An evaluation of the experimental approaches to detection of small ions in CE

This review points out some important trends in the development of the detection techniques for small ions in CE. On the basis of selected literature references it briefly discusses some general requirements on detection techniques in CE. Various optical measurements, mass spectrometric approaches and electrochemical detection techniques are dealt with. Some specific features of microchip CE separation and detection are pointed out and possibilities of dual detection are mentioned. The principal parameters of the above detection techniques are then briefly compared.     

Challenges and applications of isotachophoresis coupled to mass spectrometry: A review

Electrophoretic separations are of growing interest to tackle complex analytical challenges. Nevertheless, capillary electrophoresis, as the most common mode, still suffers from insufficient detection limits due to low capillary loadability. ITP is of growing interest as preconcentration method for capillary electrophoresis and is also interesting to be applied as an independent analytical method. While mass spectrometric detection is common for capillary electrophoresis, the combination of ITP with MS is still a niche technique. In this work, we want to give an overview on isotachophoretic effects in CE-MS and ITP-MS methods, as well as coupling techniques of ITP with CE-MS. The challenges and possibilities associated with mass spectrometric detection in ITP and its coupling to capillary electrophoresis are critically discussed.     

Mass spectrometric detection in chromatography. Trends and perspectives

The newest results in the use of miscellaneous mass spectrometric detection methods in various chromatographic techniques are compiled and critically evaluated. Examples of application in clinical chemistry, health care, and in the analysis of pharmaceuticals, environmental pollutants, foods and food products are given. The benefits and drawbacks of MS detection are discussed, and future trends are briefly discussed.     

Multielement trace-element speciation in metal-biomolecules by chromatography coupled with ICP-MS

The state-of-the-art of multi-element speciation in biological materials by hybrid techniques with inductively coupled plasma-mass spectrometric (ICP-MS) detection is critically reviewed with special attention to multi-metal speciation in metallothioneins (MT) and metallothionein-like proteins (MLP). The most common separation techniques used for the purpose include conventional size-exclusion chromatography (SEC) (with off-line detection) and anion-exchange (AE) or reversed-phase (RP) HPLC coupled on-line to ICP-MS. Advantages and limitations of the different commercial element-selective ICP-MS detectors, including the quadrupole (Q), double focusing (DF), and time-of-flight (TOF) mass analysers, are discussed. Procedures reported for speciation analysis, by use of hybrid techniques, for multi-metal speciation in mussel MLP and rabbit liver MT are illustrated with special emphasis on work performed in the authors' laboratory.     

Analysis of paralytic shellfish poisons by capillary electrophoresis

A capillary electrophoresis (CE) method with UV detection is described for the separation and determination of underivatized toxins associated with paralytic shellfish poisoning (PSP). Confirmation of the electrophoretic peaks was facilitated by mass spectrometric (MS) detection using an ionspray CE-MS interface and by high-performance liquid chromatography with fluorescence detection. The determination of PSP toxins, such as saxitoxin and neosaxitoxin, in toxic dinoflagellates and scallops is demonstrated and comparisons are made with existing techniques.     

Plasma-based mass spectrometry for simultaneous acquisition of elemental and molecular information

Chemical speciation studies are commonly accomplished by resorting to hyphenated analytical techniques, consisting of a powerful chromatographic separation technique coupled to a highly sensitive elemental spectrometric detector. However, in addition to this element-selective information, complementary molecular spectrometric tools are often required for a complete identification of macromolecules. Therefore, there is an increased research effort focused towards the development of integrated instruments to carry out the complete chemical speciation within a sample using a single instrument. An outline of recent developments in plasma-based mass spectrometric instrumentation for such comprehensive chemical speciation studies is here presented and their pros and cons detailed. In this context, the use of complementary techniques operating in parallel after splitting to a single chromatographic separation (dual sources) providing simultaneously elemental and molecular information is critically reviewed. Also, instrumental developments involving the use of stationary plasma sources operated in non-traditional modes (e.g. low pressure and low power) are also discussed. Moreover, the capabilities of tunable plasma-based ionization sources (allowing different ionization processes and, so, quasi-simultaneously providing elemental and molecular information with a single instrument) as a relatively simple and cheap approach are revised.     

Determination of Underivatized Polyamines: A Review of Analytical Methods and Applications

Putrescine, cadaverine, spermidine, and spermine are ubiquitous polyamines that are essentially found in diverse organisms (e.g., bacteria, fungi), animals, and higher plants. Analysis of these analytes is traditionally performed either by chromatographic or electrophoretic techniques. The majority of assays employ liquid chromatography with fluorimetric detection either with pre-column or post-column derivatization. However, the derivatization procedures have several disadvantages to the whole analytical process. This article describes the analytical method developments in the determination of underivatized polyamines. This includes flow injection analysis, high performance liquid chromatography (using conductivity, condensation nucleation light scattering, chemiluminescence, indirect fluorescence, and mass spectrometric detection) and electromigration methods. The reported systems are essentially based on the work developed by the authors since 1995. A comparison of the methods highlighting their main advantages and disadvantages and sensitivity was also provided. The most promising system seems to be the liquid chromatography-tandem mass spectrometric due to its high sensitivity and specificity.     

Recent methods for the determination of peroxide-based explosives

In the last few years, the need to determine peroxide-based explosives in solid samples and air samples has resulted in the development of a series of new analytical methods for triacetonetriperoxide (TATP, acetone peroxide) and hexamethylenetriperoxidediamine (HMTD). In this review, after a short introduction describing the state of the art in the field, these new analytical methods are critically discussed. Particular emphasis is placed on spectroscopic and mass spectrometric methods as well as on chromatographic techniques with selective detection schemes. The potential of these methods to analyse unknown solid samples that might contain one or more of the explosives and to analyse peroxide-based explosives in air is evaluated.     

Development of ultratrace laser spectrometry techniques for measurements of arsenic

Several techniques based on laser induced fluorescence (LIF) spectrometry and laser enhanced ionization (LEI) spectrometry have been investigated for ultratrace measurements of arsenic. Studies by our group in this area that have been published previously are reviewed here, and are presented along with the results of recent studies that have not yet been published. The techniques presented include LIF detection in the inductively coupled plasma atomizer, the electrothermal atomizer, the tungsten coil atomizer, the flame atomizer and LEI detection in the flame atomizer, and include approaches that utilize hydride generation or laser ablation sample introduction. Recent efforts have been directed towards developing speciation approaches for arsenic that utilize LIF spectrometric detection. The capabilities of each technique are summarized including the sensitivity and limits of detection, which range from sub-pg ml(-1) to ng ml(-1) levels. Selected applications of the techniques are presented to demonstrate their utility for environmental and biological samples, and areas for future investigation and further development are discussed.     

Preparation and certification of solutions of perdeuterated polycyclic aromatic compounds intended for use as surrogate internal standards

Two standard solutions of deuterated polycyclic aromatic compounds (PACs) have been prepared for use as surrogate internal standards. Solution DPAC-1 contains 21 deuterated PACs, and is intended for use with mass spectrometric (MS) detection. Most of the difficulties in certifying concentrations in DPAC-1 arose from the fact that none of the individual compounds was 100% deuterated, so that effects of mass spectrometric fragmentation are convoluted with those of isotopic distributions. The best methods are discussed for using such internal standards so as to minimize these problems, together with those arising from kinetic isotope effects. Solution DPAC-2 contains 6 deuterated PACs, and is primarily intended for use with reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection (FLD, dual programmed wavelength mode), in which the signals for analyte and internal standard are separated chromatographically rather than via the detector. Full details of the preparation of these solutions are described. In addition, examples of their use in the analysis of a certified coal-tar extract (NIST SRM 1597) are described briefly. In one example a novel HPLC-MS technique was employed, and in the other the HPLC-FLD technique was used.NRCC No. 38030     

Ambient ionization mass spectrometry: a tutorial

Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.     

Metabolism and toxicological detection of a new designer drug, N-(1-phenylcyclohexyl)propanamine, in rat urine using gas chromatography-mass spectrometry

Studies are described on the metabolism and the toxicological detection of the phencyclidine-derived designer drug N-(1-phenylcyclohexyl)-propanamine (PCPR) in rat urine using gas chromatographic-mass spectrometric techniques. The identified metabolites indicated that PCPR was metabolized by hydroxylation of the cyclohexyl ring at different positions, hydroxylation of the phenyl ring, N-dealkylation, and combinations of these steps. Parts of the metabolites were excreted in conjugated form. The authors' systematic toxicological analysis (STA) procedure using full-scan GC-MS after acid hydrolysis, liquid-liquid extraction and microwave-assisted acetylation allowed the detection of an intake of a common drug users' dose of PCPR in rat urine. Assuming similar metabolism in humans, the STA should be suitable for proof of an intake of PCPR in human urine.     

Reference materials for PAHs in foodstuffs: results of a preliminary intercomparison of methods in experienced laboratories

Summary A preliminary intercomparison of methods which can be applied to the determination of trace amounts of PAHs in coconut oil and green kale samples has been made under an interlaboratory cooperative analytical programme organised by the Community Bureau of Reference. The techniques which were utilised were glass-capillary gas chromatography with flame-ionisation or mass spectrometric detection, and high-performance liquid chromatography with fluorescence and/or ultra-violet detection. Analyses were made for five environmentally important PAHs and the results, the methods and some associated problems are discussed.

---

Referenzmaterialien für PAKs in Lebensmitteln: Ergebnisse eines vorlÄufigen Ringversuchs erfahrener Laboratorien

     

Investigations on novel electrolytes,solvents and SEI additives for use in lithium-ion batteries: Systematic electrochemical characterization and detailed analysis by spectroscopic methods

Electrolyte solutions have vital function in lithium-ion batteries. Due to their modular composition, there is a broad variety of electrolyte component combinations. In this work, we present electrochemical results on newly investigated electrolyte solution components. The standard electrolyte salt in commercial batteries, LIPF₆, was replaced by new imide and sulfonate anion based salts, with enhanced stability. The use of propylene carbonate was enabled by the application of new SEI forming electrolyte additives. Electrolyte solvents, such as adiponitrile and γ-butyrolactone were investigated in combination with LiBF₄ as electrolyte salt. In order to evaluate these materials, various electrochemical techniques like galvanostatic cycling, conductivity and electrochemical stability window detection, cyclic voltammetry, etc. were applied. Furthermore, the electrode/electrolyte interfaces and interphases were studied via spectroscopic and spectrometric techniques.     

生物样品中儿茶酚胺类物质分析方法的研究进展

儿茶酚胺是人体内重要的神经递质,血浆及尿中儿茶酚胺的浓度水平可用于诊断高血压、嗜铬细胞瘤及成神经细胞瘤等病症,因而准确测定人体生物样品中儿茶酚胺类物质代谢浓度的变化,在疾病的诊断和治疗中具有重要的意义。该文综述了人体液和组织中儿茶酚胺类物质的不同分析方法,包括高效液相色谱法、毛细管电泳法、质谱法、电化学法、化学发光法、荧光光度法等。     

Proteomics based on high-efficiency capillary separations

Identifying and quantifying in a high throughput manner the proteins expressed by cells, tissues or an organism provides the basis for understanding the functions of its constituents at a "systems" level. As a result, proteome analysis has increasingly become the focus of significant interest and research over the past decade. This is especially true following the recent stunning achievements in genomics analyses. However, unlike the static genome, the complexities and dynamism of the proteome present significant analytical challenges and demand highly efficient separations and detection technologies. A number of recent technological advancements have been in direct response to these challenges. Currently, strategically mated combinations of sophisticated separations techniques and advanced mass spectrometric detection represent the best approach to addressing the intricacies of the proteome. Liquid-phase separations, often within capillaries, are increasingly recognized as the best separations technique for this approach. In combination on-line with mass spectrometry, liquid-phase separations provide the improved analytical sensitivity, sample throughput, and quantitation capabilities necessitated by the multifaceted problems within proteomics analyses. This review focuses primarily on current high-efficiency capillary separations techniques, including both capillary liquid chromatography and capillary electrophoresis, applied to the analysis of complex proteomic samples. We emphasize developments at our laboratory and illustrate technical advances that attempt to review the role of separations within the broader context of a state-of-the-art integrated proteomics effort.     

Derivatization trends in capillary electrophoresis: an update

This survey as a sequel of two earlier reports gives an overview of recent developments, starting from 1999, in the use of derivatization protocols in capillary electrophoretic (CE) analysis. Derivatization is mainly used for enhancement of the detection sensitivity in CE, for which a combination of fluorescence labeling and laser-induced fluorescence detection is favorable. Moreover, especially in the field of saccharide assay, derivatization to introduce charge into the molecule, is common. Derivatization procedures are classified in tables, focused on precapillary, on-line, on-capillary and postcapillary arrangements and divided in sections concerning the functional group that is derivatized. The most frequently reported groups are amines and the reducing end of (oligo)saccharides, but thiols, carbonyl and carboxyl groups, steroids and inorganic ions have also been reported about. Other reasons for derivatization are to enhance chiral separation, introduction of a suitable charge into the molecule or to improve mass spectrometric detection. The use of derivatization techniques for special cases, such as the analysis of neurotransmitters, insulin antibodies and mitochondria has also been incorporated as well as a study on the adsorption of proteins onto capillary walls during CE in which derivatization plays a role.     

Sampling techniques for single-cell electrophoresis

Cells are extraordinarily complex, containing thousands of different analytes with concentrations spanning at least nine orders of magnitude. Analyzing single cells instead of tissue homogenates provides unique insights into cell-to-cell heterogeneity and aids in distinguishing normal cells from pathological ones. The high sensitivity and low sample consumption of capillary and on-chip electrophoresis, when integrated with fluorescence, electrochemical, and mass spectrometric detection methods, offer an ideal toolset for examining single cells and even subcellular organelles; however, the isolation and loading of such small samples into these devices is challenging. Recent advances have addressed this issue by interfacing a variety of enhanced mechanical, microfluidic, and optical sampling techniques to capillary and on-chip electrophoresis instruments for single-cell analyses.     

Photoswitching-induced frequency-locked donor-acceptor fluorescence double modulations identify the target analyte in complex environments

Precisely identifying biological targets and accurately extracting their relatively weak signals from complicated physiological environments represent daunting challenges in biological detection and biomedical diagnosis. Fluorescence techniques have become the method of choice and offer minimally invasive and ultrasensitive detections, thus, providing a wealth of information regarding the biological mechanisms in living systems. Despite fluorescence analysis has advanced remarkably, conventional detections still encounter considerable limitations. This stems from the fact that the fluorescence intensity signal (I) is sensitive and liable to numerous external factors including temperature, light source, medium characteristics, and dye concentration. The interferences exasperatingly undermine the precision of measurements, and frequently render the signal undetectable. For example, fluorescence from single-molecule emitters can be measured on glass substrates under optimum conditions, but single-molecule events in complicated physiological environments such as live cells can hardly be detected because of autofluorescence interference and other factors. Furthermore, traditional intensity (I) and wavelength (λ) measurements do not reveal the interactive nature between the donor and the acceptor. Thus, innovative detection strategies to circumvent these aforementioned limitations of the conventional techniques are critically needed. With the use of photoswitching-induced donor-acceptor-fluorescence double modulations, we present a novel strategy that introduces three additional physical parameters: modulation amplitude (A), phase shift (ΔΦ), and lock-in frequency (ω), and demonstrate that such a strategy can circumvent the limitation of the conventional fluorescence detection techniques. Together, these five physical quantities (I, λ, A, ΔΦ, ω) reveal insightful information regarding molecular interactive strength between the probe and the analyte and enable extracting weak-fluorescence spectra from large interfering noises in complex environments.     

Label-free fluorescence detection in capillary and microchip electrophoresis

Herein, we summarize the current status of native fluorescence detection in microchannel electrophoresis, with a strong focus on chip-based systems. Fluorescence detection is a powerful technique with unsurpassed sensitivity down to the single-molecule level. Accordingly fluorescence detection is attractive in combination with miniaturised separation techniques. A drawback is, however, the need to derivatize most analytes prior to analysis. This can often be circumvented by utilising excitation light in the UV spectral range in order to excite intrinsic fluorescence. As sensitive absorbance detection is challenging in chip-based systems, deep-UV fluorescence detection is currently one of the most general optical detection techniques in microchip electrophoresis, which is especially attractive for the detection of unlabelled proteins. This review gives an overview of research on native fluorescence detection in capillary (CE) and microchip electrophoresis (MCE) between 1998 and 2008. It discusses material aspects of native fluorescence detection and the instrumentation used, with particular focus on the detector design. Newer developments, featured techniques, and their prospects in the future are also included. In the last section, applications in bioanalysis, drug determination, and environmental analysis are reviewed with regard to limits of detection.