Spray Voltage

The variation of injection/eluent flow rate is usually pre-determined at the optimization step using a standard solution with an available instrument. Such a pre-optimized parameter might not be the best condition for the analysis of each individual sample, which always contains the varied concentration and composition of lipids and/or matrix components. Accordingly, it should always be kept in mind that optimization of the flow rate is important for optimal analysis of each individual sample or any eluent stage. Moreover, variation of injection/eluent flow rates may lead us to investigate the interactions among the analytes, solvents, and other matrix components, as well as their chemical/physical consequences. 

5 VARIABLES IN BUILDING-BLOCK MONITORING WITH MS/MS SCANNING 

1 Precursor-Ion Scanning of a Fragment Ion Whose mJz Serves as a Variable 

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Factors may be classified as quantitative when they take particular values, e.g. concentration or temperature, or qualitative when their presence or absence is of interest. As mentioned previously, for an LC-MS experiment the factors could include the composition of the mobile phase employed, its pH and flow rate [3], the nature and concentration of any mobile-phase additive, e.g. buffer or ion-pair reagent, the make-up of the solution in which the sample is injected [4], the ionization technique, spray voltage for electrospray, nebulizer temperature for APCI, nebulizing gas pressure, mass spectrometer source temperature, cone voltage in the mass spectrometer source, and the nature and pressure of gas in the collision cell if MS-MS is employed. For quantification, the assessment of results is likely to be on the basis of the selectivity and sensitivity of the analysis, i.e. the chromatographic separation and the maximum production of molecular species or product ions if MS-MS is employed. 

InsAument parameters (sheath and auxiliary gas flows, spray voltage, capillary temperature, collision cell gas flow and offset, etc.) should be optimized while infusing a standard of tebuconazole prior to the Arst attempt at analysis. Optimization should be performed at an HPLC Aow rate and composition simulating those present during elution of tebuconazole using each HPLC condition set employed... 

Mode Interface Spray voltage Sheath gas Auxiliary gas Capillary temperature Manifold temperature Collision gas Total scan time QIMS resolution voltage added Q3MS resolution voltage added Parent masses... 

FIGURE 16.2 Representative base peak electropherograms from CZE runs of RPLC fractions, (a) Fraction 15 (5 peptide identifications) and (b) fraction 20 (19 peptide identifications). Column, bare fused silica capillary, 60 cm x 180 pm ODx30pm i.d. separation voltage, 15 kV observed CZE current, 1.91 p.A running electrolyte, 200 mm acetic acid + 10% isopropanol temperature, 22°C injection time, 10 s at 2 psi ( 4 nL total injection volume) supplementary pressure, 2 psi flow rate, 25nL/min spray voltage, 1.5 kV (reprinted with permission from Electrophoresis). 

Record the mass spectra in positive ion mode from the m/z 400 to 2000 range using a spray voltage of 1100 V. Set instrumental values for the ion source gas 1 to 6 and for the curtain gas to 25. Analyze the product ion spectra with the Analyst QS software (Applied Biosystems GmbH) (see Notes 12 and 13). 

Desorption electrospray ionization was implemented on this portable mass spectrometer [23], DESI experiments were carried out at ambient capillary temperature, at a spray voltage of 3kV and a nebulizing N2 gas flow of 80-120 psi. Detection of RDX from three different surfaces (paper, plastic, and metal) was demonstrated with this portable instrument in the positive-ion mode, with an analysis time of 5-10 s. The result obtained for 10 ng of RDX deposited on 1-cm2 paper is shown in Fig 11(a). Figure 11(b) shows... 

Mass spectrometry Positive ion electrospray ionization mass spectrometry (ESl-MS) analysis was performed on a PE API 2000 triple quadrupole mass spectrometer (Sciex, Toronto, Canada). Spray voltage was set to 4.8 kV, and 30 V orifice voltage was applied. Samples were dissolved in a methanol-water (1 1, v/v) mixture containing 0.1% acetic acid, and 5 pL of sample was injected with a flow rate of 100 pL/min. The instmment was used in a Qj scan mode in the range of m/z 400-1700, with a step size of 0.3 amu and a dwell time of 0.5 ms. Other chimeric peptides in this study were purified and characterized in the same or a very similar way. 

Figure 3.9 Fragmentation patterns in positive-ion mode of PCs. ESI-MS conditions spray voltage 4.5 kV sheath gas nitrogen 0.9L/min capillary voltage 35 V capillary temperature 200 °C tube lens offset voltage 15 V. (Reprinted from Pad et al., 2006. Simultaneous separation and identification of oligomeric procyani-dins and anthochyanidins-derived pigments in raw red wine by HPLC-UV-ESI-MSn, Journal of Mass Spectrometry 41, p. 869, with permission from John Wiley Sons Ltd)...

Figure 3.11 Chromatograms extracted from the TIC recorded in negative-mode of PCs and PAs dimers and trimers of a wine LC/ESI-MS analysis. Analytical conditions C18 (125 x 2 mm i.d., 3(r,m) narrow-bre column ion spray voltage —4000 V, orifice voltage —60 V. Binary solvent composed of A) aqueous 2% formic acid and B) acetonitrile/H20/formic acid (80 18 2v/v/v). Gradient program from 5% to 30% of B in 20min, 30-50% B in lOmin (flow rate 200p.L/min, flow rate in the ESI source 50p,L/min). (Reproduced from ]. Agric. Food (. hem., 1999, 47, 1023-1028, Fulcrand et al., with permission of American Chemical Society)...

Table 3.14 Anthocyanins and their derivatives identified in a Primitivo wine by LC/ESI-MS analysis performing program D in Table 3.12. The characteristic fragment ions from the MS/MS and MS3 experiments of the most intense m/z signals of mass spectra, are reported. MS conditions positive ion mode spray voltage 4.5 kV sheath gas N2 0.9 L/min capillary voltage 35 V capillary temperature 200°C tube lens offset voltage, 15 V (Pati et al., 2006).

The MS conditions positive-ion mode spray voltage 4.5 kV sheath gas N2 0.9L/min capillary voltage 35 V capillary temperature 200°C tube lens offset voltage, 15V (Pati et al.,2006). 

MS measurements were performed on a Sciex API I Plus single quadruple mass spectrometer equipped with an electrospray ionisation source. The mass spectrometer was operated in negative or positive-ion mode. Ion spray voltage/orifice voltages were selected at - 4 KV/- 70 V and + 5 KV/+ 60 V, respectively. 

Figure 3.3 SIMION electric field models for 28 pm diameter sprayers located 4.7 mm from the ion orifice counter electrode and a spray (solution) voltage of 1.6 kV. Equipotential lines are shown every 50 V. Electric field calculated at the tip of the Taylor cone for each model is shown. (B, C) A comparison of the models shows a 50-fold increase in the electric field generated at the tip of the Taylor cone when the silicon underlying a dielectric film is held at ground potential rather than at the spray potential. Electric field shown in (B) is equivalent to that of a 2 pm diameter pulled capillary with a 1.0 kV spray voltage at a distance of 3 mm from a counter electrode.

Figure 3.6 Pipette tip aligned and sealed around the inlet to a nozzle of the ESI Chip using the NanoMate system that automates nanoelectrospray infusion. Spray voltage and backing pressure are optimized based on the solution solvent composition to obtain a stable spray. The NanoMate system loads a new sample into a new pipette tip and automatically positions it to a new nozzle. The chip is automatically moved to the optimized spray position.

Figure 3.7 First coupling of a nanoLC column to the ESI Chip using a liquid electrode to apply spray voltage to the effluent exiting a capillary positioned at the inlet to the ESI Chip. Make-up flow was optionally applied to adjust solvent composition to enhance ionization.

Interfacing CE to ESI-MS The requirements to the interface are similar to those discussed earlier. The closing of electrical circuit from CE during ion evaporation is provided by an electrolyte sheath flow. Effective ion production is possible by a suitable spray voltage easily controlled by instrument software. Eor older instruments, a laboratory-made device is necessary for reproducible optimized positioning of the CE capillary to the ESI-tip (Schramel et al. 1999). The potential of this hyphenated technique, in addition to that of CE, is direct species detection. When the element of interest imposes its specific isotope pattern on the molecular mass spectmm, elemental information within the species is also possible this means that maximized species information is gained in one analytical effort. If the elemental pattern is not seen, structural... 

Huorescence Excitation 250 nm, emission 395 nm Positive ion mode, mass range m/z 100-2000. Ionization parameters capillary temperature 300 1°C, spray voltage... 

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