Plasma mass spectrometry as a detector for chemical speciation studies

Urinary chromium is associated with changes in leukocyte miRNA expression in obese subjects

BACKGROUND/OBJECTIVES

Epidemiological studies suggest a link between chromium (Cr) status and cardiovascular disease. Increased urinary excretion of Cr was reported in subjects with diabetes compared with non-diabetic controls and those with non-diabetic insulin resistance. Epigenetic alterations have been linked to the presence of Cr, and microRNA (miRNA) expression has been implicated in the pathogenesis of metabolic diseases and cardiovascular diseases (CVDs). We investigated the association between Cr excretion and miRNA expression in leukocytes from obese subjects. We also examined the relationship between altered miRNA expression and selected clinical parameters to further investigate mechanisms linking Cr to metabolic diseases and CVDs.

SUBJECTS/METHODS

We analyzed urinary Cr in 90 Italian subjects using inductively coupled plasma-mass spectrometry. Peripheral blood miRNA levels were screened with TaqMan Low-Density Array Human MicroRNA A. Cr level-associated expression of miRNAs was detected with multivariate regression analyses, and the top 10 candidate miRNAs were selected for validation. We also used multivariate regression analyses to assess possible associations between validated miRNAs and glycated hemoglobin (A1c) and blood pressure (BP). The validated miRNAs were further investigated by functional analysis with Ingenuity Pathway Analysis software.

RESULTS

Urinary Cr levels (mean: 0.35 μg/l; s.d.=0.24) ranged from 0.05 to 1.27 μg/l. In the screening phase, 43 miRNAs were negatively associated with Cr. Of the top 10 miRNAs selected for validation, nine (miR-451, miR-301, miR-15b, miR-21, miR-26a, miR-362-3p, miR-182, miR-183 and miR-486-3p) were downregulated in association with Cr (P-false discovery rate (FDR)<0.10). miR-451 expression was associated with A1c (β=-0.06; P=0.0416), whereas miR-486-3p expression was associated both with diastolic (β=2.1; P=0.004) and systolic BP (β=3.3; P=0.003).

CONCLUSIONS

These results indicate that miR-451 and miR-486-3p are involved in the link between Cr levels and metabolic diseases and CVDs.

Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry

During the recent years, capillary electrophoresis (CE) has been fully established as a powerful tool in separation sciences as well as in element speciation. This road of success is based on the rapid analysis time, low sample requirements, high separation efficiency, and low operating costs of CE. Inductively coupled plasma mass spectrometry (ICP-MS) is known for superior detection and multielement capability. Consequently, the combination of both instruments is approved for analysis of complex sample types at low element concentrations which require high detection power. Also the diversity of potential applications brings CE-ICP-MS coupling into central focus of element speciation. The key to successful combination of ICP-MS as an (multi-)element selective detector for CE is the availability of a suitable and effective interface.Therefore, this chapter summarizes the most important and basic principles about coupling of capillary electrophoresis to ICP-MS. Specifically, the major requirements for interfacing are described and technical solutions are given. Such solutions include the closing of the electrical circuit from CE at the nebulization, the adoption of flow rates for efficient nebulization, the reduction of a suction flow through the capillary, caused by the nebulizer, and maintaining the high separation resolution from CE across the interface for ICP-MS detection. Additionally, detailed information is presented to determine and quantify the siphoning suction through the CE capillary by the nebulizer. Finally, two applications, namely, the manganese and selenium speciation in cerebrospinal fluid are shown as examples, providing the relevant operational parameter.

Determination of total arsenic and arsenic species in drinking water, surface water, wastewater, and snow from Wielkopolska, Kujawy-Pomerania, and Lower Silesia provinces, Poland

Arsenic is a ubiquitous element which may be found in surface water, groundwater, and drinking water. In higher concentrations, this element is considered genotoxic and carcinogenic; thus, its level must be strictly controlled. We investigated the concentration of total arsenic and arsenic species: As(III), As(V), MMA, DMA, and AsB in drinking water, surface water, wastewater, and snow collected from the provinces of Wielkopolska, Kujawy-Pomerania, and Lower Silesia (Poland). The total arsenic was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and arsenic species were analyzed with use of high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC/ICP-MS). Obtained results revealed that maximum total arsenic concentration determined in drinking water samples was equal to 1.01 μg L(-1). The highest concentration of total arsenic in surface water, equal to 3778 μg L(-1) was determined in Trująca Stream situated in the area affected by geogenic arsenic contamination. Total arsenic concentration in wastewater samples was comparable to those determined in drinking water samples. However, significantly higher arsenic concentration, equal to 83.1 ± 5.9 μg L(-1), was found in a snow sample collected in Legnica. As(V) was present in all of the investigated samples, and in most of them, it was the sole species observed. However, in snow sample collected in Legnica, more than 97 % of the determined concentration, amounting to 81 ± 11 μg L(-1), was in the form of As(III), the most toxic arsenic species.

Chromium and its speciation in water samples by HPLC/ICP-MS--technique establishing metrological traceability: a review since 2000

Chromium holds a special position among living organisms because depending on its species it can be either essential or toxic. Cr(VI) even at very low concentrations is harmful and carcinogenic, while Cr(III) is a necessary microelement for cellular metabolism. Therefore, a simple analysis of Cr concentration in collected samples will not be able to distinguish these differences effectively: for a proper chemical analysis we need to perform a reliable detection and quantification of Cr species. Separation and detection of chromium can be accomplished with high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC/ICP-MS) in a one-step. Our review assembles articles published since 2000 regarding chromium speciation in water samples with the use of HPLC/ICP-MS. It addresses the following issues: chromium chemistry, the possibilities of dealing with interferences, metrological aspects, analytical performance and speciated isotope dilution mass spectrometry (SIDMS) which is a definitive measurement method. The authors would like to advocate this hyphenated advanced technique as well as the metrological approach in speciation analysis of chromium.

Arsenic and its speciation in water samples by high performance liquid chromatography inductively coupled plasma mass spectrometry--last decade review

Arsenic composes a danger for human health all over the world as it is responsible for water resources contamination. The toxicity of arsenic depends on its chemical form. However, occurrence of particular arsenic species is dependent on processes occurring in water. Nowadays, more arsenic species is detected and analyzed in different kind of water (mineral, tap, waste), mainly owing to great possibilities resulting from coupling high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS). This review mainly describes arsenic speciation analysis by HPLC-ICP-MS technique on the basis of articles that have been published since 2000. Arsenic chemistry, occurrence in different kind of water, total arsenic determination with interferences elimination and its validation and analytical performance are also reviewed.

Selenium speciation analysis using inductively coupled plasma-mass spectrometry

Selenium exists in several oxidation states and a variety of inorganic and organic compounds, and the chemistry of selenium is complex in both the environment and living systems. Selenium is an essential element at trace levels and toxic at greater levels. Interest in speciation analysis for selenium has grown rapidly in this last decade, especially in the use of chromatographic separation coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Complete characterization of selenium compounds is necessary to understand selenium's significance in metabolic processes, clinical chemistry, biology, toxicology, nutrition and the environment. This review describes some of the essential background of selenium, and more importantly, some of the currently used separation methodologies, both chromatographic and electrophoretic, with emphasis on applications of selenium speciation analysis using ICP-MS detection.

Modeling and separation-detection methods to evaluate the speciation of metals for toxicity assessment

There is an increasing appreciation for the importance of speciation in the assessment of metal toxicity. In this review, two approaches to speciation are discussed, with an emphasis on their application to biological samples. One approach is the direct separation and detection of metal species of toxicological interest. Various "hyphenated" techniques, consisting of a chromatographic system coupled to inductively coupled plasma-mass spectrometry (ICP-MS), are discussed. The chromatographic strategies employed for separation emphasize liquid chromatography (LC), but the increasing use of gas chromatography (GC) and capillary electrophoresis (CE) in speciation analysis is discussed. The second approach to speciation is the use of computer models to calculate the speciation of a metal ion within a complex mixture of ligands. This approach is applicable to systems in which the metal cation exchanges ligands rapidly, so that the sample represents an equilibrium mixture of metal complexes. These computational models are based on the equilibrium constants for the metal complexes and a series of mass balance equations and give the distribution of metal complexes in the original sample. This approach is illustrated using the speciation of Al(III) in serum as an example.

Arsenic speciation analysis in water samples: a review of the hyphenated techniques

Interests in the determination of different arsenic species in natural waters is caused by the fact that toxic effects of arsenic are connected with its chemical forms and oxidation states. In determinations of water samples inorganic arsenate (As(III), As(V)), methylated metabolities (MMAA, DMAA) and other organic forms such as AsB, AsC, arsenosugars or arsenic containing lipids have the most importance. This article provides information about occurrence of the dominant arsenic forms in various water environments. The main factors controlling arsenic speciation in water are described. The quantification of species is difficult because the concentrations of different forms in water samples are relatively low compared to the detection limits of the available analytical techniques. Several hyphenated methods used in arsenic speciation analysis are described. Specific advantages and disadvantages of methods can define their application for a particular sample analysis. Insufficient selectivity and sensitivity of arsenic speciation methods cause searching for a new or modifications already existing techniques. Some aspects of improvement and modifications of the methods are highlighted.

Capillary electrophoresis-inductively coupled plasma-mass spectrometry: A report on technical principles and problem solutions, potential, and limitations of this technology as well as on examples of application

This paper summarizes some basic principles of capillary electrophoresis (CE), inductively coupled plasma-mass spectrometry (ICP-MS), and coupling of both devices. Especially the interfacing is described in detail. A special focus is drawn to various interface developments reported in literature and technical problems, i.e., requirements to the interface setup and respective solutions. Nowadays, typically sheath flow-based interfaces are used. The sheath flow fulfills two requirements of hyphenation, (i) the closing of the electrical circuit of CE and (ii) the feeding of the used nebulizer with an adequate flow rate. In the beginning of CE-ICP-MS coupling predominantly home-made interface-nebulizer constructions were developed and tested for various speciation problems. Now increasingly such laboratory-constructed interfaces are left. Mostly commercial nebulizers are employed being combined with commercially available tee or cross fittings to connect the CE capillary to the electrode, the additional sheath flow, and the nebulizer. Due to the low sample amounts and low flow rates from CE, such nebulizers are typically low-flow nebulizers like, e.g., the microconcentric nebulizer (MCN) and the direct injection nebulizer (DIN). However, there are also reports on couplings using standard Meinhard systems. Still the control and reduction of a siphoning sucting flow and sufficient detection limits are the major problems in hyphenating CE to ICP-MS. Different solutions are reported on these problems and summarized here. Finally numerous applications are reported. Mostly, applications are performed on speciation of selenium, arsenic, metallothionein isoforms, mercury, or cobalt.

Arsenic and its speciation analysis using high-performance liquid chromatography and inductively coupled plasma mass spectrometry

It is known that arsenic has different toxicological properties dependent upon both its oxidation state for inorganic compounds, as well as the different toxicity levels exhibited for organic arsenic compounds. The field of arsenic speciation analysis has grown rapidly in recent years, especially with the utilization of high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS), a highly sensitive and robust detector system. Complete characterization of arsenic compounds is necessary to understand intake, accumulation, transport, storage, detoxification and activation of this element in the natural environment and living systems. This review describes the essential background and toxicity of arsenic in the environment, and more importantly, some currently used chromatographic applications and sample handling procedures necessary to accurately detect and quantify arsenic in its various chemical forms. Applications and work using only HPLC-ICP-MS for arsenic speciation of environmental and biological samples are presented in this review.

On-line coupling of capillary electrophoresis to hydride generation atomic fluorescence spectrometry for arsenic speciation analysis

A novel hyphenated technique, on-line coupling of capillary electrophoresis (CE) to atomic fluorescence spectrometry (AFS), was developed for speciation analysis of four environmentally significant and toxic forms of arsenic: arsenite, arsenate, monomethylarsenic acid, and dimethylarsenic acid. Baseline separation of the four arsenic species was achieved by capillary electrophoresis in a 50 cm x 100 microm i.d. fused-silica capillary at 20 kV and using a 20 mmol L(-1) phosphate buffer (pH 6.5). A hydride generation (HG) technique was employed to convert the arsenic species from the CE effluent into their respective hydrides. The CE-AFS interface was constructed on the basis of a cross design for introducing a sheath flow around the CE capillary and a Pt electrode, which provided an electrical connection for stable electrophoretic separations and allowed on-line volatile hydride formation. A laboratory-made gas-liquid separator was used to isolate the generated volatile species from the reaction mixture solution, and an argon flow was used to transport the volatile hydrides into the atomizer of AFS for on-line detection. The precision (RSD, n = 7) ranged from 2.1 to 3.1% for migration time, from 2.8 to 4.2% for peak area response, and from 2.0 to 4.1% for peak height response for the arsenic species at the 1 mg L(-1) (as As) level. The detection limits were in the range of 9-18 microg L(-1) (as As). The recoveries of the four arsenic species in locally collected water samples and urine sample ranged from 91 to 115%. The developed technique was successfully applied to the speciation of the water-methanol extractable arsenic in a sediment sample.

A high-efficiency cross-flow micronebulizer interface for capillary electrophoresis and inductively coupled plasma mass spectrometry

A pneumatic nebulizer interface for capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICPMS) is reported. The interface is constructed using a high-efficiency cross-flow micronebulizer (HECFMN) and has the following features. (1) Makeup solutions can be fed to the interface by nebulizer self-aspiration and liquid gravity pressurization. (2) The liquid dead volume of the interface is approximately 65 nL, much smaller than those (200-2500 nL) reported for other interfaces. (3) The interface can be stably operated at a liquid flow rate down to 5 microL/min with a high analyte transport efficiency up to 95% to the plasma and (4) does not induce noticeable laminar flow in the CE capillary at typical nebulizer gas flow rates of 0.8-1.2 L/min. Because of these features, baseline resolution of 10 lanthanides with a CE-ICPMS system using the HECFMN interface is achieved, and detection limits and peak asymmetry are 0.05-1 microg/L and 0.93-1.23, respectively, improved significantly over those reported previously for a CE-ICPMS system using a high-efficiency nebulizer interface. Peak precision for the 10 lanthanides is in the range of 6.2-12.3% RSD (N = 5). Peak widths are from 9.1 s for 139La to 17.9 s for 175Lu. The effects of nebulizer gas flow rate, makeup solution flow rate, and spray chamber volume on CE-ICPMS signal intensity and separation are also evaluated for the HECFMN interface by the separation of Cr3+ and Cr2O7(2-).

Metal speciation using capillary electrophoresis--inductively coupled plasma atomic emission spectrometry and polytetrafluoroethylene capillaries

A capillary electrophoresis--inductively coupled plasma atomic-emission spectrometry (CE-ICP-AES) system using a polytetrafluoroethylene (PTFE) capillary has been developed. The CE-ICP interface was a modified concentric nebulizer. The PTFE capillary (50 microm internal diameter) was used as the central capillary of the nebulizer. Using the PTFE capillaries, the solution flow rate induced by the carrier gas flow was smaller than that of glass capillary. Solution flow was mainly induced by the CE electric field. Baseline separation of Ba2+/Mg2+ ion pair using simple buffer solution of 0.014 M sodium acetate was reported. Separation and correlation of metal species in metallothioneins (MT-1 and MT-2 in MT) of rabbit liver using the CE-ICP system were also discussed.

Simple interface for capillary electrophoresis-inductively coupled plasma atomic emission spectrometry

A simple interface has been developed to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES) for metal speciation. A concentric glass nebulizer with elongated tip is used as the CE-ICP interface. The CE capillary is the central tube of the nebulizer. A platinum wire is wrapped across the exit end of the CE capillary to provide electrical connection to the CE power supply. No sheath flow of buffer solution is needed. A simple cooling system has also been developed. A peristaltic pump circulates water through a plastic tube that encloses the section of the CE capillary between the CE instrument and the ICP spectrometer. Characteristics of the CE-ICP interface, e.g., elution time, nebulization and transport efficiency and peak broadening, versus carrier gas flow-rate have been studied. Comparisons to a previous design with the Pt electrode inserted into the end of the CE capillary are made where appropriate. The reproducibility (RSD) in ICP emission intensity of the system is <4%. Detection limits of Cr and Cu are approximately 5 ng/ml.

Element selective detection for supercritical-fluid chromatography

This manuscript describes the use of Supercritical-Fluid Chromatography (SFC) with plasma spectrometric detection for the analysis of organometallics. An introduction on the principles and characteristics of Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is included, along with a discussion about requirements for coupling SFC to plasma detection and the different approaches for interfacing SFC to ICP. The last part of this review paper provides a comprehensive description of SFC-ICP applications for the analysis of organometallics containing iron, silicon, tin, chromium, arsenic, lead, mercury and antimony.

Analysis of inorganic species in environmental samples by capillary electrophoresis

The use of capillary electrophoresis for the determination of inorganic species in environmental samples is reviewed. Topics covered include the separation of inorganic anions, inorganic cations, transition metal cations and organometals in different environmental matrices, such as atmospheric deposition, atmospheric aerosols, gases, natural waters, waste waters, soil, sediment and marine biological samples. Cited literature is gathered according to the type of matrix, so that the focus is on the discussion of matrix effects rather than on the method development for a single class of compounds. For each matrix, surveyed methods are tabulated in order to assist the method selection. Innovative applications of capillary electrophoresis to advanced environmental research are also emphasised.

Short-column liquid chromatography with hydride generation atomic fluorescence detection for the speciation of arsenic

Increasing concerns over human exposure to arsenic and more stringent environmental regulations require rapid determination of trace levels of individual arsenic species, which presents an analytical challenge. We describe a method that is capable of speciating nanogram-per-milliliter levels of arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA) within 3 min. Speciation of two common inorganic species in drinking water, As(III) and As(V), is complete in 1.5 min. The method is based on a combination of fast high-performance liquid chromatography (HPLC) separation of arsenic species on 3-cm HPLC guard columns and the sensitive detection of arsenic hydride by atomic fluorescence spectrometry. Detection limits for the four arsenic species in urine samples are 0.4-0.8 ng/mL. This simple method allows for the direct speciation of arsenic present in natural water samples and in human urine samples from the general population, with no need of any sample pretreatment. Our results from the determination of arsenic species in urine and water standard reference materials are in good agreement with the certified values of total arsenic concentration. The method has been successfully applied to speciation studies of metabolism of arsenosugars following the consumption of arsenosugar-containing mussels by human volunteers. Speciation of arsenic in urine samples collected from four volunteers after the ingestion of musseles reveals significant increases of DMAA concentration, resulting from the metabolism of arsenosugars. These results suggest that the commonly used biomarkers for assessing human exposure to inorganic arsenic, which are based on the determination of urinary arsenite, arsenate, MMAA, and DMAA, are not reliable when arsenosugar-containing seafood is ingested.

Inductively coupled plasma mass spectrometric detection for chromatography and capillary electrophoresis

Inductively coupled plasma mass spectrometry (ICP-MS) is now a well established detection technique for liquid chromatography, gas chromatography, supercritical fluid chromatography and capillary electrophoresis. A review of the literature with particular regard to ICP-MS as a chromatographic and capillary electrophoretic detector is presented. The various modes of chromatography and capillary electrophoresis are discussed and practical descriptions for hyphenating the techniques with the ICP mass spectrometer are given. Sample introduction systems and data acquisition methods are reviewed along with the numerous applications of ICP-MS as a chromatographic detector. In addition, alternative plasma sources, such as the atmospheric and reduced pressure helium microwave-induced plasmas for chromatographic detection are described.

Determination of metal ions by capillary electrophoresis

The increasing use of capillary electrophoresis (CE) in all areas of analytical chemistry has been reflected in the appearance since 1990 of significant numbers of fundamental studies and applications of CE in the area of separations of metal ions. In this article all aspects of separations of metal ions by CE are reviewed and discussed, including general concepts and approaches, sample introduction, complex formation and sample stacking, separation selectivity, the role of kinetics, capillary wall chemistry, detection techniques, method validation, and applications to metal determinations in various matrices.