Inductively coupled plasma mass spectrometry and electrospray mass spectrometry for speciation analysis: applications and instrumentation

To gain an understanding of the function, toxicity and distribution of trace elements, it is necessary to determine not only the presence and concentration of the elements of interest, but also their speciation, by identifying and characterizing the compounds within which each is present. For sensitive detection of compounds containing elements of interest, inductively coupled plasma mass spectrometry (ICP-MS) is a popular method, and for identification of compounds via determination of molecular weight, electrospray ionization mass spectrometry (ESI-MS) is gaining increasing use. ICP-MS and ESI-MS, usually coupled to a separation technique such as chromatography or capillary electrophoresis, have already been applied to a large number of research problems in such diverse fields as environmental chemistry, nutritional science, and bioinorganic chemistry, but a great deal of work remains to be completed. Current areas of research to which ICP-MS and ESI-MS have been applied are discussed, and the existing instrumentation used to solve speciation problems is described.     

Multielemental speciation of trace elements in estuarine waters with automated on-site UV photolysis and resin chelation coupled to inductively coupled plasma mass spectrometry

An integrated approach for the accurate determination of total, labile and organically bound dissolved trace metal concentration in the field is presented. Two independent automated platforms consisting of an ultraviolet (UV) on-line unit and a chelation/preconcentration/matrix elimination module were specifically developed to process samples on-site to avoid sample storage prior to inductively coupled plasma mass spectrometry (ICP-MS) analysis. The speciation scheme allowed simultaneous discrimination between labile and organic stable dissolved species of seven trace elements including Cd, Cu, Mn, Ni, Pb, U and Zn, using only 5 ml of sample with detection limits ranging between 0.6 ng l⁻¹ for Cd and 33 ng l⁻¹ for Ni. The influence of UV photolysis on organic matter and its associated metal complexes was investigated by fluorescence spectroscopy and validated against natural samples spiked with humic substances standards. The chelation/preconcentration/matrix elimination procedure was validated against an artificial seawater spiked sample and two certified reference materials (SLRS-4 and CASS-4) to ensure homogenous performance across freshwater, estuarine and seawater samples. The speciation scheme was applied to two natural freshwater and seawater samples collected in the Adour Estuary (Southwestern, France) and processed in the field. The results indicated that the organic complexation levels were high and unchanged for Cu in both samples, whereas different signatures were observed for Cd, Mn, Ni, Pb, U and Zn, suggesting organic ligands of different origin and/or their transformation/alteration along estuarine water mixing.     

Concepts and recent advances in microchip electrophoresis coupled to mass spectrometry: Technologies and applications

The online coupling of microchip electrophoresis (ME) as a fast, highly efficient, and low-cost miniaturized separation technique to mass spectrometry (MS) as an information-rich and sensitive characterization technique results in ME–MS an attractive tool for various applications. In this paper, we review the basic concepts and latest advances in technology for ME coupled to MS during the period of 2016–2021, covering microchip materials, structures, fabrication techniques, and interfacing to electrospray ionization (ESI)–MS and matrix-assisted laser desorption/ionization–MS. Two critical issues in coupling ME and ESI–MS include the electrical connection used to define the electrophoretic field strength along the separation channel and the generation of the electrospray for MS detection, as well as, a miniaturized ESI-tip. The recent commercialization of ME–MS in zone electrophoresis and isoelectric focusing modes has led to the widespread application of these techniques in academia and industry. Here we summarize recent applications of ME–MS for the separation and detection of antibodies, proteins, peptides, carbohydrates, metabolites, and so on. Throughout the paper these applications are discussed in the context of benefits and limitations of ME–MS in comparison to alternative techniques.     

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: A tutorial review. Part II. Practical considerations

Inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are increasingly used to carry out analyses in organic/hydro-organic matrices. The introduction of such matrices into ICP sources is particularly challenging and can be the cause of numerous drawbacks. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP sources. Part I provided theoretical considerations associated with the physico-chemical properties of such matrices, in an attempt to understand the induced phenomena. Part II of this tutorial review is dedicated to more practical considerations on instrumentation, instrumental and operating parameters, as well as analytical strategies for elemental quantification in such matrices.     

On-line preconcentration of palladium on alumina microcolumns and determination in urban waters by inductively coupled plasma mass spectrometry

A method for on-line preconcentration of palladium at ultra-trace level on alumina microcolumns and determination by inductively coupled plasma mass spectrometry (ICP-MS) has been developed. A sampling time of 10 min (30 ml) and an eluent (KCN) volume of 300 μl provides a limit of detection of 1 ng l⁻¹. The precision was 4% at the 25 ng l⁻¹ level. The proposed system allows the on-line removal of the primary interferents (Cu and Y) providing the credible accuracy of the results. The proposed method is suitable for palladium determination in urban water samples. Platinum concentration in the analysed urban water samples was also determined.     

Applications of coupled LC-GC: A review

Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.     

Flame atomic absorption spectrometry determination of trace amounts of copper after separation and preconcentration onto TDMBAC-treated analcime pyrocatechol-immobilized

A simple and reliable method has been developed for green separation and preconcentration of trace amounts of copper ions in aqueous solutions for subsequent measurement by flame atomic absorption spectrometry (FAAS). The Cu²⁺ ions are adsorbed selectively and quantitatively during the passage of an aqueous solution through TDMBAC-treated analcime pyrocatechol-immobilized. The retained copper ions were desorbed from the column with 5.0 mL of 4 mol L⁻¹ nitric acid solutions as eluent and were determined by FAAS. The linear range was 0.2-75 ng mL⁻¹ in the original solution with a correlation coefficient of 0.9987. In this case we can concentrate 0.1 μg of copper from 1000 mL of solution and the proposed method permits a large enrichment factor (about 200). The detection limit of the proposed method is 0.05 ng mL⁻¹ in the original solution (2σ_bl). Determination of copper in standard alloys showed that the proposed method has good accuracy (recovery was more than 97%). The method was successfully applied for recovery and determination of copper in several water samples.     

Matrix effects in inductively coupled plasma mass spectrometry: a review

Fundamental research on non-spectroscopic interferences, also known as matrix effects, in inductively coupled plasma (ICP) mass spectrometry with sample introduction using nebulization is critically and exclusively examined in this review, starting with fundamental processes that may be a source of matrix effects during sample introduction, ion generation in the ICP, ion extraction through the interface, and ion transport through the ion optics to the detector. Various methods for attenuating matrix effects are then reviewed and illustrated with some examples. Instead of exhaustively reviewing the literature, representative references are used to comprehensively describe the main issues, several of which are also common to ICP optical emission spectrometry.     

Determination of picomolar beryllium levels in seawater with inductively coupled plasma mass spectrometry following silica-gel preconcentration

A robust and rapid method for the determination of natural levels of beryllium (Be) in seawater was developed to facilitate mapping Be concentrations in the ocean. A solid-phase extraction method using a silica gel column was applied for preconcentration and purification of Be in seawater prior to determination of Be concentrations with inductively coupled plasma mass spectrometry (ICP-MS). Be was quantitatively adsorbed onto silica gel from solutions with pH values ranging from 6.3 to 9, including natural seawater. The chelating agent ethylenediamine tetraacetic acid was used to remove other ions in the seawater matrix (Na, Mg, and Ca) that interfere with the ICP-MS analysis. The reproducibility of the method was 3% based on triplicate analyses of natural seawater samples, and the detection limit was 0.4 pmol kg⁻¹ for 250 mL of seawater, which is sufficient for the analysis of seawater in the open ocean. The method was then used to determine the vertical profile of Be in the eastern North Pacific Ocean, which was found to be a recycled-type profile in which the Be concentration increased with depth from the surface (7.2 pmol kg⁻¹ at <200 m) to deep water (29.2 pmol kg⁻¹ from 3500 m to the bottom).     

Selective determination of airborne hexavalent chromium using inductively coupled plasma mass spectrometry

A new method for determining ultra-trace levels of hexavalent chromium in ambient air has been developed. The method involves a 24-h sampling of air into potassium hydroxide solution, followed by silica gel column separation of chromium (VI), then preconcentration by complexation and solvent extraction. The chromium (VI) complex was dissolved in nitric acid. The resultant chromium ions were determined by inductively coupled plasma mass spectrometry (ICP–MS) using a dynamic reaction cell (DRC) with ammonia as the reactive gas to reduce polyatomic interferences. The interconversion of chromium in potassium hydroxide solution and air sample matrix were investigated under ambient conditions. It was found that there was no conversion of chromium (VI) into chromium (III) species. However, it was observed that some chromium (III) species were converted into chromium (VI) species. For a KOH solution containing 100 μg l⁻¹ of chromium (III) species, the rate of conversion was found to be 3% after 24 h exposure, 8% after 48 h, 10% after 72 h and no further conversion was observed thereafter. However, in a solution containing air sample matrix, 9.3% of chromium (III) converted to chromium (VI) within 6 h, and during the course of a 11-day exposure period, 13% (range 8–17%) of chromium (III) converted to chromium (VI). The method detection limit (MDL) for chromium (VI) in potassium hydroxide solution (0.025 M) was found to be 2×10⁻² μg l⁻¹. This is equivalent to 0.2 ng m⁻³ (for 23 m³ air sampled into 200 ml of KOH solution over a 24-h period). The recovery of spiked chromium (VI) from solutions containing air sample matrix was 95±9% (n=8). Matrix related interferences were estimated to be less than 10% based on recovery studies. The concentration of airborne chromium (VI) in Sydney residential areas was found to be less than 0.2 ng m⁻³, however, in industrial areas the concentrations ranged from 0.2 to 1.3 ng m⁻³ using this analytical procedure.     

The use of carbon nanofibers microcolumn preconcentration for inductively coupled plasma mass spectrometry determination of Mn,Co and Ni

Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP–MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0–9.0, and then eluted completely with 0.5 mol ml^− 1 HNO₃. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml^− 1, respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%.     

Direct analysis of dried blood spots coupled with mass spectrometry: concepts and biomedical applications

Because of the emergence of dried blood spots (DBS) as an attractive alternative to conventional venous plasma sampling in many pharmaceutical companies and clinical laboratories, different analytical approaches have been developed to enable automated handling of DBS samples without any pretreatment. Associated with selective and sensitive MS–MS detection, these procedures give good results in the rapid identification and quantification of drugs (generally less than 3 min total run time), which is desirable because of the high throughput requirements of analytical laboratories. The objective of this review is to describe the analytical concepts of current direct DBS techniques and to present their advantages and disadvantages, with particular focus on automation capacity and commercial availability. Finally, an overview of the different biomedical applications in which these concepts could be of major interest will be presented.     

Advantages and limitations of coupling isotachophoresis and comprehensive isotachophoresis-capillary electrophoresis to time-of-flight mass spectrometry

Capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were successfully coupled to electrospray ionization (ESI) orthogonal acceleration time-of-flight mass spectrometry (TOF-MS) using angiotensin peptides as model analytes. The utility of ITP-TOF-MS and ITP-CE-TOF-MS for the analysis of samples containing analyte amounts sufficient to form flat-top ITP zones (30 microM) as well as for samples with trace analyte amounts (0.3 microM) was studied. Separations were performed in 150 microm internal diameter (I.D.) capillaries for the ITP experiments, and in 200 microm I.D. (ITP) and 50 microm I.D. (CE) capillaries for ITP-CE experiments. The fused-silica columns were coated with poly(vinyl alcohol) to suppress electroosmotic flow that can disrupt ITP zone profiles. The sample loading capacity in both ITP and comprehensive ITP-CE was greatly enhanced (up to 10 microl) compared with typical nanoliter-sized injection volumes in CE. It was concluded that ITP-TOF-MS alone was adequate for the separation and detection of high concentration samples. The outcome was different at lower analyte concentrations where mixed zones or very sharp peaks formed. With formation of mixed zones, ion suppression and discrimination could occur, complicating quantitative determination of the analytes. This problem was effectively overcome by inserting a CE capillary between the ITP and TOF-MS. In such an arrangement, samples were preconcentrated in the high load WTP capillary and then injected into a CE capillary where they were separated into non-overlapping peaks prior to their detection by TOF-MS. The advantage of this comprehensive arrangement, which we have described previously, is that there is no need to discard portions of the sample in order to avoid overloading of the CE capillary. The whole sample is analyzed by multiple injections from ITP to CE. Thus, this method can be used for the analysis of complex samples with wide ranges of component concentrations.     

A comparison of enrichment factor of knotted and serpentine reactors using flow injection sorption and preconcentration for the off-line determination of some trace elements by inductively coupled plasma mass spectrometry

The preconcentration efficiency expressed as an enrichment factor (EF) in knotted and serpentine reactors (SR) for FI sorption and preconcentration for the off-line determination of Cd(II), Ni(II), Co(II),Cu(II), Pb(II), Zn(II), Mo(VI), Cr(VI) and W(VI) with ICP-MS was investigated. The preconcentration was carried out by the formation of metal–pyrrolidine dithiocarbamate complex in an acidic solution and sorbed onto the inner wall of the PTFE reactors. The EFs were determined as the ratio between the analyte intensities after preconcentration using the reactors and that obtained without using the reactors. Comparing the two procedures for the equal reactor length (150 cm), the higher EFs obtained by using knotted reactor (KR) were observed for all elements. With the preconcentration time of 120 s and a sample flow rate of 1.2 ml min⁻¹, the EFs of 4–36 and 3–12 were gained using knotted and SRs, respectively. The results obtained indicate that the KR is preferable to use for flow injection sorption preconcentration system over the SR.     

Quantitative and confirmative performance of liquid chromatography coupled to high-resolution mass spectrometry compared to tandem mass spectrometry

The quantitative and confirmative performance of two different mass spectrometry (MS) techniques (high-resolution MS and tandem MS) was critically compared. Evaluated was a new extraction and clean-up protocol which was developed to cover more than 100 different veterinary drugs at trace levels in a number of animal tissues and honey matrices. Both detection techniques, high-resolution mass spectrometry (HRMS) (single-stage Orbitrap instrument operated at 50 000 full width at half maximum) and tandem mass spectrometry (MS/MS) (quadrupole technology) were used to validate the method according to the EU Commission Decision 2002/657/EEC. Equal or even a slightly better quantitative performance was observed for the HRMS-based approach. Sensitivity is higher for unit mass resolution MS/MS if only a subset of the 100 compounds has to be monitored. Confirmation of suspected positive findings can be done by evaluating the intensity ratio between different MS/MS transitions, or by accurate mass based product ion traces (no precursor selection applied). MS/MS relies on compound-specific optimized transitions; hence the second, confirmatory transition generally shows relatively high ion abundance (fragmentation efficacy). This is often not the case in single-stage HRMS, since a generic (not compound-optimized) collision energy is applied. Hence, confirmation of analytes present at low levels is superior when performed by MS/MS. Slightly better precision, but poorer accuracy (fortified matrix extracts versus pure standard solution) of ion ratios were observed when comparing data obtained by HRMS versus MS/MS.     

Heart-cutting multidimensional gas chromatography: A review of recent evolution,applications, and future prospects

The present contribution is focused on the main advances made in the field of heart-cutting multidimensional gas chromatography (MDGC), over approximately the last decade. Brief details on the history of classical MDGC are also given. A series of applications, carried out with modern-day commercially available instrumentation are shown, demonstrating the usefulness of the bidimensional methodology in specific analytical situations. Finally, the future prospects of MDGC are considered, within the shadow projected by a very powerful GC technique, namely comprehensive two-dimensional gas chromatography.     

Microfluidic chip-based liquid chromatography coupled to mass spectrometry for determination of small molecules in bioanalytical applications

The development and integration of microfabricated liquid chromatography (LC) microchips have increased dramatically in the last decade due to the needs of enhanced sensitivity and rapid analysis as well as the rising concern on reducing environmental impacts of chemicals used in various types of chemical and biochemical analyses. Recent development of microfluidic chip-based LC mass spectrometry (chip-based LC-MS) has played an important role in proteomic research for high throughput analysis. To date, the use of chip-based LC-MS for determination of small molecules, such as biomarkers, active pharmaceutical ingredients (APIs), and drugs of abuse and their metabolites, in clinical and pharmaceutical applications has not been thoroughly investigated. This mini-review summarizes the utilization of commercial chip-based LC-MS systems for determination of small molecules in bioanalytical applications, including drug metabolites and disease/tumor-associated biomarkers in clinical samples as well as adsorption, distribution, metabolism, and excretion studies of APIs in drug discovery and development. The different types of commercial chip-based interfaces for LC-MS analysis are discussed first and followed by applications of chip-based LC-MS on biological samples as well as the comparison with other LC-MS techniques.