Ionspray

The HPLC system used consisted of a 30 x 2 mm Luna CN column with linear gradient elution employing two mobile phases A and B (A, 90% H2O 10% acetonitrile B, 10% H2O 90% acetonittile) with both phases containing 5 mM ammonium acetate and 0.2% formic acid. The hnear gradient commenced with 50 50 A B increasing to 100% B after 1 min of the analysis this composition was maintained for 1 min before returning to 50 50 A B after 4 min. Positive-ion ionspray (pneumatically assisted electrospray) was used to obtain mass spectra, with the spectrometer operating at a resolution of 5000. 

ES ionisation can be pneumatically assisted by a nebulising gas a variant called ionspray (IS) [129]. ESI is conducted at near ambient temperature too high a temperature will cause the solvent to start evaporating before it reaches the tip of the capillary, causing decomposition of the analyte during ionisation and too low a temperature will allow excess solvent to accumulate in the sources. Table 6.20 indicates the electrospray ionisation efficiency for various solvents. 

The ionspray (ISP, or pneumatically assisted electrospray) LC-MS interface offers all the benefits of electrospray ionisation with the additional advantages of accommodating a wide liquid flow range (up to 1 rnl.rnin ) and improved ion current stability [536]. In most LC-MS applications, one aims at introducing the highest possible flow-rate to the interface. While early ESI interfaces show best performance at 5-l() iLrnin, ion-spray interfaces are optimised for flow-rates between 50 and 200 xLmin 1. A gradient capillary HPLC system (320 xm i.d., 3-5 xLmin 1) is ideally suited for direct coupling to an electrospray mass spectrometer [537]. In sample-limited cases, nano-ISP interfaces are applied which can efficiently be operated at sub-p,Lmin 1 flow-rates [538,539]. These flow-rates are directly compatible with micro- and capillary HPLC systems, and with other separation techniques (CE, CEC). 

Determination of trace levels of tributyltin residues in sediments can be accomplished by solvent extraction, dilution and FIA (flow injection analysis) into the ionspray of a tandem mass spectrometer, using the 179/291 m/z pair LOD 0.2 p-g Sn/g103. 

The multiple reaction monitoring (MRM) conditions for each analyte were optimized by infusing 0.1 jxglmL of analyte in mobile phase. The Ionspray needle was maintained at 4.0 kV and the turbo gas temperature was 650°C. Nebulizing gas, auxiliary gas, curtain gas, and collision gas flows were set at 35, 35,40, and 4, respectively. In the MRM mode, collision energies of 17,16, and 15 eV... 

MS condition — An API 4000 equipped with a Turbo Ionspray from Applied Biosystems was used as the mass detector and [M + NH4]+ was chosen as the precursor ion for multiple reaction monitoring (MRM) due to the lack of protonated molecular ions. A transition of m/z 434.4 — 273.2 was chosen for paricalcitol and m/z 450.5 —> 379.2 was selected for the structure analog internal standard. 

MS condition — An API 3000 equipped with a Turbo Ionspray from Applied Biosystems was used as the mass detector. [M - II was chosen as the precursor ion for multiple reaction monitoring... 

The first reported case of timesharing for a mass spectrometer9 involved the design of an Ionspray interface with multiple sprayers to support the analysis of effluents from multiple columns. This approach led to the development of a multiplexed electrospray interface (MUX)10 using an LC/MS interface and multiple (identical) sprayers linked to a HPLC system and a spinning screen to allow the output of only a single sprayer to enter the MS (Figure 4.5). The injections of the HPLC systems... 

Zell M., Husser C., and Hopfgartner G., 1997b. Column-switching high-performance liquid chromatography combined with ionspray tandem mass spectrometry for the simultaneous determination of the platelet inhibitor Ro 44-3888 and its pro-drug and precursor metabolite in plasma. J Mass Spectrom 32 23. 

Cuzzola et al. have studied, using ionspray and electrospray MS and SPME-GC-MS, the Fenton oxidation products of surfactants such as lauryl sulfate [90] and AES [91]. The oxidation leads to the formation of products with hydroxyl and epoxide groups because of insertion of oxygen atoms or aldehydes [90] or terminal ethoxylic moieties [91] derived from the loss of the hydrophilic sulfate group. 

These solutions are not always practicable and HPLC flow rates of up to 2 ml min-1 may be accommodated directly by the use of electrospray in conjunction with pneumatically assisted nebulization (the combination is also known as Ionspray ) and/or a heated source inlet. The former is accomplished experimentally by using a probe that provides a flow of gas concentrically to the mobile phase stream, as shown in Figure 4.8, which aids the formation of droplets from the bulk liquid, and will allow a flow rate of around 200 xl min-1 to be used. 

Ionspray Pneumatically assisted electrospray - a process in which nebulizing gas is used in conjunction with a high voltage to form droplets from a liquid stream. 

In recent decades the hyphenated technique, HPLC-MS, also become the method of preference in HPLC practice. Various techniques have been developed and applied for MS detection such as thermo-spray interface, atmospheric ionization (API), electrospray or ionspray ionization (ESI or ISI), and particle beam ionization. 

Hsieh F.Y., Cai J., and Henion J. (1994), Identification of trace impurities of peptides and alkaloids by capillary electrophoresis-ionspray mass spectrometry, J. Chro-matogr. A 679, 206-211. 

Petritis, K. et al., Simultaneous analysis of underivatized chiral amino acids by liquid chromatography—ionspray tandem mass spectrometry using a teicoplanin chiral stationary phase, J. Chromatogr. A, 913, 331, 2001. 

Gergov M, Ojanpera I, Vuori E. 2003. Simultaneous screening for 238 drugs in blood by liquid chromatography-ionspray tandem mass spectrometry with multiple-reaction monitoring. J Chromatogr B 795 41. 

A number of interfaces such as thermospray (TSP), ionspray (IS), atmospheric chemical ionization (APCI) and electrospray (ES) can tolerate much higher flow rates without requiring that the flow be split at the end of the LC column. Ions that are produced in atmospheric pressure ionization sources are moved directly into the mass spectrometer through small apertures. 

Zook, D.R. Bruins, A.P. On cluster ions, ion transmission, and linear dynamic range limitations in electrospray (ionspray) mass spectrometry. Int. J. Mass Spectrom. 1997, 162, 129-147. 

P Cescutti, D Carozzo, R Rizzo. Study of the inclusion complexes of aromatic molecules with cyclodextrins using ionspray mass spectrometry. Carbohydr Res 290 105-115, 1996. 

Nebulizing gas (usually nitrogen) hows concentrically around the capillary, which shears droplets off as the liquid hows out of the end of the capillary. In the older literature, authors distinguish between pure electrospray without nebulizing gas and pneumatically assisted electrospray or ionspray. This is because of the mechanistic difference between the way the primary droplets form. Since all commercially available instruments allow the use of nebulizing gas, it is just a question of how rate as to whether it makes sense or not. 

Charles L, Pepin D. 1998. Analysis of oxyhalides in water by ion chromatography-ionspray mass spectrometry. J Chromatogr A 804 105-111. 

The first ESI design at the end of the 1980s proved to work properly as the HPLC interface with mobile phase flow rates between 1 and lOpL/min. Meanwhile, the development of the HPLC instrumentation and columns was oriented in the mL/min flow rate mode. In addition, the nebulization process based only on the application of an electrical field does not produce a stable spray from aqueous mobile phases. A modified ESI source, called ionspray, was then introduced [39], in which the nebulization of a liquid solution is pneumatically assisted by a coaxial flow of nitrogen (sheath gas) that allows the formation of a stable aerosol at mobile-phase flow rates between 10 and 500 pL/ min and the use of aqueous mobile phases. When working at higher flow rates (500-1000 pL/min), an additional nittogen flow rate can be used (auxiliary gas) to assist the desolvation of the droplets. This modified source is called turboionspray. 

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