Hyphenated techniques, sample introduction

Various efficient devices have been utilized for sample introduction into an inductive plasma source, for example the application of several nebulizers, hyphenated techniques, hydride generation, laser ablation and electrothermal vaporization. The role of the solution introduction system in an inductively coupled plasma source is to convert the liquid sample into a suitable form (e.g.,... 

Because ICP-MS with different instrumentations and sample introduction systems (besides solution nebulization, also laser ablation or hyphenated methods, such as HPLC, CE, SPME) is today the most frequently used analytical technique for precise and accurate isotope ratio measurements, the following section will mainly focus on this form of mass spectrometry with an inductively coupled plasma source. 

Methods for the analysis of organic and organometallic compounds are discussed in this chapter. It has become evident that for the analysis of these two classes of compounds, the analyst can draw on a very similar repertoire of analytical techniques with respect to sample preparation, separation, and detection. Chromatographic and, in particular, hyphenated techniques are the workhorses of environmental water analysis. The various formats and technical realizations of mass spectrometers are the most versatile detectors. Their sensitivity and ability to provide structural information at the low and even sub-pg level are an asset and at the same time a prerequisite for (ultra)trace analysis in the aquatic environment. As further significant improvements in detector sensitivity are unlikely, the probable focus of attention in the future will again be on sample preparation. Here, the introduction of new approaches, techniques, and materials for sample preparation can be expected to make a significant impact in this field. 

As analytical capabilities improve, multiple procedures are linked together in series to effect analyses. Procedures combined in this manner are called hyphenated techniques. Ferrer and Furlong [124] combined multiple techniques—accelerated solvent extraction (ASE) followed by online SPE coupled to ion trap HPLC/MS/MS—to determine benzalkonium chlorides in sediment samples. Online SPE, especially coupled to HPLC, is being used more routinely. This approach allowed online cleanup of the ASE extract prior to introduction to the analytical column. 

An examination of the publication trends concerning the use of ICP-MS in food-related areas (Fig. 8.6) shows that after less than one decade from its first application in this field, the number of published works increased by a factor of 10. In recent years, about 50-70 papers on food-related topics have appeared annually and nearly half of them concern speciation topics. ICP-MS represents today an essential tool for inorganic and bioinorganic research on foods and its versatility, that is, the ease of coupling with different sample introduction systems, as well as the hyphenation with devices for species separation, is undoubtedly a key point of its success. Moreover, the progress in instrumentation has overcome most of the past limitations of the technique and with the availability of MC-, CC-, and DRC-ICP-MS instruments a growing number of applications in any area of food and nutrition research are expected. 

Introduction to Derivatization For many years derivatization by alkylation -especially as ethylation, but also as propylation - has been applied to transform Hg species into volatile Hg species before measurement with hyphenated techniques [2, 50, 52]. Sodium tetraphenylborate (NaBPh4) was also used for derivatization prior to measurement with GC-MIP-AED [53], Studies of possible species transformation, for example, during the analytical procedure, have been carried out with isotope-specific determination methods. The results showed that a direct ethylation of Me-Hg in an atmospheric precipitation sample by NaBEt4 produced no significant amount of artifactual Me-Hg [54]. Others investigated the species transformation processes in synthetic solutions to simulate environmental matrices. From the experiments it could be concluded that the species conversion, for example, of Me-Hg into zerovalent Hg, depends on the concentration levels of the halide [2]. Furthermore, the procedural order is of great importance, for example, ethylation should be done after addition of the organic phase to avoid species transformation [55]. 

Stationary phases, detection devices, etc. However, advances in instrumentation were not the only important factor in the development of analytical methods for essential oils in plants. Sample extraction and concentration were also improved. The most outstanding improvements in the determination of the composition of essential oils came from the introduction of tandem techniques involving prior/further chromatography or spectroscopy. The great amount of information on the application of GC and hyphenated techniques to essential oils has led to much research in this field, and to the pubhcation of... 

Figure 2.9 Overview of sample introduction methods and hyphenated techniques used in ICP-AES. (A) Pneumatic concentric (sometimes called the Meinhard nebuliser) (B) Babington (C) fritted disc (D) Hildebrand nebuliser (E) cross flow (G) standard ultrasonic nebuliser for aqueous and non-aqueous solvents (H) electro-thermal graphite ( ) electro-thermal carbon cup (K) graphite tip filament (L) laser ablation (M) hydride generation (P) flow injection...

Different manifold geometries have been proposed for implementing in-line SPE in flow analysis, generally involving the placement of a minicolumn before, at or after the sample introduction port. Alternatively, by integrating SPE within the detection unit, moving beads, hyphenated techniques and/or commutation facilities can be exploited, as discussed at the end of this section. 

The book covers several subtopics of miniaturization and mass spectrometry. It combines (i) technological developments in the quest for miniaturization of sample preparation and how to connect micrometer-sized devices to a mass spectrometer, (ii) various illustrations of fields that benefit from such a hyphenated technique and (iii) technological developments for the miniaturization of the mass spectrometer. Additionally, the book is not restricted to one ionization technique as is often the case for many reviews, but it reports on efforts for both the ESI and MALDI ionization techniques. After an introduction to miniaturization and mass spectrometry, the book is divided in three sections that respectively concern (i) ESI-MS applications, (ii) MALDI-MS applications and... 

Conventional packed column injection ports are used for the sample introduction on packed and megabore columns. In case of capillary columns, unless a special injection technique is used, the low maximum allowable sample volume which may be introduced on the column negatively affects the experimental detection limits as only a tiny fraction of the derivatized extract is finally processed in the hyphenated system. Online preconcentration and injection of derivatized organolead species can solve that problem. It consists of three consecutive processes taking place in the injection hner sample injection, solvent venting and release of the analytes on to the column. Up to 25 fil can be processed at a time and larger amounts can be handled by successive injections of 20 to 25 /a1 volumes at 1 min intervals to remove the solvent. 

Mass spectrometer (MS) [S] sales have always been high, especially since MS is the principal detector in a number of hyphenated techniques such as GC-MS, MS-MS, and LC-MS. The GC — MS combination accounts for about 60% of MS sales since it is used widely in drug and environmental testing. Innovations in interface technology such as inductively coupled plasma (ICP)-MS, FC-MS and thermospray or particle beam interfaces for LC-MS have both advanced the technology and expanded the interest in applications. Recent introductions of lower cost MS instruments with automated sampling and computerized data analysis have added to the attraction of the technique for first-time users. 

The first step of the analysis of a sample is its introduction to the MS instrument A pure sample can be introduced directly by dissolving the substance in a small amount of an appropriate solvent and injecting it. It is also possible to introduce solid samples through an inlet. This is not the case when we have a hyphenated technique because usually we have the issue of relatively high flow rates of organic solvent (from the HPLC instrument) and these cannot be introduced to the MS instrument. If it is necessary for the LC method to stay the same (with high flow rates), an interface will have to be employed to reduce the chromatographic mobile phase. 

A current trend is the coupling of another technique with AES, such as liquid chromatography, ion chromatography, or flow injection analysis, to enhance the capability of the plasma, particularly in the field of speciation (the so-called hyphenated techniques). This coupling can be considered as a highly sophisticated sample introduction system. In... 

Each chapter provides a discussion of the fundamental principles underlying the techniques, descriptions of the instrumentation, and numerous applications. The chapters also contain updated bibliographies and problems, and most have suggested experiments appropriate to the techniques. This completely revised and updated edition covers subjects in more detail, such as a completely revised x-ray chapter, expanded coverage of electroanalytical techniques, and expansion of chromatography and mass spectrometry topics to reflect the predominance of these instruments in laboratories. This includes state-of-the-art sample introduction and mass analyzers and the latest developments in UPLC and hyphenated techniques. The book also contains new graphics and addresses several new topics ... 

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