On-line coupling between chromatography and inductively coupled plasma mass spectrometry — a current assessment

The current state of on-line coupling between liquid chromatography and inductively coupled plasma mass spectrometry is reviewed. The applications can be divided into three subgroups by changing the importance of the coupling partners. An overview is given of applications in these subgroups, of its use as preconcentration and matrix elimination techniques, for the elimination of spectral interferences and as a tool for speciation analysis. A discussion of current and future development areas in on-line HPLC-ICP-MS is also included.     

On-line coupling of ion chromatography and atomic spectrometry and use of direct graphite furnace atomic absorption spectrometry as new tools for ultra trace determinations in refractory metals

On-line coupling of inductively coupled plasma (ICP) techniques such as ICP-AES and ICP-MS with ion chromatography (IC) offers unique features for ultra-trace analysis. An on-line preconcentration procedure based on cation exchange enables sub-ng/g analysis in complex matrices like molybdenum and tungsten. The best dissolution reagent for these matrices is hydrogen peroxide, which can be cleaned to ultra high purity with the same metal free chromatography equipment used for the preconcentration. Preconcentration is possible for elements that show cationic reactions within acidic peroxide containing solutions. In this study 28 elements detrimental for microelectronics applications are observed. A comparison of the combinations IC-ICP-AES and IC-ICP-MS with glow discharge mass spectrometry (GDMS) for the analysis of today's purest tungsten samples shows the analytical power and accuracy of the coupled devices. Graphite furnace atomic absorption spectrometry (GFAAS) as an extremely sensitive analytical technique is applied with and without the same sample pretreatment as used for the on-line coupling. Direct GFAAS measurements of alkali metals are complementary to IC-ICP techniques. The data evaluated with these wet chemical techniques are compared to the usual manufacturers characterisation technique GDMS. With respect to the low concentrations present in these high purity materials (ng/g level in the solid) the discrepancies between all methods are acceptable. The sensitivity of IC-ICP-MS is in most cases far superior to IC-ICP-AES and for some elements also to GDMS. Furthermore the specific advantages of on-line coupling such as the elimination of isobaric interferences in ICP-MS or spectral interferences in ICP-AES are shown for ICP-AES and ICP-MS determinations.     

Flow/sequential injection sample treatment coupled to capillary electrophoresis. A review

Various flow sample handling approaches coupled to capillary electrophoresis (CE) are reviewed, covering the research in this field in the 12 years since the milestone year of 1997, when practical interfaces to on-line couple flow injection (FI) and capillary electrophoresis were first developed independently by two research groups. Some previous attempts are also presented. Since 1997 a plethora of ingenious coupled systems have been developed. Although several reviews are available on various aspects of the topic, we have opted for a comprehensive overview of all FI-CE systems, as well as related and similar systems. This coupling has thus also led to the development of systems based on hybrids between the classical and microchip approaches. Truly microchip FI-CE systems are also included in this review.The developed systems have been used for various sample treatments, including on-line membrane-assisted sample treatment, column-based preconcentration, on-line derivatization and monitoring, to name just a few. The utility of coupling flow sampling to CE has been demonstrated in various practical applications that are discussed in detail. The current state-of-the-art and foreseeable future developments are also discussed.     

On-line coupling of ion chromatography and atomic spectrometry for ultra trace analysis in high purity molybdenum- and tungsten-silicide

The well-established technique of on-line coupling ion chromatography and atomic spectrometry for ultra trace analysis in high purity molybdenum and tungsten is extended to include the silicides MoSi(x) and WSi(x). An additionally included matrix elimination step allows an almost interference-free trace analysis in the silicide matrices. Reproducibility and accuracy of the on-line method were checked by comparison with several other methods, such as isotope dilution, radiochemical neutron activation analysis, direct determination by atomic absorption analysis and not at least with glow discharge mass spectrometry. The results show the high potential of the on-line method for reaching detection limits in the pg g(-1) range, but they show also remaining problems with contamination and system calibration.     

Overview on advances in capillary electrophoresis-mass spectrometry of carbohydrates: a tabulated review

The increasing interest for carbohydrates as holder of essential bioinformations has boosted their full characterization through analytical techniques. The intent of this review is to summarize the recent trends regarding on-line and off-line CE-MS coupling for carbohydrate analysis. A statistical survey on the articles that use derivatizing agents as well as on the analyzer and type of instrument coupling (i.e. on- or off-line) is depicted. From a general overview it can be concluded that, whereas derivatization might be useful for the detection of neutral carbohydrates improving separation selectivity with volatile buffers and increasing sensitivity of the MS detection, relatively few works with derivatized carbohydrates were found; this was noticed in particular for glycosides and saccharides carrying ionizable groups, which are normally analyzed without any chemical modification. The most applied coupling is the on-line sheath-liquid interface; for on-line applications, ESI is the sole source used, whilst the most common analyzer is the IT. MS(n) is often exploited, as fragmentation increases the achieved structural information. CE-MS turned out to be mainly used for the analysis of carbohydrates in drug development (i.e. study of oligosaccharides from pathogens, carbohydrate-based drugs and drug metabolites), in nutrition and for characterization of glycans from glycoproteins. The reader will find elucidating tables regarding these recent CE-MS applications, including the main information on the analysis conditions. Comments are meant to help the immediate focus on the usefulness of the analytical technique and predict the difficulties found during analysis and, in case, their overcoming.     

On-line coupling of ion chromatography with ICP–AES and ICP–MS

Ion chromatography (IC) and atomic spectrometry are sometimes rivalling and sometimes ideally cooperating techniques. The cooperating applications of the on-line coupling of IC and inductively coupled plasma–atomic emission spectroscopy or –mass spectrometry span from ultra trace analysis utilizing ion exchange as preconcentration technique via speciation applications taking advantage of the unique element specific detection offered by atomic spectroscopy until classical IC applications with atomic spectrometry as a sensitive and selective detector. Characteristics of this type of hyphenated technique are the simple physical coupling, the unique sensitivity for most elements and the superior selectivity obtainable for specific applications.     

Supercritical fluid extraction-capillary gas chromatography: On-line coupling with a programmed temperature vaporizer

A simple and versatile system is described for the on-line coupling of SFE to capillary GC. The interfacing consists of a programmed temperature vaporizer (PTV) injector. With this injector it is possible to combine solute trapping, elimination of a high flow of extraction fluid, and quantitative transfer of solutes to the seperation column. The problems caused by impurities in the extraction fluid in on-line SFE-GC are discussed. Simple methods are described for the purification of commercially available carbon dioxide. The trapping efficiency of the PTV injector is studied. Applications of the SFE-PTV-GC system are given for the analysis of polymer anti-degradants, polar compounds, and samples with environmental relevance.     

Capillary electrophoresis-mass spectrometry, an attractive tool for drug bioanalysis and biomarker discovery

The coupling of CE with MS detection, a relatively recent hyphenated technique, has gained increasing respect in the field of bioanalytical applications over the past few years. The first part of this review presents CE-MS applications dealing with drug bioanalysis, including forensic analysis and metabolism studies. Practical considerations to achieve a robust and sensitive CE-MS coupling are also presented. It is indeed essential to strictly control some critical electrospray parameters, such as the sheath liquid composition and flow rate, the nebulizing gas pressure as well as the capillary outlet position. The second part of the review critically describes the applications of CE coupled on-line to MS for the identification of biomarkers in body fluids for diagnostic purposes. Since the sample preparation procedures strongly differ according to the intended use (drug bioanalysis or biomarker discovery), they are discussed separately, taking into account the particular properties of plasma and urine matrices.     

On-line-Bestimmung von Enzymen in der Bioproze?analytik unter Berücksichtigung von Probenahme und Flie?injektionstechnik

Summary The on-line determination of enzymes in biotechnical processes becomes an important factor with regard to process development and optimization. At present, most commonly enzymes are determined off-line in the laboratory after withdrawal of a separate sample. Wet chemical methods dominate in this respect, mainly because enzymes have to be measured according to the reaction schemes which are catalyzed by them. For an efficient process monitoring and control the time delay, the limited reliability and the man power needed for analysis of a large number of samples are crucial points. By using the technique of flow injection analysis (FIA) it should in general become easy to develop automatically operated enzyme determination procedures based on reaction schemes which can be used for fast and efficient process monitoring, providing the problems with the coupling of the analyzer at the bioreactor are solved. Continuous sampling in this respect plays a key role in developing on-line measuring techniques. This paper reviews the current status of on-line enzyme analysis, using flow-injection techniques. It is shown that the coupling problems can be solved by using a newly developed sampling module, which is based on membrane filtration. Some examples of on-line enzyme determinations in fermentation as well as in downstream processing illustrate the ease and reliability of the proposed concept for using FIA in connection with membrane separation.     

New advances in countercurrent chromatography and centrifugal partition chromatography: focus on coupling strategy

Countercurrent chromatography (CCC) is an attractive separation method because the analytes are partitioned between two immiscible liquid phases avoiding problems related to solid stationary phase. In recent years, this technique has made great progress in separation power and detection potential. This review describes coupling strategies involving high speed CCC (HSCCC) or centrifugal partition chromatography (CPC). It includes on-line extraction–isolation, hyphenation with mass spectrometry (MS) and nuclear magnetic resonance (NMR) detectors, multidimensional CCC (MDCCC), two-dimensional CCC (2D-CCC), on-line coupling with liquid chromatography (LC), and biological tests, and innovative off-line developments. The basic principles of each method are presented and applications are summarized.