Capillary nanospray

Several reports concerning the development of stable and rugged sheathless interfaces were proposed. The first sheathless interface was developed by Olivares et al., and two types of sheathless interfaces are currently distinguished. The first one consists of a nanospray needle, which is inserted with a connection unit to the CE capillary. This setup allows changing the spray needle alone independently on the capillary exchange.The second approach involves the use of the end of capillary tip as an emitter with the help of a capillary-outlet conductive coating " or by inserting a conductive wire into the capillary outlet. 

Vuorensola, K., Siren, H., Kostiainen, R., and Kotiaho, T. (2002). Analysis of catecholamines by capillary electrophoresis and capillary electrophoresis-nanospray mass spectrometry. Use of aqueous and non-aqueous solutions compared with physical parameters. /. Chromatogr. A 979, 179—189. 

Warriner, R. N., Craze, A. S., Games, D. E., and Lane, S. J. (1998). Capillary electrochromato-graphy/mass spectrometry a comparison of the sensitivity of nanospray and microspray ionization techniques. Rapid Commun. Mass Spectrom. 12, 1143-1149. 

Nanospray is a miniaturized version of electrospray. In the original setup of Wilm and Mann (8) it is utilized as an off-line technique using disposable, finely drawn (1 -gm tip), metallized glass capillaries to infuse samples at 10-30 nL/min flow rates. This allows more than 50 min analysis time with just a 1-pT sample. Due to the formation of much smaller droplets and the more effective ionization, there is often no need for LC separation, since the separation is accomplished in m/z or by MS/MS. However, limited reproducibility with respect to quantification and a more complex sample preparation can be seen as drawbacks. An on-line version for hyphenation with capillary and nano-LC as well as CE (slightly modified) is now commercially available. 

The optimization of the process in recent years, led to defined ion formation with solvent evaporation and complete desolvatation of analyte ions, which are then accelerated towards the mass separator. Analyte molecules often form multiply charged ions. ESI can be carried out both in positive and in negative mode. The sample introduction can be performed with microscale tips mainly made of fused silica capillaries, which are inexpensive and available in various sizes and geometric forms. Recently, nanospray technologies as microvariants of ESI with increased sensitivity were developed, which allowed the analysis of extremely small sample amounts [57]. 

Miniaturization of HPLC-ICP-MS is an important issue in bioanalytical chemistry when small amounts of sample (e.g., single cells) need to be investigated.33 ICP-MS (with an octopole collision cell) in combination with nano-HPLC (75 pun column) was optimized for the detection of selenopeptides in a selenium-yeast protein digest after 100-fold preconcentration on a C18 capillary precolumn (300 (im column for salt removal and cleanup).34 Under identical separation and preconcentration conditions, electrospray MS/MS (using Nanospray qQqToF-MS - QSTAR from Applied... 

Nanoflow HPLC—HPLC system with accurately controlled reciprocating and syringe pumps designed to use capillary and small diameter, high-resolution columns as front ends for electrospray and nanospray mass spectrometer interfaces. 

Vrouwe, E. X. Gysler, J. Tjaden, U. R. van der Grccf, J. 2000. Chip-based capillary electrophoresis with an electrodeless nanospray interface. Rapid Commun. Mass Spectrom., 14,1682-1688. 

Gold/palladium-coated nanospray capillaries (Protana) or a PicoTip emitter (New Objective). 

For nano-ESI-MS MS , the sample is loaded either in a previously rinsed gold/palladium-coated nanospray capillary (Promega) or in a PicoTip emitter (New Objective) and analyzed in a nanospray source. 

For static nanoESI-MS connect the static nanospray source (Protana, Odense, Denmark) to the mass spectrometer and use for each sample to be analyzed a new borosilicate spray capillary (ES380 Medium , PROXEON Biosystems AIS, Odense, Denmark see Note 3). 

The surface of the nanospray capillary tips is coated with a thin metal film to apply the voltage. Do not scratch this coating or touch it, as this may reduce the spray performance. Be careful not to break the thin tip of the needle when mounting it in the tip holder. 

Fig. 8.7. Schematic of a CEC—nanospray ESI-MS interface with conducting vacuum transfer conduit and heated capillary.

Lu, C.Y. and Feng, C.H. Micro-scale analysis of aminoglycoside antibiotics in human plasma by capillary hquid chromatography and nanospray tandem mass spectrometry with column switching. /. Chromatogr. A. 2007, 1156, 249-253. 

The nano-electrospray (nanoES) source is essentially a miniaturized version of the ES source. This technique allows very small amounts of sample to be ionized efficiently at nanoliters per minute flow rates and it involves loading sample volumes of 1-2 pi into a gold-coated capillary needle, which is introduced to the ion source. Alternatively for on-line nanoLC-MS experiments the end of the nanoLC column serves as the nanospray needle. The nanoES source disperses the liquid analyte entirely by electrostatic means [27] and does not require assistance such as solvent pumps or nebulizing gas. This improves sample desolvation and ionization and sample loading can be made to last 30 minutes or more. Also, the creation of nanodroplets means a high surface area to volume ratio allowing the efficient use of the sample without losses. Additionally, the introduction of the Z-spray ion source on some instruments has enabled an increase in sensitivity. In a Z-spray ion source, the analyte ions follow a Z-shaped trajectory between the inlet tube to the final skimmer which differs from the linear trajectory of a conventional inlet. This allows ions to be diverted from neutral molecules such as solvents and buffers, resulting in enhanced sensitivity. 

Ramsey and Ramseyalso described microchip interfacing to an ion trap mass spectrometer. Microfluidic delivery was realized by electroosmotically induced pressures and electrostatic spray at the channel terminus was achieved by applying a potential between the microchip and a conductor spaced 3-5 mm from the channel terminus. Tetrabutylammonium iodide was tested as a model compound with this device. Later, Ramsey et reported use of a microchip nanoelectrospray tip coupled to a time-of-flight mass spectrometer for subattomole sensitivity detection of peptides and proteins. A fluid delivery rate of 20-30 nL/min was readily obtained by applying an electrospray voltage to the microchip and the nanospray capillary attached at the end of the microfabricated channel without any pressure assistance. 

Traditional static nanospray can be a time-intensive effort and typically requires the expertise of a skilled operator. Automated methods can increase throughput and involve either traditional capillaries or microfluidic chips. 

Neugebauer, J. Moseley, M.A. Vissers, J.P.C. Moyer, M. Comparison of Nanospray and Fully Automated Nanoscale Capillary LC/MS/MS for Protein Identification, in Proceedings of the 47th ASMS Conference on Mass Spectrometry and Allied Topics, Dallas, TX, June 13-17, 1999, 2877-2878. 

Microreactor chips were mounted on a dedicated holder (Figure 9.4a and b), placed on the Nanospray interface of the mass spectrometer using a metal plate. Solutions were introduced on-chip via fused silica capillaries (o.d. = 360 pm) of 100, 40 or 20 pm (i.d.), depending on the microchannel cross-sectional... 

Construct the sheathless interface by attaching the CE separation capillary to the commercial distal coated nanospray needle through a teflon joint. The length of the CE capillary is to be set to 100-130 cm. 

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