Liquid chromatography-mass common technique

Other combinations are available. For example, liquid chromatographs connected to mass spectrometers (known as liquid chromatography-mass spectrometry [LC-MS]) are fairly common. Almost any combination of two instruments that can be thought of has been built. In addition, two of the same instruments can be connected so that the output from one is fed directly into the other for further separation and analysis. Examples include two mass spectrometers in an MS-MS arrangement and two different gas chromatography columns connected in a series, known as GC-GC. To keep up with these advances, one needs to have a working knowledge of the fundamental principles involved in the techniques and of the abbreviations used for the various instrumentation methods. 

They are still the workhorses of coupled mass spectrometric applications, as they are relatively simple to run and service, relatively inexpensive (for a mass spectrometer), and provide unit mass resolution and scanning speeds up to approximately 10,000 amu/s. This even allows for simultaneous scan/ selected ion monitoring (SIM) operation, in which one part of the data acquisition time is used to scan an entire spectrum, whereas the other part is used to record the intensities of selected ions, thus providing both qualitative information and sensitive quantitation. They are thus suitable for many GC-MS and liquid chromatography-mass spectrometry (LC-MS) applications. In contrast to GC-MS with electron impact (El) ionization, however, LC-MS provides only limited structural information as a consequence of the soft ionization techniques commonly used with LC-MS instruments [electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)]. Because of this limitation, other types of mass spectrometers are increasingly gaining in importance for LC-MS. 

As part of the specific transfer, the number of lots, replicates, and injections (in the case of HPLC) should be expressly presented. For dissolution transfers, the number of individual dosage forms that will be tested should be stipulated. It is necessary to spell out such details so that small differences in the everyday analytical philosophies do not perturb the transfer process. In the case of new techniques that may not be common to the receiving laboratory (i.e., capillary electrophoresis or liquid chromatography/mass spectroscopy), specific training may be necessary before the execution of a transfer protocol. 

Gas and liquid chromatography, mass spectrometry, and UV and IR spectrophotometry are among the common instrumental techniques applied to analyze aromatic hydrocarbons. Benzene and alkylbenzenes pollutants in water, soils, and solid wastes may be analyzed by various GC or GC/MS methods as specified by the EPA (1984, Methods 602 and 624 1986, Methods 8020, 8024). In general, any mononuclear aromatic in any matrix may be analyzed in a similar way. Analysis of these substances in air may be performed by NIOSH Methods involving adsorption over coconut charcoal, desorption with carbon disulfide, and analysis by GC-FID. 

The most commonly used analytical technique for sugars is HPLC with a refractive index detector (RID). Although the HPLC-RID method is simple, the RID lacks sensitivity and selectivity. Therefore, UV and fluorescence detection is frequently used, coupled with pre- or postcolumn derivatization, for analysis with higher sensitivity. Liquid chromatography-mass spectrometry (LC-MS) using electrospray ionization also requires pre- or postcolumn derivatization. LC-MS using atmospheric pressure chemical ionization does... 

Traditionally, products and adsorbates had to be volatile enough so that they could be carried from the cell into the mass spectrometer, either by headspace sampling, or, more commonly for near-simultaneous analysis (referred to as differential electrochemical mass spectrometry), across a nanoporous, gas-permeable membrane (e.g., Teflon) supported at the tip of a microcapillary placed close to the electrode. Alternatively, a Pt-coated membrane electrode can be used. But the advent of the so-called soft atmospheric pressure desorption/ionization techniques associated with liquid chromatography-mass spectrometry has allowed the sampling of the solvent and involatile solutes directly. The spectra are more... 

High-performance liquid chromatography-mass spectrometry (HPLC-MS) is a powerful analytical technique widely used in recent years for the analysis of biomarkers and metabolites. Biomarker determination and quantification, whether metabolic or adducted biomolecules, are commonly used to evaluate exposure and support biomonitoring research, especially in the area of occupational exposure and health. Some of the common problems and strategies of HPLC-MS biomarker analysis involve matrix effects, the use of isotope-labeled internal standard compounds, and sample cleanup usually all of these factors must be evaluated within the development phase of an analysis procedure. Specific examples of biomarker analysis using HPLC-MS include acrylamide, aromatic compounds, and 1-bromopropane, and these examples are discussed in detail. 

The identification of the individual molecular constituents isolated from meteorites using solvent extraction, chemical degradation, or pyrolytic techniques, which may also include isolation and derivatization, commonly culminates in analysis by GC-MS and/or liquid chromatography-mass spectrometry (LC-MS). However, with the high isomeric diversity present in meteoritic organic material, it is not often possible to unambiguously resolve individual components. 

Natural products and natural-like compounds, generally coming from microbes, plants, sponges and animals [2, 3] may be fully identified and quantified by means of modem and advanced analytical techniques, such as high-performance liquid chromatography (HPLC) coupled to various detectors - from the most common UV/Vis to mass spectrometry and tandem mass spectrometry (HPLC-MS and HPLC-MS/MS). The role of MS is to provide quantitative and qualitative information about mixtures separated by liquid chromatography [4],... 

Mass spectrometry (MS) is probably a famhiar tool to chemistry and biology students as a technique commonly used to measure the molecular mass of a sample. Often, MS is used in tandem with other techniques for chromatic separation of the sample before mass measurement. Some common hyphenated techniques include HPLC-MS, high-pressure liquid chromatography coupled to MS GC-MS, gas chromatography coupled to MS or CE-MS, capillary electrophoresis coupled to MS. 

Reverse-phase columns with a gradient elution in combination with UV-Vis spectrophotometers using photodiode-array (PDA) (Fig. 1.6) and spectrofiuorimeters are common devices employed in this technique. In a lesser extent, MS, tandem mass spectrometry (MS-MS), and nano liquid chromatography-electrospray ionization-quadrupole time-of-flight tandem mass spectrometry (nanoLC-nanoESI-Q-qTOF-MS-MS) has been used as detection system. This instrumentation has been mainly used in the analysis of dyes and proteinaceous media, and in some extent, in the analysis of drying oils and terpenoid varnishes [47,48],... 

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