Electrospray-ionization adducts

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

Koenigs LL, Peter RM, Hunter AP, et al. Electrospray ionization mass spectrometric analysis of intact cytochrome P450 identification of tienilic acid adducts to P450 2C9. Biochemistry 1999 38(8) 2312 2319. 

The mechanism of zinc deprivation by 3-nitrosobenzamide was elucidated most recently. When the reconstituted nucleocapsid protein p7 of HIV-1 (15 i-M) was incubated with 3-nitrosobenzamide (300 iM) at pH 7.5, three disulfide bonds per protein molecule were formed while 3-nitrosobenzamide was reduced to the hydroxylamine. Molecular masses of p7 adducts augmented by one or two 3-nitrosobenzamide residues were observed by electrospray ionization MS, consistent with covalent bond formation between cysteine sulfur and the nitroso nitrogen atom127. 

Also, a brief note has appeared concerning electrospray ionization mass spectrometry of mixtures of -carotene with ft- and with y-cyclodexlrin in aqueous methanol solutions. Whereas negative ion ESI produced 1 1 adduct ions of -carotene with both of the cyclodextrin isomers, positive ESI gave these adducts only in the case of ft-cyclodextrin302. 

Cui, M., Song, F., Liu, Z., and Liu, S. (2001). Metal ion adducts in the structural analysis of ginsenosides by electrospray ionization with multi-stage mass spectrometry. Rapid Commun. Mass Spectrom. 15, 586-595. 

Carini, M., Aldini, G., Beretta, G., Arlandini, E., and Facino, R. M. (2003). Acrolein-sequestering ability of endogenous dipeptides Characterization of carnosine and homocarnosine/ acrolein adducts by electrospray ionization tandem mass spectrometry. J. Mass Spectrom. 38,996-1006. 

Some combinations of IC with MS detection are available, including ICP-MS (element-specific detection), particle beam MS and MS with atmospheric pressure ionization (API) operated in either electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) modes that give information on molecular ions or adducts. 

Francolic JD, Lehr GJ, Barry TL, Petzinger G. Isolation of a 2 1 hydrochlorothiazide-formaldehyde adduct impurity in hydrochlorothiazide drug substance by preparative chromatography and characterization by electrospray ionization LC-MS. J Pharm Biomed Anal 2001 26 651-663. 

The electrospray ionization mass spectrometry (ESI-MS) analysis of the incubation between porcine pancreatic elastase (PPE) and the tert-butylammonium salt of clavulanic acid 54 (R1 = R2 = H) at time points of between 3 min and 5h revealed that there were no mass increments relative to PPE. However, when the benzyl derivative 54 (R1 = Bn, R2 = H) was used, a peak was observed at 26187 Da after 3 min, which corresponded to the formation of an initial acyl-enzyme complex. The intensity of the peak decreased significantly and two clear additional peaks at 25 968 and 25 967 Da appeared after 5 min, which corresponded to adducts with mass increments at 77 and 88 Da, respectively. The intensities of both peaks decreased after 60 min and almost disappeared after 5 h. The corresponding />-nitrobenzyl ester 54 (R1 = CH2PhN02, Rz = H) showed similar results except that the formation of adducts appeared slightly faster <2000T5729>. 

Hsu, F.-F., and Turk, 1 1999. Structural Characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument. J. Am. Soc. Mass Spectrom., 10, 587-599. 

Electrospray ionization with the high resolving power of Fourier transform mass spectrometry (FTMS) makes possible the detection of adducts and subpicomole impurities that confuse lower resolution measurements, as shown in Figure 8.30. This method achieves accurate determination of molecular weights (<0.002 %) and permits the verification of 50-100-mer DNA and RNA sequences. [169,170]... 

Elaboration of nerve agent toxicokinetics requires sophisticated analytical tools to detect and, if possible, to quantify the free toxicants as well as adducts with proteins and enzymes. Analysis of OP nerve agents has been performed by capillary electrophoresis (CE), biosensors, matrix-assisted laser desorption/ionization (MALDI) MS, desorption electrospray ionization MS (DESI MS), ion mobility time-of-flight MS (IM-TOF MS), nuclear magnetic resonance spectroscopy (NMR), LC-UV, gas chromatography (GC), and many more techniques (Hooijschuur et al, 2002 John et al, 2008). 

C. Identification of OP-ButyrylchoIinesterase Adducts by Electrospray-Ionization Tandem Mass Spectrometry... 

K. Schug and H. M. McNair, Adduct formation in electrospray ionization. Part 1 Common acidic pharmacenticals,/. Sep. Set. 25 (2002), 760-766. 

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