MS ionization modes

Electrospray ionization (ESI), a very powerful MS ionization mode, has been coupled with liquid chromatography becoming a popular tool in biomolecular analysis and drug analysis applications [1], Use of HPLC or ultra performance liquid chromatography (UPLC) combined with a mass spectrometry through the interface—ESI has become a powerful and routinely used analytical tool for many fields in scientific research, pharma industry, healthcare, and clinical diagnostic applications. 

Table 7.1 Suitability of LC-MS ionization mode for various classes of pesticides [9] ...

Advances in both EC separations and MS ionization modes have also in-... 

FIGURE 10.8 Raw urine chromatograms using a C18 column, step gradient, and negative (a) and positive (b) MS ionization modes. (Reprinted from Waybright, T.J. et al., J. Liquid Chromatogr. Related Technol., 29, 2475, 2006. With permission.)... 

Mass Spectrometry. As of 1996, ms characteristics of pyrazoles and derivatives had not been described in depth. The fate of unsubstituted pyrazole (23) in the mass spectrometer operated in the electron ionization mode may be depicted as follows ... 

A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

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,... 

Instrument Acquisition mode Ionization mode MS quadrupole MS source MSD transfer line heater Ion masses... 

Inherent MS information content (ionization mode dependent). 

Step 5. Automated pyrolysis MS using a novel, highly reproducible ionization mode and a TOF mass analyzer. 

FIGURE 7.11 Multimode assay based on UPLC/MS/MS system. A four-compound mixture was assayed in one injection. The mass spectrometer switched among the four ionization modes quickly. The ionization modes for the analytes are shown. (Source Adapted from Yu, K. et al., Rapid Commun. Mass Spectrom., 2007, 21, 893. With permission of John Wiley Sons.)... 

Compounds were optimized in positive ionization mode and in negative mode if necessary. Automaton can also perform automatic MS method development from solutions containing multiple compounds to increase throughput. When mixture solutions are used, Automaton injects a mixture once to determine all precursor ions and DP values and then injects once per compound to determine product ion and CE value. This approach allows automatic and unattended optimization of MS parameters for hundreds of compounds. The optimized parameters are stored in a compound database that permits fast and efficient retrieval of information about a specific compound and allows a compound to be used in multiple assays, eliminating the need to re-optimize the LC/MS/MS conditions. 

R.B. Desai, M.S. Schwartz and B.K. Matuszewski, The identification of three human metabolites of a peptide-doxorubicin conjugate using HLPC-MS-MS in positive and negative ionization modes. J. Chromatogr. Sci. 42 (2004) 317-322. 

Interference occurs when compounds co-elute with the analytes and are not detected directly by a specific detector. The effect is to create negative peaks or an erratic response for the analyte. This problem can be identified by using a non-specific detector such as an ion trap MS detector, an MS in the electron impact ionization mode, or a flame ionization GC detector. 

HPLC-mass spectrometry (MS). MS conditions ionization mode, atmospheric pressure ionization-electrospray (API-ES) polarity, positive Vcap, 4000 V nebulizer pressure, 35 psig drying gas, 10 L min gas temperature, 350 °C fragmentor, 70 V scan range, 120-600 atm. 

Note MS analysis was carried out in negative ionization mode due to the moderate acidity of glucuroconjugates. The mobile phase ionic strength was adjusted to 5 mM ammonium acetate at pH 5.0 in order to facilitate in-liquid ionization under established... 

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. 

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