Mass positive ionization

Electrospray is the softest mass spectrometry ionization technique and electrospray spectra therefore usually consist solely of molecular ions. Electrospray is unique, however, in that if the analyte contains more than one site at which protonation (in the positive-ion mode) or deprotonation (in the negative-ion mode) may occur, a number of molecular ions with a range of charge states is usually observed. For low-molecular-weight materials (< 1000 Da), the number of sites... 

As with GC/MS, LC/MS offers the possibility of unequivocal confirmation of analyte identity and accurate quantiation. Similarly, both quadrupole and ion-trap instruments are commercially available. However, the responses of different analytes are extremely dependent on the type of interface used to remove the mobile phase and to introduce the target analytes into the mass spectrometer. For pesticide residue analyses, the most popular interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Both negative and positive ionization can be used as applicable to produce characteristically abundant ions. 

A Waters Micromass triple quadrupole mass spectrometer was used with an electrospray ionization interface in positive ionization mode desolvation gas (400), cone gas (70), collision gas (2.74 x 10 3 mbar), capillary (3.0 kV), cone (14 (kV), source temperature (105°C), and desolvation temperature (300°C). The detection and quantitation of amlodipine and nimodipine were performed... 

Protonated and cationized species are the most commonly detected ions using the ES process if a positive ionization mode is selected. Protonation is a result of the addition of proton(s) to a neutral molecule for every proton added, a net charge of +1 will result. Similarly, canonization is due to the addition of cation(s) to a neutral molecule. Detection of cationized ions can be useful in the determination of molecular mass of unknown analytes.If ESI is operated under negative ion mode, deprotonated ions will usually be the most dominant ions. Eor either operation mode, solvent adducts of the protonated/deprotonated ions are frequently detected in ESI/MS mass spectra. 

Fig. 2.6 Titration assay of BSA and methyl orange (MO, MW 305 Da, Kj = 450 pM) by GPC spin column/ESI-MS methodology as a function of [MO]/[BSA] molar ratios in the positive ionization mode (A) and the negative ionization mode (B). The mass spectra in the top five panels are exploded...

Fig. 2.7 ESI mass spectra of ligands present in CPC spin column eluates have a linear response with increasing concentration ESI (positive ionization mode) mass spectral analysis of the eluate from the CPC spin column titration ofWY252 (MW 457 Da) with MM P-1 where the molar ratios of MM P-1/ WY252 are constant at 1 5 while their individual concentrations linearly increase. The volume injected for each sample was...

There are approximately 2700 compounds per primary screening mixture, and the readout is in essence multiplexed the ligands are individually ionized and identified in the mass spectrometer according to their exact mass positions. The readout, however, does not unambiguously identify compounds, as multiple compounds in a single mixture may have the same mass, i.e., a particular peak may correspond to as many as 31 compounds with closely related masses. The protein excess over individual compounds coupled with the rarity of potent ligands within a randomly assembled library minimizes competition between ligands for... 

Although negative-ion mass spectra are easily obtained in most mass spectrometers by relatively simple reversal of magnetic and electric field polarities, frequent absence of molecular ions and low negative-ion intensities [about 10 that of positive ionization (244)] have meant, until recently, few negative-ion studies. 

A Finnigan MAT TSQ mass spectrometer was used to record the mass spectra of brinzolamide. The conditions were 0.3 mA current, 1100-volt acceleration voltage and 10 preamp sensitivity. The ionization voltage was 70 eV for El (electron impact) ionization mode. For Cl (chemical ionization) mode, a positive ionization voltage of 100 eV and a pressure of 0.3 torr of methane were used. The El and Cl spectra are shown in Figures 12 and 13, respectively. Peak assignments for the El and Cl spectra are listed in Table 6. Both the Cl and El spectra have an MH peak at m/z = 384. 

To establish a sensitive and specific liquid chromatography-mass spectrometry (time-of-flight) [LC-MS (TOF)] method for the determination of donepezil in human plasma after an oral administration of 5 mg donepezil hydrochloride tablet [29]. Alkalized plasma was extracted with isopropa-nol-n-hexane (3 97) and loratadine was used as internal standard (IS). Solutes were separated on a Cis column with a mobile phase of metha-nokacetate buffer (pH 4.0) (80 20). Detection was performed on a TOF mass spectrometry equipped with an electrospray ionization interface and operated in positive-ionization mode. Donepezil quantitation was realized by computing the peak area ratio (donepezil-loratadine) (donepezil m/z 380 [M + H]+ and loratadine m/z 383[M + H]+) and comparing them with calibration curve (r = 0.9998). The linear calibration curve was obtained in the concentration range of 0.1-15 jUg/1. The detection limit of donepezil was 0.1 /zg/1. The average recovery was more than 90%. The intra- and inter-run precision was measured to be below 15% of RSD... 

Hultman et al. [130] developed a LC/MS/MS method for the quantitative determination of esomeprazole and its two main metabolites 5-hydro-xyesomeprazole and omeprazole sulfone in 25 /il human, rat, or dog plasma. The analytes and their internal standards were extracted from plasma into methyl ferf-butyl ether-dichloromethane (3 2). After evaporation and reconstitution of the organic extract, the analytes were separated on a reversed-phase liquid chromatography column and measured by atmospheric-pressure positive ionization mass spectrometry. 

The mass spectrum of pantoprazole sodium is shown in Figure 9, and the mass fragments with their assignments are shown in Table 5. The molecular weight of pantoprazole sodium was determined by using a Finnigan AQA LC/MS system (Thermoquest) operating in positive ionization mode (probe 4.00 kV, cone 200 V). 

For the detection, a tandem mass spectrometer Quattro Micro API ESCI (Waters Corp., Milford, MA) with a triple quadrupole was employed. The instrument was operated in electrospray in the positive ionization mode (ESI+) with the following optimized parameters capillary voltage, 0.5 kV source block temperature, 130 °C nebulization and desolvation gas (nitrogen) heated at 400 °C and delivered at 800 L/h, and as cone gas at 50 L/h collision cell pressure, 3 x 1(F6 bar (argon). Data was recorded in the multiple reaction monitoring (MRM) mode by selection of the two most intense precursor-to-product ion transitions for each analyte, except for the ISs, for which only one transition was monitored. The most intense transition for each analyte was used for quantitative purposes. Table 2 shows MRM transitions, cone voltages and collision energies used for the analysis of the antidepressants included in the LC-MS/MS method. 

The FAB, TSP, APCI and ESI mass spectra in the positive ionization mode display the protonated molecular ion, generally accompanied by other adducts of the molecular species and fragments resulting from the loss of one or several water molecules originating from the ring hydroxyl groups. [300-302] As an acidic function is always present in these compounds, they also yield intense ions in the negative ion mode. [303-305] The spectra... 

PDE5 inhibitor (Fig. 8.17). The anal)d e and internal standard (sildenafil, II) were extracted by liquid-liquid extraction with diethyl ether/dichlor-omethane (70 /30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on reverse phase Xterra MS C18 column with a mobile phase of 10 mM ammonium formate/acetonitrile (10/90, v/v, pH adjusted to 3.0 with formic acid). The protonate of analyte was quantitated in positive ionization by MRM with a mass spectrometer. The mass transitions m/z 390.4 > 268.0 and m/z 475.5 > 58.3 were used to measure I and II, respectively. The assay... 

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