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Optimal Online Analysis
Online analysis is characterized by continuously pumped mobile phase at low flow rates through an emitter most commonly provided via syringe pump or LC pump. High voltage is applied to the mobile phase to generate an even spray for delivery of the sample to the mass spectrometer. Sheath gas may be applied in microspray applications
Fused-silica PicoTip® emitters for online electrospray are available in the SilicaTip™ and the TaperTip™, which differ in size and operational flow rates. TaperTips are very robust emitters used in microspray applications. Your emitter-mounting hardware must accommodate 150 or 360 µm outside diameter (OD) fused-silica tubing.
Offline analysis is characterized as loading a discrete sample, usually by syringe or pipette, into an emitter that is then mounted into the mass spectrometer's source. Sample flow is generated by the electrostatic attraction of the liquid inside the emitter, which has been changed by high voltage, or by the gentle pressurization of the source.
Borosilicate glass and quartz PicoTips® are an improved version of the traditional nanospray ionization emitters. Their special taper makes them virtually self-filling, and their specified tip opening eliminates the need to break open the tips prior to use. The proper OD for the emitter is determined by the manufacturer of your nanospray source. The Micromass® ZSpray™ uses PicoTips with a 1 mm OD while the ABI Mariner™/QSTAR®, Bruker NanoSpray™, MDS Proteomics/Protana NanoES, and Thermo Finnigan Nanospray Ion Sources take PicoTips with a 1.2 mm OD.
Determine your target flow rate; then locate the corresponding tip size. EconoTips™ have a 1 µm ID tip and are perfect for routine sampling with a standard single-layer conductive coating. GlassTips™ are available in 2 and 4 µm tip IDs, with or without a durable, inert, multi-layer conductive coating (U.S. Patent 5,788,166) and undergo rigorous inspection by video microscopy. Select QuartzTips™ for samples that are sodium-sensitive or require an emitter with better resistance to high pH solvents.
In order to perform electrospray, high voltage must be supplied to the mobile phase. The electrical contact can be made in either of two methods indirectly through a conductive coating on the emitter, or directly through a junction. Each of these methods requires different styles of emitters. Once you have determined your contact method, select the corresponding coating. Distal coatings are most durable.
|Junction Contact with Distal-Coating (D)|
The electrical contact is made to the outside of the emitter, which has a conductive coating on the distal end. The voltage contacts the mobile phase through the gap between the emitter and the transfer line. PicoTips® with a distal coating have -D- in their stock numbers. Use primarily with PEEK™ fittings.
|Tip Contact Using the Standard Coating (CE)|
The electrical contact is made to the outside of the emitter. The emitter has a conductive coating on the tip where the voltage contacts the mobile phase. PicoTips® with a standard coating have - CE- in their stock numbers. Use primarily with PEEK™ fittings.
|Junction Contact for Uncoated Tips (N)|
The electrical contact is made to the fitting holding the emitter. Voltage contact is made directly to the mobile phase. PicoTips® that are uncoated have -N- in their stock numbers. Use primarily with metal fittings.