Liquid chromatography-mass spectrometry electrospray technique

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

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. 

A variety of MS formats are widely accepted and applied in the pharmaceutical industry. The specific MS application is often defined by the sample introduction technique. The pharmaceutical applications highlighted in this article feature two types of sample introduction techniques dynamic and static. Dynamic sample introduction involves the use of high-performance liquid chromatography (HPLC) on-line with MS. The resulting liquid chromatography/mass spectrometry (LC/MS) format provides unique and enabling capabilities for pharmaceutical analysis. The electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) modes are the most widely used. Static sample introduction techniques primarily use matrix-assisted laser desorption/ionization (MALDI). ... 

It has become painfully obvious that most of the excellent approaches and techniques that have been developed for use in liquid chromatography are not applicable to liquid chromatography/mass spectrometry (LC/MS) with atmospheric pressure ionization. Chapter 5 described the reagents and the range of mobile-phase compositions that are compatible with electrospray and atmospheric pressure chemical ionization (APCI), and these are limited to volatile components that do not cause significant ion suppression. Certain problems that are not significant with standard LC separations become difficult to deal with because of the limitations placed on the mobile phase by atmospheric pressure ionization (API) LC/MS. 

Liquid chromatography-mass spectrometry The initial attempts to couple LC with MS lacked important attributes for trace analysis sensitivity, robustness, and reliable quantitation. Moreover, the cost of the early LC-MS instruments was prohibitive for most laboratories. The revolutionary introduction of atmospheric pressure ionization (API) techniques, mainly electrospray (ESI) and atmospheric pressure chemical ionization (APCI), resulted in greater applicability of LC-MS and manufacture of more reliable, affordable, and user-friendly instruments. Thus, LC-MS is now becoming an indispensable part of the analytical strategy in many routine laboratories, enabling direct, selective, and sensitive multiclass, multiresidue analysis of more polar, low volatile, and/or thermolabile pesticides, such as carbamates, phenylureas, sulfonylureas, imidazoles, triazoles, imidazolinones, chlorophenoxy acids, and many others. 

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... 

See also Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Gas Chromatography Mass Spectrometry. Liquid Chromatography Liquid Chromatography-Mass Spectrometry. Mass Spectrometry Ionization Methods Overview Atmospheric Pressure Ionization Techniques Electrospray Liquid Secondary Ion Mass Spectrometry Matrix-Assisted Laser Desorption/ionization. Surface Analysis Secondary Ion Mass Spectrometry of Polymers Laser Ionization. 

Leinonen, A. Kuuranne, T. Kostiainen, R. Liquid chromatography/mass spectrometry in anabolic steroid analysis—optimization and comparison of three ionization techniques Electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization. J. Mass Spectrom. 2002, 37 (7), 693-698. 

Traditional analytical methods to analyze amphetamines include gas chromatography-mass spectrometry where derivatization is often required to fecilitate analysis. Besides sample preparation issues, it has been demonstrated that injection port chemistry in the GC can lead to misleading results with some members of the amphetamine class. To circumvent these issues, liquid chromatography-mass spectrometry (LC-MS/ MS) offers the promise of a simpler sample preparation procedure and fewer analytical concerns. This chapter describes an LC-MS/MS technique for the analysis of 14 ATSs in blood, serum/plasma, and urine. The method is quantitative and has reporting limits in the low ng/mL range. Electrospray ionization is used in the positive ion mode. Two transitions for each compound are monitored along with ion ratios. 

Hsu, F.-F. and Turk, J. (2005) Electrospray ionization with low-energy coUisionaUy activated dissociation tandem mass spectrometry of complex lipids Structural characterization and mechanism of fragmentation. In Modern Methods for Lipid Analysis by Liquid Chromatography/Mass Spectrometry and Related Techniques (ByrdweU, W.C., ed.). pp. 61-178, AOCS Press, Champaign, IL... 

A wide variety of liquid chromatography-mass spectrometry (LC-MS) techniques have been reported for retinoid analysis including direct liquid introduction with Cl (281,282,299-301), particle beam (302-304), thermospray (305-307), electrospray (308,309), and atmospheric pressure chemical ionization (APCI) (310). Because many of the early LC-MS applications to retinoids carried out hydrolysis of retinyl esters and then derivatization of retinoic acid and related retinoids, Wyss (141) predicted in a review of retinoid analysis that derivatization of retinoids would be necessary for all LC-MS techniques, even the anticipated application of atmospheric pressure chemical ionization (APCI). Recently, LC-MS analyses of retinoids have been carried out using APCI (310) and electrospray (308,309), and highly sensitive LC-MS analyses of retinoic acid and retinyl esters were achieved without hydrolysis or derivatization. 

Interfacing mass spectrometry with other analytical techniques (Section F) necessitates the use of specially designed interfaces and ionizing sources. These include thermospray, electrospray and ionspray for liquid chromatography-mass spectrometry (LC-MS), and an inductively coupled plasma torch (ICP) for ICP-MS (Topic E5). For gas chromatography-mass spectrometry (GC-MS), the carrier gas flows directly into the spectrometer where El ionization can then be used. 

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