Ionspray interface

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... 

A. High-performance liquid chromatography-mass spectrometry Weidolf and Covey [121] described the application of the ionspray interface for liquid chromatography and atmospheric-pressure ionization mass spectrometry to samples obtained in a study on the metabolism of... 

Figure 5.3 Schematic diagram of the ionspray interface. Reprinted from [14] with permission, 1987, American Chemical Society.

Pinkston, J.D. and Baker, T., Modified ionspray interface for supercritical fluid chromatography/mass spectrometry Interface design and initial results, Rapid Commun. Mass Spectrom., 9(12), 1087, 1995. 

A third API source is the ionspray interface. It combines the best features of both ESI and APCI. It can accept higher flow rates and is therefore sometimes called high flow electrospray. This source can tolerate highly aqueous mobile phases and gradient elution. 

Determination. HPLC-ionspray interface-MS LODs <10ng/l 196... 

Curini, R., Gentili, A., Marchese, S., Marino, A., and Perret, D., SPE followed by high-performance liquid chromatography-ionspray interface-mass spectrometry for monitoring of herbicides in environmental water, J. Chromatogr. A, 874, 187-198, 2000. 

The first LC-MS method for identification of YTX in shellfish was proposed in 1998 by Draisci et al. The method, requiring preliminary studies by flow injection analysis (FIA)-MS and MS/MS on a pure standard of YTX, was based on the use of an ionspray interface. The most abundant molecular-related ion observed was the [M-H] ion at ni/z 1141 that was selected as precursor ion for MS/MS experiments. The resulting MS/MS spectra showed fragment ions similar to those produced by FAB MS/MS. 

Silvestro, L., Dacol, R., Scappaticci, E. et al. (1993) Development of a HPLC-MS technique, with an ionspray interface, for the determination of platelet-activating factor (PAF) and lyso-PAF in biological samples. J. Chromatogr., 647, 261-9. 

In ESI-MS, and also in APCI-MS, the appearance of the mass spectrum depends on the mobile-phase composition. In addition, the appearance of mass spectra may change by applying instruments from different manufacturers and/or with different ion source geometries. Some results with the cholesterol reducing agent simvastatin may serve as an example. In acetonitrile/water or acetonitrile/aqueous ammonium acetate (1 nunol/L, adjusted to pH 4.0), simvastatin shows [M+Na] (Sci-ex ionspray interface and API-Ill) [113]. Under similar mobile-phase conditions but on a different instrument (Sciex turboionspray and API-365), [M-i-H]+ and were most abundant. With 2 nunol/L ammonium acetate in the mobile phase, the [M+NH ]" actually is the most abundant ion, next to [M-i-H]+, [M-l-Na] and [M+K]+being present [114, 115]. Attempts to force the ionization toward the generation of [M -i-Na]+ by the addition of sodium acetate in the case of simvastatin compromised the performance of the method. 

Detector MS, PE Sciex API-Ill Plus quadrupole, ionspray, positive ionization, ionspray interface 4400 V, orifice 67 V, nebulizer gas nitrogen at 60 psi, curtain gas nitrogen at 1.8 L/min, collision gas argon, m/z 415—163... 

Detector MS, PE Sciex API III triple quadrupole, atmospheric pressure ion source, positive ion, laboratory-constructed ionspray interface (details provided), nebulizer gas nitrogen at 67 psi, curtain gas nitrogen, collision gas argon, 40 p.L/min entered the detector, m/z 265-177 or 528-352-177... 

Detector MS, PE Sciex API 2000 triple quadrupole, 50 rL/min entered the detector, negative ionization, ionspray interface 150°, ionspray 4.5 kV, orifice 30 eV, nebulizer gas nitrogen, m/z 269—82 UV 254... 

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). 

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. 

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. 

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. 

Ionization methods such as electrospray, ionspray, and atmospheric pressure chemical ionization, in which the analyte is sprayed at atmospheric pressure into an interface to the vacuum of the MS ion source, constitute the category of the atmospheric pressure ionization. 

The ionspray (ISP) interface is closely related to the ESP. Unlike the ESP interface, ISP allows higher flow rates by virtue of pneumatically assisted vaporization... 

Coupling of liquid chromatography with mass spectrometry allows unequivocal online spectrometric identification of all nitrofurans at the very low residue concentrations required by regulatory agencies for confirmatory analysis in animal-derived foods. Typical examples of mass spectrometry applications in confirming nitrofuran residues in edible animal products employ thermospray (174, 176), ionspray (166), or atmospheric pressure chemical ionization (157) interfaces. 

Bruins, A. P. (1991). Liquid chromatography-mass spectrometry with ionspray and electrospray interfaces in pharmaceutical and biomedical research. J. Chromatogr. 554 39-46. 

The research efforts in the late 1960 s of the group of Dole (41-43) on electrospray sample introduction found continuation in the work of the group of Perm (86-87) in 1984 and later. An LC-MS interface based on ESI introduction into an atmospheric-pressure ion (API) source was described by Whitehouse et al. [88] in 1985. The flow-rate limitations of the latter system were to some extent removed by the introduction of a pneumatically-assisted ESI interface (ionspray ) for LC-MS by Bruins et al. (89) in 1987. This system was developed for a Seiex API instrument which in those days was the only commercially available instmment equipped with an API source. A major breaktlnough in ESI, and as a result of this also in the commercial availability of API instruments, was aehieved in 1988 by the observation of multiple-charge ions from peptides and proteins [90-91]. This made the ESI interface to one of the most popular and powerful methods for LC-MS. The development of API interfacing for LC-MS is discussed in detail in Ch. 5. 

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