Electrospray Ionization Interface ESI

The next generation of HPLC detectors, namely mass spectrometers, are now available and being deployed for water-soluble vitamin determinations in dietary supplements with electrospray ionization interface (ESI) (Holler et al. 2006). There remain obstacles to overcome for multivitamin analyses in complex food matrices, as co-elution of vitamins or excipients can compromise... 

Note Over the last decade, NICI applications have diminished because these analyses have mostly been carried out by negative-ion atmospheric pressure chemical ionization (APCI). APCI is compatible with liquid chromatography (Chap. 14) and can readily be implemented on instruments with electrospray ionization interface (ESI, Chap. 12). Such instruments have an enormous market share, and thus, it is often more convenient and economic to switch between ESI and APCI as required. Although being a type of Cl, APCI will be dealt in conjunction with ESI. 

Plastic microdevices for high-throughput screening with MS detection were also prepared for detection of aflatoxins and barbiturates. These devices incorporated concentration techniques interfaced with electrospray ionization MS (ESI-MS) through capillaries [2], The microfluidic device for aflatoxin detection employed an affinity dialysis technique, in which a poly (vinylidene fluoride) (PVDF) membrane was incorporated in the microchip between two channels. Small molecules were dialyzed from the aflatoxin/antibody complexes, which were then analyzed by MS. A similar device was used for concentrating barbiturate/antibody complexes using an affinity ultrafiltration technique. A barbiturate solution was mixed with antibodies and then flowed into the device, where uncomplexed barbiturates were removed by filtration. The antibody complex was then dissociated and electrokinetically mobilized for MS analysis. In each case, the affinity preconcentration improved the sensitivity by at least one to two orders of magnitude over previously reported detection limits. 

Capillary electrochromatography-electrospray ionization-mass spectrometry (CEC-ESI-MS) is an analytical technique combining electrochroma-tographic separation and mass spectrometric detection with an electrospray ionization interface. 

Smith, R.D. Barinaga, C.J. Udseth, H.R. Improved electrospray ionization interface for capillary zone electrophor-esis-mass spectrometry. Anal. Chem. 1988, 60, 1948-1952. 

Chapter 7, titled Interfacing TLC with Laser-Based Ambient Mass Spectrometry, provides an overview of mass spectrometric techniques that can be coupled with TLC under the most convenient working conditions, that is, at room temperature and atmospheric pressure. The authors introduce readers to electrospray laser desorption ionization (ELDI), plasma-assisted multiwavelength laser desorption/ionization (PAMLDI), laser desorption atmospheric pressure chemical ionization (LD-APCI), laser desorption-dual electrospray and atmospheric pressure chemical ionization I (LD - ESI-I-APCI), laser-induced acoustic desorption electrospray ionization (LIAD-ESI), and laser-induced acoustic desorption-dielectric barrier discharge ionization (LIAD-DBDI). Chapters 6 and 7 are largely complementary because in the former one, main attention is paid to practical applications of a wide number of... 

Mass spectrometry (MS) is combined to TLC through an ESI (electrospray ionization) interface or a MALDI (matrix-assisted laser desorption ionization) interface. In the first case, E SI-M S is carried out using the extracts of the eluted compounds. The spots/zones need to be scraped oflF from the plate before the compounds are extracted. MALDI can be carried out directly on the plate after adding an appropriate MALDI matrix. 

Nowadays, there is no validated LC—MS method for the quantitation of TTX. Testing different analytical columns and optimized LC—MS conditions are needed to separate and identify all TTXs in a sample. The main MS system for TTX detection uses atmospheric pressure ionization (API) in an electrospray ionization source (ESI) and collision-induced dissociation (CID) for identification using a triple quadrupole mass analyzer. For TTXs detection, the ESI interface uses the positive ionization mode. Thus, TTX exhibit a molecular mass of 320 Da. assignable to TTX - -H (C11H17N3O3 = 320). All its analogs are analyzed by LC—MS, in which positive ionization produces a t)q)ical molecular ion of [M - - H] for each compound. Table 15.4 shows the molecular formulas for TTX and several of its analogs detected in puffer fish and many other marine animals and their m/z for [M -f- H] ions. 

Reversed-phase Cig chromatography column. Keystone Scientific Betasil, 100 x 2.0-mm i.d., 5-pm particle size, 100 A, Part No. 105-701-2-CPF TSQ 7000 LC/MS/MS system with electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) interface and gradient high-performance liquid chromatography (HPLC) unit, or equivalent Vacuum manifold for use with SPE cartridges (Varian Vac Elut 10 or equivalent)... 

As with GC/MS, LC/MS offers the possibility of unequivocal confirmation of analyte identity and accurate quantiation. Similarly, both quadrupole and ion-trap instruments are commercially available. However, the responses of different analytes are extremely dependent on the type of interface used to remove the mobile phase and to introduce the target analytes into the mass spectrometer. For pesticide residue analyses, the most popular interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Both negative and positive ionization can be used as applicable to produce characteristically abundant ions. 

Confirmatory system Agilent Series 1100 liquid chromatograph Eclipse XDB Cig HPLC columu, 150 x 4.0-mm i.d., 3.5- im particle size MicroMass Quattro II triple-quadrupole mass spectrometer using an electrospray ionization (ESI) interface... 

Detection of the effluent in a 2D system is carried out at the end of the second dimension s column. UVand LIF are the most widely used and the simplest methods of detection for CE separations because they are performed on-column. MS detection, unlike UV and LIF, is carried out on the effluent as it exits the CE column. The direct coupling of CE with mass spectrometry has shown great potential in proteomic research (Janini et al., 2004). The method of choice for detection of peptides is MS-electrospray ionization (ESI). However, ESI requires a special interface between the CE column and the mass spectrometer that has proven not to be a simple matter (Issaq et al., 2004). 

Electrospray ionization (ESI) is ideally suited as a detection technique for the online interfacing of liquid-phase separations (HPLC and CE) to MS, because it facilitates the transfer of analytes from the liquid phase of the HPLC or CE column to the gas phase of the MS. Also, it allows the detection of high molecular weight species, such as peptides. Three interface designs have been developed in the past 18 years for coupling CE with MS. The first CE-MS interface, coaxial sheath flow, was introduced by Smith and his group in 1987 (Olivares et al., 1987) and was improved upon in later work (Smith et al., 1988). Coaxial sheath flow is formed using two concentric metal capillaries, whereby the CE terminus and the makeup flow line are inserted into the... 

Currently, LC-MS is widely used for the analysis of polar compounds, such as medicinal metabolites and bioactive peptides, since the interface has been improved and several new ionization methods have been developed. The sensitivity and reproducibility are sufficient for a daily quantitative analysis. The usefulness of the LC-MS has been demonstrated for studies on Type II pheromones using a time-of-flight MS with electrospray ionization (ESI) [180]. Each epoxydiene derived from the (Z3,Z6,Z9)-triene shows three ion series of [M+NHJ+, [M+H]+, and [M-OH]+ with high resolution and good sensitivity, indicating its molecular formula. In addition to these, characteristic fragment... 

In IC-MS systems, the core of the equipment is the interface. In fact, inside the interface evaporation of the liquid, ionization of neutral species to charged species and removal of a huge amount of mobile phase to keep the vacuum conditions required from the mass analyzer take place. Two main interfaces are used coupled to IC, namely electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). In the ESI mode, ions are produced by evaporation of charged droplets obtained through spraying and an electrical field, whilst in the APCI mode the spray created by a pneumatic nebulizer is directed towards a heated region (400°C-550°C) in which desolvation and vaporization take place. The eluent vapors are ionized by the corona effect (the partial discharge... 

Several interfaces had been developed, but at present, mainly electrospray ionization (ESI) and atmospheric pressnre chemical ionization (APCI) are widely used. In the ESI interface, HPLC... 

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