar Suchaneck; Gerald Gerlach (pp. 396-401).

Thin polyimide (PI) and polyethersulfone (PES) films are widely used as functional layers for microelectronic sensors. Ion implantation modifies the layer structure and morphology of these polymers and hence results in new mechanical and optical properties. However, ion-modified layers also show a change in sensitivity to moisture uptake under specific conditions. This is important for developing humidity sensors. Therefore, the water sorption ability of such modified polymer layers is studied by spectroscopic ellipsometry under definite relative humidity conditions (1–95%). Swelling data were obtained by fitting procedures based on changes of effective layer thickness and optical constants due to water uptake. Irradiation doses from 0.5 to 5×10¹⁵ B⁺ cm⁻²at an energy of 180 keV were used for polymer modification. At irradiation doses from 0.5 to 0.7×10¹⁵ B⁺ cm⁻², the maximum out-of-plane swelling is reached. At higher doses >2×10¹⁵ B⁺ cm⁻², the swelling decreases and corresponds to values of the pure polymer layers. The wetting properties of the layer surfaces determined by contact angle measurements are important to explain this behavior.

Keywords: Polymer layers; Ion implantation; Water sorption; Spectroscopic ellipsometry

Chromotropic acid, a fluorogenic chelating agent for aluminium(III) by Émilie Destandau; Valérie Alain; Élisabeth Bardez (pp. 402-410).

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH≈4 was shown to lead to a 1:1 complex with a stability constant log β ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L⁻¹, questionable, whereas a 10⁻² mol L⁻¹ formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 μg L⁻¹; the detection limit was 0.65 μg L⁻¹ (3SD _blank, n=10, SD=±1.4% at 10 μg L⁻¹ and ±0.8% at 100 μg L⁻¹). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.

Keywords: Fluorimetric determination; Complexation; Aluminium; Al(III); Chromotropic acid

Specific properties of fine SnO₂ powders connected with surface segregation by S. Oswald; G. Behr; D. Dobler; J. Werner; K. Wetzig; W. Arabczyk (pp. 411-415).

The effect of surface segregation in Sb- and In-doped SnO₂ fine-grained powders has been analyzed in comparison with single-crystalline samples. The kinetics and thermodynamics of the Sb and In segregation processes were studied as a function of annealing temperature by X-ray photoelectron spectroscopy (XPS) after annealing in an oxygen-containing atmosphere. Significant differences between diffusion and segregation were revealed for doped powders and single crystals, obviously because of simultaneous diffusion and particle-growth processes proceeding during annealing of powders. For doped single crystals the thermodynamic equilibrium is approached after 24 h annealing above 850 °C and at 1000 °C for Sb and In, respectively. Higher effective activation energies of diffusion are observed for doped powders and the thermodynamic equilibrium is not achieved under technologically relevant annealing conditions. On the basis of dopant profile measurements anomalies in the electrical resistivity at 300 °C of Sb-doped SnO₂ powders annealed at 700 and 900 °C were attributed to an Sb-depleted zone formed beneath the segregated surface during the kinetic regime. To achieve optimum resistivity behavior for commercial application, inhomogeneous doping of powders must be avoided by appropriate preparation steps.

Keywords: XPS; SnO₂ ; Segregation; Powders; Single crystal

Beam-injection flame furnace AAS: comparison of different nozzle types for beam generation and application of sub-critical liquid carbon dioxide as carrier and gas pressure pump by Annelen Ratka; Harald Berndt (pp. 416-422).

In beam injection flame furnace AAS (BIFF-AAS) the sample is introduced as a free-flying high-speed liquid beam into an AAS flame-heated nickel tube, resulting in a considerable improvement in the power of detection. For optimization of beam generation different nozzle types (smooth jet nozzles, turbulent working nozzles) have been compared at different pressures. It was found that the type of the nozzle hardly influences the analytical signal. However, the flow rates resulting from the different inner diameters of the nozzles and the applied pressures led to drastic changes in the analytical signal. For these investigations a recently developed 0.6 MPa (84 psig) diaphragm pump system was used. Furthermore, for the first time ever sub-critical liquid carbon dioxide has been used simultaneously as a liquid gas-pressure pump, as carrier in a flow-injection system (FIA), and for the beam generation. Transport of the carrier takes place as a result of the head pressure (6 MPa) of the liquid CO₂ in the gas cylinder. For volatile elements (e.g. Cd, Hg, Pb, and Tl) detection limits between 0.2 µg L⁻¹ (Cd) and 28 µg L⁻¹ (Hg) were found, the standard deviation was from 0.6% to 3.2% depending on the element, concentration, and sample volume used. The use of liquid CO₂ as a carrier in FIA systems opens up new possibilities for online sample pretreatment and trace preconcentration.

Keywords: Beam injection flame furnace AAS (BIFF-AAS); Diaphragm pump flow system; Liquid gas pressure pump; Sub-critical CO₂ ; Hydraulic high-pressure nebulization (HHPN); Nozzles for beam generation; Loop-in-loop technique (nested injection)

On-line preconcentration and determination of cobalt by DPTH-gel chelating microcolumn and flow injection inductively coupled plasma atomic emission spectrometry by Mohammed Zougagh; Pedro Cañada Rudner; Amparo García de Torres; José M. Cano Pavón (pp. 423-428).

This paper reports the development of a new methodology for the determination of cobalt in biological samples by using a flow injection system with loaded DPTH-gel as solid phase to preconcentrate analytes. The procedure is based on the on-line preconcentration of cobalt on a microcolumn of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). The trapped cobalt is then eluted with 1% tartaric acid and 1% citric acid (7.1 mL) and determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The analytical figures of merit for the determination of cobalt are as follows: detection limit (3S), 8.5 ng mL⁻¹; precision (RSD), 5.8% for 100 ng mL⁻¹ of cobalt; enrichment factor, 13 (using 7.3 mL of sample); sampling frequency, 40 h⁻¹ using a 60-s preconcentration time. For a 120-s preconcentration time (14.6 mL of sample volume) a detection limit of 5.7 ng mL⁻¹, an RSD under 5% at 50 ng mL⁻¹, an enrichment factor of 25, and a sampling frequency of 24 h⁻¹ were reported. The precision and accuracy of the method were checked by analysis of biological certified reference materials.

Keywords: Cobalt; Flow injection; On-line preconcentration; DPTH-gel microcolumn; ICP-AES; Biological samples

Continuous-flow separation and pre-concentration coupled on-line to solid-surface fluorescence spectroscopy for the simultaneous determination of o-phenylphenol and thiabendazole by J. F. García Reyes; E. J. Llorent Martínez; P. Ortega Barrales; A. Molina Díaz (pp. 429-437).

A novel and single flow-injection system combined with solid-surface fluorescence detection is proposed in this work for the resolution of a mixture of two widely used pesticides (o-phenylphenol and thiabendazole). The continuous-flow methodology is based on the implementation of on-line pre-concentration and separation of both analytes on the surface of C₁₈ silica gel beads placed just inside the flow cell, implemented with gel-phase fluorimetric multi-wavelength detection (using 305/358 and 250/345 nm as excitation/emission wavelengths for thiabendazole and o-phenylphenol, respectively). The separation of the pesticides was possible owing to the different retention/desorption kinetics of their interactions with the solid support in the zone where the stream impinges on the solid material. No previous separation of the analytes before they reach the flow cell is needed thereby simplifying substantially both the procedure and the manifold. By using a sample volume of 2,600 μL, the system was calibrated in the range 0.5–16 and 5–120 ng mL⁻¹ with detection limits of 0.09 and 0.60 ng mL⁻¹ for thiabendazole and o-phenylphenol, respectively. The RSD values (n=10) were about 1% for both analytes. The proposed methodology was applied to environmental water samples and also to various commercial pesticide formulations containing both analytes. Recovery percentages were 97–103% and 98–102% for thiabendazole and o-phenylphenol, respectively.

Keywords: Flow injection; Fluorescence; Pesticides; o-Phenylphenol; Thiabendazole

Performance evaluation of two chelating ion-exchange sorbents for the fractionation of labile and inert metal species from aquatic media by Mónica B. Alvarez; Mónica E. Malla; Daniel A. Batistoni (pp. 438-446).

The performance of two iminodiacetate chelating resins, applied in an element fractionation scheme, was investigated for the characterization of marine and stream water samples collected in potentially contaminated harbor and industrial zones. The comparison involved an evaluation of the sorption/desorption behavior of Cd, Cu, Pb and Zn on Chelex-100, a sorbent extensively employed for metal speciation studies, and on Lewatit TP-207, a material with similar chelating characteristics for which no applications for fractionation studies are reported. A characterization of the latter resin in terms of the influence of sample pH on the uptake of metals from aqueous solutions and their subsequent acid elution was carried out. Fractionation studies were performed on natural water samples and model solutions resembling their composition, spiked with micromolar concentrations of the metals. The operationally defined fractionation scheme is based on dynamic adsorption of the resin-labile fractions of metals on microcolumns made of the sorbents. This stage is followed by a batch procedure in which the eluent from the column is contacted with fresh resin to discriminate between the relatively stable species unable to react with the resin during the column interaction time, and the strongly complexed metals that do not interact with the sorbent even for periods of several hours. Results were obtained from coarsely filtered sub-samples and from specimens passed through membrane filters of pore size 0.45 and 0.22 µm. The method was also assessed with model solutions of the metals containing variable concentrations (in the 10^-3–10^-7 molar range) of complex forming agents such as nitrilotriacetic acid and trans-1,2-diaminocyclohexane-N,N,N’,N’-tetraacetic acid. An additional batch method, in which a fixed amount of resin was contacted with sample solution for increasing periods of time and the amount of metal remaining in solution measured as a function of the elapsed time, was used to obtain information on the kinetics of dissociation of species formed in the presence of added complexants. The behavior of both resins was similar, demonstrating that the discrimination of species derived from experiments with Chelex-100 may be properly validated by independent fractionation tests carried out with Lewatit TP-207. The behavior of the sorbents is also discussed in terms of the possible influence of particulate or colloidal materials and of kinetic effects related to the presence of complexing agents.

Keywords: Marine water; Stream water; Fractionation; Metal species; Chelating sorbents

Chemical modifiers in arsenic determination in biological materials by tungsten coil electrothermal atomic absorption spectrometry by C. G. Bruhn; V. N. Huerta; J. Y. Neira (pp. 447-455).

Palladium, iridium, and rhodium are evaluated as possible chemical modifiers in the determination of As in digest solutions of biological materials (human hair and clam) by tungsten coil electrothermal atomic absorption spectrophotometry (TCA-AAS). The modifier in solution was applied onto the coil and thermally pre-reduced; the pre-reduction conditions, the amount of modifier, and the thermal program were optimized. Palladium was not satisfactory, whereas Ir and Rh were effective modifiers and rendered better relative sensitivity for As by a factor of 1.4 and 1.9, respectively compared to the case without modifier. Upon optimization of thermal conditions for As in pre-reduced Ir (2.0 µg) and Rh (2.0 µg) modifiers and in the digest solutions of the study matrices, Rh (2.0 µg) was more effective modifier and was selected as such. The mean within-day repeatability was 2.8% in consecutive measurements (25–100 µg L⁻¹) (3 cycles, each of n=6) and confirmed good short-term stability of the absorbance measurements. The mean reproducibility was 4.4% (n=20 in a 3-day period) and the detection limit (3σ _blank/slope) was 29 pg (n=15). The useful coil lifetime in Rh modifier was extended to 300–400 firings. Validation was by determination of As in the certified reference material (CRM) of “Oyster tissue” solution with a percentage relative error (E _rel%) of 2% and percentage relative standard deviation (RSD%) of 3% (n=4), and by analytical recovery of As spiked in CRM of human hair [94±8% (n=4)]. The methodology is simple, fast (sample readout frequency 21 h⁻¹), reliable, of low cost, and was applied to the determination of As in hair samples of exposed and unexposed workers.

Keywords: Chemical modifiers; Arsenic; Tungsten coil electrothermal atomizer; Human hair; Clam

Low-temperature electrothermal vaporization of thenoyltrifluoroacetone complex of Sc(III) and Y(III) for sample introduction in an inductively coupled plasma atomic emission spectrometry, and their determination in biological samples by Zhefeng Fan; Bin Hu; Zucheng Jiang; Shengqing Li (pp. 456-459).

A new method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace Sc and Y, based on gaseous compound introduction into the plasma as their thenoyltrifluoroacetone (TTA) complexes by electrothermal vaporization was developed. Using the reagent TTA as chemical modifier can not only enhance the analytical signals, but also reduce the vaporization temperature. At a temperature of 1,000 °C the trace Sc and Y can be vaporized completely into ICP. The factors affecting the formation of the chelate and its vaporization behavior, such as drying time, vaporization temperature/time, reaction medium and the amount of TTA, were investigated in detail. Under the optimized conditions (drying temperature/time 100 °C/10 s, vaporization temperature/time 1,000 °C/4 s), the limits of detection for Sc and Y were 19 pg and 34 pg (3σ), respectively, and the relative standard deviations for Sc and Y were 4.2% (c _Sc=0.2 μg mL⁻¹; n=7) and 2.6% (c _Y=0.5 μg mL⁻¹; n=7). The linear ranges of the calibration graphs cover three orders of magnitude. The method was applied to the analysis of the biological reference materials (GBW 07602, bush branches and leaves; GBW 07604, poplar leaves), and the results obtained were in good agreement with the certified values.

Keywords: Low temperature electrothermal vaporization; Inductively coupled plasma atomic emission spectrometry; Thenoyltrifluoroacetone; Chemical modifier; Scandium and yttrium

Iron analysis in atmospheric water samples by atomic absorption spectroscopy (AAS) in water–methanol by A. M. Sofikitis; J. L. Colin; K. V. Desboeufs; R. Losno (pp. 460-464).

To distinguish between Fe(II) and Fe(III) species in atmospheric water samples, we have adapted an analytical procedure based on the formation of a specific complex between Fe(II) and ferrozine (FZ) on a chromatographic column. After elution of Fe(III), the Fe(II) complex is recovered with water–methanol (4:1). The possibility of trace iron measurements in this complex medium by graphite-furnace atomic-absorption spectrometry has been investigated. A simplex optimization routine was required to complete the development of the analytical method.

Keywords: GFAAS; Iron; Water–methanol; Atmospheric samples; Simplex optimization

Total arsenic content of nine species of Antarctic macro algae as determined by electrothermal atomic absorption spectrometry by Patricia Smichowski; Silvia Farías; Liliana Valiente; María Lorena Iribarren; Cristian Vodopivez (pp. 465-469).

Total arsenic in nine species Antarctic macro algae has been measured, by electrothermal atomic absorption spectrometry using a Pd/Mg(NO₃)₂ matrix modifier, to determine their capacity to accumulate the element. Macro algae were collected in February during the 2000 austral summer season at Jubany Station (Argentinean scientific station) around Potter Cove, King George Island. An optimized two-step microwave (MW) program was used to digest the samples. Dried samples were treated with HNO₃, H₂O₂, and HF, left overnight, then subjected to the first MW cycle. After cooling HNO₃ and HClO₄ were added and samples were subjected to the second MW cycle of digestion treatment. The effect of power and time on As recovery was examined. The analytical features of the method were: detection limit, 0.24 μg g⁻¹ (dry mass); precision (RSD), 4.2–5.7%; recovery 91–105%. A wide range of As-retention capacity (41.0–447 μg g⁻¹ dry mass) was observed among the different species. The highest levels of As were found in Phaeurus antarcticus (447 μg g⁻¹ dry mass). This organism satisfies several prerequisites to be considered for consideration as a biomonitor in future studies.

Keywords: Arsenic; Macro algae; Antarctica; Microwave digestion; Electrothermal atomic absorption spectrometry; Retention capacity

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline by M. F. El-Shahat; E. A. Moawed; M. A. A. Zaid (pp. 470-478).

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for ΔH, ΔS, and ΔG of 41.99, 158.23, and −5.1 kJ mol⁻¹, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g⁻¹ for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD≈6.18). The quantitative results were obtained from experiments performed using certified reference materials.

Keywords: Polyurethane foam; 8-Hydroxyquinoline; Separation; Preconcentration; Zinc(II); Cadmium(II); Mercury(II)

Determination of the oxidative stability of olive oil, using focused-microwave energy to accelerate the oxidation process by M. P. Cañizares-Macías; José A. García-Mesa; M. D. Luque de Castro (pp. 479-483).

A new method is proposed for rapid monitoring of the oxidative stability of virgin olive oil. Samples were irradiated with microwave energy to accelerate the oxidation process and photometric monitoring was performed at 232 and 270 nm. Conditions such as microwave irradiation power, number of irradiation cycles, and irradiation time were optimized by means of multivariate screening that showed that irradiation power is the most significant condition in the oil oxidation process. Twelve samples of extra virgin olive oil of different oxidative stability—between 19 and 130 h calculated from the induction time of the Rancimat method, usual for analysis of olive oil in routine laboratories—were analyzed by the proposed microwave-assisted method, and a decrease in the induction time between 60 and 68% was obtained. The results obtained showed that correlation between the proposed method and the Rancimat method was excellent. The correlation coefficients were 0.9953 and 0.9963 for monitoring at 232 and 270 nm, respectively.

Keywords: Focused-microwave energy; Oxidative stability; Olive oil; Ultraviolet photometric monitoring

Rapid immunoanalytical method for the determination of atrazine residues in olive oil by Marta Garcés-García; Sergi Morais; Miguel Ángel González-Martínez; Rosa Puchades; Ángel Maquieira (pp. 484-489).

A sensitive, simple and reliable method has been developed for the determination of atrazine in extra virgin olive oil. The analytical procedure involves direct extraction of the target analyte from oil matrix with methanol and a freezing clean-up step (−80 °C) followed by plate or sensor immunoassay determination. A detection limit of 0.7 ng/mL, with a dynamic range from 1.0 to 10.4 ng/mL, was reached. The method was highly selective for atrazine and propazine, showing little or no cross-reactivity to other similar compounds. The excellent recoveries obtained (mean value 91.3%) confirm the potential of this approach to detect atrazine in olive oil for application as screening and complementary method in pesticide regulatory and food safety programs. The proposed method correlates well with the reference gas chromatography (GC-MS) technique.

Keywords: Immunoassay; Atrazine; Olive oil; Food analysis

Study of a bis-furaldehyde Schiff base copper(II) complex as carrier for preparation of highly selective thiocyanate electrodes by Z.-Y. Sun; R. Yuan; Y.-Q. Chai; L. Xu; X.-X. Gan; W.-J. Xu (pp. 490-494).

A new highly selective thiocyanate electrode based on N,N′-bis-(furaldehyde)-1,2-phenylenediamine-dipicolyl copper(II) complex [Cu(II)-BFPD] as neutral carrier is described. The electrode has an anti-Hofmeister selectivity sequence: SCN⁻>I⁻>Sal⁻>ClO₄ ⁻>Br⁻>NO₂ ⁻>Cl⁻>NO₃ ⁻>SO₄ ²⁻>SO₃ ²⁻>H₂PO₄ ⁻ and a near-Nernstian potential linear range for thiocyanate from 1.0×10⁻¹ to 5.0×10⁻⁶ mol L⁻¹ with a detection limit 2.0×10⁻⁶ mol L⁻¹ and a slope of 57.5 mV decade⁻¹ in pH 5.0 of phosphate buffer solution at 20 °C. The response mechanism is discussed on the basis of results from A.C. impedance measurement and UV spectroscopy. The anti-Hofmeister behavior of the electrode results from a direct interaction between the central metal and the analyte ion and a steric effect associated with the structure of the carrier. The electrode has the advantages of simplicity, fast response, fair stability and reproducibility, and low detection limit. The selectivity of electrodes based on [Cu(II)-BFPD] exceeds that of classical anion-sensitive membrane electrodes based on ion exchangers such as lipophilic quaternary ammonium or phosphonium salts. Application of the electrode for determination of thiocyanate in waste water samples from a laboratory and a gas factory, and in human urine samples, is reported. The results obtained were fair agreement with the results obtained by HPLC.

Keywords: N,N′-bis-(furaldehyde)-1,2-phenylenediamine copper(II) complex; Thiocyanate; Furaldehyde Schiff base; Ion-selective electrode

Electrochemical studies and square-wave voltammetric determination of fenofibrate in pharmaceutical formulations by Ceren Yardımcı; Nuran Özaltın (pp. 495-498).

The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0–10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)–tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at −1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38×10⁻⁶ cm² s⁻¹ as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146–4.96 μg mL⁻¹ of fenofibrate with a limit of detection of 0.025 μg mL⁻¹. Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically.

Keywords: Fenofibrate; Square-wave voltammetry; Pharmaceutical formulations

LC-APCI-MS-MS methodology for determination of glybenclamide in human plasma by Mirian R. L. Moura; Gilberto de Nucci; Susanne Rath; Felix G. R. Reyes (pp. 499-503).

A liquid chromatographic/atmospheric pressure chemical ionization tandem mass spectrometric method (LC-APCI-MS-MS) for the determination of glybenclamide in human plasma is described. Glypizide, an analogue of glybenclamide, was used as internal standard. The analyte was extracted from plasma with diethyl ether/dichloromethane (70:30 v/v). The chromatography uses C₁₈ and 0.01 mol L⁻¹acetic acid/acetonitrile (20:80 v/v) as stationary and mobile phase, respectively. Quantitation was preformed by using multiple reaction monitoring (MRM) of the precursor ion (m/z 494.2→368.8) and the related product ion (m/z 446.0→347.3) using the internal standard method. The analytical curve was linear in the range 1–300 ng mL⁻¹, and for a 400-μL sample of human plasma, the limit of determination of the method was 1 ng mL⁻¹. The coefficients of variation of the method for intra-assay (within-run precision) and inter-assay (between-run precision) were less than 10%. The method was shown to be suitable for pharmacokinetic studies.

Keywords: Glybenclamide; Sulfonylureas; Plasma; Mass spectrometry; LC-APCI-MS-MS

Determination of rofecoxib, in the presence of its photodegradation product, in pharmaceutical preparations by micellar electrokinetic capillary chromatography by Emirhan Nemutlu; Nuran Özaltın; Sacide Altınöz (pp. 504-509).

A simple and rapid micellar electrokinetic capillary chromatographic (MEKC) method for analysis of rofecoxib (ROF) and its photodegradation product (PDP) in pharmaceutical preparations has been developed and validated. Analyses were conducted in a fused silica capillary (72 cm effective length, 50 μm i.d.) with a background electrolyte consisting of 25 mmol L⁻¹ borate buffer at pH 7.0 containing 15 mmol L⁻¹ sodium dodecyl sulfate (SDS) and 10% acetonitrile (ACN). The separation was performed by voltage-controlled system, applying 30 kV at 30 °C, detecting at 225 nm; injection was hydrodynamic at 50 mbar for 2 s. Nifedipine was used as internal standard (IS). Under the optimum conditions ROF, PDP, and IS were well separated with in 10 min. The method was validated with regard to linearity, limit of detection and quantitation, precision, accuracy, specificity, and robustness. The detection limit of the method was low, 0.8 μg mL⁻¹, and the linearity range was wide, 2.5 to 125 μg mL⁻¹. The method was highly efficient—5×10⁵ plates m⁻¹ for ROF. The method was applied to the tablet form of ROF-containing pharmaceutical preparations. The data were compared with those from the voltammetric method described in literature. No statistically significant difference was found.

Keywords: Rofecoxib; Photodegradation product; Capillary electrophoresis; Micellar electrokinetic capillary chromatography; Validation; Pharmaceuticals

Application of combined approach to analyze the constituents of essential oil from Dong quai by Lan-Fang Huang; Bo-Yan Li; Yi-Zeng Liang; Fang-Qiu Guo; Ya-Li Wang (pp. 510-517).

A combined approach of sub-window factor analysis and spectral correlative chromatography has been employed to analyze the constituents of essential oils of Dong quai. Essential oils are the main pharmacological active individuals of Dong quai. Some constituents in the main root of Dong quai have been identified by GC-MS with the help of sub-window factor analysis resolving two-dimensional original data into mass spectra and chromatograms. Correlative constituents in another part of the root fiber have been recognized by spectral correlative chromatography. Seventy six of 97 separated constituents in the essential oil of main root were identified and quantified, accounting for about 91.36% of the total content. Sixty seven correlative components in the essential oil of root fiber were recognized. The result proves that the combined approach is powerful enough for the analysis of complex herbal samples.

Keywords: Dong quai; Chemometrics; Gas chromatography–mass spectrometry; Sub-window factor analysis; Spectral correlative chromatography

Gas chromatography-mass spectrometry with solid-phase microextraction method for determination of methyl salicylate and other volatile compounds in leaves of Lycopersicon esculentum by Chunhui Deng; Xiangmin Zhang; Weimin Zhu; Ji Qian (pp. 518-522).

Methyl salicylate (MeSA) in many plants is a important signaling compound, which plays an important role in a pathogen-induced defense response. In this paper, gas chromatography-mass spectrometry (GC-MS) with headspace solid-phase microextraction (HS-SPME) was developed for determination of MeSA and other volatile compounds in leaves of a tomato plant (Lycopersicon esculentum). Tomato leaves were ground under liquid nitrogen and sampled by HS-SPME, with a 100 μm polydimethylsiloxane fiber, and finally analyzed by GC-MS. Eighteen compounds in the leaves of tomato plant infested by tobacco mosaic virus (TMV) were separated and identified, among them MeSA, which was quantitatively analyzed by the standard addition method. MeSA concentrations higher than 2.0 μg g^–1 fresh weight accumulated in leaves of TMV-infested tomato plant as the defense response to TMV. A similar concentration of MeSA in the leaves of MeSA-treated tomato plant was also found. No MeSA in leaves of control tomato plant was detected. These findings suggest that MeSA might be a signaling compound in the tomato plant response to TMV. The present method for determination of MeSA required only simple sample preparation and no organic solvent, and provided an excellent relative standard deviation of less than 5.0% and a low detection limit of 10 ng g⁻¹ fresh weight for MeSA. These results show that GC-MS-HS-SPME is a simple, rapid and sensitive method for determination of MeSA and other plant-signaling compounds in plant tissues.

Keywords: Methyl salicylate; Headspace solid-phase microextraction; Lycopersicon esculentum

Simple and rapid catalytic spectrophotometric determination of superoxide anion radical and superoxide dismutase activity in natural medical vegetables using phenol as the substrate for horseradish peroxidase by Bo Tang; Yan Wang; Li Ma (pp. 523-528).

The coupling reaction of 4-aminoantipyrine (4-AAP) with phenol using the superoxide anion radical ( % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! 2 (V_B2) was spectrophotometrically determined at 510 nm. Under the optimum experimental conditions, the relationship between A ₅₁₀ and % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX! −6–1.2×10⁻⁴ mol L⁻¹. The detection limit was determined to be 1.37×10⁻⁶ mol L⁻¹. A possible reaction mechanism was discussed. The effect of interferences and surfactants on the determination of % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!

Keywords: Horseradish peroxidase; Superoxide anion radical; Superoxide dismutase; Catalytic spectrophotometry

A study of the chemiluminescence behavior of myoglobin with luminol and its analytical applications by Zhenghua Song; Lin Wang; Shuang Hou (pp. 529-535).

A chemiluminescence signal at 425 nm was observed when ferric state myoglobin was mixed with luminol in alkaline medium. Because the signal was remarkably enhanced in the presence of Fe(CN)₆ ⁴⁻, analytical applications were investigated in a flow-injection system. The increase in chemiluminescence was linearly dependent on myoglobin concentration in the range 0.1 to 100 nmol L⁻¹, and the limit of detection was 0.04 nmol L⁻¹ with relative standard deviation 3.2% (3σ). It was also found that binding of Mb with the ligands CN⁻, SCN⁻, and F⁻ significantly inhibited the chemiluminescence reaction. The linear dynamic ranges for the ligands were 1.0–300.0, 0.1–3.0, and 0.5–100.0 nmol L⁻¹, and the limits of detection (S/N=3) 0.4, 0.04, and 0.2 nmol L⁻¹, for F⁻, CN⁻, and SCN⁻, respectively. The relative standard deviations were 5.32%, 6.13%, and 3.38% for 0.1 nmol L⁻¹ CN⁻, 0.5 nmol L⁻¹ SCN⁻, and 1.0 nmol L⁻¹ F⁻, respectively. At a flow rate of 2.0 mL min⁻¹ the assay could be accomplished in 1 min, including sampling and washing. The method has been successfully applied to the determination of myoglobin in human urine and F⁻ in water samples. A possible mechanism of chemiluminescence production by myoglobin and luminol is presented.

Keywords: Myoglobin; Chemiluminescence; Luminol; Ferrocyanide; Fluoride; Flow injection

A rapid HPLC method for the determination of carboxylic acids in human urine using a monolithic column by I. Šperlingová; L. Dabrowská; V. Stránský; M. Tichý (pp. 536-543).

A rapid HPLC method for the determination of carboxylic acids in urine samples using a Chromolith Performance RP/18e 100/4.6 with Chromolith Guard Cartridge RP/18e 10/4.6 (Merck KgaA, Darmstadt, Germany) was developed. The method facilitates the simultaneous determination of aromatic hydrocarbon metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene and ethylbenzene, hippuric acid (HA) from toluene and 2-, 3-, 4-methylhippuric acids (MHA) from xylene. 3-Hydroxybenzoic acid (3-HBA) was used as internal standard. A chromatographic run is completed within less than 5 min for styrene, ethylbenzene and toluene metabolites, and within 10 min for xylene metabolites. The detection limits are 9 mg L⁻¹ urine for MA, 1.25 mg L⁻¹ urine for PGA, 4.9 mg L⁻¹ urine for HA, 22 mg L⁻¹ urine for 2-MHA, and 18.5 mg L⁻¹ urine for 3-MHA.No significant differences of the MA, PGA and HA concentrations in human urine samples obtained by HPLC chromatography on LiChrosorb RP 18 and on Chromolith RP/18e columns were found. The results were evaluated by using ANOVA.

Keywords: Carboxylic acids; Monolithic column; Human urine

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Analytical and Bioanalytical Chemistry (v.378, #2)