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Analytical and Bioanalytical Chemistry (v.383, #3)
Addressing faculty objections to the implementation of active learning strategies in the analytical chemistry course
by Patricia Ann Mabrouk (pp. 365-367).
Addressing faculty objections to the implementation of active learning strategies in the analytical chemistry course
by Patricia Ann Mabrouk (pp. 365-367).
Application of CE–ICP–MS and CE–ESI–MS in metalloproteomics: challenges, developments, and limitations by Andreas Prange; Daniel Pröfrock (pp. 372-389).
Application of capillary electrophoresis (CE) as a high-resolution separation technique in metalloproteomics research is critically reviewed. The focus is on the requirements and challenges involved in coupling CE to sensitive element and molecule-specific detection techniques such as inductively coupled plasma mass spectrometry (ICP–MS) or electrospray ionisation mass spectrometry (ESI–MS). The complementary application of both detection techniques to the structural and functional characterisation of metal-binding proteins and their structural metal-binding moieties is emphasised. Beneficial aspects and limitations of mass spectrometry hyphenated to CE are discussed, on the basis of the literature published in this field over the last decade. Recent metalloproteomics applications of CE are reviewed to demonstrate its potential and limitations in modern biochemical speciation analysis and to indicate future directions of this technique.
Keywords: Capillary electrophoresis; ICP–MS; HR-ICP–MS; ESI–MS; Metallomics; Metalloproteomics; Metallothioneine; Selenoprotein; Proteins; Interface; Nebuliser; Hyphenated techniques
Application of CE–ICP–MS and CE–ESI–MS in metalloproteomics: challenges, developments, and limitations by Andreas Prange; Daniel Pröfrock (pp. 372-389).
Application of capillary electrophoresis (CE) as a high-resolution separation technique in metalloproteomics research is critically reviewed. The focus is on the requirements and challenges involved in coupling CE to sensitive element and molecule-specific detection techniques such as inductively coupled plasma mass spectrometry (ICP–MS) or electrospray ionisation mass spectrometry (ESI–MS). The complementary application of both detection techniques to the structural and functional characterisation of metal-binding proteins and their structural metal-binding moieties is emphasised. Beneficial aspects and limitations of mass spectrometry hyphenated to CE are discussed, on the basis of the literature published in this field over the last decade. Recent metalloproteomics applications of CE are reviewed to demonstrate its potential and limitations in modern biochemical speciation analysis and to indicate future directions of this technique.
Keywords: Capillary electrophoresis; ICP–MS; HR-ICP–MS; ESI–MS; Metallomics; Metalloproteomics; Metallothioneine; Selenoprotein; Proteins; Interface; Nebuliser; Hyphenated techniques
Detection of transferrin isoforms in human serum: comparison of UV and ICP–MS detection after CZE and HPLC separations by Sandra Arizaga Rodríguez; Elisa Blanco González; Gloria Alvarez Llamas; Maria Montes-Bayón; Alfredo Sanz-Medel (pp. 390-397).
Two methods for separation of transferrin (Tf) sialoforms, capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) with conventional UV absorbance detection, have been investigated and compared. First, conditions affecting the separation of the Tf isoforms by capillary zone electrophoresis and HPLC were carefully optimized. The use of 15 mmol L−1 borate buffer (pH 8.4) containing 3 mmol L−1 diaminobutane (DAB) as additive enabled good separation of the Tf isoforms by CE (75 cm×50 μm i.d. fused silica capillary) at 25 kV. In HPLC, a gradient of ammonium acetate (from 0 to 250 mmol L−1 in 45 min) buffered at pH 6 (Tris-HCl) proved suitable for separation of Tf isoforms on a Mono-Q HR 5/5 anion-exchange column. On-line specific detection of the iron associated with the different Tf isoforms, after Fe saturation, by inductively coupled plasma mass spectrometry (ICP–MS) was studied in detail to compare its analytical performance with UV detection. For both CE and HPLC an octapole reaction system (ORS) ICP–MS instrument was used to minimize polyatomic interferences on the 56Fe major isotope. Limits of detection of the different isoforms were in the range of 0.02–0.04 μmol L−1 Tf for HPLC–ICP (ORS)–MS. This hybrid technique proved more selective and reliable detection of transferrin isoforms with 2, 3, 4, 5, and 6 sialic acid residues (S2, S3, S4, S5, and S6) in real serum samples. Interesting results from iron speciation of Tf in serum from healthy individuals and from pregnant women are given.
Keywords: Transferrin isoforms; Iron; Capillary electrophoresis; Liquid chromatography; UV detection; Inductively coupled plasma–mass spectrometry
Detection of transferrin isoforms in human serum: comparison of UV and ICP–MS detection after CZE and HPLC separations by Sandra Arizaga Rodríguez; Elisa Blanco González; Gloria Alvarez Llamas; Maria Montes-Bayón; Alfredo Sanz-Medel (pp. 390-397).
Two methods for separation of transferrin (Tf) sialoforms, capillary electrophoresis (CE) and high performance liquid chromatography (HPLC) with conventional UV absorbance detection, have been investigated and compared. First, conditions affecting the separation of the Tf isoforms by capillary zone electrophoresis and HPLC were carefully optimized. The use of 15 mmol L−1 borate buffer (pH 8.4) containing 3 mmol L−1 diaminobutane (DAB) as additive enabled good separation of the Tf isoforms by CE (75 cm×50 μm i.d. fused silica capillary) at 25 kV. In HPLC, a gradient of ammonium acetate (from 0 to 250 mmol L−1 in 45 min) buffered at pH 6 (Tris-HCl) proved suitable for separation of Tf isoforms on a Mono-Q HR 5/5 anion-exchange column. On-line specific detection of the iron associated with the different Tf isoforms, after Fe saturation, by inductively coupled plasma mass spectrometry (ICP–MS) was studied in detail to compare its analytical performance with UV detection. For both CE and HPLC an octapole reaction system (ORS) ICP–MS instrument was used to minimize polyatomic interferences on the 56Fe major isotope. Limits of detection of the different isoforms were in the range of 0.02–0.04 μmol L−1 Tf for HPLC–ICP (ORS)–MS. This hybrid technique proved more selective and reliable detection of transferrin isoforms with 2, 3, 4, 5, and 6 sialic acid residues (S2, S3, S4, S5, and S6) in real serum samples. Interesting results from iron speciation of Tf in serum from healthy individuals and from pregnant women are given.
Keywords: Transferrin isoforms; Iron; Capillary electrophoresis; Liquid chromatography; UV detection; Inductively coupled plasma–mass spectrometry
Biosynthesis of Cd-bound phytochelatins by Phaeodactylum tricornutum and their speciation by size-exclusion chromatography and ion-pair chromatography coupled to ICP–MS by Valeria Loreti; Daniel Toncelli; Elisabetta Morelli; Gioacchino Scarano; Jörg Bettmer (pp. 398-403).
Cd-bound phytochelatins (Cd–PCs) have been synthesised by incubation of Phaeodactylum tricornutum cell cultures with Cd and purified by size-exclusion chromatography–UV–Vis. These complexes, which were identified in previous work, have now been used as model substances to develop and optimise ion-pair chromatography (IPC) coupled to inductively coupled plasma–mass spectrometry (ICP–MS) for analysis of Cd–PCs. Subsequent analysis of samples taken from Silene vulgaris plants cultivated under heavy metal stress conditions revealed Cd signals but no Cd–PC signals. By use of isotopically enriched 116Cd–PCs the sample preparation steps were verified to determine the stability of the analytes. We observed species transformation between Cd–PCs and other unidentified Cd complexes. Consequently, the kinetic and thermodynamic lability of Cd–PCs are decisive factors in their detection.
Keywords: ICP–MS; SEC; Ion-pair chromatography; Phytochelatins; Glutathione; Cadmium; Phaeodactylum tricornutum ; Silene vulgaris
Biosynthesis of Cd-bound phytochelatins by Phaeodactylum tricornutum and their speciation by size-exclusion chromatography and ion-pair chromatography coupled to ICP–MS by Valeria Loreti; Daniel Toncelli; Elisabetta Morelli; Gioacchino Scarano; Jörg Bettmer (pp. 398-403).
Cd-bound phytochelatins (Cd–PCs) have been synthesised by incubation of Phaeodactylum tricornutum cell cultures with Cd and purified by size-exclusion chromatography–UV–Vis. These complexes, which were identified in previous work, have now been used as model substances to develop and optimise ion-pair chromatography (IPC) coupled to inductively coupled plasma–mass spectrometry (ICP–MS) for analysis of Cd–PCs. Subsequent analysis of samples taken from Silene vulgaris plants cultivated under heavy metal stress conditions revealed Cd signals but no Cd–PC signals. By use of isotopically enriched 116Cd–PCs the sample preparation steps were verified to determine the stability of the analytes. We observed species transformation between Cd–PCs and other unidentified Cd complexes. Consequently, the kinetic and thermodynamic lability of Cd–PCs are decisive factors in their detection.
Keywords: ICP–MS; SEC; Ion-pair chromatography; Phytochelatins; Glutathione; Cadmium; Phaeodactylum tricornutum ; Silene vulgaris
Nickel species analysis of human colonic tissue using liquid chromatography, gel electrophoresis and mass spectrometry by Tina Knispel; Christiane Ruhnau; Stephan Lassen; Simone Griesel; Andreas Prange; Evelin Denkhaus (pp. 404-413).
Studies to specify metal-binding species, such as metalloproteins that are present in trace amounts in colonic cell cytosol, using chromatographic separation methods in combination with inductively coupled plasma mass spectrometry (ICP-MS) as element-specific detection require an optimised sample preparation regarding the solubilisation of the proteins. Focus should be taken to avoid metal contamination, enzymatic digestion by different proteases and oxidation. In this article different sample preparation methods are studied to find a suitable method for the isolation and characterisation of Ni species previously found in cytosols from normal and malignant tissues of the human colon. The total Ni concentrations of the cytosols were determined as well as the total protein content. Thus, a Ni-containing protein could be isolated from cytosols of malignant human colonic tissues using size-exclusion chromatography with ICP-MS for element-specific detection. Ni-containing species in the molecular mass range from 10,000 to 20,000 Da were found and pre-concentrated. The determination of the molecular mass of the species was performed through online coupling of reversed-phase chromatography with electrospray ionisation quadrupole time-of-flight MS. Using identical chromatographic conditions and ICP-MS the detected protein was shown to contain Ni.
Keywords: Nickel; Species analysis; Size-exclusion chromatography; Inductively coupled plasma mass spectrometry; Electrospray ionisation quadrupole time-of-flight mass spectrometry
Nickel species analysis of human colonic tissue using liquid chromatography, gel electrophoresis and mass spectrometry by Tina Knispel; Christiane Ruhnau; Stephan Lassen; Simone Griesel; Andreas Prange; Evelin Denkhaus (pp. 404-413).
Studies to specify metal-binding species, such as metalloproteins that are present in trace amounts in colonic cell cytosol, using chromatographic separation methods in combination with inductively coupled plasma mass spectrometry (ICP-MS) as element-specific detection require an optimised sample preparation regarding the solubilisation of the proteins. Focus should be taken to avoid metal contamination, enzymatic digestion by different proteases and oxidation. In this article different sample preparation methods are studied to find a suitable method for the isolation and characterisation of Ni species previously found in cytosols from normal and malignant tissues of the human colon. The total Ni concentrations of the cytosols were determined as well as the total protein content. Thus, a Ni-containing protein could be isolated from cytosols of malignant human colonic tissues using size-exclusion chromatography with ICP-MS for element-specific detection. Ni-containing species in the molecular mass range from 10,000 to 20,000 Da were found and pre-concentrated. The determination of the molecular mass of the species was performed through online coupling of reversed-phase chromatography with electrospray ionisation quadrupole time-of-flight MS. Using identical chromatographic conditions and ICP-MS the detected protein was shown to contain Ni.
Keywords: Nickel; Species analysis; Size-exclusion chromatography; Inductively coupled plasma mass spectrometry; Electrospray ionisation quadrupole time-of-flight mass spectrometry
Combination of gel electrophoresis and ICP-mass spectrometry—novel strategies for phosphoprotein measurement by Victoria L. Elliott; Cameron W. McLeod; Peter S. Marshall (pp. 416-423).
The potential for developing improved procedures for phosphate measurement through combinations of gel electrophoresis and quadrupole-based ICP mass spectrometry utilising 47PO+ is investigated. Laser ablation of gels offers a rapid and direct quantitation route, but is subject to high blanks due to P impurities in gels and associated reagents; nevertheless optimisation of laser sampling afforded improved method sensitivity (limit of detection 0.09 μg g−1). Implementation of whole gel elution (WGE) with FI-ICP-MS (conventional solution nebulisation) following gel electrophoresis permitted quantitation at the sub μg l−1 level, and microcolumn processing (activated alumina) was effective at rejecting phosphate contamination. The potential for S-induced molecular ion interference at mass 47 was demonstrated.
Keywords: Inductively-coupled plasma mass spectrometry; Laser ablation; Flow injection; Gel electrophoresis; Whole gel elution; Phosphoprotein measurement
Combination of gel electrophoresis and ICP-mass spectrometry—novel strategies for phosphoprotein measurement by Victoria L. Elliott; Cameron W. McLeod; Peter S. Marshall (pp. 416-423).
The potential for developing improved procedures for phosphate measurement through combinations of gel electrophoresis and quadrupole-based ICP mass spectrometry utilising 47PO+ is investigated. Laser ablation of gels offers a rapid and direct quantitation route, but is subject to high blanks due to P impurities in gels and associated reagents; nevertheless optimisation of laser sampling afforded improved method sensitivity (limit of detection 0.09 μg g−1). Implementation of whole gel elution (WGE) with FI-ICP-MS (conventional solution nebulisation) following gel electrophoresis permitted quantitation at the sub μg l−1 level, and microcolumn processing (activated alumina) was effective at rejecting phosphate contamination. The potential for S-induced molecular ion interference at mass 47 was demonstrated.
Keywords: Inductively-coupled plasma mass spectrometry; Laser ablation; Flow injection; Gel electrophoresis; Whole gel elution; Phosphoprotein measurement
Radio frequency glow discharge source with integrated voltage and current probes used for sputtering rate and emission yield measurements at insulating samples by L. Wilken; V. Hoffmann; K. Wetzig (pp. 424-433).
Radio frequency glow discharge optical emission spectroscopy (RF-GD-OES) is routinely used for the chemical analysis of solid samples. Two independent electrical signals from the discharge are required for quantification. When sputtering insulating samples, the voltage over the discharge is not directly measurable. The coupling capacity of the sample is required in order to calculate the discharge voltage. A procedure is outlined where the coupling capacity is determined using an electrical measurement without discharge. The calculated time-dependent discharge voltage and current are evaluated using a plasma equivalent circuit. An insulating sample is sputtered at constant cathode voltage and current. The emission yield for an aluminium line is comparable to that of conducting reference material.
Keywords: Radio frequency; Glow discharge; Optical emission spectroscopy; Plasma equivalent circuit
Radio frequency glow discharge source with integrated voltage and current probes used for sputtering rate and emission yield measurements at insulating samples by L. Wilken; V. Hoffmann; K. Wetzig (pp. 424-433).
Radio frequency glow discharge optical emission spectroscopy (RF-GD-OES) is routinely used for the chemical analysis of solid samples. Two independent electrical signals from the discharge are required for quantification. When sputtering insulating samples, the voltage over the discharge is not directly measurable. The coupling capacity of the sample is required in order to calculate the discharge voltage. A procedure is outlined where the coupling capacity is determined using an electrical measurement without discharge. The calculated time-dependent discharge voltage and current are evaluated using a plasma equivalent circuit. An insulating sample is sputtered at constant cathode voltage and current. The emission yield for an aluminium line is comparable to that of conducting reference material.
Keywords: Radio frequency; Glow discharge; Optical emission spectroscopy; Plasma equivalent circuit
The agglomeration state of nanosecond laser-generated aerosol particles entering the ICP by Hans-Rudolf Kuhn; Detlef Günther (pp. 434-441).
Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving laser-ablation ICP–MS. To obtain more information about particles entering the ICP, laser aerosols generated under different ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent (NIST SRM 610) glass, CaF2, and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the condensed nano-particles (∼10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF2 have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection.
Keywords: Laser-ablation ICP–MS; Aerosol transport; Particles; Particle agglomeration
The agglomeration state of nanosecond laser-generated aerosol particles entering the ICP by Hans-Rudolf Kuhn; Detlef Günther (pp. 434-441).
Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving laser-ablation ICP–MS. To obtain more information about particles entering the ICP, laser aerosols generated under different ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent (NIST SRM 610) glass, CaF2, and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the condensed nano-particles (∼10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF2 have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection.
Keywords: Laser-ablation ICP–MS; Aerosol transport; Particles; Particle agglomeration
Direct determination of platinum group elements and their distributions in geological and environmental samples at the ng g−1 level using LA–ICP–IDMS by Sergei F. Boulyga; Klaus G. Heumann (pp. 442-447).
Laser ablation inductively coupled plasma isotope dilution mass spectrometry (LA–ICP–IDMS) was applied to the direct and simultaneous determination of the platinum group elements (PGEs) Pt, Pd, Ru, and Ir in geological and environmental samples. A special laser ablation system with high ablation rates was used, along with sector field ICP–MS. Special attention was paid to deriving the distributions of PGEs in the pulverized samples. IDMS could not be applied to the (mono-isotopic) Rh, but the similar ablation behavior of Ru and Rh allowed Rh to be simultaneously determined via relative sensitivity coefficients. The laser ablation process produces hardly any oxide ions (which usually cause interference in PGE analysis with liquid sample injection), so the ICP–MS can be run in its low mass resolution but high-sensitivity mode. The detection limits obtained for the geological samples were 0.16 ng g−1, 0.14 ng g−1, 0.08 ng g−1, 0.01 ng g−1 and 0.06 ng g−1 for Ru, Rh, Pd, Ir and Pt, respectively. LA–ICP–IDMS was applied to different geological reference materials (TDB-1, WGB-1, UMT-1, WMG-1, SARM-7) and the road dust reference material BCR-723, which are only certified for some of the PGEs. Comparisons with certified values as well as with indicative values from the literature demonstrated the validity of the LA–ICP–IDMS method. The PGE concentrations in subsamples of the road dust reference material correspond to a normal distribution, whereas the distributions in the geological reference materials TDB-1, WGB-1, UMT-1, WMG-1, and SARM-7 are more complex. For example, in the case of Ru, a logarithmic normal distribution best fits the analyzed concentrations in TDB-1 subsamples, whereas a pronounced nugget effect was found for Pt in most geological samples.
Keywords: Platinum group elements; Rock samples; Reference materials; Isotope dilution; Laser ablation; Inductively coupled plasma mass spectrometry
Direct determination of platinum group elements and their distributions in geological and environmental samples at the ng g−1 level using LA–ICP–IDMS by Sergei F. Boulyga; Klaus G. Heumann (pp. 442-447).
Laser ablation inductively coupled plasma isotope dilution mass spectrometry (LA–ICP–IDMS) was applied to the direct and simultaneous determination of the platinum group elements (PGEs) Pt, Pd, Ru, and Ir in geological and environmental samples. A special laser ablation system with high ablation rates was used, along with sector field ICP–MS. Special attention was paid to deriving the distributions of PGEs in the pulverized samples. IDMS could not be applied to the (mono-isotopic) Rh, but the similar ablation behavior of Ru and Rh allowed Rh to be simultaneously determined via relative sensitivity coefficients. The laser ablation process produces hardly any oxide ions (which usually cause interference in PGE analysis with liquid sample injection), so the ICP–MS can be run in its low mass resolution but high-sensitivity mode. The detection limits obtained for the geological samples were 0.16 ng g−1, 0.14 ng g−1, 0.08 ng g−1, 0.01 ng g−1 and 0.06 ng g−1 for Ru, Rh, Pd, Ir and Pt, respectively. LA–ICP–IDMS was applied to different geological reference materials (TDB-1, WGB-1, UMT-1, WMG-1, SARM-7) and the road dust reference material BCR-723, which are only certified for some of the PGEs. Comparisons with certified values as well as with indicative values from the literature demonstrated the validity of the LA–ICP–IDMS method. The PGE concentrations in subsamples of the road dust reference material correspond to a normal distribution, whereas the distributions in the geological reference materials TDB-1, WGB-1, UMT-1, WMG-1, and SARM-7 are more complex. For example, in the case of Ru, a logarithmic normal distribution best fits the analyzed concentrations in TDB-1 subsamples, whereas a pronounced nugget effect was found for Pt in most geological samples.
Keywords: Platinum group elements; Rock samples; Reference materials; Isotope dilution; Laser ablation; Inductively coupled plasma mass spectrometry
Investigation of the species-specific degradation behaviour of methylmercury and ethylmercury under microwave irradiation by László Abrankó; Zsuzsa Jókai; Péter Fodor (pp. 448-453).
The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh4). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min. The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte loss was observed for EtHg after 2 minutes at 40 W of microwave power.
Keywords: Methylmercury; Ethylmercury; Microwave; Degradation; Phenylation
Investigation of the species-specific degradation behaviour of methylmercury and ethylmercury under microwave irradiation by László Abrankó; Zsuzsa Jókai; Péter Fodor (pp. 448-453).
The degradation behaviour of methylmercury (MeHg) under microwave irradiation is investigated, as is the (different) degradation behaviour of ethylmercury (EtHg) under similar irradiation. A simple and highly sensitive SPME-GC-pyrolysis-AFS system was used to analyse the aqueous MeHg and EtHg standard solutions after derivatization with sodium tetraphenylborate (NaBPh4). Samples were irradiated in a microwave digester at microwave powers ranging from 20 to 160 W for durations of 2 to 10 min. The different tolerances towards microwave treatment of the two organomercury species were evident. Practically no degradation was experienced for MeHg for up to 8 minutes of irradiation at 120 W or for up to 4 minutes at 160 W. Significant analyte loss was observed for EtHg after 2 minutes at 40 W of microwave power.
Keywords: Methylmercury; Ethylmercury; Microwave; Degradation; Phenylation
Determination of arsenic species and arsenosugars in marine samples by HPLC–ICP–MS by Shizuko Hirata; Hideki Toshimitsu (pp. 454-460).
Arsenic-speciation analysis in marine samples was performed by high-pressure liquid chromatography (HPLC) with ICP–MS detection. Separation of eight arsenic species—AsIII, MMA, DMA, AsV, AB, TMAO, AC and TeMAs+—was achieved on a C18 column with isocratic elution (pH 3.0), under which conditions AsIII and MMA co-eluted. The entire separation was accomplished in 15 min. The HPLC–ICP–MS detection limits for the eight arsenic species were in the range 0.03–0.23 μg L−1 based on 3σ for the blank response (n=5). The precision was calculated to be 2.4–8.0% (RSD) for the eight species. The method was successfully applied to several marine samples, e.g. oysters, fish, shrimps, and marine algae. Low-power microwave digestion was employed for extraction of arsenic from seafood products; ultrasonic extraction was employed for the extraction of arsenic from seaweeds. Separation of arsenosugars was achieved on an anion-exchange column. Concentrations of arsenosugars 2, 3, and 4 in marine algae were in the range 0.18–9.59 μg g−1.
Keywords: HPLC–ICP–MS; Arsenic species; Arsenosugars; Marine algae; Microwave extraction; Sonication
Determination of arsenic species and arsenosugars in marine samples by HPLC–ICP–MS by Shizuko Hirata; Hideki Toshimitsu (pp. 454-460).
Arsenic-speciation analysis in marine samples was performed by high-pressure liquid chromatography (HPLC) with ICP–MS detection. Separation of eight arsenic species—AsIII, MMA, DMA, AsV, AB, TMAO, AC and TeMAs+—was achieved on a C18 column with isocratic elution (pH 3.0), under which conditions AsIII and MMA co-eluted. The entire separation was accomplished in 15 min. The HPLC–ICP–MS detection limits for the eight arsenic species were in the range 0.03–0.23 μg L−1 based on 3σ for the blank response (n=5). The precision was calculated to be 2.4–8.0% (RSD) for the eight species. The method was successfully applied to several marine samples, e.g. oysters, fish, shrimps, and marine algae. Low-power microwave digestion was employed for extraction of arsenic from seafood products; ultrasonic extraction was employed for the extraction of arsenic from seaweeds. Separation of arsenosugars was achieved on an anion-exchange column. Concentrations of arsenosugars 2, 3, and 4 in marine algae were in the range 0.18–9.59 μg g−1.
Keywords: HPLC–ICP–MS; Arsenic species; Arsenosugars; Marine algae; Microwave extraction; Sonication
Arsenic speciation in xylem sap of cucumber (Cucumis sativus L.) by Victor G. Mihucz; Enikő Tatár; István Virág; Edit Cseh; Ferenc Fodor; Gyula Záray (pp. 461-466).
Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm−3 arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.
Keywords: Plants; Xylem; Arsenic; Speciation; HPLC; ICP-MS
Arsenic speciation in xylem sap of cucumber (Cucumis sativus L.) by Victor G. Mihucz; Enikő Tatár; István Virág; Edit Cseh; Ferenc Fodor; Gyula Záray (pp. 461-466).
Flow injection analysis (FIA) and high-performance liquid chromatography double-focusing sector field inductively coupled plasma mass spectrometry (HPLC-DF-ICP-MS) were used for total arsenic determination and arsenic speciation of xylem sap of cucumber plants (Cucumis sativus L.) grown in hydroponics containing 2 μmol dm−3 arsenate or arsenite, respectively. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMA) were identified in the sap of the plants. Arsenite was the predominant arsenic species in the xylem saps regardless of the type of arsenic treatment, and the following concentration order was determined: As(III) > As(V) > DMA. The amount of total As, calculated taking into consideration the mass of xylem sap collected, was almost equal for both treatments. Arsenite was taken up more easily by cucumber than arsenate. Partial oxidation of arsenite to arsenate (<10% in 48 h) was observed in the case of arsenite-containing nutrient solutions, which may explain the detection of arsenate in the saps of plants treated with arsenite.
Keywords: Plants; Xylem; Arsenic; Speciation; HPLC; ICP-MS
Speciation of aluminium in tea infusions by use of SEC and FPLC with ICP–OES and ES–MS–MS detection by Blaž Kralj; Igor Križaj; Peter Bukovec; Simon Slejko; Radmila Milačič (pp. 467-475).
Speciation of Al in tea infusions was studied by size exclusion chromatography (SEC) and anion-exchange fast protein liquid chromatography (FPLC). Fractions were collected throughout the chromatographic separations and Al was determined “off line” by inductively coupled plasma optical emission spectroscopy (ICP–OES). Black, green, and red tea samples were investigated. The total concentration of Al in tea infusions was determined by ICP–OES and ranged between 0.5 and 4 mg dm−3. The pH of tea infusions ranged between 5.3 and 5.5. Data from SEC–ICP–OES analysis indicated that 10–35% of total Al in tea infusions was eluted at a retention volume corresponding to a molecular mass of approximately 3800 Da. The remaining Al was adsorbed on the column resin. The same tea infusions were also analysed by anion-exchange FPLC–ICP–OES. It was found experimentally that the same percentage of total Al as from the SEC column was eluted at a retention volume that corresponded to negatively charged Al-citrate. The remaining Al was adsorbed on the column resin. Identification of Al-binding ligands eluting under the chromatographic peak was performed by electrospray ionisation tandem mass spectrometry (ES–MS–MS) analysis. It was proven that ionic Al species in tea infusions (10–35% of the total Al) corresponded to negatively charged Al-citrate. The remaining species that was adsorbed on the SEC or FPLC columns was most probably bound to phenolic compounds. Speciation of Al in tea with milk or lemon was also studied. Results for tea with milk indicated that Al-citrate was not transformed and that approximately 60% of total Al was transformed into high-molecular-mass Al species. This fraction was subjected to sodium dodecyl sulfonate polyacryl gel electrophoresis (SDS–PAGE). The results indicated that Al was occluded by milk proteins (mostly caseins). When citric acid was added to tea infusions the percentage of negatively charged Al-citrate remained either the same or increased to 40% of total Al.
Keywords: Al speciation; Tea infusions; Size-exclusion chromatography; Fast protein liquid chromatography; UV detection; Electrospray MS–MS; SDS–PAGE; Inductively coupled plasma–optical emission spectrometry
Speciation of aluminium in tea infusions by use of SEC and FPLC with ICP–OES and ES–MS–MS detection by Blaž Kralj; Igor Križaj; Peter Bukovec; Simon Slejko; Radmila Milačič (pp. 467-475).
Speciation of Al in tea infusions was studied by size exclusion chromatography (SEC) and anion-exchange fast protein liquid chromatography (FPLC). Fractions were collected throughout the chromatographic separations and Al was determined “off line” by inductively coupled plasma optical emission spectroscopy (ICP–OES). Black, green, and red tea samples were investigated. The total concentration of Al in tea infusions was determined by ICP–OES and ranged between 0.5 and 4 mg dm−3. The pH of tea infusions ranged between 5.3 and 5.5. Data from SEC–ICP–OES analysis indicated that 10–35% of total Al in tea infusions was eluted at a retention volume corresponding to a molecular mass of approximately 3800 Da. The remaining Al was adsorbed on the column resin. The same tea infusions were also analysed by anion-exchange FPLC–ICP–OES. It was found experimentally that the same percentage of total Al as from the SEC column was eluted at a retention volume that corresponded to negatively charged Al-citrate. The remaining Al was adsorbed on the column resin. Identification of Al-binding ligands eluting under the chromatographic peak was performed by electrospray ionisation tandem mass spectrometry (ES–MS–MS) analysis. It was proven that ionic Al species in tea infusions (10–35% of the total Al) corresponded to negatively charged Al-citrate. The remaining species that was adsorbed on the SEC or FPLC columns was most probably bound to phenolic compounds. Speciation of Al in tea with milk or lemon was also studied. Results for tea with milk indicated that Al-citrate was not transformed and that approximately 60% of total Al was transformed into high-molecular-mass Al species. This fraction was subjected to sodium dodecyl sulfonate polyacryl gel electrophoresis (SDS–PAGE). The results indicated that Al was occluded by milk proteins (mostly caseins). When citric acid was added to tea infusions the percentage of negatively charged Al-citrate remained either the same or increased to 40% of total Al.
Keywords: Al speciation; Tea infusions; Size-exclusion chromatography; Fast protein liquid chromatography; UV detection; Electrospray MS–MS; SDS–PAGE; Inductively coupled plasma–optical emission spectrometry
Determination of trace elements in human liver biopsy samples by ICP–MS and TXRF: hepatic steatosis and nickel accumulation by Imre Varga; Ágnes Szebeni; Norbert Szoboszlai; Béla Kovács (pp. 476-482).
Human liver biopsy samples, collected from 52 individuals, were analysed by inductively coupled plasma–mass spectrometry (ICP–MS) and total reflection X-ray fluorescence (TXRF) spectrometry in a retrospective study (i.e. patient selection and liver biopsy were not for the purpose of element analysis). The freeze-dried samples (typically 0.5–2 mg dry weight) were digested in a laboratory microwave digestion system and solutions with a final volume of 1 mL were prepared. The concentrations of Cr, Mn, Fe, Ni, Cu, Zn, Rb, and Pb were determined by use of a Thermo Elemental X7 ICP–MS spectrometer. TXRF measurements were performed with an Atomika Extra IIA spectrometer. Yttrium was employed as an internal standard, prepared by dissolution of 5N-purity yttria (Y2O3) in our laboratory. The accuracy was tested by analysis of NIST 1577a Bovine Liver certified reference material. The concentrations of Fe, Cu, Zn, and Rb determined in human liver biopsy samples were in good agreement with data published by other authors. The distribution of nickel in the samples was surprisingly uneven—nickel concentrations ranged from 0.7 to 12 μg g−1 (dry weight) in 38 samples and in several samples were extremely high, 36–693 μg g−1. Analysis of replicate procedural blanks and control measurements were performed to prevent misinterpretation of the data. For patients with steatosis (n=14) Ni concentrations were consistently high except for two who had levels close to those measured for the normal group. As far as we are aware no previous literature data are available on the association of steatosis with high concentration of nickel in human liver biopsies taken from living patients.
Keywords: Human liver biopsy; Hepatic steatosis; ICP–mass spectrometry; X-ray fluorescence analysis; Nickel
Determination of trace elements in human liver biopsy samples by ICP–MS and TXRF: hepatic steatosis and nickel accumulation by Imre Varga; Ágnes Szebeni; Norbert Szoboszlai; Béla Kovács (pp. 476-482).
Human liver biopsy samples, collected from 52 individuals, were analysed by inductively coupled plasma–mass spectrometry (ICP–MS) and total reflection X-ray fluorescence (TXRF) spectrometry in a retrospective study (i.e. patient selection and liver biopsy were not for the purpose of element analysis). The freeze-dried samples (typically 0.5–2 mg dry weight) were digested in a laboratory microwave digestion system and solutions with a final volume of 1 mL were prepared. The concentrations of Cr, Mn, Fe, Ni, Cu, Zn, Rb, and Pb were determined by use of a Thermo Elemental X7 ICP–MS spectrometer. TXRF measurements were performed with an Atomika Extra IIA spectrometer. Yttrium was employed as an internal standard, prepared by dissolution of 5N-purity yttria (Y2O3) in our laboratory. The accuracy was tested by analysis of NIST 1577a Bovine Liver certified reference material. The concentrations of Fe, Cu, Zn, and Rb determined in human liver biopsy samples were in good agreement with data published by other authors. The distribution of nickel in the samples was surprisingly uneven—nickel concentrations ranged from 0.7 to 12 μg g−1 (dry weight) in 38 samples and in several samples were extremely high, 36–693 μg g−1. Analysis of replicate procedural blanks and control measurements were performed to prevent misinterpretation of the data. For patients with steatosis (n=14) Ni concentrations were consistently high except for two who had levels close to those measured for the normal group. As far as we are aware no previous literature data are available on the association of steatosis with high concentration of nickel in human liver biopsies taken from living patients.
Keywords: Human liver biopsy; Hepatic steatosis; ICP–mass spectrometry; X-ray fluorescence analysis; Nickel
Determination of free and total sulfur dioxide in wine samples by vapour-generation inductively coupled plasma–optical-emission spectrometry by Jiří Čmelík; Jiří Machát; Eva Niedobová; Vítězslav Otruba; Viktor Kanický (pp. 483-488).
Sulfur dioxide (SO2) is used as a preservative and stabilizer in wine production to prevent undesired biochemical processes in the must and the final product. The concentration of SO2 is restricted by national regulations. There are two main forms of SO2 in wine—free (inorganic forms) and bound (fixed to organic compounds, e.g. aldehydes). Iodometric titration is commonly employed for determination of SO2 concentration (either by direct titration or after pre-separation by distillation); other techniques are also used. In this work inductively coupled plasma–optical-emission spectrometry with vapour generation was used for determination of free and total SO2 in wine. Gaseous SO2 is released from the sample by addition of acid and swept into the ICP by an argon stream. The intensity of the sulfur atomic emission lines is measured in the vacuum UV region. Determination of total SO2 is performed after hydrolysis of bound forms with sodium hydroxide (NaOH). Concentrations of acid for vapour generation and NaOH for hydrolysis were optimised. The method was used for determination of free and total SO2 in red and white wine samples and results were compared with those from iodometric titration.
Keywords: Sulfur dioxide; Wine; Vapour generation; ICP–OES
Determination of free and total sulfur dioxide in wine samples by vapour-generation inductively coupled plasma–optical-emission spectrometry by Jiří Čmelík; Jiří Machát; Eva Niedobová; Vítězslav Otruba; Viktor Kanický (pp. 483-488).
Sulfur dioxide (SO2) is used as a preservative and stabilizer in wine production to prevent undesired biochemical processes in the must and the final product. The concentration of SO2 is restricted by national regulations. There are two main forms of SO2 in wine—free (inorganic forms) and bound (fixed to organic compounds, e.g. aldehydes). Iodometric titration is commonly employed for determination of SO2 concentration (either by direct titration or after pre-separation by distillation); other techniques are also used. In this work inductively coupled plasma–optical-emission spectrometry with vapour generation was used for determination of free and total SO2 in wine. Gaseous SO2 is released from the sample by addition of acid and swept into the ICP by an argon stream. The intensity of the sulfur atomic emission lines is measured in the vacuum UV region. Determination of total SO2 is performed after hydrolysis of bound forms with sodium hydroxide (NaOH). Concentrations of acid for vapour generation and NaOH for hydrolysis were optimised. The method was used for determination of free and total SO2 in red and white wine samples and results were compared with those from iodometric titration.
Keywords: Sulfur dioxide; Wine; Vapour generation; ICP–OES
Analytical evidence of amorphous microdomains within nitridosilicate and nitridoaluminosilicate single crystals by Frank Ottinger; Ivana Kroslakova; Kathrin Hametner; Eric Reusser; Reinhard Nesper; Detlef Günther (pp. 489-499).
Single crystals of new nitridosilicates and nitridoaluminosilicates with excellent R values in X-ray investigations were analysed quantitatively using 30 to 60 μm single-spot LA-ICP-MS. Significant discrepancies between expected and measured chemical composition could not be explained by the crystallographic data. High spatial resolution analysis using electron probe microanalysis (EPMA, 10 μm) leads to the discovery of inhomogeneities in the crystalline material. The application of standard single-spot LA-ICP-MS with a spatial resolution of 30 to 60 μm is not suitable for the analysis of these crystals as the existing inhomogeneities dominate and alter the determined concentrations. However, owing to the better detection capabilities, a scanning LA-ICP-MS procedure enables a more representative analysis of single crystals of Ca5Si2Al2N8 than single-spot LA-ICP-MS as a result of a larger sampling volume. It is highly likely that these impurities consist of amorphous, vitreous phases as powder diffraction X-ray data indicates the existence of a significant fraction of an X-ray amorphous material besides crystalline silicates. These microdomains contain less aluminium, silicon and calcium or are nearly free of aluminium, which explains the detected discrepancies in the chemical composition.
Keywords: Nitridosilicates; Single crystals; Microprobe; LA-ICP-MS
Analytical evidence of amorphous microdomains within nitridosilicate and nitridoaluminosilicate single crystals by Frank Ottinger; Ivana Kroslakova; Kathrin Hametner; Eric Reusser; Reinhard Nesper; Detlef Günther (pp. 489-499).
Single crystals of new nitridosilicates and nitridoaluminosilicates with excellent R values in X-ray investigations were analysed quantitatively using 30 to 60 μm single-spot LA-ICP-MS. Significant discrepancies between expected and measured chemical composition could not be explained by the crystallographic data. High spatial resolution analysis using electron probe microanalysis (EPMA, 10 μm) leads to the discovery of inhomogeneities in the crystalline material. The application of standard single-spot LA-ICP-MS with a spatial resolution of 30 to 60 μm is not suitable for the analysis of these crystals as the existing inhomogeneities dominate and alter the determined concentrations. However, owing to the better detection capabilities, a scanning LA-ICP-MS procedure enables a more representative analysis of single crystals of Ca5Si2Al2N8 than single-spot LA-ICP-MS as a result of a larger sampling volume. It is highly likely that these impurities consist of amorphous, vitreous phases as powder diffraction X-ray data indicates the existence of a significant fraction of an X-ray amorphous material besides crystalline silicates. These microdomains contain less aluminium, silicon and calcium or are nearly free of aluminium, which explains the detected discrepancies in the chemical composition.
Keywords: Nitridosilicates; Single crystals; Microprobe; LA-ICP-MS
Time-resolved monitoring of heavy-metal intoxication in single hair by laser ablation ICP–DRCMS by Christina Stadlbauer; Thomas Prohaska; Christian Reiter; Anna Knaus; Gerhard Stingeder (pp. 500-508).
The potential of laser ablation inductively coupled plasma mass spectrometry for the time-resolved analysis of heavy-metal intoxication in human bodies by analysis of hair is demonstrated. As application, we analyzed forensic samples from one individual after Hg intake and from one treated with a Pt-containing cytostatic remedy. Single hairs were analyzed from the hair root to the tip by laser ablation ICP–MS with a spatial resolution of 20 μm (corresponding to approx. 2 h growth of the hair). Sulfur was used as internal standard and was analyzed by using oxygen as reaction gas in the dynamic reaction cell of the ICP–DRCMS. The detection limits for Hg and Pt were found to be 0.3 µg g–1 and 0.5 ng g−1, respectively. Standard uncertainties for the quantification results were 10% for Hg and approximately 15 % for Pt. The analyzed hair samples reflected the forensic evidence in both cases. A significant increase of Hg concentration, by a factor of 50, at the time of HgO administration could be shown, and variation of Pt in the hair strands could be used to monitor the time and relative amount of Pt intake by the patient. The investigations also revealed that the concentrations in the outer and the inner parts of the hair varied similarly with time, even though the concentration in the core of the hair is approximately 0.25 that at the surface for both Pt and Hg.
Keywords: Biomonitoring; Forensic analysis; Heavy-metal intoxication; ICP–MS; LA–ICP–MS
Time-resolved monitoring of heavy-metal intoxication in single hair by laser ablation ICP–DRCMS by Christina Stadlbauer; Thomas Prohaska; Christian Reiter; Anna Knaus; Gerhard Stingeder (pp. 500-508).
The potential of laser ablation inductively coupled plasma mass spectrometry for the time-resolved analysis of heavy-metal intoxication in human bodies by analysis of hair is demonstrated. As application, we analyzed forensic samples from one individual after Hg intake and from one treated with a Pt-containing cytostatic remedy. Single hairs were analyzed from the hair root to the tip by laser ablation ICP–MS with a spatial resolution of 20 μm (corresponding to approx. 2 h growth of the hair). Sulfur was used as internal standard and was analyzed by using oxygen as reaction gas in the dynamic reaction cell of the ICP–DRCMS. The detection limits for Hg and Pt were found to be 0.3 µg g–1 and 0.5 ng g−1, respectively. Standard uncertainties for the quantification results were 10% for Hg and approximately 15 % for Pt. The analyzed hair samples reflected the forensic evidence in both cases. A significant increase of Hg concentration, by a factor of 50, at the time of HgO administration could be shown, and variation of Pt in the hair strands could be used to monitor the time and relative amount of Pt intake by the patient. The investigations also revealed that the concentrations in the outer and the inner parts of the hair varied similarly with time, even though the concentration in the core of the hair is approximately 0.25 that at the surface for both Pt and Hg.
Keywords: Biomonitoring; Forensic analysis; Heavy-metal intoxication; ICP–MS; LA–ICP–MS
GC–ICP–MS determination of dimethylselenide in human breath after ingestion of 77Se-enriched selenite: monitoring of in-vivo methylation of selenium by Daniel Kremer; Gunter Ilgen; Jörg Feldmann (pp. 509-515).
The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg 77Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked 77Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R 2=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L−1, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of 77Se-enriched selenite. Additional DM77Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of 77Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R 2=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L−1 whereas the dietary background level was less than 0.4 ng Se L−1. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.
Keywords: GC–ICP–MS; Selenium; Breath; Urine; Dimethylselenide; Isotope labelling
GC–ICP–MS determination of dimethylselenide in human breath after ingestion of 77Se-enriched selenite: monitoring of in-vivo methylation of selenium by Daniel Kremer; Gunter Ilgen; Jörg Feldmann (pp. 509-515).
The amount of volatile dimethylselenide (DMSe) in breath has been monitored after ingestion of sub-toxic amounts of selenium (300 μg 77Se, as selenite) by a healthy male volunteer. The breath samples were collected in Tedlar bags every hour in the first 12 h and then at longer intervals for the next 10 days. The samples were subjected to speciation analysis for volatile selenium compounds by use of cryotrapping–cryofocussing–GC–ICP–MS. Simultaneously, all urine was collected and subjected to total selenium determination by use of ICP–MS. By monitoring m/z 82 and 77, background or dietary selenium and selenium from the administered selenite were simultaneously determined in the urine and in the breath—dietary selenium only was measured by monitoring m/z 82 whereas the amount of spiked 77Se (99.1% [enriched spike]) and naturally occurring selenium (7.6% [natural abundance]) were measured by monitoring m/z 77. Quantification of DMSe was performed by using DMSe gas samples prepared in Tedlar bags (linear range 10–300 pg, R 2=0.996, detection limit of Se as DMSe was 10 pg Se, or 0.02 ng L−1, when 0.5 L gas was collected). Dimethylselenide was the only selenium species detected in breath samples before and after the ingestion of 77Se-enriched selenite. Additional DM77Se was identified as early as 15 min after ingestion of the isotopically-labelled selenite. Although the maximum concentration of 77Se in DMSe was recorded 90 min after ingestion, the natural isotope ratio for selenium in DMSe (77/82) was not reached after 20 days. The concentration of DMSe correlated with the total Se concentration in the urine during the experiment (R 2=0.80). Furthermore, the sub-toxic dose of 300 μg selenium led to a significant increase of DMSe and renal excretion of background selenium, confirming that selenium ingested as selenite is homeostatically controlled by excretion. The maximum concentration of DMSe resulting from the spiked selenite was 1.4 ng Se L−1 whereas the dietary background level was less than 0.4 ng Se L−1. Overall excretion as DMSe was calculated to be 11.2% from the ingested selenite within the first 10 days whereas urinary excretion accounts for nearly 18.5%.
Keywords: GC–ICP–MS; Selenium; Breath; Urine; Dimethylselenide; Isotope labelling
Analysis of the selenium species distribution in cow blood by size exclusion liquid chromatography–inductively coupled plasma collision cell mass spectrometry (SEC–ICPccMS) by Òscar Palacios; Jorge Ruiz Encinar; Gérard Bertin; Ryszard Lobinski (pp. 516-522).
A method for performing rapid semiquantitative screening of the distribution of Se species in the blood of cows fed with a diet enriched in selenized yeast was optimized. The method was based on direct injection of a blood sample onto a high resolution size exclusion chromatographic column and fractionation of the selenium species. Selenium was detected on-line by ICP-MS with a collision cell. The concentrations of selenized haemoglobin and free selenomethionine were estimated using the chromatogram. The method was applied to a study involving 15 control and 15 treated dairy cows at four different supplementation time points. The increase in the selenomethionine and selenized haemoglobin was a linear function of the total selenium concentration. A threshold value of 600 ng ml−1 of total Se was established beyond which selenomethionine could not be incorporated into the protein. No inorganic selenium was found to be present. The total selenium in cow blood correlated well with that in milk. The selenium supplementation did not change the protein distribution profiles for other essential elements (Cu, Fe, Mn, Zn).
Keywords: Selenium speciation; Collision cell ICP-MS; Selenium supplementation; Cow blood and milk; Size exclusion HPLC
Analysis of the selenium species distribution in cow blood by size exclusion liquid chromatography–inductively coupled plasma collision cell mass spectrometry (SEC–ICPccMS) by Òscar Palacios; Jorge Ruiz Encinar; Gérard Bertin; Ryszard Lobinski (pp. 516-522).
A method for performing rapid semiquantitative screening of the distribution of Se species in the blood of cows fed with a diet enriched in selenized yeast was optimized. The method was based on direct injection of a blood sample onto a high resolution size exclusion chromatographic column and fractionation of the selenium species. Selenium was detected on-line by ICP-MS with a collision cell. The concentrations of selenized haemoglobin and free selenomethionine were estimated using the chromatogram. The method was applied to a study involving 15 control and 15 treated dairy cows at four different supplementation time points. The increase in the selenomethionine and selenized haemoglobin was a linear function of the total selenium concentration. A threshold value of 600 ng ml−1 of total Se was established beyond which selenomethionine could not be incorporated into the protein. No inorganic selenium was found to be present. The total selenium in cow blood correlated well with that in milk. The selenium supplementation did not change the protein distribution profiles for other essential elements (Cu, Fe, Mn, Zn).
Keywords: Selenium speciation; Collision cell ICP-MS; Selenium supplementation; Cow blood and milk; Size exclusion HPLC
Indirect detection of substituted phenols and cannabis based on the electrochemical adaptation of the Gibbs reaction by Eleanor R. Lowe; Craig E. Banks; Richard G. Compton (pp. 523-531).
The voltammetric behaviour of 2,6-dichloro-p-aminophenol (PAP) in aqueous solution at an edge plane pyrolytic graphite electrode was explored and its sensitivity to additions of substituted phenols examined. Proof of concept is shown for the electrochemical adaptation of the Gibbs reaction, where reaction of the oxidised form of PAP with substituted phenols provides an indirect methodology for the analytical detection of these compounds. This indirect protocol provides an attractive alterative to the direct electrochemical oxidation of phenolic compounds, since the latter is plagued by electrode passivation, leading to low sensitivity. It is observed that phenol, 4-phenoxyphenol, methylphenol (para and meta), nitrophenol and most importantly, tetrahydrocannabinol, can be detected voltammetrically. Such a protocol is particularly attractive for roadside testing for cannabis in drug drivers.
Keywords: Edge plane pyrolytic graphite electrodes; Tetrahydrocannabinol; 2,6-dichloro-p-aminophenol; Phenol detection; Gibbs reaction
Indirect detection of substituted phenols and cannabis based on the electrochemical adaptation of the Gibbs reaction by Eleanor R. Lowe; Craig E. Banks; Richard G. Compton (pp. 523-531).
The voltammetric behaviour of 2,6-dichloro-p-aminophenol (PAP) in aqueous solution at an edge plane pyrolytic graphite electrode was explored and its sensitivity to additions of substituted phenols examined. Proof of concept is shown for the electrochemical adaptation of the Gibbs reaction, where reaction of the oxidised form of PAP with substituted phenols provides an indirect methodology for the analytical detection of these compounds. This indirect protocol provides an attractive alterative to the direct electrochemical oxidation of phenolic compounds, since the latter is plagued by electrode passivation, leading to low sensitivity. It is observed that phenol, 4-phenoxyphenol, methylphenol (para and meta), nitrophenol and most importantly, tetrahydrocannabinol, can be detected voltammetrically. Such a protocol is particularly attractive for roadside testing for cannabis in drug drivers.
Keywords: Edge plane pyrolytic graphite electrodes; Tetrahydrocannabinol; 2,6-dichloro-p-aminophenol; Phenol detection; Gibbs reaction
Electrochemical study on screen-printed carbon electrodes with modification by iron nanoparticles in Fe(CN)6 4−/3− redox system by Shyh-Hwang Lee; Hung-Yuan Fang; Wen-Chang Chen; Hong-Ming Lin; C. Allen Chang (pp. 532-538).
The remarkable enhancement of electron transfer on screen-printed carbon electrodes (SPCEs) with modification by iron nanoparticles (Fenano), coupled with Fe(CN)6 4−/3− redox species, was characterized with an increase of electroactive area (A ea) at electrode surface together with a decrease of heterogeneous electron transfer rate constant (k°) in the system. Hence, Fenano-Fe(CN)6 3− SPCEs with deposition of glucose oxidase (GOD) demonstrated a higher sensitivity to various glucose concentrations than Fe(CN)6 3−/GOD-deposited SPCEs. In addition, an inhibited diffusion current from cyclic voltammograms was also observed with an increase in redox concentration and complicated the estimation of A ea. Further analysis by the electrochemical impedance method, it was shown that this effect might be resulted from the electrode surface blocking by the products of activated complex decomposition.
Keywords: Heterogeneous electron transfer rate constant; Electroactive area; Screen-printed carbon electrode; Iron nanoparticles; Fe(CN)6 4−/3− redox couple
Electrochemical study on screen-printed carbon electrodes with modification by iron nanoparticles in Fe(CN)6 4−/3− redox system by Shyh-Hwang Lee; Hung-Yuan Fang; Wen-Chang Chen; Hong-Ming Lin; C. Allen Chang (pp. 532-538).
The remarkable enhancement of electron transfer on screen-printed carbon electrodes (SPCEs) with modification by iron nanoparticles (Fenano), coupled with Fe(CN)6 4−/3− redox species, was characterized with an increase of electroactive area (A ea) at electrode surface together with a decrease of heterogeneous electron transfer rate constant (k°) in the system. Hence, Fenano-Fe(CN)6 3− SPCEs with deposition of glucose oxidase (GOD) demonstrated a higher sensitivity to various glucose concentrations than Fe(CN)6 3−/GOD-deposited SPCEs. In addition, an inhibited diffusion current from cyclic voltammograms was also observed with an increase in redox concentration and complicated the estimation of A ea. Further analysis by the electrochemical impedance method, it was shown that this effect might be resulted from the electrode surface blocking by the products of activated complex decomposition.
Keywords: Heterogeneous electron transfer rate constant; Electroactive area; Screen-printed carbon electrode; Iron nanoparticles; Fe(CN)6 4−/3− redox couple
Acid–base characterization of 5-hydroxypyrazine-2-carboxylic acid and the role of ionic equilibria in the optimization of some process conditions for its biocatalytic production by M. Sak-Bosnar; K. Kovar (pp. 539-545).
This paper describes the use of potentiometric titration to determine the relevant acid–base properties of 5-hydroxypyrazine-2-carboxylic acid (5OH-PYCA), an important intermediate in the production of tuberculostatics. The data obtained were used for calculation of the dissociation constants of 5OH-PYCA. It was found that 5OH-PYCA dissociates in two steps, with the corresponding dissociation constants pK a1=3.42 and pK a2=7.96, designating 5OH-PYCA as a medium weak acid (1st step). The distribution diagram of dissociated species and the buffer-strength diagram of 5OH-PYCA provide useful information about its behaviour at different pH. The ionic equilibria data obtained can be used for selection of the optimum pH for biotransformation of pyrazine-2-carboxylic acid (PYCA) and for prediction of pH changes during the biotransformation. These data can also be used for selection of the optimum pH for precipitating 5OH-PYCA in downstream processing. All computations have been optimized by mathematical modelling using Solver.
Keywords: Pyrazine-2-carboxylic acid; Biotransformation; 5-Hydroxypyrazine-2-carboxylic acid; Potentiometry; Ionic equilibria
Acid–base characterization of 5-hydroxypyrazine-2-carboxylic acid and the role of ionic equilibria in the optimization of some process conditions for its biocatalytic production by M. Sak-Bosnar; K. Kovar (pp. 539-545).
This paper describes the use of potentiometric titration to determine the relevant acid–base properties of 5-hydroxypyrazine-2-carboxylic acid (5OH-PYCA), an important intermediate in the production of tuberculostatics. The data obtained were used for calculation of the dissociation constants of 5OH-PYCA. It was found that 5OH-PYCA dissociates in two steps, with the corresponding dissociation constants pK a1=3.42 and pK a2=7.96, designating 5OH-PYCA as a medium weak acid (1st step). The distribution diagram of dissociated species and the buffer-strength diagram of 5OH-PYCA provide useful information about its behaviour at different pH. The ionic equilibria data obtained can be used for selection of the optimum pH for biotransformation of pyrazine-2-carboxylic acid (PYCA) and for prediction of pH changes during the biotransformation. These data can also be used for selection of the optimum pH for precipitating 5OH-PYCA in downstream processing. All computations have been optimized by mathematical modelling using Solver.
Keywords: Pyrazine-2-carboxylic acid; Biotransformation; 5-Hydroxypyrazine-2-carboxylic acid; Potentiometry; Ionic equilibria