Nanoflow-ESI

BordoU, R., Hoyes, J., Langridge, J., Chervet, J-P., Vissers, H. and van Veelen, P., Nanobore HPLC-MS and HPLC-MS/MS using a nanoflow ESI interface and a Q-Tof hybrid mass spectrometer . Micromass Technical Note 108, Micromass, Manchester, UK, 1998. 

Isotachophoresis. In isotachophoresis (ITP), or displacement electrophoresis or multizonal electrophoresis, the sample is inserted between two different buffers (electrolytes) without electroosmotic flow. The electrolytes are chosen so that one (the leading electrolyte) has a higher mobility and the other (the trailing electrolyte) has a lower mobility than the sample ions. An electric field is applied and the ions start to migrate towards the anode (anions) or cathode (cations). The ions separate into zones (bands) determined by their mobilities, after which each band migrates at a steady-state velocity and steady-state stacking of bands is achieved. Note that in ITP, unlike ZE, there is no electroosmotic flow and cations and anions cannot be separated simultaneously. Reference 26 provides a recent example of capillary isotachophoresis/zone electrophoresis coupled with nanoflow ESI-MS. 

K. Vanhoutte, W. van Dongen, E.L. Esmans, On-line nano-LC-ESI-MS Effect of the mobile-phase composition and the ESI tip design on the performance of a NanoFlow ESI, Rapid Conunun. Mass Spectrom., 12 (1998) 15. 

In conclusion, the NESI-chip system combines the advantages of microfluidics, such as fast, low-volume sample handling, with high sensitivity and specificity of nanoflow ESI-MS analysis, and rapid screening offered by on-line detection. 

QToF-MS >20 000 ESI, APCI, MALDI Mass accuracy <5 ppm (m/z 150-900) resolution 5000 nanoflow... 

The minimum amount of analyte required for analysis depends strongly (as always) on the nature of the substance and on the properties of the ion source. Less than 100 zeptomole of tryptic peptides from bovine semm albumin has been detected by coupling nanoflow LC to an ESI source [264] and 0.4 nM of equine cytochrome c by employing an RF-field focusing funnel to improve transmission [265]. 

Le Bihan, T., Pinto, D., and Eigeys, D., Nanoflow gradient generator coupled with mu-LC-ESI-MS/MS for protein identification. Analytical Chemistry 73(6), 1307-1315, 2001. 

Nanoelectrospray ionization (nanoESI), also known as nanospray, nanoflow electrospray, and micro-electrospray, is a low flow/high sensitivity approach to ESI. NanoESI15 is a slight variation on ESI such that the spray needle has been made very small and is positioned close to the entrance of the vacuum of the mass spectrometer and the mass analyzer (Figure 6). This greatly reduces required sample amounts allowing nanoliter flow rates and femto-mole sample consumption. The end result is increased efficiency since the flow rates for... 

Figure 7.10 A commercial FTMS system with a front-end nanoflow LC system. The schematic cutaway view depicts the sequential vacuum stages that are required to transfer ions in the ESI source (formed at atmospheric pressure) to the mass analyzer cell of the FTMS (10 ° mbar).

Vanhoutte et al. [81] compared various nano-ESI tips. With the uncoated non-tapered 20-pm-lD fused-silica tips, delivered with the Mcromass NanoFlow probe, the sensitivity was dependent of the mobile-phase compositiom Replacing these tips by uncoated tapered ones (20 9 pm ID) showed some improvement, while the best results, especially at low percentages of methanol in the mobile phase, were achieved with gold-coated tapered fused-silica tips. 

In order to reduce peak broadening in the nano-ESI needle attached to the nano-LC column, the use of packed needles has been promoted. Gatiin et al. [58] reports the use of 100-pm-ID fused-silica in-needle packed columns (10-pm particles) with a laser-pulled tip with a diameter of -2 pm. Figeys and Aebersold [59] reported the use of such in-needle RPLC columns for the LC-MS analysis of tryptic digests in combination with a nucrofluidic device to generate a nanoflow solvent gradient via electroosmotic flows. 

D. Figeys, R. Aebersold, Nanoflow solvent gradient delivery from a microfabricated device for protein identifications by ESI-MS, Anal. Chem., 70 (1998) 3721. 

Meiring, H.D. Barroso, B.M. Heeft, E.v.d. Hove, G.J.t. Jong, A.P.J.M.d. Sheathless Nanoflow HPLC-ESI/MS in Proteome Research and MHC Bound Peptide Identification, in Proceedings ofthe 47th ASMS Conference on Mass Spectrometry and Allied Topics. Dallas, Texas, June 13-17, 1999. 

The liquid volume of a sample required for analysis depends on the ionization technique, MALDI or ESI, and the introduction technique (see Table 4.1). The following statements assume that we are analyzing a sample near the detection limit of the analyte in a specific mass spectrometer. For MALDI-MS, the researcher typically spots 0.1 to 1 jL onto the MALDI sample plate. Thus, a minimum starting volume of 1 of 5 jL of sample is recommended. For ESI, the required sample volume is primarily dependent on the sample introduction technique. If the researcher uses a nanoflow electrospray technique, capillary EC, or capillary electrophoresis, then typically a l-pL voliune is required. However, larger sample volumes are recommended for ease of handhng. If the voliune is small, then the analysis may be limited to one experiment when additional MS or MS-MS experiments are desired. For higher flow rate ESI sources, the researcher should supply 50 pL or more for direct infusion experiments or for loading 5 to 20 pL onto an analytical EC column. 

There has recently been some interest in nanoflow LC as a mean of normalizing the mass spectrometric response [55-58], Nanospray is more than simply a reduction of ESI flow rate. ESI is an electrohydrodynamic process, with daughter droplets generated when Columb repulsion in a charged liquid (the parent droplet) overcomes... 

Gases Low relative molecular mass (100-600) Polar materials (200-2000) Drugs and metabolites Peptides, proteins Carbon dioxide, anesthetics Steroids, fatty acids Sugars, nucleosides, small peptides Glucuronides, sulfates Endorphins, albumin, proteomics Gas analyzer Isotope ratio MS GC-MS, LC-MS LC-MS, FAB-MS LC-MS/MS, FAB-MS/MS Digest followed by LC-ESI-MS/MS, nanoflow-MS/MS, MALDI-ToF-MS... 

ESI is the most commonly used interface in IC-MS applications. Standard ESI interfaces are generally optimized for analytical flow rates (>100pF/min) or nanoflow rates (<1 pE/min). Because capillary IC features flow rates from 10 to 20 pL/ min, modification and optimization of existing ESI interfaces are required. Using a standard MSQ Plus ESI probe with low flow option, the probe temperature is set... 

One of the major attractions of ESI is its ability to serve as an interface between liquid chromatography and mass spectrometry. There are currently a number of low-flow HPLC systems on the market that are compatible with electrospray, microspray, and nanospray sources. Capillary HPLC systems are interfaced with electrospray conducted in the pL/min flow regime, while nanoflow systems can accommodate nL/min flow rates. When electrospray is coupled with conventional HPLC, it is necessary to accommodate a higher sample flow rate ( 0.1—2mL/min) than normal electrospray can tolerate. To facilitate operation at these higher flow rates, a technique called pneumatically assisted electrospray or ion spray is employed, in which sample nebulization by aflow of gas is used to stimulate a more... 

---