Acetate ions, introduction into

Absorption, HSC>3, 180 Accommodation coefficients calculations, 111 measurements, 104-105 ozone, 109-116 sulfur dioxide, 109-116,154 Accuracy, estimation for an instrument, 188 Acetate ions, introduction into precipitation, 219-227 Acetic acid... 

Introduction of Formate and Acetate Ions into Precipitation Assessment of Possible Pathways... 

Most of the research performed in this field is based on tryptic peptides. As discussed earlier, such peptides contain basic amino acid residues on their C-terminus, which causes formation of the high intensity C-terminal ion series, mostly y-ions. In such peptides the N-terminal ions have lower intensity and do not provide important sequence information. Introduction of a highly basic group, such as dimethylalkyl-ammonium acetyl (DMAA) or tra(2,4,6-trimcthoxyphcnyl)phosphonium acetate into... 

Calibrants are required to calibrate the mass scale of any mass spectrometer, and it is important to find reference compounds that are compatible with a particular ion source. Calibrants commonly used in electron ionization (El) and chemical ionization (Cl), such as perfluorocarbons, are not applicable in the ESI mode. The right calibrants for LC-ESI-MS should (1) not give memory effects (2) not cause source contamination through the introduction of nonvolatile material (3) be applicable in both positive- and negative-ion mode. The main calibrants used or still in use to calibrate ESI-MS can be divided into the following categories polymers, perfluoroalkyl triazines, proteins, alkali metal salt clusters, polyethers, water clusters, and acetate salts. 

The chemistry outlined in Scheme 24 was then put into effect catalytic hydrogenation of the tris-isoxazole (302) and recyclization with triethylamine gave a tricyclic ligand which was chelated with nickel ions to give (303). Introduction of the fourth nitrogen atom was accomplished by treatment of (303) with ammonium acetate, giving (304). Treatment with cyanide removed the nickel ion which was then replaced with zinc(II) to give (305). The reasons for this transmetallation step were two-fold firstly, zinc(II) corrins, as shown by Eschenmoser, can be readily demetallated, and this fact opens up many options later in the synthesis, but secondly, and more importantly, Eschenmoser s photochemical cyclization of seco-corrins (see Section 3.07.3.4.2.3) does not proceed with nickel complexes of seco-corrins, whereas zinc(II) seco-corrins can be cyclized in almost quantitative yield... 

In order to craft the lactone ring, 38 was oxidized to 40 under Swem conditions in a prelude to intramolecular 1,4-addition of the hemiacetal anion [20] formed via nucleophilic attack by methoxide ion at the aldehyde site. With the availability of acetal 41, it became necessary to consider carefully whether to elaborate the epoxy lactone segment in advance of, or subsequent to, introduction of the a,p-unsaturated ester subunit. Since the latter option was considered more workable, 41 was transformed into the enol triflate and subjected to palladium(II) catalyzed methoxycarbonylation [21]. This methodology allowed for proper homologation of 42 to 43, and subsequent conversion to 44, in totally regiocontrolled fashion. 

Inorganic and organic ions can also be introduced into an IMS through the electrospray process, opening up the possibility for the rapid separation of anions and cations in the gas phase rather than the slow processes that are involved using ion chromatography or capillary electrophoresis. In an early application, the anions chloride, nitrite, formate, nitrate, and acetate were all separated by IMS after ESI introduction. 

The column effluent from the LC is nebulized into the atmospheric-pressure ion source region. Typical solvents used are mixtures of water and methanol or acetonitrile, containing up to lOmmoll electrolyte, such as formic acid or ammonium acetate. Nebulization can be performed either by means of a strong electrical field, or by a combination of the strong electric field and pneumatic nebulization. The latter is sometimes named pneumatically assisted electrospray or ionspray . The pure electrospray process is limited to flow rates up to 10 pi min Pneumatically assisted electrospray enables the introduction of higher flow rates, up to Imlmin. Since ion production mechanisms between the two modes are identical, the term electrospray is used here throughout. 

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