Detection techniques mass separation

A comparison of laser ionization mass spectrometry (LI-MS) and LA-ICP-MS for the characterization of compact ceramics [123,124] provided limits of detection that were much lower (in the nanogram-per-gram range) with the former technique than with the latter. However, Ll-MS is a time-consuming analytical technique with photoplate detection of mass-separated ions compared to LA-ICP-MS, which uses fast electrical ion registration. 

A further extension of the DFG S19 method was achieved when polar analytes and those unsuitable for GC were determined by LC/MS or more preferably by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Triple-quadrupole MS/MS and ion trap MS" have become more affordable and acceptable in the recent past. These techniques provide multiple analyte methods by employing modes such as time segments, scan events or multiple injections. By improving the selectivity and sensitivity of detection after HPLC separation, the DFG S19 extraction and cleanup scheme can be applied to polar or high molecular weight analytes, and cleanup steps such as Si02 fractionation or even GPC become unnecessary. 

A survey of the literature with a key phrase tissue residue analysis yielded a distribution of separation and detection techniques as outlined in Table 2. LC with either UV or fluorescence detection was the most common separation and detection technique, representing 61% of the citations. The results are an indication of the maturity of LC as a common, well-understood technique. The second most commonly used technique cited in the literature (13%) was GC with either a mass-selective or electron capture detector. GC is also a mature technology and a good choice owing to the... 

Either gas chromatography (GC) or liquid chromatography (LC) can be used as a separation technique coupled with a variety of detection methods. Mass spectrometry (MS) is one of the most popular means of detection. When using GC-MS, a capillary column should be used, while any suitable LC column can be used for LC-MS. It is advisable to obtain a print-out of the chromatogram so that the shapes of individual peaks can be assessed. Electronically produced data using integrators should be treated with some suspicion and always examined visually to check the selected baseline, start- and end-points of peak integration, etc. 

HPLC is a universal separation technique that is capable of separating both volatiles and non-volatiles without the need for derivatization. We are developing methods that employ both on-line photodiode array (PDA) detection and mass selective detection, HPLC/PDA/MS. This approach also utilizes an ion-trap mass... 

Whilst these methods are informative for the characterisation of synthetic mixtures, the information gained and the nature of these techniques precludes their use in routine quantitative analysis of environmental samples, which requires methods amenable to the direct introduction of aqueous samples and in particular selective and sensitive detection. Conventionally, online separation techniques coupled to mass spectrometric detection are used for this, namely gas (GC) and liquid chromatography (LC). As a technique for agrochemical and environmental analyses, high performance liquid chromatography (HPLC) coupled to atmospheric pressure ionisation-mass spectrometry (API-MS) is extremely attractive, with the ability to analyse relatively polar compounds and provide detection to very low levels. 

CEC is a miniaturized separation technique that combines capabilities of both interactive chromatography and CE. In Chapter 17, the theory of CEC and the factors affecting separation, such as the stationary phase and mobile phase, are discussed. The chapter focuses on the preparation of various types of columns used in CEC and describes the progress made in the development of open-tubular, particle-packed, and monolithic columns. The detection techniques in CEC, such as traditional UV detection and improvements made by coupling with more sensitive detectors like mass spectrometry (MS), are also described. Furthermore, some of the applications of CEC in the analysis of pharmaceuticals and biotechnology products are provided. 

A major consequence of using regulatory limits based on degradant formation, rather than absolute change of the API level in the drug product, is that it necessitates the application and routine use of very sensitive analytical techniques [ 10]. In addition, the need to resolve both structurally similar, as well as structurally diverse degradants of the API, mandates the use of analytical separation techniques, for example, HPLC, CE, often coupled with highly sensitive detection modes, for example, ultraviolet (UV) spectroscopy, fluorescence (F) spectroscopy, electrochemical detection (EC), mass spectroscopy (MS), tandem mass spectroscopy (MS-MS) and so forth. 

One of the most topical ways of approaching this type of system, where separation and detection take place sequentially in space and time, to current trends in Science and Technology (e.g. automation and miniaturization) involves integrating both steps. Integrated systems of this type meet the requirements of chemical sensors [7,8] and differ clearly from conventional flow systems, where detection and mass transfer take place at different locations in the continuous configuration. In fact, the characteristic mass transfer of separation techniques takes place simultaneously with detection... 

Mass spectrometry (MS) has changed its appearance in the scientific world considerably during recent years. At the beginning of the 20 century first applications in physics were described. Gradually MS methods entered more and more into the fields of biology, biochemistry and biomedicine and became a major tool in life sciences. Mass spectrometers consist of a sequence of functional units for sample introduction, ion formation, mass separation, and detection. The data handling is carried out by computers. Currently, a variety of different mass spectrometric techniques are used for the analysis of biomolecules (Fig. 6). 

Although a great variety of analytical techniques have been applied to the simultaneous determination of methylxanthines in various matrices, HPLC is the one most frequently used nowadays. Most of the methods are based on reversed-phase HPLC, using ACN, MeOH, or THF in acetate or phosphate buffer as mobile phase and UV spectrophotometric detection (256 -270). Some RP-HPLC methods were proposed in combination with solid-surface room-temperature phosphori-metric detection (271), mass spectrometry (272), or amperometric (273) detection. The separation can also be achieved by RP ion-pair or ion-interaction HPLC (274-277) or micellar HPLC (278). In contrast, in recent years few normal-phase HPLC methods (279) were reported (see Table 5). 

---