The PST-mTips (patent-pending) provide the superb sensitivity of nanospray while allowing the robust experimental setup of microflow LC-MS. The PST-mTips achieves this high sensitivity by enabling the cone-jet mode of spray even at flow rates up to 10’s of uL/min. At 5 uL/min, our customer has achieved a sensitivity which was 20X that of conventional ESI, and 2X that of the Captivespray ® with negative ion spray and for a gradient that started at 97% aqueous to full organic. The PST-mTips are made of a stainless metal and are tapered only on the outside., which makes the emitters robust and non-clogging. We manipulate the interfacial properties between the emitter channel and the buffer, be it aqueous or organic or a mixture of both, to optimize the cone-jet mode formation, which results in the best ionization and vaporization conditions for the analytes in the buffer. This improvement also facilitates negative ion spray without the interference of corona discharge.
We have further developed the mTips into two sub-categories:
PST-mgTip: Robust and long-lasting for positive ion spray, but require a higher spray voltage, Typically ~3.3 KV
PST-mTip: Robust for both positive and negative ion spray at 1.8-2.4 KV, and long-lasting with negative ion spray. However, when used for positive ion spray, it may require regeneration by immersion in dilute nitric acid (<1% in water for a few minutes) after continuous use for 2-3 days.
The PST-mTips or PST-mgTips can be purchased as a spray emitter to replace any fused silica or stainless steel spray tips. The PST-mTip, which has a 25 um i.d. and 360 um o.d. are best suited for nanoflow up to about 5 uL/min. The PST-mTip-50 has a 50 um i.d. and 360 um o.d. is capable of nanoflow and flowrates up to 10’s of uL/min.
Microspray sources that are plug-and-play in existing mass spectrometer nanospray and other electroionization sources are also under development. The first one of these microspray source is the “Jailbreak 2.0” Make-easy microspray source for the Thermo Easy-spray source. Customers can convert to microspray with the minimal investment in money and effort.
Proteomics researchers have the fixed idea that nanospray alone can provide high enough sensitivity for the protein/peptide samples. However by increasing the flowrates to under 10 uL/min, the van Deemter plot would suggest that the plate height (approximately equivalent to the peak width) would decrease when compared to that in the nanoflow regime. The “dead-volume” of even a a 50 um i.d. emitter when the flow is 5-10 uL/min is negligible to cause any noticeable effect on the peak width and sensitivity. The resistance for corona discharge during negative ion spray makes the PST-mTips unique and unparallel in sensitivity especially with large oligonucleotides (>1 kDa).