Electrospray interface metabolites

For HPLC/MS/MS analysis, a triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and speciflcity in the quantitative determination of oxime carbamates and their metabolites. This allows... 

The observation of multiple charging of proteins in electrospray ionization attracted much attention all major instrument manufacturers introduced an API system to be used in combination with an electrospray interface. At the same time, it was found that electrospray ionization is not only suitable for the mass analysis of large molecules, but is also a very efficient ionization technique of small polar or ionic molecules, e.g. drugs and their metabolites. In the past few years, hundreds of dedicated API-MS systems equipped with electrospray and APCI interfaces have found their way into many different laboratories, especially within pharmaceutical companies and biochemistry/biotechnology laboratories. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Currently, LC-MS is widely used for the analysis of polar compounds, such as medicinal metabolites and bioactive peptides, since the interface has been improved and several new ionization methods have been developed. The sensitivity and reproducibility are sufficient for a daily quantitative analysis. The usefulness of the LC-MS has been demonstrated for studies on Type II pheromones using a time-of-flight MS with electrospray ionization (ESI) [180]. Each epoxydiene derived from the (Z3,Z6,Z9)-triene shows three ion series of [M+NHJ+, [M+H]+, and [M-OH]+ with high resolution and good sensitivity, indicating its molecular formula. In addition to these, characteristic fragment... 

In off-line coupling of LC and MS for the analysis of surfactants in water samples, the suitability of desorption techniques such as Fast Atom Bombardment (FAB) and Desorption Chemical Ionisation was well established early on. In rapid succession, new interfaces like Atmospheric Pressure Chemical Ionisation (APCI) and Electrospray Ionisation (ESI) were applied successfully to solve a large number of analytical problems with these substance classes. In order to perform structure analysis on the metabolites and to improve sensitivity for the detection of the various surfactants and their metabolites in the environment, the use of various MS-MS techniques has also proven very useful, if not necessary, and in some cases even high-resolution MS is required. 

Detection of imatinib is performed by triple quadrupole mass spectrometer with an electrospray ionization (ESI) interface operated in positive ion mode [103, 104, 106,107,109,110]. Except the methods published by Parise et al. for imatinib and its main metabolite [108], and for nilotinib [111], where a single quadrupole mass spectrometer was used, most TKIs are analyzed in plasma by atmospheric pressure ionization (electrospray or turbo ion spray) coupled to triple stage mass spectrometer. Expectedly, higher limit of quantifications for imatinib (30 ng/ml) [108], and nilotinib (5 ng/ml) [111], are obtained for the assays using single quadrupole MS (see Table 2). 

Simultaneous determination of LAS and their main metabolites SPC was enabled by LC-MS with an electrospray ionization (ESI) interface. Problems with high salt loads of the mobile phase due to the ion pair reagent have been overcome by incorporation of a suppressor between the LC column and the mass spectrometer. A LC-MS method for the determination of AES and AS was introduced by Popenoe et al. After separation on a C8 column the analytes are determined by ion spray LC-MS. The mass chromatograms obtained give information about both the distribution of the alkyl homologues and distribution of the oligomeric ethoxylates as well. 

The most recent significant advance in plant hormone analysis has been the use of combined HPLC-MS for the analysis of GA conjugates, lAA conjugates and cytokinins. A number of interfaces have been developed for HPLC-MS, including thermospray, atmospheric pressure chemical ionisation, electrospray, particle beam, continuous flow fast atom bombardment (FAB) and frit-FAB (see reference [94]). GA standards have been analysed by HPLC-MS with a thermospray interface [95], an atmospheric pressure chemical ionisation interface has been used with GA conjugates [96] and cytokinins [97] while ion spray and plasma spray have been used to analyse ABA and its metabolites [98]. There are, however, many more reports on the use of frit-FAB HPLC-MS for the analysis of not only standards, but also endogenous hormones and their isotopically-labelled metabolites [18-23,99-101]. 

The advent of API MS has revolutionized the analysis of drugs and metabolites in biological samples. The API source provides an ideal interface to link HPLC to MS utilizing two ionization methods electrospray ionization (ESI), which ionizes the molecules in the mobile phase, before the ions arrive in the gas phase, and atmospheric pressure chemical ionization (APCI), which ionizes the molecules after they are already in the gas phase. In APCI mode, both solvent and solutes are rapidly evaporated by heat. After evaporation of neutral species, ions are formed in a gas phase at atmospheric pressure. All species in the gas phase undergo... 

Nowadays, interfacing separation methods such as high-performance hquid chromatography (HPLC) or CE [54] to MS is already a routine technique. MS methods based on so-called soft ionization techniques, which include fast atom bombardment, laser desorption and electrospray ionization (ESI), have allowed the analysis of biological macromolecules that in the past could have been analyzed only by extensive cleavage and derivatization. Of these methods, the two most preferred for biomolecules are ESI [55] and matrix-assisted laser desorption/ionization(MALDI) [56,57], for which time-of-flight (TOE) and ion trap mass analyzers are the most frequentiy used mass analysis methods. However, these methods are equally suitable for small molecules, such as metabolites or the products of organochemical reactions. 

The total taxane (TTAX) concentration, a sum of the concentrations for CT-2103, TXL, and TXL-metabohtes was determined from scintillation counting of the plasma or tissue sample homogenates. Extractable taxanes, including TXL and organically extractable TXL metabolites, were determined by scintillation counting of ethyl acetate extractions of the plasma, tumour, liver, and spleen samples. Plasma and tissue TXL concentrations were also determined by HPLC/radiometric analysis of the extracts. Metabolites were identified by HPLC followed by mass spectrometry on a Quattro It (Micromass, Manchester, UK) triple quadrupole mass spectrometer fitted with an electrospray orthogonal Z spray ion interface operating in the positive ion mode. ... 

The introduction of liquid samples into the mass spectrometer has proved especially difficult. However, the advent of electrospray ionisation (ESI) and atmospheric pressure chemical ionisation (APCI) have overcome this problem and revolutionized the interfacing of HPLC with mass spectrometry. This success has pointed the way toward a major change in the mass spectrometric analysis of vitamin D, its analogs, and their metabolites. A disadvantage at the present time is that ionization using ESI and APCI is less efficient than the EI(+) used in GC-MS, but the immediate advantage is that it obviates the need for derivatiza-tion. 

Mass spectrometers with single or triple quadrupole are most commonly used in the determination of polyphenolic compounds where electrospray ionization (ESI) is used as an interface. UHPLC-MS and UHPLC-MS/MS, which work in a selected ion mode (SIM) and multiple reaction monitoring mode (MRM), respectively, offer high sensitivity, selectivity, and high throughput for the determination of polyphenols and their metabolites in biological fluids. 

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