Mass spectrometry detectors overview

Laser-induced fluorescence (LIF) has also been utilized as a highly sensitive detection principle for CE [48-51]. However, while the LIF detector is now able to achieve zeptomole (10 21) detection limits, conventional derivatization techniques are inefficient at these exceptional levels [52]. Also, CE has successfully been coupled with mass spectrometry (MS) [53], nuclear magnetic resonance (NMR) [54, 55], near-infrared fluorescence (NIRF) [56, 57], radiometric [58], flame photometric [59], absorption imaging [60], and electrochemical (conductivity, amperometric, and potentiometry) [61-63] detectors. A general overview of the main detection methods is shown is Table 1 [64]. 

Mass spectrometry data is often paired with UV-Visible spectra, NMR, or HPLC retention time for carotenoid identification. In addition, HPLC coupled with MS as a detector has been reported to be 100 times more sensitive than PDA for detection and quantification of some carotenoids (van Breemen, 1995 van Breemen et ah, 1996). While mass spectrometry can be a powerful tool, it should be noted that the analysis of carotenoids (which are nonvolatile, thermally labile, and inherently unstable) presents a special challenge to the mass spectrometry analyst. An overview of common MS components and techniques is provided in Chapter 2 (techniques not previously mentioned are briefly described below). 

In the early 90s, a new technique called solid-phase-micro extraction (SPME), was developed (Arthur and Pawliszyn, 1990). The key-part component of the SPME device is a fused silica fiber coated with an adsorbent material such as polydimethylsiloxane (PDMS), polyacrylate (PA) and carbowax (CW), or mixed phases such as polydimethylsiloxane-divinylbenzene (PDMS-DVB), carboxen-polydimethylsiloxane (CAR-PDMS) and carboxen-polydimethyl-siloxane-divinylbenzene (CAR-PDMS-DVB). The sampling can be made either in the headspace (Vas et al., 1998) or in the liquid phase (De la Calle et al., 1996) of the samples. The headspace sampling in wine analyses is mainly useful for quantifying trace compounds with a particular affinity to the fiber phase, not easily measurable with other techniques. Exhaustive overviews on materials used for the extraction-concentration of aroma compounds were published by Ferreira et al. (1996), Eberler (2001), Cabredo-Pinillos et al. (2004) and Nongonierma et al. (2006). Analysis of the volatile compounds is usually performed by gas chromatography (GC) coupled with either a flame ionization (FID) or mass spectrometry (MS) detector. 

Figure 5.4-1. Schematic overview of typical reversed phase-HPLC with precolumn and column loading for peptide separation. The central switching valve has two positions In position one, the sample is loaded onto the precolumn with the loading pump. After trapping and desalting of the sample, the valve is switched and the precolumn is integrated into the flow of the gradient pump. By increasing the amount of solvent B, the single peptides are separated on the separation column and afterward detected with a UV-detector and/or by mass spectrometry.

See also Chromatography Overview Multidimensional Techniques. Gas Chromatography Detectors Mass Spectrometry. Liquid Chromatography Liquid Chromatography-Mass Spectrometry. Thin-Layer Chromatography Overview Principles. 

See also Bloassays Overview. Derivatizatlon of Analytes. Extraction Solvent Extraction Principles. Fluorescence Food Applications. Food and Nutritional Analysis Contaminants. Gas Chromatography Detectors Mass Spectrometry. Immunoassays Production of Antibodies. Immunoassays, Applications Food. Immunoassays, Techniques Enzyme Immunoassays. Liquid Chromatography Instrumentation Liquid Chromatography-Mass Spectrometry Food Applications. Sampling Theory. 

See also Derivatization of Analytes. Gas Chromatography Column Technology High-Temperature Techniques High-Speed Techniques Detectors Environ-mentai Appiications Forensic Appiications Petro-chemicai Appiications. Mass Spectrometry Ionization Methods Overview Mass Separation Selected Ion Monitoring. 

Distillation. Essential Oils. Extraction Solvent Extraction Principles Solid-Phase Extraction Solid-Phase Microextraction. Gas Chromatography Detectors Mass Spectrometry Chiral Separations. Headspace Analysis Static Purge and Trap. Mass Spectrometry Principles Selected Ion Monitoring. Quality Assurance Quality Control. Sensors Overview. 

Chapter 6, titled Selection of Ionization Methods of Analytes in the TLC-MS Techniques provides an overview of mass spectrometric techniques that can be coupled with TLC and act as specific detectors in this hyphenated approach. The mass spectrometric techniques discussed in this chapter are secondary mass spectrometry (SIMS), liquid secondary ion mass spectrometry (LSIMS), fast atom bombardment (FAB), matrix-assisted laser desorption/ionization (MALDI), atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI), electrospray ionization (ESI), desorption electrospray ionization (DESI), electrospry-assisted laser desorption/ionization (ELDI), easy ambient sonic spray ionization (EASI), direct analysis in real time (DART), laser-induced acoustic desorption/electrospray ionization (LIAD/ESI), plasma-assisted multiwavelength laser desorption/ionization (PAMLDI), atmospheric-pressure chemical ionization (APCI), and dielectric barrier discharge ionization (DBDI). For the sake of illustration, the authors introduce practical examples of implementing TLC separations with detection carried out by means of individual mass spectrometric techniques for the systematically arranged compounds belonging to different chemical classes. 

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