Comparison of external calibration and isotope dilution LC-ICP-MS/MS for quantitation of oxytocin and its selenium analogue in human plasma.

In the present study, a method for quantitation of the pharmaceutical peptide oxytocin (OT) and its diselenide-containing analogue (SeOT) in human plasma was developed using gradient elution LC-ICP-MS/MS. Plasma samples were precipitated with acetonitrile containing 1.0% TFA in a volume ratio of 1+3 (sample+precipitation agent) before analysis. Post-column isotope dilution analysis (IDA) was applied for quantitation and was compared with external calibration. Both calibration methods appeared to be fit for purpose regarding figures of merit including linearity, precision, LOD, LOQ and recovery. Analysis of OT and SeOT showed that selenium-based analysis is considerably more sensitive and selective compared to the sulfur-based analysis. Despite the relatively simpler setup of external calibration, IDA can be advantageous because it compensates for instrument drift and changes in organic solvent concentration. The method was applied for a stability study showing the degradation of OT and SeOT in plasma. The degradation of SeOT was faster than the degradation of OT in plasma. Thus, possible stability effects should be considered before replacing a disulfide bridge with a diselenide bridge or introducing a diselenide label in a potential drug.

Analysis of selenium nanoparticles in human plasma by capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry.

Nanoparticles (NPs) are increasingly applied in research and development of new therapies. Characterization of NP systems most often include size, shape, size distribution, and charge but information on the chemical stability of NPs and investigation of the presence of dissolved species is most often missing in efficacy studies due to lack of appropriate methods. In this study, a method based on capillary electrophoresis coupled to inductively coupled plasma mass spectrometry (CE-ICP-MS) was established for analysis of selenium (Se) NPs and dissolved Se species in aqueous media. Peak area and migration time precisions (RSD) of 1.4-3.0% and 1.0-2.6%, respectively, were obtained. CE-ICP-MS analysis of a commercially available SeNP suspension (Q-SeNP) revealed large amounts of selenite corresponding to 32% of the total Se content in the suspension, indicating considerable NP degradation upon storage. The CE-ICP-MS method was modified using a coated fused silica capillary in order to analyze SeNPs in human plasma. Peak area and migration time precisions (RSD) in the range of 3.3-10.7% and 0.8-2.8%, respectively, were achieved. Degradation of polyvinyl alcohol (PVA)-coated SeNPs to selenite in human plasma was demonstrated using the modified method. The amounts of SeNP and selenite were estimated based on a correction factor for the ICP-MS signals of PVA-SeNP and dissolved Se. To the best of our knowledge, this is the first study of SeNPs by CE-ICP-MS and highlights the potential of CE-ICP-MS for quantitative characterization of the behavior of SeNPs in biological media.

Cisplatin Encapsulation Generates Morphologically Different Multicompartments in the Internal Nanostructures of Nonlamellar Liquid-Crystalline Self-Assemblies.

Cisplatin ( cis-diamminedichloroplatinum(II)) is among the most potent cytotoxic agents used in cancer chemotherapy. The encapsulation of cisplatin in lipid-based drug carriers has been challenging owing to its low solubility in both aqueous and lipid phases. Here, we investigated cisplatin encapsulation in nonlamellar liquid-crystalline (LC) nanodispersions formed from a ternary mixture of phytantriol (PHYT), vitamin E (Vit E), and an anionic phospholipid [either phosphatidylglycerol (DSPG) or phosphatidylserine (DPPS)]. We show an increase in cisplatin encapsulation efficiency (EE) in nanodispersions containing 1.5-4 wt % phospholipid. The EE was highest in DPPS-containing nanodispersions (53-98%) compared to DSPG-containing counterparts (25-40%) under similar experimental conditions. Through structural and morphological characterizations involving synchrotron small-angle X-ray scattering and cryogenic transmission electron microscopy, we further show that varying the phospholipid content of cisplatin-free nanodispersions triggers an internal phase transition from a neat hexagonal (H2) phase to a biphasic phase (internal H2 phase coexisting with the lamellar (Lα) phase). However, cisplatin encapsulation in both DPPS- and DSPG-containing nanodispersions generates the coexistence of morphologically different multicompartments in the internal nanostructures comprising vesicles as a core, enveloped by an inverted-type surface bicontinuous cubic Im3 m (primitive, QIIP) phase or H2 phase. We discuss the biophysical basis of these drug-induced morphological alterations and provide insights into the potential development of inverted-type LC nanodispersions for cisplatin delivery.

Quantification of low molecular weight selenium metabolites in human plasma after treatment with selenite in pharmacological doses by LC-ICP-MS.

The paper presents an analytical method for quantification of low molecular weight (LMW) selenium compounds in human plasma based on liquid chromatography inductively coupled plasma mass spectrometry (LC-ICP-MS) and post column isotope dilution-based quantification. Prior to analysis, samples were ultrafiltrated using a cut-off value of 3000 Da. The method was validated in aqueous solution as well as plasma using standards of selenomethionine (SeMet), Se-methylselenocysteine (MeSeCys), selenite, and the selenosugar Se-methylseleno-N-acetylgalactosamine (SeGal) for linearity, precision, recoveries, and limits of detection and quantitation with satisfactory results. The method was applied for analysis of a set of plasma samples from cancer patients receiving selenite treatment in a clinical trial. Three LMW selenium compounds were observed. The main compounds, SeGal and selenite were tentatively identified by retention time matching with standards in different chromatographic systems, while the third minor compound was not identified. The identity of the selenosugar was verified by ESI-MS-MS product ion scanning, while selenite was identified indirectly as the glutathione (GSH) reaction product, GS-Se-SG.

The selenium metabolite methylselenol regulates the expression of ligands that trigger immune activation through the lymphocyte receptor NKG2D.

For decades, selenium research has been focused on the identification of active metabolites, which are crucial for selenium chemoprevention of cancer. In this context, the metabolite methylselenol (CH3SeH) is known for its action to selectively kill transformed cells through mechanisms that include increased formation of reactive oxygen species, induction of DNA damage, triggering of apoptosis, and inhibition of angiogenesis. Here we reveal that CH3SeH modulates the cell surface expression of NKG2D ligands. The expression of NKG2D ligands is induced by stress-associated pathways that occur early during malignant transformation and enable the recognition and elimination of tumors by activating the lymphocyte receptor NKG2D. CH3SeH regulated NKG2D ligands both on the transcriptional and the posttranscriptional levels. CH3SeH induced the transcription of MHC class I polypeptide-related sequence MICA/B and ULBP2 mRNA. However, the induction of cell surface expression was restricted to the ligands MICA/B. Remarkably, our studies showed that CH3SeH inhibited ULBP2 surface transport through inhibition of the autophagic transport pathway. Finally, we identified extracellular calcium as being essential for CH3SeH regulation of NKG2D ligands. A balanced cell surface expression of NKG2D ligands is considered to be an innate barrier against tumor development. Therefore, our work indicates that the application of selenium compounds that are metabolized to CH3SeH could improve NKG2D-based immune therapy.

Modulatory effect of human plasma on the internal nanostructure and size characteristics of liquid-crystalline nanocarriers.

The inverted-type liquid-crystalline dispersions comprising cubosomes and hexosomes hold much potential for drug solubilization and site-specific targeting on intravenous administration. Limited information, however, is available on the influence of plasma components on nanostructural and morphological features of cubosome and hexosome dispersions, which may modulate their stability in the blood and their overall biological performance. Through an integrated approach involving SAXS, cryo-TEM, and nanoparticle tracking analysis (NTA) we have studied the time-dependent effect of human plasma (and the plasma complement system) on the integrity of the internal nanostructure, morphology, and fluctuation in size distribution of phytantriol (PHYT)-based nonlamellar crystalline dispersions. The results indicate that in the presence of plasma the internal nanostructure undergoes a transition from the biphasic phase (a bicontinuous cubic phase with symmetry Pn3m coexisting with an inverted-type hexagonal (H2) phase) to a neat hexagonal (H2) phase, which decreases the median particle size. These observations were independent of a direct effect by serum albumin and dispersion-mediated complement activation. The implication of these observations in relation to soft nanocarrier design for intravenous drug delivery is discussed.

A method for studies on interactions between a gold-based drug and plasma proteins based on capillary electrophoresis with inductively coupled plasma mass spectrometry detection.

An analytical method based on capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICP-MS) detection was developed for studies on the interaction of gold-containing drugs and plasma proteins using auranofin as example. A detection limit of 18 ng/mL of auranofin corresponding to 5.2 ng/mL Au and a precision of 1.5 % were obtained. Kinetic studies of the interaction between auranofin and protein were performed by incubation in aqueous solutions as well as 20 % human plasma at 37 °C. The reaction of auranofin with human serum albumin (HSA) and plasma proceeded fast; 50 % of un-bound auranofin disappeared within 2 and 3 min, respectively. By blocking the free cysteine (Cys-34) by iodoacetamide on HSA, it was shown that Cys-34 was the main reaction site for auranofin. By selective labeling of HSA present in 20 % human plasma with iophenoxate, it was demonstrated that HSA was the major auranofin-interacting protein in plasma. The CE-ICP-MS method is proposed as a novel approach for kinetic studies of the interactions between gold-based drugs and plasma proteins. Graphical Abstract Development of a CE-ICP-MS based method allows for studies on interaction of the gold containing drug auranofin with plasma proteins.

Selective analysis of human serum albumin based on SEC-ICP-MS after labelling with iophenoxic acid.

Human serum albumin (HSA) is the most abundant protein in the human plasma. HSA has several physiological roles in the human body, including storage and transport. Owing to the predominance of albumin in plasma, HSA is often involved in the protein binding of drugs. The aim of this work was to develop a selective, quantitative method for determining albumin in plasma with the purpose of clarifying the fate of metal-based drugs in biological systems. The method can also be applied for determination of urine albumin, which is of relevance in diagnostics of kidney disease. A selective method for quantification of HSA based on labelling the protein with iophenoxic acid (IPA) was developed. Samples were subjected to size exclusion chromatography (SEC) and detection by inductively coupled plasma mass spectrometry (ICP-MS) monitoring iodine and platinum. The iodine signal for the HSA-IPA complex showed linearity in the range 1 to 250 mg L(-1). The precision was 3.7% and the accuracy 100.7% determined by analysis of a certified HSA reference material. The limit of detection (LOD) and limit of quantification (LOQ) were 0.23 and 9.79 mg L(-1), respectively. The method was applied for analysis of HSA in human plasma and urine samples and for studying the binding of cisplatin to proteins in the human plasma.

Pharmacy students' process of learning of real patients in a simple first-person perspective patient simulation exercise - A qualitative analysis.

INTRODUCTION: Pharmacists need more insight into patients' perspectives on medicine to target their counseling and improve patient outcomes. Patient simulation exercises, where pharmacy students are asked to consume medicine-like products, have been shown to foster such understandings, although the specifics of how this occurs, in particularly, how students turn their first-person perspectives toward generalizations about real patients' lives with medicines, are not well documented. The aim was to identify central aspects of the learning process by introducing reflection questions about real patients and follow students' development during a study period. METHODS: The study was conducted with students in their 4th semester in the second year of Pharmacy Education at the University of Copenhagen who were asked to respond to free text questions in a survey instrument about their daily experiences of taking a licorice product for one week as well as answering patient reflection questions. Qualitative deductive analysis was performed by coding students' experiences according to concepts of 'experiential learning'. Pattern identification within each concept was then inferred, as were their interrelationships. RESULTS: Patient reflection questions enabled students to turn their first-person perspectives toward relevant generalizations about real patients' lives with medicines, including involved psychological mechanisms and how real patient groups differ in their ability to take medicine regularly. Students who during the week faced challenges with following the required dosing scheme came to more nuanced realizations that medicine adherence requires special efforts and restricts one's daily life; hence, negative emotions were involved in the learning process. CONCLUSIONS: The design of the simple patient simulation exercise gave rise to new types of insights into real patients' lives with medicines. Negative emotions due to interference between the requirements of the exercise and students' normal social lives, as well as commitment to the exercise, were important aspects of this process.

Metallomics in drug development: characterization of a liposomal cisplatin drug formulation in human plasma by CE-ICP-MS.

A capillary electrophoresis inductively coupled plasma mass spectrometry method for separation of free cisplatin from liposome-encapsulated cisplatin and protein-bound cisplatin was developed. A liposomal formulation of cisplatin based on PEGylated liposomes was used as model drug formulation. The effect of human plasma matrix on the analysis of liposome-encapsulated cisplatin and intact cisplatin was studied. The presence of 1 % of dextran and 4 mM of sodium dodecyl sulfate in HEPES buffer was demonstrated to be effective in improving the separation of liposomes and cisplatin bound to proteins in plasma. A detection limit of 41 ng/mL of platinum and a precision of 2.1 % (for 10 µg/mL of cisplatin standard) were obtained. Simultaneous measurements of phosphorous and platinum allows the simultaneous monitoring of the liposomes, liposome-encapsulated cisplatin, free cisplatin and cisplatin bound to plasma constituents in plasma samples. It was demonstrated that this approach is suitable for studies of the stability of liposome formulations as leakage of active drug from the liposomes and subsequent binding to biomolecules in plasma can be monitored. This methodology has not been reported before and will improve characterization of liposomal drugs during drug development and in studies on kinetics.

Intravenous Infusion of High Dose Selenite in End-Stage Cancer Patients: Analysis of Systemic Exposure to Selenite and Seleno-Metabolites.

Cancer is one of the main causes of human death globally and novel chemotherapeutics are desperately required. As a simple selenium oxide, selenite is a very promising chemotherapeutic because of pronounced its dose-dependent tumor-specific cytotoxicity. We previously published a first-in-man systematic phase I clinical trial in patients with cancer (from IV to end-stage) (the SECAR trial) showing that selenite is safe and tolerable with an unexpectable high maximum tolerated dose (MTD) and short half-life. In the present study, we analyzed the selenium species in plasma samples, from the patients participating in the SECAR trial and from various time points and dose cohorts using LC-ICP-MS. In conclusion, selenite, selenosugars, and 1-2 unidentified peaks that did not correspond to any standard, herein denoted ui-selenium, were detected in the plasma. However, trimethylated selenium (trimethylselenonoium) was not detected. The unidentified ui-selenium was eluting close to the selenium-containing amino acids (selenomethionine and selenocysteine) but was not part of a protein fraction. Our data demonstrate that the major metabolite detected was selenosugar. Furthermore, the identification of selenite even long after the administration is remarkable and unexpected. The kinetic analysis did not support that dosing per the body surface area would reduce interindividual variability of the systemic exposure in terms of trough concentrations.

Selenomethionine as alternative label to the fluorophore TAMRA when exploiting cell-penetrating peptides as blood-brain barrier shuttles to better mimic the physicochemical properties of the non-labelled peptides.

The cell-penetrating peptides (CPPs) Tat and penetratin are frequently explored as shuttles for drug delivery across the blood-brain barrier (BBB). CPPs are often labelled with fluorophores for analytical purposes, with 5(6)-carboxytetramethylrhodamine (TAMRA) being a popular choice. However, TAMRA labelling affects the physicochemical properties of the resulting fluorophore-CPP construct when compared to the CPP alone. Selenomethionine (MSe) may be introduced as alternative label, which, due to its small size and amino acid nature, likely results in minimal alterations of the peptide physicochemical properties. With this study we compared, head-to-head, the effect of MSe and TAMRA labelling of Tat and penetratin with respect to their physicochemical properties, and investigated effects hereof on brain capillary endothelial cell (BCEC) models. TAMRA labelling positively affected the ability of the peptides to adhere to the cell membranes as well being internalized into the BCECs when compared to MSe labelling. TAMRA labelling of penetratin added toxicity to the BCECs to a higher extent than TAMRA labelling of Tat, whereas MSe labelling did not affect the cellular viability. Both TAMRA and MSe labelling of penetratin decreased the barrier integrity of BCEC monolayers, but not to an extent that improved transport of the paracellular marker 14C-mannitol. In conclusion, MSe labelling of Tat and penetratin adds minimal alterations to the physicochemical properties of these CPPs and their resulting effects on BCECs, and thereby represents a preferred alternative to TAMRA for peptide quantification purposes.

Cu(II) mediates kinetically distinct, non-amyloidogenic aggregation of amyloid-beta peptides.

Cu(II) ions are implicated in the pathogenesis of Alzheimer disease by influencing the aggregation of the amyloid-ß (Aß) peptide. Elucidating the underlying Cu(II)-induced Aß aggregation is paramount for understanding the role of Cu(II) in the pathology of Alzheimer disease. The aim of this study was to characterize the qualitative and quantitative influence of Cu(II) on the extracellular aggregation mechanism and aggregate morphology of Aß(1-40) using spectroscopic, microelectrophoretic, mass spectrometric, and ultrastructural techniques. We found that the Cu(II):Aß ratio in solution has a major influence on (i) the aggregation kinetics/mechanism of Aß, because three different kinetic scenarios were observed depending on the Cu(II):Aß ratio, (ii) the metal:peptide stoichiometry in the aggregates, which increased to 1.4 at supra-equimolar Cu(II):Aß ratio; and (iii) the morphology of the aggregates, which shifted from fibrillar to non-fibrillar at increasing Cu(II):Aß ratios. We observed dynamic morphological changes of the aggregates, and that the formation of spherical aggregates appeared to be a common morphological end point independent on the Cu(II) concentration. Experiments with Aß(1-42) were compatible with the conclusions for Aß(1-40) even though the low solubility of Aß(1-42) precluded examination under the same conditions as for the Aß(1-40). Experiments with Aß(1-16) and Aß(1-28) showed that other parts than the Cu(II)-binding His residues were important for Cu(II)-induced Aß aggregation. Based on this study we propose three mechanistic models for the Cu(II)-induced aggregation of Aß(1-40) depending on the Cu(II):Aß ratio, and identify key reaction steps that may be feasible targets for preventing Cu(II)-associated aggregation or toxicity in Alzheimer disease.

Investigation of a liposomal oxaliplatin drug formulation by capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry (CE-ICP-MS).

A capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) method was developed for separation of the free oxaliplatin drug substance from liposome-entrapped oxaliplatin. Simultaneous determination of phosphorous and platinum opened the possibility to simultaneously monitor the liposomes (phospholipids) and platinum-based drug. In order to suppress the interferences, argon gas was used as a collision gas in ICP-MS. A detection limit of 29 ng/mL of platinum and a precision of 2.9% (for 10 µg/mL of oxaliplatin standard) were obtained. Measurement of the total concentration of free and encapsulated oxaliplatin by CE-ICP-MS was compared with total determination by ICP-MS after microwave digestion and showed a good agreement. A liposomal formulation of oxaliplatin based on PEGylated liposomes was used as a model drug formulation. Studies of accelerated drug release induced by sonication and phospholipase A(2) catalyzed hydrolysis were performed. It was demonstrated that the CE-ICP-MS was an efficient in vitro characterization method in the development and quality assurance purposes of lipsome-based formulation of metallodrugs.

Internal correction of spectral interferences and mass bias for selenium metabolism studies using enriched stable isotopes in combination with multiple linear regression.

The analytical methodology for the in vivo study of selenium metabolism using two enriched selenium isotopes has been modified, allowing for the internal correction of spectral interferences and mass bias both for total selenium and speciation analysis. The method is based on the combination of an already described dual-isotope procedure with a new data treatment strategy based on multiple linear regression. A metabolic enriched isotope ((77)Se) is given orally to the test subject and a second isotope ((74)Se) is employed for quantification. In our approach, all possible polyatomic interferences occurring in the measurement of the isotope composition of selenium by collision cell quadrupole ICP-MS are taken into account and their relative contribution calculated by multiple linear regression after minimisation of the residuals. As a result, all spectral interferences and mass bias are corrected internally allowing the fast and independent quantification of natural abundance selenium ((nat)Se) and enriched (77)Se. In this sense, the calculation of the tracer/tracee ratio in each sample is straightforward. The method has been applied to study the time-related tissue incorporation of (77)Se in male Wistar rats while maintaining the (nat)Se steady-state conditions. Additionally, metabolically relevant information such as selenoprotein synthesis and selenium elimination in urine could be studied using the proposed methodology. In this case, serum proteins were separated by affinity chromatography while reverse phase was employed for urine metabolites. In both cases, (74)Se was used as a post-column isotope dilution spike. The application of multiple linear regression to the whole chromatogram allowed us to calculate the contribution of bromine hydride, selenium hydride, argon polyatomics and mass bias on the observed selenium isotope patterns. By minimising the square sum of residuals for the whole chromatogram, internal correction of spectral interferences and mass bias could be accomplished. As a result, the tracer/tracee ratio could be calculated for each selenium-containing species and a time relationship for synthesis and degradation established. Both selenite and selenized yeast labelled with (77)Se were employed for comparative purposes.

Quantitative HPLC-ICP-MS analysis of antimony redox speciation in complex sample matrices: new insights into the Sb-chemistry causing poor chromatographic recoveries.

In solution antimony exists either in the pentavalent or trivalent oxidation state. As Sb(III) is more toxic than Sb(V), it is important to be able to perform a quantitative speciation analysis of Sb's oxidation state. The most commonly applied chromatographic methods used for this redox speciation analysis do, however, often show a low chromatographic Sb recovery when samples of environmental or biological origin are analysed. In this study we explored basal chemistry of antimony and found that formation of macromolecules, presumably oligomeric and polymeric Sb(V) species, is the primary cause of low chromatographic recoveries. A combination of HPLC-ICP-MS, AFFF-ICP-MS and spin-filtration was applied for analysis of model compounds and biological samples. Quantitative chromatographic Sb redox speciation analysis was possible by acidic hydrolysis of the antimony polymers prior to analysis. Sample treatment procedures were studied and the optimum solution was acidic hydrolysis by 1 M HCl in the presence of chelating ligands (EDTA, citrate), which stabilise the trivalent oxidation state of Sb.

Surveying selenium speciation from soil to cell--forms and transformations.

The aim of this review is to present and evaluate the present knowledge of which selenium species are available to the general population in the form of food and common supplements and how these species are metabolized in mammals. The overview of the selenium sources takes a horizontal approach, which encompasses identification of new metabolites in yeast and food of plant and animal origin, whereas the survey of the mammalian metabolism takes a horizontal as well as a vertical approach. The vertical approach encompasses studies on dynamic conversions of selenium compounds within cells, tissues or whole organisms. New and improved sample preparation, separation and detection methods are evaluated from an analytical chemical perspective to cover the progress in horizontal speciation, whereas the analytical methods for the vertical speciation and the interpretations of the results are evaluated from a biological angle as well.

Modulation of hypochlorous acid (HOCl) induced damage to vascular smooth muscle cells by thiocyanate and selenium analogues.

The production of hypochlorous acid (HOCl) by myeloperoxidase (MPO) plays a key role in immune defense, but also induces host tissue damage, particularly in chronic inflammatory pathologies, including atherosclerosis. This has sparked interest in the development of therapeutic approaches that decrease HOCl formation during chronic inflammation, including the use of alternative MPO substrates. Thiocyanate (SCN-) supplementation decreases HOCl production by favouring formation of hypothiocyanous acid (HOSCN), which is more selectively toxic to bacterial cells. Selenium-containing compounds are also attractive therapeutic agents as they react rapidly with HOCl and can be catalytically recycled. In this study, we examined the ability of SCN-, selenocyanate (SeCN-) and selenomethionine (SeMet) to modulate HOCl-induced damage to human coronary artery smooth muscle cells (HCASMC), which are critical to both normal vessel function and lesion formation in atherosclerosis. Addition of SCN- prevented HOCl-induced cell death, altered the pattern and extent of intracellular thiol oxidation, and decreased perturbations to calcium homeostasis and pro-inflammatory signaling. Protection was also observed with SeCN- and SeMet, though SeMet was less effective than SeCN- and SCN-. Amelioration of damage was detected with sub-stoichiometric ratios of the added compound to HOCl. The effects of SCN- are consistent with conversion of HOCl to HOSCN. Whilst SeCN- prevented HOCl-induced damage to a similar extent to SCN-, the resulting product hyposelenocyanous acid (HOSeCN), was more toxic to HCASMC than HOSCN. These results provide support for the use of SCN- and/or selenium analogues as scavengers, to decrease HOCl-induced cellular damage and HOCl production at inflammatory sites in atherosclerosis and other pathologies.

A method for analysis of dimethyl selenide and dimethyl diselenide by LC-ICP-DRC-MS.

The aim of this work was to develop a simple and fast high performance liquid chromatography-inductively coupled argon plasma (ICP) mass spectrometry (MS) method capable of separating and detecting the two volatile selenium species dimethyl selenide (DMeSe) and dimethyl diselenide (DMeDSe) in biological samples. Dimethyl selenide and dimethyl diselenide were separated on a short reversed phase column using an eluent containing 40% methanol and detected by dynamic reaction cell ICP-MS monitoring the (80)Se isotope. The limit of detection was 8 nM for both species (corresponding to 0.6 and 1.3 µg Se/L for DMeDSe and DMeSe, respectively). Both compounds exhibited a linear signal-concentration relationship in the investigated concentration range of 0.1-1 µM with a precision on the determinations better than 3%. The method was applied for analysis of samples from cancer cell lines incubated with methylseleninic acid, selenomethionine, Se-methylselenocysteine, and sodium selenite. DMeDSe were detected in some samples. The method offers a simple and fast analysis of DMeDSe and DMeSe using standard liquid chromatography coupled with ICP-MS equipment and interfacing.

Elevated antimony concentrations in commercial juices.

Antimony concentrations up to a factor of 2.7 above the EU limit for drinking water were found in commercial juices and may either be leached from the packaging material or introduced during manufacturing, pointing out the need for further research on the area.